Hydrophobic acceleration of p-styrenesulfonate polymerization by γ-gyclodextrin

Abstract

Radiation-induced radical polymerization of p-styrenesulfonate (SS) in aqueous solution is accelerated in the presence of γ-cyclodextrin (γ-CD). The polymer yield tends to be independent of γ-CD concentration above [γ-CD]/[SS]= 0.5. indicating that γ-CD forms a 1 : 2 complex with SS to promote the polymerization. p-Ethylbenzenesulfonate (EBS) suppresses the accelerating effect of γ-CD. This is attributed to competitive complexation of EBS with γ-CD. Molecular weight of the polymer becomes higher in the presence of γ-CD. Molecular weight distribution curves of the polymers obtained at [γ-CD]/[SS]= 0.15–0.30 are clearly bimodal, suggesting contributions of complexed and dissociated propagating radicals. An aggregation of the 1 : 2 complexes is proposed to account for the independent propagation of the complexed and dissociated radicals. Glucose (Glc), a component unit of CDs, also accelerates the polymerization, but to a smaller extent than γ-CD. The polymer yield continues to increase with Glc concentration up to [Glc]/[SS]= 6, and is hardly affected by EBS. A hydrophobic aggregation of SS may be responsible for the acceleration of the polymerization in the presence of Glc.