A number of aspects on the processing of PMDA-ODA polyimides have been investigated. These aspects included the effects of curing procedure on residual stress development in polyimide films, characterization of stresses arising in films during processing on tenter frames and the effects of stress history on irreversible shrinkage behavior. Chemical curing using a gel technique was found to reduce the development of residual stresses in PMDA-ODA films during cooling. Chemically cured polyimide films made from a gelatin technique possessed consistently lower in-plane thermal expansion coefficients than thermally cured films. This was due to increased in-plane orientation development in the chemically cured films during drying. An analysis of stresses arising during tenter frame processing of polymeric films indicates the presence of large in-plane shear stresses as a result of stress gradients along the machine direction. These shear stresses vary linearly across the width of the line and are responsible for creating orientational anisotropy and non-uniformity profiles across the width as well. The principal directions of stress tend to lie at $\pm 45\sp\circ$ to the machine direction but may be altered by machine and transverse drawing by the frame. Methods to eliminate or at least reduce in-plane anisotropy were discussed as well. An investigation of strain storage behavior revealed a strong relationship between irreversible shrinkage and stress history in several different polymeric materials. Irreversible shrinkage in polyimide films was found to be largely due to the cooling of the materials under stress. Shrinkage behavior in PMDA-ODA and Upilex-R$\sp\circler$ films could be described in a quantitative manner using linear viscoelasticity. Two forms of highly crystalline PMDA-ODA based polyimide were formed by a high pressure imidization process. Polyimide powder with a density of 1.46 $\pm$ 0.01 g/cm$\sp3$ was formed by curing a polyamic acid solution in dimethylacetamide at 200$\sp\circ$C and 1.38 MPa. Heat treatment of chemically cured gel films under the same conditions resulted in films with a density of 1.44 $\pm$ 0.01 g/cm$\sp3$.

There has been increased interest in late transition metal catalyzed olefin polymerizations. This is due, in part, to the ability of late transition metal catalysts to yield new polymers. Among them, neutral nickel salicylaldiminato catalysts have gained importance in recent years due to their functional group tolerance. Schiff's base chemistry was employed to synthesize a wide variety of ligand frameworks. These ligands, combined with discrete metal precursors led to the synthesis of neutral nickel salicylaldiminato catalysts 11-13. A phosphine sponge was needed to activate these catalysts for olefin polymerization. An inexpensive phosphine sponge such as copper (I) halide was successfully used as a cocatalyst to perform polymerization of ethylene in organic media. The functional group tolerance of the catalyst and cocatalyst allowed for polymerization of ethylene in water leading to polyethylene latexes. The polymerizations were performed under moderate conditions of pressure and temperature to yield low molecular weight polyethylene with up to 100 branches/1000 C atoms. The effect of the nature of the ligand framework on the activity of the catalyst and the molecular weight of the polymer obtained was studied. Copolymerization of ethylene with functional monomers was performed in organic or aqueous media leading to polyolefins with incorporated functionality. Norbornene was also polymerized by complexes 11-13 with either a borane or methyl aluminoxane (MAO) cocatalysts. The microstructure of the polynorbornene obtained was found to be dependent on the nature of the cocatalyst. A wide variety of functionalized norbornenes were also effectively copolymerized with norbornene. A variety of chain transfer agents such as 1-octene and 5-bromo-1-pentene were used to control the molecular weight of polynorbornenes. These chain transfer agents were also used successfully to control the molecular weight of the copolymers of norbornene with functional norbornenes. All of the polymers were characterized by spectroscopic and thermal methods of analysis.

