Influence of Tacticity on Structural Ordering of Isotactic Polypropylene under Annealing

Abstract

Abstract:Influence of tacticity on phase transition from disordered to ordered state was investigated for isotactic polypropylenes (iPPs) synthesized using Ziegler-Natta (ZN) and metallocene (M) catalysis method. The less stable and disordered   rich iPPs samples were annealed at higher temperature for few days. The more stable and ordered  2 fraction, average lamellae thickness (<l>) and melt temperature (T m ) as a function of annealing temperature (T a ) were studied by using solid state NMR, small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) techniques. The  2 fraction, crystals lamellae thickness and melt temperatures were strongly influenced by annealing temperature and tacticity of the iPPs. The less stable and thinner  1 crystal having relatively lower melting temperature shows a significant increase of stability and thickening with annealing. The ordered fraction starts to increase with temperatures while the disordered phase partially melted. Thus, the melting of the disordered phase and simultaneous reorganization and/or re-crystallization into more ordered phase is considered for structural ordering and thickening of iPPs under annealing conditions.