Abstract
The glass-transition temperatures (Tg) of a series of polytetramethylene terephthalate/polytetramethylene isophthalate, copolyesters have been measured by a variety of methods including differential thermal analysis, dilatometry, and broad- line nuclear magnetic resonance. The values measured for Tg are discussed in relation to differences in copolymer com position, sample crystallinity and the method used in the measurement of Tg. An increase in the isophthalate content of the copolyester has been found to decrease T g, whereas annealing and increasing the test frequency have both been shown to raise Tg. Values calculated for the apparent activation energy of the glass-transition (Δ ETg) for the series of copoly esters are also reported. In addition, the influence of water on the Tg of polyesters has been investigated.
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