The crystallization behavior of poly(p-phenylene sulfide) PPS has been studied. Two PPS samples with < M_w > = 43K and < M_w > = 83K were fractionated to remove low molecular weight oligomers yielding fractionated PPS samples with < M_w > = 57K and < Mw > = 113K. The fractionated samples were then treated with an ion exchange process to allow control over the nature of endgroup counterion. Isothermal rates of hulk crystallization were analyzed as a function of n1olecular weight of PPS, fractionation, and chen1ical nature of the endgroup counter-ion. Additionally the spherulitic growth rates and nucleation densities were studied as a function of the chemical nature of the endgroup counter-ion for fractionated PPS with < M_w > = 57K. As a function of endgroup counter-ion, crystal growth rates and overall rates of crystallization decreased in the following order: H > Zn > Na. No significant trends in nucleation density as a function of endgroup counter-ion were observed. Bulk crystallization rates, nucleation density, general morphological features, equilibrium melting point, and abso1ute crystalline percentage of linear and starbranched nylon-6 have been studied as a function of branch-point functionality and crystallization temperature. Overall bulk crystallization rates were described in terms of the Avrami equation. The crystallization half-times of star-branched nylon-6 as a function of <i>supercooling</i> were reduced relative to those of linear nylon-6 of comparable molecular weight. Irregularities in lame1lar structure were implied by SAXS experiments on samples with branch-point functionality as low as three. The effects of changing the block length of poly(dimethylsiloxane), PSX, blocks in poly(etheretherketone)-poly(dimethylsiloxane), PEEK-PSX, multi block copolymers and their ketimine precursors, PEEKt-PSX, were investigated. A dran1atic dependence on thermal history prior to crystallization was observed in both block copolymer systems. Block copolyn1crs crystallized from the glassy state obtained a much higher degree of crystallinity at a n1uch faster rate of crystallization than copolymers crystallized from the melt at identical crystallization temperatures. Thermal and mechanical behavior of bisphenol-A polycarbonate was studied as a function of thermal history and absorbed mass fraction of C0₂. Mechanical testing and gas absorption experiments were performed on physically aged and unaged polycarbonate. Gas absorption studies indicated that although initial diffusion was somewhat retarded in the aged samples, both aged and unaged polycarbonate samples showed identical equilibrium absorbed gas values at 6500KPa and identical gas desorption behavior. Absorbed C0₂ was shown to plasticize polycarbonate. Polymeric liquid crystalline foams were produced from star-branched polyoxybenzoate-po1yoxyphenoxybenzoate copolymers (POB-co-POPB) via gas supersaturation followed by thermal blowing. Solid state C0₂ gas absorption well as melt processability of star-branched POB-co-POPB was increased relative to the linear polymer of comparable molecular weight. While C0₂ blown foams of linear POB-co-POPB produced by the gas supersaturation technique had a relatively high density and showed highly anisotropic bubble growth, well defined, nearly isotropic foams of star-branched POB-co-POPB with mean cell size from 200 to 400μ were made using the gas supersaturation technique. / Ph. D.

The classical route for the synthesis of this family of macromolecules is via nucleophilic aromatic substitution using dimethylsulfoxide (DMSO) as a dipolar aprotic solvent and aqueous sodium hydroxide as a base. High molecular weight homopolymers can be synthesized in a short time (1 hour). However, hydrolytic side reactions can limit its scope for the synthesis of block copolymers. An alternate route using potassium carbonate/dimethyl acetamide as base and solvent respectively has been cited in the patent literature. We have used this method for the synthesis of several homopolymers and copolymers derived from various bisphenols. Our investigation into the kinetics and mechanism of this process has demonstrated that this route deviates from simple second order kinetics. This deviation has been rationalized to be due to the heterogeneous nature of the reaction. The utility of these polymers is a direct function of their excellent stability (hydrolytic, thermal and dimensional) wide use range and good mechanical properties. However, their poor solvent resistance can be considered and "Achilles heel". We reasoned that the introduction of a second ordered or crystalline component would vastly improve its solvent resistance. Hydroquinone polysulfone, homopolymer was reported to be semi-crystalline "as made". We thus synthesized and studied "random" copolymers obtained by reacting various mole ratio combinations of bisphenol-A and hydroquinone with dichlorodiphenyl sulfone. The molecular weight (M_n) of these copolymers ranged from 20,000-40,000. Their glass transition temperature (T_g) increased monotonically from 185°C for pure bis-A homopolymer to 210°C for hydroquinone homopolymer. Two different types of mechanical tests together with DSC and SEM measurements showed that improved solvent resistance (especially to liquids of interest to NASA for aerospace functions) could be achieved via a novel liquid induced crystallization process. ¹³C and proton NMR spectral assignments were successfully made using model compounds. The composition of the copolymers by NMR accurage to ±3%. Multiblock (-A-B-) copolymer of bisphenolA polycarbonate and several poly(arylether sulfones) were synthesized from well characterized oligomers. It was possible to prepare one or two phase block copolymers by controlling the molecular weights and/or interaction parameters of the parent oligomers. Surface characterization showed surface segregation even for the single phase material. Triad distribution of monomers in non-equilibrium copolycondensation was investigated by Monte' Carlo simulation. In the one step process, where the intermonomer and/or comonomers had independent functional group reactivities, the resulting copolymer was always random irrespective of the reactivity ratio of the comonomers. A non random distribution was obtained when the reactivity ratio of the funtional groups in the intermonomer and those of the comonomer were much greater than unit. Monomers that resulted in a random copolymer in a one step process could be made with a non random distribution by a multi-step process. / Ph. D.

