摘要:

AbstractExperiments with seeded polymerization in emulsifier‐free systems were carried out with styrene in order to test the theory of particle nucleation presented in the first article in this series. The effect of amount, size, and surface charge density of the seed particles on the formation of new particles was investigated. An expression for the capture rate of oligomeric radicals from the water phase was evaluated in which the rate of capture was considered to be governed by the absorption of oligomers with chain length one less than the critical chain length for precipitation of the oligomer. Coagulation of primary particles was also included in the expression for the number of new particles obtained in the system. Limited coagulation of primary particles with already formed particles and with seed particles was found to play an important role in determining the final number of new particles found at the end of the run

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171001

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractStudies of seeded and unseeded polymerization of styrene using sodium dodecylsulfate as emulsifier have been carried out in order to investigate the mechanism of particle nucleation in such systems and to test the theory presented in Part I of this series. The rate of capture of water‐soluble oligomeric radicals was considered to be governed by absorption of oligomers with chain length one less than the critical chain length. It was concluded that the micelles became the dominating loci for particle nucleation above CMC for the emulsifier. A complete nonsteady‐state model for particle initiation above CMC which takes into account radical desorption and reabsorption has been developed. It was indicated that, even for styrene, desorption of radicals may play a role in controlling the radical and particle number of interval I under certain conditions. The model also showed that the efficiencies of particles in absorbing radicals could be calculated from physical parameters, such as diffusion constants and surface charge densities, which are available for the sys

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171002

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractNucleation in finely dispersed monomer emulsions in competition with homogeneous and micellar mechanism was studied. The emulsions were prepared with a high‐pressure homogenizer under varying homogenizing conditions and made stable by the addition of hexadecane to the monomer. Sodium dodecyl sulfate was used as emulsifer. The number of particles in latexes polymerized with potassium persulfate and benzoyl peroxide initiators was measured and plotted as a function of the free emulsifier concentrations. With persulfate initiator the particle number achieved a minimum in the transition region between droplet and water phase–micellar nucleation mechanisms. With very fine emulsions Smith–Ewart case II kinetics withn= 0.5 applied. The reaction rate, which differed from conventional emulsion polymerizations, decreased with time up to the point at whichnbegan to increase. In these runs the particle size distribution became nearly monodis

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171003

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractInterpenetrating polymer networks (IPN) of polyurethane and polyurethane acrylate were obtained. A small‐angle x‐ray scattering technique was used to study the character of the microheterogeneities in IPN and their variation with composition. It was shown that IPN formation is accompanied by phase separation of constituent components. On the basis of experimental data, which involved the mean square of fluctuations of electron densities in IPN, scattering intensity extrapolated to the zero angle, thickness of the transition layer between two phases, degrees of component segregation and diffuseness of phase boundary, degree of miscibility of components on the molecular level, specific inner surface, and the extent of the heterogeneous regions and their mean radius were determined. Parameters that characterize the intensity of microphase separation are dependent on composition: at a higher content of PUA the segregation degree is higher than that of low content. The dimensions of the heterogeneous regions, which extend from one network to the matrix of the other, depend on the composition of IPN and changes most sharply in the range of mean composition due to phase inversion. Thickness of the transition layer ranges from 20 to 4

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171004

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA polymer with high aromatic ring content in the chain backbone usually has high heat and flame resistance. Three diglycidyl ethers of epoxy resins were prepared from bisphenol A (DGEBA), phenolphthalein (DGEPP), and 9,9‐bis(4‐hydroxyphenyl)fluorene (DGEBF) in a study of the relation between the cured polymer structure and properties. The epoxy resin prepared from phenolphthalein was separated by liquid chromatography and three fractions were obtained. The fractions had a basic structure of 3,3‐disubstituted phthalide and differed only in molecular weight. The DGEPP resin changed color from yellow to red after mixing with trimethoxyboroxine (TMB), the curing agent, and to orange after completing the curing cycle. To prepare a highly crosslinked material with good thermal stability, TMB with three active Lewis sites in a molecule was used as the curing agent. The reactivity of the three different resins toward TMB, measured by differential scanning calorimetry (DSC), was DGEBA>DGEBF>DGEPP. For the same curing conditions the order of crosslink density was DGEBA>DGEPP>DGEBF. To modify the flammability of DGEBA, the conventional epoxy resin, it was copolymerized with DGEPP and DGEBF, the higher‐performance epoxy resins. The glass transition temperatures of poly(DGEBA‐co‐DGEPP) and poly(DGEBA‐co‐DGEBF) systems deviated from this relationship. The DGEBF copolymers showed an increased char residue (40 wt % at 700°C) at 20 mole % of DGEBF. This deviation may be due to the lower crosslinking densit

