ISSN:0959-8103    

DOI:10.1002/pi.4990270402

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe kinetics of crystallization of gutta percha (trans‐polyisoprene) were studied both in its native form and as the commercial product currently used for dental purposes. Mixtures of native gutta percha with selected low molecular weight substances (BaSO4, CdSO4, Bi2O3, ZnO), ‘Thermoplast’—a commercially formulated plasticizer, and colouring agents were also examined. It was shown that any incompatibility of the aforementioned substances caused an increase in the crystallization rate, while compatibility decreased the rate of crystall

ISSN:0959-8103    

DOI:10.1002/pi.4990270403

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractLatex and solvent‐cast films have been prepared from poly(butyl methacrylate) surfactant‐free latices and their permeabilities to water vapour and an aqueous organic solute (p‐nitrophenol) have been studied. Latex films show considerable ageing effects and their performance is very dependent upon the conditions of film formation but their barrier properties are not necessarily inferior. A greater dependence on film orientation is evident for latex

ISSN:0959-8103    

DOI:10.1002/pi.4990270404

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe Michael‐type addition reaction of ethylene‐vinyl alcohol copolymer (EVAL) with a series of vinyl sulfoxides namely methyl, ethyl,t‐butyl and phenyl vinyl sulfoxides, was performed with NaOH as a catalyst in DMSO solution to produce 2‐(alkyl or phenyl sulfinyl)ethyl EVAL derivatives. The high perm‐selectivity of sulfur dioxide against nitrogen was achieved through these sulfoxide‐modified EVA

ISSN:0959-8103    

DOI:10.1002/pi.4990270405

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractRadical copolymerization of acrylonitrile (AN) with styrene (Sty), usingx,x′‐azobisisobutyronitrile as initiator, was carried out in the presence of zinc chloride (ZnCl2) dilatometrically at 65/pm 0.1 C for 120min. The rate of polymerization was a direct function of the concentrations of ZnCl2, AN and Sty, and polymerization temperature. The viscosity‐average molecular weight of the copolymer increased with ZnCl2concentration. The energy of activation in the presence and absence of the complex was evaluated as 82.5 kJ mol−1and 115.5 kJ mol−1, respectively. The copolymerization of AN with Sty proceeded via the radical‐comple

ISSN:0959-8103    

DOI:10.1002/pi.4990270406

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractDielectric relaxation measurements are reported on plasticized commercial and heterogeneously substituted cellulose acetate. Differences in the observed behaviour are attributed to the retention of a degree of crystallinity and microscopic structure in the original substituted cellulose samples. A comparison of dynamic mechanical and dielectric relaxation data further emphasizes the influence of the nature of the original morphology on the micro dynamics.

ISSN:0959-8103    

DOI:10.1002/pi.4990270407

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTernary copolymerization reactions ofN‐acryloyloxyphthalimide (NAP) orN‐methacryloyloxyphthalimide (NMP) and acrylonitrile with methyl acrylate or methyl methacrylate were carried out in solution at 60°C in the presence of a free radical initiator. Experimental terpolymerization data agree well with calculations based on the Alfrey‐Goldfinger equation. The determination of unitary, binary, and ternary azeotropies of the various systems studied was easily handled by a computer program. The results show that there is no ternary azeotropic composition for any terpolymer system studied. Selective unitary and binary azeotropic compositions were polymerized and the results show good agreement between the theoretical and experimental terpolymer composition in each case. The estimation of terpolymer compositions was carried out by1H NMR spectr

ISSN:0959-8103    

DOI:10.1002/pi.4990270408

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIntrinsic viscosities of poly(4‐chlorostyrene) solutions in isopropyl‐benzene andn‐propylbenzene at temperatures above and below the theta (θ) temperatures of these solvents were measured using a capillary viscometer. The viscosity measurements were performed on three poly(4‐chlorostyrene) samples having molecular weights (M̄;v) 1.75 × 106, 6.5 × 105and 2.7 × 105. A smooth and continuous contraction below the θ temperatures was observed for both solvents. The temperature dependence of [/eta] can be represented by a master curve in a plot of α3/eta|/tau|M1/2(g1/2mol−1/2) versus |/tau|M1/2(g1/2mol−1/2), where α/eta = [/eta(T)]/[/eta(θ)]1/3is the expansion factor and /tau = (T‐ θ)/Tis the reduced temperature. A universal plot of reduced viscosity size (α/eta) versus reduced blob parameter (N/Nc) shows the achievement of collapsed state forTθ. The temperature dependence of intrinsic viscosity, both below and above the θ temperature, exhibits similar behaviour to the temperature dependence of dipole moments

ISSN:0959-8103    

DOI:10.1002/pi.4990270409

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAn attempt was made to clarify the change in the structure of immature cotton (Gossypiumspp.) boll during its growth. For this purpose, five immature cotton bolls with length less than 4.64 cm were adopted as samples and cellulose fibres taken from these bolls were subjected to SEM observation,13C NMR, X‐ray diffraction and IR analysis. Intramolecular hydrogen bonds were progressively formed during the growth of first cell wall but crystallization did not occur at this stage. Crystallization, as detected by X‐ray diffraction, takes place after the formation of O3…O'5and O2…O'6intramolecular hydrogen bonds. The crystallization is well correlated with the formation of intermolecular hydrogen bonds, as detected by IR analysis. The conformational regularity of molecular chains (formation of intramolecular hydrogen bonds) is concluded to be prerequisite for the crystallization of cotto

ISSN:0959-8103    

DOI:10.1002/pi.4990270410

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCyclization of α,ω;‐dilithiopolyisoprenes has been achieved in hexane solution in the presence of tetrahydrofuran (15% in volume) at −40 to ‐ 50°C. Using as linking agent the non‐conjugated diene 1,2‐bis(isopropenyl‐4‐phenyl)‐ethane, macrocyclic polyisoprenes could be obtained with yields of at least 90%, even for molecular weights as high as 30 000 mol g−1. With SiCl4as coupling agent no gelation occurred and yields of about 70% in cyclic dimers, probably bicyclic, have been observed.These results are compared to those obtained by various authors with α,ω;‐dilithiopolystyrenes or α,ω;‐disodiopolystyrenes and are attributed mainly to the presence, in the polyisoprene case, of predominant cyclic aggregates even at low

ISSN:0959-8103    

DOI:10.1002/pi.4990270411

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY