Changes in the Viscoelastic Mechanisms of Polyisobutylene by Plasticization

Abstract

Our dynamic mechanical measurements in the glass–rubber transition zone of polyisobutylene (PIB), expressed in terms of the relaxation spectrum H(τ) and loss tangent (tan δ), have found an additional shoulder. Following the interpretation of previous works, the shoulder is attributed to the sub-Rouse modes, which account for motions intermediate in length scale to the Rouse and local segmental modes. The fact that the sub-Rouse modes are well resolved in PIB and not in other amorphous polymers was traced to its weak intermolecular coupling, which ultimately originates from the compact and symmetrical structure of its repeat unit. We test this interpretation further by studying the change on adding liquid paraffin (LP) to PIB, which should disrupt the effective chain packing of undiluted PIB. We found on adding LP to PIB that the softening dispersion becomes narrower, and eventually the disappearance of the shoulder. The effect is due to the mobility of entropic Rouse modes enhanced significantly more than...