Deformation mechanisms and rheology of semi-syndiotactic polypropylenes
Abstract
Metallocene catalysis provides a way to control the tacticity in polymers in a 'precise' way.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, using NMR, mechanical testing, and rheo-optical FTIR spectroscopy, WAXD and Raman spectroscopy. In the semi-syndiotactic PPs, the rate of crystallization is significantly slower that s-PP, and the crystal structure is very different. These materials appear to form a meso-phase consisting of trans-planar and/or helical chains, depending on regularity and annealing conditions. 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, and is explored using rheo-FTIR and Raman spectroscopy.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARN29015K