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171005

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThree cured epoxy resins were investigated under various degradation conditions by Fourier transform infrared (FTIR) spectroscopy for measurement. The epoxy resins were the diglyadyl ethers of bisphenol A (DGEBA), phenolphthalein (DGEPP), and 9,9‐bis(4‐hydroxyphenyl)fluorene (DGEBF). The thermal stability order of functional groups that incurred DGEBA was total methyl group ∼ total benzene ring>methylene>p‐phenylene>ether linkage>isopropylidene. The oxidative thermal and photodegradation processes were found to be related to the classical autocatalytical oxidation of aliphatic hydrocarbon segments. The Wieland rearrangement, Norrish‐type reaction, Claisen rearrangement, and other possible degradation mechanisms were suggested by

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171006

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractViologens that bore a terminal vinyl group were synthesized by four sequences of reactions: (1)N‐vinylbenzyl‐N′‐n‐propyl‐4,4′‐bipyridinium bromide chloride (V) was synthesized by the reaction of 4‐(4′‐pyrodyl)‐N‐n‐propyl pyridinium bromide (III) with vinylbenzyl chloride; (2)N‐β‐acrylamidoethyl‐N′‐n‐propyl‐4,4′‐bipyridinium dibromide (IX) was synthesized by the Menschutkin reaction of III with 2‐aminoethyl bromide hydrobromide and subsequent reaction with acryloyl chloride; (3)N‐β‐methacryloyloxyethyl‐N′‐n‐propyl‐4,4′‐bipyridinium dibromide and its analogs (XI) were synthesized by the reactions of III with the corresponding acyloxyalkyl bromides; and (4)N‐vinyloxycarbonylmethyl‐N′‐n‐propyl‐4,4′‐bipyridinium bromide chloride (XIII) was synthesized by the reaction of III with vinyl chloroacetate. With the exception of monomer XIII in which hydrolysis in large extent was observed during attempted polymerization, the synthesized monomers polymerized smoothly in aqueous solutions by a conventional radical procedure. Comparisons of the absorption peaks of the radical cations produced by reductions in aqueous solutions with those produced in films by ultraviolet (UV) irradiation indicate that t

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171007

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA spectrophotometric method was used for the quantitative determination of binding in the poly‐vinylpyrrolidone–rose bengal system. Binding of tiron, another anionic dye, onto polyvinylpyrrolidone was investigated by equilibrium dialysis. Comparison of binding constants of the two systems indicated the importance of hydrophobic interactions in binding. Because rose bengal can serve as a fluorescent probe, a fluorimetric method was also used and the increase in fluorescence confirmed the significance of hydrophobic interactions in the binding of the dye onto the poly

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171008

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractDiethyl 2‐vinylcyclopropane‐1,1‐dicarboxylate (Ia), 2‐vinylcyclopropane‐1,1‐dicarbonitrile (Ib), ethyl 1‐cyano‐2‐vinylcyclopropanecarboxylate (Ic), and 1,1‐diphenyl‐2‐vinylcyclopropane (Id) were radically homo‐ and copolymerized. Ia, Ib, and Ic polymerized cleanly in 1,5‐type ring‐opening fashion to yield polymers of high molecular weight. Id failed to homopolymerize but copolymerized with common monomers which included maleic anhydride. Infrared (IR) spectra indicated that the double bonds of the polymer chains were in trans form. All polymers were soluble in solvents and solution‐cast films were clear and flexible, showingTgvalues in the 25–40°C range. Model reactions of those monomers with benzenethiol also indicated predominant 1,5‐addition reactions. From the results of our investigation it was concluded that the driving force for the facile radical 1,5‐polymerization of Ia, Ib, and Ic was the stabilization o

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171009

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractAmong the four 1,1‐disubstituted 2‐vinylcyclopropanes, diethyl 2‐vinylcyclopropane‐1,1‐dicarboxylate (Ia), 2‐vinylcyclopropane‐1,1‐dicarbonitrile (Ib), ethyl 1‐cyano‐2‐vinylcyclopropanecarboxylate (Ic), and 1,1‐diphenyl‐2‐vinylcyclopropane (Id), Ib and Ic polymerized well with sodium cyanide inN,N‐dimethylformamide. Ib was most reactive and a polymer (IIb) from Ib exhibited an inherent viscosity of 1.05 dl/g (concentration of 1.0 g in 100 ml of 95% H2SO4). All experimental results indicated that the polymerization proceeded by ring opening and that the structure of the polymers had pendant vinyl groups. The polymer IIc from Ic was soluble in common solvents like acetone, but IIb was soluble only in 95% H2SO4. Reactions of those compounds with benzenethiolate ion in ethanol yielded addition products that supported the ring‐opening polymerization of those monomers. In the postulated mechanism of polymerization cyanide ion attacks the carbon of a cyclopropane ring with electron‐releasing vinyl group and the resulting anion is thereby stabilized by two electron‐withdrawing substituents. The propagation takes place by the reaction of the

ISSN:0360-6376    

DOI:10.1002/pol.1979.170171010

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY