@article{mcdowell_partin_freeman_mcneely_1999, title={Acetone solubility and diffusivity in poly(ethylene terephthalate) modified with low levels of 2,6-naphthalene dicarboxylic acid, isophthalic acid, and 2,5-bis-(4-carboxyphenyl)-1,3,4-oxadiazole}, volume={163}, ISSN={["0376-7388"]}, DOI={10.1016/S0376-7388(99)00151-9}, abstractNote={A series of random copolyesters was prepared by replacing up to 10 wt.% of the dimethyl terephthalate (DMT) in poly(ethylene terephthalate) (PET) with dimethyl 2,6-naphthalene dicarboxylate (NDC), isophthalic acid (IPA), or 2,5-bis-(4-carboxyphenyl)-1,3,4-oxadiazole (ODCA). Solution cast films of the resulting copolymers were prepared and characterized. Modification of PET with NDC and ODCA led to copolymers with glass transition temperatures higher than that of PET, while modification with IPA decreased the glass transition temperature. Copolymerization decreased crystallinity levels in all cases. The acetone solubility and acetone diffusion coefficient were determined by integral kinetic gravimetric sorption experiments at 35°C and 5.4 cm Hg acetone pressure. PET containing low levels of NDC had lower amorphous phase acetone diffusivity and solubility than PET, while PET modified with IPA had amorphous phase acetone diffusivity and acetone solubility similar to that of PET. PET modified with 5% ODCA had amorphous phase acetone diffusivity similar to that of PET, while PET modified with 10% ODCA had an amorphous phase acetone diffusivity value slightly lower than that of PET. Copolymers containing ODCA had somewhat higher acetone solubilities that PET, due mainly to the lower levels of crystallinity in the ODCA-containing polymers than in PET.}, number={1}, journal={JOURNAL OF MEMBRANE SCIENCE}, author={McDowell, CC and Partin, JM and Freeman, BD and McNeely, GW}, year={1999}, month={Oct}, pages={39–49} }
 @article{mcdowell_freeman_mcneely_1999, title={Acetone sorption and uptake kinetic in poly(ethylene terephthalate)}, volume={40}, ISSN={["1873-2291"]}, DOI={10.1016/S0032-3861(98)00403-0}, abstractNote={The sorption and kinetics of acetone uptake in solvent cast films of poly(ethylene terephthalate) are reported at 35°C for acetone pressures ranging from 0 to 7.3 cm Hg. The equilibrium sorption isotherm is well described by the dual-mode sorption model with the following parameters: kD=61 cm3(STP)/(cm3·atm), C′H=7.2cm3(STP)/cm3, and b=50 atm−1. Sorption kinetics are described using a two-stage model which incorporates both Fickian diffusion and protracted polymer structural relaxation. The characteristic time associated with the relaxation process is essentially independent of acetone concentration and has an average value of approximately 15 hours. The fraction of sorption associated with polymer relaxation increases linearly with acetone concentration in the equilibrium-densified matrix of the polymer. Acetone diffusion coefficients increase with increasing acetone concentration. The concentration dependence of the acetone diffusion coefficient is well described by the dual-mobility model if the assumption of constant diffusion coefficients in the two modes is relaxed.}, number={12}, journal={POLYMER}, author={McDowell, CC and Freeman, BD and McNeely, GW}, year={1999}, month={Jun}, pages={3487–3499} }
 @article{mcdowell_freeman_mcneely_1999, title={Interval kinetic gravimetric sorption of acetone in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)}, volume={37}, ISSN={["0887-6266"]}, DOI={10.1002/(SICI)1099-0488(19991101)37:21<2973::AID-POLB7>3.0.CO;2-M}, abstractNote={Interval sorption kinetics of acetone in solvent cast films of random poly(ethylene terephthalate)-co-(ethylene 2,6-naphthalate) (PET-co-PEN) are reported at 35°C and at acetone pressures ranging from 0 to 7.3 cm Hg. Polymer composition is varied systematically from 0% to 50% poly(ethylene 2,6-naphthalate). Equilibrium sorption is well described by the dual-mode sorption model. Interval sorption kinetics are described using a two-stage model that incorporates both Fickian diffusion and protracted polymer structural relaxation. The incorporation of low levels of PEN into PET significantly reduces the excess free volume associated with the glassy state and, for these interval acetone sorption experiments in ∼ 5 μm-thick films, decreases the fraction of acetone uptake controlled by penetrant-induced polymer structural relaxation.}, number={21}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={McDowell, CC and Freeman, BD and McNeely, GW}, year={1999}, month={Nov}, pages={2973–2984} }
