Structural and dynamic nanoheterogeneities in higher poly(alkyl methacrylate)s

The relation between structural features and the dynamics of higher poly(n-alkyl methacrylate)s (PnAMAs) is studied. A nanophase separation of incompatible main and side chain parts is indicated by the co-existence of two dynamic glass transitions and the occurrence of a pre-peak in small angle X-ray scattering (SAXS) data corresponding to a structural length scale of 1-3 nm. SAXS data for amorphous PnAMAs with different number of alkyl carbons in the side chain (1 less than or equal to m less than or equal to 10) are presented. A systematic, non-linear increase of the equivalent Bragg spacing d(11) (m) is observed. The pre-peak is connected with the existence of alkyl nanodomains formed by aggregated alkyl rests of different monomeric units. The 'polyethylene-like' glass transition (alpha(PE)) within these alkyl nanodomains, being a self-organized confinement, is studied by dielectrics, shear, and the 3omega method of heat capacity spectroscopy. The size of the relevant dynamic heterogeneities xi(xPE), i.e. the size of cooperatively rearranging regions (CRRs), is estimated from calorimetric data for the alpha(PE) process in poly(n-decyl methacrylate) (m = 10) using different thermodynamic approaches. The predicted CRR sizes xi(xPE) are compared with typical structural length scales in this side chain polymer and discussed in the context of glass transition cooperativity. (C) 2002 Elsevier Science B.V. All rights reserved.