摘要:

AbstractAnionic copolymerizations of styrene (M1) with excess 1‐(4‐dimethyl‐aminophenyl)‐1‐phenylethylene (M2) were conducted in benzene at 25°C for 24h, usingsec‐butyllithium as initiator. Narrow molecular weight distribution copolymers with M̄;n= 16.1 × 103g/mol (M̄w/M̄n= 1.04) and 38.2 × 103g/mol (M̄w/M̄n= 1.05), and 24 and 38 moles of M2per macromolecule, respectively, were characterized by size exclusion chromatography,1H NMR spectroscopy and DSC. The monomer reactivity ratio, r1= 5.6, was obtained from the copolymer composition at complete consumption of M1, assuming that the rate constant k22=0,i.e. r2=0. The polymers exhibitedTgvalues of 128 and 119°C, respectively, which correspond to an estimatedTg= 217°C for the hypotheti

ISSN:0959-8103    

DOI:10.1002/pi.4990270102

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMastication of gutta percha (trans‐polyisoprene) resulted in the selective scission of molecules, producing a narrower distribution of lower molecular weights. The mechanical properties of the samples also underwent a significant change due to mastication. The greater the content of incompatible substances (salts and oxides) in commercial gutta percha. the more substantial were these effects. The atmosphere (air, N2, O2) in which the experiments were conducted yielded significantly different results. The decrease in molecular weight was far greater in an O2atmosphere than under a current of nitrogen or air, owing to the combination of double bonds with O

ISSN:0959-8103    

DOI:10.1002/pi.4990270103

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractKraft lignin was treated with dicarboxylic aliphatic (sebacoyl) or aromatic (terephthaloyl) acid chlorides inN,N‐dimethylacetamide orN‐methyl‐2‐pyrrolidone as solvents in the presence of triethylamine or pyridine as catalysts. The polyester gels obtained were characterized by IR after specific extractions and the chemical incorporation of lignin was proved unambiguously. Their thermal behaviour was determined by DSC and TGA; they are amorphous and stable up to 200°C in a nitrogen atmosphere. The reactivities of the two types of hydroxyl group (aliphatic and phenolic) were assessed from model reactions carried out in the same co

ISSN:0959-8103    

DOI:10.1002/pi.4990270104

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe synthesis of high molecular weight acrylic water‐soluble polymers in heterophase water‐in‐oil polymerizations is discussed. A mechanism has been elucidated which includes elementary reactions in the continuous (organic) and dispersed (aqueous) phases, as well as the interfacial layer. The latter allows for the identification of interfacially active species which can concurrently enhance stability and increase the linear molecular weight of the polymer. Suitable species are found to contain multiple radically active functional groups on either the hydrophilic or hydrophobic moieties.A one‐point light‐scattering method is also developed which improves the accuracy in molecular‐weight estimation to /pi5%. compared with /pi10% for the conventional dilution procedure. This is demonstrated for high molecular weight polyacrylamides and is found to reduce the sample measurement time fourfold

ISSN:0959-8103    

DOI:10.1002/pi.4990270105

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractSurface activity of aqueous solutions of cellulose acetate (CA) with total degree of substitution (〈F〉) ranging from 0.58 to 0.80 was examined. Critical micelle concentration (CMC) of the aqueous CA solutions, determined from the polymer concentration dependence of surface tension (γ), is unequivocally determined by 〈F〉, and an increase in 〈F〉 of CA brings about a lowering of the CMC. From light scattering measurements on aqueous solutions of CA with 〈F〉 = 0.8 at 20°C, it was revealed that in the vicinity of the CMC the micelles in the solution consist ofc. four CA molecules, which is very close to the value obtained by analysing the data obtained from the mass action model. The surface tension of aqueous solutions of CA (〈F〉 = 0.8) in the polymer concentration range above the CMC wasc.0.74 times that of pure water over the tem

ISSN:0959-8103    

DOI:10.1002/pi.4990270106

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPoly(butyl methacrylate) films have been prepared from surfactant‐free latices which had post‐added commonly used latex stabilisers. Water vapour transmission rates were used to study film permeability in relation to morphology, which was also studied by freeze fracture replication transmission electron microscopy. The extent of latex coalescence depended upon the chemical nature of the stabiliser employed and at monolayer coverage was not necessarily deleterious to the barrier properties of the fi

ISSN:0959-8103    

DOI:10.1002/pi.4990270107

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe transport ofp‐nitrophenol across films formed from surfactant‐free poly(butyl methacrylate) latices has been investigated with a view to better understanding the morphology of, and morphological changes occurring in, such films. The importance of the temperature and time, both of film formation and of storage, are identified and related to the state of coalescence of the latex particles within the films. especially with respect to interparticle boundar

ISSN:0959-8103    

DOI:10.1002/pi.4990270108

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA DSC thermogram showed two separate glass transition temperatures in PVC/PMMA mixtures over the entire composition range; multiphase structures were observed in an optical microscope. FTIR spectra indicate that there are no strong specific interactions between these two polymers. The earlier studies on this blend system are briefly reviewed.

ISSN:0959-8103    

DOI:10.1002/pi.4990270109

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of solvent on the formation of excimer from copolymers of 2‐(1‐naphthylacetyl)ethylacrylate (NAEA) with both acrylamide (AM) andN‐vinyl pyrollidone (VP) in dilute solution was investigated. A minimum in excimer intensity was observed for each of the copolymers at approximately 2.20 × 104(J/m3)0.5. It is suggested that the relatively high content of NAEA in the copolymers (between 30 and 60%) governs the overall solubility parameter of the p

ISSN:0959-8103    

DOI:10.1002/pi.4990270110

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPoly(L‐ornithine)s having various azo‐contents in the side chains were synthesized by the water‐soluble carbodiimide procedure. The photochemical properties of the polypeptides poly[Nδ‐p‐(phenylazo)benzoyl‐L‐ornithine] (PPABLO) containing 3–77 mol% azobenzene were investigated by absorption and circular dichroism spectroscopy in hexafluoro‐2‐propanol (HFIP) or water, and in HFIP‐water or methanol‐water solvent mixtures. The photochromism of the dichroic bands of the PPABLOs containing 20–77 mol% azobenzene in the visible and ultraviolet wavelength regions was found to be mostly reversible as a function of irradiation time at different wavelengths due to the photostationary state (above 80%trans‐cisphotoisomerization) of the azo aromatic moieties. The PPABLO containing 3.2 mol% azobenzene in water exhibited conformational changes from random coil to helix by the addition of methanol or sodium dodecyl sulphate (SDS). The photo‐induced conformational change was observed in HFIP‐water‐SDS solvent mixtures, while no conformational change was seen in wat

ISSN:0959-8103    

DOI:10.1002/pi.4990270111

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY