Influence of polymerization conditions on the hydrolytic degradation of poly(DL-lactide) polymerized in the presence of stannous octoate or zinc-metal.
Laboratory- and pilot-scale racemic polylactides (PLA50) were synthesized in the presence of stannous octoate (SnOct2) or zinc-metal as initiators in the absence of alcohol. The resulting polymers were processed by compression molding or injection molding depending on the batch scale. The hydrolytic degradation of compression-molded samples selected to be comparable was investigated first in order to show the influence of the initiator system. Differences in water uptake were found between PLA50-Zn (zinc-metal initiation) and PLA50-Sn (SnOct2 initiation). PLA50-Zn being much more hydrophilic. PLA50-Sn exhibited a slower molecular weight decrease and delayed onsets of weight loss, release of acidity and stereocomplex formation, with respect to PLA-Zn. The concentration in residual tin in PLA50-Sn increased from 306 to 795 ppm during aging. In the case of PLA50-Zn the residual metal remains constant at ca. 40 ppm. In a second series of experiments, high molecular weight PLA50 different in characteristics and in initiator, synthesized under pilot-scale, were compared. The effects of the initiator on the degradation of the polymers well agreed with laboratory-scale findings, differences in hydrophobicity being enlarged by the up scaling. PLA50-Sn polymers appeared much more degradation resistant than PLA50-Zn ones. Contributions of the other characteristics (e.g. molecular weight, purity, stereoregularity, processing) were shown to be important as well.
Schwach
Grégoire
G
Centre de Recherche sur les Biopolyméres Artificiels, UMR CNRS 5473, University Montpellier I, Faculty of Pharmacy, France.
Coudane
Jean
J
Engel
Robert
R
Vert
Michel
M
D000042:Absorption; D001672:Biocompatible Materials / Q000737:chemistry*; D001673:Biodegradation, Environmental; D002208:Caproates; D003460:Crystallization; D004355:Drug Stability; D006868:Hydrolysis; D066298:In Vitro Techniques; D008422:Materials Testing; D008970:Molecular Weight; D010865:Pilot Projects; D011091:Polyesters / Q000737:chemistry*; D014001:Tin; D014867:Water; D015032:Zinc
D001672:Biocompatible Materials; D002208:Caproates; D011091:Polyesters; D014867:Water; C033616:poly(lactide); C419565:2-ethylhexanoic acid tin(II) salt; D014001:Tin; D015032:Zinc