摘要:

AbstractThere appear to be very few literature estimates of the size or the shape of the plastic zone in polybismaleimides, whether calculated or observed experimentally. Bismaleimides are characteristically much more brittle on a macroscopic scale than other thermosetting resins and might be expected to have exceptionally small plastic zone radii. In this paper, experimental investigations are described, which conclude that the plastic zone must be much smaller in bismaleimides than in epoxies, even after rubber toughening, and before the network is fully developed by postcure. No direct observation of the zone radius could be made, but model calculations were carried out using Irwin, Dugdale, Tresca and von Mises expressions. The estimated zone radii declined with cure time, and became more or less negligible for all except the highest rubber concentrations after postcure. Plane stress models gave higher radii than plane strain ones. The very small calculated plastic zones of bismaleimides were consistent with the low observed ratio of tensile to compressive strength. This ratio implies marked resistance to yielding compared with that to crack propagation, and suggests a morphology consisting of exxtensive regions of continuous, rigid crosslinked structures, with minimum scope for shear.

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360101

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractPartial specific volumes,v02, of poly(D‐β‐hydroxybutyrate), PHB, were determined by density measurements in several chloroaliphatic hydrocarbons. We observed thatv02of PHB in tetrachloroethane is influenced only very little by temperature. This can be generalized for the group of solvents used. The experimental results are comapred with the data obtained theoretically using the concept of additivity of group contribut

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360102

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractControlled two step block copolymerization of styrene, methyl methacrylate and ethyl acrylate with aliphatic and aromatic disulphides under UV irradiation took place in bulk and in THF solution. In the first step of the polymerization, the most reactive system was ethyl acrylate with aromatic disulphides.The molecular weights and yields of polymerizations increased with reaction time. The macromolecules were terminated by primary. SR radicals and by combination of two macroadicals which was observed by NMR spectroscopy. Aninsignificant portion of uninitiated photopolymerization was detected only for MMA. In the second step of polymerization, the purified macroinitiators from the first step reacted with additional monomers to form block copolymers with a small quantity of unreacted macroinitiator. The molecular weights of copolymers increased, the bonding segments between the blocks being detected by1H NMR. The overall reaction is an insertion of monomers between two thiyl groups.

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360103

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe Polymerization of ethylene oxide catalysed by protonic acids and proceeding via the activated monomer mechanism differs from the polymerizations of substituted epoxides like propylene oxide and epichlorohydrin. The kinetics of ethylene oxide polymerization were investigated and compared with the kinetics of model reactions, namely addition of oligomers of ethylene oxide to ethylene oxide. The mechanism of polymerization involves, besides the addition of monomer to the terminal hydroxyl groups, the addition to the polymer ether groups. This reaction does not take place for substituted oxiranes, most probably because of steric hindrance.

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360104

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolymerization oft‐butylacetylene initiated by a tungsten carbene complex (I) was investigated under various conditions.t‐Butylacetylene was polymerized in high yield in chlorinated hydrocarbons such as CHCI3and CCI4and in the presence of AICI3. The molar mass of the polymers formed was as high as 8.2 ×104∼ 3.2 × 105. Moreover, when the solution of tungsten carbene complex in CCI4was irradiated with UV light, the molar mass was remarkably enhanced. This phenomenon may occur because tungsten dichlorocarbene immediately forms. Apparent rate constants were determined by gas chromatography. NMR spectra show a predominant characteristic of highciscontent in the structure of poly(t‐butylacetylene) in contrast to poly(phenylacetylene). Theciscontent increasedca. 11% when poly(t‐butylacetylene) was heated in decalin at 110°C. X‐Ray diffraction diagrams show that poly(t‐butylacetylene) has an amo

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360105

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA study of transient currents in discharging mode in vacuum aluminized pure and iodine doped ethyl cellulose (EC) films, approximately 20 μm in thickness, measured at various temperatures (303–353K) and applied fields (2.0 × 104−4.5 × 104V/cm) is described. The order of current has been found to increase considerably with increase in poling temperature, field and iodine mixing. The currents have been found to showI ∝︁ t−n(i.e. Curie–Von Schweidler law) time dependence with different slopes in the short and long time regions. The conductivity of the films is increased on doping with iodine. The dopant molecules are considered to act as additional trapping centres and provide a link between the polymer molecules in the amorphous region, thus resulting in the formation of a charge transfer complex. The results of the experiments and the mechanisms involved are discussed on the basis of avai

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360106

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractMgCl2‐supported CoBr2catalysts were prepared from mixture of MgCl2and CoBr2L2(L = triphenylphosphine or pyridine) in toluene. Polymerization of 1,3‐butadiene was conducted over the catalysts combined with ordinary alkylaluminums as cocatalyst. The CoBr2(PPh3)2/MgCl2catalyst gave polybutadiene with approximately 80% of 1,2 units, whereascis‐1,4‐poly‐butadiene was obtained with the CoBr2(C5H5N)2/MgCl2catalyst.Addition of triphenylphospine to the latter catalyst caused a marked increase in the content of 1,2 units. The content of 1,2 units could be thus controlled in the range from 0 to 80% by changing the amount of triphenylphosphine.On the other hand, the CoBr2(PPh3)2/MgCl2catalyst with very low content of CoBr2(PPh3)2hardly displayed any activity. Addition of dimethoxydiphenylsilane to the catalyst gave polybutadiene containing 90 % of 1,2 units with a fairly high

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360107

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractGraft copolymers were obtained by radiation‐induced grafting of vinyl acetate (VAc) andN‐vinylpyrrolidone (NVP) individually and in binary mixture on to polypropylene (PP) films. The effect of some grafting conditions on the grafting yield was determined. The addition of Cu2Cl2as inhibitor to the reaction medium inhibited the homopolymerization of the comonomer. The grafting process was remarkably enhanced by using dioxan as a diluent compared with other solvents used. The addition of some inorganic salts has a great influence on the individual grafting of both monomers. The gel percent in the graft copolymer was determined; it increased as the grafting yield increased. The swelling behaviour and electrical conductivity for the grafted films slightly increased by grafting. The changes in thermal parameters such as glass transition (Tg), melting (Tm) and recrystallization (Trc) temperatures and heats of melting (ΔHm) and recrystallization (ΔHrc) of the graft copolymers were also followed by differential scanning calorimetry (DSC). These thermal parameters of PP were varied by grafting with VAc and NVP and depend on the graft yield, which reflects the change in its crystalline domains and formation of crosslinks in the graft chains. The heat of recrystallization of the graft copolymer by cooling from the molten state decreases by grafting which is a good indication of crosslink formation, since crosslinking decreases the crystallizability of the polymer m

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360108

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of polycondensation of tetramethyldisiloxane 1,3‐diol (HD2OH) have been followed by stopping the reaction at increasing times (by neutralization of the acid and trimethylsilylation of the silanol end‐groups). Analyses of the linear and cyclic oligomers and of the higher polymer have been made by gas–liquid chromatography and by steric exclusion chromatography. At the beginning of the reaction (e. g. between 1 min and 1 h) the main products are linear oligomer H(D)2nOH and D4(formed by cyclization of HD4OH). There are only very small amounts of large cycles. Linear high polymer is then formed slowly together with increasing amounts of cycles D5, D6, D7, …, formed by backbiting reactions. After 24h, the yield of D4is 40–50% and that of linear polymer 40–30% (Mpeak× 104–105). With disilanol concentration 0.45–0.9 mol liter−1and CF3SO3H concentration about 10−3mol liter−1, the reaction is very rapid during 1–2 min and the medium becomes heterogenous with the formation of an inverse water emulsion. The reaction then slows down considerably, most of the hydrated acid being trapped in the water droplets. Silanol consumption is second order in [SiOH] and first order [TfOH]o. Polymerizations made in polar and non‐polar solvents have similar rates, which however increase moderately in the order toluene<1,2‐dichloro‐ethane

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360109

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractMacromonomers were obtained by cationic polymerization of propylene oxide and epichlorohydrin proceeding by the activated monomer mechanism with hydroxyethyl acrylate as initiator. Up toDPn∼ 15 for propylene oxide andDPn∼ 20 for epichlorohydrin, polymerization proceeds as a living process, giving with quantitative yields macromonomers with functionality equal to one, controlled molecular weight and narrow molecular weight distribution (MwMn<1.2) free of side products. In the higer molecular weight region, side reactions become increasingly noticeable. Propylene oxide macromonomers undergo radical homopolymerization. Homopolymerization of macromonomer withMn= 8×102gives graft copolymers withMnup to 7.2×103in copolymerization with styrene, completely soluble graft copolymers withMn∼ 2×104were obtained. Radical copolymerization of epichlorohydrin macromonomers with styrene gives initially soluble products withMn∼ 6×104were obtained. Radical copolymerization of epichlorohydrin macromonomers with styrene gives initially soluble products withMn∼ 6×104, which are converted in the later stages into insoluble gels, apparently due to the chain transfer to chloromethly groups of the polyepichlor

ISSN:0959-8103    

DOI:10.1002/pi.1995.210360110

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY