Binary Blends of Entangled Star and Linear Poly(hydroxybutyrate):Effect of Constraint Release and Dynamic Tube Dilation

Ebrahimi, Tannaz [UBC] Taghipour, Hamid [UCL] griessl, Desiree [UCL] Mehrkhodavandi, Parisa [UBC] G. Hatzikiriakos, Savvas [UCL] Van Ruymbeke, Evelyne [UCL] et al.

In order to further understand the relaxation behavior of binary blends of star and linear chains, new polymer blends consisting of linear poly(hydroxybutyrate) (PHB) matrix and PHB star molecules are designed, and their dynamics is investigated by varying the star concentrations and the molar mass of the linear matrix, while keeping few or no star−star entanglements in the blends. By studying the constraint release Rouse (CRR) relaxation of the star polymer diluted in the linear matrix at concentrations low enough to neglect star−star entanglements, we first point out the importance of the number of short linear chain entanglements on the CRR time of the long chains. For the blends composed of a larger proportion of star molecules, we then use this new definition of CRR time to determine the necessary time of a star−star entanglement segment to relax by CRR and explore its dilated tube, at the rhythm of the disentanglement/re-entanglements of the short chains. By considering this as the new reference time for describing the contour length fluctuations of the arm in its “fat” tube, i.e., the tube which only involves star−star entanglements, we propose a simple and consistent way to take into account two opposite effects resulting from the short linear matrix. On the one hand, fast relaxation leads to a large dilution effect, which is reflected by the dilation of the tube in which the long chains are moving. On the other hand, the long chains can only move in their fat tube at the rhythm of the motion of the short chains, which can slow down their relaxation compared to the motion of the same stars diluted in a real solvent. 1. INTRODUCTION Since its development in early 1970s, tube molecular theory1−3 has been the center of attention to improve our understanding of polymer dynamics.4,5 Although mathematical models based on this theory have been developed on the behavior of welldefined, narrow-dispersed polymers such as linear,6 star,7,8 H,9 combs,10−