摘要:

AbstractThe kinetics of graft copolymerization of polyacrylamide on to a natural polysaccharide guar gum have been studied in aqueous medium at 35 ± 0.2°C. Chemical initiation, using a water‐soluble redox system, potassium bromate/thiomalic acid, was used. This redox pair works in the presence of oxygen and thus makes the whole system cost‐effective. A plausible mechanism of graft copolymerization has been suggested on the basis of the experimental results obtained by varying the param

ISSN:0959-8103    

DOI:10.1002/pi.4990310102

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe temperature dependence of1H spin‐lattice,T1(H), and spin‐spin,T2(H), relaxation times of isotactic polypropylene with relatively low molecular weight, M̄w= 1.95 × 105, and ultra‐high molecular weight, M̄w= 1.78 × 106, crystallized at high temperature (155° C) for a long time (200 h), was measured with a broad line pulse spectrometer.T1(H) for the ultra‐high molecular weight sample is shorter than that for the low molecular weight sample, whileT2(H) for the ultra‐high molecular weight sample is longer than that for the low molecular weight sample. From the analysis of free induction decay (FID), three components ofT2(H), i.e.T2c(H),T2m(H) andT2a(H), were obtained. These relaxation times are associated with the crystalline, intermediate and amorphous regions, respectively. Here the intermediate regions are the regions in which chain molecules have intermediate mobility between that of crystalline and amorphous regions. A decrease in signal intensity of methylene, methine and methyl carbons was measured as a function of delay time following a 90° pulse before cross‐polarization. From the slope of a log (intensity) versust2plot a relaxation time associated with rigid regions of proton nuclei,T2r(H), was obtained, where the rigid regions are the regions in which cross‐polarization occurs easily. The value ofT2r(H) lies between that ofT2c(H) andT2m(H), indicating that the intermediate regions act as the rigid regions so far as cross‐pola

ISSN:0959-8103    

DOI:10.1002/pi.4990310103

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractBlends of nylon 6 (Ny6) with poly(acrylic acid) (PAA) were prepared in film form from solutions in a mixture of formic acid and water by evaporating the solvent. The miscibility and phase constitution of the binary blends obtained over a wide composition range (5/95–95/5) were examined by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical measurements. A Ny6 homopolymer film and Ny6/PAA blends with PAA concentrations ≥ 50 wt% exhibited a WAXD profile stemmed from the coexistence of two different crystalline modifications of Ny6, i.e. the α and γ forms. Above 50 wt% PAA content, the solution‐cast blends showed no definite crystallinity. It was found by DSC thermal analysis that the polymer pair is substantially miscible in the non‐crystalline state, since a single glass transition temperature (Tg) was situated between theTgs of the two homopolymers at every composition; however, theTgversus composition plots did not follow a monotonic function but yielded a peak maximum at a PAA concentration ofc. 25 wt%. In order to interpret this phenomenon, attention was given to the following point revealed by dynamic mechanical measurements: at the compositions of Ny6/PAA = 100/0–50/50, a phase of low regularity such as a nematic structure is formed in

ISSN:0959-8103    

DOI:10.1002/pi.4990310104

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractSynthesis and curing behaviour of urethane‐modified epoxy resins were studied. The epoxy resins were synthesized by the reaction of 4‐cresol‐type epoxy resin having hydroxymethyl group (EPCDA) with isocyanates. First, as a model compound, EPCDAPI was synthesized by the reaction of EPCDA with phenyl isocyanate (PI). EPCDAPI was heated at 180°C and the reaction products were identified and the reaction mechanism was studied. The following reactions occurred: regeneration of hydroxymethyl group and PI by thermal dissociation of urethane linkage; reaction of epoxide ring and urethane linkage; reaction of epoxide ring and regenerated PI. Urethane‐modified epoxy resin having hydroxymethyl group and urethane linkage (EPCDAMDI) was synthesized by the reaction of EPCDA with 4,4′‐diphenylmethane diisocynate (MDI). The structure was identified by IR,1H NMR and13C NMR. The epoxy resin was cured with a mixture of 4,4′‐diaminodiphenylmethane and 1.3‐phenylenediamine (molar ratio 6:4) as a hardener. Curing behaviour of the epoxy resin with hardener was examined by differential scanning calorimetry (DSC). It was found that onset and peak temperatures of the exothermic cure reaction of the EPCDAMDI system were lower than those of the 2‐cresol novolac‐type epoxy resin (EOCN) system, and the rate constant (k) of the cure reaction at 100° C of the former system was about six times larger than that of the latter system and was the same as that of 2‐cresol resol‐type epoxy resin (EOCDA). Viscoelastic properties of the cured resin were studied by dynamic mechanical analysis. It was found that the tan δ of the EPCDAMDI system had two peaks and the lower temperature peak disappeared afte

ISSN:0959-8103    

DOI:10.1002/pi.4990310105

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractSide‐chain liquid crystalline polymers with laterally attached mesogenic group were synthesized. Polymers having polyoxetane main chain were obtained by cationic polymerization, and with polymethacrylate main chain by radical polymerization. Some of the polymers showed nematic phase, and polyoxetanes having mesogen with electron‐withdrawing and electron‐donating groups in the molecule showed a little more discrete meso

ISSN:0959-8103    

DOI:10.1002/pi.4990310106

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo types of ethylene‐vinylacetate copolymers, containing 16% and 9% of vinylacetate, respectively, were crosslinked with dicumyl peroxide in a Brabender plastograf. The time of the torque maximum was proportional to the degree of crosslinking. The degree of crosslinking was determined by extraction and depended on the concentration of the crosslinking agent and of vinylacetate in the copolymer, and on the crosslinking temperature and time. It was found by DSC and by solid‐state CP‐MAS13C NMR that with the progress of crosslinking the crystalline phase of the copolymers changed to the amorphous phase. Crosslinking took place mostly on the acetate g

ISSN:0959-8103    

DOI:10.1002/pi.4990310107

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe electrochemical behaviour, FTIR spectrum and the morphology of polypyrrole‐polystyrenesulphonate (PPy‐PSS) films obtained potentiostatically at 0.6 V in a 0.05m Py + 1.7 × 10−2m NaPSS medium have been analysed. Different electrochemical parameters have been modified in order to establish the first polaron formation, the reversibility of the redox process and the doping mechanism.The FTIR spectrum confirms the existence of CO groups in the film structure and two possible explanations are suggested. SEM reveals a higher homogeneity in these films than in PPy films doped with smaller cou

ISSN:0959-8103    

DOI:10.1002/pi.4990310108

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstractω,ω‐Diphenolpolystyrenes (6) can be synthesized in quantitative yields by reacting poly(styryl)lithium with 1,1‐bis(4‐t‐butyldimethylsiloxyphenyl)ethylene (1), followed by methanol termination and hydrolysis with dilute acid. The initially formed 1,1‐bis(4‐t‐butyldimethylsiloxyphenyl)alkyllithium can be reacted with additional styrene monomer to form a polystyrene internally substituted with two in‐chain phenol groups after methanol termination and acid hydrolysis. The diphenol‐substituted polystyrene condensation macromonomers have been characterized by end‐group titration, size exclusion chromatography, thin‐layer chromatography, and ultraviolet‐visible,1H and13C NMR spectroscopy. Chain‐extension reactions of 6 (Mn= 2.6 × 103g mol−1) with bis(trichloromethyl)carbonate produced the corresponding comb‐type, branched polymer with estimatedMn(SEC, polystyrene standards) = 1.2 × 104g mol−1and no detectable residual condensation macromonomer. The second order rate constants for the addition reaction of excess poly(styryl)lithium with 1 and with 1‐(4‐t‐butyldimethylsiloxy‐phenyl)‐1‐phenylethylene (3) have been estimated to be 1.7 × 10−3M−1/2S−1and 3.2 × 10−3M−1/2S−1respectively. A sigma value (σ) of −

ISSN:0959-8103    

DOI:10.1002/pi.4990310109

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractCo‐oligomers of chloral and bromal were synthesized by initiating a 1:1 mixture of chloral and bromal with about 20mol% of lithiumtertiary‐butoxide or lithium bornyl oxide followed by acetate endcapping. The co‐oligomer compositions were analyzed by GC, capillary GC, high resolution NMR spectroscopy and HPLC. Co‐oligomers up to the pentamers were characterized by potassium ionization of desorbed species (K+IDS) mass spect

ISSN:0959-8103    

DOI:10.1002/pi.4990310110

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDifunctional cyclohexadienes with dihydrophthalimide central units and phenyl side groups to increase solubility are used as bisdienes in repetitive Diels‐Alder polyadditions with bis(4‐(1,2,4,‐triazoline‐3,5‐dione‐4‐yl)phenyl)methane as a difunctional dienophile. The polymers show good solubility in CH2CI2and CHCI3.Non‐stoichiometric Diels‐Alder polyaddition with slight excess of the bistriazo‐linedione provides the possibility of synthesizing telechelics with highly reactive triazol

ISSN:0959-8103    

DOI:10.1002/pi.4990310111

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY