Substituted glycolides from natural sources:preparation, alcoholysis and polymerization
Polylactides, polyglycolides and copolymers containing both glycolate and lactate fragments are biocom-patible and biodegradable materials that can be used for environmentally friendly packaging, 3D printing,surgery, drug delivery and other applications. Here we present afirst comparative study of a series of 1,4-dioxan-2,5-diones (glycolides:MeGL,iPrGL,iBuGL,BnGL,PhGLandMePhGL) that can be synthesizedfrom naturalL-α-hydroxy acids orL-α-amino acids. The formation of (R,R)(S,S)-MePhGLwas confirmed byX-ray diffractometry and explained using density functional theory (DFT). We found that diester fragmentsare retained during the non-catalytic methanolysis of these compounds and that ring-opening regois-electivity depends on the bulkiness of the substituents. Ring-opening polymerization, catalyzed by 1,5,7-triazabicyclo[4.4.0]undec-5-ene, yielded alkyl-substituted polyglycolides with given MWs. Controlledpolymerization ofPhGLwas possible at low monomer/initiator ratios, while (R,R)/(S,S)-MePhGLformedoligomers and epimerized products. DFT modeling provided an explanation for the observed patternsbased on the ease of enolization and the stability of the enolate-anions of phenyl-substituted glycolides.Solutions ofMeGL,iPrGL,iBuGL,BnGLandPhGLhomopolymers in hexafluoroisopropanol were electro-spun intofibrous mats whose morphologies, mechanical characteristics, biodegradabilities and thermalproperties varied widely and depended on the substituents on the glycolide.