Production and Chemical Modification of Unsaturated Poly[( R)-3-hydroxyalkanoates] for Expanded Physical Properties and Application

Naturally occurring plastics are of great interest both for their biodegradability and biocompatibility, with potential as petroleum-based plastic replacement and as biomedical materials, respectively. Poly[(R)-3-hydroxyalkanoates] (PHAs) are a class of biodegradable/biocompatible polyester that are produced by several types of bacteria as an energy storage compound. When isolated from the bacterial cell, PHAs have physical properties similar to plastics derived from petroleum. While similar, the properties of these natural plastics often express a trade-off between properties such as strength and flexibility, and this phenomenon limits their potential applications. If the physical properties of PHAs could be modified while maintaining their desirable biodegradable/biocompatible aspects, the resulting material could become a competitive replacement for current synthetic plastics.;In this work, the physical property limitation in PHAs was addressed via chemical modification. While common PHAs containing saturated alkyl side-chains have limited sites for modification, there exist bacteria which can produce unsaturated PHAs, with terminal alkene functional groups in the side-chain of the polymer. These pendant functional groups can be used as a chemical handle for modification, and allow for types of chemical reactions not applicable to saturated PHAs. Unsaturated PHAs were produced and chemically modified via thiol-ene click chemistry, where thiol containing molecules were covalently attached to the side-chain alkene functional groups in the PHA polymer. This approach resulted in the addition of novel moieties to the PHA, which directly affected the polymers physical properties.;In addition to characterizing the effect of chemical modification on polymer physical properties, one type of modified PHA polymer was studied for use in tissue-engineering scaffolds. In order for PHAs to remain an attractive candidate for in vivo applications, any chemical changes to the material must be studied to ensure cell viability and biocompatibility have been maintained. If the modified PHA did not induce a stress response in human cell culture, then this type of chemical modification would represent a promising strategy to alter polymer properties for enhanced applications.;The work in this dissertation has resulted in the production of two types of unsaturated PHA polymers, which were subsequently modified with control over functional group concentration. The physical properties of the modified polymer were extended beyond what are currently available in common PHA polymers, and in some cases overcame the limitation of strength vs. flexibility. One of these modified PHAs was analyzed in human cell culture for cell viability, where it was shown that chemical modification of PHAs via thiol-ene click chemistry did not induce significant toxicity. The strategies developed here represent a new method for tailoring the physical properties of PHAs toward improved and novel applications.