摘要:

AbstractImproved compatibility of blends of polystyrene and an amorphous polyamide was achieved by lightly sulfonating the polystyrene. Hydrogen bonding between amide groups and either sulfonic acid or metal sulfonate groups lowered the interfacial tension between the two polymers, which led to a much finer dispersed phase size in blends involving the sulfonated polystyrene. At relatively high sulfonate to amide ratios, the two polymers formed a miscible blend. Improved mixing of the phases was verified by shifts in the glass transitions, and the specific interactions that occurred were characterized by Fourier transform infrared spectroscopy.

ISSN:0032-3888    

DOI:10.1002/pen.760320802

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractRecent work has shown that moisture diffusion coefficients can be measured in thin polymer films through monitoring changes in permittivity with microdielectric sensors. The sensor is constructed in silicon and consists of an interdigitated electrode and two depletion mode field effect transistors. When operated in conjunction with appropriate external circuitry, the sensor measures dielectric constant and loss factor of any material placed on the SiO2insulator and aluminum electrodes. The dielectric properties are measured locally within the first 10 microns of the film in contact with the sensor. As a thin polymer film on the sensor is exposed to a high relative humidity, the dynamically measured dielectric constant can be used to determine exactly when the moisture arrives at the polymer‐SiO2interface and the rate at which the concentration increases. The magnitude of the change in permittivity after equilibration has also been related to total amount of moisture uptake. In this investigation, several epoxy/amine films of varying mix ratios and cure state are cured on microdielectric sensors. The films, approximately 100 microns thick, are alternately exposed to wet and dry environments. Diffusion coefficients for both absorption and desorption are determined from the dielectric data as a function of cure state and epoxy/amine mix ratio. In addition, relative changes in amount of moisture uptake after equilibration is monitore

ISSN:0032-3888    

DOI:10.1002/pen.760320803

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe network formation processes for imidazole‐cured epoxy resins were examined by relating the reaction chemistry and the physical properties during cure. Network formation models were developed based on kinetic studies and the laws of conditional probability. These models were used to predict the weight‐average molecular weight, the gel point, and the sol fraction as a function of the resin composition and the processing conditions. Rheological and extraction experiments were conducted to confirm the model results and to develop criteria for identifying the gel po

ISSN:0032-3888    

DOI:10.1002/pen.760320804

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe kinetics of cyclotrimerization and the thermal stability of bisphenol Abased cyanate ester resin systems were determined using Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. The bisphenol A dicyanate was cured with 4 phr nonylphenol and with the octoates of zinc and manganese, and cobalt acetylacetonate at concentrations ranging from 0 to 750 ppm metal. An empirical rate law was used to predict the cyanate concentration profiles. The observed reaction rate showed a first‐order dependenće on the initial metal concentration and a second‐order dependence on the cyanate concentration in the kinetically controlled regime. For the uncatalyzed systems, the kinetics was described by a second‐order autocatalytic model. The thermal stability of the network was found to be dependent on the catalyst concentration for the zinc catalysts. For the samples cured with manganese, no effect of concentration on the thermal stability was ob

ISSN:0032-3888    

DOI:10.1002/pen.760320805

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe rheological behavior of polymers in the neighborhood of the glass transition is investigated in the framework of the free volume theory of nonlinear viscoelastic behavior. Free volume theory as normally applied above the glass transition is modified to account for the effect of the residual volume of vacancies below the glass transition; this modification is accomplished by modeling the changes in the state of the polymer as the sum of viscoelastic changes and a random disturbance deriving from the thermal collisions between molecule segments. The changes in mechanical properties in passing across the glass transition follow from the freezing‐in of relaxation mechanisms and of free volume; the model, which also incorporates a time‐dependent coefficient of thermal expansion under isobaric conditions, does not require additional parameters other than those characterizing the rubbery state. The pressure dependence of the glass transition is found to be in qualitiative agreement with measurements on PVAc, while the ratio of the glassy and rubbery heat capacities is found to coincide with the ratio of the equilibrium bulk compliances in the glassy and rubbery doma

ISSN:0032-3888    

DOI:10.1002/pen.760320806

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractAr+irradiation and annealing at an elevated temperature are used to improve the adhesion of deposited Cr thin films by vacuum evaporation onto polyimide (PI) substrates. The Ar+ions of 50 and 200 keV and various Ar+doses ranging from 1 × 1013to 2 × 1016ions/cm2are chosen for the experiments, after many preliminary trials. The surface analyses are conducted employing Rutherford Backscattering Spectroscopy (RBS), Fourier transform infrared spectrometry (FTIR), X‐ray photoelectron spectroscopy (XPS), and Scanning electron microscopy (SEM). Ar+irradiation produces an interfacial layer of about 100 Å (10 nm) thick in which Cr particles and PI molecules are physically mixed and chemically bonded. The chemical bonds of CrO and a trace of CrC are observed by XPS and FTIR. Impact‐wear tests are also conducted in order to determine the effects of the Ar+irradiation on the wear property of a Cr/PI system. A significant increase in the property is observed and the increase appears to be a function of the degree of adhesion of the Cr film to the PI

ISSN:0032-3888    

DOI:10.1002/pen.760320807

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe kinetics of the accelerated photo‐oxidation of low‐density polyethylene (LDPE) films has been studied within a range of temperatures, using an ultraviolet radiation enclosure. A simple, lumped parameter, kinetic model was developed to interpret the results of measurements of carbonyl and hydroperoxide absorbances as functions of time; the model predicts, with reasonable accuracy, the general experimental behavior and also that both the formation of hydroperoxides and carbonyl Norrish‐I reactions are important initiation steps. Slightly more complex models may thus have the potential of interpreting other fine details of the degradation behavior, namely the generation of other chemical species and the chain scission and cross‐linking processes, which are directly related to changes in the mechanical pro

ISSN:0032-3888    

DOI:10.1002/pen.760320808

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractBased on a linear stress‐optical relation, off‐center and centerline velocities along with the orientation angle measurements (via the birefringence method) can be used to test constitutive equations for polymeric melts without the need to measure viscosity hood stresses directly. For polydimethylsiloxane (Dow Corning type 200 grade 300 Pa · s) melt in a 60° wedge flow cell (inward flow) at a pressure drop of 70 psi, the orientation angles computed by the Power‐Law model and Goddard‐Miller model with two terms in the Taylor Series and a single relaxation time of 0.005 s were compared with the experimentally measured values. It was found that the Goddard‐Miller model agreed quite well with the measured data. The stress‐optical coefficient (C) was evaluated from the velocity, birefringence, and orientation data. It was calculated to be 1.44 × 10−10m2/N for combined shear and extension using the two‐term Goddard‐Miller Model. For centerline flow (purely extensional), the zero‐extension‐rate elongational viscosity (η0) was calculated to be 930 Pa · s, slightly greater than three times the zero‐shear‐rate viscosity (η0). The cell can be adapted

ISSN:0032-3888    

DOI:10.1002/pen.760320809

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760320801

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY