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Isotactic Polypropylene
EditIsotactic polypropylene is a polyolefin in which every methyl group lies on the same side of the chain, and the regular arrangement allows the chains to crystallise. Commercial grades contain a few percent of chain defects that interrupt the regular sequence and lower both the crystallinity and the melting point [1]. The polymer crystallises in several polymorphs, the monoclinic alpha form being the most common, while the hexagonal beta form appears in the presence of a specific nucleating agent and gives a higher toughness [2]. Adding a nucleating agent raises the crystallisation temperature and shortens the cycle time, and a clarifying agent reduces the size of the spherulites enough to make the part transparent [3]. The impact strength falls with temperature and with the crystallinity, and a rubbery phase is usually copolymerised or blended in to recover it [4]. Because stereoregularity is set by the catalyst, the properties of a grade cannot be reproduced without the same catalyst system [5].
References
- Chen, J.; Chang, Y. Isothermal crystallization kinetics and morphology development of isotactic polypropylene blends with atactic polypropylene. Journal of Applied Polymer Science 2007, 103, 1093-1104. [CrossRef]
- Hamad, F.G.; Colby, R.H.; Milner, S.T. Transition in Crystal Morphology for Flow-Induced Crystallization of Isotactic Polypropylene. Macromolecules 2016, 49, 5561-5575. [CrossRef]
- Speranza, V.; Salomone, R.; Pantani, R. Effects of Pressure and Cooling Rates on Crystallization Behavior and Morphology of Isotactic Polypropylene. Crystals 2023, 13, 922. [CrossRef]
- Chen, J.H.; Tsai, F.C.; Nien, Y.H.; Yeh, P.H. Isothermal crystallization of isotactic polypropylene blended with low molecular weight atactic polypropylene. Part I. Thermal properties and morphology development. Polymer 2005, 46, 5680-5688. [CrossRef]
- De Carvalho, B.; Bretas, R.E.S. Quiescent crystallization kinetics and morphology of isotactic polypropylene resins for injection molding. I. Isothermal crystallization. Journal of Applied Polymer Science 1998, 68, 1159-1176. [CrossRef]
