摘要:

Complexation behavior of deoxycholic acid was studied for poly(oxy-ethylene), poly(propylene oxide), poly(tetrahydrofuran), and several poly(oxyethylene) derivatives with various chain lengths. The complexes were obtained for poly(oxyethylene) with an average molecular weight greater than 200 (average degree of polymerizationn= 4). In spite of very short ethylene oxide chains, poly(oxyethylene) monostearate and poly(oxyethylene) mono-p-nonylphenyl ether withn= 2 formed the complexes. The unit cells of all complexes corresponded to the orthorhombic crystal which is most commonly observed for the complexes with low molecular weight compounds. Dimensionain the complexes of poly(propylene oxide) and poly(oxyethylene) mono-p-nonylphenyl ether withn= 2 and 5 was larger than those in other complexes, whilebandcdid not differ much. Most of the complexes exhibited an increase in the melting points with increasing length of the polymer chains, while the melting points of poly(oxyethylene) monostearate complexes decreased withnand those of poly(oxyethylene) mono-p-nonylphenyl ether showed a minimum betweenn= 5 andn= 10.

ISSN:0022-2348    

DOI:10.1080/00222349408248075

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Dynamic mechnical properties of unfilled and glass fiber filled liquid crystal polyester (LCP) have been investigated in the temperature range from -100° to 250°C. Two transitions, atTgandTβ, were observed with decreasing temperature, whereTgis the glass transition of the samples; however, the origin ofTβis unknown. Both LCP and LCP composites exhibit strong dynamic mechanical anisotropy with respect to the molding flow direction. As the glass fiber content increases, the reinforcing effect is improved due to the increase in the effective storage modulus, while the modulus anisotropy is reduced.

ISSN:0022-2348    

DOI:10.1080/00222349408248076

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The method of Debye-Hückel is extended so as to be applicable for the purposes of evaluating the electrostatic field caused by charged groups, dipoles, and multipoles, in globular molecules. Charged groups and dipoles may be situated arbitrarily in the protein molecule. The problem is solved using the spherical coordinate system. General expressions for the potential are given. In the case of a protein molecule having a strong dipole moment, the general problem is approximately solved presuming that the potential is caused by an effective dipole moment. The numerical simulation of electrostatic interaction between two molecules with strong dipoles is provided.

ISSN:0022-2348    

DOI:10.1080/00222349408248077

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Isothermal and nonisothermal crystallization kinetics of different poly(aryl ether ketones) (PAEK) were investigated by means of differential scanning calorimetry (DSC). For comparison, a poly(phenylene sulfide) was also included. Systematic relationships between the chemical structure of these materials and their crystallization behavior could be derived. The equilibrium melting temperatures of the different PAEKs were estimated using the extrapolation scheme given by Hoffman and Weeks. Due to the higher flexibility with increasing ether/ketone ratio, the glass transition, crystallization, and melting temperatures decreased, and the melt crystallization was accelerated. The cold crystallization, however, was retarded with more flexible chains relative to that with stiffer chains due to the increased order of stiffer molecules in the quenched amorphous state, which results in a higher nucleation density. Independent of the chemical structure, Avrami exponents of 2.0 ≤n≤ 2.8 were found for cold- and melt-crystallized samples. This can be explained by either two-dimensional or three-dimensional diffusion-controlled crystal growth, depending on the amount of thermal or athermal nucleation, respectively. The ranking of the crystallization rates for both cold and melt crystallization could be estimated using simple nonisothermal routine methods based on the temperatures of glass transition, crystallization, and melting.

ISSN:0022-2348    

DOI:10.1080/00222349408248078

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Polyimides are one of the important heat-resistant polymers. A large number of wholly aromatic and aromatic/aliphatic polyimides have been developed since this class of polymer was first reported in the 1960s. These polyimides are in general either not processable or processable with great difficulty. In most cases, solutions of the corresponding polyamic acid (PAA) in polar solvents are used for processing.

ISSN:0022-2348    

DOI:10.1080/00222349408248079

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0022-2348    

DOI:10.1080/00222349408248080

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Analyzed in this paper are the deformation relationships between temperature; stress, strain; and stress rate in polyethylene terephthalate (PET) near the glass transition temperature. The uniaxial stress rate of inelastic deformation was found to be proportional to the square of the effective stress. A physical model of two simultaneous rate-activated processes with a general activation energy barrier is utilized. We call this “second-order kinetics.” Experimental data obtained by measuring load rate versus load point displacement were analyzed to describe stress relaxation of thin uniaxial strips. The activation enthalpy and activation volume show that the rate-controlling process is second-order.

ISSN:0022-2348    

DOI:10.1080/00222349408248081

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The fast structure development process in the early stage of crystallization in commercial polyethylene terephthalate (PET) fibers during carefully controlled postspinning annealing treatments has been followed. In addition to conventional structure characterization techniques, transmission electron microscopy (TEM) has been employed to probe the sequence of structural events. In the earliest stage of structural development, direct observation showed an embryonic microfibrillar structure, the microfibril diameter being ca. 5 nm. Upon modest heat treatment, the microfibrils become axially punctuated with crystallites. As further crystallization occurs, the crystallites become more perfect and lateral alignment of crystallites takes place, particularly in extensively crystallized materials, that is, higher temperature and/or longer time of heat treatment. The lateral alignment results finally in a lamellar microstructure.

ISSN:0022-2348    

DOI:10.1080/00222349408248082

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor