摘要:

AbstractThe molecular structure of Bombyx mori fibroin is still subjected to much controversy; there are discordant reports in the literature on both the value of the molecular weight and the subunit structure of the molecule. The method reported in the present paper allows the molecular weight of Na2CO3extracted fibroin samples to be unambiguously determined, and investigations on the composition and the molecular weight of the peptides arising from the degradation process succeeded in establishing some overall aspects of the structure of the subunits. The main results are: (1) the molecular weight of undegraded fibrion is 4 · 105; (2) two small subunits are disulfide linked to the main chain; (3) the subunits are located near the terminals of the main chain; (4) in agreement with previous partial literature data, the small subunits are rich in bulky and acid amino acids; our work further shows that they possess a three‐block structure, consisting of a central hydrophobic core bearing two strongly acid sequences at the terminals. The mechanism of degradation of the fiber appears to be directed by structural, rather than chemical, factors, and its detailed investigation may represent a valuable method to determine the molecular architecture of the fib

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810601

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractThe kinetics of Polymerization of acrylonitrile initiated by the redox systems cyanoacetic acid/Mn(III) and 2‐butanone/Mn(III) were investigated in the temperature range of 30 – 50°C in aqueous sulfuric acid. The kinetics are consistent with the formation of a 1 : 1 complex between the reducing agent and Mn(III), its unimolecular decomposition yielding the initiating radical. Extensive oxidation of the primary radical with exclusively mutual termination of growing radicals accounts for the kinetics of the polymerization. Rate and equilibrium constants as well as thermodynamic parameters were evaluated and their significance is discu

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810602

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractThe kinetics of the polymerization of acrylonitrile, methyl methacrylate, and acrylamide initiated by the redox system cyanoacetic acid/manganese triacetate in dimethylformamide solution were investigated in the temperature range of 25 – 40°C. It was found that an initial complexation between the reactants followed by an electron transfer yields radicals. In contrast to acrylamide, acrylonitrile and methyl methacrylate effectively suppress further oxidation of the primary radicals. Exclusively the mutual termination accounts for the kinetics of these polymerizations. Data on the average degrees of the polymerizations support the suggested mechanisms. Rate and equilibrium constants were evaluated and their significance is discuss

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810603

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractAmphipathic liposaccharides were synthesized by condensation of glyco‐amino acid Oβof Ovomucoid with fatty acids containing 8 to 24 carbon atoms. Condensation was achieved by reaction of the carboxyl group of the acid (via acid chloride orO‐acylisourea as active ester) with the amino group of the asparagine residue in the glyco‐amino acid. X‐ray diffraction showed that liposaccharides exhibit in the dry state and in concentrated water solution a hexagonal structure. In this structure, long and parallel cylinders formed by the hydrophobic paraffinic chains of liposaccharides are arranged in a two dimensional hexagonal array while hydrophilic carbohydrate chains and water fill the space between the cylinders. Freeze fracture electron microscopy allowed the visualization of the hexagonal structure. The influence of the water content and of the length of the paraffinic chains on the periodic structure of the amphipathic liposaccharides was

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810604

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractSpectrophotometric studies in the UV region were carried out for a series of chlorine and bromine derivatives ofN‐ethylcarbazole and poly(N‐vinylcarbazole). All the examined polymers, in the whole spectral range, exhibit considerably less absorptivity than their low molecular models, i.e. ethylcarbazoles. Absorption bands of the polymers are shifted, in comparison to the respective absorption bands of halogenethylcarbazoles, towards shorter wavelenghts. Halogen substituents in the carbazole ring reduce the transfer energy π → π*. This bathochromic effect is especially observable for low‐energy bands1Laand1Lb, and it was noticed that the bromine substituent exerts more influence than the chlorine su

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810605

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractPoly(ethylene oxide) was irradiated with pulses of 16 MeV electrons (pulse length up to 100 ns) in aqueous and acetonitrile solutions in the absence and presence of oxygen. The change of the light scattering intensity (LSI) after the pulse was monitored. In acetonitrile solution, at a concentration of 2,3 · 10−2base mol/1, main chain rupture occurred both in the presence and in the absence of O2. In aqueous solutions at [PEO] = 2,3 · 10−2base mol/1 the LSI increased after the pulse in the absence of O2(crosslinking) and decreased at [O2] = 1,4. 10−3mol/1 (main chain scission). The rate of LSI decrease was correlated with a diffusion process in the case of O2free acetonitrile solution and with a chemical reaction in the cases of O2saturated aqueous and acetonitrile solutions. In the latter two cases it was found that a bimolecular reaction precedes bond scission in the main chain. It is assumed that peroxyl macroradicals (PO 2•) react with each other forming oxyl macroradicals (PO•) which decompose relatively rapidly by main c

