摘要:

AbstractAddition of hydrogen iodide to isobutyl vinyl ether (1) yields 1‐(1‐iodoethoxy)‐2‐methylpropane (2). The cationic polymerization of1initiated by2/tetraalkylammonium salts (R4N+A−) shows the characterstics of a living polymerization. Different tetraalkylammonium salts were investigated. The coinitiator R4N+A−has no effect on the molar mass and the molar mass distribution of the resulting polymers. However, the rate of polymerization depends heavily on the nature and concentration of the coinitiator. The effect of the coinitiator is discussed on the basis of a special

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910101

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractGraft copolymers of butyl rubber (BR) with polytetrahydrofuran (PTHF) were prepared from bromobutyl rubber by a cationic “grafting‐from” reaction initiated by silver perchlorate at allylic bromine sites on the rubber. By studying the influence of variables, such as temperature etc., it was shown that initiation at −20°C for 30 min, followed by polymerisation at 0°C with a [AgClO4]/[Br]ratio of ca. unity, produced near optimum reaction conditions with grafting efficiencies>90%. Copolymers containing upto 40% of grafted PTHF were obtained by this means. The BR‐g‐PTHF copolymers have a two‐phase morphology comprising amorphous BR with crystalline domains of PTHF which function as points of reinforcement in the rubber

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910102

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe synthesis and characterization of thermotropic main‐chain liquid‐crystalline polyethers MBPE‐Xand copolyethers MBPE‐X/Ybased on 3‐methyl‐4,4′‐ethylenediphenol [1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane (MBPE)], which is flexible rod‐like mesogenic unit or a rod‐like mesogenic unit based on conformational isomerism, and flexible spacers containing an even number of methylene units,X,Y, are described. The particular examples presented in this paper refer to polyethers MBPE‐4, MBPE‐6, MBPE‐8, MBPE‐10, and MBPE‐12, and copolyethers MBPE‐X/Y; whereX,Y= 4, 6, 8, 10, 12. MBPE‐4, MBPE‐6, MBPE‐10 and MBPE‐12 are crystalline. MBPE‐8 displays an enantiotropic nematic mesophase. Copolymerization of MBPE with different pairs of spacers containing even numbers of methylene units leads to MBPE‐X/Ycopolymers displaying monotropic or enantiotropic nematic mesophases. Both liquid‐crystalline transition temperatures and the corresponding enthalpy changes of the copolymers represent weight‐averaged values of the similar parameters of the parent homopolymers. Extrapolation of the isotropic‐nematic and nematic‐isotropic transition temperatures and their corresponding enthalpy changes demonstrated that all homopolymers containing an even number of methylene units in the flexible spacer exhibit virtual nematic mesophases. The virtual isotropic‐nematic transition temperatures and the corresponding enthalpy changes were determined for MBPE‐4, MBPE‐6, MBPE‐10 and MBPE‐12. The virtual nematic‐isotropic transition and the co

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910103

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe synthesis and characterization of thermotropic main‐chain liquid‐crystalline copolyethers based on 3‐methyl‐4,4′‐ethylenediphenol [1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyhenyl)‐ethane (MBPE)], which is a flexible rod‐like mesogenic unit or a rod‐like mesogenic unit based on conformational isomerism, and pairs of flexible spacers containing odd and even numbers of methylene units,X,Y, i.e., MBPE‐X/Y, whereX/Y= 5/12, 5/10, 5/8, 6/11, 6/9, 4/11 and 4/9, are described. Copolymerization decreases the rate of crystallization and subsequently transforms virtual or monotropic mesophases of homopolymers into monotropic or even enantiotropic mesophases. Both liquid‐crystalline transition temperatures and enthalpy changes of the identical mesophases displayed by copolymers represent weight‐averaged values of the similar parameters of the parent homopolymers. Their extrapolation leads to the determination of the virtual mesomorphic transition temperatures and enthal

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910104

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSome unexpected results were observed in the phase transfer of catalyzed (PTC) (two phase, aqueous‐organic) polymerization of α,ω‐dibromoalkanes with sodium sulfide. Alkane dielectrophiles containing fewer than six methylene units give rise to large, and sometimes quantitative, amounts of cyclic thioethers. These cyclic sulfides are formed under “polymerization” conditions and can be minimized by using only the monomer as the organic phase. Alkane dielectrophiles containing more than six methylene units yield only polymer. When a comonomer system composed of a 1:1 mixture of 1,4‐dibromobutane (DBB) and 1,8‐dibromooctane (DBO) is employed, the resulting copolymer's molecular weight and polydispersity are vastly improved compared to the corresponding homopolymerizations. Microstructurally, this copolymer is formed by complete consumption of DBO and partial incorporation of DBB. The remaining DBB forms tetrahydrothiophene (THT). These two odd and seemingly conflicting results could not be explained by “normal” or “inverse” PTC extraction mechanisms. Support of this new mechanism is given in the PTC polymerization of DBO with sodium sulfide in the presence of a catalytic amount of THT. The resulting polymer is of very high molecular weight and narrow polydispersity; it also does not contain tetramethylene sequences. Using this new mechanism, all results suggest the participation of cyclic sulfides either facilitates cyclic formation or enhance polymer reactivity as controlled by the length of the

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910105

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract5,11,17,23‐Tetra‐tert‐butyl‐25,26,27,28‐tetrahydroxy‐2,8,14,20‐tetraoxocalix[4]arene (4) was synthesized by oxidation of the tetraacetate of 5,11,17,23‐tetra‐tert‐butyl‐25,26,27,28‐tetrahydroxycalix[4]arene (1). Compound4was characterized by chemical and spectroscopic methods. Reduction of4with hydrazine forms the starting material1. 4reacts with sodium borohydride to give 5,11,17,23‐tetra‐tert‐butyl‐2,8,14,20,25,26,27,

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910106

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe microstructure distributions of ethylene‐propene(EP) copolymers and propene homopolymers prepared with supported titanium catalyst were analyzed by13C NMR spectroscopy. A two‐site model with an isospecific site and a non‐stereospecific site was used to describe the stereospecific polymerization of propene. A second two‐site model with individualr1r2= 1 was applied to the analysis of the ethylene‐propene copolymerization. The addition of an external base, ethyl benzoate (EB), alters the relative concentrations of catalytic sites. Based on the comparison of the results from the homopolymers and copolymers prepared under different EB concentrations, the correlations between the stereospecificity and the activity toward the monomers were established: the isospecific site produces the copolymer with lower ethylene content; the non‐stereospecific site gives the copolymer with higher ethyl

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910107

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract1,3,5‐Trioxane (1) and 1,3‐dioxep‐5‐ene (2) were copolymerized with BF3OEt2at 65°C. The products, after base hydrolysis, were characterized by13C and1H NMR and were found to assume the chemical structure4of a copolymer containing oxymethylene and oxy‐2‐butenylene units with 4‐hydroxy‐2‐butenyl and methoxy end groups, with the ratio of hydroxy‐2‐butenylene to methoxy end groups varying with experimental conditions. The copolymer demonstrates crystallinity and thermal stability comparable to poly(trioxane‐co‐ethylene oxide)s. Copolymer melting point was observed to decrease with increasing comonomer incorporation. The upper limit for incorporation of the comonomer2was found to be ca. 4 mol per cent. Viscosity and end group analysis (by1H NMR) indicate molecular weights in the range of 104to 105. The comonomeric unit demonstrates the ability to act as both a stopper against unzipping and as a trap fo

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910108

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract1,2‐Epoxycyclohexane (1) was found to behave differently from propylene oxide (PO) in polymerization reactions with organozinc compounds as initiators. A chair‐type complex, [Zn‐MP]2,2, is the only compound that shows high catalytic activity for both polymerization of1and PO, following an anionic coordination mechanism. On the other hand, the polymerization of1with ZnEt2or (EtZnOMe)4as initiator proceeds according to a cationic mechanism. Cationic polymerization of1with ZnEt2has two modes of termination reaction resulting in the formation of terminal units containing vinyl ether and allyl ether moieties. The initiation and propagation mechanism of1by [Zn‐MP]2;2is similar to that of PO, but chain transfer reaction takes place in the polymerization of1owing to the low stability of the growing chain end. By using [Zn‐MP]2,2as initiator, it was possible to prepare a block copolymer consisting of an isotactic sequence of monomeric units of PO and a syndiotactic sequence of monomeric

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910109

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe aqueous‐phase polymerization ofN,N′‐methylenebis(acrylamide) initiated by potassium peroxodisulfate in the absence and in the presence of the anionic emulsifier sodium dodecylsulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization is found to be proportional to the 0,75 and 0,24 oder with respect to potassium peroxodisulfate andN,N′‐methylenebis(acrylamide) concentrations, respectively. On the other hand, it is independent of the concentration of sodium dodecylsulfate. This agrees with the polymerization of a monomer soluble in water. Therefore, the equations for a homogeneous polymerization were applied to evaluate the experimental results. The calculated ratiokp/kt0,5of the rate constants of propagationkpand terminationktfor theN,N′‐methylenebis(acrylamide) polymerization at zero conversion in the absence of emulsifier are scattered in the interval between 3,1 and 3,4 dm1,5· mol−0,5· s−0,5and in the presence of emulsifier in the interval between 2,4 and 3,5 dm1,5· mol−0,5· s−0,5. They are close to those obtained for the homogeneous polymerization of acrylamide in the aqueous phase. The lower values ofkp/kt0,5≈ 0,3–0,6 dm1,5· mol−0,5· s−0,5determined for the polymerization ofN,N′‐methylenebis(acrylamide) for conversions between 30 and 60% follow from the hindered termination reaction within the polymer particles. The polymer dispersions formed are unstable. The growth of the polymer particles proceeds predominantly by coalescence. This suggests a kinetics which does not follow the Smith‐Ewart theory but is characterized by a continuous particle nucleation and agglomeration. The interval 1 occurs at the beginning of the dispersion polymerization when polymer particles are being formed. Interval 2 follows, once the

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910110

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY