Synthesis and characterisation of poly(vinyl butyral) graft copolymers
Graft copolymers based on a poly(vinyl butyral)(PVB) backbone were prepared using a non-ionic grafting onto procedure. Monofunctionalised poly( methyl methacrylate)(PMMA) and poly(phenyl ethyl methacrylate)(PPEMA) were prepared using a matched free radical initiator and chain transfer system of 4,4 '-azobis-4-cyano valeric acid (ACV A) and thioglycollic acid (TGA) respectively. By changing the concentration of TGA, two series of prepolymers having molecular masses from 1400 to 4300 g mor1 were prepared. The carboxylic acid groups at the chain ends of prepolymers were then converted to the corresponding acid chloride groups. These were reacted onto the PVB backbone by a condensation reaction with some of the hydroxyl groups on the PVB. The PVB was chosen so that 21% of the polymer was vinyl alcohol, 3% was vinyl acetate and the remainder was vinyl butyral. Reaction conditions were chosen carefully, because PVB was known to aggregate in solution, and this ensured that grafting frequencies up to 10 grafts per chain were achieved. The PVB backbone, prepolymers and graft copolymers were all characterised so that the full architecture of the final graft copolymer was known. GPC was used, relative to a polystyrene calibration plot, to obtain molecular mass distributions of polymers. However, PVB and graft copolymers were seen to aggregate and this resulted in erroneously high molecular mass values. IR spectroscopy was used qualitatively and quantitatively so that the types of bonds and grafting frequencies could be obtained. 1H and 13C NMR spectroscopy were used qualitatively and 1H NMR spectroscopy was used quantitatively so that prepolymer molecular masses and graft copolymer grafting frequencies could be determined. Solution viscometry was used to obtain intrinsic viscosities of all polymers in solution. This showed that the GPC results were correct and that the main method of separation was due to size exclusion. Slope constants from Huggins and Kraemer plots suggested that PVB and graft copolymers formed aggregates in solution. Laser light scattering was used but Zimm plots obtained were markedly curved and this provides evidence to the existence of aggregates in solution.