The friction and wear behavior of three thin polyimide films of known chemical structure was tested. An attempt was made to correlate differences in chemical structure, primarily the presence of flexible linkages and highly polar side groups, to differences in tribological properties. The wear test results showed lowest wear for the polyimide with the flexible oxygen linkage. The wear mechanism was deduced to be fatigue since wear did not occur immediately and a strong correlation was noted between wear rate and elastic modulus. Increasing sliding speed increased both wear rate and friction coefficient. The friction results showed highest friction for the polyimide with the highest density of polar side groups. Even though some effects of the deformation component of friction were seen, the adhesive component of friction predominated. / Master of Science

The modification of polyimide films by tin-complex incorporation has been studied with the aim of producing materials with the mechanical and thermal properties of polyimide with enhanced electrical properties. A variety of Sn(II) and Sn(IV) complexes have been incorporated into BTDA/ODA (3,3 14,4 1-benzophenonetetracarboxylic acid dianhydride / 4,41- oxydianiline) and PMDA/ODA (pyromellitic dianhydride/4,4 1 -oxydianiline) derived polyimides in a 1:4 (complex/polymer repeat unit) molar ratio. Tin-complex incorporation was seen to have a variety of effects upon polyimide properties, depending upon the particular tin-complex employed. All films produced were thermally stable with decomposition temperatures> 500°C. Most films were homogeneous and flexible. / Master of Science

The class of real nxn matrices M, known as K-matrices, for t which the linear complementarity problem w-Mz=q, w≥O, z≥O, w^tz=O has a solution whenever w-Mz=q, w≥O, z≥O has a solution is characterized for dimensions n<4. The characterization is finite and"practical". Several necessary conditions, sufficient conditions, and counterexamples pertaining to K-matrices are also given. A finite characterization of completely K-matrices (K-matrices all of whose principal submatrices are also K-matrices) is proved for dimensions < 4. / M.S.

M. S.

Thermosetting polyurethane films were prepared from solution by crosslinking hydroxypropyl lignin derivatives with diisocyanates. The network structure, characterized by the crosslink density, was controlled by two variables: the hydroxy content of the lignin polyol and the molar ratio of NCO:OH. In addition, the effect of network structure on thermal and viscoelastic properties was determined. Both the thermal and viscoelastic properties of the polyurethane films followed the trends found for crosslink density. For those films prepared from the various polyols with reduced hydroxy functionality, T_g was found to vary linearly with the extent of crosslinking as well as with the T_g of the polyol from which it was prepared. As the NCO:OH ratio was increased, the major difference in T_g occurred within the range from 1:1 to 3:1. Similar trends were noted for the viscoelastic properties in both instances. However, it was apparent that the sol fraction contributed significantly to the overall properties of the network, particularly at the high weight fractions. Fracture surface analysis of model substrates (cellulose acetate and cellulose tri-acetate) bonded with a lignin-polyisocyanate resin by Electron Spectroscopy for Chemical Analysis (ESCA) revealed the formation of interfacial bonds on the surface of the cellulose acetate adherend. Furthermore, it was indicated that failure occurred well within the bulk of the cellulose acetate while interfacial failure was apparent for the cellulose tri-acetate model. While mechanical attachment is unquestionably a contributing mechanism, the formation of interfacial bonds should significantly contribute to the performance of bonded joints for this particular adhesive system. / M.S.

Spruce wood meal (Picea pungens), sequentially solvent pre-extracted with water, ethyl ether, and ethanol were subjected to acidolytic delignification treatments of increasing severity, and the lignin sol fractions were analyzed with regard to chemical structure and molecular architecture. Treatments with 0.2 N HCL in 90% aqueous dioxane ranged between 12 hr. at room temperature and 8 hrs. at reflux. The analysis of the dissolved lignin (sol) fractions indicate significant changes in the chemical structures only with regard to aryl-alkyl ether and phenolic hydroxyl content, and with regard to molecular weights and molecular weight distributions. While alkyl-aryl ether content decreases rapidly with acidolysis treatment under reflex conditions, phenolic hydroxyl content increases conversely. Molecular weight increases as delignification procedes. As crosslink density is a function of alkyl-aryl ether content, these results suggest that the 6 7 crosslink density of the sol fraction decreases while molecular weight increases. This contradicts to the theoretical behavior for the degradation of an infinite network and suggests that lignin in wood exists as a gel (network polymer) of extremely low crosslink density or as an ungelled, branched polymer only. Delignification is therefore not controlled by degelation but rather by interaction with carbohydrates via covalent or hydrogen bonds and/or by physical entrapment in the cell wall matrix. This is in accord with earlier hypothesis on the controlling effects of pore structure by Goring et. al. and transient ether linkages by Glasser. / M.S.

