Multicomponent vapor deposition polymerization of poly(methyl methacrylate) in an axisymmetric vacuum reactor

Abstract

An axisymmetric, multicomponent initiated chemical vapor deposition (i-CVD) apparatus was designed to study the vapor-phase growth of glassy poly(methyl methacrylate) (PMMA) films. Preheated monomer (methyl methacrylate) and initiator (t-butyl peroxide) vapors were metered into a pressure-controlled reaction chamber. Inside the chamber, gases pass through a high-temperature hot-zone where primary free radicals are formed. The gas mixture then condenses and polymerizes on a back-cooled target substrate. Key reactor operating parameters were systematically varied to understand film growth kinetics. These include the hot-zone temperature, reactor base-pressure, substrate temperature, and the monomer/initiator molar feed ratio. Polymer deposition requires good thermal contact between feed gases and the hot-zone. Packed with glass beads, the hot-zone reactor resulted in more efficient initiation and film growth. Experiments also show that polymer deposition rate is limited by thermal initiation of primary free radicals, transport of primary free radicals to the target substrate, and by monomer adsorption. Size exclusion chromatography of deposited polymers is used to relate molecular weight to the monomer-to-initiator feed ratio. The addition of a third vapor component, 1-butanol, was also found to affect polymer molecular weight.