Controlled functionalization of olefin/styrene copolymers through free radical processes

Abstract

The functionalization of styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) and styrene-co-butadiene (SBR) random copolymer by free radical processes is presented. SEBS was functionalized in the melt with diethyl maleate (DEM) and dicumyl peroxide (DCP) as initiator. The functionalization degree (FD) ranges from 0.1 to 1.6% mol and depends on the feed composition and in particular on the DEM/DCP ratio. Such functionalization takes place with a very large preference at the aliphatic carbons of the polyolefin block. The functionalization of SBR was performed by radical addition in solution of two functional thiols (thioglicolic acid and its aliphatic ester), in the presence of free radical initiators. The addition occurs at the vinyl double bonds of the 1-2 butadiene units with high selectivity. FD can be tuned in the range 1-10mol%. These data are rationalized in the frame of the general reaction mechanism of free radical polymerization. A general reaction scheme is proposed which allows the design of proper conditions for favoring functionalization versus degradation and crosslinking depending on the nature of molecules and macromolecules involved.