Abstract not available

The mechanical properties of high modulus/high strength fibers of poly-(p-phenylene benzobisthiazole) (PBT) have been investigated in relation to fiber microstructure and fibrillar morphology. Heat treatment processing of dry-jet wet spun PBT fibers was undertaken to provide fiber samples for a systematic comparison of structure-property relationships. Heat treated PBT fibers possessing a tensile modulus as high as 300 GPa with tensile strength of 3 GPa have been produced by employing heat treatment conditions bordering on polymer degradation; temperatures of 630(DEGREES)C - 680(DEGREES)C in a nitrogen atmosphere with applied tensions approaching fiber breakage. Quantitative measures of mechanical anisotropy were obtained for PBT fibers in torsional and bending experiments. Torsional shear modulus values of 1 - 1.5 GPa were measured in free torsional oscillation experiments and shear strengths of 60 - 140 MPa were obtained from twisting experiments. Bending studies provided a measure of compressive strength, with fibers exhibiting buckling for compressive stresses of approximately 700 MPa. The state of stress in model cylindically orthotropic fiber structures was analyzed using anisotropic elasticity theory. Tension.compression, torsion and bending were examined in order to compare the predicted level of transverse stress with the measured (relatively low) lateral strength. Optical microscopy, transmission and scanning electron microscopy and x-ray diffraction were used to examine the structure of PBT fibers. Crystallite size perpendicular to the fiber axis increases from approximately 2 nm in as-spun fibers to 10 - 12 nm in fibers heat treated at temperatures above 600(DEGREES)C. Fiber tensile strength was found to increase with increase in the extent of the lateral molecular order. However, tensile modulus and tensile strength did not depend directly on heat treatment parameters of temperature, time but rather indirectly through the affect of applied tension during heat treatment on the overall axial orientation. The highest values of fiber tensile modulus and tensile strength were exhibited by the more highly oriented fibers.

No description available.

Nature has demonstrated that a powerful strategy for tuning adhesion lies in the development of patterns at an interface. Inspired by the amazing attachment abilities of geckos, we demonstrate that similar design approaches can tune the adhesion of polymer interfaces. In this research, we investigate the role of patterned surfaces in the control of polymer adhesion. Specifically, we demonstrate that patterned surfaces control adhesion by enhancement of the total contact line, or perimeter of the interface, as opposed to increasing the total contact area. This insight is very powerful as it provides new strategies for designing patterned adhesives. To demonstrate that the pattern control of adhesion is associated with the enhancement in contact line, we explore two unique types of patterned interfaces and their control in adhesion. First, we begin our investigation of patterned adhesion (Chapter 2) by understanding how surface-chemical patterns - i.e. a pattern of periodic variation in surface chemistry, can tune the adhesion of a commercial silicone elastomer. This type of patterned adhesive is unique as almost all previous patterned adhesives are based on topographic patterns. We find a surface-chemical pattern can enhance the adhesion of the elastomer and significant increases are observed for specific pattern geometries. More importantly, the mechanism of enhancement is linked to the changes in the contact line which is controlled by the periodic variation in surface chemistry. Our results on the adhesion of surface-chemical patterns open new opportunities for developing alternative patterned interfaces for adhesion control. Since the mechanism of control is associated with the enhancement in contact line, we explore an alternative patterning strategy without the use of lithography. In Chapter 3, we explore the concept of surface wrinkling to pattern polymers. We use a combination of osmotic stress, coupled with lateral confinement to generate wrinkles on polymer surfaces. We show control of both the orientation and the length-scale the wrinkle patterns. The wrinkles form as a result of the development of a compressive stress within the polymer film due to the balance between osmotic stress and lateral confinement. There are two main contributions from this work. First, we demonstrate the control of the degree of lateral confinement determines the wrinkling morphology. More importantly, this control leads to the discovery of two new wrinkling morphologies that have not been observed previously. Second, our approach provides direct applications of these structured materials as functional devices. Specifically, we illustrate that our wrinkled polymers can directly be used as an optical array or patterned adhesive (Chapter 4). In Chapter 4, we combine the lessons learned in the adhesion of surface-chemical patterns (Chapter 2) along with the patterning approach based on surface wrinkling (Chapter 3) to generate a “self-patterned” wrinkled “smart” adhesive. We demonstrate that the adhesive properties are connected with the wavelength of the surfaces wrinkles. With the understanding of the mechanism of contact line enhancement, wrinkled patterns are developed that enhance adhesion by increasing the total contact line during separation. Based on the mechanism of contact line splitting, we develop a scaling relationship that explains how the contact line enhancement is controlled by the wavelength of the wrinkles.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 233-241). Also available via World Wide Web.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 222-232).

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis--M. Phil., University of Hong Kong, 1974. / Mimeographed.