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Hindawi Publishing CorporationJournal of ChemistryVolume 2013 Article ID 947137 9 pageshttpdxdoiorg1011552013947137

Research ArticleOptimization of Environmentally Benign Polymers Based onThymine and Polyvinyl Sulfonate Using Plackett-Burman Designand Surface Response

Julieta Ledesma1 Santiago A Bortolato2 Carlos E Boschetti1 and Deacutebora M Martino23

1 Area Tecnologıa Quımica Facultad de Ciencias Bioquımicas y Farmaceuticas Universidad Nacional de RosarioSuipacha 531 S2002LRK Rosario Argentina

2 Instituto de Desarrollo Tecnologico para la Industria Quımica (INTEC) Guemes 3450 S3000GLN Santa Fe Argentina3 Facultad de Humanidades y Ciencias Universidad Nacional del Litoral Paraje El Pozo S3080HOF Santa Fe Argentina

Correspondence should be addressed to Santiago A Bortolato sbortolatointecunleduar

Received 15 February 2013 Accepted 24 April 2013

Academic Editor Sofia Trakhtenberg

Copyright copy 2013 Julieta Ledesma et alThis is an open access article distributed under the Creative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Traditional approaches to the development of integrated circuits involve the use andor manufacture of toxic materials that havea potential environmental impact An extensive research has been done to design environmentally benign synthetic polymerscontaining nucleic acid bases which can be used to enhance the photoresistor technologies Water soluble environmentally benignphotopolymers of 1-(4-vinylbenzyl) thymine (VBT) and vinylphenyl sufonate (VPS) undergo a photodimerization reaction whenexposed to low levels of ultraviolet irradiation leading to an immobilization of the copolymer on a variety of substrates Plackett-Burman design (PBD) and central composite design (CCD) were applied to identify the significant factors influencing the polymercrosslinking and dye adsorption processes which are relevant in the fabrication of copolymer films for potential photoresist useThe PBD results assigned a maximum absorption signal of 067 while optimal conditions obtained in this experiment followingthe CCD method predictions provided a response of 083plusmn 003 being a solid foundation for further use of this methodologyin the production of potential photoresistors The pH effect was relevant for low concentrations but not significant for higherconcentrations To the best of our knowledge this was the first report applying statistical experimental designs to optimize thecrosslinking of thymine-based polymers

1 Introduction

The success of semiconductor technologies in recent decadeshas been based primarily on what is called the photolithog-raphy technique often used to make integrated circuits [1]Photolithography is the process by which optical methodsare used to transfer the circuit patterns from master images(masks) to substrates typically silicon wafersThe traditionalapproaches to the development of integrated circuits involveobtaining small pieces at low cost without considering thetoxicity of the materials used andor manufactured and theirpotential environmental impact During the last decadesextensive research has been done to design environmentallybenign synthetic polymers containing nucleic acid baseswhich can be used to enhance the photoresistor technologies

[2ndash5] The need for an inexpensive stable and versatilesystem which incorporates thymine moieties in the polymerbackbone leads to the design of a new synthetic monomerthe 1-(4-vinylbenzyl) thymine (VBT) [6] that has the abilityto photocrosslink upon irradiation with short-wavelengthultraviolet (UV) component of sunlight [6ndash8] This processwas bioinspired on the photodimerization of thymine one ofthe DNA bases both in vivo and in vitro under irradiationwith ultraviolet light which disrupts the helical structure ofDNA [4 5]

The versatility of VBT makes it an attractive researchplatform since the balance between photoreactivity solu-bility and noncovalent interactions can be fine-tuned fora variety of applications Since the VBT homopolymer iswater insoluble due to strong intermolecular interactions

2 Journal of Chemistry

the copolymerization of VBT with charged functionalgroups can improve its solubility Among them substitutedstyrenes either cationic such as vinylbenzyl triethylammo-nium chloride (VBA) and N-butyl-NN-dimethyl-(4-vin-ylbenzyl)ammonium chloride (BDMQ) or anionic such asvinylphenyl sufonate (VPS) allow for obtaining a fully water-processable photoresist eliminating the need of toxic solvents[9 10] The resulting photopolymers of VBT and VPS orVBA are water soluble environmentally benign and undergoa photodimerization reaction of the pendant thymine unitswhen exposed to low levels of ultraviolet irradiation Thisprocess leads to an immobilization of the copolymer on avariety of substrates in response to irradiation and allows theremoval of unexposed regions by aqueouswash (photoresist)having potential applications in a variety of fields [9ndash19]Trakhtenberg et al introduced the photoresistive capacityof VBT-VPS copolymers and demonstrated that they can beused as a viable template for enzymatic synthesis of conduc-tive polyaniline allowing for surface photopatterning witha conductive polymer under mild conditions [15] The samecopolymer was also used in photoresist applications [9 20]In those works the authors immobilized the copolymers toform thin films on polyethylene terephthalate (PET) substrateand demonstrated that the process is potentially useful for theadvancement of photoresistors [20]

In photolithography technique in order to create thepatterns the wafers are coated with a photosensitive materialcalled photoresist which changes its solubility upon exposureto light through an appropriate mask of UV opaque materialThis allows the selective irradiation of only the desired areasof the photoresist-coated wafer thus transferring the patternfrom themask onto thewafer After being exposed to light thephotoresist-coated wafer goes into a developing solution thatselectively removes the resist layer from unexposed areasresulting in a wafer with the semiconductor surface partiallyprotected by the resist [21] In subsequent steps the unpro-tected areas are modified for example by chemical etchingwhile protected areas remain intact Finally the remainingphotoresist is stripped off the wafer which now features thepattern identical to the one on the mask This process canbe repeated several times using different masks [1] Figure 1schematically presents the photolithography process

Taking into account that the photoimmobilized copoly-mer film is very thin (lt1120583m) and translucent the immobi-lized copolymer coatings are typically visualized by dippingthe resulting patterned films into a solution of an oppositelycharged dye The dye chosen for VPS was methylene blue(MB) given that it has a net positive charge that favorsthe physisorption process on the polymer as it was shown[9] The dye selectively adsorbs on the charges of the pho-tocrosslinked copolymer providing clear contrast from theunreacted regions The amount of adsorbed dye can be mon-itored by UV-VIS spectroscopy measuring the absorbanceat 610 nm (MB absorbance maximum) and therefore acorrespondence among the measured absorbance and theamount of immobilized charged groups on the substratesurface can be made [9]

The technological applications of these polymers wereseen earlier than the necessary basic studies which could

Step 1 clean substrate

Step 2 coat substrate withphotoresist

Step 3 expose to UV lightthrough mask

Step 4 develop unexposed resist

Step 5 transfer pattern tosubstrate via etching

Step 6 strip photoresist

ℎ

Figure 1 Description of photolitography process

help to understand their behavior and improve their serviceTherefore more studies need to be done in order to optimizethe proposed photocrosslinking method due to the largeamount of variables that have effect on the processing anddevelopment of these copolymers To begin with thymine isa compound having acid-base behavior with a pKa sim9 and ithas been demonstrated that at pH greater than pKa thymineexists mostly in its anionic form in an equilibrium betweentwo tautomers (ratio 1 1) one of which cannot crosslink [22]It was found experimentally that increasing the proportionof VPS in its VBT-VPS copolymer the pH of the solutionincreases to values close to 11 which could produce a signif-icant reduction in the efficiency of the crosslinking processHowever the efficiency and reproducibility of the methodused to prepare VBT-VPS coatings may depend on otherfactors including the coating thickness and the copolymercomposition [20] Although the works cited before [9 20]are very helpful to screen important factors influencing filmpreparation they are insufficient to establish a general rulefor manufacturing certain photoresist polymers with reliableproperties In general it is difficult to obtain the comprehen-sive effects of some factors through a reasonable number ofexperiments Solving this problem in a rational way involvesperforming an experimental design [23] This procedure canbe summarized in three stages (1) identification of factorsthat can influence the results of the experiments (2) useof statistical analysis to separate and evaluate the effectsof the various factors involved ldquoscreening phaserdquo and (3)with the significant factors get the best response possiblefor the developed experiment ldquoresponse surface phaserdquo [23]The primordial difference between the classical one-variable-at-a-time method and the experimental design is that inthe latter case the values of all the factors are varied ineach experiment in a programmed and rational way Someof the studied factors will probably have no influence onthe experiment and only few will act upon the responsetherefore the essential factors can be detected while keepingthe number of trials to a minimum

Plackett-Burman design (PBD) is a method that caninspect up to119873minus1 factors in119873 experiments and is commonly

Journal of Chemistry 3

used in the screening phase of a wide range of processes [24ndash26] It has been proven to be an efficient way of evaluatinga large number of variables and identifying the significantones from a statistical point of view [23ndash26] Thereforein this study PBD method was applied to identify thesignificant factors influencing the polymer crosslinking anddye adsorption processes that are relevant in the fabricationof copolymer films for potential photoresist use The effectsof seven controllable factors on the process performanceswere studied Selected operational variables were pH con-centration dyeing time solution stability coating thicknesscomonomer ratios and film drying time The absorbancecorresponding to the methylene blue dye at 610 nm as anindication of VBT-VPS crosslinking efficiency was chosen asthe response value of the PBD experiments

Once the various factors affecting the results of anexperiment have been identified through PBD a separatemethod is needed to determine the combination of factorlevels which will provide the optimum response First it isnecessary to carefully define what is meant by ldquooptimumresponserdquo in a given experimental procedure in our case theoptimumoutcome of the experiment would be themaximumsignal-to-noise ratio in the absorbance measurements Withthat in mind the response surface methodology (RSM) is anefficient experimental tool with which the optimal conditionsof a multivariable system may be determined This strategyincludes a large number of statistical techniques [23 27] inparticular the Central Composite Design (CCD) which wasused to explore the relationships between several descriptivevariables and one response variable

In this work the optimization of the main factorsaffecting the polymer photocrosslinking and subsequentdye adsortion processes was carried out by means of anexperimental design The goal of the present research is toquantitatively assess the effects of numerous variables overthe photocrosslinking process and to propose the best exper-imental conditions for the improvement of photoresistorsbased on VBT and VPS copolymers in a rational way and atlow cost of experiments

2 Materials and Methods

21 Materials All reagents were purchased in the purestavailable form and were used as received Sodium hydroxideisopropanol and acetone were purchased from Cicarelli(Buenos Aires Argentina) 4-Vinylbenzyl chloride 221015840-azobis-2-methylpropionitrile (AIBN) 26-di-tert-butyl-4-methylphenol thymine and methylene blue (MB) were pur-chased from Sigma-Aldrich (SA) (Buenos Aires Argentina)VBT was synthesized from thymine and vinylbenzyl chlorideas described previously [6] VPS salt was purchased fromFluka (Buenos Aires Argentina) Based on 1H NMR spectraand melting point results the monomeric products weredeemed pure enough for the synthesis of the polymers

Hydrophilic polyethylenterephthalate film (PET-X4C1Dupont) was used as substrate without previous treatmentCoatings were done using wire-round milled coating rodspurchased from RDS Corp (Webster NY USA) Irradiations

N

N OO

H

S OO

Ominus

Na+

119898119899

Scheme 1 Structure of VBT-VPS copolymers (119899 = 1 and 119898 = 1 48 16 or 32)

were performed using a UV hand lamp (Spectroline ULModel ENF 260c Spectronics Corporation Westbury NYUSA)Absorbancemeasurementswere takenwith SpectronicGenesys spectrophotometer (Thermo Electron CorporationUSA) UV-VIS spectra were collected on Jasco V-630 UV-VISspectrophotometer (Jasco Inc USA) and 1H NMR spectrawere taken on Bruker 300MHz NMR spectrometer

22 Copolymer Synthesis and Characterization To producewater-soluble polymers VBT was copolymerized in a freeradical process with the anionic monomer VPS The ratio ofVBT VPS comonomers influences the behavior of the VBTpolymeric system and varies depending on the applicationTherefore VBT

119899 VPS119898have been synthesized with 119899 = 1

and119898 = 1 4 8 16 32VBT VPS 1 1 copolymer to a 300mL 3-neck round-

bottomed flask containing 250mL of a 50 (vv) aqueoussolution of isopropanol VBT (119 g 0049mol) and VPS(101 g 0049mol) were added The solution was heatedto 65∘C while stirring and 022 g of AIBN was addedStirring was continued for 16 h while the temperature wasmaintained at 65∘C The reaction mixture was cooled toroom temperature and rotary evaporated to concentrate to125mL in vacuo Adding the aqueous solution to 1 L of coldacetone precipitated the polymer Subsequently the whitesolid precipitate was filtered and then dried under vacuumfor 2 days To verify the absence of unreacted monomers theprecipitated polymer was analyzed by 1HNMR spectroscopyand the typical vinyl group signal at chemical shifts between5 and 6 ppm was not observed in the spectra Additionallyelemental analysis was used to confirm copolymer ratios [9]Scheme 1 presents the structure of the VBT-VPS copolymers

VBT VPS 1 4 1 8 1 16 and 1 32 copolymers weresynthesized with identical procedures only varying the cor-responding ratios of starting monomers

23 Coating Preparation and Film Irradiation Aqueous solu-tions of each VBT VPS

119898(119898 = 1 4 8 16 32) copoly-

mers were distributed homogeneously on PET film usingeither a no 3 or no 6 wire-round milled coating rod Thefilms were dried at room temperature for one hour and in


Table 1 Experimental variables used in the Plackett-Burman design

Variable Type Units Symbol Low level High levelpH Numerical a A 6 12Concentration Numerical g Lminus1 B 2 10Dyeing time Numerical Sec C 30 120Stability Numerical Day D 1 30Coating thickness Numerical 120583m E 68 136

Level one Level twoDrying filmb Categorical a F Yes NoComonomer ratioc Categorical a G 1 1 1 4aNot applicable bDrying as explained in Section 23 c1 1 = VBT VPS1 1 4 = VBT VPS4

Table 2 Twelve-trial PBD matrix for seven variables (A to G) experimental input values and observed and predicted absorbancea

Run order Experimental values Absorbanceb

A B C D E F G Observed Predicted1 120 2 30 1 136 Yes 1 4 018 0172 600 10 30 30 136 No 1 4 054 0523 120 10 120 1 136 No 1 1 058 0614 120 2 120 30 136 Yes 1 4 010 0115 120 2 30 30 68 No 1 1 044 0376 600 2 30 1 68 Yes 1 1 039 0437 600 10 30 30 136 Yes 1 1 067 0708 600 2 120 1 136 No 1 1 061 0589 600 2 120 30 68 No 1 4 015 01910 120 10 30 1 68 No 1 4 024 02811 600 10 120 1 68 Yes 1 4 036 02912 600 2 120 30 68 No 1 4 017 019aAndashG are symbols shown in Table 1 bAbsorbance measured at 610 nm

a vacuum oven (at 80∘C sim20 torr) for another hour to give auniform wet thickness of 68 120583m or 136 120583m according to thecoating rod specifications [28] Filmswere protected from theenvironmental light throughout the process

All copolymer-coated films were irradiated with a UVhand lamp at 254 nm from a distance of 1 cm at different times(from 10 to 60 seconds) for the preliminary studies and oneminute for the experimental design This process leads to theimmobilization of the polymer in response to the irradiation(photoresist material) The curing reaction due to radiationwas achieved at room temperature thus these coatings canbe prepared on heat sensitive materials

The samples were then immersed into an aqueous solu-tion of MB dye (1 times 10minus3M) for 30 or 120 s Next theywere dried by hot air or at room temperature and visuallyexamined for uniform coloring The photocrosslinking wasmonitored indirectly by UV-VIS spectroscopy measuring theefficiency of dye adsorption

24 Plackett-Burman Design Plackett-Burman design(PBD) [29] was used in the present study to screenthe essential variables that significantly influence thephotocrosslinking process In this study a 12-run PBDincluding a replicated one to analyze the model lack of fitwas applied to evaluate seven factors five numerical andtwo categorical Each variable was examined at two levels

according to the guidelines of PBD [29] Table 1 illustrates theseven variables and their corresponding levels (lowhigh fornumerical variables and onetwo for categorical variables)used in the experimental designThe values of the levels wereset according to our preliminary experimental results

The PBD and the response values of absorbance corre-sponding toMB dye adsorption on photocrosslinked copoly-mer both the observed and predicted by the PBD model areshown in Table 2

25 Response Surface Methodology The optimal levels of thesignificant factors and the interactions of these variablesin a photocrosslinking process were analyzed by CentralComposite Design (CCD) In this study a two-factor five-level CCD with 10 runs was employed The tested variables(pH and polymer concentration) were denoted as 119883

1and

1198832 respectivelyThe numerical variables were assessed at five

different levels combining factorial axial and central pointsaccording to the guidelines of CCD [27] The values for thethree tested variables are shown in Table 3

26 Statistical Analysis and Software Theanalysis of variance(ANOVA)was conducted to determine the importance of themodels and the regression coefficients both in PBD andCCDassays The statistical significance of the employed models


Table 3 Levels of the variables tested in the CCD

Variable Type Symbol Factorial levels Axial levels Central levelpH Numerical 119883

1750 1050 600 1200 900

Concentration Numerical 1198832

400 800 200 1000 600

their terms and their lack of fits were checked by Fisherrsquos F-test [30] This test is used for comparing the model variancewith the residual (error) variance if the variances are close tothe same value their ratio will be close to unity and it is lesslikely that any of the factors terms or lack of fits will have asignificant effect on the response

In CCD the quality of the polynomial equation wasjudged from the determination coefficient (R2) the predictedR2 (pred-R2) whichmeasures how good themodel predicts aresponse value the R2 adjusted for the number of parametersin the model relative to the number of points in the design(Adj-R2) which estimates the amount of variation around themean explained by the model and its statistical significanceswere checked also by Fisherrsquos F-test [30]The surface responseand the contour plots of the predicted model responseswere used to assess the interactive relationships between thesignificant variables

Design-Expert software [27] was used for designing theexperiments as well as for the regression and graphical anal-ysis of the experimental data obtained

3 Results and Discussion

31 Preliminary Step The variables that could influence thepolymer photocrosslinking and subsequent dye adsorptionprocess were defined as follows It was demonstrated that theirradiation time is positively related to the degree of pho-tocrosslinking and how this relationship is modified whenchanging the VBT VPS copolymer ratio up to a proportion1 16 [9] However such analysis was carried out qualitativelyand therefore it is not possible to predict accurately thebehavior of the photocrosslinking process

Figure 2 shows the total intensity ofMB absorption signalas function of irradiation time for polymer films at thesame concentration (2) with different VBT to VPS ratios(1 1 to 1 32) It can clearly be observed that the greaterthe proportion of VPS to VBT the larger the irradiationtime required to immobilize the polymer on the substratesurface and the lower the amount of dye adsorbed on thepolymer after saturation In general these results are in goodagreement with previous reported data [9] However fromthe potential technological-utility point of view it is clear thatmixtures with higher proportion of VPS (1 8 1 16 and 1 32)are not convenient since the sensitivity of the absorptionsignal is poor at 60 seconds compared with the VBT VPS(1 1) Based on these preliminary results the analysis of theexperiments was completed only with the polymers of thelowest ratio of VPS (1 1 and 1 4)

On the other hand it is reasonable that the dyeing timesignificantly influences the observed signal as this processfavors the physisorption although previous studies did not

explain in detail the effect of this factor [9]Therefore dyeingtime is defined as a potential influential variable in theprocess

Experimentally it was found that the pH value of theVBT1 VPS32

solution increases to 11 Furthermore the pHof the solution containing fewer amounts of VPS is around65 On this basis the pH influence on the photocrosslink-ing process was analyzed since it can affect the acid-basebehavior of thymine [22] and therefore reduce the efficiencyof photocrosslinking process

In addition it was found experimentally that the pH ofthe solutions with greater VPS percentage (1 8 to 1 32) wasmodified over time and after 30 days of preparation the pHstabilized in a value close to 6 While the explanation forthis phenomenon is not completely clear the stability of thesolutions was considered as a potential influential variable inthe process

It has been shown that the film thickness controls thecrosslinking process being more effective as the thicknessreduces [31] Therefore two coating thicknesses were com-pared to see how this variable could influence the processSimilarly it is likely that increasing the polymer concentra-tion in the solution influences the process Previous worksused 10 aqueous solution of VBT-VPS [9 20] From anenvironmentally perspective it seemed interesting to ver-ify whether or not lower concentration values give goodresponses as well

Finally it was reported that the retained water in thecoated film could modify the process [31 32] Two alter-native drying methods were compared to test the statisticalsignificance of the drying method (a) one hour at roomtemperature and (b) an additional hour in oven at 100∘C

In summary the seven experimental variables used in thePBD are shown in Table 1

32 Screening Step The data listed in Table 2 indicates a widevariation in the absorption signal corresponding to methy-lene blue dye adsorbed on the photocrosslinked polymerfrom 010 to 067 in the 12 trials This variation suggeststhat the optimization process is crucial for improving andcontrolling the dye adsorption after the photocrosslinkingprocessThe analysis of the regression coefficients of the sevenfactors presented in Table 4 showed that factors B C and Fhad positive effects on dye adsortion whereas factors A D Eand G had negative effects

A Model F value of 1312 (see Table 4) indicates that themodel is significant there is only a 128 chance that a ldquoModelF Valuerdquo this large could occur due to noise [30]The variablewith ldquoProbgtFrdquo value lower than 00500 points out thatmodelterms are significant while values greater than 01000 indicatethat the model terms are insignificant [30] It was clear thatvariables A B E and G were the significant factors while


06

05

04

03

02

01

0

120100806040200

Irradiation time (s)

VBT1 VPS4VBT1 VPS8

VBT1 VPS16VBT1 VPS32

VBT1 VPS1

119860610

nm(A

U)

(a)

06

05

04

03

02

01

0

400 500 600 700 800 900

Wavelength (nm)

Abso

rban

ce (A

U)

(b)

Figure 2 (a) Time evolution of MB absorption signal for polymer films at the same concentration (2) with different VBT to VPS ratios(1 1 to 1 32) (b) UV-VIS absorption spectra of polymer film of VBT VPS

1at 2 and 60 seconds irradiation

Table 4 Effects of the variables and statistical analysis of the PBD

Source Coefficient estimatea Sum of squares dfb Mean square 119865 value 119875 valueProb gt 119865

Model 04215968 7 006022811 131201459 00128A minus00630 003967072 1 003967072 864190442 00424B 0079 006239922 1 006239922 13593102 00211C minus002242 000503972 1 000503972 109785677 03539D minus00058 000034116 1 000034116 007431762 07986E 00600 003602371 1 003602371 784743665 00487F 00368 001359198 1 001359198 296088871 01604G minus01287 01657404 1 01657404 361050351 00039Residual 001836203 4 000459051

Lack of fit 001812003 3 000604001 249587134 01458Pure error 0000242 1 0000242

Cor Totalc 043995883 11aIn terms of coded factors For the intercept the estimated coefficient is 039 bDegree of freedom cSum of total squares corrected for the meanThe significant factors (at 5 significance level) are shown in bold type

variables C D and F were considered insignificant and werenot included in the next step of the CCD experiments (seeTable 4)

Figure 3 shows the time evolution of the MB adsorptionsignal for copolymer films of VBT VPS

