A Comparison of the Rheological and Mechanical Properties of Isotactic, Syndiotactic, and Heterotactic Poly(lactide)

作者：Chile Love Ese; Mehrkhodavandi Parisa; Hatzikiriakos Savvas G

来源：Macromolecules, 2016, 49(3): 909-919.

DOI：10.1021/acs.macromol.5b02568

A series of poly(lactide) (PLA) samples, exhibiting various levels of syndiotactic enrichment, were formed via the ring-opening polymerization of meso-lactide using two families of dinuclear indium catalysts: (RR/RR)- [ (NNO)InCl](2)(mu-Cl)(mu-OEt) (1) and (RR/RR)-[(ONNO)In(mu-OEt)](2) (2). Isotactic and heterotactic PLAs were also synthesized using known methodologies, and the thermal and rheological behaviors of these PLAs with different microstructures were compared. Solution theological studies showed that the values of intrinsic viscosities and hydrodynamic radii as functions of molecular weight (M-w) were highest for iso-PLAs, followed by hetero and then syndio-PLAs. The viscosities of the heterotactically enriched PLAs were in agreement with literature values reported for atactic PLAs. The molecular weight between entanglements (M-e) was greatest for the syndiotactically enriched PLAs, giving rise to the lowest zero-shear viscosity. hi addition, hetero- and isotactically enriched PLA had higher flow activation energies (E-a,E-flow) than syndiotactic variants, implying the inclusion of transient aggregate regions within these polymers due to enhanced L- and D-interactions. Although hardening was observed for all types of PLAs, it was more dominant for isotactic PLAs due to stronger L- and D-interactions possibly leading to a, small degree of stereocomplex microcrystallites.

• 出版日期2016-2-9