Synthesis and characterization of aromatic substituted polylactides

Polylactides are important biodegradable and biocompatible polymers with a variety of uses such as surgical sutures and bone fixation devices. However, its low glass transition temperature (T_g) limits the available uses. A biodegradable analog of polystyrene would be desirable for a number of packaging uses. Aromatic rings have also been shown to increase the T _g in the structurally similar poly(hydroxyalkanoate)s. Poly(2-hydroxy-5-phenylvalerate) has a T_g of 13°C compared to −15°C for the unsubstituted poly(hydroxyvalerate). A variety of aromatic substituted lactides were synthesized based on phenyllactic acid, mandelic acid, and methylphenyllactic acid.; For all aromatic substituted polylactides, the polymerization rate is slower than for the polymerization of lactide. In addition, the solution polymerizations do not reach completion, indicating that there could be catalyst degradation, terminating the reaction, or that the reaction follows an equilibrium mechanism. Both models can be fit to the kinetic data obtained, but it appears both mechanisms take place, with equilibrium dominating at lower reaction times, and catalyst degradation dominating the kinetics at longer reaction times.; Degradation studies were carried out for poly(phenyllactic acid) and poly(p-methylphenyllactic acid) and compared to the degradation of poly(lactic acid). The degradation rate for the polymers were slower than polylactide, most likely because the addition of an aromatic ring causes the polymer to be more hydrophobic. The degradation for poly(phenyllactic acid) and poly(p-methylphenyllactic acid) is initially slower than the model because the hydrophobicity causes the concentration of water within the polymer sample to be relatively low, decreasing the rate of hydrolysis. As the polymer chains are hydrolyzed, the sample becomes more hydrophillic and the degradation rate increases. As the reaction approaches completion, the degradation rate increases. During the degradation reaction, the polymer sample aggregates, concentrating the acidic sites within the polymer, and catalyzing the hydrolysis.; Polyphenyllactide was found to have a glass transition temperature of 50°C which is nearly the same as polylactide. We believe that the methylene group allows for greater flexibility and prevents the T_g from being higher. By removing the methylene by producing polymandelide, we found a T _g of 96°C. However, there were difficulties in obtaining high molecular weight materials.; A number of substituted polystyrenes have been synthesized and the properties varied by changing substituents. This idea was adapted to polyphenyllactide by polymerizing methyl-substituted phenyllactic acids. o-, m-, and p-Methylphenyllactic acids were synthesized from the corresponding methyl-substituted benzaldehyde in relatively low yields. Poly(p-methylphenyllactic acid) has the highest glass transition temperature, 59°C and poly(m-methylphenyllactic acid) the lowest, 42°C. This demonstrates that poly(phenyllactic acid) can be modified through substituents on the aromatic ring. By choosing the correct substituent, a polymer with a higher glass transition temperature, like polystyrene's T_g of 100°C should be possible.