摘要:

Abstract2‐Mono‐ and 2,4,5‐trisubstituted 1,3‐dioxolan‐2‐ylium salts were reacted with dimethoxymethane representing the model of the polydioxolane chain. The products were identified and analysed by means of1H NMR spectroscopy and gas chromatography. The reaction was found to proceed mainly via interchange of the C‐2 carbon atom of the salt and the methylene group of dimethoxymethane yielding 1,3‐dioxolane or 4,5‐disubstituted dioxolane and the unstable dimethoxymethylium derivative, which decomposes into the respective methyl ester and methyl cation. The formation of some by‐products follows the main reaction path. The amount and the kind of substituents as well as the configuration influence the reactivity of the salts in the pro

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880401

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractSyntheses of polymers on the basis of betulinol (1), a pentacyclic triterpene glycol obtained from the birch bark, were investigated. Catalytic polyesterification of1with terephthaloyl chloride in various solvents gave only oligomers. Kinetic investigations indicated a very low activity of the hydroxyl groups of1. Chemical modification of betulinol revealed the possibility of a successful addition of its OH‐groups to anhydrides at high‐temperature. Unsaturated polyesters, based on maleic anhydride, betulinol and acyclic glycols, were synthesized and investigated. Samples of betulinol‐containing polyesters cured by copolymerization with styrene show improved water and chemical resis

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880402

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effect of 2,2′‐azoisobutyronitrile (AIBN) on the kinetics and mechanism of emulsion polymerization of butyl methacrylate was studied in the presence of anionic emulsifier disodium dodecylphenoxybenzene disulfonate (Dowfax® 2A1) at 60°C. The ratio between the proportion of the polymerization in monomer droplets and that of the polymerization in the aqueous phase was determined for the overall initial rate of butyl methacrylate polymerization in the region of the increasing polymerization rate (interval I). Using the model of polymerization in discrete particles, the portion of the polymerization in monomer droplets with a diameter of 100 nm in the overall polymerization rate is 24,4%; the portion of the polymerization in the water phase is only 0,022% for a concentration of Dowfax® 2A1 of 5 · 10−2mol · dm−3, and 60,4% and 0,054% for a Dowfax® 2A1 concentration of 1 · 10−2mol · dm−3. The exponent of the emulsifier concentration in the equation for the polymerization rate is 0,56 for interval I and 0,36 for interval II; the exponent for the concentration of AIBN over the conversion range between 0 and 30% is 0,34. For the proposed reaction mechanism it is assumed that 2‐cyanoisopropyl radicals, generated from AIBN in the water phase, are responsible for the initiation of polymerization in micelles swollen by monomer and in polymer/monomer particles. Polymer/monomer particles are formed also by co‐precipitation of oligomer radicals, which in turn are formed by polymerization of monomer molecules present in the water phase. Polymerization within monomer droplets has no significant influence on the course of

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880403

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe applicability of the modified Smith‐Ewart model to the butyl methacrylate emulsion polymerization in interval II, initiated by both 2,2′‐azoisobutyronitrile (AIBN) and ammonium persulfate at 60°C, was tested. The equilibrium monomer concentration in the latex particles in interval II was found to be constant and independent of the emulsifier concentration and the initiator type used. The rate of initiation increases with increasing emulsifier concentration for the polymerizations initiated with a water‐soluble initiator. In the systems with the oil‐soluble initiator, the rate of initiation is independent of the emulsifier concentration. The rate of polymerization increase with increasing emulsifier concentration for both initiator systems. In the system with the oil‐soluble initiator lower values of the polymerization rate and higher values of the viscosity‐average molecular masses of the polymer were observed. The number of particles, the radical concentration within polymer particles and the calculated rate of polymerization increase, while the mean particle radius decreases with increasing concentration of the emulsifier for both systems. The average‐number of radicals per particle and the ratio of the rate constants for propagation and termination was found to be independent of the emulsifier concentration and the initiator type. A good agreement was observed between the estimated and observed particle radii for both initiator systems. The Smith‐Ewart model was found to be applicable for the emulsion polymerization of butyl methacrylate initiated by both ammonium p

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880404

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe reaction conditions for the ring‐opening polymerization ofcis‐3,4‐dimethoxyoxolane (1,4‐anhydro‐2,3‐di‐O‐methyl‐D‐erythritol,3) using fluorosulfonic acid as initiator are described. The resulting polyether4, poly[oxy(2,3‐dimethoxytetramethylene)], is characterized by elucidation of M̄nand M̄w, elemental analysis,1H NMR spectroscopy as well as terminal group determination. The optimum conditions for obtaining high molecular weight polymers4are es

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880405

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractMonoazacrown ether containing styrene derivatives and monoazacrown ether end‐capped 3‐(or 4‐)vinyl substituted styrene oligomers and polymers were synthesized using 1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (1a).N‐Lithio‐1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (1b) reacts with styrene to form a 1:1 adduct,N‐phenethyl‐1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (4). The reactivity of1btoward styrene, however, is lower than that of other lithium dialkylamides such a lithium diethylamide.1breacts also with divinylbenzene to form a 1:1 adduct,N‐(4‐vinylphenethyl)‐1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (7), in non‐polar media. The reactivity of1btoward divinylbenzene is much higher than toward styrene. The yield of the 1:1 adduct7was found to attain more than 70% in cyclohexane. In polar media, however,1binduced a prompt polymerization of divinylbenzene to form asolublepolymer, each molecule of which was found to have one crown ether unit at the end of the polymer chain and

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880406

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effect of the nature of the crosslinking agents in template‐imprinted polymers on the selectivity during racemic resolution was investigated. Ethylene dimethacrylate was found to be the best crosslinking agent. The highest selectivity was achieved with polymers which have been prepared with 70‐95% crosslinking agent in the monomeric mixture. A new optically active crosslinking agent, 1,4;3,6‐dianhydro‐D‐sorbitol 2,5‐dimethacrylate, was synthesized and was used for the preparation of template‐imprinted polymers. Interpenetrating networks consisting of two different crosslinking systems did not bring about any significant improvement in selectivity for racemic resolution. A strong temperature effect for racemic resolution was observed; an ethylene dimethacrylate‐crosslinked, template‐imprinted polymer showed an optimum selectivity at 75°C with a ratio of distribution coefficients of the D‐ and L‐isomers of α = 4,56 for the separation of the r

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880407

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe influence of the structure of the binding sites in template‐imprinted polymers on the selectivity for racemic resolution was investigated, taking boronic acids as the binding sites. A number of different polymerizable boronic acids, possessing varying degrees of flexibility between the polymerizable double bond and the boron, were synthesized and were bound to the phenyl α‐D‐mannopyranoside template. After polymerizing to highly crosslinked polymers and splitting off the template, the selectivity for racemic resolution of the racemate of the template was investigated. An inverse relationship between the flexibility of the binding sites and the selectivity for racemic resolution was ob

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880408

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractBiological materials, rich in hemicelluloses (birch and pine wood, wheat straw and rice hulls) were disintegrated batchwise in a flow reactor with pure water at elevated temperatures and pressures. The resulting extractives and residual fibre compounds were characterized. Because of rapid removal of carbohydrate based extractives from the hot reaction zone, the degradation of pentosans and hexosans to furfural and hydroxymethylfurfural could be limited to only a small amount. Contrary to normal prehydrolysis conditions employing a sealed batch reactor, temperatures of 190 to 210°C and residence times of goods of 60 min are the optimum. Thus, hemicelluloses are dissolved and isolated with up to more than 90% yield. At temperatures above 225°C severe destruction of hemicelluloses and solvolysis of cellulose starts. Depending on disintegration temperatures, pentosan average molecular weights (M̄w) vary in case of birch wood between 3800 at 150°C and 900 at 225°C. The content of monomers rises with temperature and reaches a maximum of 45% at 225°C.DPwof residual cellulose is also temperature dependent and varies in case of birch wood and wheat straw between 1500 and 450. Lignin, which is mostly not dissolved, can be removed almost quantitatively by further treatment of the residue with ethanol/water at 250°C, thus allowing the isolation of relatively pure cel

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880409

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractA novel method was applied to improve the activity of enzymes immobilized in photocrosslinked poly(vinyl alcohol). Whereas the addition of glycerol to photosensitive poly(vinyl alcohol), bearing a styrylpyridinium group, diminishes the rate of photocrosslinking as well as the mechanical strength of the insolubilized gel, no considerable decrease in the rate of photoreaction was observed when poly(vinyl alcohol) was mixed with poly(ethylene glycol). This difference is based on the phase separation of the two water‐soluble polymers, resulting in the formation of a porous structure of the photocrosslinked gel. Immobilization of invertase in the photocrosslinked gel in the presence of poly(ethylene glycol) changes the activity, because of the case of diffusion of the substrate into the porous matri

ISSN:0025-116X    

DOI:10.1002/macp.1987.021880410

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY