ИСТИНА

Understanding of the mechanisms of polymer microstructural reorganization during thermal treatments as well as explaining the complexity of the thermal behavior of semicrystalline polymers has a great importance for polymer physics. Semirigid-chain polymers, such as poly(trimethylene terephthalate) (PTT), exhibit, upon heating after isothermal crystallization, a series of melting peaks in differential scanning calorimetry (DSC) curves. Two main models were put forward to explain the origin of this multiple melting phenomenon. The “multiple-crystal-population-model” assumes that semi-rigid chain polymers contain several distinct populations of crystals having different structural properties and therefore different thermal stability. The alternative “melting-recrystallization model” invokes instead structural reorganization phenomena that take place during heating, via melting and recrystallization steps that are possible because the starting polymer structures are thermodynamically metastable. In this work, we have combined ultrafast Nanocalorimetry (NC) and Atomic force microscopy (AFM) in order to probe dynamically the crystallization and melting of PTT undergoing variable thermal treatments in-situ. AFM provides the possibility to examine non-destructively and with high spatial resolution the semi-crystalline structure of PTT down to the lamellar organization level. Nanocalorimetry provides the possibility of applying very high heating/cooling rates ( > 103 K/s) to very small amounts of sample (< 1 ng). [3] This NC/AFM combination allowed performing short-term annealing of the sample at elevated temperatures followed by virtually instantaneous cooling of the sample down to the target crystallization temperature. Repetitive short-term annealing followed by imaging at lower temperatures allows to unravel high-rate reorganization mechanisms in semicrystalline polymers. We present here our first NC/AFM results on PTT crystallized in-situ at 200°C. We obtain close views of the surface of PTT spherulites in the regions where the lamellae are mainly edge-on with apparent spacing of 10-15 nm. Data taken from room temperature up to the PTT melting temperature exhibit variable contrast in the AFM phase images and give first hints about the temperature dependent reorganization of the lamellar nanostructure.