All ETDs from UAB

Advisory Committee Chair

Sergey Vyazovkin

Advisory Committee Members

David E Graves

Gary M Gray

Renata Hawthorne

John C Middleton

Document Type

Dissertation

Date of Award

2012

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

Novel biomaterials composed of a polyglycidol backbone with polyester branches consisting of poly(lactide) or poly(lactide-co-glycolide) are synthesized and characterized. Thermal stability, mechanical properties, and hydrolytic degradation of these polymers are essential factors of their processing and practical application. Data from the analysis of the polymer properties is used to determine structure-property relationships for the branched polyesters. Poly(glycidol) (PG), poly(glycidol)-g-L-lactide (PG-g-La), and poly(glycidol)-g-glycolide (PG-g-Gly) are synthesized for evaluation of the core material and simple branched systems. Thermogravimetry, Fourier transform infrared spectroscopy, and isoconversional kinetic analysis are used to evaluate the kinetic and mechanistic aspects of nonoxidative thermal degradation. It is found that PG degrades in a single mass loss step, whereas, PG-g-La and PG-g-Gly degrade in two. It is demonstrated that the first step in degradation of PG-g-La and PG-g-Gly is associated with decomposition of the pendant groups and the second is due to degradation of the PG backbone. Poly(lactide)s and poly(lactide-co-glycolide)s with different number of arms are synthesized from L-lactide and glycolide monomers using stannous (II) 2-ethylhexanoate and alcohols containing 1, 2, 25 and 51 hydroxyl groups. 1-dodecanol is used to produce the 1-arm polymer, poly(ethylene glycol) for the 2-arm polymer, and polyglycidols of appropriate molecular weight are used to initiate the 25- and 51-arm branched polyesters. Polymer composition and molecular weight are characterized by 1H NMR and gel permeation chromatography (GPC). Thermal properties of the polymers are studied using differential scanning calorimetry (DSC). Thermal degradation behavior is investigated using a combination of thermogravimetry, FTIR spectroscopy, and isoconversional kinetic analysis. Polymer processing and use are evaluated by melt rheology, dynamic mechanical analysis (DMA), and in vitro degradation. Melt rheology demonstrates branched polymers have favorable processing temperatures. DMA demonstrates melt-processed polymer samples have similar storage and loss modulus values at room temperature and body temperature. Hydrolytic degradation and erosion is investigated in phosphate buffer pH 7.4 at 37 °C for 28 days. Degraded samples are analyzed by gravimetry, DSC, dilute solution viscometry (Cannon-Fenske), and GPC.

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