摘要:

Kevlar 29 is an aromatic polyamide fiber spun from the polymer poly(p-phenylene terephthalamide). It has a paracrystalline structure with a lattice distortion parameter g = 5.9% and an a* constant = 0.51. The equatorial x-ray “crystallinity” is 68%; the microparacrystal (mPC) sizes areD002= 50 nm,D110= 4.4 nm, andD200= 3.6 nm. The mPCs are well oriented; the orientation parameter <sin2ψ200> = 0.047. The small-angle x-ray diffraction pattern indicated that the fiber has nc chain folding. It has high tenacity (2.81 GNm−2), close to the tenacity of steel; high Young's modulus (63.9 GNm−2); small breaking strain (3.8%); and a very high melting point (600°C). Wide- and small-angle x-ray diffraction techniques, differential scanning calorimetry (DSC), and an Amsler tensile tester have been used to characterize the fiber and to assess the effect of annealing on its morphology and mechanical properties.

ISSN:0022-2348    

DOI:10.1080/00222348408219461

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Dielectric studies on the side-chain dispersion of poly(γ-butyl glutamate)/poly(γ-benzyl glutamate) blend and copoly (γ-butyl glutamate—γ-benzyl glutamate) were performed to determine the degree of interhelix and/or intrahelix compatibility. The dielectric side-chain dispersion of the polypeptide blend demonstrated a double peak ascribed to the nearly pure components, poly(γ-butyl glutamate) and poly (γ-benzyl glutamate), indicative of the interhelix incompatibility of the butyl and benzyl groups. The results indicate nearly complete phase segregation of the two components. On the other hand, the side-chain dispersion of copoly (γ-butyl glutamate—γ-benzyl glutamate) showed a single peak in the region between those of the two homopolypeptides. The butyl and benzyl groups of this copolyglutamate were apparently compatible along the α helix axis direction, confirming the randomness of the copolymerization.

ISSN:0022-2348    

DOI:10.1080/00222348408219462

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The dielectric properties of poly (α-dimethyl β-propiolactone), also called polypivalolactone (PPL), have been investigated over a frequency range of 0.01 to 100 kHz and from 230 to 490 K. A limited number of dynamic mechanical measurements were also performed using a Rheovibron viscoelastometer and a torsion pendulum apparatus. Two relaxation regions, called β and γ in order of decreasing temperatures, were observed at about 410 K and 275 K. The γ relaxation process is associated with the crystalline phase of the polymer, and the β relaxation is attributed to its glass transition temperature. The analysis of the dielectric data leads to the conclusion that, despite the high degree of crystallinity of PPL, the frequency-temperature superposition principle is applicable to its γ relaxation peak, in agreement with earlier stress relaxation measurements. However, it could not be applied to its β relaxation peak except at low temperatures and high frequencies.

ISSN:0022-2348    

DOI:10.1080/00222348408219463

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Block and random copolymers of butadiene and styrene as well as polybutadiene and polystyrene homopolymers have been investigated with respect to their monolayer properties and photooxidation behavior. Whereas polystyrene and block copolymers of styrene and butadiene form stable monolayers, polybutadienes and random copolymers do not interact with the aqueous subphase. The monolayer properties of block copolymers with different styrene content indicate that polybutadiene also contributes to the surface pressure. Photo-oxidation of random and block copolymers of styrene and butadiene leads to a significant enhancement in surface pressure of the monolayers due to the generation of groups which can effectively interact with the aqueous surface. FTIR spectral studies show the formation of carbonyl, hydroxyl, and hydroperoxyl groups in the polymers on photooxidation. A comparison of the pressure-area isotherms of random and block copolymers oxidized in solution indicates that there is an energy transfer from butadiene to styrene units in the case of random copolymers, resulting in a protective effect of butadiene units from oxidation. In addition, in the monolayers of oxidized block copolymers, a phase transition occurs which is attributed to the extrusion of polystyrene blocks from the monolayer. The surface pressure-area isotherms and the rates of photooxidation are strongly dependent on the microstructure of polybutadiene as well as on whether oxidation is performed in solution or at the oxygen-water interface.

ISSN:0022-2348    

DOI:10.1080/00222348408219464

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor