| Polylactide is one of the most widely used degradable polyesters with applications ranging from surgical sutures to packaging materials. Because of its low glass transition temperature, polylactide materials designed for use above 50°C typically rely on crystallinity to provide dimensional stability and higher use temperatures. Glassy polylactides analogous to polystyrene are currently unavailable. The goal of this research is the synthesis of amorphous polylactide derivatives with high glass transition temperatures ( Tg).; We synthesized lactide monomers with bulky substituents such as cyclohexyl and isopropyl groups, which were polymerized using Sn(2-ethylhexanote) 2 as the catalyst and 4-tert-butylbenzyl alcohol as the initiator. Ring-opening polymerization of dicyclohexylglycolide, diisopropylglycolide, and methylcyclohexylglycolide yielded high molecular weight polylactide derivatives with Tgs as high as 98°C. The effect of chirality on the properties of poly(dicyclohexylglycolide) were examined by comparing poly(rac-dicyclohexylglycolide), poly(meso-dicyclohexylglycolide), and poly(R,R-dicyclohexylglycolide). Their stereosequence differences were confirmed by 1H and 13C NMR, but no crystallinity was observed from poly(R,R-dicyclohexylglycolide), despite its stereoregularity. All poly(dicyclohexylglycolide)s are amorphous with Tgs ranging from 96°C--104°C.; Dicyclohexylglycolide-based random and block copolymers were synthesized and characterized. The Tg of random copolymers of dicyclohexylglycolide and dihexylglycolide ranged from -38°C to 92°C. To improve toughness and ductility by introducing phase separation, the ABA triblock copolymer poly(dicyclohexylglycolide)-block-poly(ethylene glycol)-block-poly(dicyclohexylglycolide) (PDCG-PEG-PDCG) with a low Tg PEG middle block were designed and synthesized. With a medium-sized PEG middle block (number average molecular weight: 2000), PDCG-PEG2000-PDCG copolymer showed clear sign of phase separation with two distinct glass transitions on DSC, and no PEG crystallization. Phase separation was further confirmed by Tappingmode Atomic Force Microscopy.; We synthesized poly(1,4-benzodioxepin-3-methyl-2,5-dione) and poly(1,4-benzodioxepin-3-cyclohexyl-2,5-dione) via ring-opening polymerization catalyzed by 4-(dimethylamino)pyridine. The kinetics of solution and bulk polymerizations of 1,4-benzodioxepin-3-alkyl-2,5-diones are first-order in monomer. Incorporating salicylic acid repeating units into the polymer backbone provided amorphous poly(1,4-benzodioxepin-3-methyl-2,5-dione) and poly(1,4-benzodioxepin-3-cyclohexyl-2,5-dione) with glass transition temperatures of 92°C and 120°C, which marks them as degradable alternatives to polystyrene. |
