Vinyl group oscillation

An empirical rule which has been observed for many polymers is that Tg 2/3T m, where the temperatures are in Kelvin. This rule is applicable to most vinyl, vinylidene, and condensation polymers. This ratio is lower for pol5uners with unsubstituted backbones and higher for polyCa-olefins) with long alkyl side groups. Tac occurs in crystalline and semicrystalline polymers and is ascribed to an oscillation about the chain axes within the chain-folded crystals or a translation along the axis. Tac is related to I m by... 

R.F. Boyer Coupling between the alternating electric field and the electric dipole is direct that between the sinusoidal mechanical field and the "mechanical dipole" may be diffuse. One example of this which we studied (unpublished) is the glassy state response of poly(vinyl acetate) to an electric field which senses high frequency rotation of the dipole about the oxygen-carbonyl carbon bond in the side chain, and low frequency mechanical motion which probably detects local motion of the entire side group about the backbone. The latter occurs at 0.75 Tg (K) at 1 Hz and should be classified as a p relaxation the former occurs 0.75 Tg and is a y relaxation. The dipole oscillates about the backbone above Tg. 

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