Influence of chain extension agents on the properties of polyether-based urethane elastomers at elevated temperatures

Previous work has shown that whilst the excellent physical and mechanical properties of polyurethane elastomers can be varied by changes in the molecular structure of their constituent units, these advantages are considerably diminished at elevated temperatures. The present work was carried out to investigate the effect of hard segment chemical structure on the properties of a polyether based polyurethane elastomer, particularly at elevated temperature. [Continues.

Classification of Steroid Partition Coefficients by a Pattern Recognition Technique

A pattern recognition technique, the linear learning machine method, has been used to determine structure-activity relationships for certain steroids. The steroids used in this study were classified into two categories according to their observed partition coefficient and a correlation made with certain substructural descriptors. The linear learning machine method was employed to calculate a suitable decision surface that would classify each steroid into its correct category. The resulting structure-activity relationship and the relative contributions of the various structural variables are discussed, and a comparison made with resultsobtained from a study using a different approach

Structure - Activity Relationships in the Antiinflammatory Steroids: A Pattern Recognition Approach

A pattern recognition technique has been used to determine structure-activity relationships for antiinflammatory steroids. Expe.:. rimental results using the human vasoconstrictor test of McKenzie and Stoughton and the rat granuloma cotton pellet method of Meier were correlated with the various substructural descriptors. Steroids were classified into two categories according to potency and a pattern recognition method was applied to determine their relative ranking. The resulting structure-activity relationships obtained and the relative contributions of the various structural variables for both bioassays are discussed. A synergistic effect was predicted to be in operation between certain pairs of substituents

Macromolecular structure and organization of alpha keratin

The small-angle equatorial X-ray scattering of alpha keratin (African porcupine quill) was studied using a direct type of analysis, which allows the separation of the intermicro-fibrillar interference effects from those of the intramicrofibrillar scattering without the use of prior assumptions. X-ray data were obtained from 470–21 Å; their analysis by the above method resulted in a z -axis projection of the microfibrillar electron density, which extends over a diameter of 80 Å and has a core region surrounded by a peak located at a radius of 28 Å. The macromolecular organization of the 80-Å-diameter microfibrils was found to be an arc-like layer type of aggregation and not a pseudohexagonal packing. When the specimen was subjected to silver staining the aggregation of the microfibrils did not change except for a slight contraction. The z -axis projection of the stained microfibril, however, was significantly different. The silver appears to build up slightly around the outer periphery of the microfibril, stains the peripheral region very little, deposits on the inside of the peripheral region, and outlines the core area.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37835/1/360130203_ftp.pd

Low-angle Equatorial X-ray Analysis Of Fibrous Systems With Application To The Keratins.

PhDBiophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/188496/2/7021676.pd

Direct analysis of small-angle equatorial x-ray scattering from fibrous systems. II. Methods of extracting physical parameters describing the scattering system

Small-angle equatorial x-ray scattering from fibrous systems is often complicated by the effects of morphological organization and/or heterogeneities as well as by macromolecular structure and organization influencing this same region of scattering space. In previous work it was shown that closed form mathematical expressions could be obtained for the Patterson function, without prior assumptions about the scattering system, when the intensity data were purposely truncated. In this paper the use of these expressions to extract the physical parameters describing the scattering system is demonstrated by application to a model system. The expressions are also expanded to include lattice distortions and long range coherency. A second approach is presented for cases when the coherence is small, and finally the use of higher-resolution data is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38773/1/160100512_ftp.pd