Organometallic polymers. XXV. Preparation of polyvinylferrocene

The synthetic details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported. In benzene solutions, with azobisisobutyronitrile (AIBN) as the initiator, small yields of low-polydispersity low molecular weight (M?_n ? 5000) polyvinylferrocene is obtained. However, high yields can be obtained by continuous or multiple AIBN addition. Higher molecular weight polymers and binodal polymers can be obtained as the monomer concentration is increased. In bulk polymerizations, yields of 80% can be obtained. The molecular weight increases as temperature decreases from 80 to 60°C in bulk polymerizations, and an increasing amount of insoluble polymer results. The soluble portion is often binodal, the higher molecular weight node consisting of an increasingly branched structure. Lower molecular weight polymer was readily fractionated into narrow fractions from benzene–methanol systems, but higher molecular weight polymer proved impossible to fractionate into narrow fractions due to branching.     

Polymerization and reaction rate studies on substituted phenylmethylbis(dimethylamino)silanes

The synthesis of seven para- or meta-substituted phenylmethylbis(dimethylamino)-silane monomers has been carried out. These silanes were polymerized with 1,4-bis(hydroxydimethylsilyl)benzene in tetrahydrofuran at 30°C, and the polymerization kinetics were followed by monitoring dimethylamine evolution for 200 min. The polymers were quenched by precipitation in methanol and molecular weight data were obtained. The polymerizations followed second-order kinetics in every case as evidenced by the linear plots of 1/(a ? x) versus time. The molecular weight data generally correlated with the specific reaction rate constant k₂ to show an increasing polymer molecular weight with increasing polymerization rate, although the range of k₂ values obtained for the substituted aminosilanes was relatively small (2.50 × 10^?5–6.67 × 10^?5 l./mole-sec). The value of k₂ increased in the following order: p-OCH₃, p-F, m-CH₃, H, m-OCH₃, p-CF₃, 3,5-di(CF₃). The logarithms of the rate constants correlated with the σ constants for the substituents, with a reaction constant, ρ of 0.391. The displacement at silicon in these reactions is discussed in terms of bimolecular mechanisms in which a four-center transition state may participate.     

Synthesis of block copolymers containing poly(ferrocenylmethyl methacrylate) units

Ferrocenylmethyl methacrylate (FMMA) has been polymerized by using LiAlH₄–tetramethyl-ethylenediamine initiation to form living polymers in high vacuum systems. The addition of methyl methacrylate or acrylonitrile to these living systems gave the block copolymers FMMA-block MMA and FMMA-block AN. The anions were not nucleophilic enough to initiate styrene polymerization. Therefore, living polystyrene was prepared (sodium naphthalide initiation in THF at ?78°C) and upon FMMA addition, styrene-block FMMA copolymers were formed. Extraction, precipitation, and gel-permeation chromatography studies were performed to examine the purity of the block copolymers.     

X-ray radiation from nonlinear Thomson scattering of an intense femtosecond laser on relativistic electrons in a helium plasma

We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs/1.5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked at 0.15 keV with a significant tail up to 2 keV has been observed. These characteristics are found to depend strongly on the laser strength parameter a(0). This radiative process is dominant for a(0) greater than unity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma.     

The preparation,polymerization and copolymerization of (η5-vinylcyclopentadienyl)dicarbonylnitrosylchromium, (η5-C5H4CHCH2)Cr(CO)2NO

The first report on the preparation, polymerization, and copolymerization of a nitrosyl-containing vinylcyclopentadienylmetal monomer, (η⁵-C₅H₄CHCH₂)-Cr(CO)₂NO, is described. (η⁵-Vinylcyclopentadienyl)-dicarbonylnitrosylchromium (A) was prepared in good yield by the acylation of η⁵-cyclopentadienyl-carbonylnitrosylchromium followed by sodium borohydride reduction of the keto function and acid-catalyzed dehydration. Monomer A homopolymerizes and copolymerizes with styrene, N-vinylpyrrolidone, and vinyl cymantrene in the presence of azo initiators. Reactivity ratios in the copolymerization of A with styrene were r₁ = 0.30 and r₂ = 0.82 from which the value of e for A was found to be ?1.98. Thus, A is an exceptionally electron-rich monomer.     

High-fidelity quantum logic operations using linear optical elements

Knill, Laflamme, and Milburn [Nature (London) 409, 46 ((2001))]] have shown that quantum logic operations can be performed using linear optical elements and additional ancilla photons. Their approach is probabilistic in the sense that the logic devices fail to produce an output with a failure rate that scales as 1/n, where n is the number of ancilla. Here we present an alternative approach in which the logic devices always produce an output with an intrinsic error rate that scales as 1/n(2), which may have several advantages in quantum computing applications.