High‑<i>T</i>_g Functional\nAromatic Polymers

Abstract

A novel\nseries of linear, high-molecular-weight polymers and copolymers\nwere synthesized by one-pot, metal-free superacid-catalyzed polymerization\nof aliphatic 1,2-diketones (2,3-butanedione (<b>1a</b>), 2,3-hexadione\n(<b>1b</b>), 3,4-hexadione (<b>1c</b>), 2,3-butanedione\nmonoxime (<b>1d</b>), pyruvic acid (<b>1e</b>), 1,4-dibromo-2,3-butanedione\n(<b>1f</b>), 2-bromopyruvic acid (<b>1g</b>), and methyl-3,3,3-trifluoropyruvate\n(<b>1h</b>) with linear, nonactivated, multiring aromatic hydrocarbons\nterphenyl (<b>A</b>), biphenyl (<b>B</b>), fluorene (<b>C</b>), and <i>N</i>-ethyl carbazole (<b>D</b>). Depending on the reaction system, the polymerizations were carried\nout as stoichiometric or non stoichiometric, with direct or inverse\nmonomer addition. Copolymers were obtained by polymerization of 1,2-diketones\nwith a mixture of aromatic hydrocarbons. In the course of the polymerization\nonly one carbonyl group of a 1,2-diketone reacts to form C–C\nbonds with aromatic fragments while the other functional groups (including\nthe second carbonyl group) are incorporated unchanged into polymer\nchain. The polymerizations performed at room temperature in the Brønsted\nsuperacid CF₃SO₃H (TFSA) and in a mixture of\nTFSA with methylene chloride or trifluoroacetic acid (TFA) tolerant\nof carbonyl, acetyl, <i>N</i>-oxime, carboxy, methoxy, and\nbromomethyl groups. The polymers obtained were soluble in most common\norganic solvents, and flexible transparent, colorless films could\nbe cast from the solutions. ¹H and ¹³C NMR analyses\nof the polymers synthesized revealed high regio-selectivity of the\npolymerizations and yielded linear structures with para-substitution\nin the phenylene fragments of the main chains. An electron affinity\n(<b>EA</b>) of the carbonyl component and the heterolytic C–O\nbond dissociation energy (<b>DE</b>) in carbinol <b>3</b> (correlating with the activation energy of carbocation <b>4</b> formation) have been used to rationalize the reactivity of carbonyl\ncomponents. The calculations show the following reactivity order of\nthe diketones. <b>1f</b> > <b>1g</b> ≈ <b>1e</b>> <b>1a</b>> <b>1d</b> > <b>1h</b>> <b>1b</b>><b>1c</b> which is totally in agreement\nwith the experimental\ndata. The new functional polymers obtained demonstrate good processability,\nhigh <i>T</i>_g and thermal stability. Unexpected\nwhite light emission was observed for polymer <b>2gA</b>.