A Precision Ethylene‐Styrene Copolymer with High Styrene Content from Ring‐Opening Metathesis Polymerization of 4‐Phenylcyclopentene

Ring‐opening metathesis polymerization of 4‐phenylcyclopentene is investigated for the first time under various conditions. Thermodynamic analysis reveals a polymerization enthalpy and entropy sufficient for high molar mass and conversions at lower temperatures. In one example, neat polymerization using Hoveyda–Grubbs second generation catalyst at −15 °C yields 81% conversion to poly(4‐phenylcyclopentene) (P4PCP) with a number average molar mass of 151 kg mol⁻¹ and dispersity of 1.77. Quantitative homogeneous hydrogenation of P4PCP results in a precision ethylene‐styrene copolymer (H₂‐P4PCP) with a phenyl branch at every fifth carbon along the backbone. This equates to a perfectly alternating trimethylene‐styrene sequence with 71.2% w/w styrene content that is inaccessible through molecular catalyst copolymerization strategies. Differential scanning calorimetry confirms P4PCP and H₂‐P4PCP are amorphous materials with similar glass transition temperatures (T_g) of 17 ± 2 °C. Both materials present well‐defined styrenic analogs for application in specialty materials or composites where lower softening temperatures may be desired.

     

Physical aging and glass transition of hairy nanoparticle assemblies

Matrix free assemblies of polymer-grafted, “hairy” nanoparticles (aHNP) exhibit novel morphology, dielectric, and mechanical properties, as well as providing means to overcome dispersion challenges ubiquitous to conventional polymer-inorganic nanocomposite blends. Physical aging of the amorphous polymer glass between the close-packed nanoparticles (NPs) will dominate long-term stability; however, the energetics of volume recovery within the aHNPs is unknown. Herein, we compare glass transition temperature (T_g) and enthalpy recovery of aHNPs to NP-polymer blends, across different nano-silica loadings (0–50 v/v%) and canopy architecture of polystyrene (PS) grafted silica. For aHNPs, the grafting of PS to silica imposes an additional design constraint between silica volume fraction, graft density, and graft molecular weight. At low and intermediate silica volume fraction, the T_g of blended nanocomposites is independent of silica content, reflecting a neutral polymer-NP interface. For aHNPs, the T_g decreases with silica content, implying that chain tethering decreases local segment density more than the effect of molecular weight or polymer-NP interactions. Additionally, the T_g of the aHNPs is higher than a linear matrix of comparable molecular weight, implying a complementary effect to local segment density that constrains cooperativity. In contrast, enthalpy recovery rate in the blend or aHNP glass is retarded comparably. In addition, a cross-over temperature, T_x, emerges deep within the glass where the enthalpy recovery process of all nanocomposites becomes similar to linear unfilled matrices. Differences between structural recovery in aHNP and blended nanocomposites occur only at the highest silica loadings (∼ 50 v/v%), where enthalpy recovery for aHNPs is substantially suppressed relative to the blended counterparts. The absence of physical aging at these loadings is independent of brush architecture (graft density or molecular weight of tethered chains) and indicates that the impact of chain tethering on effective bulk structural relaxation starts to appear at particle-particle surface separations on the order of the Kuhn length. Overall, these observations can be understood within the context of how three separate structural characteristics impact local segment density and relaxation processes: the dimension and architecture of the tethered polymer chains, the separation between NP surfaces, and the confinement imposed by chain tethering and space filling within the aHNP. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 319–330     

Through‐space 19F–19F spin–spin coupling in ortho‐fluoro Z‐azobenzene

We report through‐space (TS) ¹⁹F–¹⁹F coupling for ortho‐fluoro‐substituted Z ‐azobenzenes. The magnitude of the TS‐coupling constant (^TSJ_FF) ranged from 2.2–5.9 Hz. Using empirical formulas reported in the literature, these coupling constants correspond to non‐bonded F–F distances (d_FF) of 3.0–3.5 Å. These non‐bonded distances are significantly smaller than those determined by X‐ray crystallography or density functional theory, which argues that simple models of ¹⁹F–¹⁹F TS spin–spin coupling solely based d_FF are not applicable. ¹H, ¹³C and ¹⁹F data are reported for both the E and Z isomers of ten fluorinated azobenzenes. Density functional theory [B3YLP/6‐311++G(d,p)] was used to calculate ¹⁹F chemical shifts, and the calculated values deviated 0.3–10.0 ppm compared with experimental values. Copyright © 2015 John Wiley & Sons, Ltd.     

Cascade Mn‐Mediated γ‐Alkylation/oxa‐Michael Addition of Enones with 1,3‐Dicarbonyls

A radical‐based strategy for regioselective γ‐C?C bond formation/oxa‐conjugate addition, forming the tetrahydrobenzofuran core common to many bioactive natural products is described. The technique utilizes readily available enone derivatives and 1,3‐dicarbonyl compounds as coupling partners in an oxidative formal [3+2] cycloaddition mediated by Mn^III. The transformation delivers polycyclic products in good yields and proceeds with complete regiocontrol and excellent stereoselectivity. Sterically encumbered substrates are notably well‐tolerated and bond formation occurs readily to form neopentyl and all‐carbon quaternary centers in good yields. Several stereo‐ and chemoselective transformations of the products are described.     

Synthesis of fluoroalkyl-containing β-hydroxyketones by reduction of the corresponding β-diketone derivatives

The rcgioselective synthesis of fluoroalkyl-containing P-hydroxyketones by the reduction of the salts of the corresponding -diketones with LiAlH₄ was proposed. This is the sole method for the synthesis of -hydroxyketones with two fluoroalkyl substituents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1493–1495, June, 1996.     

Nanostructures,Microscale Technologies,and Plasma Deposited Films

Plasmas and Polymers -     

Reactions of fluoroalkyl-containing bis-β-diketones with hydrazine and hydroxylamine

Polyfluoroalkyl-containing bispyrazoles, bis(5-hydroxy-Δ²-isoxazolines), and bisisoxazoles were synthesized for the first time by reactions of polyfluoroalkyl-containing bis-β-diketones with hydrazine, phenylhydrazine, and hydroxylamine, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 762–764, April, 1999.     

Conditional Detection of Fluctuations of Light from an Optical Cavity with One Atom

Fluctuations of light provide a window on the underlying quantum dynamical evolution of the source emitting light. Emission of a photon by a source signals quantum fluctuations in progress. Hence a measurement that is conditioned upon a photodetection allows us to follow the time evolution of the fluctuations and the framework of conditioned measurements provides a powerful conceptual tool for understanding nonclassical features of quantum dynamics. We discuss the connection between quantum dynamics and photon fluctuations in terms of conditional measurements of intensity and field quadratures of light from a single atom in an optical cavity. Using the Fokker- Planck equation for a single atom in a high-Q cavity, we describe the light from the cavity in terms of Gaussian random variables and a coherent component. These are used to study conditional measurements of intensity and quadrature squeezing. It is found that when the coherent component is completely removed conditional light intensity shows large fluctuations, whereas conditional squeezing exhibits strong nonclassical behavior. Indeed both field quadratures exhibit nonclassical behavior. On the other hand a small coherent component results in a sizable reduction in intensity fluctuations and small squeezing.