Linear soluble polybenzyls

Abstract

Linear soluble polybenzyls, although deceptively simple in structure, have been strangely elusive. We report for the first time the synthesis of perfectly linear soluble polybenzyls by the polycondensation of 1,2,4,5-tetrasubstituted benzenes with formaldehyde using CHCl₃/trifluoroacetic acid (TFA) as the medium, wherein TFA served both as an acidic catalyst as well as a cosolvent. The number-average molecular weights (M_n's) of the polymers, as determined by gel permeation chromatography, varied from about 1000 to 37,000, depending on the nature of the substituent on the benzene ring; M_n was highest when all four substituents were alkoxy groups and was lowest when they were all alkyl groups. This correlated well with susceptibility of the aromatic ring toward electrophilic aromatic substitution, which is the underlying polymerization mechanism. Differential scanning calorimetry of the polymers showed that most of the samples were amorphous with glass-transition temperatures ranging from about -80° to +80 °C, whereas a few that were either symmetrically substituted or possessed a long alkyl substituent were partially crystalline. Preliminary studies suggested that the methylene unit linking the phenyl rings in these polybenzyls could be readily oxidized to generate conjugated polymers that may be perceived as carbon analogues of polyaniline-poly(arylmethine)s.