A prediction technique for gas permeability from polymer structure has been developed on the basis of a specific free volume diffusion theory. In this theory, the free volume available per unit mass in a polymer structure controls the rate of gas diffusion and, hence, its rate of permeation. The smaller this specific free volume is, the more difficult the gas diffusion and, thus, the better its barrier to gases becomes. Specifically, the theory predicts a linear relationship between log (permeability) and (−1/specific volume). A number of existing polymers covering six orders of magnitude in CO2 permeability and O2 permeability were found to follow this correlation. The specific free volume in a polymer was obtained from group contribution calculations. As a result, the gas permeabilities become predictable from the specific volume in a polymer which, in turn, varies with its molecular structure. The advent of this specific free volume theory for gas permeation simplifies greatly the selection of barrier materials for packaging applications. For a given barrier application, a critical specific free volume is first defined from its gas barrier requirement. The polymer structures having specific free volumes smaller than the critical value are then identified. These are the polymers that would have the necessary barrier performance. By this theory, molecular structures, with string polar‐to‐polar interactions and hydrogen‐bonding forces are found to be good barriers to CO2 and O2.

The thermal polymerization reaction of divinyl siloxane bis-benzocyclobutene (DVS bis-BCB) was monitored in-situ with FT-IR spectroscopy in order to follow specific chemical changes and determine the reaction order and rate constants at temperatures from 150° to 210°C. FT-IR spectra were obtained at regular intervals throughout the reaction with a Nicolet 170SX spectrophotometer.Monomeric DVS bis-BCB contains mixed stereo and positional isomers of 1,3- bis(2-bicyclo[4.2.0]octa-1, 3, 5-trien-3-ylethenyl)-1, 1, 3, 3-tetramethyl disiloxane (CAS 117732-87-3). It polymerizes via Diels-Alder cycloaddition reactions between vinyl groups and an intermediate o-quinodimethane formed by first-order, thermally initiated ring openings of the benzocyclobutene rings. Gaseous byproducts are not produced; therefore, the cure is easier to manage than are cures for polyimides which evolve water in polycondensation reactions. The DVS bis-BCB has four reactive elements per monomer unit and, thus, polymerizes into a very highly cross linked and solvent resistant network.With the FT-IR methodology, the reaction was easily monitored through the points of gel formation and vitrification. With the exception of DSC (i.e., calorimetry) which does not sense specific chemistry, other methods were not successful in following the reaction after a gel was formed. We have found that the polymerization was first-order until vitrification occurs; the gelation alone had no apparent effect on the reaction rate.DVS bis-BCB is under development at Dow as high performance dielectric material for multilayer interconnect coating applications for the microelectronics industry. Methodology reported here is employed in developing effective cure management strategies.