R. G. Bass

Strain effects on thermal transitions and mechanical properties of thermoplastic polyurethane elastomers

Abstract An investigation on the effect of strain on the domain structure of thermoplastic polyurethane elastomers (TPEs) is reported. Thermal characterization utilizing differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) is presented along with mechanical properties of model TPEs before, and after, varying degrees of strain aging. Model TPEs were subjected to tensile strains between 100 and 400% elongation and aged for varying lengths of time at ambient and elevated temperatures. DSC and DMA were utilized to investigate the changes in morphology that occurred as a result of strain elongation. The effect of strain aging on the TPEs mechanical properties such as abrasion resistance is also discussed. DSC results indicated that the polymer undergoes morphology changes due to strain, resulting in some degree of phase mixing. DMA data indicated that polyester TPEs and polyether TPEs respond differently to induced strain, suggesting that domain re-ordering in these materials may occur by different mechanisms.

Imide/Arylene Ether Copolymers-Part I

Two series of imide/arylene ether block copolymers were prepared using an arylene ether block and either an amorphous or semi-crystalline imide block. The resulting copolymers were characterized, and selected physical and mechanical properties were determined. These resuls, as well as comparisons with the homopolymer properties, are discussed.

Synthesis of Mesoionic Xanthine Nucleosides

Abstract The preparation of (anhydro-8-D-ribofuranosyl)-, (anhydro-8-D-glucopyranosyl)-, and (anhydro-8-α-D-2-deoxyribofuranosyl)-5-hydroxy-7-oxothiazolo[3,2-a]pyrimidinium hydroxide is described. These nucleoside analogs are the first examples of Class II mesoionic nucleosides.

Polymer Synthesis via a Diels–Alder Reaction between Bis(Isobenzofuran)s and Bis(Phenylacetylene)s Containing Preformed Phthalimide Rings

Polymers have been prepared by the Diels–Alder reaction between novel bis(isobenzofuran)s and bis(phenylacetylene)s containing preformed phthalimide rings. The initial polymer undergoes a thermal rearrangement without volatile evolution that effectively prevents a retro Diels–Alder reaction from occurring. The polymers were soluble in common organic solvents such as chloroform, N-methyl-2-pyrrolidinone, N, N-dimethylacetamide and chlorinated aromatic solvents. The polymers exhibited glass transitions ranging from 251 to 359 °C and a 10%weightloss ranging from 451 to 486 °C in air and 482 to520 °C in helium as determined by thermogravimetric analysis. Thissynthetic approach offers advantages over other Diels–Alder polymerizations since no volatile by-products are generated and a thermal rearrangement eliminates a retro Diels–Alder reaction.

Preparation and characterization of poly (arylene ether isoxazole)s by fluoride ion-mediated aromatic nucleophilic displacement reactions

As part of a continuing effort to prepare novel thermally stable high-performance polymers, poly(arylene ether isoxazole)s have been prepared by fluoride ion-catalysed aromatic nucleophilic substitution reactions with bis(trimethylsiloxyphenyl) isoxazoles and activated bisarylhalides in diphenyl sulphone. Initial investigations involving the preparation of these materials with isoxazole bisphenols and activated bisarylhalides in the presence of potassium carbonate indicated that, under reaction conditions necessary to prepare high-molecular-weight materials, the isoxazole monomer was converted to an enamino ketone. This side reaction was avoided by using fluoride as a base. However, trimethylsilyt ether derivatives of the isoxazole bisphenols were required in these polymerizations for the preparation of high-molecular-weight materials. Moderate to high inherent viscosity (htAh: 0.43-0.87 dl g -) materials with good thermal stability (air: 409-477C, helium: 435-512C) can be prepared by the silyl ether method. Glass transition temperatures ranged from 182 to 225 C for polymers with phenyl pendants and from 170 to 214 C for those without. Molecular weight control by 2% endcapping and the incorporation of a phenyl pendant at the 4 position of the isoxazole is necessary to yield polymers soluble in polar aprotic solvents at room temperature. There is evidence, however, indicating the existence of crosslinks between the polymer chains when the silyl ether approach is utilized.

Synthesis and Properties of Poly(Arylene Ether Pyrazole)S

Poly(arylene ether pyrazole)s containing N–H and N-phenyl groups have been prepared by the aromatic nucleophilic displacement reaction of two new bisphenols containing a pyrazole ring with activated aromatic dihalides in N,N-dimethylacetamide at 155 °C in the presence of anhydrous potassium carbonate. The polymers exhibited glass transition temperatures (Tg ) ranging from 190–296 °C and inherent viscosities from 0.44–1.96 dl g−1. Poly(arylene ether-pyrazole)s containing N–H groups exhibited higher T g and mechanical properties than the corresponding N-phenyl-containing poly(arylene ether pyrazole)s. The chemistry, physical and mechanical properties of these polymers are discussed.

Imide/Arylene Ether Copolymers-Part II:

A series of novel imide/arylene ether copolymers were prepared from the reaction of an amorphous arylene ether oligomer and a semi-crystalline imide oligomer. These copolymers were thermally characterized and mechanical properties were measured. One block copolymer was end-capped and the molecular weight was controlled to provide a material that displayed good compression moldability and attractive adhesive and composite properties.