Linear Viscoelastic Response of Comb/Linear Polymer Blends: A Three-Step Relaxation Process

This study addresses the linear viscoelasticity of blends involving monodisperse comb and linear polymers, the latter being the matrix of varying molar mass. This is dynamically a three-component system, comprising linear chains, branches (which are short enough to undergo essentially Rouse relaxation), and backbones. We examine systematically the relaxation of the same comb diluted in the linear matrix as a function of the molar mass of the linear chain for all possible situations (when the latter is oligomer or polymer relaxing faster or slower than the branches) as well as the case of backbone self-entanglements. We develop a simple tube model for the contributions of the three components to comb relaxation by accounting for the dynamic dilution and two delay factors, one for the matrix and another for the comb. The former represents the frictional contribution of the linear polymers to the constraint release Rouse process of the branches and backbone, and the latter represents the relevant effect of the branches on the backbone motion. The model provides an excellent quantitative description of the experimental data. The resulting retardation factors controlling the relaxation process of the combs as a function of the linear polymer’s molar mass complement and extend our earlier investigations with blends involving H-polymers in linear matrices, pointing toward a universal description of the dynamic response of architecturally complex polymers in linear matrices based on constraint release mechanisms. This finding enhances our ability to tailor the dynamics of topological homopolymer blends as per our wish. The remaining challenges associated with the possible universality of the delay factor of combs and the coupling of branch and backbone motion are discussed