Mary E. Rezac

Kinetic aspects of the thermal degradation of poly(dimethyl siloxane) and poly(dimethyl diphenyl siloxane)

The kinetics of degradation of polysiloxanes with different starting chemistries is reported in this paper. The polymers used in the study were vinyl-terminated polydimethylsiloxane (PDMS) and poly(diphenyl-dimethyl)siloxane (3.5 and 25% diphenyl content, DP-3.5 and DP-25). These polymers were inert pyrolyzed under isothermal conditions at temperatures from 325 to 400 � C for 5 h. Additionally, these polymers were pyrolyzed under dynamic heating (rate 6.25 � C/min) up to 925 � C. The kinetic rate constants were calculated for each of the polymers, from both isothermal TGA and dynamic, non-isothermal TGA. The Van Krevelen and Coats-Redfern methods of analysis were used for calculating the energy of activation from dynamic TGA. The various analysis

Gas transport properties of a series of high Tg polynorbornenes with aliphatic pendant groups

A study of gas transport properties of novel polynorbornenes with increas- ing length of an aliphatic pendant group R (CH3{ ,C H 3(CH2)3{ ,C H 3(CH2)5{, CH3(CH2)9{) has been performed. These polymers were synthesized using novel or- ganometallic complex catalysts via an addition polymerization route. This reaction route maintained the bridged norbornene ring structure in the final polymer backbone. Gas permeability and glass transition temperature were found to be higher than those for polynorbornenes prepared by ring-opening metathesis and reported in the literature. It was shown that for noncondensable gases such as H2 and He the selectivity over N2 decreased when the length of the pendant group increased, but remained relatively stable for the more condensable gases (O2 and CO2). The permeability coefficient is correlated well to the inverse of the fractional free volume of the polymers. The more condensable gases showed a deviation from this correlation for the longest pendant group, probably due to an increase of the solubility effect. This polymer series demon- strated a simultaneous increase in permeability and selectivity, uncommon for poly- mers. 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 797-803, 1998

Effect of copolymer composition on the solubility and diffusivity of water and methanol in a series of polyether amides

Sorption and diffusion of water and methanol in polydimethylsiloxane and a series of PEBAX™ copolymers (polyether block amide copolymers) were measured over a wide range of activities near room temperature. The goal was to identify a membrane material for separation of the hazardous air pollutant methanol from wet air streams in the pulp and paper industry. The PEBAX™ copolymer series used here allows a unique insight into transport of small molecules, because solubilities are virtually constant, while diffusion coefficients vary. This is due to the similar chemical structure, but different chain mobility of the homopolymers. The grade PEBAX™ 2533 is most promising for the separation process due to high solubility and diffusivity. The unwanted simultaneous highly selective separation of methanol and water from the targeted air/vapor streams will be addressed in future work.

Correlation of penetrant transport with polymer free volume: Additional evidence from block copolymers

Abstract The transport rates of methanol and water through a series of PEBAX® block copolymers were measured and correlated with the fractional free volume. Excellent agreement between the logarithm of the diffusion coefficient and the inverse of the fractional free volume of the polymer was observed. This provides new evidence of the utility of the free volume theory to describe the transport of highly condensable vapours. Correlation was also quite good when the logarithmic additivity relationship was employed. This relationship has been previously shown to correlate the properties of homogenous blends with copolymer composition. The successful use of this theory for a series of blends that exhibit two glass transition temperature is discussed.

Transport properties of crosslinkable polyimide blends

Abstract The use of polymeric membranes for separation of chemically aggressive media, or at elevated temperatures, has been limited by membrane availability. While a number of polymers are both resistant to chemical dissolution and thermally stable to over 300°C, none has been shown to be simultaneously capable of the selective transport of gases at high rates. The research reported here analyzes the influence of solid-state crosslinking of polyimides to achieve this unique combination of properties. Polyimide blends consisting of an inert polymer base with a diacetylene-functionalized additive were prepared and the properties evaluated before and after crosslinking by thermal annealing. Crosslinking rendered the resultant polymers insoluble in what were previously solvents, but had no measurable influence on gas permeabilities or selectivities. The permeability/permselectivity of these new crosslinked polyimide blends are competitive with the best known polymers. Moreover, the combined ease of processing and resultant stability are unmatched.

Influence of crosslinking technique on the physical and transport properties of ethynyl-terminated monomer/polyetherimide asymmetric membranes

Abstract Integrally-skinned asymmetric membranes prepared from blends of polyimides and a reactive monomer were prepared and treated with various energy sources to promote crosslinking. The extent of crosslinking was monitored through differential scanning calorimetry measurements. The influence of crosslinking on the physical and transport properties was measured. Activation procedures included irradiation (UV, γ, and electron-beam) and thermal (at temperatures above and below the glass transition temperature of the polymer). Surface treatment by irradiation resulted in modest improvements in separation selectivity with little reduction in fast gas flux. Limited conversion of the ethynyl moieties was achieved (average

Nanoporous organic/inorganic hybrid materials produced from poly(dimethyl siloxane)

Abstract The partial pyrolysis of poly(dimethyl siloxane) is reported. Pyrolysis is completed in a two step process, inert pyrolysis in a nitrogen atmosphere followed by oxidative pyrolysis in air. Treatment temperatures were from 300–400°C for the inert processing and 260–300°C for oxidative treatment. This thermal processing required no solvents or bulky catalysts, whose transport into the matrix is diffusion controlled and thus limit product uniformity. Therefore, high sample uniformity was achieved. Hybrid materials with reduced carbon and hydrogen content and an increased oxygen/silicon ratio resulted. These composites were shown to be stronger than composites reported in the literature with similar elemental compositions, but prepared in such a way as to achieve only limited interphase interaction. At high oxidation temperatures, microporosity developed in the materials.