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Chemistry 367L/392N
Macromolecular ChemistryMacromolecular Chemistry
Lecture 11 Lecture 11 B
HT
Chemistry 367L/392N
Light Scattering ExperimentLight Scattering Experiment
MeasureI/I0 = f(θ)
Chemistry 367L/392N
Standard ApproachStandard Approach
� Measure scattering of an analyte relative to a well characterized very pure liquid
� Toluene is often used due to good scattering signal and values well characterized for a range ottemperatures and wavelengths. Ratio is tabulated in many reference books.
CH3
Chemistry 367L/392N
IA = lntensity of analyte (sample I – solvent I)no = Solvent RIIS = Intensity of standard (Toluene?)nS = RI of Standard RS = Rayleigh ratio of standard
22
0044
00
2222
==dcdcdndn
nnNN
KKAA
λλππ
λo = laser wavelengthNA = Avogadros numberno = Solvent RIdn/dc = differential RI increment
SS
SSSS
AA RRnnIInnII
RR22
22
00==θθ
KCKC22
1122
θθ
ccAAMMRR
++==
Some Messy but accessible Constants Some Messy but accessible Constants
Chemistry 367L/392N
Molecular Weight ExampleMolecular Weight Example
Chemistry 367L/392N
Light ScatteringLight Scattering
Therefore a Therefore a ““ Debye plotDebye plot”” of of KC/KC/RRθθ
versusversuscc should give a straight should give a straight line whose intercept at zero concentration will be line whose intercept at zero concentration will be 1/Mw1/Mw and and whose slope will be 2whose slope will be 2AA22!!
For Rayleigh For Rayleigh scatterersscatterers, ,
KCKC22
1122
θθ
ccAAMMRR
++== (y = b + (y = b + mxmx))
Note that the moment of the distribution is Mw !Note that the moment of the distribution is Mw !
Chemistry 367L/392N
The Debye PlotThe Debye PlotK
C/Rө
(1/M
w)
Conc (g/ml)
xx
xx
x
1/Mw1/Mw KCKC22
1122
θθ
ccAAMMRR
++==
Chemistry 367L/392N
Chain Transfer in Free Radical Chain Transfer in Free Radical PolymerizationPolymerization
� A termination and re-initiation reaction
Chemistry 367L/392N
Chain Transfer Agents (Chain Transfer Agents (CTAsCTAs))
� Thiols are efficient examples
Chemistry 367L/392N
Chain Transfer to PolymerChain Transfer to Polymer� Creation of branches� “ Back biting”
Chemistry 367L/392N
Branching in PolyethyleneBranching in Polyethylene� Common Branch length is 4 or 5….why ???
H
H3C
H3C
Chemistry 367L/392N
Chain Transfer to InitiatorChain Transfer to Initiator� Example for acrylonitrile and BPO
� What effect does this process have on DP, PDI??
Chemistry 367L/392N
Chain Transfer KineticsChain Transfer Kinetics
The chain transfer constant, C is defined as the ratioThe chain transfer constant, C is defined as the ratioof the chain transfer and propagation rate constants;of the chain transfer and propagation rate constants;
C = kC = ktrtr/k/kpp
There is some C, which includes a term for transfer to a There is some C, which includes a term for transfer to a CTA, and one to monomer, solvent, polymer, etc.CTA, and one to monomer, solvent, polymer, etc.
The higher the value of C the smaller the amount The higher the value of C the smaller the amount required to lower the molecular weightrequired to lower the molecular weight
Chemistry 367L/392N
Chain transfer constant
B uSHI n H
BuS*I n
* + +
ptr kk=
ptrI
kk=CI
ptrS
kk=CS p
trMk
k=CM
Chemistry 367L/392N
DPDPnn = degree of = degree of polymerisationpolymerisationWITH transfer agentWITH transfer agent
DPDPoo = degree of = degree of polymerisationpolymerisationWITHOUT transfer agentWITHOUT transfer agent
Measurement of Chain Transfer ConstantsMeasurement of Chain Transfer Constants
+=monomer
gentTransfer aCs
DPDPn 0
11
CCSS = Chain Transfer = Chain Transfer ““ constantconstant”” or or ““ coefficientcoefficient””
The Mayo Equation:The Mayo Equation:
Chemistry 367L/392N
1/DP0
Cs
1/D
P
[S]/[M]
Generic Mayo plot
Chemistry 367L/392N
CHAIN TRANSFER AGENTSCHAIN TRANSFER AGENTS
Chain transfer activity dependent upon the monomer being Chain transfer activity dependent upon the monomer being polymerisedpolymerisedandandthe structure of the CTAthe structure of the CTA
For Styrene @ 60oC
CTA Cs x 104 Comment
Benzene 0.02 Addition to propagating radicalToluene 0.1 Resonance stabilizedEthyl Benzene 0.7 Weakening of C-H BondAcetone 4.1CCl4 110 Weak C-C1 BondCH3(CH2)3SH 210,000 Weak S-H Bond
Chemistry 367L/392N
Chain Transfer constants at 60 Chain Transfer constants at 60 °°CC
480,000210,000n-Butyl Mercaptan
10,700110CCl4
7.0n-Butyl amine
1503.4CHCl3
201.6n-Butanol
21.60.125Toluene
1.20.023Benzene
Vinyl acetateSryreneCTA
Chemistry 367L/392N
no CTA
Benzene(CS = 0.02)
CCl4 (CS = 110)
n-Butyl mercaptan (CS = 210,000)
[Transfer Agent][Styrene]
1/D
P ~
1/(
mol
.wt)
Effect of CTA on DP of Styrene @ 60Effect of CTA on DP of Styrene @ 60OOCC
Chemistry 367L/392N
Transfer to PolymerTransfer to Polymer
IntraIntramolecularmolecularreaction/backbiting reaction/backbiting →→
-- short chain branchesshort chain branches
InterIntermolecular reaction molecular reaction →→
-- long chain brancheslong chain branches
C(Psty) = 10 * 104
C(PMMA)= 0.1 - 360 * 104
Chemistry 367L/392N
Trapping RadicalsTrapping Radicals
OH
BHT
O
RHR
+
O
O
R
R
Chemistry 367L/392N
Trapping carbon centered radicalsTrapping carbon centered radicals� Carbon centered radicals stopped by addition to
oxygen or carbon
O O OR
O
Benzoquinone
R.
O OR
O O
R HR O O
R
R H+
HO O
R
Tautomerize
Chemistry 367L/392N
Stable Radical InhibitorsStable Radical Inhibitors
N N
O2N
NO2
O2N
Diphenylpicrylhydrazyl, DPPH
N
O
TEMPO
O
O
Galvanoxyl
NN
NN
Triphenylverdazyl
Chemistry 367L/392N
Some Familiar CTASome Familiar CTA’’ss
αα--tocopheroltocopherol Vit E
Ascorbic acid Ascorbic acid VitVit CC Butylated HydroxyAnisole BHA
Chemistry 367L/392N
BButylatedutylated HHydroxyydroxyTTolueneoluene� BHT radical will not initiate new chains
Chemistry 367L/392N
Interesting CTAInteresting CTA’’ss
N
O
N
O
PhenylPhenyl--aa--tt--butylnitronebutylnitrone
PBNPBN
TEMPOTEMPO
Chemistry 367L/392N
Chemistry 367L/392N
Radical Theory of AgingRadical Theory of Aging
Recent Review: Mechanisms of Ageing and Development Volume 125, Issues 10-11, October-November 2004
BH
T
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