Synthesis and characterization of poly(3,3,3-trifluorolactic acid)

A long-standing goal in polymer research is to predictably relate the primary molecular structural features of polymeric materials with ultimate macroscopic physical characteristics. This continues to be a challenging undertaking in polymer science, considering the statistical nature of synthetic macromolecules. The science and technology of naturally occurring polymers in the form of proteins offer an opportunity from which potentially substantial advances can be made in synthetic polymer science. Application of what is understood about the molecular structures of natural macromolecules and processes by which they are formed can be applied in synthetic polymer science The investigation of polymers of $\alpha$-hydroxyacids represents a reasonable starting point for application of what is known about proteins and applying it to wholly synthetic materials. Lactic acid is the simplest asymmetric $\alpha$-hydroxyacid. A model monomer, trifluorolactic acid, is formed when the methyl group is replaced by a trifluoromethyl group. Acidity of the methine hydrogen of an $\alpha$-hydroxyacid is expected to increase when the strongly electron withdrawing trifluoromethyl group is introduced to the stereogenic carbon. In this way, the hydrogen bonding capability of the polymer molecule would be enhanced. Polymerization of trifluorolactic acid represents a part of the effort toward the ultimate goal of the production of bio-inspired synthetic polymers with predictable and enhanced physical characteristics. Racemic 3,3,3-trifluorlactic acid ((RS)-3,3,3-trifluorolactic acid) was characterized and contrasted with lactic acid. Unlike lactic acid, it does not form intermolecular esters in the presence of trace water. Poly((RS)-3,3,3-trifluorolactic acid) was synthesized by esterification with 1,3-diisopropylcarbodimide condensing agent and catalytic salts of 4-dimethylaminopyridine and protic acids. Infrared and NMR spectroscopy as well as molecular weight characterization by inherent viscosity, GPC, and light scattering showed that the target polymer was produced. The DSC thermal trace indicated a T$\sp{\rm g}$ of 36$\sp\circ$C. TGA indicated that the fluoropolyester compared favorably with poly(sc D,L-lactide) in thermal stability. Surface properties of poly(sc D,L-lactide) blends with poly((RS)-3,3,3-trifluorolactic acid) showed increased contact angle with the presence of the fluorinated polymer. Wide angle x-ray diffraction patterns indicated the emergence of a band indicative of weak interchain correlation despite the lack of chain stereoregularity. The analogous poly(sc D,L-lactide) showed no such correlation