Date of Award

5-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Polymer and Fiber Science

Advisor

Drews, Michael J

Committee Member

Lickfield , Gary C

Committee Member

Brown , Philip J

Abstract

Renewable resource monomer, lactide, derived copolymers and terpolymers were synthesized on a few hundred gram scale with specialty/commodity co-monomers such as perfluoropolyether and bisphenol A derivatives. The modifications resulted in improved properties such as surface energy, crystallization, and glass transition temperature of the polylactide.
Ring-opening polymerizations of L-lactide were performed using different block length perfluoropolyethers as macro-initiators and tin octoate as the catalyst. The resultant polylactide-perfluoropolyether-polylactide block copolymers were characterized by various analytical and microscopic techniques such as differential scanning calorimetry, thermogravimetric analysis, nuclear magnetic resonance spectroscopy, dynamic mechanical analysis, wide-angle x-ray diffraction spectroscopy, polarized optical microscopy, etc.
The incorporation of low surface energy perfluoropolyether into the polylactide backbone modified its surface energy and the copolymers possessed a very low surface energy (16-20 mN/m) compared to that of polylactide (35-40 mN/m) even when at a very low concentration of perfluoropolyether.
The copolymerization affected the thermal properties of the polylactide and the copolymers exhibited lowered glass-transition, crystallization, and melting temperatures compared to the homopolymer, polylactide. The copolymers exhibited unique crystallization behavior and higher crystallinity and faster crystallization rates of the copolymers were found in comparison to polylactide. The enhanced crystallization properties of copolymers were speculated to be due to the nucleating action of perfluoropolyether. The high density and low surface energy perfluoropolyether enables it to behave as a foreign material and as an ideal sight for nucleation. The crystallization half-time, spherulitic growth rate, Avarami's parameters, etc., were studied.
The hydrolytic stability of polylactide-perfluoropolyether-polylactide block copolymers was studied in acidic, alkaline and neutral conditions. Degradation parameters such as weight loss, decrease in molecular weight, and change in thermal properties, hydrolytic solution properties, and surface morphology were monitored. Films hydrolyzed in alkaline conditions showed significant weight loss whereas in acidic and neutral conditions, the weight loss was comparatively low. Initial resistance to the weight loss of the films in alkaline conditions can be seen for the copolymers due to their hydrophobic nature. Molecular weight loss was observed for both homopolymer and the copolymers in all of the hydrolytic conditions. The melting temperatures of hydrolyzed films decreased with increasing hydrolysis time as the ester cleaved chain ends acted as impurities in the crystalline phase. Melt spinning of polylactide and block copolymers were performed to obtain monofilaments.
The terpolymerization of lactide and bisphenol A derivatives resulted in a moderate molecular weight (Mn ~ 12 kg/mol) and a high glass transition (ca. 100 °C) terpolymer. The terpolymer also showed better thermal stability than PLA and the surface properties were unchanged compared to the PLA. Successful electro-spinning of the terpolymer was performed from chloroform and tetrahydrofuran solutions.

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