摘要:

AbstractWe report the synthesis, characterization, thermal and dilute‐solution properties of zwitterionic copolymers of the sulfobetaine type, where the proportion of ionic groups is varied over a wide range. Two different structures are considered: poly (2‐vinyl pyridine sulfopropyl betaine) and poly (4‐vinyl pyridine sulfopropyl betaine). Synthesis is carried out to obtain random copolymers which are further characterized and their ionic content determined. At low proportions of ionic groups, the behavior is similar to that observed in ionomers, with substantial differences between the two structures, Increased interaction among the zwitterionic groups at higher charge densities is evidenced, which leads to the formation of clusters and agglomerates. An increase in the intrinsic viscosity with salt content in aqueous solutions is also observed. This behavior is analogous to that of homopolymers with 100% ionic content, but with particular features of int

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290601

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThermal, dielectric, and mechanical relaxation measurements on miscible blends of polybenzimidazole (PBI) and a polyetherimide (PEI, Ultem 1000) prepared by solution casting from dimethylacetamide (DMAc) reveal a number of structurally related features. Annealing below the glass transition temperature induces an enthalpy relaxation process typical of single‐phase glasses of nonequilibrium structure. Dielectric relaxation experiments on samples annealed at ambient conditions reveal two relaxation processes below 400°C. At lower temperatures (50–200°C), the desorption of water is observed. Above 200°C in the first run, a composition‐dependent relaxation is seen at the highest frequencies (100 kHz) while a relaxation approximately independent of composition appears in the second run. The latter corresponds to the glass transition of the PEI phase. The glass transition of PBI at this frequency is above the degradation temperature. At lower frequencies a strongly dispersive electrode polarization process masks the high‐temperature relaxations. Dynamic mechanical results show similar features with respect to phase separation; the main difference is that the tan δ curves in the first run are complicated by the desorption of resid

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290602

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractUsing nuclear magnetic resonance (NMR)T2relaxation and pulsed‐gradient spin‐echo diffusion experiments at 175.5°C, molecular motions of the sole and gel of several epoxies of the type diglycidyl ether of bisphenol‐A (DGEBA; Shell Epon 1007F and 1009F) cured with 4,4′‐diaminodiphenyl sulfone (DDS) have been studies as a function of curative content. It was found that the fraction of protons associated with the shorterT2component cannot be identified as the gel fraction until the substantial bimodal polymer polydispersity is accounted for in the spin relaxation model. The gel fraction and both relaxation rates have maxima near curing stoichiometry, and fall off more rapidly on the curative‐poor side. The diffusion spectrum of the sol fraction was consistent with a light species (Epon 828 remnants) plus a polydisperse (M̄w/M̄n≅2) heavier species, in agreement with resin and sol gel permeation chromatography (GPC) results. Numerical simulations also show that polymer polydispersity is likely to affect the interpretation ofT2relaxation found i

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290603

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractCharge transfer (CT) interactions between poly[[o‐(trimethylsilyl)phenyl]acetylene]or poly(o‐Me3SiPA) and some electron acceptors were studied by ultraviolet‐visible and infrared absorption spectroscopy and by x‐ray photoelectron spectroscopy, (XPS). The electron acceptors used included iodine, bromine,o‐chloranil,o‐bromanil, 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), and tetracyanoethylene (TCNE). Varying degrees of CT interactions were observed in all of the polymer/acceptor complexes studied. The electrical conductivities σ of the organic acceptor complexes exhibited a strong acceptor concentration dependence at low acceptor levels, with the DDQ complex exhibiting the highest σ. The extent of CT and the redistribution of charges resulting from the CT in all the complexes were revealed by XPS. The poly (o‐Me3SiPA)/I2complex film lost iodine spontaneously while more than half of the bromine in the poly (o‐Me3SiPA)/Br2complex existed as covalently bonded bromine,

