摘要:

AbstractA method for photochemically induced graft copolymerization of acrylamide (AM) onto polypropylene (PP) film surface by a continuous presoaking process under nitrogen atmosphere has been developed. After removal of homopolymer formed, ESCA, UV spectroscopy, contact angle, and adhesion measurements confirmed a photografted layer on the surface of the PP film. The results from spectral analysis and surface properties measurements were consistent. The best grafting yield was obtained for 7–10 s irradiation time. Stabilizing additives in the PP film had no evident effect on the photografting. Benzophenone was an efficient photoinitiator for photografting of PP film with AM. An AM concentration of 0.5–1.3Min the presoaking solution was appropriate in the present case. Acetone was the best solvent among the three alifatic ketones tested (acetone, methylethylketone, and methylpropylketo

ISSN:0021-8995    

DOI:10.1002/app.1991.070430401

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper presents the kinetic study of polymerization of ethylene with VOCl3and aluminum alkyls such as Et3Al and Et2AlCl. The effect of various parameters like the [Al]/[V]ratio, catalyst concentration, reaction time, temperature, solvents, and additives on rate of the reaction, yield, and molecular weight is reported. Each of these parameters has a remarkable effect on the yield and the rate of polymerization for both catalyst systems. Triethylamine is found to increase the catalyst efficiency and the rate. It is also observed that aliphatic hydrocarbons acted as a better polymerization medium than did the aromatic ones.

ISSN:0021-8995    

DOI:10.1002/app.1991.070430402

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

年代:1991

数据来源: WILEY

摘要:

AbstractStructural characteristics of the silk fibroin fiber‐modified with epoxide treatment were elucidated by refractive index measurement, differential scanning calorimetry, and thermomechanical analysis and on the basis of strength–elongation measurements. The four epoxides used were glycidol (G), ethylene glycol diglycidyl ether (E), tolyl glycidyl ether (T), and resorcinol diglycidyl ether (R). The values of the isotropic refractive index of the silk fiber increased by the action of T or R. The position of the endothermic peak attributed to the thermal decomposition and the position of the onset of the contraction of each of the samples treated with epoxides shifted to higher temperature, suggesting the more thermal stability. However, the values of the molecular orientation and the crystallinity of the specimen evaluated from X‐ray diffraction analysis remained unchanged regardless of the epoxide treatment. These experimental results have been interpreted in terms of the cross‐links between the adjacent silk fibroin molecules and of the hydrogen bonds between the hydroxyl groups of the epoxide molecules attached to the side chains of the silk

ISSN:0021-8995    

DOI:10.1002/app.1991.070430403

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

年代:1991

数据来源: WILEY

摘要:

AbstractWeather‐induced degradation of polymer properties is caused by all the factors of weather, which include solar radiation, temperature, humidity, wind, rain, environmental pollutants, thermal cycling (cold night and hot days), and sand abrasion. Linear low‐density polyethylene (LLDPE) is exposed to natural weather, and degradation is monitored by the mechanical properties testing system, Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). Three mathematical models were developed with weather parameters as independent parameters and mechanical property (tensile strength), chemical change (carbonyl growth), and thermal property (percent crystallinity) as dependent parameters. The mechanical property was found to be more dependent on the ultraviolet (UV) portion of the total solar radiation, chemical change was found to be synergestically effected by UV and total solar radiation, and change in thermal property was because of UV, total solar radiation, and temperature. Humidity and other weather parameters were found to play a less significant role in the weather‐induced degradation of LLDPE prope

ISSN:0021-8995    

DOI:10.1002/app.1991.070430404

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

年代:1991

数据来源: WILEY

摘要:

AbstractSince the itaconic acid (IA) comonomer is the potential initiator of cyclization, therefore the introduction of IA comonomer into polyacrylonitrile (PAN) precursor can depress the onset of exotherm (or cyclized temperature) and peak temperature. However, the more the IA content, the lower the conversion of acrylonitrile (AN) in the polymerization reaction. Although 2‐ethylhexyl acrylate (2‐EHA) comonomer in PAN precursor may prevent the cyclization propagation of nitrile groups during oxidation, PAN precursor with a few percent of 2‐EHA comonomer has a more preferred orientation. As the content of 2‐EHA comonomer further increases, the orientation of the resulting carbon fiber decreases correspondingly.In this study, PAN precursor, with the composition of 98 mol % AN, 1.5 mol % 2‐EHA, and 0.5 mol % IA, and its resulting carbon fiber have the best mechanical properties. From the results, it is shown that there is a good relationship between the tenacity and modulus of PAN precursor and those of its resulting car

ISSN:0021-8995    

DOI:10.1002/app.1991.070430405

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

年代:1991

数据来源: WILEY

摘要:

AbstractPolyurethane prepolymers were prepared in ethylacetate from TDI and poly(oxypropilene)glicols) (PE‐PU) or poly(tetramethyleneglycoladipate)diols (PES‐PU) of different molecular weights (M). Homogeneous membranes were prepared by spreading the pre‐polymer solution added with a three, four or pentafunctional crosslinking agent, in the presence of stannous octoate as a catalyst. On increasing M, the PUs Tg decreases regularly in the range +30 to −47°C. PU's are amorphous with the exception of PES‐PU obtained from highest M polyester diols. Permeability P, diffusivity D, solubility coefficient S of N2, O2, CO2, CH4, CO were measured at T=35°C (>Tg).P, D, S do not depend on the crosslinker functionality, but mainly on M. P and D in PE‐PU are linear function of T‐Tgwhile in PES‐PU the function is not linear. Gas solubility fulfills in general the regular solution theory. P, D, S of water vapor is also given. Permeability decreases in the order H2O>CO2>O2>CH4>CO>N2. Some practical application based on particular selectivi

ISSN:0021-8995    

DOI:10.1002/app.1991.070430406

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of structural segments on the thermal stability of photocurable urethane acrylates was studied. A series of model compounds, where one segment of the molecular structure was varied at a time while keeping the remainder of the molecule unchanged, was tested for thermal stability. The results from this study indicate a prominent equivalent weight effect: Increasing the equivalent weight decreases the thermal stability within a given series of model compounds. Polyol‐based urethanes were found to be more stable than their amine counterparts. Of the hydroxy‐terminated starting materials, polycaprolactones were found to produce the greatest thermal stability, whereas polyethers resulted in the least stable photocurable materials. The diisocyanate segment exhibits a marked effect on the thermal stability of the cured material also. Surprisingly, the dicycloaliphatic diisocyanates resulted in greater stability than the aromatic diisocyanates, while the monocycloaliphatic diisocyanates yielded the least stable materials in the model compound series tes

ISSN:0021-8995    

DOI:10.1002/app.1991.070430407

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

年代:1991

数据来源: WILEY

摘要:

AbstractSolvent transport in multilayer thin film structures can induce damaging stresses. It is important to understand these quantitatively for the design of processing methods for microelectronics manufacture. As a model for such systems, this article focuses on the connection between solvent transport in a thin, supported film and the induced bending curvature of the film/substrate combination. We develop a simple mechanical model to calculate the bending curvature based on the transport‐induced stresses. A phenomenological moving boundary description of non‐Fickian solvent transport often found in glassy polymers has been used. The evaluation of dimensionless bending curvature for a number of generic cases is presented. As an application of the model, experimental data for a polymide (PI)/quartz‐n‐methyl‐2‐pyrrolidinone (NMP) system involving significant swelling (15–20%) of the PI film is analyzed. The analysis shows that the measured bending during the transport of NMP in the PI film compares well with that predicted based on an “intermediate,” non‐Fickian diffusion mechanism of NMP, consistent with the finding obtained from a laser interferometric study. Estimation of the swelling‐induced stress shows that it is large and as significant as that du

ISSN:0021-8995    

DOI:10.1002/app.1991.070430408

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe activation energy analysis of the dynamic‐mechanical α relaxation has been carried out as a function of thermal history for several high‐density polyethylenes. The air‐quenched samples display a unique α relaxation whose temperature dependence fits a constant activation energy regardless of the structural features of the samples, whilst the isothermally crystallized samples, on the other hand, display an asymmetric α peak that, often, splits into two, which does not fit a constant activation energy. The asymmetry of the α peak as well as the splitting has been explained accounting for two different relaxation time distributions. The dependence of the intensity of the α and α′ relaxations on frequency have been discussed in terms of different mean relaxation times and amorphous la

ISSN:0021-8995    

DOI:10.1002/app.1991.070430409

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe structure of graft copolymers of PCA with PMAA obtained by the methods of chemically initiated liquid‐phase grafting polymerization has been investigated with the use of electron microscopy, electron‐probe microanalysis, and X‐ray radiography. The concentration profiles of the graft copolymer distribution along the fiber cross section and diffusion coefficients of the monomer solutions correlated with the kinetics of the graft layer penetration inside the polymeric matrix have been determined. The concentration profile of the graft polymer distribution has been shown to have drops down to the zero level. Grafting proceeds both in the amorphous regions and on the surface of imperfect crystals. The structure of the graft layer, in which the segregated chains of graft PMAA constitutes the dispersed medium and the PCA inclusions represent the dispersed phase, has been found to be heteroge

ISSN:0021-8995    

DOI:10.1002/app.1991.070430410

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

年代:1991

数据来源: WILEY