Functional Thin Films Resulting from Parylene–Vinyl Copolymerization

Abstract

Quantum and kinetic studies of novel materials based on parylene polymers and variously substituted vinyl molecules are presented and discussed. It is demonstrated that the thin films which are the products of the copolymerization reactions can be prepared (i) within the parylene CVD process on active vinyl substrates or (ii) employing the same process but involving an additional source of vinyl molecules transported to the reaction chamber. Both methods lead to differently functionalized microstructures, primarily dominated by the parylene units, while the vinyl molecules appear relatively seldom (depending on the nature of the substituents used). The copolymerization is shown to be independent of penultimate monomers in linear chains and to undergo composition drift within certain scope. Namely, it is found that even a small amount of p-xylylene monomers in feed leads to the formation of long blocks of pure parylene while the substituted vinyl molecules are expected to appear occasionally in chains. Finally, it is predicted that the two types of parylene functionalization result in specific structures and thus behavior of the corresponding thin films.

Chemical vapour deposition of soluble poly(p-xylylene) copolymers with tuneable properties

“…One explanation for this was the sample's compositional inhomogeneity due to reactor geometry, as already explained (Figure 3). The presence of longer PPXblocks in the copolymers is also supported by quantum calculations on reactivity ratios of p-xylylene units with vinylic/acrylic comonomers in CVD copolymerizations made by Bobrowski et al 19 They showed that p-xylylene is far more reactive compared to the comonomer, and therefore is the dominant species in the copolymer chains over a wide range of monomer feed ratios. The occasionally random distribution of comonomer units along the chain, as described by Bobrowski et al, is also supported by the presence of multiple carbonyl resonances in 13 C-NMR, as discussed above.…”

“…17,18 These studies have evoked further theoretical interest in the copolymerization mechanism and reactivity of p-xylylene moieties with conventional double bond containing monomers. 19,20 In this work, we copolymerized alkyl substituted [2.2] …”

“…17,18 These studies have evoked further theoretical interest in the copolymerization mechanism and reactivity of p-xylylene moieties with conventional double bond containing monomers. 19,20 In this work, we copolymerized alkyl substituted [2.2]paracyclophanes, which are known to yield soluble PPX-homopolymers, 21 with 2-hydroxyethyl methacrylate (HEMA) as comonomer. To our knowledge, this is the first report of any soluble PPX-copolymers obtained via CVD and their analysis by NMR spectroscopy.…”

Polymerization of chloro-p-xylylenes, quantum-chemical study

“…This is caused by the fact that the vinyl and etin polymerizations are characterized generally by higher reaction barriers; many such processes require catalizers. Copolymerization of vinyl and parylene leads almost always (for various substituents present in vinyl moieties) to only insubstantial presence of vinyl units in the parylene main chains [12]. Hence the reveal that one possible unfolding for achievement of higher molar ratio for vinyl molecules in parylene-based copolymers might be the decrease of relative reactivity of parylene N, C and D’s monomers for instance by substitution of a larger amount of hydrogen atoms both in aromatic ring as well as in aliphatic segments.…”

“…For optimized products and for transition states found the characterization of extremes was performed by calculating various geometry, energy and charge properties. The choice of chloro-substituted p-xylylenes for polymerization reactions was dictated by the absence of the collective polymerization of parylene and styrene [15] in spite of the fact that p-xylylenes and some alkenes indeed react with each other as it was proven by FT-IR, FT-Raman and XPS spectra [12, 13, 42]. On the other hand, the substitution of terminal hydrogen atoms (in aliphatic positions) by chlorine atoms in p-xylylene makes the copolymerization feasible and 7,7,8,8-tetrachloro-p-xylylene as well as 2,5,7,7,8,8-hexachloro-p-xylylene copolymerize well with styrene, vinyl acetate, acrylonitryle and methyl methacrylate as it has also been proven experimentally [31].…”