Copolymerization of silyl vinyl ethers with olefins by (alpha-diimine)PdR+

This paper reports that (alpha-diimine)PdMe+ catalyzes the copolymerization of olefins and silyl vinyl ethers. The reactions of (alpha-diimine)PdMe+ (alpha-diimine = (2,6-iPr2-C6H3)N=CMe-CMe=N(2,6-iPr2-C6H3)) with excess vinyl ethers CH2=CHOR (1a-d: R = tBu (a), SiMe3 (b), SiPh3 (c), Ph (d)) in CH2Cl2 at 20 degrees C afford polymers for 1a (rapidly) and 1b (slowly) but not for 1c or 1d. The structures of poly(1a,b) indicate a cationic polymerization mechanism. The reaction of (alpha-diimine)PdMe+ with 1-2 equiv of 1a-d proceeds by sequential C=C pi-complexation to form (alpha-diimine)PdMe(CH2=CHOR)+ (2a-d), 1,2 insertion to form (alpha-diimine)Pd(CH2CHMeOR)+ (3a-d), reversible isomerization to (alpha-diimine)Pd(CMe2OR)+ (4a-d), beta-OR elimination to generate (alpha-diimine)Pd(OR)(CH2=CHMe)+ (not observed), and allylic C-H activation to yield (alpha-diimine)Pd(eta3-C3H5)+ (5) and ROH. The reaction of (alpha-diimine)PdMe+ with 1-hexene/1b and 1-hexene/1c mixtures in CH2Cl2 at 20 degrees C affords copolymers containing up to 20 mol % silyl vinyl ether. The copolymers were purified to be free of any -[CH2CHOSiR3]n- homopolymer. The copolymer structures are similar to that of homopoly(1-hexene) generated under the same conditions. The major comonomer units are CH3CH(OSiR3)CH2-, CH2(OSiR3)CH2- and -CH2CH(OSiR3)CH2-. The 1-hexene/CH2=CHOSiR3 copolymers can be desilylated to give 1-hexene/CH2=CHOH copolymers. The results of control experiments argue against cationic and radical mechanisms for the copolymerization, and an insertion/chain-walking mechanism is proposed.     

Stereoregularity of poly(vinyl ether)

α-Methylvinyl isobutyl and methyl ethers were polymerized cationically and the structure of the polymers was studied by NMR. Poly(α-methylvinyl methyl ether) polymerized with iodine or ferric chloride as catalyst was found to be almost atactic, whereas poly(α-methylvinyl isobutyl ether) polymerized in toluene with BF₃OEt₂ or AlEt₂Cl as catalyst was found to be isotactic. In both cases, the addition of polar solvent resulted in the increase of syndiotactic structure as is the case with polymerization of alkyl vinyl ether. tert-Butyl vinyl ether was polymerized, and the polymer was converted into poly(vinyl acetate), the structure of which was studied by NMR. A nearly linear relationship between the optical density ratio D₇₂₂/D₇₃₆ in poly(tert-butyl vinyl ether) and the isotacticity of the converted poly(vinyl acetate) was observed.     

Interdiffusion in a polystyrene-poly(vinyl methyl ether) system

Interdiffusion in polystyrene-poly(vinyl methyl ether) systems is studied by optical-interferometry method in wide temperature and concentration ranges. For these systems, temperature-concentration dependences are constructed, activation energies are calculated, and dependences of the diffusion coefficient on the molecular mass of polystyrene are examined. The results are compared with the phase diagrams of the systems, and it is shown that the diffusion coefficient decreases as the binodal curve is approached, thereby leading to corresponding changes in the Arrhenius coordinates.     

Synthesis of poly(silyl ether)s via copper-catalyzed dehydrocoupling polymerization

The development of efficient method to prepare poly(silyl ether)s (PSEs) is highly desirable. Herein, an environmentally sustainable copper-catalyzed dehydrocoupling polymerization was developed with good yields and high molecular weight (up to 48,400 of Mn and up to 97% yield). Monomers of different types (AB type or AA and BB type) are suitable to afford PSEs. The PSEs show good thermal stability and low glass-transition temperature.     

N+离子注入聚对苯乙炔衍生物的非线性光学性能

以对甲氧基苯酚和溴代异戊烷为原料,用脱氯化氢反应制备可溶性聚[2-甲氧基-5-(3'-甲基)丁氧基]对苯乙炔(MMB-PPV),通过核磁氢谱(1HNMR)和红外光谱(FTIR)对产物分子的结构进行表征.用能量为15keV、剂量为3.8×1015～9.6×1016ions/cm2的氮正离子(N+)对MMB-PPV薄膜进行注入改性.紫外-可见吸收光谱(UV-Vis)显示,注入离子在MMB-PPV薄膜内部引入杂质能级,破坏了分子的共轭结构.随着注入剂量增加,吸收边逐渐向长波方向移动,且分子激发态和基态间的光学带隙由2.12eV减小至1.81eV.用简并四波混频(DFWM)技术研究了离子注入MMB-PPV薄膜的三阶非线性光学性能.结果表明,未注入薄膜的三阶非线性极化率(χ(3))值为7.1×10-10esu,随着注入剂量的增加,χ(3)值逐渐增大,当注入剂量达到3.8×1016ions/cm2时,χ(3)值提高到9.3×10-9esu,继续增加注入剂量,χ(3)值开始下降,当注入剂量为9.6×1016ions/cm2时,χ(3)值降低到1.5×10-10esu.对离子注入MMB-PPV薄膜χ(3)值变化的机理进行了探讨.     

Heat capacity of poly(vinyl methyl ether)

The heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (?25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ₁ = 647 K, Θ₂ = Θ₃ = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by C_p(liquid) = 72.36 + 0.136 T in J K^?1 mol^?1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing C_p of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005     

Poly(vinyl methyl ether) hydrogel formed by high energy irradiation

Poly(vinyl methyl ether) shows a lower critical solution temperature behavior in water. The dimension of the polymer molecules depends on the temperature. A thermo‐sensitive hydrogel was synthesized by irradiation of an aqueous solution of poly(vinyl methyl ether) with electron beam and γ‐rays. At high polymer concentration a bulk gel was formed. The structure of the gel in the dry, swollen and shrunken state was investigated by field emission scanning electron microscopy (FESEM). It could be shown, that the gel synthesized by electron beam has a sponge‐like structure consisting of cavities (≈1 μm) separated from each other by a polymer layer full of holes (≈10 nm). The macroscopic gel is characterized by several techniques, e.g. determination of the M_c‐value by NMR‐relaxation measurements.     

Temperature-sensitive poly(vinyl methyl ether) hydrogel beads

Temperature-sensitive hydrogel beads were prepared by radiation crosslinking of poly(vinyl methyl ether) PVME spheres wrapped in Ca-alginate. The obtained gel beads have diameters in the sub-millimeter or millimeter range (depending on the PVME concentration). They were characterized by sol-gel analysis, swelling measurements, and differential scanning calorimetry. The gel content g increases with increasing radiation dose D. The swelling degree Q_v decreases with increasing PVME concentration c_p and increasing D. In comparison to PVME bulkgels the phase-transition temperature of the synthesized PVME gel beads is a little decreased.     

Photobehavior of (alpha-diimine)dimesitylplatinum(II) complexes

The photobehavior of complexes of the type Pt(diimine)(mes)2 is investigated (where diimine = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), and 4,7-diphenyl-1,10-phenanthroline (dpp) and mes = the mesityl (2,4,6-trimethylphenyl) anion). For all compounds studied, solution RT emission is observed to be weak and excited-state lifetimes are found to be short (< or = 20 ns) regardless of solvent choice. Evidence is presented for energy-transfer quenching of Pt(dpp)(mes)2 luminescence in toluene by dissolved O2 (primarily producing singlet oxygen) with an observed quenching rate constant of kq > or = 1.3 x 10(9) M-1 s-1. Electron-transfer quenching is also observed in the presence of 3,5-dinitrobenzonitrile, yielding a quenching rate constant of kq > or = 1.6 x 10(9) M-1 s-1. The latter observation suggests that phase Pt(II) systems may have future value as excited-state reductants. All of the complexes display a much more intense and longer-lived luminescence in the solid state at room temperature. Several possible explanations for this dependence on phase are proposed, with the most probable mechanism involving radiationless deactivation in solution via rotation of the o-methyl groups of the mesityl ligands.     

Synthesis and characterization of amphiphilic diblock copolymers of methyl tri(ethylene glycol) vinyl ether and isobutyl vinyl ether

Water-soluble diblock copolymers of methyl tri(ethylene glycol) vinyl ether (hydrophilic block) and isobutyl vinyl ether (hydrophobic block) of different molecular weights and composition were synthesized by living cationic polymerization. The molecular weight and comonomer composition of these copolymers were determined by GPC and ¹H NMR spectroscopy, respectively. Aqueous solutions of the copolymers were characterized in terms of their micellar behavior using dynamic light scattering, aqueous GPC, and dye solubilization. All the copolymers formed aggregates with the exception of a diblock copolymer with only two hydrophobic monomer units. The micellar hydrodynamic size scaled with the 0.61 power of the number of hydrophobic units, in good agreement with a theoretical exponent of 0.73. An increase in the length of the hydrophobic block at constant hydrophilic block length or an increase in the overall polymer size at constant block length ratio both resulted in lower critical micelle concentrations (cmcs). The cloud points of 1% w/w aqueous solutions of the polymers were determined by turbidimetry. An increase in the length of the hydrophobic block at constant hydrophilic block length caused a decrease in the cloud points of the copolymers. However, an increase in the overall polymer size at constant block length ratio led to an increase in the cloud point. © 1996 John Wiley & Sons, Inc.     

Blends of poly(vinyl methyl ether) with styrenic copolymers

Blends of poly(vinyl methyl ether) (PVME) with styrene/acrylonitrile (SAN), with styrene/maleic anhydride (SMA), and with styrene/acrylic acid (SAA) copolymers were examined for glass transition and lower critical solution temperature behavior. These copolymers were found to be completely miscible with PVME at levels of 3% or less of AA; below 10–11% AN, and below 15% MA (w%). Small amounts of the comonomers raised the temperature at which blends with PVME undergo phase separation on heating. This effect was greatest in the order AA > AN > MA. An interpretation of these results is given in terms of recent theories for homopolymer-copolymer blends, and the extent to which solubility parameter theory can be useful is considered.     

Catalytic version of epoxy silyl ether rearrangements

Catalytic version of epoxy silyl ether rearrangements using Me₃SiX (X=I, OTf: 5 mol %) as the Lewis acid catalyst is reported, which leads to generally higher yields of the aldol products than stoichiometric version.