摘要:

AbstractPoly(1,4‐phenylenevinylene) (PPV) and its derivatives are readily processable and thermally stable polyconjugated polymers. Since PPV contains phenylene units, its structure can be easily altered and modified in the electronic structure. Moreover, PPV and the derivatives are easily prepared via water‐soluble or organic‐soluble precursor polymers. Various PPVs substituted with electron‐donating or ‐withdrawing groups were synthesized and their third‐order optical nonlinearities were investigated by third‐harmonic generation method or degenerate four‐wave mixing technique. When phenylene rings carry two alkoxy electron‐donating groups, the substituted PPVs show third‐order nonlinear optical properties up to an χ(3)value of about 10−9esu. In order to obtain polymeric materials having high optical quality, PPV and silica alkoxide can be mixed successfully by sol‐gel processing without any phase separation or precipitation. This unusual organic‐inorganic hybrid shows a great advantage in

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971101

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractPolymerizations of butadiene (BD) with transition metals (MtX) and methylaluminoxane (MAO) catalysts were studied. Among the catalysts examined, nicke(II) acetylacetonate [Ni(acac)2] in combination with MAO revealed the highest catalytic activities for the polymerization of BD, giving high molecular weight polymers consisting of mainlycis‐1,4‐units in the microstructure. With Ni(acac)2‐MAO catalyst, the overall activation energy for the polymerization of BD between 0°C and 60°C was estimated to be 18 kJ/mol. From a kinetic study, the rate equation for the polymerization of BD with the Ni(acac)2‐MAO catalyst at 30°C can be expressed as follows:Rp= [BD]1.8[Ni(acac)2‐MAO]0.9. The polymerization mechanism of the polymerization of BD with the Ni(acac)2‐MAO catalys

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971102

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe crystallinities of compression‐molded polypropene sheets were investigated by applying Fourier‐transform (FT)‐IR and attenuated total reflection (ATR) FT‐IR analyses. Two internal reflection elements, Ge and KRS‐5, with an angle of incidence of 45°, were used to obtain the depth profiles of the crystallinity of polypropene sheets from the surface to bulk. The crystallinity in the region from the surface to about 0,7 μm depth was considerably lower than that in bulk. Polypropene sheets with higher comonomer content showed the same tendency, which was enhanced with decreasing molding

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971103

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA critical concentration was found for different compositions of UHMWPE/SBPE solutions, at which the concentration dependence of the reduced viscosity changes from low to high power. The critical concentration (Cc) is shifted to a higher value with increasing amount of SBPE in the UHMWPE/SBPE gel. The birefringence of the drawn films suggests that the degree of orientation of UHMWPE molecules along the drawing direction increases with the draw ratio. The increased orientation of UHMWPE improves the tensile strength and moduli of the drawn films. The draw ratios of gel films prepared from each blend of UHMWPE and SBPE exhibits a maximum value when the samples were prepared at concentrations close to their critical concentration. On the other hand, the maximum draw ratio obtained for gel films prepared near theirCcdecreases significantly at higher weight ratios of SBPE to UHMWPE. In contrast, the gel films with less than 2 wt.‐% of SBPE in UHMWPE yield a higher maximum draw ratio than the sample prepared from pure UHMWPE gel. Possible mechanisms accounting for this behavior are propose

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971104

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe aged system of lanthanum versatate (1) andp‐chlorobenzenediazonium tetrafluoroborate (2) was found to initiate effectively the radical polymerization of acrylic monomers including alkyl methacrylates, butyl acrylate and acrylonitrile, although its initiating activity is lower than that of the non‐aged system. The polymerization of methyl methacrylate (3) with the aged1/2system was studied kinetically in acetone. The initial polymerization rate (Rp) is expressed byRp= Kċ[aged1/2]0.80ċ [3]1.1at 50°C. The overall activation energy of the polymerization is 59.0 kJ ċ mol−1. The molecular weight of the resulting poly(3) formed in the early stage increases with increasing conversion. The polymerization system involves a persistent radical showing a four‐line EPR spectrum with ag‐value of 2.004. A three‐line spectrum due to the nitroxyl radical was also observed at lower monomer concentrations. The total concentration of persistent radicals was found to correspond well to the instantaneous polymerization rate. The copolymerization of styrene (M1) and3(M2) with the aged initiator system was examined at 50°C in acetone.r1andr2are 0.19 and 0.47, respectively. The former is considerably smaller than that (0.52) reported for the conventional radica

