Synthesis and characterization of multiphase copolymers

[摘要] ENGLISH ABSTRACT: Multiphase copolymers generally consist of copolymers where the disparate natures of eachof the segments results in complex phase-segregated morphologies in the solid state. Theoutstanding properties and wide range of applications of multiphase copolymers has led tothe need for more sophisticated synthesis methods to produce copolymers with controlledstructures. Associated with developments in synthetic methods is the need to developsuitable techniques to characterize these materials in order to obtain a better understandingof their structure–property relationships.The synthesis of multiphase copolymers presents many challenges. These arerelated to the nature of the molecular requirements, were the monomers of each of thedifferent components may not be polymerized by all available polymerization techniques.This has led to the need to combine different polymerization techniques to overcome suchlimitations.The focus of this study is the combination of living controlled polymerizationtechniques, namely anionic polymerization and RAFT polymerization, withhydroboration/autoxidation, to produce non-polyolefin block and graft copolymers. Blockcopolymers were synthesized by coupling anionic polymerization andhydroboration/autoxidation reactions. The first block segment was prepared via anionicpolymerization, and then end-functionalized with a suitable functional group (e.g. an allylgroup). A hydroboration/autoxidation reaction was then used to initiate the polymerization ofthe second block by the slow addition of oxygen at room temperature.Graft copolymers were synthesized using the 'grafting from' technique, by couplingRAFT copolymerization with hydroboration/autoxidation reactions. The backbone polymerwas synthesized via RAFT copolymerization of symmetric and asymmetric monomer, afterwhich a hydroboration/autoxidation reaction was carried out to produce graft copolymers.The hydroboration/hydroxylation reaction could also be used to modify anunsaturated polymer chain. The EPDM rubber chain was modified by transforming thedouble bond into an hydroxyl group, which could undergo an esterification reaction with anacid chloride RAFT agent to produce the multifunctional RAFT polymer. This was used forthe controlled living free radical polymerization of the graft chains. Significant amounts ofhomopolymerization in addition to graft formation were obtained.Solid state NMR (SS NMR) and positron annihilation lifetime spectroscopy were usedto determine the compositional phase segregation point in the graft copolymers. The spindiffusion data from the SS NMR provided insight into the seemingly anomalous positron dataat the phase segregation point. It is demonstrated how these two techniques can providecomplimentary data on the solid state morphology of these multiphase materials.

[发布机构] Stellenbosch University