1and VBT VPS

4at

2 concentration It can clearly be seen that the time evo-lution of 1 1 is faster than 1 4 reaching a similar maximumabsorption value at 60 sec and 450 sec respectivelyThereforeat the irradiation time used in the experiments (60 sec) thesignal intensity of the MB dye adsorbed on the crosslinkedpolymers is about 65 lower for 1 4 than 1 1 being theformer less energy efficient These results are consistent withthe fact that decreasing the amount of the crosslinkablemonomer VBT also slows down the curing process andconsequently the amount of dye adsorbed after washing Forthat reason the comonomer ratio 1 4 was not included in

the CCD model On the other hand as it was shown in areported work [31] films made using coating rods no 6 giverise to thicker films (136 120583m) that need longer irradiationtimes to crosslink and produce comparable signal intensitiesof the adsorbed dyeTherefore the coating thickness was alsoexcluded in the CCD model

Finally the inclusion of a duplicate as mentioned in theexperimental section allowed the model fit determinationThe ldquolack of fit F valuerdquo of 2496 suggests that it is notsignificant relative to the pure error there is a 1458 chancethat a ldquoLack of Fit F-valuerdquo this large could occur due toexperimental noise [30]

33 Optimization Step CCD was used to study the correla-tions between the significant factors and to determine their


Table 5 Central composite design matrix and the correspond-ing experimental and predicted responses for dye adsorption oncrosslinked polymer process

Run order pH Concentration Absorbancea

Observed Predicted1 90 6 063 0572 75 8 060 0583 75 4 049 0504 90 2 041 0415 105 4 046 0486 60 6 048 0507 105 8 075 0738 90 6 057 0579 90 10 071 07410 120 6 063 064aAbsorbance measured at 610 nm

05

04

03

02

01

0

0 400300200100


VBT VPS1VBT VPS4

119860610

nm(A

U)

Figure 3 Time evolution of MB adsorption signal for the copoly-mers VBT VPS

1(∙) and VBT VPS

4(998779) at the same concentration

(2)

optimal levels The central composite design matrix of testedvariables and the experimental results are represented inTable 5

The competence of the model was checked usingANOVA as shown in Table 6The ldquoF valuerdquo of the model was344 and the 119875 value of ldquoProb gt Frdquo was lt005 suggesting thatthe model proposed for the raised CCD (two-factor interac-tion) was significant Linear terms of 119883

1 1198832and interaction

term of11988311198832were significant for dye adsorption process

From ANOVA the experimental results of RSM fitted viathe response surface regression procedure is a polynomialequation with the following expression

119884 = 1205730+ 12057311198831+ 12057321198832+ 1205731211988311198832 (1)

in which 119884 is the predicted response119883119894are the independent

variables with 119894 = 1 and 2 1205730is the offset term 120573

119894is the

119894th linear coefficient and 12057312

is the 1198831and 119883

2interaction

coefficient

The coefficient of determination (R2) was calculatedas 09451 for dye adsortion according to (1) indicating agood agreement between the experimental and the predictedvalues The pred-R2 of 08627 was in reasonable agreementwith adj-R2 of 09176 The value of ldquoadequate precisionrdquowhich measures the signal-to-noise ratio resulted in a valueof 165 suggesting an adequate signal [27] The ldquolack of fit Fvaluerdquo of 051 implied that the ldquolack of fitrdquowas not significantlyrelative to the pure errorThemodel was found to be adequatefor prediction within the range of variables employed

The graphical representations of the regression model(see (1)) and their corresponding contour plot were obtainedusing Design-Expert software and are presented in Figure 4for comonomer ratio 1 1 The surface response plot repre-sents the effect of two independent numerical variables thatis pH and polymer concentration The shape of the corre-sponding contour plot indicates whether or not the mutualinteraction between the independent variables is significantAs shown in Figure 4 the surface response of absorbanceindicates the presence of two regions of maximum responseone at high concentration and pH and the other at low pHThe optimum value found for the numerical variables for thiscopolymer composition using the CCDmodel equation is 9for concentration and 107 for pH

A decrease in absorbance happens when the pH value isincreased from 6 to 12 for concentrations up to 6 givingrise to a relative maximum in the surface The observeddecrease of the absorbance at low concentration suggestedthat at high pH value the thymine moiety is present in theanionic formproducing a strong reduction of the crosslinkingprocess as it was mentioned above

At concentrations higher than 6 the tendency is inverseso that the absorbance enlarges when pH varies from 6 to12 showing an absolute maximum at 10 concentrationTherefore at higher concentrations that effect of pH isdiminished and the absorbance turns out to be in directrelation to the polymer concentration

The nature of the contour plot indicates that the mutualinteraction between the two independent variables (119883

1 1198832)

was significant which means that the effect of pH on theresponse was dependent on the level of concentration usedbeing negligible at concentrations larger than 6

34 Validation of the RSM Model The validation of thestatistical model and the regression equation were conductedby taking into account the values of the variables corre-sponding to maximum response calculated from (1) Underthese optimized conditions the predicted response for dyeadsortion was 082 and the observed experimental valuewas 083 plusmn 003 an average of triplicate measurementsThese results confirmed the validity of the model and theexperimental values were regarded to be quite close to thepredicted values

4 Conclusions

Results suggested that statistical strategy is an effectiveand important tool for the optimization of experimental


Table 6 ANOVA for RSM two factor interaction model


Model 010592423 3 003530808 343997072 000041198831-pH minus0069 001380408 1 001380408 134489461 001051198832-Conc minus0095 008377837 1 008377837 816230066 0000111988311198832

0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641

Lack of Fit 000441794 5 000088359 050766308 07806Pure Error 00017405 1 00017405 343997072 00004

Cor Totalc 011208267 9aIn terms of actual factors For the intercept the coefficient estimate is 09406 bDegree of freedom cSum of total squares corrected for the mean

028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH

Figure 4 Three-dimensional response surface plots and two-dimensional contour plots for dye adsorption process on photocrosslinkingpolymer showing the interactions between pH and concentration variables for VBT VPS

1

parameters involved in dye adsorption on crosslinked poly-mer processes In addition to the best of our knowledge thiswas the first report applying statistical experimental designsto optimize the crosslinking of thymine-based polymersThePBD results assigned a maximum absorption signal of 067while following the CCD method predictions a responseof 083 was obtained The pH effect was relevant for lowconcentrations (less than 6) but as it was shown notimportant for higher concentrations Optimal conditionsobtained in this experiment lead to a solid foundation forfurther use of thismethodology in the production of potentialphotoresistors

Conflict of Interests

The authors do not have any direct financial relation withany commercial identity mentioned in the paper and havedeclared that there is no conflict of interests

Acknowledgments

Debora M Martino Carlos E Boschetti and Santiago ABortolato aremembers of the ResearchCouncil of CONICETThe authors would like to thank Universidad Nacional delLitoral (CAI+DTipo II PI 11-57) CONICET (PIP 112-200801-01079 and D-12802011) and the NSF OISE (Grant no1031394) for the financial support

References

[1] H J Levinson Principles of Lithography SPIEThe InternationalSociety for Optical Engineering 2001

[2] K Takemoto ldquoFunctional monomers and polymers containingnucleic acid basesrdquo Journal of Polymer Science Polymer Sym-posia vol 55 pp 105ndash125 1976

[3] Y Inaki ldquoThymine polymers as high resolution photoresists andreversible photo-recordingmaterialsrdquo Polymer News vol 17 pp367ndash371 1992


[4] G M Blackburn and R J H Davies ldquoThe structure of thyminephoto-dimerrdquo Journal of the Chemical Society C vol 23 pp2239ndash2244 1966

[5] A A Lamola and J P Mittal ldquoSolution photochemistry ofthymine and uracilrdquo Science vol 154 no 3756 pp 1560ndash15611966

[6] C M Cheng M J Egbe M J Grasshoff et al ldquoSynthesisof 1-(vinylbenzyl)thymine a novel versatile multi-functionalmonomer rdquo Journal of Polymer Science A vol 33 pp 2515ndash25191995

[7] J M Grasshoff L D Taylor and J C Warner ldquoCopolymericmordants and photographic products and processes containingsamerdquo US Patent 5395731 March 1995

[8] J M Grasshoff L D Taylor and J C Warner ldquoVinylbenzylthymine monomersrdquo US Patent 5455349 October 1995

[9] C Kiarie J Bianchini S Trakhtenberg and J C WarnerldquoMethylene blue adsorption on thymine based polyvinylphen-ylsulfonate filmsrdquo Journal of Macromolecular Science A vol 42no 11 pp 1489ndash1496 2005

[10] J R Bianchini K Saito T B Balin V Dua and J C WarnerldquoThymine-based water-soluble phototerpolymers their prepa-ration and synthesisrdquo Journal of Polymer Science A vol 45 no7 pp 1296ndash1303 2007

[11] A S Cannon J Raudys A Undurti and J CWarner ldquoPhotore-active Polymers and Devices for use in Hair Treatmentsrdquo PCTInt Appl WO 2004058187 p 23 2004

[12] J M Grasshoff L D Taylor and J CWarner ldquoMethod of imag-ing using a polymeric photoresist having pendant vinylbenzylthymine groupsrdquo US Patent 5616451 April 1997

[13] JMGrasshoff L D Taylor and J CWarner ldquoCopolymers hav-ing pendant functional thymine groupsrdquo US Patent 5708106January 1998

[14] L Lloyd-Kindstrand and J C Warner ldquoThymine-containingstyrene polymers as environmentally benign photoresistsrdquo inBiopolymers S Matsumura and A Steinbuchel Eds vol 9 pp165ndash174 John Wiley amp Sons Weinheim Germany 2003

[15] S Trakhtenberg Y Hangun-Balkir J C Warner et al ldquoPhoto-cross-linked immobilization of polyelectrolytes for enzymaticconstruction of conductive nanocompositesrdquo Journal of theAmerican Chemical Society vol 127 no 25 pp 9100ndash9104 2005

[16] K Saito L R Ingalls J Lee and J C Warner ldquoCore-bound polymeric micellar system based on photocrosslinkingof thyminerdquo Chemical Communications no 24 pp 2503ndash25052007

[17] K Saito and J C Warner ldquoCore-shell thymine containing poly-meric micelle system study of controlled release of riboflavinrdquoGreen Chemistry Letters and Reviews vol 2 no 2 pp 71ndash762009

[18] G Kaur S L Y Chang T D M Bell M T W Hearn and KJ Saito ldquoBioinspired core-crosslinked micelles from thymine-functionalized amphiphilic block copolymers hydrogen bond-ing and photo-crosslinking studyrdquo Journal of Polymer Science Avol 49 pp 4121ndash4128 2011

[19] S A Bortolato A L Barbarini R M Benitez D A Estenozand D M Martino ldquoPhoto-induced curing of thymine-basedbioinspired polymers A chemometric analysisrdquoLatin AmericanApplied Research In press

[20] S Trakhtenberg J C Warner R Nagarajan F F Bruno LA Samuelson and J Kumar ldquoSpectroscopic and microscopicanalysis of photo-cross-linked vinylbenzylthymine copolymersfor photoresist applicationsrdquo Chemistry of Materials vol 18 no12 pp 2873ndash2881 2006

[21] M J Bowden ldquoA perspective on resist materials for fine-line lithographyrdquo in Materials For Microlithography Radiation-Sensitive Polymers L F Thompson C G Willson and J M JFrechet Eds ACS Washington DC USA 1984

[22] M A Morsy A M Ai-Somali and A Suwaiyan ldquoFluores-cence of thymine tautomers at room temperature in aqueoussolutionsrdquo Journal of Physical Chemistry B vol 103 no 50 pp11205ndash11210 1999

[23] N J Miller and N C Miller Statistics and Chemometrics ForAnalytical Chemistry chapter 7 Prentice Hall 5th edition 2005

[24] D B Hibbert ldquoExperimental design in chromatography atutorial reviewrdquo Journal of Chromatography A vol 910 pp 2ndash13 2012

[25] P Wang Z Wang and Z Wu ldquoInsights into the effect ofpreparation variables on morphology and performance ofpolyacrylonitrile membranes using Plackett-Burman designexperimentsrdquoChemical Engineering Journal vol 193 pp 50ndash582012

[26] J Zhou X Yu C Ding et al ldquoOptimization of phenol degrada-tion by Candida tropicalis Z-04 using Plackett-Burman designand response surface methodologyrdquo Journal of EnvironmentalSciences vol 23 no 1 pp 22ndash30 2011

[27] Design Expert Version 7 Stat-Ease Inc Minneapolis MinnUSA

[28] D M MacLeod ldquoWire-Wound rod coatingrdquo in Coating Tech-nology Handbook D Satas Ed Marcel Dekker New York NYUSA 1991

[29] R L Plackett and J P Burman ldquoThe design of optimummultifactorial experimentsrdquo Biometrika vol 33 pp 305ndash3251946

[30] W P Gardiner Statistical Analysis Methods For Chemists ASoftware-Based Approach The Royal Society of ChemistryLondon UK 1997

[31] A L Barbarini D L Reyna and D M Martino ldquoThe effectof light intensity film thickness and monomer composition instyrene-based bioinspired polymersrdquo Green Chemistry Lettersand Reviews vol 3 no 3 pp 231ndash237 2010

[32] A L Barbarini D M Martino and D A Estenoz ldquoSynthesischaracterization and curing of bioinspired polymers basedon vinyl benzyl thymine and triethyl ammonium chloriderdquoMacromolecular Reaction Engineering vol 4 pp 453ndash460 2010

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


the copolymerization of VBT with charged functionalgroups can improve its solubility Among them substitutedstyrenes either cationic such as vinylbenzyl triethylammo-nium chloride (VBA) and N-butyl-NN-dimethyl-(4-vin-ylbenzyl)ammonium chloride (BDMQ) or anionic such asvinylphenyl sufonate (VPS) allow for obtaining a fully water-processable photoresist eliminating the need of toxic solvents[9 10] The resulting photopolymers of VBT and VPS orVBA are water soluble environmentally benign and undergoa photodimerization reaction of the pendant thymine unitswhen exposed to low levels of ultraviolet irradiation Thisprocess leads to an immobilization of the copolymer on avariety of substrates in response to irradiation and allows theremoval of unexposed regions by aqueouswash (photoresist)having potential applications in a variety of fields [9ndash19]Trakhtenberg et al introduced the photoresistive capacityof VBT-VPS copolymers and demonstrated that they can beused as a viable template for enzymatic synthesis of conduc-tive polyaniline allowing for surface photopatterning witha conductive polymer under mild conditions [15] The samecopolymer was also used in photoresist applications [9 20]In those works the authors immobilized the copolymers toform thin films on polyethylene terephthalate (PET) substrateand demonstrated that the process is potentially useful for theadvancement of photoresistors [20]

In photolithography technique in order to create thepatterns the wafers are coated with a photosensitive materialcalled photoresist which changes its solubility upon exposureto light through an appropriate mask of UV opaque materialThis allows the selective irradiation of only the desired areasof the photoresist-coated wafer thus transferring the patternfrom themask onto thewafer After being exposed to light thephotoresist-coated wafer goes into a developing solution thatselectively removes the resist layer from unexposed areasresulting in a wafer with the semiconductor surface partiallyprotected by the resist [21] In subsequent steps the unpro-tected areas are modified for example by chemical etchingwhile protected areas remain intact Finally the remainingphotoresist is stripped off the wafer which now features thepattern identical to the one on the mask This process canbe repeated several times using different masks [1] Figure 1schematically presents the photolithography process

Taking into account that the photoimmobilized copoly-mer film is very thin (lt1120583m) and translucent the immobi-lized copolymer coatings are typically visualized by dippingthe resulting patterned films into a solution of an oppositelycharged dye The dye chosen for VPS was methylene blue(MB) given that it has a net positive charge that favorsthe physisorption process on the polymer as it was shown[9] The dye selectively adsorbs on the charges of the pho-tocrosslinked copolymer providing clear contrast from theunreacted regions The amount of adsorbed dye can be mon-itored by UV-VIS spectroscopy measuring the absorbanceat 610 nm (MB absorbance maximum) and therefore acorrespondence among the measured absorbance and theamount of immobilized charged groups on the substratesurface can be made [9]

The technological applications of these polymers wereseen earlier than the necessary basic studies which could

Step 1 clean substrate

Step 2 coat substrate withphotoresist

Step 3 expose to UV lightthrough mask

Step 4 develop unexposed resist

Step 5 transfer pattern tosubstrate via etching

Step 6 strip photoresist

ℎ

Figure 1 Description of photolitography process

help to understand their behavior and improve their serviceTherefore more studies need to be done in order to optimizethe proposed photocrosslinking method due to the largeamount of variables that have effect on the processing anddevelopment of these copolymers To begin with thymine isa compound having acid-base behavior with a pKa sim9 and ithas been demonstrated that at pH greater than pKa thymineexists mostly in its anionic form in an equilibrium betweentwo tautomers (ratio 1 1) one of which cannot crosslink [22]It was found experimentally that increasing the proportionof VPS in its VBT-VPS copolymer the pH of the solutionincreases to values close to 11 which could produce a signif-icant reduction in the efficiency of the crosslinking processHowever the efficiency and reproducibility of the methodused to prepare VBT-VPS coatings may depend on otherfactors including the coating thickness and the copolymercomposition [20] Although the works cited before [9 20]are very helpful to screen important factors influencing filmpreparation they are insufficient to establish a general rulefor manufacturing certain photoresist polymers with reliableproperties In general it is difficult to obtain the comprehen-sive effects of some factors through a reasonable number ofexperiments Solving this problem in a rational way involvesperforming an experimental design [23] This procedure canbe summarized in three stages (1) identification of factorsthat can influence the results of the experiments (2) useof statistical analysis to separate and evaluate the effectsof the various factors involved ldquoscreening phaserdquo and (3)with the significant factors get the best response possiblefor the developed experiment ldquoresponse surface phaserdquo [23]The primordial difference between the classical one-variable-at-a-time method and the experimental design is that inthe latter case the values of all the factors are varied ineach experiment in a programmed and rational way Someof the studied factors will probably have no influence onthe experiment and only few will act upon the responsetherefore the essential factors can be detected while keepingthe number of trials to a minimum

