Characteristic ratio of poly(tetrahydrofurfuryl acrylate) and poly(2-ethylbutyl acrylate)

The synthesis, characteristic ratio C_∞ and glass transition temperature (T_g) of poly(tetrahydrofurfuryl acrylate) (PTHFA) and of poly(2-ethylbutyl acrylate) (P2EBA) are reported. P2EBA has slightly lower flexibility (C_∞ = 9.2) than PTHFA (C_∞ = 8.6), mainly because of the higher bulkiness of its side group and the closer proximity to the main chain. The C_∞ results compared with the corresponding polymethacrylates show an increase in flexibility due to the absence of the α-methyl group. Comparison with poly(methyl acrylate) clearly shows the influence of the bulkiness of the side group on the chain flexibility. The lower T_g of P2EBA than that of PTHFA may be explained by the higher flexibility of the 2-ethylbutyl side group. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1589–1592, 1997     

Crystal Structure Investigation of 2-Pheny limidazo [f]1,10-phenanthroline

The crystal structure of the title compound (PIP) has been determined by single crystal X-ray diffraction methods. C₁₉H₁₂N₄. C₂H₅OH crystallizes in the monoclinic space group P2₁/n with a = 11.4414(8), b = 12.6052(9), c = 12.4627(8) Å, β = 100.345(2)°, Z = 4, V = 1768.17 ų, D_cal = 1.286 Mg. m⁻³, μ (MoKα) = 0.80 cm^-1, F(000) = 720. The structure was solved by the direct methods and refined by full-matrix least-squares method to a final R = 0.0337 and R_w = 0.0332 for 2306 reflections with F₀ > 4σ(F₀). The phenl ring and the imidazo[f]1,10-phenanthroline moiety are coplanar in the crystal. The packing of the molecules involves hydrogen bonded association of the hydroxyl group of ethanol both with the N H of the imidazole moiety of one PIP and one nitrogen atom of the phenanthroline moiety of another PIP.     

Star‐branched polystyrenes by nitroxide living free‐radical polymerization

Star‐branched polystyrenes, with polydispersity indices of 1.15–1.56 and 4–644 equal arms, were synthesized by the reaction of 2,2,6,6‐tetramethylpiperidin‐1‐yloxy (TEMPO)‐capped polystyrene (PS‐T) with divinylbenzene (DVB). The characterization of PS‐T and the final star polymers was carried out by size exclusion chromatography, low‐angle laser light scattering, and viscometry. The degree of branching of the star polymers depended on the DVB/PS‐T ratio and the PS‐T molecular weight. An asymmetric (or miktoarm) star homopolymer of the PS_nPS′_n type was made by the reaction of the PS_n symmetric star, which had n TEMPO molecules on its nucleus and consisted of a multifunctional initiator, with extra styrene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 320–325, 2001     

Synthesis and characterization of model diblock copolymers of poly(dimethylsiloxane) with poly(1,4‐butadiene) or poly(ethylene)

Model diblock copolymers of poly(1,4‐butadiene) (PB) and poly(dimethylsiloxane) (PDMS), PB‐b‐PDMS, were synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene and hexamethylciclotrisiloxane (D₃) in the presence of sec‐BuLi. By homogeneous hydrogenation of PB‐b‐PDMS, the corresponding poly(ethylene) and poly(dimethylsiloxane) block copolymers, PE‐b‐PDMS, were obtained. The synthesized block copolymers were characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size‐exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and rheology. SEC combined with ¹H NMR analysis indicates that the polydispersity index of the samples (M_w/M_n) is low, and that the chemical composition of the copolymers varies from low to medium PDMS content. According to DSC and TGA experiments, the thermal stability of these block copolymers depends on the PDMS content, whereas TEM analysis reveals ordered arrangements of the microphases. The morphologies observed vary from spherical and cylindrical to lamellar domains. This ordered state (even at high temperatures) was further confirmed by small‐amplitude oscillatory shear flow tests. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1579–1590, 2006     

Novel well-defined star homopolymers and star-block copolymers of poly(n-hexyl isocyanate) by anionic polymerization

Anionic polymerization high-vacuum techniques and appropriate multifunctional initiators/additives were employed for the synthesis of novel star structures of poly(n-hexyl isocyanate) (PHIC). A new trifunctional initiator prepared by the reaction of tris(4-isocyanatophenyl)methane with benzyl sodium was used for the synthesis of three-arm star PHIC. Divinyl benzene and the core-first or the arm-first/core-first (in-out) approach were utilized for the synthesis of multiarm star homopolymers, (PHIC)_n, star-block copolymers, (PHIC-b-PI)_n, and miktoarm star copolymers, (PS)_n(PHIC)_n, where PS is polystyrene. The molecular characteristics obtained by size-exclusion chromatography, equipped with refractive index and two-angle light scattering detectors, nuclear magnetic resonance, spectroscopy, and dilute solution viscometry showed that well-defined structures were synthesized in this study. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2387–2399, 2007     

Controlled vinyl‐type polymerization of norbornene with a Nickel(II) diphosphinoamine/methylaluminoxane catalytic system

A novel nickel‐based complex coordinated with an asymmetric diphosphinoamine ligand was synthesized and fully characterized. Single crystals of good quality were also obtained, and the solid‐state structure of the complex was studied via X‐rays diffraction. The catalytic activity of this Ni(II) complex in the vinyl‐type polymerization of norbornene was studied with methylaluminoxane (MAO) as the cocatalyst/activator. The influence of the reaction time, the equivalents of MAO used, and the concentration of the monomer on: (i) the activity of the catalytic system; (ii) the isolated yield of the polymer; and (iii) the molecular weight and molecular weight distribution of the polymer were investigated. The isolated polynorbornene (PNB) yields are significantly higher compared with those reported for other similar nickel‐based systems. The as‐obtained PNBs are characterized by high molecular weights and relatively narrow and monomodal molecular weight distributions (amongst the narrowest reported in the literature). The linear dependence of the molecular weight of the obtained PNB on the concentration of norbornene points toward a controlled polymerization reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5241–5250, 2009     

Synthesis of exact comb polybutadienes with two and three branches

Two methodologies, based on living star polymers and anionic polymerization high vacuum techniques, were used for the synthesis of exact comb polybutadienes (PBds) with two (C‐2 or H‐type) and three identical branches (symmetric, sC‐3, H‐type with an extra identical branch at the middle of the connector and asymmetric, aC‐3, H‐type with the extra identical branch at any other position along the connector). The first methodology involves (a) the selective replacement of the two chlorines of 4‐(dichloromethylsilyl)diphenylethylene (DCMSDPE, key molecule) with 3‐arm star PBds, by titration with identical (C‐2, sC‐3) or different (aC‐3) living 3‐arm star PBds, (b) the addition of s‐BuLi to the double bond of DPE, and (c) the polymerization of butadiene from the newly created anionic site (sC‐3, aC‐3).The second methodology involves the reaction of living stars with dichlorodimethylsilane (C‐2) or the selective replacement of the three chlorines of trichloromethylsilane with star and linear chains (sC‐3, aC‐3). Intermediate and final products were characterized via size exclusion chromatography, low angle laser light scattering and ¹H‐NMR. The first methodology does not require fractionation, but in contrast to the second methodology, cannot afford polymers with branches of identical molecular weight. Both methods are general and can be extended to combs with two or three different branches at controllable positions along the backbone. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2597–2607, 2009     

Exponential convergence for a periodically driven semilinear heat equation

We consider a semilinear heat equation in one space dimension, with a periodic source at the origin. We study the solution, which describes the equilibrium of this system and we prove that, as the space variable tends to infinity, the solution becomes, exponentially fast, asymptotic to a steady state. The key to the proof of this result is a Harnack type inequality, which we obtain using probabilistic ideas.