Bisphenol A polycarbonate is an engineering thermosplastic which can be utilized for a variety of applications. Modifications to improve upon the properties of this useful material have been attempted since its invention. Three modifications of bisphenol A polycarbonate and its copolymers have been examined in this work. The hydrolytic stability of copolymers of polydimethylsiloxane and polycarbonate was improved by the synthesis of pre-formed phenol functional polydimethylsiloxane oligomers in which the Si is attached directly to the aromatic ring of the hydroxyaryl functional component. <i>In situ</i> random block copolymers of polydimethylsiloxane and polycarbonate were synthesized by interfacial polymerization techniques. The Si-aryl bonds of the novel polydimethylsiloxane oligomers were found to impart good thermal and hydrolytiC stability to the random block copolymers. Terminally reactive polycarbonate oligomers were also synthesized in order to form polycarbonate network materials. 4-Acetoxystyrene was utilized as a stable precursor to 4-vinylphenol which could then be used to quantitatvely control the molecular weight and functionality of the polycarbonate chains. The reactive oligomers were found to undergo a thermal cure above the respective glass transition temperatures to form insoluble networks. These network materials were found to have superior solvent resistance as compared to the linear material while retaining much of the useful mechanical properties (high fracture toughness, etc.) of bisphenol A polycarbonate. Furthermore, the glass transition temperatures of the networks were found to increase with a decrease in the molecular weight between crosslinks. The fire resistance properties of polycarbonate were modified by the copolymerization of bisphenol A with phenol derivatives of triphenylphosphine oxide. The effect of changes in the composition were determined by differential scanning calorimetry and thermogravimetric analysis. The glass transition temperature, as well as the residual char yield at elevated temperatures was found to increase with an increase in the phosphorus monomer content as measured by the two respective methods. Cone calorimetry was also performed on the samples to determine the heat release rate, which reflected an increase in the fire resistance properties with an increase in the phosphorus content. / Ph. D.