Role of molecular tacticity on the plastic deformation behavior of semi-syndiotactic polypropylenes
Abstract
Metallocene catalysis enables synthesis of polymers with well-defined tacticity, thereby providing materials with a wide range of properties, all from same monomer. However, understanding the role of tacticity at the molecular level, on the crystallization, mechanical, and flow behavior has been a challenge. We are studying custom synthesized semi-syndiotactic polypropylenes (ss-PP) with varying degrees of syndiotacticity', ranging from nearly atactic to nearly syndiotactic. These materials are characterized using NMR, modulated DSC, mechanical testing, rheology, and rheo-optical FTIR and Raman spectroscopy. In the highly polymorphic, highly syndiotactic s-PPs, in the plastic deformation region, there appears to be a gradual transition in macromolecular conformation from helical to trans-planar. The trans-planar chains appear to form a meso-phase, before forming a well-defined crystalline phase at even higher strains. The nature of the conformation transition and the elastic' behavior (in the plastic region) appears to be strongly dependent on tacticity, temperature, and the orientation in the amorphous, meso-phase and the crystalline region, and are explored using rheo-FTIR and Raman spectroscopy.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2003
- Bibcode:
- 2003APS..MARB18015K