Amorphous polymers an introduction

It is customary to label relaxation transitions in polymers as a, P, y, d, etc. in alphabetical order with decreasing temperature. Three of the four transitions in polymethyl methacrylate (PMMA)  

Many other amorphous polymers display a high-temperature transition, the glass transition, associated with the onset of main-chain segmental motion, and secondary transitions that have been assigned to either motion of side groups or 

An Introduction to the Mechanical Properties of Solid Polymers I. M. Ward and J. Sweeney 2004 John Wiley Sons, Ltd ISBN 0471 49625 1 (HB) 0471 49626 X (PB) 

The case of amorphous poly(ethylene terephthalate) (PET), where there are no side groups, is considered in Section 10.3.2 in conjunction with semi-crystalline forms of this polymer. Worthy of mention is the use of antiplasticisers to show that the p relaxation is composite [8,9]. In studies of bisphenol A (and tetramethyl bisphenol A), polycarbonate intramolecular cooperativity associated with the carbonate residue was shown by the introduction of the methyl groups on the phenyl rings [10], and intermolecular cooperativity was shown by the dielectric behaviour of blends [11]. Further evidence for intermolecular contributions to the ring motions was obtained from the observed pressure dependence of the proton NMR transverse relaxation time [12]. There is a key conclusion for polymers 

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