Factors that affect the value of Tg

In sections 5.7.5 and 7.5.3 the origin of the glass transition is explained as the freezing out of various complicated motions of whole chain segments that can take place at higher temperatures. It is therefore not surprising that the glass-transition temperature of a polymer is influenced by 

The influence of factors (i) and (ii) can be seen in some of the values given in table 6.1. For instance, the fact that Tg is lower for nylon, in which all the bonds in the backbone are single, than it is for poly(ethylene ter-ephthalate), which contains a large fraction of inflexible phenylene groups in the backbone, is an example of (i). An example of (ii) is the fact that polypropylene has a lower Tg than those of polystyrene and poly(methyl methacrylate), which have larger side groups. 

A plasticiser is a small-molecule additive deliberately introduced into a polymer in order to act as a sort of internal lubricant to reduce Tg. A very familiar example is the use of plasticisers to make PVC flexible at room 

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This section provides a comprehensive list of the factors that affect the value of Tg for polymers and discusses many of these factors in detail. 

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