摘要:

AbstractBackground, principles and prospects of some recent modifications and new ideas for the following techniques of chemical pulping processes of wood are reviewed: Application of catalysts, extended delignification, delignification by means of oxidizing agents, organosolv pulping.

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390111

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe load transmission through macromolecules is determined by the nature and the rate of their external interaction with the surroundings and by internal relaxation mechanisms. The time scales for the orientation, disentanglement, and scission of chains in elongational flows, polymer melts, and solids will be discussed in this paper.

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390112

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe systematic study of intramolecular reaction and gel points together with measurements of moduli of tri‐ and tetra‐functional end‐linked networks show that network imperfections always result from the gel‐gel intramolecular reaction which must occur when such networks are formed. Even in the limit of zero pre‐gel intramolecular reaction, post‐gel intramolecular reaction and network imperfections still persist (law‐of‐mass‐action effect) to give marked reductions in modulus, particularly for trifu

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390113

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractLong‐range density or concentration fluctuations in the critical region of phase changes are directly tractable in modern “universal” models (Ising, Potts, percolation). Real polymers are apt to display “non‐universal” phase transitions depending on their detailed individual structures. Here mean field model can be refined in steps to portray critical fluctuations of individual systems through an approach via pseudo‐phase equilibria. Comparison between the “bridging theory” for semi‐dilute polymer solutions, originated by Koningsveld et al. (1974), and the model for the condensation of argon vapour by Gibbs, Pavlin and Yang (1983) reveals some common ingredients for a general but adaptable meanfield methodology. The mathematical mechanisms behind quasi‐linear “cross‐over” behaviour of phase loci and of plots for criti

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390114

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractA general theory of scattering by polymer solutions has been proposed recently. This theory uses as a parameter the excluded volumevbetween segments belonging to different chains. In this paper we discuss the effect of polymer concentration onv. As a first approximation one recovers the Flory expression for the free energy. As a second approximation one obtains an expression forvor χ as function of the polymer concentration. There is good agreement between theory and experiment for poor solvents and a volume fraction of polymer less than 0.25

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390115

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractNew catalyst systems for the synthesis of polypropylene and polypropylene copolymers have been developed. The growth mechanisms of morphological structure of the polymers and some features of the process are described. Some properties of the obtained homopolymers and copolymers are presented, and the advantages and future developments of the process technology are discussed.

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390116

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractA new reaction between a conjugated carbonyl group and an olefinic double bond is described. The reaction takes place in the presence of transition metal halides and represents a new route to several conjugated polymers. Investigations of the influence of the reaction conditions on the yield and the molecular weight of the polymeric products show that the reaction proceeds as a typical polycondensation. Starting from different monomers several well known and new conjugated polymers are prepared.

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390117

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe block copolymer poly(ethylene succinate)‐b‐poly(ethylene glycol) gave fibres that degrade rapidly and no tensile strength remained after 10 days of degradation, whereas fibres of the block copolymer poly(ethylene succinate)‐b‐poly(tetramethylene glycol) degraded more slowly and the tensile strength was lost after 170 days. The surface composition and the crystallinity of the poly(ethylene succinate) block are probably the properties that determine the rate of degradation. The results also show that it is possible to obtain degradable materials which are thermoplastic elastomers and that the rate of degradation can be varied by changing the polyether composition. The decrease in tensile strength seems to follow a three‐stage curve, where a plateau value is maintained for a certain time and then decreases rapidly to zero. This behaviour makes these block copolymers interesting as materials for degradabl

ISSN:0323-7648    

DOI:10.1002/actp.1988.010390118

出版商:Akademie Verlag GmbH    

年代:1988

数据来源: WILEY