Abstract: Gradient copolymers are copolymers in which the instantaneous composition varies continuously along the chain contour, that is, gradient copolymers have a continuous change in composition from one end of the chain to the other. In order to achieve this continuous change in instantaneous composition, all chains must be initiated simultaneously, and must survive until the end of the polymerization. The recent emergence of techniques for implementing living radical polymerization has provided a new set of tools for polymer chemists that allow preparing the gradient copolymers. However, controlled/living radical copolymerization (CLRcoP) operated in batch experiences composition drifting and thus produces spontaneous gradient copolymer. The composition profile along chain length of individual chains is solely determined by the reactivities of comonomers and the as-synthesized product is uncontrolled.
In this work, a novel series of styrene/butyl acrylate (St/BA) copolymers with precisely designed composition profiles (uniform, linear gradient, tanh gradient, and tri-block with a linear gradient mid-block) were produced using a semi-batch reversible addition-fragmentation chain transfer (RAFT) copolymerization mediated by benzyl dithioisobutyrate (BDIB). The comonomer feeding rate was programmed based on a kinetic model with the targeted composition profile as an objective functions. The experimental composition and molecular weight profiles agreed very well with the model predictions. The polymer molecular weight distributions were narrow with polydispersity index values about 1.3.
Key words: Semi-batch reactor system; RAFT polymerization; Gradient copolymer; Copolymer composition