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1.
Norman G. Gaylord Achyut B. Deshpande Sunit S. Dixit Sukumar Maiti Birendra K. Patnaik 《Journal of polymer science. Part A, Polymer chemistry》1975,13(2):467-482
α-Methylstyrene (MS) and isobutyl vinyl ether (VE) readily polymerize, styrene (S) polymerizes to a small extent, and isobutylene (IB), butadiene (BD), and isoprene (IP) fail to polymerize in the presence of catalytic amounts of AlCl3 when propionitrile, ethyl propionate, and methyl isobutyrate are used as reaction media. MS polymerizes readily and S polymerizes with difficulty in the presence of AlCl3 to yield homopolymers when acrylonitrile (AN) is present and copolymers with ethyl acrylate (EA) and methyl methacrylate (MMA). VE readily homopolymerizes, while IB, BD, and IP fail to polymerize in the presence of AlCl3 and the acrylic monomers. VE readily homopolymerizes, S and MS polymerize to a very small extent, and IB, BD, and IP do not polymerize in the presence of ethylaluminum sesquichloride (EASC) in polar solvents. VE readily homopolymerizes in the presence of EASC and the acrylic monomers. MS polymerizes to a small extent in the presence of EASC and the acrylic monomers to yield equimolar copolymers with EA and MMA and a mixture of cationic homopolymer and equimolar copolymer with AN. S yields equimolar copolymers in low yield in the presence of EASC and the acrylic monomers. IB, BD, and IP in the presence of EASC do not polymerize to any significant extent when EA is present, form AN-rich copolymers and yield poly(methyl methacrylate) in the presence of MMA. A revised mechanism is presented for the formation of cationic, radical, random, and alternating copolymers as well as alternating copolymer graft copolymers in the copolymerization of donor and acceptor monomers. 相似文献
2.
Norman G. Gaylord Birendra K. Patnaik Zvonimir Janovic 《Journal of polymer science. Part A, Polymer chemistry》1973,11(1):203-214
Equimolar alternating copolymers of styrene and methyl methacrylate (prepared with Et1.5AlCl1.5, SnCl4, and ZnCl2) as well as equimolar random copolymer were treated with polyphosphoric acid at 135°C. The extent of cyclization of the alternating copolymers was about 40%, independent of the cotacticity of the copolymer, and there was little or no crosslinking. The random copolymer underwent only 10% cyclization and considerable crosslinking. The extent of cyclization of the alternating copolymer of styrene and methyl acrylate (prepared with Et1.5AlCl1.5) was the same as that of the random copolymer and was lower than that of the corresponding methyl methacrylate copolymer. Both alternating and random copolymers underwent extensive crosslinking. 相似文献
3.
Understanding the kinetics of grain growth, under the influence of second phase (such as impurities, voids and bubbles) is fundamental to advances in the control of microstructural evolution. As a precursor to this objective, we have investigated the grain growth kinetics in a polycrystalline material using a standard Q-state Potts’ model under Monte Carlo settings. Based on physical reasoning, new modifications are suggested to circumvent some of the disadvantages in the basic Potts model. The efficacy of these modifications vis-à-vis the basic model is verified. The influence of second phase particles on the impurity loaded grain boundaries is investigated for the study of grain growth kinetics. 相似文献
4.
We present a study of the magnetic properties of Co nanoparticles having a combination of both spherical and disk shapes. The hcp Co nanospheres with an average diameter of 11 nm and nanodiscs of dimensions ∼2.5×15 nm2 were prepared by thermal decomposition of di-cobalt octacarbonyl in the presence of an amine surfactant. The as-synthesized nanoparticles were oxidized to grow an antiferromagnetic layer. High resolution transmission electron microscopy showed the presence of a ferromagnet/antiferromagnet (Co/CoO) interface with a 2.2-nm thick CoO shell on the spherical nanoparticles and 0.5 nm thick on nanodiscs. We report the temperature and field dependent DC magnetization, frequency, field, and temperature dependent AC susceptibility, and the radio frequency transverse susceptibility. A low temperature paramagnetic behavior was observed in the DC magnetization at high fields and is assigned to defects in the CoO shell that are not coupled to the antiferromagnetic lattice. Our results support the existence of a low temperature frozen, disordered magnetic state, characterized by a strong exchange coupling between the structurally disordered, spin-glass CoO shell and Co core. 相似文献
5.
