Vapor Deposition and Curing of Polybenzoxazole Precursors

Abstract

Here we report on the vapor deposition polymerization of polybenzoxazole precursors. 3,3‘-Dihydroxybenzidine and pyromellitic dianhydride were codeposited onto flat substrates to form poly(amic acid) films. As-deposited films contained poly(amic acid) species as well as unreacted dianhydride and diamine reactants. Quality films were obtained when reactant fluxes were well balanced. Coatings were cured under inert gas conditions and resulted in the conversion to polyimides (150−250 °C) and, at higher temperatures (500−550 °C), to semiaromatic polybenzoxazoles. Physical and chemical changes occurring during the curing process were studied with FT-IR, TGA, and nanoindentation experiments. The fully cured material is brittle and hard, and for thin films (<1 μm), films do not delaminate from glass substrates. Nanoindentation studies of both solution-prepared and vapor-deposited PBO precursors revealed that the elastic modulus improved upon conversion to the imide and benzoxazole forms, and polyimide showed the highest hardness value compared with poly(amic acid) and PBO.

Initiated and Oxidative Chemical Vapor Deposition of Polymeric Thin Films: iCVD and oCVD

“…The new abilities to vapor deposit freeradical initiated and oxidative step growth polymers also complement the previously established method for growing thin films of condensation polymers. Often termed, vapor deposition polymerization (VDP), [43] this method has been successfully used for polyamides, [44] polyimides, [45] polybenzoxazoles, [46] and poly(amino acids). [47] For initiated CVD (iCVD), a volatile initiator molecule is introduced into the vacuum chamber along with one or more types of polymeric monomers.…”

Monomer Crystallization During Vapor‐Deposition Polymerization

“…Our laboratory has studied VDP of poly(amic acid)s by co-deposition of a dianhydride with a diamine -the resulting films can be thermally cured to form polyimides and polybenzoxazoles. [10,11] We recently studied crystallization of copper phthalocyanine (CuPc) during simultaneous VDP and subsequent curing of poly(amic acid). [12] As-deposited films showed predominantly CuPc-rich amorphous domains.…”

Rigid‐Rod Polymers

“…Then the soluble precursors are converted to PBZT or PBO via a thermal cyclization. The two-step method provides some advantages such as avoidance of corrosive acidic solvents and an increase of processability, but the molecular weight of the resulting polymers is lower than the ones prepared in PPA and methanesulfonic acid (MSA) (43)(44)(45)(46)(47)(48). PBI polymers are also prepared from tetraamines and aromatic dialdehydes (49,50).…”