Regulation of molecular weight of styrene—butadiene rubber. I. Choice of regulator from the homologous series of xanthogen disulfides

Abstract

SynopsisThe regulating efficiency of 14 dialkyl xanthogen disulfides in emulsion copolymerisation of butadiene with styrene a t +5OC. with the use of a diisopropylbenzene hydroperoxide-complexed ferrous iron-sodium formaldehyde sulfoxylate redox system in the presence of sodium soap of disproportionated rosin as an emulsifier, waa evaluated. The apparent chain transfer constants of n-alkyl and isoalkyl derivatives decreased logarithmically with increasing length of the alkyl group, which see1114 to be related to the analogous dependency of their solubilities in water. The dialkyl xanthogen disulfides, especially the lower homologs, acted as retarders of polymerization. The retardation did not affect their regulation efficiency. On the basis of values of the apparent chain transfer constants it is possibld to predict the molecular weight of polymers, except for the region where the regulation is poor and where the deteriorative influence of termination and crosslinking reactions takes place. The diisopropyl xanthogen disulfide has been selected as the most convenient of the compounds studied for molecular weight regulation of emulsion copolymerization of butadiene with styrene in the system mentioned.

Reversible addition-fragmentation chain transfer (co)polymerization of conjugated diene monomers: butadiene, isoprene and chloroprene

“…78 Mention should also be made of the work of Václavek. 79,80 In 1967, he described the emulsion polymerization of styrene-butadiene at 5 ∘ C using a typical recipe 'cold SBR' (see Appendix B) but in the presence of a series of dialkylxanthogen disulfides differing in the length of the alkyl groups ((CH 2 ) n CH 3 ; Scheme 4). A strong dependence of the transfer constant and the rate of polymerization on alkyl chain length was observed (decreasing from 16.4 for n = 0, to less than 2 for n > 5; Scheme 4), which may be related to the decreasing solubilities in water.…”

“…Mention should also be made of the work of Václavek . In 1967, he described the emulsion polymerization of styrene–butadiene at 5 °C using a typical recipe ‘cold SBR’ (see Appendix B) but in the presence of a series of dialkylxanthogen disulfides differing in the length of the alkyl groups ((CH 2 ) n CH 3 ; Scheme ).…”