Characteristics of the biodegradability and physical properties of stereocomplexes between poly(L‐lactide) and poly(D‐lactide) copolymers

Abstract

Random and block copolymerizations of L‐ or D‐lactide with ε‐caprolactone (CL) were performed with a novel anionic initiator, (C5Me5)2SmMe(THF), and they resulted in partial epimerization, generating D,L‐ or meso‐lactide polymers with enhanced biodegradability. A blend of PLLA‐r‐PCL [82/18; PLLA = poly(L‐LA) and PCL = poly(ε‐caprolactone)] and PDLA‐r‐PCL [79/21; PDLA = poly(D‐LA)] prepared by the solution‐casting method generated a stereocomplex, the melting temperature of which was about 40 °C higher than that of the nonblended copolymers. A blend of PLLA‐b‐PCL (85/15) and PDLA‐b‐PCL (82/18) showed a lower elongation at break and a remarkably higher tensile modulus than stereocomplexes of PLLA‐r‐PCL/PDLA‐r‐PCL and PLLA/PDLA. The biodegradability of a blend of PLLA‐r‐PCL (65/35) and PDLA‐r‐PCL (66/34) with proteinase K was higher than that of PLLA‐b‐PCL (47/53) and PDLA‐b‐PCL (45/55), the degradability of which was higher than that of a PLLA/PDLA blend. A blend film of PLLA‐r‐PDLLA (69/31)/PDLA‐r‐PDLLA (68/32) exhibited higher degradability than a film of PLLA/PDLLA [PDLLA = poly(D,L‐LA)]. A stereocomplex of PLLA‐r‐PCL‐r‐PDMO [80/18/2; PDMO = poly(L‐3,D,L‐6‐dimethyl‐2,5‐morpholinedion)] with PDLA‐r‐PCL‐r‐PDMO (81/17/2) showed higher degradability than PLLA‐r‐PDMO (98/2)/PDLA‐r‐PDMO (98/2) and PLLA‐r‐PCL (82/18)/PDLA‐r‐PCL (79/21) blends. The tensile modulus of a blend of PLLA‐r‐PCL‐r‐PDMO and PDLA‐r‐PCL‐r‐PDMO was much higher than that of a blend of PLLA‐r‐PDMO and PDLA‐r‐PDMO. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 438–454, 2005

Properties of a poly(L‐lactic acid)/poly(D‐lactic acid) stereocomplex and the stereocomplex crosslinked with triallyl isocyanurate by irradiation

“…Enzymatic degradations of different stereocomplexes and their crosslinked samples were estimated with proteinase K 30, 32, 33. The samples were cut into square sheets of 10 mm × 10 mm.…”

Rubber toughening of poly(lactic acid): Effect of stereocomplex formation at the rubber‐matrix interface

“…The improvement of the properties was attributed to micro‐phase structure difference generated as a result of formation of many stereocomplex crystallites which acted as intermolecular cross‐links. Attempt to toughen PLA by combining block copolymerization and stereocomplexation has also been reported recently 38–40. The increases in Young's modulus and elongation at break of blends were observed in some samples compared to the corresponding enantiopure analogues.…”

Synthesis and Biodegradation of Poly(l-lactide-co-β-propiolactone)

“…Rare earth alkoxides such as Y(OMe)(C 5 Me 5 ) 2 (THF) [35] and Sm(OEt)(C 5 Me 5 ) 2 (THF) [35] were reported to catalyze the polymerization of PL and BL to give polymers with relatively high molecular weights. TfOH [36,37] and rare earth metal complexes similar to Sm-1 [12,38] are also active for the polymerization of lactide. Sn(Oct) 2 have commonly been used for the polymerization of lactide and middle size lactones such as CL [39,40].…”