Abstract The copolymerization of styrene (S) with methyl acrylate (MA) and with methyl methacrylate (MMA) in the presence of AlEt3 yields equimolar, alternating copolymers while no polymer is formed in α-methylstyrene (MS)-MA and MS-MMA systems. In the presence of AlEt1.5Cll,5 (EASC), S-MA and S-MMA yield alternating copolymers, S-methyl a-chloroacrylate (MCA), MS-MA and MS-MMA yield a mixture of alternating and cationic polymers, and MS-MCA yields cationic polymer only. In the presence of A1C13, S-MA and MS-MA yield a mixture of alternating and cationic polymers and S-MMA and MS-MMA yield cationic polymer only. The cotacticity distributions of the alternating S-MA and S-MMA copolymers prepared in the presence of AlEt3, EASC, and A1C1, are the same; the coisotactic, co-heterotactic, and cosyndiotactic fractions being approximately in the ratio 1:2:1. The cosyndiotactic fractions of the alter-nating copolymers prepared in the presence of EASC are in the order MS-MMA > MS-MA > S-MCA > S-MMA=S-MA. 相似文献
6.
Nonlinear Dynamics - Many physical processes in nature exhibit complex dynamics that result from a combination of multiscale, nonlinear, non-local, and memory effects. Recent experimental... 相似文献
7.
Smita Patnaik Aaron D. Sadow 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2527-2531
The high catalytic reactivity of homoleptic tris(alkyl) lanthanum La{C(SiHMe2)3}3 is highlighted by C?O bond cleavage in the hydroboration of esters and epoxides at room temperature. The catalytic hydroboration tolerates functionality typically susceptible to insertion, reduction, or cleavage reactions. Turnover numbers (TON) up to 10 000 are observed for aliphatic esters. Lanthanum hydrides, generated by reactions with pinacolborane, are competent for reduction of ketones but are inert toward esters. Instead, catalytic reduction of esters requires activation of the lanthanum hydride by pinacolborane. 相似文献
8.
Spherical fractal aggregates of approximately 10 microm were formed from a pi-electronic amphiphile, C(60)-didodecyloxybenzene dyad when extracted from THF into water, necessitating a critical dielectric constant epsilon > or =30 in binary THF-water mixtures. Molecular dynamics simulations revealed the unit cluster to such a form involves an aggregation number approximately 90 with predominant soft associative molecular interactions which corroborated the octadecahedral model proposed for the cluster growth. 相似文献
9.
Langmuir-Blodgett monolayer films of C60-didodecyloxybenzene dyad, with a C60 acceptor and didodecyloxybenzene donor, exhibit rectification with high rectification ratios of 87-158 at 3 V. 相似文献
10.
Spontaneous separation of chiral phases was observed in the monolayers of a racemate of gemini-type twin-tailed, twin-chiral amphiphiles, (2R,3R)-(+)-bis(decyloxy)succinic acid and (2S,3S)-(-)-bis(decyloxy)succinic acid. The pressure-area isotherms of the interfacial monolayers formed at the liquid-air interface, and the 2D lattice structures studied through surface probe measurements revealed that the racemate exhibits a homochiral discrimination of the enantiomers in two dimensions. An enantiomeric excess (e,e) of 20% was sufficient to break the chiral symmetry at the air-water interface for a homochiral interaction. Langmuir monolayers on ZnCl2 and CaCl2 subphases manifested chiral discrimination with Zn2+ evidencing homochiral interaction with a chelate-type complex, whereas Ca2+ resulted in a heterochiral interaction forming an ionic-type complex. For the chiral asymmetric units, oblique and rectangular unit cells of the racemic monolayer had exclusive requirements of homo- and heterochiral recognitions for Zn2+ and Ca2+ ions, respectively. Monolayers transferred from the condensed phase at 25 mN/m onto hydrophilic Si(100) and quartz substrates revealed the formation of bilayers through transfer-induced monolayer buckling. The emergence of homochiral discrimination was explained using the effective-pair-potential (EPP) approach. 相似文献