Crystalline polymer, intermediate temperature

Structurally the difference between PEN and PET is in the double (naphthenic) ring of the former compared to the single (benzene) ring of the latter. This leads to a stiffer chain so that both and are higher for PEN than for PET (Tg is 124°C for PEN, 75°C for PET is 270-273°C for PEN and 256-265°C for PET). Although PEN crystallises at a slower rate than PET, crystallization is (as with PET) enhanced by biaxial orientation and the barrier properties are much superior to PET with up to a fivefold enhancement in some cases. (As with many crystalline polymers the maximum rate of crystallisation occurs at temperatures about midway between Tg and in the case of both PEN and PET). At the present time PEN is significantly more expensive than PET partly due to the economies of scale and partly due to the fact that the transesterification route used with PEN is inherently more expensive than the direct acid routes now used with PET. This has led to the availability of copolymers and of blends which have intermediate properties. 

Nesterov and Lipatov studied the compatibility of mixtures of crystallizable polymers (77) and the effects of quartz fillers on polymer-solute interactions (78). Information on the compatibility of these systems was obtained via the determination of melting points and crystallinities of the mixed stationary phases. Depending on the polymers considered a single melting transition at an intermediate temperature or distinct melting transitions for each polymer could be detected. 

For semicrystalline polymers, the curve of specific volume versus temperature follows an intermediate path between the ones for pure amorphous and pure crystalline polymers. 

Small molecules display both glass and fluid states, but not the mbber state. The mbber state is a unique feature for non-crystalline or semi-crystalline polymers in the intermediate temperature regime between the glass and the fluid states. With the decrease of temperature from the fluid state, various modes of polymer motions will be gradually frozen, corresponding to their different scales of length and time (a dynamic stmcture). First, the fluid-mbber transition occurs, which freezes the... 

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