Abstract
Reactive extrusion of poly(L-lactide) (PLLA) was carried out in the presence of a small amount of various peroxides with relatively slow decomposition rates. The resulting crosslinked, four-armed randomly branched PLLA (χ-PLLA) was characterized by size exclusion chromatography equipped with multiangle laser light scattering (SEC-MALS), and the results were interpreted according to the type of peroxide used. A new component with a higher molecular weight than the original PLLA was observed in the SEC-MALS chromatograms of the χ-PLLA. The weight-averaged molecular weight (Mw) of the χ-PLLA was found to increase with increasing effective radical number per PLLA precursor (n), where n is the overall hydrogen abstraction ability of peroxide times the mole ratio of radical to PLLA precursor molecule. This implies that the hydrogen abstraction ability is a good index for the crosslinking efficiency of PLLA. The extent of branching of χ-PLLA was estimated by the shrinking factor, g=〈Rg2〉b/〈Rg2〉l, and rationalized with n, where 〈Rg2〉b and 〈Rg2〉l are the mean square radii of gyration of branched and linear polymers with the same molecular weight, respectively. The nucleation and overall crystallization rate of χ-PLLA in the nonisothermal crystallization from the melt was discussed from the viewpoints of branching and entanglement density.
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Acknowledgements
We express our grateful appreciation to associate professor Masataka Sugimoto, Yamagata University, for valuable suggestions and discussions. We also thank Mr Daiki Izuta and Mr Hideyuki Uematsu for SEC-MALS and dynamic viscoelasticity measurements, respectively.
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Takamura, M., Nakamura, T., Kawaguchi, S. et al. Molecular characterization and crystallization behavior of peroxide-induced slightly crosslinked poly(L-lactide) during extrusion. Polym J 42, 600–608 (2010). https://doi.org/10.1038/pj.2010.42
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DOI: https://doi.org/10.1038/pj.2010.42
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