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290604

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA new surface force apparatus is used for investigating the viscoelastic properties of high‐polymer solutions or polymer melts confined between two solid surfaces. We describe the experimental setup and discuss how to obtain the rheological behavior of the liquid from the transfer function given by two capacitance displacement transducers. In particular, we point out that for a distance between the surfaces enclosing a thin film below some thousands of Angströms, the elastic deformation of the solids is no longer negligible. Experiments conducted on a semidilute solution of polybutadiene show the applicability of the device for study of the dynamic properties of thin‐film poly

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290605

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractOriented polyethylene (PE) films with surfaces bounded by the (100) plane were prepared. On the film surfaces, isotactic polypropylene (iPP) was crystallized epitaxially from solution as quadrits with their sides parallel and perpendicular to the polyethylene chain axis. In thethroughwide‐angle x‐ray diffraction pattern (taken with incident x‐rays normal to the polyethylene film surface), the 111 iPP reflections was observed on the meridian (Parallel to the polyethylene chain axis). In theedgepatterns (taken with x‐rays incident on the edge of the polyethylene film), 040 and 060 reflections were observed on the equator. From the diffraction patterns, the following lattice coincidence was observed between polyethylene and isotactic polypropylene: (010)iPP//(100) PE, [101]iPP//[001]PE. The Small‐angle x‐ray scattering patterns showed that edge‐on isotactic polypropylene lamellae 9 nm thick were arranged with their long axes inclined at an angle of 40° from the polyethylene axis. Molecular chains were oriented within the lamellae normal t

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290606

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe permeability of annealed poly (l‐(trimethylsilyl)‐l‐propyne) was studied from the viewpoint of structural information obtained from x‐ray diffraction and density. The sample cast from benzene solution had low density (0.82 g/cm3) and high permeability, whereas the annealed sample had a higher density (0.88 g/cm3) and permeability lower by two orders of magnitude. The smaller‐angle x‐ray diffraction peak for each sample, which was likely to reflect the distance between intermolecular chains, increased in intensity and shifted toward higher angle, corresponding to the change of the density with annealing. The logarithmic oxygen permeability was proportional to the density, namely the free volume fraction correlated with the diffusion coefficient and controlled by annealing and swelling

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290607

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractGas permeation measurements were performed by the time‐lag method for 13 gases in poly [bis(trifluoroethoxy) phosphazene] above the mesophase transition, T (1) transition, of the crystals. Hysteresis was found in the temperature dependence of the permeability coefficients for CO2, O2, and N2in the transition region as observed by dilatometry and differential scanning calorimetry. Independently the solubility of CO2was determined gravimetrically above and below T(1). Noticeable change and hysteresis were also observed in the temperature dependence of the solubility coefficients. Diffusion of CO2in the measophase is suggested from the permeation and sorption measurements. Gas transport parameters of CO2in the mesophase are estimated, and the contributions of the mesophase and the crystalline phase to gas transport are considere

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290608

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractAn amphoteric ion‐exchange membrane was prepared by chemical grafting of acrylic acid and dimethyl amino‐2‐ethyl methacrylate on ozonized polyethylene. The effects of the variation of external pH on the physicochemical properties of this membrane were studied (exchange capacity, electrical resistance, water and electrolyte content, and membrane potential). The determination of the mean activity coefficient of the NaCl in the membrane phase using the Donnan equilibrium equation reveals that this coefficient increases with the NaCl concentration in the external solution. Fundamental electrochemical properties of the amphoteric membrane are discussed on the basis of the variation of the membrane selectivity with the external electrolyte concentrations and the pH. The properties at neutral pH are accounted for by a mutual neutralization of some acidic and basic groups in the membrane

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290609

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA novel chromatographic method is proposed to determine the polydispersity index, without reference to standards, for polymers that contain a specified number of functional groups. Refractive index and ultraviolet‐visible (or infrared) detectors are employed for detecting the weight and number fractions, respectively, of the sample eluted in size exclusion chromatography (SEC). Pyrene‐labeled polystyrenes were used to demonstrate the validity of this method. The polydispersity index,Mw/Mn, measured by the new method underestimates the true value by 3%, whereas the application of the calibration curve overestimates the polydispersity index of the same sample by 6%. An illustrative SEC model including the effect of diffusion was used to explain the production of errors in different directions by the two meth

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290610

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY