摘要:

AbstractThe influence of the temperature of the meltT1on the kinetics and the morphology of a semicrystalline polymer (poly(oxymethylene)) was investigated using thermal analysis and optical microscopy. The thermodynamic melting pointT f0and the enthalpy of melting at thermodynamical equilibrium ΔH f0were determined by extrapolation of the graphsTf=f(Tc) and ΔHf=f(Tc); (T f0= 198°C, ΔH f0= 251 J/g). For different temperatures of the melt (T1= 185°C, 195°C, 205°C), isothermal and non‐isothermal crystallizations were analysed using the Avrami and Ozawa equations. Nucleation and spherulitic growth in this polymer were studied by using optical microscopy at elevated temperatures. Using different analyses, we observed initial nucleation followed by spherulite growth with the following influence of the temperature of the melt on the distribution and the number of spherulites:T1T f0gives rise to f

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910201

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe molecular species proposed for the initial steps in the cationic polymerization of alkenylfurans were modeled by MNDO theoretically fully optimized structures. It was confirmed that the anomalous reactivity of ring C‐5 of the monomers is determined by HOMO electron densitites, whereas calculated proton affinities from the semiempirical heats of formation fail to explain the low temperature experimental behavior of 2‐vinylfuran (1c) from the point of view of stability of intermediate species. However,ab initio4‐31G calculations of proton affinities agree with the experimental facts and allow further explanations of the reactivity of furan derivatives in electrophilic

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910202

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractMonte Carlo calculations for a modification reaction of 1,4‐polybutadiene were carried out. The simulated process consisted in the substitution in α‐position to the double bond, partially coupled with double‐bond shift. The reaction model included mono‐ and disubstitution (one or two substituents at a carbon atom) and the formation of substituted double bonds in shift reactions. The number of molecules, the degree of polymerization and the degree of substitution were varied. The resulting multicomponent copolymers were evaluated with respect to different units (considered from one double bond to the next) and to their mole fractions. For example, more than 800 different units resulted for a mean of two substituents per unit. Units with up to 10 carbon atoms of the chain were found. Small molecule collectives gave representative results if only units above a minimum mole fraction were considered. The constitution of the products depended on the molecular size in the oligomer range. The distribution of the length of the units and of the number of substituents in a unit were de

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910203

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractNovel segmented multiblock copolymers (7) were synthesized by linking poly(ethylene oxide) (PEO) blocks with poly(β‐benzylL‐aspartate)(PBLA) blocks via urethane and urea bonds, which were formed by the reaction of 4,4′‐methylenediphenyl isocyanate (5) with the terminal hydroxyl groups of α‐hydro‐ω‐hydroxypoly(oxyethylene) (4) and the terminal amino groups of poly(β‐benzylL‐aspartate)‐block‐iminohexamethyleneimino‐block‐poly(β‐benzylL‐aspartate) (3) [prepared from 1,6‐hexanediamine (1) and β‐benzylL‐aspartateN‐carboxy anhydride (2)], respectively. Membranes with various water contents were obtained from these copolymers by changing the lengths of the PEO and PBLA segments. The study of the permeation of 1‐phenyl‐1,2‐ethanediol, vitamin B12and myoglobin through the membranes showed a high dependency of the pe

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910204

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract3‐Dodecylthiophene (1a) and 3‐methylthiophene (1b) were copolymerized electrochemically. The visible and IR spectra of the neutral copolymers prove the copolymers to be of random structure, which can be denoted as that of poly(3‐alkyl‐2,5‐thienylene)s.1bpolymerizes with preference over1a. With increasing fraction of monomeric units of1bin the copolymers, the conductivity increases and the solubility of the neutral copolymers decreases. The copolymer containing 58 mol‐% monomeric units of1bhas a high conductivity of 220 S/cm and a good solubility of 75 wt.‐% in chloroform.1H NMR spectra of poly(3‐dodecylthienylene) and copolymers show two chemical shifts for the α(1)‐methylene protons of the monomeric units of1aas well as of the methyl protons of the monomeric units of1b. This fact may be explained by the presence of head‐to‐head a

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910205

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractPolymer‐water interaction parameters, sequence length distributions and contents of total, freezing and non‐freezing water have been discussed for a family of hydrogels. The xerogel precursors containedN‐vinyl‐2‐pyrrolidone (VP) with several co‐monomers of different levels of hydrophobicity present in the xerogel over a wide range of composition. Common trends in the behaviour of these systems have been noted and rationalised. In particular the findings indicate that (i) in the poly‐VP hydrogel ther are ca. 8–10 molecules of non‐freezing water per VP unit and (ii) in the copolymeric hydrogels the maximum occurring in the variation of mole fraction of VP versus mole fraction of water is due substantially to the sharp increase in uptake of freezing (or bulk) water by copo

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910206

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe γ‐ray initiated copolymerisation ofN‐vinyl‐2‐pyrrolidone with methyl methacrylate in the presence of crosslinker has been effected to high conversion. At two fixed compositions of the principal monomers, the inclusion of different concentrations of the tetrafunctional crosslinkers ethylene dimethacrylate and a low molar mass poly(ethylene glycol) dimethacrylate produced crosslinked xerogels, which were subsequently swollen in water and 1,4‐dioxane to yield hydrogels and organogels, respectively. These gels were characterised by determinations of sol fraction, equilibrium solvent content and uniaxial compression stress/strain measurements. Differences among the swelling and mechanical properties according to the nature and concentration of crosslinking agent and according to the nature of the swelling medium are noted and

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910207

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe molecular motions of three kinds of poly(γ‐alkylarylL‐glutamate)s (1–3) having a phenylene or a biphenylylene group and alkyl groups with various length, containing 6 to 22 carbon atoms, were investigated by means of13C NMR spectroscopy as a function of temperature. The observed range of temperature covers the “crystal‐to‐liquid‐crystal” phase transition temperature,Tm. It was found that these phase transitions are caused by an increase of the motions of aromatic or alkyl groups in the side chain, depending on the samples, and that the motion of main chains of polymers1–3with α‐helical conformation does not occur on the NMR time scale at least up to 160°C. The degree of the mobility of the alkyl chain in the side chain of1–3depends

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910208

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractConformational and packing energy calculations were performed on crystalline isotacticcis‐1,4‐poly(1,3‐pentadiene). Internal parameters corresponding to a chain conformation similar to that of other polydienes were found by conformational energy calculations. The packing energy calculations indicate that the most stable mode of packing is obtained in theP212121space group. A possible structure of the polymer is also sugg

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910209

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper describes the key to successful metathesis polycondensation chemistry. Model compound reactions with styrene and styrene derivatives show that metathesis chemistry can occur exclusively if carbocation formation can be obviated through the proper choice of a Lewis acid free catalyst. Vinyl terminated oligo(octenylene)s were synthesized in this manner, which in turn were converted to polymers of high molecular weight.

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910210

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY