Hydrolytic Degradation of Amorphous Films of L‐Lactide Copolymers with Glycolide and D‐Lactide

Abstract

Summary: Films of poly(L‐lactic acid) (PLLA) and copolymers of L‐lactide (LLA) with either glycolide [P(LLA‐GA)](81/19) or D‐lactide [P(LLA‐DLA)](77/23) were prepared and an effect of comonomer type on the hydrolytic degradation of the films was studied in phosphate‐buffered solutions at 37 °C. The degraded films were investigated using gravimetry (weight loss and water absorption), gel permeation chromatography, DSC, X‐ray diffractometry, tensile testing and polarization optical microscopy. To exclude the effects of molecular weight and crystallinity on hydrolytic degradation, the films were prepared from polymers with similar molecular weights and were made amorphous by melt quenching. It was found that the hydrolytic degradation rate decreased in the order P(LLA‐GA) > P(LLA‐DLA) > PLLA. The hydrolytic degradation rate constant of PLLA and LLA copolymer films increased with increasing the water absorption (hydrophilicity), or with decreasing the initial glass transition temperature or the L‐lactyl unit sequence length, indicating that the hydrolytic degradation rate of the copolymers was closely related to these three parameters. The crystallization of P(LLA‐GA) film occurred within hydrolytic degradation for 20 weeks.Mn of PLLA and LLA copolymer films as a function of hydrolytic degradation time.magnified imageMn of PLLA and LLA copolymer films as a function of hydrolytic degradation time.

Hydrolytic Degradation

“…For hydrolytic degradation of P(LA-co-GA), Vert and coworkers and other research groups [6,270,296,297] intensively investigated and obtained information that is summarized in several review articles. With respect to the acceleration of alkaline and NHD of LLA-based copolymers, the effect of the incorporation of hydrophilic GA is higher than that of hydrophobic CL [21,40,54,159]. In the case of the NHD of P(LLA-co-GA), nonexponential decay was observed for degradation periods exceeding 12 months.…”

“…As stated below, in regard to the triblock copolymer of PLLA and poly(ethylene oxide) (PEO) (abbreviated as PLLA-b-PEO-b-PLLA), the ester groups connecting PLLA and PEO rather than those connecting the lactyl units were preferentially hydrolytically degraded at an early stage. Chaubal et al [217] showed that in the NHD of poly(DLlactide)-b-poly(ethylphosphate) (PDLLA-b-PEP), the cleavage of the ethylphosphate-lactyl linkage first occurs and then Solid [17,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Solid (crystalline residues) [41,42] Solid (porous) [43] Ringer solution Solid (including fibers) [44][45][46] Simulated body fluid Solid [ [57] HCl solution, DL-lactic acid solution (pH 2.0) Solid [58] HCl solution (pH À0.9, 0.2), NaOH solution (pH 11.8, 12 Solid [190] PLLA-PCL multiblock copolymer Not specified Phosphate-buffered solution Solid [191] PLLA-b-poly(1,5-dioxepan-2-one)-b-PLLA and multiblock copolymer 37 Phosphate-buffered solution (pH 7.4) Solid [192,193] (continued ) the cleavage of the lactyl-lactyl linkage takes place. For this reason, the hydrolytic degradation of PLLA-b-PEO-b-PLLA and PDLLA-b-PEP was faster at an early stage than at a late stage.…”

“…Figure 21.13 shows the change in number-average molecular weight (M n ) of PLLA with different molecular weights and its copolymers with D-lactide (DLA), glycolide (GA), and e-caprolactone (CL) (P(LLA-co-DLA), P(LLA-co-GA), and P(LLA-co-CL), respectively) [39,40,159]. As can be seen, the effect of copolymerization was dramatic, whereas that of M n was insignificant or very small, at least in the range of 8 Â 10 4 -4 Â 10 5 g/mol [39,44].…”

Influence of macromolecular structure of novel 2- and 4-armed polylactides on their physicochemical properties and in vitro degradation process

“…8 a). This decrease of characteristic temperatures is known and described in literature [38,39]. This is an effect of decreasing of molecular weight, presence of residual monomers, oligomers and water molecules in polymers, which act as plasticizers.…”

Synthesis and characterization of methoxy poly(ethylene glycol)-b-poly(DL-lactide-co-glycolide-co-ε-caprolactone) di block copolymers: Effects of block lengths and compositions

“…Co-and terpolymers of DLL, G and CL have all been reported either as random or block co-and terpolymers [3][4][5][6][7][8]. Random copolymers with different compositions and types of monomer units give a range of materials with different mechanical and biodegradable properties [9].…”