Synthesis and Properties of Fluorine-Containing poly alpha-esters

Abstract

The synthesis and polymerisation of the anhydrocarboxylate of 2-hydroxy-2-pentafluorophenyl propanoic acid (5-methyl-5-pentafluorophenyl-1,3-dioxolan-2,4-dione) has been examined and compared with anhydrocarboxylates of other α-hydroxy acids in order to assess the effect of fluoroaromatic substituents on the polymerisation reaction and the properties of the polymers (poly α-esters) produced. It has been shown that the relatively low molecular weights obtained by the tertiary base initiated polymerisation of this monomer are not a function of monomer purity nor of the fluoroaromatic substituent but are common to tertiary base initiated polymerisations of this series of monomers in general. Kinetic studies coupled with analysis of the polymers produced have been carried out using various combinations of monomer, initiator, and solvent (reaction medium). The results have been tentatively interpreted in terms of a polymer mechanism including a termination step which produces a carboxyl excess over the 1:1 hydroxyl: carboxyl ratio encountered with poly α-esters produced by related ring-opening reaction. Good structure-reactivity correlations for both monomers and initiators were obtained using the Taft equation. The synthesis of other fluorine-containing α-hydroxy acids has been examined, in particular that of decafluorobenzilic acid since this provides a potential route to the perfluoro aromatic poly α-ester: Diagram- see thesis The low yields encountered in the synthesis of the parent acid from the Grignard reaction between pentafluoro phenyl magnesium bromide and various derivatives of oxalic acid are explained in terms of competitive reactions producing unwanted by-products such as perfluorobenzilide. An improved procedure is suggested involving the ‘in situ’ formation of an insoluble salt of the desired product concurrently with hydrolysis of the Grignard complex. Selected properties of the poly α-esters prepared in the course of the work were examined with the particular purpose of determining the difference in behaviour conferred by phenyl and pentafluoro phenyl substituents. X-ray diffraction, differential scanning calorimetry, thermal and UV stability, and surface properties were studied. As expected, the differences were relatively small, the most significant being associated with glass transition temperature and surface properties