ON SPECIFIC FACTORS AFFECTING THE CRYSTALLIZATION OF PET - THE ROLE OF CARBOXYL-TERMINAL GROUPS AND RESIDUAL CATALYSTS ON THE CRYSTALLIZATION RATE

The non-isothermal crystallization rate of poly(ethylene terephthalate ) (PET) has been studied in differential scanning calorimetry experime nts, by cooling from the molten state of samples of various molecular weights, prepared using various catalysts (mainly Ti(O-n-Bu)(4)). The crystallization temperature, T-cc, was obviously influenced by the mol ecular weight, but also by the carboxyl group content, by the type of residual catalyst, by dissolution-reprecipitation treatments and by re -melting phenomena. The observed effects were interpreted assuming tha t interactions of terminal groups of the PET chains (mutual or with re sidual catalyst) led to an apparent increase in molecular weight, whic h in turn determined a decrease in the chain mobility and was responsi ble for a decrease in the rate of crystallization. Thus, a higher conc entration of carboxyl terminal groups as well as interactions of PET t erminal groups with the catalyst decreased T-cc. Any factor which was able to destroy these interactions (treatments of dissolution-reprecip itation, phosphorous derivatives, aging) led to an increase of the ove rall crystallization rate. (C) 1997 Elsevier Science Ltd.