Benzyl ether polymers: Crystallinity and pendant adamantanyl effect highly soluble polyimides from sterically hindered diamines vapor phase deposition of polybenzoxazoles

Tina Lynn Grubb

Abstract

The research presented in this dissertation is from three different areas. The first involves the synthesis of a series of benzyl ether polymers with and without pendant adamantyl groups. A-B homopolymers with dibenzylether and thioether connecting units were made by phase transfer reaction of 2-(4-bromomethylphenyl)-6-bromomethyl benzoxazole with KOH or Na$\sb2$S. The ether-linked material was soluble only in concentrated $\rm H\sb2SO\sb4$ while the thioether polymer was only soluble in a mixture of trifluoroethanol and chloroform. The parent AA-BB polyether from resorcinol and $\alpha,\alpha\sp\prime$-dichloro-p-xylene (or the dibromo analog) was obtained as a very high molecular weight product which showed multiple crystalline forms. Solid state $\sp{13}$C NMR spectroscopy and x-ray diffraction patterns were obtained on two samples (each with a different type of crystalline domain), a high molecular weight sample displaying both types, and on amorphous material. Incorporation of pendent adamantyl groups was also examined. The second part of this dissertation involves the synthesis of polyimides with enhanced solubility from various aromatic tetracarboxylic dianhydrides and sterically hindered diamines. Intrinsic viscosities in 1-methyl-2-pyrrolidinone (NMP) ranged from 0.28 to 1.05 dL/g. Most of the polyimides were soluble in common solvents. Polyimides derived from thianthrene-2,3,7,8-tetacarboxylic dianhydride (TDAN) and diamino mesitylene (DAM) or diethyltoluene diamine (DETDA) were insoluble in all solvents. Glass transition temperatures ranged from 252 to 398$\sp\circ$C with the polymers showing little or no weight loss by TGA up to 400$\sp\circ$C in both air and nitrogen. The glass transition temperatures of the polyimides increased 15 to 95$\sp\circ$C when one or more methyl group was placed ortho to the imide nitrogen, hindering backbone rotation, chain packing, and flexibility. More importantly, tough, transparent films of the soluble polyimides could be cast from solution. The final part of this dissertation discusses the synthesis of multi-functional aliphatic and aromatic benzoxazoles as potential intermediates for benzoxazole cyclic dimers. Aliphatic benzoxazoles were found to undergo hydrolysis under the normal basic conditions required for cyclic dimer formation. In attempts to form aromatic benzoxazole cyclic dimers, polymerization occurred, demonstrating facile reaction. However, cyclics were never isolated from oligomers due to insolubility except in polar aprotic solvents. Instead, vapor phase deposition was carried out on dihalomethyl and monohalomethyl benzoxazoles (intermediates for cyclic dimers) to give poly-(dimethylene benzoxazoles). These polymers were synthesized through solution methods. Both aromatic and aliphatic polybenzoxazoles containing -$\rm CH\sb2CH\sb2$- units in the polymer backbone displayed catastrophic weight loss over very narrow temperature ranges. Pyrolysis of the polymers at the temperatures where this catastrophic weight loss occurs gave similar polymer (by FTIR) in the collection zone. This suggests a degradation pathway facilitated by the two adjacent methylene groups to form a xylyene structure analogous to the polymerization of (2.2) paracyclophane. (Abstract shortened by UMI.)