Page 236 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Free Radical Chain Polymerization 199

A B
C D

E
F G

1/DP H

I
J
K
L
M
N
[S]/[M]

FIGURE 6.3 Molecular weight of polystyrene as a function of solvent and solvent concentration:
A = n-butylmercaptan, B = carbon tetrabromide, C = carbon tetrachloride, D = o-cresol, E= p-cresol,
F = m-cresol, G = phenol, H = sec-butylbenzene, I = cumene, J = ethylbenzene, K = chloroform, L = n-hep-
tant, M = toluene, N = benzene where [S] = concentration of chain-transfer agent and [M] = concentration of
styrene monomer.

TABLE 6.4
Chain-Transfer Constants of Solvent to Styrene in Free
o
Radical Chain Polymerization at 60 C
Transfer Agent C s × 10 4 Transfer Agent C s × 10 4
Acetic acid 2.0 1-Dodecanethiol 148,000
Benzene 0.01 Hexane 0.9
Butyl alcohol 0.06 N,N-Dimethylaniline 12
t-Butyl alcohol 6.7 1-Naphthalenethiol 1,500
Butyl disulfi de 0.24 1-Octanethiol 190,000
Carbon tetrabromide 18,000 p-Methoxyphenol 260
Carbon tetrachloride 84 Phenol 8.1
Chloroform 0.5 Triethylamine 1.4
o-Chlorophenol 6.0 Toluene 0.105
2,6-Ditert-butylphenol 49 Water 0

Chain-transfer constants of various solvents, including those given in Figure 6.3, are given in
Table 6.4.
Chain-transfer agents have been called and employed as regulators (of molecular weight). When
used in large proportions, they are called telogens, since they produce low molecular weight poly-
mers (telomers).

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