Design, synthesis, and characterization of linear fluorinated poly(benzyl ether)s: A comparison study with isomeric hyperbranched fluoropolymers

A well-defined compositionally-equivalent linear analog to a previously reported hyperbranched fluoropolymer (HBFP) was synthesized and each was subjected to characterization studies as a fundamental investigation of the role of architecture on solution and solid-state properties. Condensation polymerization of 3-{[(tert-butyl)dimethylsilyl]oxy}-5-[(2′,3′, 4′,5′,6′-pentafluoro)oxy]benzyl alcohol in the presence of an excess of elemental sodium dispersion, followed by removal of the TBDMS protecting group, and finally alkylation with 2,3,4,5,6-pentafluorobenzyl bromide afforded linear fluorinated poly(benzyl ether)s (LFP)s. Molecular weights were typically 7000 to 15000 Da (M_n) with molecular weight distributions of ca. 2, as determined by size exclusion chromatography. Confirmation of the isomeric structures of LFP and HBFP was made by ¹H, ¹⁹F, and ¹³C NMR, and IR spectroscopies. Evaluation of the effects of molecular architecture on solution behavior were examined by solubility and ¹⁹F NMR diffusion measurements. There was no significant difference in solubility in a wide range of organic solvents. ¹⁹F NMR diffusion experiments measured diffusion coefficients of ca. 3 × 10^-6 cm² s^-1 and estimated Stokes radii of 15-26 Å, depending upon the solvent, regardless of polymer architecture. Differential scanning calorimetry and thermogravimetric analysis studies revealed similar thermolytic profiles with a glass transition temperature of 53°C for both systems and thermal stability up to 290°C. Our studies show that the difference in polymer architecture (linear versus hyperbranched) does not necessarily mandate obvious discrepancies in spectroscopic or solution behavior, although the molecular weights for these polymers were maintained at relatively low values.