The 1,4-cycloaddition reactions of the singlet (1Δg) oxygen with s-cis-1,3-butadiene and benzene, with the formation of 3,6-dihydro[1,2]dioxin and 2,3-dioxabicyclo[2.2.2]octa-5,7-diene, respectively, were studied by means of the CAS MCSCF/CAS MCQDPT2 ab initio method with the 6-31G* basis set. In the case of butadiene the reaction was found to be exoenergetic and the product was found to have C 2 symmetry, with the peroxide moiety in the gauche configuration. In the case of benzene the reaction was found to be endoenergetic and the bicyclic product formed was found to have C 2 v symmetry, with the peroxide moiety in the syn configuration. Three possible reaction routes were studied:  (i) concerted cycloaddition, (ii) stepwise cheletropic cycloaddition with the formation of zwitterionic 2,5-dihydrofuran l-oxide as an intermediate, and (iii) stepwise cycloaddition with the formation of a linear intermediate. In the case of butadiene routes (i) and (ii) were excluded, because only second-order saddle points were found on the corresponding reaction pathways. The linear intermediate (I1) found in route (iii) has a biradical character, and its energy relative to that of the separate reactants is 4.1 kcal/mol. The dominant activation barrier corresponds to the transition structure T1 leading to I1 and amounts to 9.9 kcal/mol. The rearrangement of I1 to the product (P) involves only a minor activation barrier of 7.5 kcal/mol (relative to I1). In the case of benzene the reaction occurs in a concerted manner with a single transition structure having C 2 v symmetry; the activation barrier is 25.3 kcal/mol. This difference in binding mechanism can be explained in terms of the configuration of the peroxide moiety in the adduct.

The mechanism of polymerization of p-xylylene and its derivatives is analyzed at the theoretical level. The polymerization reaction takes place in vacuo without any catalyst. The first step is a pyrolytic decomposition of starting material for polymerization, p-cyclophane, a cyclic dimer of p-xylylene, into biradical linear dimer and finally into two quinonoid monomeric molecules of p-xylylene. The quinonoid monomer is diamagnetic; i.e., it has a singlet ground state. The monomers after pyrolysis, when the temperature is lowered, do not re-form cyclic dimers but instead polymerize into long chain molecules. The initiation of polymerization requires dimerization of two monomers leading to formation of a genuine noncoupled biradical dimer. The chain molecules grow through the propagation reaction only one unit at a time, by the attachment of a monomer to a radical chain end. In this work the pyrolysis reaction, the initiation reaction and the first propagation steps of parylene polymerization (up to pentamer) are studied in details using different quantum chemical methods: AM1 and PM6 semiempirical methods and density functional theory (DFT) approach using B3LYP functional with two basis sets of different size (SVP and TZVP).

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Two possible mechanisms for the reaction of four halogenated (metha)acrylate‐based molecules with Parylene [poly (paraxylylene)] during its chemical vapor deposition were proposed. The chemical reactivity of acrylate double bond with the paraxylylene biradical was calculated for all four (metha)acrylate‐based molecules. These calculations allowed the evaluation of the energetically favorable mechanism and indeed a direct correlation was found between both predicted and experimental reactivities. Next, the reactivity of the (metha)acrylate‐modified Parylene films was evaluated through their reaction with different amines. The obtained amidated Parylene films were characterized with X‐ray photoelectron spectroscopy, Kaiser test for primary amines, and fluorescence microscopy. The strong reactivity of (metha)acrylate‐modified Parylene films toward nucleophilic substitution emphasizes a general method for the functionalization of self‐supported Parylene films grown on the reacting solutions using the novel solid on liquid deposition process. This paves the way to the development of multifunctional materials in a one‐step process resulting from the deposition Parylene over liquid patterns. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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