FINE-STRUCTURE OF THE MAIN TRANSITION IN AMORPHOUS POLYMERS - ENTANGLEMENT SPACING AND CHARACTERISTIC LENGTH OF THE GLASS-TRANSITION - DISCUSSION OF EXAMPLES

The main transition of amorphous polymers is analyzed with respect to a fine structure by means of new experimental dynamic shear, dielectri c, and heat capacity data for the following polymers: poly(n-alkyl met hacrylate)s with alkyl = methyl, ethyl, propyl, butyl, and hexyl, poly styrene, poly(vinyl acetate), a series of weakly vulcanized natural ru bbers, a series of butyl rubbers with different carbon black content, polyisobutylene, and bromobutyl rubber. The components of the fine str ucture are assumed to be a proper glass transition at short times, fol lowed by a confined flow zone, and, at large times, a hindering zone c aused by entanglements at large times. Two lengths are assumed to corr espond to the first and third components, respectively, the characteri stic length to the proper glass transition and the entanglement spacin g to the hindering zone. The confined flow will be described by a disp ersion law (general scaling) across the main transition. The character istic length of the glass transition for the poly(n-alkyl methacrylate )s-only of order 1 nm as determined by calorimetry-is confirmed by bac kscaling from the entanglement spacing by means of a Rouse dispersion law for shear. The fate of the Rouse modes below the alpha beta splitt ing of the glass transition is discussed for the other amorphous polym ers. Finally, a speculative molecular picture of the different modes i n the main transition is described. The new element is a low-viscosity longitudinal motion of individual chain parts in the confined flow zo ne. A simple rheological model for the confined flow is also presented .