 @article{cantrell_mcdowell_freeman_noel_1999, title={The influence of annealing on thermal transitions in a nematic copolyester}, volume={37}, DOI={10.1002/(SICI)1099-0488(19990315)37:6<505::AID-POLB3>3.0.CO;2-9}, abstractNote={Thermal transitions of a glassy, main chain, liquid crystalline, random copolyester, HIQ-40, have been characterized. HIQ-40 is made from 40 mol percent p-hydroxybenzoic acid (HBA) and 30 mol % each of p-hydroquinone (HQ) and isophthalic acid (IA). This polymer is soluble in organic solvents, permitting the preparation of thin, solution-cast films that are in a glassy, metastable, optically isotropic state. On first heating of an isotropic HIQ-40 film in a calorimeter, one glass transition is observed at low temperature (approximately 42°C), and is ascribed to the glass/rubber transition of the isotropic polymer. A cold crystallization exotherm centered near 150°C is observed. This is associated with the development of low levels of crystalline order. A broad melting endotherm is centered at about 310°C; this endotherm marks the melting of crystallites and the transformation to a nematic fluid. A nematic to isotropic transition was not observed by calorimetry. After quenching from the nematic melt, a T g is observed in the range of 110-115°C and is associated with the glass/rubber transition of the nematically ordered polymer. Annealing optically isotropic films at temperatures above the isotropic glass transition results in the systematic development of axial order. In these annealed samples, T g increases rapidly until it is near the annealing temperature, then T g increases more slowly at longer annealing times. In as-cast films annealed at 120-135°C, the light intensity transmitted through a sample held between crossed polarizers in an optical microscope (a qualitative measure of birefringence and, in turn, axial order) initially increases rapidly and uniformly throughout the sample and, at longer annealing times, approaches asymptotic values that are higher at higher annealing temperatures. The increase in transmitted intensity is ascribed to the development of axial order. The uniform increase in transmitted intensity suggests that ordering occurs by a rather global process and not via a nucleation and growth mechanism.}, number={6}, journal={Journal of Polymer Science. Part B, Polymer Physics}, author={Cantrell, G. R. and McDowell, C. C. and Freeman, B. D. and Noel, C.}, year={1999}, pages={505–522} }
 @article{mcdowell_coker_freeman_1998, title={An automated spring balance for kinetic gravimetric sorption of gases and vapors in polymers}, volume={69}, ISSN={["0034-6748"]}, DOI={10.1063/1.1148456}, abstractNote={A method for automation of a McBain-type spring balance using a charge coupled device camera, a computer equipped with a frame-grabber card, and National Institutes of Health Image software is presented. This balance is used to study the sorption and transport of small molecules in polymeric materials. Kinetic gravimetric sorption data of acetone uptake in a random copolymer of 50 wt % poly(ethylene terephthalate) and 50 wt % poly(ethylene 2,6-naphthalate) at 35 °C are provided to illustrate the utility of the method. The diffusion coefficients determined from the cathetometer and camera experiments are 1.1±0.2×10−12 and 1.0±0.2×10−12 cm2/s, respectively. At an acetone partial pressure of 5.4 cm Hg, the equilibrium acetone uptake was 1.47±0.15 g acetone/100 g polymer using the cathetometer to determine spring extension and 1.52±0.15 g acetone/100 g polymer when the camera was used to determine mass uptake of acetone by the polymer. The camera-based balance was determined to be sensitive to weight changes as small as ±1 μg.}, number={6}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={McDowell, CC and Coker, DT and Freeman, BD}, year={1998}, month={Jun}, pages={2510–2513} }
 @article{mcdowell_freeman_mcneely_haider_hill_1998, title={Synthesis, physical characterization, and acetone sorption kinetics in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)}, volume={36}, ISSN={["1099-0488"]}, DOI={10.1002/(SICI)1099-0488(19981130)36:16<2981::AID-POLB13>3.0.CO;2-N}, abstractNote={Random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) were synthesized by melt condensation. In a series of thin, solvent cast films of varying PEN content, acetone diffusivity and solubility were determined at 35°C and an acetone pressure of 5.4 cm Hg. The kinetics of acetone sorption in the copolymer films are well described by a Fickian model. Both solubility and diffusivity decrease with increasing PEN content. The acetone diffusion coefficient decreases 93% from PET to PET/85PEN, a copolymer in which 85 weight percent of the dimethyl terephthalate in PET has been replace by dimethyl naphthalate 2,6-dicarboxylate. The acetone solubility coefficient in the amorphous regions of the polymer decreases by approximately a factor of two over the same composition range. The glass/rubber transition temperatures of these materials rise monotonically with increasing PEN content. Copolymers containing 20 to 80 wt % PEN are amorphous. Samples with 80% PEN contain measurable levels of crystallinity. Estimated fractional free volume in the amorphous regions of these samples is lower in the copolymers than in either of the homopolymers. Relative free volume as probed by positron annihilation lifetime spectroscopy (PALS) decreases systematically with increasing PEN content. Acetone diffusion coefficients correlate well with PALS results. Infrared spectroscopy suggests an increase in the fraction of ethylene glycol units in the trans conformation in the amorphous phase as the concentration of PEN in the copolymer increases. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2981–3000, 1998}, number={16}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={McDowell, CC and Freeman, BD and McNeely, GW and Haider, MI and Hill, AJ}, year={1998}, month={Nov}, pages={2981–3000} }