摘要:

AbstractSmall‐angle X‐ray scattering (SAXS) is a tool which allows the study of the structure and the interaction of polymer latexes with great accuracy. The low electron density of the polymers used for the synthesis of latex particles as e.g. polystyrene allows the matching of the contrast by adding sucrose to the serum. Thus, scattering intensities measured at different contrast, i.e., at different excess electron densities can be evaluated (contrast variation). This yields precise information on the radial electron density of the particles. In this article recent SAXS‐investigations on latex particles are reviewed. It is demonstrated that core‐shell latexes can be analyzed precisely by contrast variation. The same method can be applied to swollen latex particles to examine the polymer concentration near the boundary to the water phase. Here it is shown that the depletion of the polymer molecules near this boundary is very small which points to a minute wall‐repulsion effect. Since the excess electron density of polystyrene latex particles in water is very small, the scattering from adsorbed layers of surfactants dominates the measured intensity in this particular system. Therefore the adsorption equilibrium of a given surfactant as well as the competitive adsorption of two different surfactants on a polystyrene latex can be assesse

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971001

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

Abstract1,3‐Dipolar cycloaddition reactions have been used to prepare a large number of different heterocyclic and heteroaromatic polymers. Most of this work has been done in the 60's and 70's. Since then, interest in this field has vanished almost completely. While the number of polymer structures accessible by 1,3‐dipolar cycloaddition is very large, the high reactivity and tendency of the 1,3‐dipoles to undergo side reactions limits the successful applications in step growth polymer synthesis considerably.The “criss‐cross” cycloaddition reaction also proceeds via two consecutive 1,3‐dipolar cycloaddition steps. Its starting compounds, azines and diolefins or diisocyanates, are stable, can be purified easily, and do not undergo side reactions if the reaction conditions are chosen properly. Initially, the reaction between hexafluoroacetone azine and various diolefins was studied. This work was aimed at the preparation and structural characterization of soluble polymers. Later on, the “criss‐cross” cycloaddition between aromatic aldazines and diisocyanates was included in this research. Different azines and diisocyanates were studied to find the best compromise between reactivity of the monomers and solubility and glass transition temperature of the products. Due to the special reaction mechanism, the polymers have exclusively isocyanate end groups, independent of stoichiometry of the monomers and the conversion. Thus, this reaction is ideally suited for the preparation of telechelics. Prepolymers obtained by “criss‐cross” cycloaddition between 4‐methoxybenzaldazine and 4,4′‐diisocyanatodiphenyl ether were used as hard segments in segmented block copolymers. Those block copolymers with a hard segment content below 36% showed elastomeric behavior with ultimate elongations above 700% and tensil

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971002

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractCopolymers based on ethylene with different incorporations of 1‐hexene, 1‐octene and 1‐decene were obtained. There is not any marked variation of activity when different metallocenes were tested. The type and the concentration of the comonomer in the feed do not have a strong influence on the catalytic activity of the system, but the presence of the comonomer increases the activity compared with that in the absence of it. From13C NMR it was found that below 8% of comonomer incorporated the comonomer units appear isolated between polyethylene blocks, sequences of the type ethylene‐comonomer‐ethylene‐comonomer appear only above 8% of comonomer incorporated for all the systems studied. The reactivity of the comonomers for this particular system shows that the size of the lateral chain influences the percentage of comonomer incorporated, 1‐hexene being the highest one incorporated. The crystallinity of the copolymers exerts a linear relation with the amount of comonomer incorporated, and it is independent of lateral chain lengths. The molecular weight of the copolymers obtained was found to be dependent on the comonomer concentration in the feed, showing that there is a transfer reaction with the comonomer. The polydispersity (M̄w/M̄n) of the copolymers is rather narrow and dependent on the concentration of the comonom

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971003

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIn this paper we describe the light‐induced grafting reaction of poly(vinyl acetate) ontocatena‐poly[bis(4‐sec‐butylphenoxy)‐λ5‐phosphazene],catena‐poly[bis(4‐ethylphenoxy)‐λ5‐phosphazene] andcatena‐poly[bis(4‐methylphenoxy)‐λ5‐phosphazene], and the successive acid‐ (and base‐) catalyzed hydrolysis of the grafted macromolecule to poly‐(vinyl alcohol). The process was found to be dependent on the irradiation time, reaction temperature, relative monomer/methanol concentration in the reaction mixture, type of substituents present on the exploited phosphazene polymers, and on the crystallinity of these macromolecules. The new phosphazene grafted copolymers thus prepared have been characterized by IR spectroscopy, gravimetric ana

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971004

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA series of ethylene‐styrene copolymerizations was carried out in the presence of cyclopentadienyltitanium trichloride and methylalumoxane at 20°C and at different comonomer feed compositions. By sequential extraction a copolymeric material with a styrene units content up to 36 mol‐% can be separated from the homopolymeric products. Some considerations about the relative reactivity of the comonomers and the regioregularity of the styrene insertion are made on the basis of the13C NMR spe

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971005

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA series of α‐methylene‐N‐alkyl‐2‐pyrrolidone monomers with varying length of the alkyl chain from C1to C8were synthesised. The monomers were subjected to free radical polymerisation to yield a range of polymers each with a different balance in hydrophobic/hydrophilic properties originating from the pyrrolidone moiety and theN‐alkyl chain. The equilibrium water content of polymers crosslinked with ethylene dimethacrylate were found to decrease with increasing alkyl chain length. The glass transition temperatures of the polymers are reported ranging from 98°C to ‐5°C on going from the methyl to the octyl derivative. The thermal degradation of the polymers was studied using thermogravimetric analysis and pyrolysis gas chromatography‐mass spectroscopy. The polymers were found to degrade at ca. 400°C predominantly via an unzipping mechanism. Pyrolysis at 450°C resu

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971006

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAnionic living polystyrene and polyisoprene were allowed to react with sixtert‐butyl‐dimethylsilyl ethers of ω‐halo‐1‐alkanols1–6, the trimethylsilyl ether of bromohydrin (7), thetert‐butyldimethylsilyl ether of 4‐bromophenol (8), andtert‐butyldimethylsilyl 3‐chloropropyl sulfide (9), followed by acid‐catalyzed cleavage of SiO and SiS bonds to afford polystyrene and polyisoprene, respectively, with hydroxy or mercapto end groups. The alcoholic hydroxy groups were introduced quantitatively to the polymer chain end regardless of the kind of halogen atom, length of methylene spacer separating the protected hydroxy group from the halogen, and structure of protecting groups. Thetert‐butyldimethylsilyl ether of 4‐bromophenol (8) was not suitable for this reaction, since most (≈90%) of the original living polyisoprene was dimerized due to metal‐halogen exchange followed by the coupling reaction of the polymeric allyl bromide derivatives thus formed with remaining living polyisoprene. Polystyrene and polyisoprene withtert‐butyldimethylsilyl sulfide end group were obtained quantitatively by the reaction of their anionic living polymers with9. Generation of mercapto groups through deprotection was confirmed by I2oxida

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971007

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractReactions of anionic living polymers of styrene,tert‐butyl methacrylate, and 2‐(trimethylsiloxy)ethyl methacrylate with perfluoroalkyl (Rf) halides, such as C4F9(CH2)3I(1), (CF3)2CF(CF2)6I (2), C4F9(CH2)2I (3), C8F17(CH2)2O(CH2)4Br (4), were investigated to synthesize well‐defined polymers with Rf groups at the chain end. Nucleophilic attack of living polystyryl anions on1and4quantitatively proceeds to give the Rf‐terminated polystyrenes with predictable molecular weights and narrow molecular weight distributions, while low functionalities (0–50 mol‐%) were obtained in the cases of2and3, on account of electron transfer and ß‐proton elimination. The anionic propagating ends of the methacrylates with potassium countercation react with1and4to afford the Rf‐terminated poly(methacrylate)s in high efficiency. Poly[2‐(trimethylsiloxy)ethyl methacrylate] produced was deprotected under acidic conditions to give poly(2‐hydroxyethyl methacrylate) bearing the Rf‐terminal group. However, the reactions of the propagating enolate with lithium countercation with1and4result in low yields of the Rf‐terminated polymers. From the surface analyses of the Rf‐terminated polymer films by X‐ray photoelectron spectroscopy and contact angle measurements, a remarkable enrichment of the Rf group at the dry surface and a surface restructuring corresponding to the enviro

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971008

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThermal properties of poly(ether ether ketone ketone) (PEEKK)/poly(ether biphenyl ether ketone ketone) (PEDEKK) copolymers were investigated by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperature (Tg) increases from 154°C to 183°C as the content of PEDEKK units increases. The melting point (Tm) of the copolymers varied in the range between 314°C and 409°C and showed the behavior of eutectic type copolymer. From the investigation of the crystallization behavior of the copolymers, it was found that the cold‐crystallization temperature (Tc′) of the amorphous copolymers assumes a maximum value for the copolymer with a mole fraction of the PEDEKK segment (nB) of about 0.6, isothermally crystallized PEEKK and the PEEKK/PEDEKK copolymer exhibit double‐melting

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971009

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe macroviscosity of a single‐phase toluene/styrene/sodium bis(2‐ethylhexyl)sulfosuccinate/water/acrylamide Winsor IV inverse microemulsion prior to polymerization as a function of the volume fraction ϕaw, of the dispersed aqueous (water + acrylamide) phase at 20°C reaches three distinct maxima of 16, 66, and 30 mPa ·;s for ϕawvalues 25%, 46%, and 62%, respectively. At 60°C, the viscosity maxima practically vanish and the macroviscosity of the dispersion systems is in the range of 5–7 mPa · s. The overall maximum (co)polymerization rate of acrylamide and styrene increases with increasing ϕaw. On the other hand, an increase of the mass ratio styrene/toluene leads (for a given ϕawvalue) to a decrease of the overall maximum (co)polymerization rate regardless of the nature of the initiator used. This points to an effective competition between monomer in the oil phase (slow homopolymerization of styrene and/or (co)polymerization of styrene with acrylamide dissolved in the oil phase) and monomer in the water pools of inverse micelles (rapid homopolymerization of a major part of acrylamide) for initiator radicals and/or (co)olig

ISSN:1022-1352    

DOI:10.1002/macp.1996.021971010

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY