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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.

Morphological studies have been carried out on a thermotropic liquid crystalline copolyester based on poly(ethylene terephthalate) (PET) and para hydroxybenzoate (PHB) that has been subjected to different types of flow histories. Wide angle X-ray scattering investigations and chemical etching (n-propylamine is the etchant) in conjunction with electron microscopy studies conducted on end gated injection molded plaques of the 60 percent PHB and 80 percent PHB copolyesters indicate that a highly oriented skin region and a less oriented core region is present. Chemical etching studies performed on microtomed layers of end gated and center gated plaques show that the etching is less pronounced in the skin region and is more pronounced in the core. The microtomed layers of the end gated injection molded plaques when analyzed by ESCA indicate the presence of a “PHB rich” skin region and a “PET” rich core region. Biaxial orientation, as denoted by WAXS measurements, is observed when the 60 percent PHB copolyester is squeezed between lubricated parallel plates.

Novel segmented copolymers were synthesized using aminopropyl terminated linear poly(dimethylsiloxane) oligomers as the soft component and various diisocyanates as the hard segments. As a result of the large differences in the cohesive energy density (solubility parameter) between the two components, phase separation occurs to form a microdomain structure at relatively low oligomer molecular weights. Since chain extenders were not employed during the synthesis, the “hard” segments are strictly related to the length of the diisocyanate moiety utilized in the reaction, In this paper we utilize these copolymers as reasonable models for investigating the various methods available for determining the interfacial layer thickness between the hard and soft phase. Specifically, in these systems there is no hard segment length distribution as is the usual case for segmented urethanes. Utilizing Porod's law, and appropriate analysis, both positive and negative deviations were found in the systematic series of copolymers. The degree of positive and negative character was found to be dependent upon copolymer composition. Negative deviations were accounted for in terms of a finite interfacial thickness, which turned out to be relatively small as anticipated, while the positive deviations were assigned to isolated hard segments that reside within the soft segment matrix, i.e., concentration fluctuations. In calculating the interfacial thickness, several methods were applied and in general, close agreement was obtained. Finally, correlation function analysis in conjunction with determination of the coherent Porod lengths, etc. were determined and discussed accordingly. Cautionary comments are also provided for researchers who apply less complete small angle x-ray scattering (SAXS) analysis to related block or segmented copolymers with regard to phase separation behavior.

The rheological behavior of sulfonated polyisobutylene based elastomeric ionomers has been studied. The effects of molecular architecture, type of cation, and addition of excess neutralization agent were investigated. The effect of temperature was studied to a limited extent. In a specific case, the influence of an ionic plasticizer, zinc stearate was also examined. It was found that in these telechelic ionomers where the ionic groups are located exclusively at the chain ends, significant Ionic interactions may persist even at 180°C. The zinc-neutralized ionomers had the lowest viscosity as compared to the corresponding potassium- or calcium-neutralized ionomers. The covalent character of zinc is believed responsible for this behavior. Other factors being constant, the triarm based ionomers are more viscous than the monofunctional ionomers. A mixture of monofunctional ionomers with the triarm, species is a model for dangling chain ends, and results in a slight lowering of the viscosity under the conditions studied. Zinc stearate acts as an ionic plasticizer. Upon the addition of 15 percent by weight of zinc-stearate to the ionomer, the low shear rate viscosity drops by several orders of magnitude and renders the ionomer thermally processable at moderate temperatures.

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.

Mold filling studies have shown that thermotropic liquid crystalline copolyesters of p-hydroxybenzoicacid (PHB) and polyethyleneterephthalate (PET) fill by an advancing front mechanism similar to flexible chain polymers. The structure and orientation developed during filling as determined on solid specimens by an etching method, X-ray diffraction, and shrinkage study on thin microtomed samples appear to be most pronounced at the surface. Based on this information copolymers of 60 and 80 mole percent PHB/PET were co-injection molded with filled PET under various processing conditions. Because of the low viscosity of the copolyesters, they readily coated filled PET under most processing conditions to give a sheath/core structure. The bending modulus of co-injection molded bars with as little as 35 percent PHB/PET was as high as the sample consisting of 100 percent liquid crystalline copolyester. Electron micrographs of fracture surfaces revealed excellent adhesion between the two polymers.

Liquid crystalline polymers can be processed to form high strength/modulus materials. In processing these materials, it is apparent that molecular orientation is an important factor in determining the physical strength of the processed materials. In this study a systematic investigation was carried out to determine how a thermotropic copolyester of parahydroxybenzoic acid (PHB) and polyethylene terephthalate (PET) responds to two basic types of flows: shear and extensional flow. This was accomplished by preparing sheared and extended samples under controlled conditions of temperature and flow history. Sheared disks were prepared using a disk and plate geometry of a Rheometrics Mechanical Spectrometer (RMS model 605), while extended ribbons were prepared using a slit die attached to an Instron capillary rheometer. Two copolymerer compositions of 60 mole percent and 80 mol percent PHB were investigated. The sheared disks and extended ribbons were investigated for molecular orientation and morphological textures using wide angle x-ray scattering (WAXS) and scanning electron microscopy (SEM) analysis, respectively. It was found that extensional flow has a greater capacity for orienting such materials than shear flow. Samples annealed at their softening points for 1 minute (240°C for the 60 mole percent PHB/PET copolymer and 300°C for the 80 mole percent PHB/PET copolymer) showed no significant loss of orientation, indicating that once orientation is produced it may remain in the melt for a long period of time. Sheared samples prepared by shearing the sample while cooling showed significantly higher degrees of orientation than those not cooled while being sheared. This may indicate that a minimum stress level exists for the production of orientation in shear flow.

Effet important de la precontrainte sur la morphologie finale du polymere. Modele pour expliquer les resultats observes

Pulsed nuclear magnetic resonance measurements have shown that segmented polyurethanes as well as block copolymers segregate into domains with distinct mobilities. The usefulness of this technique for investigating the importance of the domain interface and for studying the mixing/ demixing of domains has been demonstrated. By examining the percent rigid material as a function of temperature, a polystyrene/butadiene block copolymer showed little evidence of domain interface effects, while in a series of segmented polyurethanes, the interface was seen to be important. The domains of a polyester soft segment and diphenylmethane diisocyanate hard segment polyurethane were mixed by annealing at 170°C. Examination of the demixing process as a function of storage temperature enabled an activation energy for domain formation of 36 ± 5 kcal/mole to be calculated. In a series of polyurethanes with varying amounts of hard segments, the material with the least amount of hard segments showed evidence of soft segment crystallinity. The mixing proces in this series was interpreted in terms of shifting correlation frequency distributions.

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.

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.

The physical structure of a number of styrene-butadiene copolymers were investigated via dynamic mechanical and swelling studies on uncrosslinked and gamma-radiation cross-linked films that had initially been solvent cast from toluene or methyl ethyl ketone. The mechanical behavior of these films before and after crosslinking was found to depend on the material history as well as the chemical structure of the copolymer, in agreement with observations made by other experimental techniques. A simple morphological interpretation was given to the dynamic mechanical spectra as a function of radiation dosage and a limited discussion of the swelling behavior is included.