Crystallinity of polyolefins with large side groups by low-field 1H NMR T2 relaxometry: Isotactic Polybutene-1 with form II and I crystals

Retarded Crystallization and Promoted Phase Transition of Freeze-Dried Polybutene-1: Direct Evidence for the Critical Role of Chain Entanglement

Polymorphism and crystal transition are common phenomena of semicrystalline polymers. These two behaviors are known to be controlled by the nucleation and chain mobility of polymers, both of which are constrained by the chain entanglement at the molecular level. However, the role of chain entanglement in polymorphic crystallization and crystal phase transition of polymers has not been well understood. Herein, we use isotactic polybutene-1 (PB-1) as a model polymorphic polymer and present the crucial role of chain entanglement in the polymorphic crystallization kinetics and solid-solid phase transition. A series of less-entangled PB-1 with different entanglement degrees were successfully prepared by freeze-drying the polymer dilute solution. Compared to the bulk sample and re-entangled one, chain disentangling of PB-1 suppressed the crystallization kinetics of form II but significantly increased the phase transition rate and final transition degree from form II to form I. The disentangling-promoted II-I phase transition originated from the reduced nucleation barrier and enhanced chain mobility. This work would advance the in-depth understanding on the formation and transition mechanisms of polymorphic polymer crystals at the molecular level.

Crystalline polysaccharides: A review

The biodegradability and mechanical properties of polysaccharides are dependent on their architecture (linear or branched) as well as their crystallinity (size of crystals and crystallinity percent). The amount of crystalline zones in the polysaccharide significantly governs their ultimate properties and applications (from packaging to biomedicine). Although synthesis, characterization, and properties of polysaccharides have been the subject of several review papers, the effects of crystallization kinetics and crystalline domains on the properties and application have not been comprehensively addressed. This review places focus on different aspects of crystallization of polysaccharides as well as applications of crystalline polysaccharides. Crystallization of cellulose, chitin, chitosan, and starch, as the main members of this family, were discussed. Then, application of the aforementioned crystalline polysaccharides and nano-polysaccharides as well as their physical and chemical interactions were overviewed. This review attempts to provide a complete picture of crystallization-property relationship in polysaccharides.