Crystallization and hydrolytic/thermal degradation of a novel stereocomplexationable blend of poly(L-2-hydroxybutyrate) and poly(D-2-hydroxybutyrate)

Abstract

The maximum radial growth rate of spherulites of the novel stereocomplexationable blend of poly(L-2-hydroxybutyrate) (P(L-2HB)) and poly(D-2-hydroxybutyrate) (P(D-2HB)) was observed to be substantially higher than those of pure P(L-2HB) and P(D-2HB). The hydrolytic degradation rate of the P(L-2HB)/P(D-2HB) blend traced by gravimetry and gel permeation chromatography was significantly lower than those of pure P(L-2HB) and P(D-2HB); this indicated that the blend had higher resistance to hydrolytic degradation. Further, the thermal degradation rate of the P(L-2HB)/P(D-2HB) blend was retarded as compared with those of pure P(L-2HB) and P(D-2HB). The results obtained in the present study indicate that the intermolecular interaction between P(L-2HB) and P(D-2HB) chains having opposite configurations in the amorphous regions or in the molten state was higher than that between P(L-2HB) or P(D-2HB) chains with the same configurations. The information obtained in the present study should be very useful for designing and processing pure, biodegradable materials of P(L-2HB), P(D-2HB) and their blends for biomedical, pharmaceutical and environmental applications. Keywords: crystallization; hydrolytic degradation; poly(hydroxybutanoic acid); poly(hydroxybutyric acid); stereocomplex; thermal degradation INTRODUCTION Poly(L-lactide) (that is, poly(L-lactic acid) or PLLA) is a biodegradable polymer produced from plant-derived renewable resources and is now used for biomedical, pharmaceutical, environmental, industrial and commercial applications. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Stereocomplexation between PLLA and its enantiomer poly(D-lactide) (that is, poly(D-lactic acid) or PDLA) can yield biodegradable materials having superior mechanical performance and resistance to hydrolytic and thermal degradation relative to pure PLLA and PDLA. [16][17][18][19][20] Poly(2-hydroxybutyrate) (that is, poly(2-hydroxybutanoic acid) or P(2HB)) is a biodegradable polymer with the structure of a poly(lactide) (that is, poly(lactic acid) or PLA) in which methyl groups are substituted with ethyl groups. A stereocomplex can also be formed by blending substituted enantiomeric PLAs, that is, poly(L-2-hydroxybutyrate) [P(L-2HB)] and poly(D-2-hydroxybutyrate) (P (D-2HB)). 21 The melting temperature (T m ) of the P(L-2HB)/P(D-2HB) stereocomplex (ca. 200 1C) is higher than those of pure P(L-2HB) and P(D-2HB) (ca. 100 1C). The spherulite growth or crystallization of the P(L-2HB)/ P(D-2HB) stereocomplex is completed in a substantially shorter period of time as compared with those of pure P(L-2HB) and P(D-2HB). From the results reported for PLLA/PDLA blends, [16][17][18][19][20] it is expected that the resistance of P(L-2HB)/P(D-2HB) blends to hydrolytic and

Cocrystallization of monomer units in lactic acid-based biodegradable copolymers, poly(l-lactic acid-co-l-2-hydroxybutanoic acid)s

“…The highest G value (1.26 mm min À1 ) was observed for the P(L-2HB) homopolymer sample at L-2HB unit content of 100 mol%. The estimated G value is in agreement with that reported for P(L-2HB) having M n of 1.6 Â 10 4 g mol À1 (about 1 mm min À1 ) [23]. The G value dramatically degreased to 0.12 mm min À1 at 74 mol% and further degreased to 0.02 mm min À1 at 27 mol%, which is slightly lower than that for the PLLA homopolymer sample at L-2HB unit content of 0 mol% (0.03 mm min À1 ).…”

“…Homostereocomplexed PLA [15,27e30] and P(2HB) [23] materials have higher mechanical performance, hydrolytic/thermal degradation resistance, gas barrier properties compared to those of neat PLA and P(2HB) materials, and have been intensively investigated in terms of biomedical, pharmaceutical, and environmental applications, as well as macromolecular science. Hetero-stereocomplex (HTSC) formation or crystallization is reported for P(2HA) polymer pairs with different types of side chains and opposite configurations.…”

Heterostereocomplex‐ and Homocrystallization and Thermal Properties and Degradation of Substituted Poly(lactic acid)s, Poly(l‐2‐hydroxybutanoic acid) and Poly(d‐2‐hydroxy‐3‐methylbutanoic acid)

“…The G values of the neat P( l ‐2HB), P( d ‐2H3MB), and their blend samples had maximum [ G (max)] values of 2.2, 183.6, and 16.8 μm min −1 at T c (max) = 75, 140, and 165 °C, respectively. The G (max) values for the neat P( l ‐2HB) and P( d ‐2H3MB) samples are in the same orders as those reported . Although the actual G (max) values of the neat P( d ‐2H3MB) and blend samples could become higher if G values could be measured at a lower T c .…”

Stereocomplex crystallization and homo-crystallization of enantiomeric substituted poly(lactic acid)s, poly(2-hydroxy-3-methylbutanoic acid)s

“…The G values of SC crystallites in the blend sample (1.0-30 µm min -1 ) were much lower than those of homo-crystallites in the neat P(L-2H3MB) (157-532 µm min -1 ) and P(D-2H3MB) samples (67-288 µm min -1 ). Surprisingly, this result is in marked contrast with those reported for PLLA and PDLA or P(L-2HB) and P(D-2HB) wherein the G values of SC crystallites in the blends are much higher than those of homo-crystallites in the neat polymers[12,33]. It is probable that alternate packing of L-and D-polymer segments during SC crystallization can be readily occur in PLLA/PDLA and P(L-2HB)/P(D-2HB) blends with small side chains (methyl and ethyl side groups, respectively) but becomes difficult in blends because large side chains (isopropyl groups) should have disturbed alternate packing of L-and D-polymer segments during SC crystallization.…”

“…i.e., poly (2-hydroxybutanoic acid) [P(2HB)] [11][12][13] and poly(2-hydroxy-3-methylbutyrate), i.e., poly(2-hydroxy-3-methylbutanoic acid) [P(2H3MB)] [14], which are biodegradable polyesters with the structures of PLAs which methyl groups are substituted with ethyl groups and isopropyl groups, respectively ( Figure 1). Hetero-stereocomplex is formed between L-and D-forms (and vice versa) of PLA and P(2HB) [15][16][17][18] and those of P(2HB) and P(2H3MB) [19].…”