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810606

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractA pair of polymers may interact with each other through hydrogen bond and form a polymer complex. Such polymer complex formation is affected by several chemical and physical factors, especially by solvent properties. This solvent effect was studied in the complex formation of poly(methacrylic acid) with a series of proton‐accepting polymers in aprotic solvents. The extraordinary behaviour of polymer complexes in dimethyl sulfoxide was well explained in terms of the strong interaction between proton‐donating polymer and dimethyl sulfoxide. In addition, a stronger proton‐accepting polymer, viz. poly(N,N‐dimethyl‐N′,N′,N″,N″‐tetramethylenephosphoramide), was synthesized. This polymer could form a polymer complex with poly(methacrylic acid) through hydrogen bond even in dimethyl sulfoxide. Selective polymer complex formation was achieved by controlling such

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810607

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractInvestigations of ten poly(ethylene glycol) samples with molecular weights of 62 to 20 000 showed that inverse gas chromatography is a sensitive tool to determine molecular weight dependent variations of thermodynamic parameters like specific retention volume, activity coefficient, and Flory‐Huggins interaction parameter. As mobile phase 27 probe molecules with various functional groups could be characterized with respect to their solubility behaviour for the oligomers and polymers due to the ability to form hydrogen bonds. By application of the factor analysis technique two factors could be extracted from the data matrix of retention values. The best fit of the corresponding simple structure was achieved with a combination of group concentrations of the terminal OH‐group and the repeating ether unit of the poly(ethylene glyco

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810608

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractNetwork structures and physical properties of products obtained either by crosslinking polyepoxides with polyphenols, and by dicyanodiamide or by catalytic polymerization are discussed and compared with those obtained by amine or anhydride curing. The highest crosslinking density is achieved by the polymerization of epoxy compounds. In polymerization, the glass transition temperature may rise by more than ΔTgv= 100 K. Amine and phenol curing result in similarly structured networks with mobile aliphatic segments and comparatively low crosslinking densities. Impact resistance based on dissipation of mechanical energy increases as network density decreases, a maximum being achieved with a medium chain length of 25 – 35 atom intervals between crosslinking points. The mechanical stability of polymers is limited by the cohesive strength KF. This latter corresponds to the maximum shear strength of bonds TKFmax, which was measured within the temperature range of 77 K to 450 K, in accordance with the equation\documentclass{article}\pagestyle{empty}\begin{document}$ {{\rm TKF}_{\max } = {\rm KF} = B - C \cdot T;} \quad {T < T_g } $\end{document}This equation was derived from Eyring's model of viscosity, correlatingBandCwith activation volume, activation energy,Tg, and strain rate.Bequals the cohesive strength at 0 K. It is determined by intermolecular forces but does not depend on the density of crosslinking. An increase ofTgdue to crosslinks or bulky segments causes a decrease ofCand therefore a reduction of the temperature dependence of KF. Hence, cohesive strength at room temperature is improv

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810609

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractDuring styrene (STY) polymerization, initiated by radicals formed by thermal or photochemical decomposition of 2,2′‐azoisobutyronitrile (AIBN) the overall polymerization rate constantKdefined by relationK=Rp/([AIBN]0,5[STY] η MIX0,5) and the ratiokp/(2kt0) increase with decreasing styrene concentration by hexane or benzene (Rpis the polymerization rate and ηMIXthe viscosity of the reaction system). In the thermally initiated polymerizationK=kp(2f kd/(2kt0))0,5and in the photochemically initiated polymerizationK=kp(2,303 ϕI0ϵd/(2kt0))0,5wherekd,kp, andkt0are respectively, the rate constants of AIBN decomposition, of propagation, and of termination (for a system of the viscosity 1 mPa·s) reactions, ϕ is the quantum yield of radicals entering into reaction with the monomer,I0the intensity of the incident light, ϵ the molar absorption coefficient of AIBN, anddthe path length of the light. The increase ofKand ofkp/(2kt0) with decreasing monomer concentration is more marked for the system styrene/hexane than for styrene/benzene and this increase is greater at 30°C than at 60°C. For Θ‐systems formed by binary mixtures like styrene/hexane, styrene/decane and styrene/C1– C4alcohols the values ofkpandkt0at 30°C range between 57 and 91 dm3·mol−1·s−1and (0,9 to 2,2)·107dm3·mPa·mol−1, i.e. they are in principle identical with the tabulated values of these rate constants

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810610

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY