Multiple glass transition and nanophase separation in poly(n-alkyl methacrylate) homopolymers

Shear data in the temperature range from -145 degrees C to the flow zone are presented for the poly(n-alkyl methacrylate)s from methyl (C = 1) to lauryl (C = 12). Three qualitatively different glass transitions are observed in the shear curves at 10 rad/s: (i) the conventional a process in the C < 5 members, (ii) the high temperature a process in the C > 5 members, and (iii) an additional polyethylene-like glass transition, ape, in the C greater than or equal to 3 members. All three processes depend systematically on side chain length. Two alternative empirical pictures for the coexistence of two glass transitions are discussed: (a) a static nanophase separation between main chains and side chains and (b) a dynamic heterogeneity with two different time and length scales.