Synthesis and characterization of block and graft copolymers by click chemistry

Abstract

Block and graft copolymers form an interesting class macromolecules newlinewith a spectrum of applications. Controlled radical polymerization newlinetechniques have been used over the years for a variety of their newlinemacromolecular architectures. However, the realisation of some specific newlinestructures with targeted properties has often been found to be impossible newlinethrough them. Click chemistry is a recently introduced approach newlineinvolving a handful of almost perfect chemical reactions, which can address newlinethis issue effectively. newlineThe objective of the present thesis is to explore click chemistry for the newlinecreation of specific molecular architectures, impossible or difficult to newlinerealize through classical anionic or controlled radical polymerizations newline newlinemethods. Among the click group of reactions, copper catalysed azide- newlinealkyne reaction (CuAAC), termed as the cream of crop of click reactions , newline newlineand nucleophilic ring opening of strained rings have been selected as the newlinestrategies for the construction of the polymeric structures. newlineInitially, the chain extension of oligomeric azides such as polydimethyl newlinesiloxane (PDMS), polypropylene oxide (PPO) and polyethylene oxide newline(PEO) have been done by using the bispropargyl ether of bisphenol A newline(BPEBA), through a copper catalysed azide-alkyne cycloaddition (CuAAC) newlinereaction. Click coupling through the formation of triazole linkage has been newlineobserved under mild reaction conditions. The product appeared to be a low newlinemelting, gummy solid, which could undergo cross-linking above 170 °C newlinethrough the thermal cleavage of terminal azide groups. A mechanism newline newlineinvolving nitrogen evolution followed by nitrene formation and cross- newlinelinking has been established. The method of azide based cross-linking has newline newlinebeen found to be a very useful route to prepare porous flexible elastomeric newlinenetworks. newline