Biodegradable poly(ethylene succinate) (PES). 1. Crystal growth kinetics and morphology

Crystal growth rates of melt-crystallized poly(ethylene succinate) (PES) with a number-average molecular weight M-n of 21 100 and polydispersity of 1.86, respectively, were studied in an extensive temperature range. On the basis of secondary nucleation theory, only one transition between regime III and regime II was found at around 71 degreesC, but no transition of regime II --> I was detected by kinetic analysis. The ratio of nucleation constants K-g(III) in regime III to K-g(II) in regime II was influenced by the value of activation energy U*, and tended to 2 as predicted by the theory when U* was set as 3688 cal/mol. The morphological changes at spherulitic level and lamellar level in regime II and regime III were examined by using an optical microscope (OM) and atomic force microscope (AFM). Although spherulitic morphologies were found in both regime II and regime III by optical microscopy, further investigations made by following the crystallization process using OM and by checking the lamellar morphology using AFM revealed morphological changes during the crystal growth process and different crystal morphologies in regime II and regime III. Meanwhile by using ultrathin film (similar to 100 nm in thickness), the morphology of lamellar crystals of lozenge-shape outline and composed of single crystals has been studied by AFM technique. The results indicate that there is indeed a transition from regime II to regime III at around 71 degreesC for the isothermal crystallization of PES with an increasing degree of undercooling.