The main transition of amorphous polymers is analyzed with respect to a fine structure by means of new experimental dynamic shear, dielectric, and heat capacity data for the following polymers:  poly(n-alkyl methacrylate)s with alkyl = methyl, ethyl, propyl, butyl, and hexyl, polystyrene, poly(vinyl acetate), a series of weakly vulcanized natural rubbers, a series of butyl rubbers with different carbon black content, polyisobutylene, and bromobutyl rubber. The components of the fine structure are assumed to be a proper glass transition at short times, followed by a confined flow zone, and, at large times, a hindering zone caused by entanglements at large times. Two lengths are assumed to correspond to the first and third components, respectively, the characteristic length to the proper glass transition and the entanglement spacing to the hindering zone. The confined flow will be described by a dispersion law (general scaling) across the main transition. The characteristic length of the glass transition for the poly(n-alkyl methacrylate)sonly of order 1 nm as determined by calorimetryis confirmed by backscaling from the entanglement spacing by means of a Rouse dispersion law for shear. The fate of the Rouse modes below the αβ splitting of the glass transition is discussed for the other amorphous polymers. Finally, a speculative molecular picture of the different modes in the main transition is described. The new element is a low-viscosity longitudinal motion of individual chain parts in the confined flow zone. A simple rheological model for the confined flow is also presented.

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A slight shoulder in the shear relaxation spectrum (H) at the relaxation time for the main maximum of the retardation spectrum (L) was detected for three amorphous polymers:  polystyrene, poly(vinyl acetate), and a slightly vulcanized natural rubber. This finding is discussed in terms of a distinctive manifestation of different molecular modes across the glass (main) transition.

ABSTRACT:The dynamic shear behavior of SBR 1500 vulcanizates filled with polymeric fillers of 24.6, 40.2, and 74.7 nm diameter and various filler loading up to 100 phr (parts per 100 parts of rubber), and its dependence of strain amplitude up to 14%, have been investigated. The results are compared with carbon-black-filled vulcanizates. The reinforcement ability of polymeric fillers is comparable to that of carbon black, depending on filler particle diameter. As expected, the smaller particles have a higher reinforcement effect than larger particles. The Payne effect, that is, the decrease of storage shear modulus GЈ with increasing strain amplitude and the appearance of a loss modulus GЉ maximum at strains of a few percent, has also been observed in vulcanizates with polymeric fillers. The loss modulus maximum of vulcanizates filled with polymeric fillers is at higher strain amplitudes and is less pronounced than for carbon-black-filled vulcanizates. The results are discussed shortly in terms of recent models based on the idea of filler networking within the rubbery matrix. The experimental GЈ data are adjusted with the deagglomeration-reagglomeration Kraus model (1984).

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