Skip to main content

Heyi Liang, Benjamin J. Morgan, Guojun Xie, Michael R. Martinez, Ekaterina B. Zhulina, Krzysztof Matyjaszewski, Sergei S. Sheiko, and Andrey V. Dobrynin

Abstract Image

A combination of scaling analysis and rheological experiments was used to study correlations between the entanglement plateau modulus and grafting density of graft polymers in a melt. Using the crowding parameter Φ, which describes overlap of side chains belonging to neighboring macromolecules, we identified two classes of graft polymers—combs and bottlebrushes—that demonstrate distinct conformational and rheological behaviors. In comb systems, both the backbones and sparsely grafted side chains are coiled that allow side chains of neighboring macromolecules to overlap (Φ < 1). In bottlebrush systems, steric repulsion between densely grafted side chains causes chain extension and inhibits side chain interpenetration (Φ ≥ 1). The ratio Ge,gr/Ge,lin ≅ φ3(1 + (Φ/0.7)3) of the plateau modulus of a graft polymer melt, Ge,gr, to that of a melt of linear chains, Ge,lin, is a universal function of the crowding parameter Φ ≅ φ–1nsc–1/2 and graft polymer composition φ = ng/(ng + nsc), where nsc and ng are the degrees of polymerization of side chains and a spacer separating two consecutive side chains along the polymer backbone, respectively. This dependence of the plateau modulus is verified for poly(n-butyl acrylate) combs and other graft polymer systems reported in the literature. In a special case of graft polymers with long entangled side chains, the Ge,gr/Ge,lin ratio is proportional to φ2.

Read Article

Comments are closed.