摘要:

AbstractPolymer chains are crosslinked to form a network. The chains are polydispersed, with an arbitrary distribution of weight and functionality. Crosslinks may form in three different ways: direct coupling (homopolymerization), direct coupling with propagation, and coupling through copolymerization with small monomers. Various network parameters are calculated. We give computational formulae for gel point, weight fraction soluble, weight fraction pendant, weight fraction effective, concentration of effective junctions, concentration of effective network strands, and the entanglement trapping factor. These formulae give exact values for systems that previously have only been solved using simplifying approximations. Examples show that such simplification may lead to sizable errors in the computation of network parameters.

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260101

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractCopolymers of vinylidene fluoride and trifluroethylene are presently being considered for many piezoelectric applications. In contrast to the poly(vinylidene fluoride) homopolymer, a transition from the room temperature ferroelectric phase to a paraelectric phase has been observed in these copolymers. The temperature of this transition was determined by measuring the position of the endothermic peak observed in the differential scanning calorimeter. The rate of cooling from the paraelectric to ferroelectric phase was found to affect the temperature at which the transition occurred on subsequent heating. Changing the conditions under which molten polymer initially crystallized into the paraelectric phase had an even greater effect on the resultant transition temperature. In addition to the DSC studies, wide‐angle x‐ray measurements were performed on samples subjected to different thermal treatments. No significant differences were found in the x‐ray scans of these copol

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260102

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractCompatibility or miscibility of polyethersulfones (ICI: Victrex 100P and 300P) and a tetrafunctional epoxy (Ciba‐Geigy: MY‐720), cured with an aromatic anhydride, has been studied using scanning electron microscopy, x‐ray microanalysis, and dynamic mechanical spectroscopy. Fracture toughness of epoxy and blends of an epoxy and polyethersulfones has been measured using three‐point bend tests (ASTM: E‐399–81), and the energy release rate (GIC) for the three materials has been compared as a function of test temperature. Fracture surfaces were examined by x‐ray microanalysis for detecting concentration of sulfur, present in polyethersulfones, in the matrix and precipitated phase. The influence of morphology of epoxy/polyethersulfone blends on its fracture toughness and toughening mechanism has been studied. A toughening criterio

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260103

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe crystal‐nematic phase transition of a copolyester consisting of 20 mol% poly(ethylene terephthalate) and 80 mol%p‐hydroxybenzoic acid (PHB) was characterized by depression of the crystal‐nematic transition by the addition of a liquid crystal diluent. This copolyester contains blocks of crystalline PHB. Its transition behavior was compared with thatrandom copolyester with diluent of the same composition. From the extrapolated transition temperature depression data, the heat of transition per mole ofp‐oxybenzoate was calculated as about 1.3 kcal/mol, with an entropy of about 2 cal/deg mol. This assumes that only thep‐oxybenzoate unit crystallized from the nematic state. The validity of the Flory‐Huggins model for this transition point depression was confirmed graphically by comparison with two different thermotropic‐liquid crystal polyesters. These results may represent the first reported crystal‐nematic temperatures and heats generated by the dilution method for liquid crystal copolyeste

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260104

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThis paper addresses the effect in chain liquids on thermodynamic behavior of a large charge in the strength of local interactions on mixing. We classified real systems according to the ability of the Flory equation of state (FES) theory to prodict the excess volume. The FES theory enables reliable estimates provided the mixture is nearly athermal and the pure components obey the Flory equation of state. These requirements arise from Flory's approximations for the lattice part of the configuration integral,ZL, and the cell part,ZC, respectively. We revisedZLwithout adding adjustable parameters by the quasichemical perturbation method to account for local ordering in the mixture because of a large change in the strength of binary interactions on mixing. The modification improves the predictions of the thermodynamic functions for systems where Flory'sZLis inadequate.

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260105

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

Abstract(Hydroxypropyl)cellulose (HPC) is known to form birefringent liquid‐crystalline phases at elevated polymer concentrations in either water or isobutyric acid (IBA). The HPC concentration at which the polymeric phase exhibits birefringence decreases as the IBA content in mixed H2O/IBA solvents decreases, even though the concentration ϕicfor the formation of an ordered phase of HPC in water is greater than that in IBA. Water is a spectator component and apparently does not participate in the formation of a birefringent phase when IBA is present. A birefringent phase forms once the concentration of HPC in the solution omitting the H2O equals the ϕicof binary HPC/IBA solutions for temperatures from 23 to 95°C. The strong preferential affinity of HPC for IBA is visually evident as an HPC coagulate separates from dilute solution when the solvent mixture contains as little as 5% IBA. The coagulate dissolves to give a monophasic isotropic solution as the IBA content in the solvent is increased. A heterogeneous system in which a clear supernatant fluid covers a pearly white polymeric phase forms when the solvent mixture is immiscible and the HPC content is less than 50%. At high HPC content, the classical appearance associated with concentrated HPC solutions is seen. The optical and rheological properties of the heterogeneous systems are compared with those of homogeneous solutions at several HPC concentrat

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260106

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractMeasurements of the pyroelectric response in both free and constrained conditions are presented for low‐draw ratio, high‐draw ratio and voided form I polyvinylidene fluoride sheets. The results are used together with related data for the piezoelectric response and for the thermal expansion behavior to estimate the primary and secondary components of the total macroscopic pyroelectricity. For the high‐draw ratio and voided sheets the primary response was approximately 90% of the total pyroelectricity compared with 40% for the low‐draw ratio nonvoided sheet. It is proposed that the role of reversible temperature‐dependent crystallinity is more pronounced in the high‐draw samples. Previous NMR studies provide support for this

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260107

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe mechanical anisotropy of oriented PVDF sheet is examined using a variety of experimental techniques. The mechanical behavior is similar to that observed previously for low‐density polyethylene and nylon and consistent with a parallel lamellar crystalline structure. Thes31compliance is reduced in magnitude by drawing to higher draw ratio, but the reduction in the piezoelectric coefficientd31is less marked, suggesting that the piezoelectric response cannot be related solely to dimensional changes under stress. Drawing to high draw ratio increases thes33compliance, and this is further increased by introducing voids. The correspondingd33piezoelectric coefficient is not changed significantly by drawing to high draw ratio, or by the introduction of voids, again indicating that the piezoelectric behavior relates to factors other than dimensional change

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260108

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractDilation of polysulfone (PSUL) and crystalline poly(ethylene terephthalate) (PET) films accompanying sorption of carbon dioxide is measured by a cathetometer under high pressure up to 50 atm over the temperature range of 35–65°C. Sorptive dilation isotherms of PSUL are concave and convex to the pressure and concentration axes, respectively, and both isotherms exhibit hysteresis. Each dilation isotherm plotted versus pressure and concentration for the CO2‐PET system shows an inflection point, i.e., a glass transition point, at which the isotherm changes from a nonlinear curve to a straight line. Dilation isotherms of PET below the glass transition point are similar to those of the CO2‐PSUL system, whereas the isotherms above the glass transition point are linear and exhibit no hysteresis. Partial molar volumes of CO2in these polymers are determined from data of sorptive dilation. On the basis of the extended dual‐mode sorption model and the current data, primitive equations for gas‐sorptive dilation of glassy polymers ar

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260109

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe flow behavior and the effect of the spinning conditions on the fiber properties and structure of poly(ethylene terephthalate) modified with 60 mol%p‐hydroxybenzoic acid (PET/60PHB) were investigated. PET and its copolyesters with 28 and 80 mol% PHB were used as control samples. The melt of PET/60PHB at temperatures above 265°C exhibited extremely low viscosity and low flow activation energy. High birefringence, indicating the presence of a mesophase, was observed between 265 and 300°C on a hot‐stage polarizing light microscope. The maximum tensile strength and initial modulus, 438 MPa and 37 GPa, respectively, were obtained at 275°C for a 0.69 IV polymer. The fiber strength and modulus were significantly lowered when extrusion was conducted at temperatures below 265°C. The fiber properties could also be improved when a high extrusion rate and/or a high draw down ratio was used. Scanning electron microscopy revealed that the fibers spun at temperatures above 265°C had a well‐developed, highly oriented fibrillar structure. The fibers spun at lower temperatures, however, were poorly oriented and nonfibrillar in character. The high orientation and superior mechanical performance achieved at high temperatures were attributed to the presence of the nematic mesophase in the po

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260110

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY