Modeling Of Semi-batch RAFT Copolymerization And Tailor-making Of Copolymer Chain Structure

Controlled/living free radical polymerization(CLRP)combines the advantages of free radical chemistry and living polymerization capabilities.It provides a very powerful tool that allows precisely control over polymer chain microstructure. CLRP has been extensively exploited for the synthesis of a large variety of polymers with pre-determined molecular weight(MW)and narrow molecular weight distribution(MWD),as well as with well-defined block,star,graft and brush architectures.However,in addition to MW and MWD,copolymer composition(CC) and copolymer composition distribution(CCD)are also the key parameters which determine the performance of a copolymer product.In this study,we aimed at developing a model-based semi-batch monomer feeding policy to tailor-make copolymer chain microstructure via CLRP.Using styrene(St)/butyl acrylate(BA)as a model system,we designed and synthesized a series of copolymers with different composition profiles via semi-batch reverse addition-fragmentation chain transfer radical polymerization(RAFT)mediated by benzyl dithioisobutyrate(BDIB).The thermal properties of this novel series of copolymer products were also investigated.Firstly,a comprehensive intrinsic kinetic model was developed to describe the polymerization kinetics,molecular weight and molecular weight distribution, composition and composition distribution,and molar fraction of dead chains.The model took into account the terminal and penultimate effects.In this model development,irreversible termination model was utilized to describe the rate retardation in RAFT copolymerization.Considering termination reactions of radical chains with approximately same chain length in the RAFT process,a free volume-based semi-empirical expression k_tii,D=k_tii,D⁰((?)_N)^-aexp(-b/v_f)was used to calculate difffusion-controlled termination rate coefficients.A kinetic model for the RAFT copolymerization covering a full conversion range was thus developed.In this work,we used St/BA as a model system mediated by BDIB and investigated the mediation ability of BDIB.It was found that the St and BA polymerizations proceeded in a controlled manner,and BDIB worked better for BA than for St.Furthermore,the influences of BDIB and monomer composition on the polymerization kinetics were systematically examined. From this set of rate data,the apparent rate constant of cross-termination between propagating and intermediate radicals(ct>)and the parameters for diffusion-controlled termination(a,b)were estimated.It was found that when...