A method for the preparation of polydimethylsiloxane-urea (A-B)n segmented or multiblock copolymers has been investigated. These copolymers were synthesized from 4,4¹-diphenylmethane diisocyanate (MDI) and a,ω-bis(aminopropyl)polydimethylsiloxane (PSX) of different molecular weights by solution polymerization. The conditions needed to synthesize well-defined and high molecular weight siloxane-urea copolymers in high yields were investigated. 2-ethoxyethyl ether (2-EEE) was a better reaction solvent than tetrahydrofuran (THF) because the polymerization kinetics appear to be faster and the molecular weights obtained were higher. The mechanism postulated was based on the fact that THF is a stronger base than 2-EEE and the former should complex, more tightly with the isocyanate groups present in the system, competing with the amine nucleophile and resulting in the decrease in the polymerization kinetics. Penetration studies as a function of temperature using TMA showed the copolymers were multiphase and retained their integrity up to 160-180°C, a temperature range at which softening and consequently thermoplastic flow was observed. Apparently, the urea hard segment domains act as physical or pseudo crosslinks in the rubbery phase and also clearly serve as reinforcing filler materials. Efforts to chain extend siloxane-urea copolymers with 1,6-diaminohexane (HMDA) using several different techniques in the presence of cosolvents such as DMAC or NMP, only resulted in low molecular weight products due to the premature precipitation of the polymer. A polyurethane prepolymer formation study done in either DMAC or o-butyrolactone (BLO) at about 105°C, showed BLO to be the better solvent. Side reactions involving isocyanate (-NCO) groups are less prevalent in BLO. ESCA was used to probe the surface chemical composition of polyether-urethane (Estane C-5), polydimethylsiloxane-urethane (PUS) copolymers and their blends. The topmost surface of the neat Estane is mostly covered with the polyether (PTMO) soft segments mixed with small amounts of the urethane hard segments. The surface of the neat polydimethylsiloxane-urethane (PUS) is almost an overlayer of the polydimethylsiloxane (PSX) segments. ESCA results strongly suggest the PSX layer to be at least 50Å thick. In the hlends studied, the trend towards having greater percentages of the silicon and hence siloxane on the surface starts dramatically at a level of around 1-2 wt. % of siloxane in the bulk. The location of such a transition in a particular blend system is important because it allows one to in a sense "tailor" the surface concentration of siloxane in these blends. / M.S.

The gymnastics manual for student-teachers has been prepared to give the student-teacher the opportunity to get acquainted with gymnastics skills, cognitive information, conditioning exercises, curriculum development, and audiovisual media, needed to teach gymnastics. Student-teachers' responsibilities and student-teachers' program are discussed. Information is also provided concerning basic material in the school curriculum to get started in the student-teaching experience. The gymnastics section presents detailed description of skills for female and male events, spotting techniques and common errors committed by beginners. Addresses of companies where audiovisual materials, gymnastics charts and safety information can be purchased, are provided. The Student-Teacher Gymnastics Manual is the beginning of a new wave of educational literature, seeking well prepared professionals in the school curriculum. / M.S.

M.S.

In the course of studies on degradation of dietary fiber by the human colon bacteria, a number of Bacteroides strains from the human colon have been found to degrade polygalacturonic acid and/or pectin. Four of these strains were examined for presence of polygalacturonate lyase (PGAL). The Bacteroides strains studied synthesized inducible, cell-associated PGALs when the bacteria were grown on media containing polygalacturonic acid or on peanut cell wall (a prototype dietary fiber with a uronide content of 14.0%) as the sole carbon source. No PGAL activity could be detected in cultures grown on media containing glucose or D-galacturonate. The PGALs produced by the four Bacteroides strains had properties similar to other bacterial PGALs: An alkaline pH optima (8.5), stimulation of activity by calcium ions. complete inhibition by ethylenediaminetetraacetic acid (EDTA), preference for polygalacturonic acid as a substrate over pectin, and accumulation of unsaturated products which absorb at 235 nm. The Bacteroides PGALs catalyzed partial degradation of the uronides of peanut cell wall substrate, but at a slower rate compared to their action on polygalacturonic acid substrate. / M.S.