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971105

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAnionic polymerization of 2‐vinylpyridine shows significant solvent effects on the polymer stereochemistry. Polymerization with butyllithium in tetrahydrofuran (THF) yields a largely isotactic polymer, while polymerization with butyllithium in tetramethyl‐ethylenediamine (TMEDA) results in a material with nearly the same stereochemistry as radical polymerization. Semiempirical molecular orbital calculations were used to explain these solvent effe

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971106

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe radical polymerization of acrylic acid and sodium 4‐styrenesulfonate in the presence of chitosan as a template gives insoluble products, identified as the polyelectrolyte complexes chitosan‐poly(acrylic acid) and chitosan‐poly(4‐styrenesulfonate). Kinetic results do not permit to propose any mechanism in the first case, while suggest a “pick‐up” one in the second. The polyelectrolyte complexes have been characterized by FT‐IR spectroscopy, X‐ray diffractometry, optical and scanning electron microscopies, differential scanning calorimetry and thermogravimetric analysis. The results obtained indicate an ordered structure for the first complex, while the second one appears similar to that obtained by reacting the parent polymers. Therefore, the template polymerization technique appears advantageous only for the synthesis of the chitosan‐poly(acrylic acid) complex. The thermal analysis shows that the complexes undergo two successive modifications on heating. FT‐IR analysis demonstrates that the first process is an esterification between the hydroxyls of chitosan and the acidic groups of both daughter polymers; the second one appears to be an amidation of the chitosan ammonium groups only with

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971107

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe lipase‐catalyzed synthesis of poly(1,6‐hexanediyl maleate‐co‐fumarate) from 1,6‐hexanediol, dimethyl maleate and dimethyl fumarate is described. No secondary reaction involving the double bounds takes place, so that the copolyester composition can be well defined by adjusting the mole fraction of the dimethyl esters in the initial monomer mixture. The average molar masses of the non‐fractionated copolyesters depend on the mole fraction of the dimethyl maleate and are correlated with the amount of macrocycles formed. The possibility that the reaction system obeys a ring‐linear chain equilibrium is discussed. Linear polyester chains and macrolactones are characterized by1H NMR spectroscopy, steric exclusion chromatography and tonometry. A comparison is made with the homopolyester syntheses which were described in p

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971108

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

Abstract1,4:3,6‐Dianhydrosorbitol (DAS) was used as chain extender in the preparation of new segmented polyurethane elastomers, based on polyoxytetramethylene or hydrogenated polybutadiene soft segments and 4,4′‐diphenylmethane diisocyanate (MDI). These materials exhibit a two‐phase microstructure, due to the thermodynamic immiscibility between hard and soft segments, which results in an elastomeric behavior over a wide temperature range. The thermal and dynamic mechanical properties of various formulations were then examined and related to the complex morphology of the corresponding (often semi‐crystalline) materials. DAS leads to particularly stiff hard segments and provides longer rubbery plateaux, compared with a classical diol such as 1,4‐butanediol. Phase separation is favored by longer and less polar soft segments. In any case, the structure of the materials strongly depends on the composition and synthesis procedure (bulk polycondensation leads to more heterogeneous samples), and most of all on the thermal history of the samples. This latter behavior is related to the existence of a possible order‐disorder transition (ODT) which explains the change‐over from a two‐phase to a one‐phase system after specific an

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971109

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractHydrosoluble poly(3,6,9‐trioxaundecamethylene phosphonate) with attached cytotoxic bis(2‐chloroethyl)amine in the side chain was synthesized by chemical modification of the corresponding polyphosphonate via the Atherton‐Todd reaction. The structure of the product was confirmed by1H,13C and31P NMR spectroscopy. Preliminary in vitro cytotoxic studies revealed that the polymeric derivative exhibited an eight fold more cytotoxic potency against human hepatocellular carcinoma cell line HepG2 than against murine leukemia cell line

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971110

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY