AMIDE MODIFIED POLYBUTYLENE TEREPHTHALATE - STRUCTURE AND PROPERTIES

Polyesteramide copolymers (PBTA) based on polybutylene terephthalate ( PET) and the diamide of butanediamine and dimethyl terephthalate (N,N' -bis(p-carbo-methoxybenzoyl)butanediamine) were studied. The amide con tent in PBTA was varied from 0-50mol%. The melting and crystallization behaviour was analysed with differential scanning calorimetry. The de gree of undercooling is taken as a measure for the rate of crystalliza tion. The torsion modulus as a function of temperature and the positio n of the glass transition temperature (T-g) were studied with dynamic mechanical analysis. On injection moulded samples the tensile properti es at RT were determined. The crystalline spacings were studied with w ide angle X-ray diffraction. In the PBTA only one T-g could be observe d which means that the amorphous phase was homogeneous. The crystallin e spacings of PET and Nylon 4,T were not the same and the PBTA has som ething of both, which means that the ester and amide repeat units are not isomorphous. Despite the absence of isomorphous crystallization th e melting temperature increased nearly linearly with the amide content , the crystallinity remained high, and very surprisingly the rate of c rystallization even increased. Also in polyethylene terephthalate thes e diamide segments increased the rate of crystallization. A model is p roposed with the diamides as homogeneous nucleation sites (adjacent cr ystallization) to explain the fast crystallization behaviour of these copolymers. (C) 1997 Elsevier Science Ltd.