Our research interests focus on the general theme of phase transitions in polymeric materials. We study crystallization and melting processes in flexible and semirigid polymers, in random copolymers and in polymer blends. Special emphasis is given to the interplay between molecular and crystal structure and the properties of polymeric materials. These studies will allow us to predict the physical properties of semicrystalline polymers through an understanding of the parameters governing their morphogenesis.
In the area of crystallization kinetics we study the effect of chain rigidity and molecular weight on the kinetic parameters controlling the nucleation process and the temperature coefficient of the crystallization. In random and star-branched copolymers the effects of the chemical or stereo type of defects, composition and distribution of deffects on the crystallization kinetics are also investigated. Comparative studies of the crystallization kinetics by differential scanning calorimetry, optical microscopy and dilatometry allow us to follow the ordering of chain molecules from the initial stages of the crystallization process and to test for conformity to nucleation and Regime theories. The linear polyethylenes, linear low density and long branched-high pressure polymerized polyethylenes are investigated as well as Ziegler-Natta and Metallocene type polypropylenes.
The molecular structure and crystallization process affect the resulting polymer morphology. The study of the morphology is centered on defining and quantifying the main independent variables that play a fundamental role in controlling the resulting crystal structure. Thus, the degree of crystallinity and amount and extension of the crystalline and lamellar regions are evaluated in terms of molecular architecture and processing conditions. Different techniques are used to follow these studies; among them, optical and electron microscopies, Raman spectroscopy and small and wide angle X-Rays scattering. Different supermolecular structures are distinguished by a combination of optical and small angle light scattering.
Studies of the miscibility and crystallization of polyolefin blends are directed toward the analysis of the morphology of the melt and of the solid state. The study of model compounds have allowed us to solve a long standing controversy about the state of miscibility of linear and branched polyethylenes in the melt. The conditions for co-crystallization are also determined. These experiments directly address the significance of morphological changes during processing conditions and have great implications in developing strategies to control mechanical and physical properties as well as for a future recycling of these products. The results allow us to predict the behavior of these blends at high processing temperatures as well as in the solid state.