Synthesis and Characterisation of Complex Polymer Architectures based on Step-Growth Polymerisation

Abstract

Block copolymers have been proposed previously as compatibilizers in blends of incompatible polymers, being able to improve the blend morphology and mechanical properties by obtaining a finer dispersion of the minor component.
The main objective of this PhD project is the synthesis of complex polymer architectures, namely grafted block copolymers, in which the backbone is an aromatic polyester, with a view to being used as compatibilizers for blends of poly(ethylene terephthalate) (PET) and polystyrene (PS). Given the variety of possible applications of PET PS blends, the design of a synthetic approach for PET PS branched block copolymers is pursued, as a promising strategy towards blend compatibilization.
The proposed synthetic strategy comprises a first step in which macromonomers, functionalised at only one chain end with a bisphenol moiety, are obtained via living/controlled chain growth mechanisms. For the synthesis of PS macromonomers, two different approaches using anionic polymerisation – the so-called initiating and the end capping approach – have been compared by extensive characterisation, exploiting NMR, SEC, MALDI ToF and interaction chromatography. Moreover, the use of a bisphenol functionalised initiator for anionic polymerisation has been investigated. A second kind of macromonomer has been synthesised by the polymerisation of poly(poly(ethylene glycol) methyl ether methacrylate) (PolyPEGMEM), initially via anionic polymerisation, and subsequently developing an ATRP strategy, with the synthesis of a bisphenol functionalised ATRP initiator.
The second step of the synthetic approach of graft copolymers is the incorporation of macromonomers (PS and PolyPEGMEM) into step growth polymerisation of polyesters, as a comonomer. The PET PS graft copolymers have been investigated as compatibilizers for PET/PS blends, testing the effect of different PS graft lengths and different structures of copolymer, by measuring PS domain size by SEM. Even if no significant differences were detected among the blends with different copolymers, their effectiveness proved to be superior than existing commercial compatibilizers.
Finally, the versatility of the synthetic approach for graft copolymers with a step growth polymer backbone was successfully demonstrated by the incorporation of macromonomers (both PS and PolyPEGMEM) into a polysulfone backbone. For PS macromonomers in particular, the effect of different amounts of PS macromonomer and different reaction solution viscosity was also investigated.