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The stretching of mineral filled polymers can create an interconnected microporous structure due to debonding at the mineral/polymer interface. Such materials can allow for the transmission of gases (breathability) while retaining a liquid barrier. Stretched polyethylene/CaCO 3 films that allow for water vapor diffusion while providing a barrier to liquid water are used for the current work. A model for the diffusion of water vapor through these films is demonstrated. This model assumes Fickian behavior. The significance of the model is that it relates the pore microstructure to breathability. Analysis of the pore structure by density and surface area measurements is combined with the results of the Fickian diffusion model to gain insights into the effects of pore geometry on breathability.

The gas permeability and free volume of a series of polyester copolymers were studied. The free volume was studied using the positron annihilation lifetime spectroscopy (PALS) technique to indicate the relative size and concentration of free volume cavities in the copolymers. The homopolymers were poly(ethylene terephthalate) (PET) and poly(1,4 cyclohexamethylene terephthalate) (PCT). The copolymers were prepared by reacting terephthalic acid with varying amounts of ethylene glycol and 1,4 cyclohexanedimethanol to produce a copolymer series containing 11.8, 30.8, 31.8, 60.9, 68.9, and 80.8 mol% PCT. The logarithm of the permeability to oxygen and carbon dioxide was found to increase linearly with vol% PCT. The mean free volume cavity size and relative concentration (as indicated by the PALS parameters τ 3 and I 3 , respectively) were found to increase approximately linearly with vol% PCT. The results are modelled using the Cohen-Turnbull theory for transport in polymers and discussed in terms of various methods of calculating, from PALS data, the free volume fraction that is important to transport properties.

Composition-dependent mechanical properties and free volumes are compared for miscible, amorphous blends of bisphenol-A polycarbonate (PC) with (a) polyaryloxysiloxane (PAS), (b) a copolyester of 1,4-cyclohexanedimethanol and a mixture of isophthalic and terephthalic acids (EASTAR) and (c) an experimental polyester of 1,4-cyclohexane dicarboxylic acid and 1,4-cyclohexanedimethanol (CDACD). The free volumes were measured by the positron annihilation lifetime spectroscopy (PALS) technique. The strength of specific interactions, as indicated by data, is relatively weak in all of the blends. However, the fractional free volume quantity measured by PALS is less than additive in the polyester blends and is additive, or greater than additive, in the PC - PAS blends. The mechanical behaviour of the blends can be rationalized in terms of the free volume behaviour. The polyester blends which lose free volume (contract) on mixing exhibit higher than averaged yield strengths and brittle impact responses. The PC - PAS blends which retain or gain free volume on mixing exhibit averaged yield strengths and averaged ductile impact responses of the constituent polymers.

Four blend systems (miscible binary polyester blends) have been examined by positron annihilation lifetime spectroscopy (PALS). The ortho-Positronium pickoff lifetime, τ 3 , is related to the mean free volume cavity size in these miscible blends. The measured free volume cavity size for the blends is compared to the size predicted from linear additivity of the homopolymers. A negative deviation from linear additivity is observed for τ 3 in each of the blend systems, and this behaviour is interpreted as a contraction of the mean free volume cavity size due to the changes in molecular packing that occur on blending. The consequence of these free volume results for the mechanical properties of miscible polyester blends is discussed and tested for the polycarbonate/Kodar system. The glass transition data suggest weak specific interactions in the blends; however, the mechanical properties are significantly affected by blending

The effect of molecular weight on the spherulite growth rate of poly(ethylene terephthalate) (PET) has been determined using a real-time small angle light scattering (RTSALS) device equipped with a two-dimensional position-sensitive detector. This detector, the design of which was previously reported, incorporates a CCD camera, a personal computer, and an imaging board as the major hardware components. The device performs real-time analysis of the light scattering pattern and calculates the average spherulite radius as a function of time during the crystallization experiment. Growth rate data were obtained for PET having number-average molecular weights of 18,000, 24,700, and 33,100. Samples were crystallized isothermally following a temperature jump from the glass at room temperature to the desired crystallization temperature, which ranged from 130 to 200°C. Both the temperature and molecular weight dependence were found to be well described by the Hoffman equation. The temperature dependence agrees well with that found by previous workers, but the molecular weight dependence is somewhat different.

A two-dimensional position-sensitive detector for real-time small-angle light scattering (RTSALS) of polymers is described. The device performs real-time image analysis of the evolving light-scattering pattern during crystallization. Such an approach provides a means of simultaneously measuring the rate of spherulite growth and the overall rate of crystallization, allowing calculation of nucleation density and/or rate. Although separation of nucleation effects from growth effects typically requires the application of two different experimental techniques, this device is unique in that it allows these two effects to be easily separated using only time-dependent light-scattering data. The device incorporates a CCD camera, a personal computer, and an imaging board as its major hardware components. Software designed specifically for this application performs real-time analysis of the light-scattering pattern at a rate of 1–3 images per second, thus allowing study of even moderately rapidly crystallizing polymers. (More recent software modifications have resulted in a speed enhancement to 5 images per s and further improvement is expected.) Intensities at various scattering and azimuthal angles are plotted at each time. In addition, the average spherulite radius is calculated and plotted. Application of the device is illustrated by measuring the spherulite growth rate of poly(ethylene terephthalate) as a function of temperature. © 1993 John Wiley & Sons, Inc.

α,ω-Dipiperazino polybutadiene (PBD) was complexed with the hydrated forms of copper chloride, iron chloride, and nickel chloride in methanol. The polymers were recovered and compression molded into films and properties investigated. In particular, the tensile stress-strain behavior as well as stress relaxation behavior were monitored with time at ambient conditions. It was observed that the polybutadiene material showed a strong association with copper providing a pseudo network behavior. The association for the iron and nickel components were considerably weaker than that of copper. Comparisons of the data obtained from these systems were also made with earlier data obtained from the same laboratory on carboxylated or sulfonated telechelic ionomers based on polyisoprene and polyisobutylene. It was concluded that the copper complex with the α,ω-dipiperazino polybutadiene has comparable or better behavior than some of the carboxylate systems. © 1992 John Wiley & Sons, Inc.

In general, the mechanical properties of polyisoprene-based telechelic ionomers having neutralized terminal sulfonate and carboxylate groups suggest that metal sulfonates form stronger aggregates than the aggregates formed by metal carboxylates. This agrees with the results of previous workers who made similar comparisons for randomly substituted ionomers. SAXS data indicate that the periodic spacings between metal sulfonate aggregates are consistently higher than for the carboxylate ionomers, suggesting that the metal sulfonate aggregates may contain more ion pairs per aggregate than the metal carboxylate aggregates. The phase boundary between the ionic and nonionic regions is very sharp for both ionomers

The effects of molecular weight, type of neutralizing cation and excess neutralizing agent on the structure and properties of carboxylato-telechelic polyisoprene have been studied. In particular, the effects of cation valence and cation size were studied for group IA and IIA elements, for which the bonding to the carboxylate anion is primarily ionic. It was found that increasing cation valence and decreasing cation size have the general effect of increasing the electrostatic association of the ion pairs, resulting in a more elastic stress-strain response. Neutralization with zinc( ii ) and nickel( ii ), elements of the first transition series that form less ionic, more coordinative complexes with the carboxylate ion, resulted in materials with quite different mechanical properties. The zinc-neutralized material displayed rather poor mechanical properties, while the nickel-neutralized material was much stronger. Materials neutralized with aluminium ( iii ) or titanium ( iv ) were observed to display a wide range of properties depending upon the amount of cation incorporated. It was determined that at least four times the stoichiometric amount of titanium ( iv ) is necessary to crosslink the material effectively. Materials of higher number-average molecular weight (33 000 vs. 15 000) displayed higher stresses and higher ultimate elongations owing to the development of a more extensive entanglement network. Finally, small-angle X-ray scattering studies of the M n = 15 000 and 33 000 materials indicate that an ionic peak is observed for the M n = 15 000 materials but is generally not observed for the M n = 33 000 materials even with 100% excess neutralizing agent. The position of this peak is essentially unaffected by the type of neutralizing agent used. Analysis of the tail region of the scattering curves indicates that the interface between the ionic and non-ionic regions is sharp.

