Configuration and diffusion of trapped polymer molecules

Abstract

The purpose of this work was to study both the static and dynamic behaviour of polymer chains "trapped" within polymeric networks. In recent years there has been a large amount of theoretical work dedicated to towards the study of polymer chains in concentrated, entangled media and quantitative theories have been advanced describing both the mechanism of diffusion of polymer chains within a polymeric network as well as the size of the loose chain within the network. There have, however been relatively few experimental studies of the properties of such systems, due to considerable the difficulties involved in the preparation of suitable samples. This work has centred on the preparation of model polymer networks containing a very low sol fraction and the trapping of a series of probe chains within these networks to determine the properties of the probe chain. A series of well characterised polymer networks containing probe chains have been prepared by anionic polymerisation using a novel difunctional initiator recently developed in another laboratory. Properties of the networks alone have been measured by both SANS and QELS and analysed in terms of renormalisation group and mean-field theories. Good agreement has been found with theory, though the correlation length of the network has been found not scale as predicted and appears to be determined by the synthetic conditions employed in the preparation of the network. SANS has been used to determine the size of the probe chain in bulk networks, the results of which have been found to be different to that predicted by the theories of a chain in a "random medium". In solvent swollen networks, the size of the chain has been found to be independent of the cross link density, the behaviour being associated with that of a semi-dilute solution and the appropriate region of the polymer phase diagram has been identified. QELS has been used in an attempt to determine the mechanism of diffusion of the probe chain within the network and in semi-dilute solutions so as to ascertain any differences between the two cases. Analysis centred around deconvolution of the autocorrelation function its components (the probe chain and the collective motions of the network). However difficulties in the interpretation of the data have prevented a fiall clarification of the experimental situation.