Polyethylene-naphthalene-2,6-dicarboxylate and Copolyesters

The kinetics of crystallization of polyethylene-naphthalene-2,6-dicarboxylate (PEN) and of copolyesters of this material with p-hydroxybenzoic acid (PHB) was studied by Wiswe, Gehrke, and Zachmann. PEN crystallizes in two different crystal modifications. One modification is obtained by crystallization at comparatively low temperatures, the other one is obtained sometimes when the material is crystallized near the melting point. Fig. 55 shows the change in the wide angle scattering during isothermal crystallization at 167 °C and 245 °C. 

Simihir studies were performed also on the copolyester. At 230 °C the copolyester goes over into the liquid crystalline state. If cooled down from this state to the crystallization temperature half-times of crystallizations can be obtained which are lying in the range of minutes. From this it is concluded that the orientation 

When the copolyester is heated up or cooled down in the liquid crystalline state fluctuations in the scattering intensity can be observed. Fig. 56 shows the intensity obtained by a position sensitive linear detector and integrated from 29 = 12° 26 = 30° as a function of time. Obviously, the time scale of the fluctuations lies in the region of minutes. Measurements at different azimutal angles reveal that the fluctuations are caused by changes in the orientation of the chains. The area of the film from which the scattering arises is about 2 mm x 2 mm. 

The stretch induced transformation of initially unoriented orthorhombic polyethylene (Vestolen A) into the monoclinic modification was studied by Heise, Riekel and Stach for stretching velocities down to 0.26 mm s T The coexistence of both modifications and the formation of two domains of monoclinic material was established by the Vidicon detector. 

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