Cyclodextrins in Polymer Synthesis: Free Radical

Polymerization of b-Cyclodextrin

Complexes of Photosensitive Mesoionic

6-Oxo-1,6-dihydropyrimidin-3-ium-4-olates

in Aqueous Medium

Alexander Theis, Helmut Ritter*

Institute of Organic Chemistry and Macromolecular Chemistry, Universitatsstraße 1, 40225 Dusseldorf, GermanyFax: þ49 211 811478; E-mail: H.Ritter@uni-duesseldorf.de

Keywords: copolymerization; cyclodextrin; inclusion chemistry; photosensitive polymers; radical polymerization

Introduction

Mesoionic 6-oxo-1,6-dihydropyrimidin-3-ium-4-olates (1)

are six-membered heterocycles which were synthesized

primarily in 1971.[1,2] Many experiments were performed in

order to investigate 1,4-dipolar cycloadditions with olefins

and alkynes.[3–10] Their pharmacological activities are of

great interest,[11,12] and it was furthermore shown that irra-

diation of mesoionic compounds 1 leads irreversibly to the

structure of bis(b-lactames) 2 as illustrated in Scheme 1.[13]

With the change in molecular structure, changes of

the physical properties, such as color, volume, dipole

moment, and refractive index, can also be expected. For

this reason, it is interesting to prepare polymers containing

mesoionic compounds 1, which can be used as photosensi-

tive materials.[14–16]

Up to now, different approaches toward preparing meso-

ionic polymers have been made using styrene as a poly-

merizable group.[14,17,18] We also prepared new types

of polymers containing mesoionic groups in the main

chain.[16,19] Recently, the preparation of polymerizable

methacrylic derivatives was successfully conducted as

shown in Scheme 2.[15]

The homopolymerization of monomers 7 as well as co-

polymerization with methyl methacrylate (MMA) was

carried out in N,N-dimethylformamide (DMF) solution

at 60 8C with 2,20-azoisobutyronitrile (AIBN) as radical

initiator.[15]

Full Paper: Solid mesoionic 2-[2-(isopropenylcarbonyl-oxy)ethylthio]-1-methyl-6-oxo-3-phenyl-5-propyl-1,6-dihy-dropyrimidin-3-ium-4-olate was complexed in water usingb-cyclodextrin (b-CD) and randomly methylated b-CD,which resulted in polymerizable complexes with 2:1 stoichio-metry. The b-CD complex was characterized using 1H NMR,ROESY NMR and UV spectroscopy. Polymerization of thecomplex prepared from methylatedb-CD led to a photosensi-tive polymer, which precipitated during polymerization andwas nearly free of CD. Polymerization was carried out with awater-soluble redox initiator. In addition, a copolymer withmethyl methacrylate was prepared from the complexes, whichshowed a different mass-dependent distribution in the incor-poration in comparison to a copolymer prepared without CDin organic solvents.

Macromol. Chem. Phys. 2003, 204, 1297–1304 1297

Macromol. Chem. Phys. 2003, 204, No. 10 � WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2003 1022-1352/2003/1007–1297$17.50þ.50/0

In recent years, a new method for the polymerization

of hydrophobic monomers in aqueous solution came

up.[20–22] It is based on the use of at least stoichiometric

amounts of cyclodextrins, which show the capability of

forming water-soluble inclusion complexes of the mono-

mers. Upon polymerization with a water-soluble radical

initiator, the cyclodextrin (CD) slips off stepwise and

can be used for further complexations, whereby the

resulting polymer is insoluble in water and precipitates.

In contrast to the classical polyreactions in emulsion,[23]

this process can also be applied with solid monomers.[24]

Up to now, this method has been expanded on many other

examples.[25–28]

In order to obtain information about the mechanism, the

kinetics of the polymerization of various monomers[29,30] as

well as the influence of chain-transfer agents[31,32] was

investigated. In addition, examples whereby CDs hinder the

polymerization are known.[33] Furthermore, the influence

of CD on the copolymerization parameters of hydrophobic

monomers was examined.[34,35] In some examples, it was

also shown that the copolymerization of CD-complexed

hydrophobic monomers together with hydrophilic mono-

mers in water could only be performed in good yields by

the use of CDs.[36,37]

Referring to these results, we were encouraged to prepare

CD complexes of high-melting crystalline methacrylic

esters containing mesoionic 6-oxo-1,6-dihydropyrimidin-

3-ium-4-olates in aqueous medium and to investigate their

polymerization behavior.

Experimental Part

Materials and Methods

Mesoionic 2-[2-(isopropenylcarbonyloxy)ethylthio]-1-methyl-6-oxo-3-phenyl-5-propyl-1,6-dihydropyrimidin-3-ium-4-olatewas prepared according to the literature.[15] b-CD was receivedfrom Fluka. Randomly methylated b-CD (Me-b-CD) with adegree of methylation of 1.8 was purchased from Wacker. 1HNMR spectra and ROESY NMR spectra were recorded on aBruker AC200 or AM400 at room temperature. The deuteratedsolvent was used as lock and internal standard for the d scalerelative to TMS. Infrared spectra were measured using a NicoletFT-IR spectrometer 5DXC (DTGS detector) or 5SXB (MCTdetector). UV-vis spectra were taken on a Zeiss diode-arrayspectrometer MCS 320 and MCS 340. Differential scanningcalorimetry (DSC) measurements were performed on a PerkinElmer DSC 7.Gelpermeation chromatography (GPC) measure-ments were measured on a PSS installation with chloroform aseluent. 150 ml were injected on a column arrangement of PSSSDV 5m, 100, 1 000, and 10 000 A porosity. A TSP UV 2000UV-vis detector, and a Shodex differential refractometer wereused as detectors. The data were evaluated using PSS-WinGPC6.20. The response factors for copolymer evaluation werecalculated from the signals of the homopolymers.

Preparation of b-CD Complex 9a

1 g (0.88 mmol) b-CD 8a was dissolved in 45 ml of warmdemineralized water and cooled to room temperature. Then0.341 g (0.88 mmol) mesoionic 2-[2-(isopropenylcarbonyl-oxy)ethylthio]-1-methyl-6-oxo-3-phenyl-5-propyl-1,6-dihydro-pyrimidin-3-ium-4-olate (7a) was added and stirred for 5 d

Scheme 1. Intramolecular photocyclization.

Scheme 2. Synthesis of methacryl-substituted mesoions.

1298 A. Theis, H. Ritter

at room temperature. The obtained insoluble precipitationwas filtered and the filtrate was lyophilized to give 0.75 g(29% relative to the guest molecule) of complex 9a as ayellow powder. Water solubility: 17 mg in 1 ml of water atroom temperature.

1H NMR (400 MHz, D2O): d¼ 0.88 (t, 3H, mesoion.-propyl-CH3), 1.44 (tq, 2H, mesoion.-propyl-CH2–CH2–CH3),1.81 (s, 3H, mesoion.-methacryl-CH3), 2.32 (t, 2H, mesoion.-propyl-CH2–CH2–CH3), 3.35 (t, 2H, mesoion.-S–CH2), 3.56(dd, 14H, CD-4-H), 3.63 (dd, 14H, CD-2-H), 3.79–3.89 (m,42H, CD-5,6,60-H), 3.91 (dd, 14H, CD-3-H), 3.93 (s, 3H,mesoion.-N–CH3), 4.36 (t, 2H, mesoion.-O–CH2), 5.04 (d, 14H,CD-1-H), 5.67 (s, 1H, mesoion.-methacryl-CH2), 5.96 (s, 1H,mesoion.-methacryl-CH2), 7.30 (d, 2H, mesoion.-aryl-ortho-CH), 7.58–7.60 (m, 3H, mesoion.-aryl-meta-þ para-CH).

IR (KBr): 3387 (O–H), 2927 (aliph. C–H), 1596 (ar. C C),further signals at 1695, 1635, 1317, 1330, 1298, 1252, 1200,1156, 1079, 1031, 947, 860, 756, 707 cm�1.

UV (H2O): lmax/nm (log e)¼ 226 (4.42), 267 (3.90),343 (3.53).

Preparation of Me-b-CD Complex 9b

4 g (3.00 mmol) Me-b-CD 8b was dissolved in 25 ml ofdemineralized water. Then 0.776 g (2.00 mmol) mesoionic 7awere added and stirred for 5 d at room temperature. Theobtained insoluble precipitation was filtered and the filtratecontaining the complex was used for further reactions withoutisolation. 5 ml of the solution were lyophilized for character-ization. Yield of complex 9b relative to the complete batch:0.87 g (71% relative to guest molecule) as a yellow powderof. Water solubility: � 800 mg in 1 ml of water at roomtemperature.

1H NMR (400 MHz, D2O): d¼ 0.89 (t, 3H, mesoion.-propyl-CH3), 1.44 (tq, 2H, mesoion.-propyl-CH2–CH2–CH3), 1.82 (s,3H, mesoion.-methacryl-CH3), 2.32 (t, 2H, mesoion.-propyl-CH2–CH2–CH3), 3.92 (s, 3H, mesoion.-N–CH3), 4.36 (t, 2H,mesoion.-O–CH2), 5.67 (s, 1H, mesoion.-methacryl-CH2), 5.96(s, mesoion.-1H, mesoion.-methacryl-CH2), 7.29 (m, 2H,mesoion.-aryl-ortho-CH), 7.55–7.59 (m, 3H, mesoion.-aryl-meta-þ para-CH). Due to the statistical methylation, the signalsof 8b are not listed, the resonance signal of mesoion.-S–CH2 isoverlapped by the Me-b-CD signals and could not be separated.Integration of the signals of host and guest resulted in a 2:1complex stoichiometry.

IR (KBr): 3427 (O–H), 2931, 2840 (aliph. C–H), furthersignals at 1689, 1640, 1455, 1386, 1325, 1253, 1194, 1157,1085, 1046, 968, 859, 757, 704 cm�1.

UV (H2O): l/nm (log e)¼ 221 (4.31), 269 (3.95), 336(3.44).

Radical Homopolymerization of Complex 9b

(a) 5 ml of complex 9b were taken. (b) For comparison, a sus-pension of 0.116 g (0.3 mmol) of 7a in 5 ml of demineralizedwater was prepared. The solutions were carefully degassedwith nitrogen; 2.695 mg potassium peroxodisulfate and1.018 mg sodium hydrogensulfite (10 mmol each) were added,and the samples were heated to 60 8C for 1 h with stirring. Then,the precipitated polymer was separated by filtration, washed

with water and dried in vacuum to give (a) 60 mg (52%) and (b)110 mg (95%) of a yellow solid.

1H NMR (200 MHz, CDCl3): d¼ 0.75–0.98 (m, syndiot.methacryl-CH3þ propyl-CH3), 1.00–1.15 (m, heterot. meth-acryl-CH3), 1.15–1.55 (m, isot. methacryl-CH3þ isot. main-chain-CH2þ propyl-CH2–CH2–CH3), 1.55–2.00 (m, isot.þsyndiot. main-chain-CH2), 2.16 (m, propyl-CH2–CH2–CH3),2.74 (m, S–CH2), 3.34 (m, N–CH3), 4.07 (m, O–CH2), 7.16 (m,aryl-ortho-CH), 7.32–7.59 (m, aryl-metaþ para-CH).

IR (KBr): 2960, 2933, 2873 (aliph. C–H), 1729 (C O), 1639(mesoion. C O), 1594 (aryl C C), further signals at 1686,1491, 1455, 1254, 1150, 1112, 1044, 968, 755, 708, 695 cm�1.

GPC (trichloromethane, polystyrene standards): (a) conver-sion: 55%; Mn¼ 3 000; Mw¼ 3 800; D¼ 1.3, and (b) conver-sion: 14%; Mn¼ 2 500; Mw¼ 11 000; D¼ 4.5

The given conversions represent the polymer fractionin the measured solid. These values have to be multi-plied with the yield of solid in order to obtain overallconversions.

Radical Copolymerization of Complexed 7a with ComplexedMMA 11

(a) 0.687 g (0.516 mmol) of 8b were dissolved in 5 ml ofdemineralized water. Then 0.133 g (0.344 mmol) mesoionic 7awere added and the complex was prepared analogously to 9b. Itwas used without previous isolation (the solution containedapprox. 0.258 mmol of the complex).

(b) 13.31 g (10.0 mmol) 8b were dissolved in 35 ml ofdemineralized water. Then 1.00 g (10.0 mmol) MMA 11 wasadded and the suspension was stirred for 1 h at room tempe-rature. For the first 30 min, the mixture was periodically sonica-ted. The dissolved complex 12 (1:1 host/guest stoichiometry)was used without previous isolation.

(c) 5 ml of each solution derived from (a) and (b) werecombined and degassed with nitrogen for 30 min. 19.32 mg(71.5 mmol) potassium peroxodisulfate and 7.44 mg(71.5 mmol) sodium hydrogensulfite were added and the mix-ture was heated with stirring for 1 h at 60 8C. Then the pre-cipitated polymer was separated by filtration, washed withwater and dried in vacuum to give 0.12 g (50%) of a yellowsolid.

(d) 0.100 g (0.258 mmol) mesoionic 7a, 0.142 g (1.42 mmol)MMA 11 and 8.26 mg (50.3 mmol) AIBN were dissolved in1 ml of dry DMF. The mixture was degassed with nitrogen for30 min and polymerized for 24 h at 60 8C. The dissolvedpolymer was precipitated in a mixture of 50 ml methanol and50 ml water and dried under vacuum. For further purification,the product was dissolved in 2 ml methylene chloride, preci-pitated in 50 ml diethyl ether and again dried under vacuum togive (d) 0.13 g (54%) of a yellow solid.

1H NMR (400 MHz, CDCl3): d¼ 0.55–2.08 (m, methacryl-CH3 þ propyl-CH3 þmain-chain-CH2 þ propyl-CH2–CH2–CH3), 2.15 (m, propyl-CH2–CH2–CH3), 2.73 (m, S–CH2), 3.31(s, N–CH3), 3.55 (s, O–CH3), 4.04 (m, O–CH2), 7.13 (d, aryl-ortho-CH), 7.37–7.59 (m, aryl-meta-þ para-CH).

IR (KBr): 2993, 2951 (aliph. C–H), 1731 (C O), 1649(mesoion. C O), further signals at 1482, 1449, 1387, 1245,1194, 1151, 1072, 989, 843, 754, 708 cm�1.

Cyclodextrins in Polymer Synthesis: Free Radical Polymerization . . . 1299

GPC (trichloromethane, polystyrene standard): (c) Mn¼8500, Mw¼ 20 000, D¼ 2.4, and (d) Mn¼ 13 000, Mw¼31 000, D¼ 2.3.

DSC: Tg¼ 96 8C.

Results and Discussion

In order to prepare complexes, monomers 7a, 7d, and 7fwere stirred in equimolar amounts in saturated solutions of

native b-CD 8a (Scheme 3). After 5 d, the insoluble mono-

mer residuals were removed by filtration. The solution of

complex 9a showed a yellow color caused by the

complexed yellow monomer 7a whereas the solutions of

monomers 7d and 7f showed only minor coloration. The

solutions were lyophilized and the solid residuals were

analyzed by 1H NMR spectroscopy in D2O. The solution of

7a showed signals of b-CD and monomer in a ratio of 2:1,

the other solutions showed only negligible amounts of

monomer, indicating that no complexation occurred. This

can be explained by the fact that the monomer must be at

least sparingly soluble in water, so that monomer and b-CD

can come in contact. Monomer 7a bears the fewest non-

polar substituents, so it should show the highest water

solubility and therefore the highest complexation kinetics.

The 1H NMR spectrum of the complex (Figure 1) shows

significant shifts of the CD protons in position 3 and 5

to higher field in comparison to pure b-CD. These protons

are directed into the cavity of b-CD (see Figure 2), thus

a shifted signal is an indicator for a different environment

inside the cavity and therefore an evidence for successful

complexation.

Table 1 shows the strong shift of the 1H NMR resonance

of inner proton 3-H in comparison to the other protons,

which are shifted only irreducibly. For pure b-CD 8a, the

signal of the inner proton 5 is overlaid by the signals of the

protons 6, 60. In complex 9a, the signal is strongly shifted to

higher field so that it is separated from the other signals.

ROESY NMR experiments show a cross-peak between the

ortho protons of the guest’s phenyl group and the CD proton

in position 3 as well as the meta/para protons of the guest

and the CD protons in position 5 and 6. Therefore, the wider

side of the CD is preferably orientated towards the meso-

ionic function. Also, methacrylic CH2 and –CH3 protons

show cross-peaks to the inner CD protons in position 3, 5,

and 6. The other aliphatic protons show minor cross-peaks

to different inner and outer CD protons. Thus, complexation

could be confirmed, but the exact structure of the 2:1

complex in aqueous solution could not be resolved.

The UV spectrum of the complexed monomer 9a in

aqueous solution shows a strong hypsochromic shift of

the longest wavelength transition from 380 nm (dichloro-

methane without CD) to 340 nm (Figure 3). This is a result

of the enlarged energy difference between the high polar

ground state and the less polar excited state of the chromo-

phore caused by a more polar environment. The same mono-

mer 7a in ethanol shows the highest wavelength transition

at 345 nm, which indicates an even more polar adjacency of

the mesoionic function of complexed monomer 9a in com-

parison to the dissolved monomer 7a in ethanol. This is a

strong hint for sandwich-like complexation, whereby the

mesoionic function is not included into the cavity of CD and

thus surrounded by highly polar water molecules.

The water solubility of complex 9a is 17 mg/ml, which

corresponds to 2.5 mg/ml of the guest molecule 7a. For a

radical polymerization, this concentration is very low. In

order to improve the water solubility of the mesoionic

monomers, complex 9b with Me-b-CD 8b was prepared.

The preparation of complex 9b was done in analogy to

complex 9a, but due to the higher water solubility, less

amounts of water were necessary. Here, the 1H NMR

resonance signals of the inner Me-b-CD protons in complex

9b were also shifted in comparison to the signals of pure

Me-b-CD 8b, however, due to the statistical methylation,

a complete assignment of the signals could not be done.

Complex 9b has a solubility of 800 mg in 1 ml of water,

which is about fifty times higher than that of complex 9a. A

clear deep-yellow highly viscous solution was obtained.

For radical polymerization, complex 9b was used in the

concentration of 160 mg/ml as received, which corresponds

to 23.4 mg/ml of the guest molecule. At this concentration,

the viscosity is comparable to that of DMF, which is nor-

mally used as a solvent for radical polymerizations of meso-

ionic monomers. However, it must be considered that

polymerizations in DMF need much higher monomer

concentrations of 200–250 mg/ml to be successful.[15] The

polymerizationofcomplex9bwascarriedoutwith3.3mol-%

of a redox initiator, which is composed of potassium

peroxodisulfate and sodium hydrogensulfite (Scheme 4).

The NMR and IR spectra of the processed product clearly

show that polymer 10 is nearly free of Me-b-CD, which

shows that the Me-b-CD is slipped off from the monomer

during polymerization.Scheme 3. Preparation of the complexes.

1300 A. Theis, H. Ritter

In Figure 4, a distinct bimodal distribution is visible.

Besides the polymer with a mass distribution from 1 000

to 10 000 g/mol, an oligomeric fraction of nearly the

same total area with chain lengths from 1 to 4 could be

found.

In order to verify the influence of Me-b-CD, a sample of

monomer 7a under the same conditions but in the absence

of CD was polymerized and characterized by means of GPC

(Figure 5).

The conversions and GPC results are listed in Table 2. The

conversion values consider only the polymer fraction in the

precipitated product referring to the amount of monomer at

the beginning.

According to the GPC results of the polymer prepared

from the non-complexed monomer 7a, 85% of 7a was unre-

acted after 1 h. Additionally, the molecular mass distribution

of the polymer is bimodal and the polystyrene of analogous

molecular weight reaches values up to 200 000 g/mol. In this

sample, initiation obviously takes place with a low amount

of dissolved monomer. Then, the resulting oligomers form

aggregates, possibly stabilized by the ionic chain ends. At

the same time, conversion is much lower because, as men-

tioned above, the effective concentration of the monomer

molecule in solution is very low.

Besides the synthesis of homopolymers, also copolymers

were prepared. On the one hand, copolymers of mesoionic

monomers with complexed liquid standard monomers

are also of technical interest,[15] and on the other hand,

Table 1. 1H NMR spectroscopic shifts of the CD protons ofcomplex 9a.

Sample 1-H 2-H 3-H 4-H

Pure CD 8a 5.049 3.627 3.947 3.564Complex 9a 5.042 3.628 3.912 3.558Difference 0.007 0.001 0.035 0.006

Figure 1. 400 MHz 1H NMR spectrum of b-CD 8a and complex 9a between b-CD and 7ain D2O.

Figure 2. Schematic representation of the b-cyclodextrin torus.

Cyclodextrins in Polymer Synthesis: Free Radical Polymerization . . . 1301

copolymerization can also give information about the

mechanism of the polymerization of complexed monomers.

Due to its comparable double bond reactivity, MMA 11was

used as comonomer. A different tendency of polymeriza-

tion therefore can only be expected due to different

solubility or different steric demand, i.e. a different

diffusion coefficient.

Complex 12 between MMA and Me-b-CD was pre-

pared from a dispersion of MMA and an aqueous solution

of Me-b-CD via stirring and ultrasonic treatment. The solu-

tions of complexes 9b and 12 were combined in a ratio

5.5:1 and polymerized with 5.2 mol-% of the redox ini-

tiator (Scheme 5). For comparison, samples of the non-

complexed monomers in DMF as the solvent with 3 mol-%

of AIBN as the initiator were also polymerized.

Both copolymers were analyzed by means of GPC. Due

to the UVabsorbance of the mesoionic monomer 7a, which

is not overlapping with the absorbance of methyl meth-

acrylate 11, both compounds of the copolymer could be

detected separately by using UVand RI detectors. The GPC

diagrams calculated according to the copolymer evaluation

are displayed in Figure 6 and Figure 7.

In the sample, which was polymerized in DMF (Figure 6)

the mesoionic compound is preferably incorporated in the

low-molecular-weight area. The GPC curve of the polymer,

which was prepared with Me-b-CD in water (Figure 7)

shows a completely different feature. The difference in the

ratio in common is lower and the low-molecular-weight area

is enriched with incorporated MMA.

Table 3 shows, that the conversion and polydispersity of

both samples is nearly identical, but the molecular weight of

the copolymer prepared with Me-b-CD in water is

somewhat lower and less amounts of the mesoionic

compounds are incorporated. Nevertheless this method of

copolymerization represents a good alternative to the

standard methods because no organic solvents are needed,

and the classical emulsion polymerization cannot be used

due to the high melting solid monomer.

The influence of CD on the kinetics and molecular

weight is strongly dependent on the monomer. Accordingly,

Me-b-CD-complexed acrylates show different copolymer-

ization parameters in comparison to the free monomers in

organic solvents, which was explained by different complex

stabilities.[33,34]

In the case of the copolymerization of 9b and 12,

the MMA component is built in preferably. At the same

Figure 3. UV spectra of monomer 7a and complex 9a in differ-ent solvents.

Scheme 4. Polymerization of complex 9b.

Figure 4. GPC diagram of 10, polymerized with 3.3 mol-%redox initiator in water by the use of Me-b-CD.

Figure 5. GPC diagram of 10, polymerized with and withoutcyclodextrin (polymer fraction).

1302 A. Theis, H. Ritter

time, the mesoionic compound is enriched in the

high-molecular-weight area. The polymerization behavior

of the considered monomer combination is obviously very

complex and is a result of an interplay of different

conditions, such as steric demand, complex stoichiometries

and complex stabilities.

Conclusion

It was shown that mesoionic 2-[2-(isopropenylcarbonyl-

oxy)ethylthio]-1-methyl-6-oxo-3-phenyl-5-propyl-1,6- dihy-

dropyrimidin-3-ium-4-olate 7a can be complexed with

b-CD (8a) and randomly methylated b-CD (8b), which

results in water-soluble complexes of 2:1 stoichiometry.

b-CD complex 9a was analyzed by means of 1H NMR

spectroscopy, whereby the signals of the inner CD pro-

tons at position 3 and 5 were shifted to higher field in

comparison to pure CD. Complexation could also be con-

firmed by cross-peaks between the host and guest molecules

in ROESY NMR spectra. Taking into account the UV

spectroscopic results, the structure of the complex could be

proposed. The complex 9b prepared from Me-b-CD was

polymerized, whereby the photosensitive mesoionic poly-

mer 10 precipitated. It was nearly free of cyclodextrin.

Polymerization was carried out with a water-soluble redox

initiator. In addition, a copolymer from the complexed

Table 2. Comparison of the polymerization batches of monomer7a with and without Me-b-CD after 1 h. The concentration of themonomer in both samples was 23.4 mg/ml.

Batch In H2Owith Me-b-CD

In H2Owithout Me-b-CD

Conversion [%] 30 15Mn [g/mol] 3 000 2 500Mw [g/mol] 3 800 11 000D 1.3 4.5

Scheme 5. Preparation of a copolymer of 7a and MMA in waterutilizing Me-b-CD.

Figure 6. GPC diagram of the copolymer prepared from MMAand 7a, polymerized in DMF.

Figure 7. GPC diagram of the copolymer prepared from MMAand 7a, polymerized in water in the presence of Me-b-CD.

Cyclodextrins in Polymer Synthesis: Free Radical Polymerization . . . 1303

mesoionic monomer 9b and complexed MMA 12 was

prepared. Copolymer 13 showed a different mass-depen-

dent distribution in the incorporation in comparison to a

copolymer, which was prepared without cyclodextrin in

organic solvents.

Received: January 13, 2003Revised: April 24, 2003Accepted: May 2, 2003

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Table 3. Comparison of the copolymerization batches in DMFand in water with Me-b-CD, resulting in copolymer 13.

Batch In H2O with Me-b-CD In DMF

Conversion [%] 50 54Mn [g/mol] 8 500 13 000Mw [g/mol] 20 000 31 000D 2.4 2.3n/m (copolymer) 13:1 5.2:1

1304 A. Theis, H. Ritter