Methacrylate-endcapped poly(d,l-lactide-co-trimethylene carbonate) oligomers. Network formation by thermal free-radical curing

doi:10.1016/S0032-3861(97)00208-5

Polymer

Volume 38, Issue 26, 1997, Pages 6295-6301

https://doi.org/10.1016/S0032-3861(97)00208-5 Get rights and content

Abstract

A series of 3-arm, methacrylate-endcapped poly(d,l-lactide-co-trimethylene carbonate) prepolymers was synthesized using d,l-lactide:trimethylene carbonate (DLL:TMC) molar feed ratios of 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. Number average molecular weights were in the range (2.3–2.6) × 10³ g mol⁻¹. The prepolymers were free-radically crosslinked in the absence of reactive diluents to give amorphous, bioabsorbable networks with a broad range of thermal, mechanical, and degradative properties. Extraction studies indicated that sol-contents ranged from 2.89%–6.17%. Tensile modulus, ultimate strength, and T_g increased with increasing d,l-lactide content. Networks containing higher contents of d,l-lactide, 100:0, 80:20, and 60:40 (DLL:TMC), were strong and fairly rigid, but failed catastrophically at the yield point; networks containing lower contents of d,l-lactide, 20:80 and 0:100, showed a higher elongation to break, failing catastrophically at the yield point. A 40:60 DLL:TMC network fit perfectly within the series of compositions with regard to modulus and tensile strengh; however, it showed a yield point, followed by a regime of plastic flow prior to break. Hydrolytic degradation experiments revealed that the network based on poly(d,l-lactide) homopolymer degraded fastest owing to its hydrophilicity. Hydrolytic degradation in the copolymer networks was controlled by two opposing effects which occurred as the trimethylene carbonate was increased: T_g depression, which increased water uptake, and increased hydrophobicity, which decreased water uptake. Increasing trimethylene carbonate in the 80:20 and 60:40 DLL:TMC copolymer networks caused a decrease in the water uptake and the degradation rate since these network are both glassy at the degradation temperature of 37°C. The observed increase in degradation rate in the 40:60 copolymer network was due to increased water uptake caused by depression of the T_g to a value below the test temperature of 37°C. The 20:80 and 0:100 DLL:TMC networks were the slowest to degrade owing to their hydrophobicity. © 1997 Elsevier Science Ltd.

Section snippets

INTRODUCTION

The recent development of totally biodegradable composites for medical and dental applications has stimulated research to develop matrix resins for these composite systems 1, 2. The semi-crystalline, thermoplastic fibres, poly(glycolide), poly(lactide), and poly(ϵ-caprolactone) are successfully used for sutures and surgical meshes since they degrade into naturally occurring metabolites; however, the semi-crystalline morphology of these materials leads to heterogeneous degradation rates whereby

Materials

All reagents were used from the supplier without further purification unless specified otherwise. 2-Butanone peroxide (30 wt.% solution in dimethyl phthalate), calcium hydride (95%, ground into a fine powder), chloroform-d (99.8 at.%, containing 0.03% v/v TMS), 1,2-dichloroethane (DCE, anhydrous, 99 + %, distilled from calcium hydride), diethyl carbonate (99%), d,l-lactide (DLL), magnesium sulfate (anhydrous, 99%), methacryloyl chloride (tech. 90%, distilled prior to use), 4-methoxyphenol

Network synthesis and characterization

A series of low molecular weight homopolymer and copolymer triols, based upon d,l-lactide and trimethylene carbonate monomers, was synthesized by the trimethylolpropane-initiated ring-opening polymerization of d,l-lactide and trimethylene carbonate in the presence of stannous octoate catalyst, as shown in Fig. 1. G.p.c. molecular weight data for the isolated copolymers, relative to polystyrene standards, are listed in Table 3; in all cases the measured number average molecular weight M_n was

CONCLUSIONS

Polyester, polycarbonate, and poly(ester-carbonate) prepolymers were synthesized by the ring opening polymerization of d,l-lactide, trimethylene carbonate, and varied ratios of the two monomers respectively. The prepolymers were endcapped with methacrylate groups yielding unsaturated prepolymers with a higher reactivity than conventional bioabsorbable unsaturated polyesters. Free-radical cross-linking yielded a novel class of bioabsorbable thermosets with a broad range of thermal, mechanical,

Acknowledgements

The research upon which this material is based was supported by the National Science Foundation through Grant Nos. RII-8902064 and EPS-9452857, the State of Mississippi, and the University of Southern Mississippi.

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^†: Present Address: Dow Corning Corporation, P.O. Box 994, Mail # C043C1, Midland, MI 48686-0994, USA

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Methacrylate-endcapped poly(d,l-lactide-co-trimethylene carbonate) oligomers. Network formation by thermal free-radical curing

Abstract

Section snippets

INTRODUCTION

Materials

Network synthesis and characterization

CONCLUSIONS

Acknowledgements

J. Controlled Rel.

Biomaterials

Polymer

Am. J. Surg.

Polymer

Trans. Soc. Biomater.

J. Biomed. Mater. Res. Symp.