摘要:

AbstractThe behavior of the monomers: styrene (St) and acrylic acid (AA) during the process of thermally initiated bulk copolymerization realized in a continuous stirred tank reactor (CSTR) is discussed in this work, on the basis of results obtained from experimental work carried out by the authors and data available from literature. GPC, GC, IR, and NMR techniques were used to examine the volatile oligomers released from the raw St–AA polymers. The mechanism of the thermal initiation of polymerization in the system under investigation is also discussed. Polymer degradation reactions in the vicinity of the ceiling temperatureTc, chain transfer reactions, and secondary reactions of carboxylic groups in high temperatures have also been considered. The behavior of the St–AA polymers during derivatographic tests in the temperature range: ambient−400°C, conducted in atmospheric air, was also evaluated. Experimental conditions, in which deep destruction of the product during the copolymerization process could be avoided, were established.Knowledge of these conditions is important from a practical point o

ISSN:0021-8995    

DOI:10.1002/app.1991.070420801

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe IR and UV spectra of poly(methyl methacrylate) (PMMA) doped with metal dithizonate were investigated. Films of the doped samples were heated in air at various temperatures from 25 to 140°C for 2 h. Other films were also exposed to UV irradiation. The doped samples were treated with iodine. The experimental results provided strong evidence that certain weak reaction occurs between the dopants and the polymer, and the rate of reaction depends on the concentration of the dopant and the nature of the metal ions. It was found that heat treatment of the doped films induces considerable changes in the intensities of their IR bands. The magnitude of these changes depends also on the concentration and the nature of the metal ion. Moreover, the results proved that exposure of the doped films to UV irradiation has no effect on their absorption spectra. Furthermore, the treatment of the doped samples with iodine causes considerable changes in their UV absorption spectra

ISSN:0021-8995    

DOI:10.1002/app.1991.070420802

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractPolyaniline perchlorate (PAP) was synthesized by electrochemical oxidation from 0.2Maniline in acetonitrile solution containing 0.1Mtetraethylammonium perchlorate as supporting electrolyte. From polarographic and cyclic voltammetry results, the values of the half‐wave potential (E1/2), transfer coefficient (α), and number of electrons related to the electrode reaction (n) were calculated to be 825 mV, 0.894, and 1, respectively. The morphology of the PAP film was observed by using an SEM analyzer. From thermal analysis of the PAP sample, the reaction rate (R) for its thermal decomposition was obtained from the TGA result and a exothermic peak at 330°C was also observed in the DSC curve. The electrical conductivity of the PAP pellet was measured at temperatures from −170 to 25°C. From a plot of conductivity vs. 1/T, the activation energy (Ea) was obtained to be 0.14 eV. The conduction mechanism in a pressed pellet of PAP is suggested to be electronic hopping conduction. The values of the ESR parameters were calculated from an ESR curve for PAP at room tempe

ISSN:0021-8995    

DOI:10.1002/app.1991.070420803

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractFluroinated epoxy resin adhesives containing diglycidylether of bisphenol AF (DGEBAF) with a fluorine content of 25.7 wt % are developed for fabrication of optical communications devices. These adhesives, formulated with a diluent of butanediol diglycidylether (BDDG) and a curing agent of polyether polyamine (Q694), can be cured at a curing temperature as low as 65°C and exhibit high transparency of more than 80% in the wavelength range of 0.5–1.3 μm. Moreover, they significantly reduce return loss at optical‐glass/adhesive interfaces because of the low refractive indices of ca. 1.52 and also improve heat durability of optical devices. They are successfully applied to submarine optical fiber transmission s

ISSN:0021-8995    

DOI:10.1002/app.1991.070420804

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe fine structure and physical properties of bright and semidull poly(ethylene terephthalate) (PET) fibers were investigated as successive layers of the polymer were removed by hydrolysis using aqueous solutions of sodium hydroxide up to weight losses of 90 and 68%, respectively. For both types large changes in molecular weight distribution did not occur, although as weight loss increased, the density of the remaining fiber increased. Alterations in fine structure with weight loss were also observed by thermal analysis. Greater strength loss with decreasing weight occurred for the semidull fiber than for the bright sample. Larger pits formed on the surface of the hydrolyzed semidull fibers than on the surface of the bright products. This observation is attributed to the titanium oxide present in the semidull fibers. It was also noted that as the density of the bright PET samples was increased by heatsetting, the rate of hydrolysis decreased.

ISSN:0021-8995    

DOI:10.1002/app.1991.070420805

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe photoinitiated graft copolymerization of hydroxyethyl methacrylate (HEMA) onto cotton cellulose was studied using uranyl nitrate (UN) and ceric ammonium nitrate (CAN) photoinitiators. Optimization of various parameters of the graft‐copolymerization reaction viz., time, temperature, initiator, and monomer concentration, was carried out. The optimized conditions of grafting were employed to cotton samples swollen in zinc chloride as well as sodium hydroxide. Graft add‐on was found to be dependent on the nature of substrate and the concentrations of monomer and photoinitiator. UN was found to be the better photoinitiator, giving higher grafting with HEMA. The grafted samples showed initially decrease and then marginal increase in the moisture regain with increase in graft add‐on. The dye uptake of both direct and reactive dyes decreased with increase in graft a

ISSN:0021-8995    

DOI:10.1002/app.1991.070420806

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe ability of near‐infrared (NIR) diffuse reflectance spectroscopy to characterize reaction‐injection‐molded (RIM) polyurethane elastomers is demonstrated. The advantage of NIR spectroscopy over other analytical methods is its ability to analyze samples without any preparation. In this work, the specific effects of composition, density, phase separation, and moisture content on the NIR spectra of the polymers are identified. In addition, the ability of NIR spectroscopy to make rapid assessments of physical properties, such as heat sag and flex modulus, is demonstrated. In order to perform these analyses, the multivariate statistical methods of principal components analysis (PCA) and partial least squares (PLS) are

ISSN:0021-8995    

DOI:10.1002/app.1991.070420807

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractUltracentrifugal techniques have been employed to investigate the degradation of hydroxypropyl guar (HPG) solutions, and of gels formed with a delayed zirconium cross‐linker, by ammonium persulphate at 90°C. Molecular weights,M, for various samples of degraded polymer were determined by sedimentation/diffusion, and an empirical relationship was established betweenMand the sedimentation coefficient at a single, low concentration. This enabled the straightforward determination ofMas functions of persulphate concentration, cross‐linker concentration, and time at temperature. It was shown that large decreases inMoccur within the first hour at temperature, but that complete degradation is not achieved. It was further shown that, when a delayed zirconium cross‐linker is used, degradation may be less effective when gels are formed and degraded at high shear

ISSN:0021-8995    

DOI:10.1002/app.1991.070420808

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA film of polyamic acid is formed by vapor deposition polymerization of pyromellitic dianhydride (PMDA) and 4,4′‐diaminodiphenyl ether (ODA). We have taken ESR spectrum during the polymerization process and compared it with the ESR spectrum of films obtained from solution polymerization. In the intermediate polymers during vapor deposition polymerization, the amide bond (CONH) is coplanar with the benzene ring and two protons in the PMDA molecule. This intermediate polymer has one unpaired electron that interacts with the two nitrogen nuclei equally. On the other hand, in the polymer obtained by solution polymerization, the amide bond and the benzene ring of PMDA are not coplanar. In this polymer, too, some of the molecules have an unpaired electron that seems to have almost no coupling with NH groups. These results imply that the polymer formation via vapor deposition proceeds through different intermediates and different molecular configurations from that via the solution

ISSN:0021-8995    

DOI:10.1002/app.1991.070420809

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo kinds of anionic polymer emulsions with different particle sizes were blended and cast on a release‐paper at 30°C. One was poly(butyl acrylate) emulsion, and the other was ethyl acrylate–methyl methacrylate (1 : 1, weight ratio) copolymer emulsion. They were produced by emulsifier‐free emulsion polymerization. The blend films prepared in an appropriate range of the blend ratio had a great difference in tackiness between both surfaces: The air‐side surface exhibited tackiness and the release‐paper side showed nontackiness. The forming mechanism is

ISSN:0021-8995    

DOI:10.1002/app.1991.070420810

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY