Date of Award

Fall 12-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymer Science and Engineering

Committee Chair

Dr. Robson Storey

Committee Chair Department

Polymers and High Performance Materials

Committee Member 2

Dr. Stephen Hoyles

Committee Member 2 Department

Polymers and High Performance Materials

Committee Member 3

Dr. Lon Mathias

Committee Member 3 Department

Polymers and High Performance Materials

Committee Member 4

Dr. Kenneth Mauritz

Committee Member 4 Department

Polymers and High Performance Materials

Committee Member 5

Dr. Jeffrey Wiggins

Committee Member 5 Department

Polymers and High Performance Materials

Committee Member 6

Dr. Douglas Wicks and Dr. Robert Moore

Abstract

In order to expand the usefulness of degradable polyesters, degradable polyurethanes were synthesized using a mixed polyol system including poly(D,L-lactideco- glycolide) (PLGA), a well-known degradable polyester. Two isocyanate systems, methyl 2,6-diisocyantocaproate (LDI) and dicyclohexylmethane-4,4'- diisocyanate(Hi2MDI), were studied in order to achieve optimal physical and thermal properties of the thermoplastic polyurethane (TPU) while maintaining degradablity. The LDI based systems had excellent physical properties as well as thermal properties that may make them suitable for biomedical devices. The H12MDI based TPUs also had excellent physical properties as well as a higher melting temperature. The aforementioned TPUs were synthesized in small batches. Another method of TPU polymerization was also developed. A reactive extrusion method was developed using a co-rotating twin screw extruder. This system was designed to emulate commercial processes, but on a smaller scale. This method proved to be very successful for synthesizing high molecular weight TPUs. In order to better understand the urethane forming isocyanate/alcohol reaction, a model system was design based on the polymerization conditions of the TPU synthesis. 1-Butanol and 2-butanol served as the representative primary and secondary alcohol respectively. Three different catalysts were investigated to determine the effect on the rate of the reaction; dibutyl tindilaurate, tin (II) 2-ethylhexanoate (SnOct), and triethylamine. The reaction of each alcohol with H12MDI was monitored by real-time transmission FTIR, utilizing a temperature controlled flow cell connected to an external reactor. The isocyanate peak at 2256 cm"1 was monitored and second order kinetic plots were generated. The rate constant of each urethane-forming reaction was determined. Ring-opening polymerization kinetics of D,L-lactide in refluxing tetrahydrofuran were investigated using a number alcohol/SnOct initiating systems. The alcohols used to initiate polymerization were of varying architecture, with functionalities of one to four, to study the effects of that architecture on the rate of polymerization. The polymerization reaction was monitored by following the 1240 cm" C-O-C asymmetric stretch and 933 cm"1 ring breathing mode of D,L-lactide in real-time using ATR-FTIR spectroscopy. First order kinetic plots were generated and apparent rate constants, kapp, were determined for each system. The kinetics of D,L-lactide/s-caprolactone copolymerization were also investigated, using two different methods of copolymerization. First, a conventional copolymerization was conducted where both monomers were polymerized in one reactor such that the monomer sequencing was controlled only by monomer reactivities. The second method was a two-pot synthesis where s-caprolactone was polymerized and used as a macro initiator for D,L-lactide. The goal of this alternate copolymerization method is to reduce the overall time required to achieve high conversion of both monomers.

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