Synthetic approaches to high-performance polymers: Polyphenylenes, fluoromethylene dipropargyl ether fiber forming polymers, poly(amide imide)s, polybenzoxazoles
The research presented in this dissertation is from four different areas. The first involves the synthesis of pendent adamantyl and benzoxazole substituted polyphenylenes (PP) by the nickel catalyzed coupling of aryl dichloride monomers. Interestingly, benzoxazole pendent polyphenylenes with meta -linked-linked backbones displayed better solubility and higher thermal stability compared to the para -linked material. For the soluble polymers, number average molecular weights ranged from only 2000-4400 by SEC relative to polystrene standards, indicating the need for further development of polymerization conditions. In the second part of this dissertation, a series of terminal diyne monomers [HCCCH 2 OCH2 (CF2 )n CH 2 OCH2 CCH, n = 4, 6, 8, 10 and HCCCH2 OCH2 (CH2 )10 CH2 OCH2 CCH] were synthesized and then polymerized via the copper catalyzed coupling of terminal acetylenes. Characterization using NMR, IR, elemental analyses and intrinsic viscosity supported the chemical structure assignments to monomer and polymer. Thin films of the semicrystalline polymers, with n = 8 and 10, displayed a necking phenomenon upon cold drawing, and could be drawn from the melt or concentrated solution into fibers. In all cases, strong exotherms with maxima at 200°C were observed by DSC, which is characteristic of diacetylene cure. The third part of this dissertation concerns the synthesis and characterization of soluble poly(amide imide)s (PAI). The purpose of this research was to synthesize new PAI with the combined gas permeation properties of polyimides and excellent mechanical properties of PAI These new materials may find use as potential gas separation membranes. Traditionally, PAI with regular repeat structures have been synthesized by multi-step reaction sequences. In the research described here, a new one-pot procedure for imide-acid monomer synthesis and polymerization is reported for four new poly(amide imide)s. The final part of this dissertation involved the thermal conversion of hydroxy-containing imides to benzoxazoles at temperatures above 350°C under nitrogen or vacuum. The reaction was studied using hydroxy-containing polyimides as well as model compound analogs. In all cases, the hydroxyl group was located ortho to the nitrogen of the imide heterocycle. It is believed that this reaction may provide an alternative procedure for producing polybenzoxazoles that are difficult or impossible to prepare by other methods.