摘要:

AbstractThe uniform structure of cellulose, combined with its hydrophilicity, biocompatibility, chirality, and structure‐forming capacity, as well as its broad synthetic potential, make the design of cellulose‐based advanced materials a challenge for polysac‐charide research. The synthesis of new cellulose products with regiocontrolled pattern of functionalization and of well defined supramolecular nanoscale architectures is a highlight in recent cellulose chemistry.The present feature will discuss regioselective functionalization of cellulose and cellulose derivatives with respect to reactivity of the polymer depending on molecular and supramolecular structure. Experimental examples of functionalization via ester intermediates of controlled stability as well as via protecting or activating ether groups are described and the efficiency of the reaction routes and procedures is evaluated.Moreover, problems and progress in techniques of product analysis and structure–property relationships as well as potential applications of regioselectively functionalized cellulosics are presented together with a discussion of possible future developments in cellulose ch

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480801

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe degree of branching (DB) as well as the ANB (average number of branches) of polymers obtained from polycondensation of AB2and ABm‐type monomers in general is analyzed in detail on the basis of kinetic considerations. Various possibilities for the enhancement of the DB of hyperbranched polymers beyond the limit for a random ABmpolycondensation (0.5 for AB2, 0.44 for AB3) are considered, i.e., (i) enhanced reactivity of linear vs. terminal units; (ii) polymerization of prefabricated, perfect dendritic units and (iii) the slow addition technique. For AB2monomers, the formation of terminal (T), linear (L) and perfect dendritic (D) units in the course of the random one‐pot polymerization is calculated. Furthermore, the evolution of the DB and ANB with conversion is calculated for ABmmonomers. It is shown that the definition of the DB for AB2systems (DB = 2D/(2D+L)) derived in the first paper on the DB (Acta Polym.1997,48, 30) in the case of a random one‐pot polycondensation exhibits the same conversion dependence as the branching parameter α = 1/2PA, defined by Flory for AB2polycondensations. The dilution principle is introduced, which is based on slow addition of ABmmonomers to a core molecule Bfor an ABm‐type hyperbranched molecule with an arbitrary DB. It is shown that the maximum DB value obtainable from such a dilution/slow addition process is 0.67 for AB2systems. Thus, the DB is considerably higher than in the case of a random one‐step polymerization (0.5). The DB for ABm‐type hyperbranched polymers prepared according to the dilution principle has been calculated t

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480802

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThis paper reports the polycondensation of benzyl 2‐amino‐2‐deoxy‐α‐D‐glucopyranoside hydrochloride (1) with carbon dioxide using the triphenylphosphine/carbon tetrachloride/DBU system as a condensing agent to give poly(urethane) (2). The polycondensation of1with CO2was carried out in DMF solvent in the presence of the condensing agent under CO2atmosphere. From the NMR and IR analyses of the product, the polymerization proceeded regioselectively to form2. The molecular weight was estimated as 2000–3000 by GPC measurement after acetylation of2, correspondi

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480803

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe amorphous polyester1aprepared by melt condensation of 1,5‐bis‐(9‐hydroxy‐1,4,7‐trioxanonyl)naphthalene (2a) and adipoylchloride (3a), which containsbis‐1,4,7‐trioxanonyl (triethyleneglycol) segments in its main chain, represents a matrix for ion‐conducting materials. Despite the fact that only triethyleneglycol segments are present, which are shorter than the minimum required for full solvation of Li+cations, ion‐conductivities of σ = 3.3 times; 10—5S cm—1at 368 K are found for Li+/1a0.25 (cationsperpolymer repeat unit). Hence, more than onebis‐1,4,7‐trioxanonyl segment (either intra‐ or interchain) has to be involved in Li+complexation. The σ value compares favorably with previous data for

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480804

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractPoly(dipentylsilylene) copolymers containing 4,7,10‐trioxadodecylmethylsilylene units as comonomer were synthesized via a Wurtz‐type coupling reaction from the corresponding dichlorosilanes. The copolymers were characterized by GPC and NMR spectroscopy. Solvent‐ and temperature‐dependent UV absorption was observed. The bulk polymers underwent broad endothermic transitions below room temperature, whose temperature and heat effect depended on the incorporation of comonomer. This suggested that the high‐temperature state can be described as a columnar mesophase corresponding to the well established case of the poly(dipentylsilylene). Correlated to this transition, the copolymers also showed thermochromic behavior at low temperatures. The materials could be oriented by shearing in the mesophase, which was demonstrated by polarized optical microscopy, polarized IR spectroscopy and UV spe

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480805

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe steady‐state fluorescence (SSF) technique was used to study interdiffusion of polymer chains across the particle–particle junction during film formation from hard latex particles. The latex films were prepared from pyrene (P) and naphthalene (N) labeled poly(methyl methacrylate) (PMMA) particles and annealed for long time intervals above the glass transition temperature (Tg) between 170 and 220°C. A novel correction method was suggested and employed to eliminate changing of the optical density of latex films after such annealing processes. P and N fluorescence intensities solely from the energy‐transfer processes were monitored versus annealing time and were used to measure the polymer chain diffusion coefficientsDpandDN, which were found to be between 4.34 × 10–14and 7.68 × 10–13cm2/s for an annealing temperature between 170 and 220°C. Using these diffusion coefficients with the Arrhenius relation, the diffusion activation energy for the polymer backbone was found to b

ISSN:0323-7648    

DOI:10.1002/actp.1997.010480806

出版商:Akademie Verlag GmbH    

年代:1997

数据来源: WILEY