ABSTRACT
Raman spectroscopy is used to elucidate fine details of the rather complex microstructure of ethylene-propylene copolymers (EPCs). This paper is focused on a series of commercial EPCs (Versify by Dow) with well-characterized ethylene content. Particular emphasis is given on the analysis of crystal type and content and their relation with EPC chain microstructure. Information provided by Raman is compared with that obtained by differential scanning calorimetry (DSC), a well-established technique widely used in the polymer field. Temperature-resolved Raman experiments are also carried out to interpret more precisely the complex melting patterns observed in the DSC traces. These experiments reveal with more detail the crystal chemical composition and melting temperature ranges of EPC samples, key features to design processing conditions that guarantee optimum lifetime and recyclability of overmolded parts.
ABSTRACT
Liquid-glassy polymer diffusion is an important topic in polymer physics, with several mechanistic aspects that still remain unclear. Here we describe the use of confocal Raman microspectroscopy (CRM) to study directly several features of interphase evolution in a system of this type. The interphase studied was generated by contact between liquid polystyrene (PS) and glassy polyphenylene oxide (PPO). Interphase evolution on thin films made from these polymers was followed by depth profiling in combination with immersion optics. We also applied regularized deconvolution to improve the spatial resolution of the measurements. With the help of these techniques, we examined interphase PPO concentration profiles and kinetics of interphase evolution in the range 120-180 degrees C, well below the glass transition temperature of the PPO-based films (185 degrees C). Overall, the experiment captures the most important features needed to discern the mechanistic factors that control this process. In this sense, confocal Raman microspectroscopy emerges as one of the best experimental techniques for the study of diffusion kinetics in this type of system.