The overall objective of this work was to enhance the mechanical properties of thermoplastics by blending with liquid crystalline polymers (LCPs). Injection molding and sheet extrusion studies of blends of poly(ethylene terephthalate) (PET) with several LCPs were conducted with an emphasis on blends containing 50 wt % or less of the LCP. It was seen that significant enhancements (50-350%) in the tensile and flex moduli of PET were achieved by blending with 0-50 wt % LCPs via injection molding. The level of property enhancements was lower in the case of-sheet extrusion due largely to processing limitations which made it difficult to obtain high draw ratios. Since thermotropic LCPs typically have high melting temperatures it is difficult to blend several thermoplastics such as polypropylene (PP) with these LCPs in the same extruder or molding unit. Thus a blending method (hereon referred to as the dual-extruder mixing method) was developed to overcome this limitation. In this method, the matrix and LCP polymers were plasticated in two separate extruders, subsequently mixed downstream in a static mixer (Kenics) and the melt blend than passed through an appropriate capillary or sheet die to generate strands or sheets, respectively. Using this method, blends of PET and PP with several LCPs were extruded into strands and sheets. In some cases, for example PP and Vectra A900 (LCP), the difference in their normal processing temperatures was in excess of 100°C. Strands of PET/Vectra A900 70/30 composition ratio were observed to have higher moduli than a blend of the same composition extruded using a single extruder at all the draw ratios tested. This was determined to be due to the different LCP fibrillar morphology in the two cases. In the case of the dual-extruder mixing method, the LcP fibrils were continuous, running the length of the extrudate, and further devoid of any skin-core structure. In contrast, the single-screw extruder blend had a distinct skin-core fibril-droplet type of structure and the LCP fibrils were not continuous. On the basis of other independent experiments, it was confirmed that the LCP fibrils in the dual-extruder mixing method were generated in the static mixer itself whereas the LCP fibrils in the case of single-screw extrusion were generated in the converging section of the die and/or by drawing at the die exit. This difference in the mode of LCP fibril generation in the two cases was attributed to the distributive mixing mechanism of the static mixer compared to the dispersive mixing in the extruder. Strands of PP/LCP and PET/LCP had significantly enhanced tensile moduli compared to the corresponding matrix tensile modulus. Enhancements of 10-20 times that of the pure matrix were achieved when blends containing about 20-30 wt % of the LCP were extruded from the dual-extruder mixing method. The tensile moduli of sheets of PET/LCP and PP/LCP blends were not much higher than that of the corresponding matrix polymer and this was attributed to the low molecular orientation achieved in the sheets due to low draw ratios. The tensile strengths of the majority of the blends were not enhanced to any appreciable degree and poor wetting and adhesion between the thermoplastic-LCP polymers was believed to be the cause. Comparison of some of the mechanical properties (tensile modulus, tensile strength, flexural modulus) of the thermoplastic/LCP blends generated in this study with data from the literature on thermoplastic/inorganic filler composites showed that when compared on the basis of equal wt % of the reinforcement in the blend, the LCP composites can yield mechanical properties which are in the same range as those obtained using inorganic fillers. / Ph. D.

Morphological studies were carried our on thermotropic liquid crystalline copolyesters based on poly(ethyleneterephthalate) (PET) and para hydroxybenzoate (PHB), where PHB content varied from 0 mole percent up to 80 mole percent. The technique of chemical etching coupled with SEM and WAXS was utilized to obtain structural information. Morphological changes that occur when these materials are exposed to solvents such as dioxane or acetone and dye carriers were also studied using SEM. Electron microscopy results on the thermally pressed, quenched and chemically etched films indicate that selective chemical etching, i.e. etching of PET rich regions, occurs. This indicates a heterogeneous structure. An oversimplified molecular model has been proposed based on these results where at low PHB levels a PET rich phase is the continuous phase and at higher PHB levels (≥60 mole%PHB) a PHB rich phase is the continuous phase. SEM results on pressed, quenched, annealed and etched films show a "bricklike" structure similar to that seen when pure PET is chemically etched. WAXS studies show that crystallization is induced by solvent (etchant) at small etching times which indicates that the etching of PET rich regions is a two step process; (i) solvent induced crystallization, (ii) chemical etching. Dyeing studies carried out the PET/PHB systems using two different dye carriers indicate that dyeing occurs preferentially in the PET regions. Morphological studies on the dyed materials show a "puffed up" structure present only in the 50 mole% PHB material. / Master of Science

The purpose of this work was to determine the enthalpies and specific heats of polymethyl methacrylate, polydimethylaminoethyl methacrylate, polycyclohexyl methacrylate, polyallyl methacrylate, and polyethyl acrylate from 120 to 300°C, and to determine a method for estimating their specific heats. Enthalpies of the selected polymers were determined by using a drop calorimeter constructed by the Chemical Engineering Department of Virginia Polytechnic Institute. Specific heats were obtained by measuring the slopes of the enthalpy-temperature curves. Good agreement with existing data for polymethyl methacrylate was obtained. An existing semi-theoretical quantum mechanical method was modified to provide specific heat estimations for linear methacrylic polymers accurate within six percent. An empirical correlation yielding estimations within twenty percent was proposed. / Master of Science

These studies developed from Scanning Electron Microscope (SEM) observations of abrasive wear of a polymer disk sliding against metal asperity models. The investigator was unable to observe actual particle formation but did identify elastic and plastic deformation of the polymer, and a debris buildup and extrusion process occurring at the leading edge of the asperity. On the assumption that this process could lead to a surface fatigue condition, pin-on-disk wear trials were completed using a spherical steel ball sliding on polycarbonate, rigid PVC, and ultra-high molecular weight polyethylene specimens in dry and lubricated conditions. A delay in debris formation was observed in the rigid PVC and polycarbonate dry sliding trials. In each case a higher rate of friction force increase coincided with debris formation. No debris was produced in the ultra-high molecular weight polyethylene dry sliding trials, and the friction force trace was flat. An SEM analysis of the polycarbonate and rigid PVC wear tracks revealed pitting consistent with the Delamination Theory of wear. The effect of the lubricants was to significantly alter the form of the friction force traces, but not to eliminate wear in rigid PVC and polycarbonate. The results of the investigation, particularly the delay in wear debris generation, indicated that a fatigue wear mechanism appeared to exist in dry metal pin-on-polymer disk sliding systems. A qualitative wear model was developed to relate the in-situ SEM observations and the results of the pin-on-disk trials. / M.S.

Poly(arylene ether)s (PAEs) were synthesized via the silyl ether displacement route. Both AA, BB, and AB silylated monomers were prepared by partial or complete hydrolysis of the dihalide using potassium hydroxide in aqueous dimethyl sulfoxide followed by silylation with hexamethyl disilazane. Both linear and star-branched structures of PAEs were synthesized and this polymerization route allowed both random and block copolymers to be prepared. Triaryl phosphine oxide containing homo-& co-PAEs exhibited very high char yields, which suggested that these polymers were potentially flame-resistant materials. The AB type halogenophenols were also polymerized in the presence of diphenylsulfone as a diluent and potassium carbonate as a base at elevated temperatures. Poly(ε-caprolactam) (Nylon 6) copolymers were prepared by the incorporation of controlled molecular weight poly(arylene ether sulfone) (PES) oligomer segments into the polymer backbone which were functionalized with carboxyl end groups. A hydrolytic melt polymerization process was used to copolymerize the oligomers with ε-caprolactam. Two series of the copolymers, with varying weight ratios and PES segment lengths, were investigated. Extensive characterization experiments including thermal analysis, mechanical property measurement, wide angle x-ray diffraction and dynamic mechanical analysis were performed to illustrate that the copolymers displayed a good balance of properties. Hydrolytically stable triaryl phosphine oxide containing dicarboxylic acid monomers were synthesized and were chemically incorporated into the poly(hexamethylene adipamide) backbone to produce improved flame-resistant copolymers. The content of triaryl phosphine oxide comonomer in the melt synthesized copolymers was controlled from 0-30 mole%. The copolymers were melt crystallizable only at 10 and 20 mole% incorporation of the phosphine oxide comonomer. Cone calorimetric tests were employed to investigate the fundamental flame retardancy behavior of the copolymers. The tests were conducted in a constant heat environment (40 kW/m²). Significantly depressed heat release rates were observed for the copolymers containing phosphine oxide moiety. The results of the cone calorimetric tests and TGA data suggested that the triaryl phosphine oxide containing nylon 6,6 copolymers had improved flame resistance properties. The triaryl phosphine oxide dicarboxylic methyl ester was also introduced into poly(ethylene terephthalate) via melt transesterification to produce copolymers which had increased char yields as the P(O) content increased. However, crystallinity was totally disrupted at 20 mole percent P(O) incorporation in compression molded specimen. Novel star-branched liquid crystalline polyarylates (LCP) were made via melt acidolysis which were subsequently transformed to liquid crystalline foams by supersaturation of carbon dioxide followed by thermal blowing. It was found that the AB type monomers were essential to generate star shaped LCPs without crosslinking. The branching agents were necessary to control the molecular weights, disrupt crystallinity and to allow for higher gas uptake by the polymer matrix. / Ph. D.

