Geoffrey Johnston-Hall

Termination in Semi-Dilute and Concentrated Polymer Solutions

The aim of the present work was to develop a deeper understanding into termination processes in the semi-dilute and concentrated regimes. The study was carried out to examine the effect of termination between linear polystyrene radical chains in linear, four-armstar, and six-armstar polymer systems using the reversible addition-fragmentation chain transfer chain length-dependent termination method. In particular, the power-law dependencies of both chain length and polymer concentration were evaluated in the semi-dilute and concentrated regimes. We found that theoretical predictions based on the blob model were in good agreement with the experimentally observed evolution of the rate coefficient for biomolecular termination, k(t)(i,i) (x), in the semi-dilute solution regime. In addition, solvent quality was found to decrease with increasing chain length, increasing polymer concentration and as a function of the matrix topology (i. e. for star polymer solutions). In the concentrated solution regime, the role of chain entanglements became evident by determining the conversion-dependent power-law exponent, beta(gel) (where k(t) approximate to x(-beta gel)), which increased in the order: linear < four-arm star < six-arm star polymer systems. Above the critical chain length i(c), termination was found to be primarily conversion-dependent, implying entanglements dominated termination between linear polymeric radicals. Although this may suggest that reptation plays an important role, our data are in disagreement with this theory, suggesting that the polymer matrix cannot be regarded as static or immobile on the diffusion time scales for bimolecular termination.