Novel siloxane block copolymers
Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008.
The research presented in this dissertation was concerned with the living radical polymerization (LRP) of an amphiphilic, water-soluble, bi-substituted and biologically compatible acrylamide derivative, namely n-acryloylmorpholine (NAM). The primary objective of this research was the synthesis of novel block copolymers containing poly(dimethylsiloxane) (PDMS) and various chain lengths of poly(acryloylmorpholine) (polyNAM) using a LRP technique, namely reversibleaddition fragmentation chain transfer (RAFT) polymerization. This is the first report on the synthesis of these block copolymers using RAFT polymerization. These novel siloxane block copolymers were synthesized using a monohydroxyterminated PDMS material which had to first be modified into a thiocarbonylthiocontaining moiety in order for it to be used as macromolecular chain transfer agent (macroCTA) in the RAFT copolymerization with NAM. Suitable reaction conditions for the synthesis of these novel block copolymers had to, firstly, be determined, and secondly, optimized. In order to determine suitable reaction conditions, a series of homopolymerizations with NAM were first performed in order to compare which chain transfer agent (CTA), solvent, temperature etc. could possibly be best suited for the block copolymerizations of PDMS-b-polyNAM. Reported in this work is the first account of the homopolymerization of NAM and 2-(dodecylsulfanyl)thiocarbonylsulfanyl-2-methyl propionic acid (DMP) as CTA using RAFT polymerization. The resulting novel siloxane block copolymers are amphiphilic in nature and the existence of these structures was confirmed by size exclusion chromatography/multiangle light scattering (SEC/MALS), proton nuclear magnetic resonance (1H-NMR) spectroscopy, gel elution chromatography (GEC) and transmission electron microscopy (TEM). Interesting phase behaviour was observed in the latter technique.