Poly(arylene ether)s containing phosphorus, sulfur, and heterocyclic pendant moieties were synthesized and their properties investigated. The preparation of monomers containing phosphorus as well as monomers derived from phenolphthalein were synthesized in high purity. These monomers were then successfully polymerized by a nucleophilic displacement reaction to prepare poly(arylene ether)s of both high and controlled molecular weight. The novel poly(arylene ether)s based on phenolphthalein had glass transition temperatures ranging from 265 to 312 °C. Furthermore, the modulus of these macromolecules was significantly higher than that of typical poly(arylene ether)s (e.g. bisphenol A based systems), probably as a result of enhanced intermolecular forces. Phenolphthalein in poly(arylene ether)s has been shown not only to improve the thermal and mechanical properties, but also it provides a pendant functional group for chemical modification of the polymer. As a result, a base polymer can be customized to a variety of new materials using derivatization techniques. The possibility of metal complexing in phenolphthalein poly(arylene ether)s was also investigated. A variety of reactive and non-reactive end-capped poly(arylene ether)s of controlled molecular weight were synthesized for use in reactive toughening modified epoxy and cyanate ester networks and these results are briefly summarized. Model studies using HPLC were also conducted to determine reaction kinetics in nucleophilic poly(arylene ether) formation. The results demonstrate that potassium carbonate mediated step polymerizations likely proceed with etherification of one of the phenolic groups, prior to difunctional coupling, which can achieve high molecular weight. The formation of cyclic oligomers in the step-growth polymerization of poly(arylene ether)s was also studied. / Ph. D.

In this thesis, the effect of interphase bonding on the cohesiveness of domain structure was addressed. The interchain attractive forces between rigid segments and the phase separation between hard and soft segments have been improved by introducing either urea groups or ionic units. The urea linkages have the possibility of extensive hydrogen bonding while ionic units interact with each other by coulombic interactions, which provide even stronger interchain associations than the hydrogen bonding effects. This thesis addressed the preparation and characterization of polytetrahydrofuran based segmented polyurethane-urea and ionene elastomers. The urea linkages were effectively introduced to the polyurethane elastomers through an unconventional route which was based on carbamate-isocyanate interactions. The carbamates were generated principally from isocyanate functional prepolymers and tertiary alcohols. The carbamates were rearranged thermally and/or catalytically to produce amines which were rapidly converted to ureas. The effects of varying the size of the rigid and flexible segments in polyurethane elastomers on physical behavior were investigated. The importance of hydrogen bonding interactions in promoting phase separation of hard and soft segments and the cohesiveness of hard segment domain structure was demonstrated. Living, difunctional polytetrahydrofuran dioxonium ions were prepared via triflic anhydride initiation. The direct coupling of these "living" polytetrahydrofuran dioxonium ions with a ditertiary amine was used to produce a novel segmented ionene elastomer. The ionenes thus synthesized displayed interesting solution behavior and could be molded, or cast to produce good physical properties. Photochromic as well as thermochromic phenomena were also noticed in these systems. / Ph. D.

Thesis (M.S.)--University of Alabama at Birmingham, 2008. / Title from PDF title page (viewed Feb. 1, 2010). Additional advisors: Derrick R. Dean, Gregg M. Janowski, Selvum (Brian) Pillay (ad hoc). Includes bibliographical references (p. 76-82).