Plackett-Burman design (PBD) is a method that caninspect up to119873minus1 factors in119873 experiments and is commonly








N

N OO

H

S OO

Ominus

Na+

119898119899









119898(119898 = 1 4 8 16 32) copoly-
















1and







1750 1050 600 1200 900


400 800 200 1000 600


















06

05

04

03

02

01

0

120100806040200


VBT1 VPS4VBT1 VPS8


VBT1 VPS1

119860610

nm(A

U)

(a)

06

05

04

03

02

01

0

400 500 600 700 800 900

Wavelength (nm)

Abso

rban

ce (A

U)

(b)










1and VBT VPS

4at









05

04

03

02

01

0

0 400300200100


VBT VPS1VBT VPS4

119860610

nm(A

U)


1(∙) and VBT VPS


(2)






119884 = 1205730+ 12057311198831+ 12057321198832+ 1205731211988311198832 (1)



119894is the


is the 1198831and 119883

2interaction

coefficient






1 1198832)



4 Conclusions






0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641



028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH


1




Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








N

N OO

H

S OO

Ominus

Na+

119898119899









119898(119898 = 1 4 8 16 32) copoly-
















1and







1750 1050 600 1200 900


400 800 200 1000 600


















06

05

04

03

02

01

0

120100806040200


VBT1 VPS4VBT1 VPS8


VBT1 VPS1

119860610

nm(A

U)

(a)

06

05

04

03

02

01

0

400 500 600 700 800 900

Wavelength (nm)

Abso

rban

ce (A

U)

(b)










1and VBT VPS

4at









05

04

03

02

01

0

0 400300200100


VBT VPS1VBT VPS4

119860610

nm(A

U)


1(∙) and VBT VPS


(2)






119884 = 1205730+ 12057311198831+ 12057321198832+ 1205731211988311198832 (1)



119894is the


is the 1198831and 119883

2interaction

coefficient






1 1198832)



4 Conclusions






0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641



028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH


1




Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of















1and







1750 1050 600 1200 900


400 800 200 1000 600


















06

05

04

03

02

01

0

120100806040200


VBT1 VPS4VBT1 VPS8


VBT1 VPS1

119860610

nm(A

U)

(a)

06

05

04

03

02

01

0

400 500 600 700 800 900

Wavelength (nm)

Abso

rban

ce (A

U)

(b)










1and VBT VPS

4at









05

04

03

02

01

0

0 400300200100


VBT VPS1VBT VPS4

119860610

nm(A

U)


1(∙) and VBT VPS


(2)






119884 = 1205730+ 12057311198831+ 12057321198832+ 1205731211988311198832 (1)



119894is the


is the 1198831and 119883

2interaction

coefficient






1 1198832)



4 Conclusions






0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641



028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH


1




Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




1750 1050 600 1200 900


400 800 200 1000 600


















06

05

04

03

02

01

0

120100806040200


VBT1 VPS4VBT1 VPS8


VBT1 VPS1

119860610

nm(A

U)

(a)

06

05

04

03

02

01

0

400 500 600 700 800 900

Wavelength (nm)

Abso

rban

ce (A

U)

(b)










1and VBT VPS

4at









05

04

03

02

01

0

0 400300200100


VBT VPS1VBT VPS4

119860610

nm(A

U)


1(∙) and VBT VPS


(2)






119884 = 1205730+ 12057311198831+ 12057321198832+ 1205731211988311198832 (1)



119894is the


is the 1198831and 119883

2interaction

coefficient






1 1198832)



4 Conclusions






0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641



028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH


1




Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


06

05

04

03

02

01

0

120100806040200


VBT1 VPS4VBT1 VPS8


VBT1 VPS1

119860610

nm(A

U)

(a)

06

05

04

03

02

01

0

400 500 600 700 800 900

Wavelength (nm)

Abso

rban

ce (A

U)

(b)










1and VBT VPS

4at









05

04

03

02

01

0

0 400300200100


VBT VPS1VBT VPS4

119860610

nm(A

U)


1(∙) and VBT VPS


(2)






119884 = 1205730+ 12057311198831+ 12057321198832+ 1205731211988311198832 (1)



119894is the


is the 1198831and 119883

2interaction

coefficient






1 1198832)



4 Conclusions






0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641



028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH


1




Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





05

04

03

02

01

0

0 400300200100


VBT VPS1VBT VPS4

119860610

nm(A

U)


1(∙) and VBT VPS


(2)






119884 = 1205730+ 12057311198831+ 12057321198832+ 1205731211988311198832 (1)



119894is the


is the 1198831and 119883

2interaction

coefficient






1 1198832)



4 Conclusions






0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641



028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH


1




Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





0015 000834178 1 000834178 812716909 00292Residual 000615844 6 000102641



028

046

064

082

1

6

75

9

105

122

4

6

8

10

6 75 9 105 12

2

4

6

8

10

0407431

0524024

0640617

0757209

0873802

Abso

rban

ce (A

U)

Absorbance (AU)

1198832 co

ncentra

tion

1198831 pH

1198832 c

once

ntra

tion

1198831 pH


1




Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Documents

Research Article Optimization of Environmentally Benign ...downloads.hindawi.com/journals/jchem/2013/947137.pdf · Optimization of Environmentally Benign Polymers Based on ... a ecting