The effect of molecular variables upon the dynamic viscoelastic behavior of solutions of sulfonated polyisobutylene telechelic ionomers in nonpolar solvents has been investigated. Intermolecular association of the ionic end groups in nonpolar media results in the formation of a transient ionic network which displays a viscous response at low frequencies and an elastic response at high frequencies. The frequency of the transition from viscous behavior to elastic behavior, as well as the plateau storage modulus, is dependent upon molecular variables such as architecture, molecular weight, neutralizing cation, and extent of neutralization. Variables which affect the strength of the ionic interactions, such as temperature and the type of solvent, also influence the viscoelastic response. Solutions of ionomers neutralized with cations of Groups IA and IIA, such as potassium and calcium, behave elastically over most of the experimentally accessible frequency range, while those neutralized with transition metals, such as zinc, display viscous flow over a rather wide range at low frequencies. As in previous studies of dilute solution viscosity behavior, the threearm star trifunctional species was found to form a more extensive network in nonpolar solvents than the linear difunctional species at equivalent concentrations. The failure of time–temperature superposition indicates that these solutions are thermoheologically complex.

Previous chapters have illustrated that interactions between ionic groups located within, or pendant to, polymer chains strongly influence the morphological structure and properties for both polymer melts and solutions. These interactions are also observed to affect the bulk viscoelastic and mechanical properties of polymeric materials considered to be in the ‘solid’ state. Such materials include those that are below the melting temperature (for semicrystalline polymers) or glass transition temperature (for amorphous polymers) as well as materials above the glass transition temperature that are sufficiently ionically crosslinked to be considered elastomeric in terms of their mechanical response. The time-dependent properties, such as stress—relaxation, creep, and dynamic mechanical properties, are particularly sensitive to the strength of ionic associations which, in turn, are dependent upon the ionic species (e.g. sulfonate or carboxylate), the neutralizing cation, competing interactions with other portions of the polymer chain, etc. In addition to the effects of ionic interaction, phase behavior may also play a role in influencing the mechanical response. Phases in the system of interest may be in the glassy state, the glass transition region, or the rubbery region. If crystallinity is present, viscoelastic and mechanical properties will also be affected by the level of crystallinity and the crystalline morphology. For example, the crystalline phase may be either continuous or distributed so that the crystallites act somewhat as rigid filler particles.

High-Temperature Properties and Applications of Polymeric Materials: An Overview Thermophysical Properties of Epoxy and Phenolic Composites High-Temperature Stability of Silicone Polymers and Related Pressure-Sensitive Adhesives Testing Materials at Elevated Temperatures Using Moire Interferometry Positron Annihilation Lifetime Spectroscopy To Probe Free- Volume Effects in High-Temperature Polymers and Composites Some Models of Material Behavior During Injection Molding Advanced Modeling of the Generation and Movement of Gases Within a Decomposing Polymer Composite The Application of Supercritical Fluid Technology to High-Performance Polymers Degradation Kinetics of High-Performance Polymers and Their Composites Monte Carlo Simulation of Polymer High-Temperature Degradation and Fracture Novel High-Performance Thermosetting Polymer Matrix Material Systems Properties and Potential Applications of Poly(arylene ether benzimidazole)s Synthesis and Characterization of Porous Polyimide Films for Dielectric Applications Synthesis and Characterization of Melt-Processible, High- Molecular-Weight Poly(amide-imides) Metal Salt-Polymer Composites: Complexation of Metal Salts with the Phosphorus-Oxygen Bond in Poly(arylene ether phosphine oxide)s Refractive Indices of Aromatic Polyimides

The influence of amorphous chains on bulk structure and material properties is examined in block and segmented copolymer systems whose components are in a variety of morphological states including: rubber-rubber; rubber-glass; glass-glass; rubber-crystalline glass-crystalline; and, crystalline-crystalline. The effects of external variables, such as temperature, time, and internal variables, such as molecular weight and composition ratio on the magnitude of the role played by the amorphous chains in these systems are discussed.

The rate of decomposition for two widely used glass- and asbestos-phenolic ablative materials were measured using standard thermogravimetric techniques. Thermograms were obtained at six heating rates ranging from 10°C min −1 to 160°C min −1 . From these data the kinetic parameters were determined by a slightly modified version of Friedman's method. Fractional weight loss calculated using the derived kinetic parameters over the temperature range of decomposition agreed with measured values with a mean error of 0.33 and 0.28%, with a standard deviation of errors 0.58 and 0.84% for glass- and asbestos-phenolic, respectively. The 95% confidence for the mean error was 0.22 and 0.44% for the glass-phenolic and 0.14 and 0.42% for the asbestos-phenolic. Also, the activation energy was calculated by the method of Flynn and Wall. The average activation energy values determined by the two methods agreed within 4.6% for both materials.

The physical aging process in styrene-butadiene and carbonate- siloxane block copolymers has been studied by monitoring the time dependent changes in mechanical and thermal properties. Specifically, stress-strain, stress relaxation and differential scanning calorimetry experiments were utilized. For the styrene-butadiene systems, it was found that the rate of physical aging increases with decreasing glassy content between 50 and 100% glass. However, the rate must decrease to zero when the percent glass reaches zero. The occurrence of physical aging was also noted in the polycarbonate siloxane block copolymer investigated. The data are discussed in light of the practical ramification of utilizing these block copolymers in material applications.

A method has been developed to determine the specific heat of a material during thermal decomposition using a combination of DSC and TGA data obtained at the same heating rate. The heat of decomposition is calculated simultaneously using the same data. This technique was used to determine the specific heat and heat of decomposition of a widely used fiberglass-filled phenol—formaldehyde resin and a fiberglass-filled acrylonitrile—butadiene (AB) copolymer. Experimental data are presented for the specific heat of both the virgin and char components for temperatures between 60 and 730°C. The calculated specific heat of the mixture during decomposition for both materials is also presented.

The kinetics of high-temperature carbon-silica reactions for a widely used glass-filled phenolic resin have been studied. Weight-loss and rate-of-weight-loss data were obtained at four heating rates ranging from 5 to 50°C per minute using standard thermogravimetric techniques. Experimental data were obtained at temperatures between 30 and approximately 1700°C. The kinetic parameters were calculated from these data using a multiple heating rate technique. Close agreement was obtained between the fractional weight loss calculated using the kinetic parameters and the measured values.

Extended X-ray absorption fine structure (EXAFS) investigations of various types of zinc-neutralized telechelic ionomers have evidenced large differences in the degree of local order within the aggregates. Among the parameters influencing the microstructure, it is shown that the conditions of neutralization play an important role.

Etude de solutions diluees; en milieu non polaire, l'association des groupes terminaux conduit a une augmentation de la viscosite et a une gelification a tres faibles concentrations. Ces ionomeres peuvent etre utilises comme modifiants de la viscosite et epaississants thermiques

The decomposition kinetics and material properties of a decomposing, expanding glass-filled polymer composite have been measured. In addition, the morphology as a function of the stage of decomposition and the decomposition-induced material damage have been monitored visually by scanning electron microscopy. The combination of these data was used to characterize the high-temperature behaviour of the material.

Physical aging of semicrystalline poly(ethylene terephthalate) has been investigated as a function of crystalline content. Stress-strain, stress relaxation, and differential scanning calorimetry experiments were used to monitor the physical aging process. It was found that both the overall extent and the rate of physical aging in this material decrease with increasing crystallinity. Several possible reasons for this behavior are advanced and discussed. It was also found that the drawing behavior of amorphous PET changes significantly as physical aging progresses. Specifically, for samples aged and then elongated, the extent of localized deformation (necking) and associated strain-induced crystallization was greater for samples aged for longer periods of time. (Author)

The solid-state mechanical properties of well defined sulphonated polyisobutylene telechelic ionomers are presented. Specifically, the effect of (1) molecular architecture, (2) molecular weight, (3) type of cation used for neutralization and (4) excess neutralizing agent has been investigated. In addition, the effect of moisture and ionic plasticizer on the stress-strain behaviour has also been studied. These ionomers do not display the characteristic small-angle X-ray scattering (SAXS) peak, which is indicative of the presence of clusters, above a number-average molecular weight of about 10 000. However, below this molecular weight a weak shoulder is sometimes observed on the SAXS curve. The tri-arm species form a network structure at ambient temperatures which results in materials with good mechanical properties. The mechanical properties of the linear difunctional species are inferior to those of the three-arm star trifunctional species due to a less well developed network structure. The monofunctional species are very tacky at ambient temperatures and cannot be handled as solid materials. However, by their incorporation into the trifunctional systems they do serve as a model for ‘dangling ends’. As expected, these blends display significantly different properties than those possessed with the pure trifunctional species. Addition of excess neutralizing agent significantly increases the high deformation properties with little effect on Young's modulus. A simple morphological model has been postulated in which it is suggested that the excess neutralizing agent resides at the ionic sites rather than being uniformly distributed throughout the matrix. Zinc-neutralized ionomers show stress-strain behaviour which is comparable to the potassium- and calcium-neutralized materials at ambient conditions, but the softening temperature is lower for the zinc neutralized material. Water absorption in these materials is relatively low. Addition of zinc stearate, an ionic plasticizer, facilitates melt processing by lowering the viscosity at high temperatures yet at ambient temperatures it crystallizes and acts as a reinforcing filler thus increasing Young's modulus.

The mechanical properties of carboxylato-telechelic polyisoprenes neutralized with barium, aluminium and zirconium have been studied. In addition to the variable of neutralizing cation valence, the effect of molecular weight was also investigated. It was found that, for those cations studied, increasing cation valence at an approximately constant molecular weight results in increased stresses during a stress-strain experiment. For the barium-neutralized materials, both modulus and observed stresses increase with molecular weight due to entanglement effects. For the zirconium-neutralized materials, this trend is reversed due to the formation of a more well developed network induced by different chemistry.

The thermochemical expansion of two very similar polymer composites has been measured from approximately 30°C to 1500°C. Expansion measurements were obtained at heating rates of 5, 10, 20 and 50°C min −1 . One material exhibited a net expansion while the other exhibited a net contraction. Both types of behaviour were successfully modelled to approximately 1040°C using a previously proposed expansion model. The constants in the model were determined using the experimental expansion data and non-linear estimation. Expansion behaviour calculated using the model is compared with the observed expansion behaviour.

It is pointed out that research efforts are at present being directed in two areas, one comprising experimental studies of this phenomenon in various glassy polymer systems and the other involving the development of a quantitative theory capable of satisfactorily predicting aging behavior for a variety of polymer materials under different conditions. Recent work in both these areas is surveyed. The basic principles of nonequilibrium behavior are outlined, with emphasis placed on changes in material properties with annealing below the glass transition temperature. Free volume theory and thermodynamic theory are discussed.

The thermal response of a polymer composite material undergoing decomposition has been modeled. A one-dimensional transient thermal model with an nth order ap proximation for the rate of decomposition was applied. The model was tested by ex perimentally measuring the temperature profiles during decomposition for a glass- filled phenol-formaldehyde polymer composite. Additionally, the specific heat and thermal conductivity of the virgin and char components, heat of decomposition, and the kinetic parameters were experimentally determined and used as input to the model. The predicted temperature profiles are in good agreement with experimental temperatures obtained using a radiant heat flux apparatus.

Network and linear epoxy resins principally based on the diglycidyl ether of bisphenol-A and its oligomers are prepared and studied using diamine and anhydride crosslinking agents. Rubber modified epoxies and a carbon fiber reinforced composite are also investigated. All materials display time-dependent changes when stored at temperatures below the glass transition temperature after quenching (sub-T/g/ annealing). Solvent sorption experiments initiated after different sub-T(g) annealing times demonstrate that the rate of solvent uptake can be indirectly related to the free volume of the epoxy resins. Residual thermal stresses and water are found to have little effect on the physical aging process, which affects the sub-T(g) properties of uniaxial carbon fiber reinforced epoxy material. Finally, the importance of the recovery phenomenon which affects the durability of epoxy glasses is considered.

An overview is given of the viscoelastic behavior of ionomers in both the bulk and solution. For bulk materials, the various regions of the viscoelastic spectrum, i.e. glassy, glass transition, rubbery, and melt flow, are addressed separately. The effects of system variables (molecular weight, molecular architecture, ion content, ion type, neutralizing ion type, excess neutralizing ion, etc.) upon the morphological structure of the ionic regions and the resulting effects on viscoelastic behavior are discussed in some detail. For ionomer solutions, in addition to the effects of the same variables, the effect of solvent environment on the viscoelastic behavior is explored. Finally, some ideas regarding potential fruitful areas for future research on ionomers are presented.

The gelation of polyisobutylene-based model ionomers with-S03 −K+ terminal groups has been studied in hexane at 25°C. Both molecular architecture and molecular weight were found to significantly influence the concentration at which gelation occurs. Specifically, three-arm star trifunctional ionomers gel at lower concentrations than linear difunctional ionomers of similar molecular weight. In addition, the gelation concentration decreases with increasing molecular weight for the three-arm star trifunctional ionomer, but the results do not fit the relationship reported previously which relates gelation concentration and molecular weight for carboxylated linear telechelic polymers.