摘要:

AbstractInternal friction (IF) was measured for two polymer liquid crystal (PLC) esters, PET/xPHB, where PET is poly(ethylene terephthalate), PHB is p‐hydroxybenzoic acid, with the mole fractions x of the PHB in the copolymers 0.5 and 0.6. Pure PET was also studied for comparison. The internal friction parameter Q−1and the square of the output vibration frequency ƒ2were determined as a function of temperature between −150°C and +400°C for a fixed input frequency. Values of the latter were varied between 0.5 and 30 Hz; all spectra were recorded under vacuum of 0.10 Torr. The IF results are virtually independent of the substrate used, namely silica glass or platinum. Multiple transitions found in each sample agree fairly well with those determined by other methods, including thermally stimulated depolarization. In contrast to other dynamic mechanical methods, a single internal friction vs. temperature run can be used to locate transitions in solid as well as in mel

ISSN:0032-3888    

DOI:10.1002/pen.760331002

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractDevelopment of crystallinity in NEW‐TPI semicrystalline polyimide has been studied using differential scanning calorimetry (DSC), wide (WAXS), and small angle X‐ray scattering (SAXS). Crystallinity of the fully imidized powder, pellet, or film processed NEW‐TPI can occur from the melt, and depends upon the holding temperature of the melt. Repetitive exposure to elevated temperatures supresses the development of crystallinity from the melt state. In amorphous pellets and film, crystallinity can also develop by cold crystallization from the rubbery amorphous state. SAXS results show that during cold crystallization, NEW‐TPI develops a periodic structure consistent with formation of alternating crystalamorphous stacks, but with crystals only a few molecular repeat units thick. Kinetics of nonisothermal crystallization were studied as a function of heating rate and could be described using the Ozawa analysis. Non‐isothermal crystallization proceeds at a slower rate in NEW‐TPI than in other high temperature thermoplastics such as PEEK, and with a much narrower processing window. The maximum degree of crystallinity that could develop during heating was 0.34, which occurred at a rate of 5°C/min. Similar degrees of crystallinity could be introduced by heating amorphous NEW‐TPI film in N‐m

ISSN:0032-3888    

DOI:10.1002/pen.760331003

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe phase separation behavior of unsaturated polyester (UPE)‐polyurethane (PU) interpenetrating polymer networks (IPNs) was investigated by light scattering measurements during simultaneous polymerization. The scattered light intensity change with time showed the formation of the dispersed domains, and the average domain correlation length could be calculated from the angle of maximum scattering intensify. It was noted that the dominant phase separation process was spinodal decomposition due to fast reaction. The morphology observed by the transmission electron micrographs for various process conditions showed similar results as obtained from the light scattering experimen

ISSN:0032-3888    

DOI:10.1002/pen.760331004

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractAcrylonitrile‐acrylic elastomer‐styrene terpolymer (AAS resin) was developed to improve weatherability of acrylonitrile‐butadiene‐styrene terpolymer (ABS resin). To compare thermal stability of both resins, test parts of AAS and ABS resins were injection molded at various temperatures and the Izod impact value of the resulting moldings was measured. A study was then made to find the relationship between this value and deterioration of the resins. AAS resin was molded at temperatures from 180°C to 280°C. The impact value of the resulting moldings was almost constant for temperatures up to 260°C, with the first major decrease occurring at 280°C. In contrast, the impact value of conventional ABS resin moldings constantly decreased as the molding temperature was elevated. To explain this phenomenon in both resins, two types of test program steps were undertaken: (1) The cause of the change in characteristics of the AAS resin was determined by obtaining its stress‐strain curve in a high‐speed flexural strength test; measuring its infrared absorption spectrum; and determining its flow properties with a constant‐pressure extrusion type rheometer; (2) the distribution of elastomer in the resin was observed with an electron microscope. It was found that the decrease of impact values of both resins at high temperatures is caused by deterionration of the elastomer. Also, it was found that the different relationships between the impact value and molding temperatures for AAS and ABS resins are due to the difference between the rates of thermal degradation of the acrylic elastomer and bu

ISSN:0032-3888    

DOI:10.1002/pen.760331005

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe glass transition temperatures in bismaleimide‐based resins were investigated using different stoichiometric ratios of 1, 1′‐(methylenedi‐4, 1‐phenylene)bismaleimide (BMI) and 4, 4′‐methylenedianiline (MDA). The resin cure involves a low temperature primary amine addition to the maleimide double bonds and a high temperature homopolymerization of the maleimide double bonds. The network topology and the glass transition temperature changes with resin composition and curing conditions were determined using differential scanning calorimetry (DSC). An empirical model was used to relate the glass transition temperature to the extents of the amine addition and the homopolymerization reactions in 1:1 and 2:1 BMI:MDA resins. The changes in thermal properties with resin post‐cure wer

ISSN:0032-3888    

DOI:10.1002/pen.760331006

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe13C spin‐lattice relaxation times,T1s, of both stereoregular poly(methyl methacrylates) (PMMA) and homologous series of n‐alkyl acetate solvents in solution have been measured at 40°C. It was observed that the motion of polar side‐chains was highly affected by the degree of interaction with solvent molecules. The stronger polymer‐solvent interactions in predominantly syndiotactic PMMA solutions than in isotactic PMMA solutions were shown from theT1values for the carbonyl, methoxy, and quaternary carbons in polymer segments and also from the carbonylT1s of solvent molecules. By relating the solvent dependences of theT1data in syndiotactic polymer solutions to that of the known dissolution rate data of atactic PMMA, it was found that the solvent dependences of theT1values of those carbon groups in which the polymer‐solvent interaction is not significant, e.g., methylene and α‐methyl carbon groups, were consistent with the solvent dependence of the dissolution rate of polymer. This result suggested that the dissolution of polymer is mainly governed not by the sorption process related to the polymer‐solvent interaction but by the transport process related to the local motions of polymer segments and so

ISSN:0032-3888    

DOI:10.1002/pen.760331007

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA polyarylate Unitika U‐Polymer 100 (PAR) was melt blended with a thermotropic liquid crystalline polymer (LCP) Vectra A950, and the processingmorphology‐properties relations were investigated. Inclusion of LCP slightly reducedTgof PAR. The PAR/LCP blend with the LCP content higher than 50 wt% exhibited a noticeable yield stress, particularly in the vicinity of crystal‐to‐nematic transition temperature (Tcn). LCP lowered the blend viscosity aboveTcnand seemed to play a role as processing aid. The tensile strength of the blends was increased with increasing spin draw ratio and level of LCP, and the spinning temperature influenced tensile strength. The relaxation behavior under dynamic shear and resultant blend morphology based on WAXD and SEM analyses are discussed

ISSN:0032-3888    

DOI:10.1002/pen.760331008

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractDynamic mechanical properties, tensile properties, and scanning electron microscopy of blends of poly(methyl methacrylate) and polycarbonate were investigated after phase separation above their cloud point temperature by annealing in a hot press. The dynamic mechanical properties show that phase separation proceeds more distinctly for the blends annealed at higher temperature and for longer time. The scanning electron micrographs show that the morphology of phase separated blends varies with the conditions of heat treatment. The tensile properties of phase separated blends deteriorate on account of the coarsening of the brittle dispersed phase over the optimum size and the occurrence of voiding during the heat treatment.

ISSN:0032-3888    

DOI:10.1002/pen.760331009

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThin plasma polymerized films of tetramethyl germanium are deposited at various substrate temperatures. The influence of substrate temperature on the deposition rate, composition, structure, and electrical properties of the films is discussed. With an increase in the substrate temperature from 25°C to 150°C under similar plasma deposition conditions, the conductivity of the film increased by four orders of magnitude. Films of plasma polymerized tetramethyl germanium deposited at 150°C show typical semiconducting behavior (increasing conductivity with increasing temperature) and have a sheet conductivity of 1.0 × 10−6S cm−1at 25°C. There is a direct correlation between the conductivity and the composition of the films, i.e., the higher the conductivity the higher the ratio of germanium to carbon at the surface. At deposition temperatures of 25 and 75°C the germanium to carbon ratio was essentially the same, but at a deposition temperature of 150°C, this ratio was considera

ISSN:0032-3888    

DOI:10.1002/pen.760331010

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760331001

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY