Impact of Branching on the Phase Behavior of Polymers

Abstract

We have studied the effect of branching on the solution phase behavior of branched homopolymers using grand canonical Monte Carlo (GCMC) simulations in conjunction with multihistogram reweighting and finite-size scaling analysis. The critical temperature (Tc) and the £ temperature (£) decrease as polymer branching is increased, but the drop in £ is less pronounced than that of Tc. The critical volume fraction (c) rises with the degree of branching. Branched polymers are found to obey the Shultz-Flory relationship and exhibit a power-law behavior in c vs chain length, with similar scaling exponents as those for their linear counterparts. Comparisons of the GCMC results are made to results of the lattice cluster theory (LCT). It is observed that the LCT significantly underestimates the impact of polymer branching on the critical behavior of polymers. We speculate this discrepancy between the two formulations to be due to an inadequate representation of the variation of polymer conformations with branching and neglect of fluctuations in the LCT theory. Branched and hyperbranched polymers (dendrimers) have received a lot of attention recently due to their emerging applications in catalysis, 1 nanomaterial syn- thesis 2 and biomedicine. 3,4 Understanding the role that branching plays in determining the rheological and thermodynamical properties of a polymer melt or its so- lution is currently an active area of research. Although significant advancements have been made in elucidating the conformational properties of branched polymers, 5 comparatively little progress has been made in under- standing the impact of branching on the miscibility and critical behavior of polymers in solution. In this study, we investigate the effect of branching on the liquid- liquid phase separation and critical parameters of