摘要:

AbstractPhysical aging of a thermoset system based on bisphenol‐A epoxy (DERTrademark of The Dow Chemical Company.383) and tetrabromobisphenol‐A cured with sulfanilamide and diaminodiphenylsulfone was studied as a function of cure history. Changes in the dynamic mechanical spectra for the thermoset system were correlated to changes in relative toughness associated with physical aging as determined by plane‐strain biaxial tension‐compression yield measurements. It was found that master curves, generated by using tan δ data obtained in the β relaxation temperature regime, are well related to the corresponding changes in mechanical properties and, hence, have predictive value. Relative toughness decreases and compressive yield increases with decreasing tan 5 because of decreased molecular segmental mobility. The relative extent of physical aging for the as‐cast thermosets was shown to be linearly related to th

ISSN:0032-3888    

DOI:10.1002/pen.760280102

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractStrain‐induced crystallization of poly(ether ether ketone) (PEEK) was studied by the use of a parallel plate rheometer. The experimental variables included preheating time, crystallization temperature, and shear rate. The crystallization kinetics were characterized by means of an induction time defined as the time elapsed from the start of shearing to the onset of crystallization. The experimental results showed that the induction time for strain‐induced crystallization of PEEK was significantly shorter than that for crystallization under quiescent condition, and that strain‐induced crystallization was much less temperature dependent than quiescent crystallization. The activation energy for strain‐induced crystallization was found to be 0.035kcal/mole, which was considerably smaller than the reported activation energy for quiescent crystallization. Photomicrographs of the sheared specimens indicated that PEEK crystallites orient along the flow di

ISSN:0032-3888    

DOI:10.1002/pen.760280103

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe kinetics of crystallization during anioiiic polymerization of ϵ‐caprolactam was studied by the adiabatic temperature rise method, A new kinetic model for the non‐isothermal crystallization was derived and the possibility of its application was Investigated. By evaluating the parameters in the model for the given adiabatic system, the crystallization behavior during the; polymerization process was analyzed. The experimental and calculated temperature rise showed a very good agreement, which indicated that the model equation was appropriate to describe the non‐isothermal reaction‐induced crystallization kinetics in this study. The melting temperature of the reaction mixture increased steadily due to the change of the crystal structure with conversion. The equilibrium crystallinity was higher when the crystallization started in the presence of unreacted monomer than when the crystallization occurred after polymerization was completed. At lower conversion, the reaction mixture was less viscous, a condition that made transport to the liquid‐crystal interlace easier, and thus the activation energy for transport decreased. On the other hand, the increasing mobility resulted in difficulty in forming stable nuclei arid the free energy of nucleation

ISSN:0032-3888    

DOI:10.1002/pen.760280104

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractAn altered free‐volume state (AFVS) model was developed for the zero‐shear viscosity of homogeneous polymer blends. The model involves a single adjustable parameter and is capable of predicting several complex features of the blend viscosity‐composition behavior. These include negative and positive deviations from additivity, maxima, minima, and sigma‐shaped curves. The validity of the model was tested by comparison of the model predictions with experimental data for several homogeneous blend systems. It is shown that the model is valid within a broad molecular weight range and is more accurate than some of the currently accepted models such as the kinetic network model. Besides, it appears that the AFVS model also may be applicable to blends of incompatible polymers under certain con

ISSN:0032-3888    

DOI:10.1002/pen.760280105

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractPolyamidethioethers were synthesized and evaluated as positive electron beam (EB) resists, The polyamidethioethers decomposed easily with EB exposure. At high doses (indicating low sensitivity), crosslinking reactions occurred for polyamidethioethers having C‐S bonds produced by Michael addition, but the other polyamidethioethers did not crosslink. The C‐S bonds produced by Michael addition may influence crosslinking rather than decomposition. The sensitivity of oxidized polyamidethioether was higher than that of the nonoxidized polymer with no change in resolution. The oxidized polyamidethioether had a high sensitivity and a high resolution, and is adaptable as a positive EB res

ISSN:0032-3888    

DOI:10.1002/pen.760280106

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe amount of diethylene glycol (DEG) formed as a result of the dehydration reaction of ethylene glycol (EG) in the presence of terephthalic acid (TPA) was measured. It became clear that the amount of DEG formed at the boiling point of EG can be expressed by a regression equation. It was confirmed that by this equation, the amount of DEG formed under the carboxylic end group concentration of 0.0 to 0.6 Eq/kg and the reaction time of 0 to 20 h can be estimated with high accuracy.

ISSN:0032-3888    

DOI:10.1002/pen.760280107

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractIntramolecular reactions in the step‐growth polymerization of multifunctional monomer,RAf, were modeled. The rate constant for this step was taken from the Monte Carlo studies of Plate and Noah. Species Pvn, withvIntramolecular bonds and chain lengthn, was defined, and differential equations governing their molecular weight distribution (MWD) in hatch reactors were written. An algorithm of computation valid up to the gel point was developed, and the process of gelation was studied under the variation of the rate constant parameters of the intramolecular reaction step. It was found that the larger the molecule, the greater is its tendency to form intramolecular bonds. We devised a mathematical method to find the conversion ofAgroups onPonspecies. Whenever this reaches a critical value {= l/(f−1)}, conditions for gelation are generated and molecules of infinite structure begin to form. In the presence of intramolecular reactions, the tendency to form a network is reduced because larger molecules undergo cyclization and there is consequently a shift in the gel point, which has been computed in this w

ISSN:0032-3888    

DOI:10.1002/pen.760280108

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA lap shear joint method was used to study strength development during welding of polystyrene surfaces‐ The surfaces previously had not been in contact and care was taken to insure rapid wetting of the interface. The shear stress at failure, τfwas measured at room temperature as a function of contact time,t, at constant welding temperatures up no 20°C above the glass transition temperature,Tg. The time dependence of welding could be well described by τfαt1/4. This result is in agreement with predictions of the reptation molecular dynamics model applied to inter‐diffusion at a symmetric amorphous polymer‐polymer interface. The activation energy for the thermally activated increase in strength development was determined asE= 96 kcal/mol atT= 113.5°C, which compares withE= 93,2 kcal/mole as predicted by the W‐L‐F theory using C1= 13.7, C2= 50 andTg= 100°C. The polystyrene samples had molecular weights,Mn= 143,000 andMw= 262.000. The time to achieve complete healing,t∞≈︁ 256 min at 118°C, was found to be of the same order of magnitude as the viscoelastic relaxation time and also with the time required for a polymer chain to diffuse a distance equal to its root mean sq

ISSN:0032-3888    

DOI:10.1002/pen.760280109

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractChanges in volume resistivity with temperature of carbon‐black‐filled polymers and a random copolymer of styrene and butyl methacrylate were measured. For polystyrene containing 20 wt % carbon black, of surface area 24 m2/g, the resistivity changes abruptly from 1013to 106ohm‐cm above 150°C. Poly(butyl methacrylate) did not show well‐defined changes in resistivity on heating. The random copolymer containing 16.7 or 28.6 wt % carbon black, of surface area 24 m2/g, showed a resistivity exceeding 1013ohm‐cm, that decreased to about 107ohm‐cm on heating above 120°C. This Copolymer containing 16.7 wt % carbon black, of surface area 625 m2/g, shows a resistivity of about 108 ohm‐cm that decreases sharply to 103ohm‐cm by 150°C. Decreases in resistivity on increasing the temperature in the quiescent state are correlated with the observation of a yield stress at low shear rates in rheological studies. It is suggested that carbon black agglomerates at elevated temperature and forms an independent conductive network

ISSN:0032-3888    

DOI:10.1002/pen.760280110

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760280101

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY