Orientation stability polymer glass transition temperature

Stretching denotes a monoaxial or biaxial mechanical stress of a molded article close to the glass transition temperature. This leads to a controlled orientation of the molecular chains in the direction of stretching and thus to a substantial change in some physical properties. Fibers and foils made of synthetic polymers gain their optimal properties only by this mechanical post-treatment. Stability, stiffness, and dimensional stability of fibers, for example, increase nearly proportionally with the stretch ratio, whereas stretchability decreases. In practice, the stretch ratio is between 1 2 and 1 6, depending on the polymer material and the desired properties. 

This high glass transition temperature polymer exhibits large electrooptic coefficients, -14-35 pm fV. The second harmonic measurements indicate long-term stability of the dipole orientation (> 800h at 100 °C). 

Due to the bulkiness of the carbazole groups, main chain and side group motions are severely restricted in PVK. The chains are stiff and the polymer has a glass transition temperature of 227°C which is among the highest known for vinyl polymers. PVK exhibits an excellent thermal stability up to at least 300°C [47-49]. Unfortunately this property has never been fully utilized because of the extreme brittleness of the material. Many attempts have been made to improve the mechanical and processing characteristics of PVK by plastification, orientation, blending and copolymerization. 

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