AB2 + A Type Copolymerization Approach for the Preparation of Thermosensitive PEGylated Hyperbranched Polymers

Hyperbranched polyethers having poly(ethylene glycol) (PEG) segments at their molecular periphery were prepared by a simple procedure wherein an AB2 type monomer was melt-polycondensed with an A-type monomer, namely, heptaethylene glycol monomethyl ether. The presence of a large number of PEG units at the termini rendered a lower critical solution temperature (LCST) to these copolymers, above which they precipitated out of an aqueous solution. In an effort to understand the effect of various molecular structural parameters on their LCST, the length of the hydrophobic spacer segment within the hyperbranched core and the extent of PEGylation were varied. Additionally, linear analogues that incorporates pendant PEG segments were also prepared and comparison of their LCST with that of the hyperbranched analogue clearly revealed that hyperbranched topology leads to a substantial increase in the LCST, highlighting the importance of the peripheral placement of the PEG units.

Peroxomonosulphate initiated graft copolymerization of aniline onto poly(propylene) fibre - A kinetic approach

Graft copolymerization of poly(aniline) (PANI) onto poly(propylene) (PP) fibre was carried out in aqueous acidic medium under nitrogen atmosphere by using peroxomonosulphate (PMS) as a lone initiator. The non-conducting fibre was now made into a conducting one through the chemical grafting of PANI units onto the PP fibre backbone. The content of PANI in the backbone was found to vary while varying the [ANI], [PMS] and amount of PP fibre. Various graft parameters were evaluated. The chemical grafting of PANI onto PP fibre was confirmed by conductivity measurements.

Oxidative copolymerization: microstructure analysis of the terpolymer of styrene, methyl methacrylate, and oxygen

This paper reports the first study of the microstructure of a copolyperoxide by nuclear magnetic resonance spectroscopy. The copolyperoxides of styrene and methyl methacrylate (MMA) of various compositions have been synthesized. An analysis of the resonance signal of the backbone methylene protons gave the diad sequence probabilities which led to the calculation of the oxidative copolymerization reactivity ratios for styrene and MMA and the microstructural parameters like average chain length of the repeat unit sequences, run number, etc. The results point to the tendency of the SO1 and MO:! units to alternate in the chain. Compared to poly(styrene peroxide), the aromatic C1 seems to be stereosensitive in the terpolymers.

High-pressure kinetics of oxidative copolymerization of styrene with alpha-methyl styrene

This is the first report on the study carried out on high-pressure free-radical initiated oxidated copolymerization of styrene (STY) with alpha-methylstyrene (AMS) at various temperatures (45-65degreesC) at constant pressure (100 psi) and then at various pressures (50-300 psi) keeping the temperature (50degreesC) constant. The compositions of the copolyperoxides obtained from the H-1 NMT spectra were utilized to determine the reactivity ratios of the monomers. The reactivity ratios indicate that STY forms an ideal copolyperoxide with AMS and the copolyperoxide is richer in AMS. The effect of temperature and oxygen pressure in the reactivity ratios of the monomers was studied. The rates of copolymerization (R-p) were used to determine the overall activation energies (E-a) and activation volume (DeltaV(#)) of copolymerization. The unusually higher values of the DeltaV(#) may be due to the pressurizing fluid oxygen which itself is a reactant in the copolymerization, the side reactions, and the chain-transfer reactions occuring during copolymerizations.

Electrochemical copolymerization of thiophene derivatives; a precursor to photovoltaic devices

This work presents an electrochemical technique for the polymerization and copolymerization of thiophene derivatives like 7,9-dithiophene-2yl-8H-cyclopenta[a]acenaphthalene-8-one and 3-hexylthiophene. The structural characterization of chemically synthesized monomers and electro-chemically synthesized polymers was carried out by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Thermal characterizations indicate that copolymer has increased thermal stability than that of homopolymer. Morphological studies of the polymerized films carried out by scanning electron microscopy shows network structure of copolymer. Optical properties of the homopolymers and copolymer were studied by UV-visible spectrometer and it was observed that band gap of copolymer is less than the homopolymers. HOMO and LUMO levels, band gap values of the respective polymers were also calculated from the cyclic voltammetry technique with various scan rates. By the peak current obtained from various scan rates shows that all polymerization reactions are diffusion controlled process. Charge transfer resistances of polymers were determined using Nyquist plots. Conductivity of synthesized polymers shows higher conductivity for copolymer than homopolymers. (C) 2011 Elsevier Ltd. All rights reserved.

Rare-earth-metal mixed hydride/aryloxide complexes bearing mono(cyclopentadienyl) ligands. Synthesis, CO2 fixation, and catalysis on copolymerization of CO2 with cyclohexene oxide

Hydrogenolysis of mono(cyclopentadienyl)-ligated rare-earth-metal bis(alkyl) complexes Cp'Ln-(CH2SiMe3)2(THF) (Ln = Y (1a), Dy (1b), Lu (1c); Cp' = C5Me4SiMe3) with PhSiH3 afforded the mixed hydride/alkyl complexes [Cp'Ln(mu-H)(CH2SiMe3)(THF)](2) (Ln = Y (2a), Dy (2b), Lu (2c)). The overall structure of complexes 2a-c is a C-2-symmetric dimer containing a planar symmetric Ln(2)H(2) core at the center of the molecule. Deprotonation of ArOH (Ar = C6H2-Bu-t(2)-2,6-Me-4) by the metal alkyl group of 2a-c led to formation of the mixed hydride/aryloxide derivatives [Cp'Ln(mu-H)(OAr)](2) (Ln = Y (3a), Dy (3b), Lu (3c)), which adopt the dimeric structure through hydride bridges with trans-accommodated terminal aryloxide groups.

Alternating Copolymerization of Cyclohexene Oxide and Carbon Dioxide Catalyzed by Noncyclopentadienyl Rare-Earth Metal Bis(alkyl) Complexes

The syntheses of several dialkyl complexes based on rare-earth metal were described. Three beta-diimine compounds with varying N-aryl substituents (HL1 = (2-CH3O(C6H4))N=C(CH3)CH=C(CH3)NH(2-CH3O(C6H4)), HL2 = (2,4,6-(CH3)(3) (C6H2))N=C(CH3)CH=C(CH3)NH(2,4,6-(CH3)(3)(C6H2)), HL3 = PhN=C(CH3)CH(CH3) NHPh) were treated with Ln(CH2SiMe3)(3)(THF)(2) to give dialkyl complexes L(1)Ln (CH2SiMe3)(2) (Ln = Y (1a), Lu (1b), Sc (1c)), L(2)Ln(CH2SiMe3)(2)(THF) (Ln = Y (2a), Lu (2b)), and (LLu)-Lu-3(CH2SiMe3)(2)(THF) (3). All these complexes were applied to the copolymerization of cyclohexene oxide (CHO) and carbon dioxide as single-component catalysts.

The copolymerization of carbon dioxide and propylene oxide with Y(CCl3COO)(3)-diphenylzinc-glycerol catalyst

Various organometallic compounds (diphenylzinc, dibenzylzinc, dicyclohexylzinc, bis( pentafluorophenyl) zinc, diethylzinc, di(n-butyl) zinc, triethylaluminum) were used to form Y(CCl3COO)(3)-organometallic compound-glycerol catalyst for the copolymerization of carbon dioxide and propylene oxide. It was found that Y(CCl3COO)(3)-diphenylzinc-glycerol catalyst showed the highest catalytic activity, at optimum conditions the yield could be as high as 478.8 ( g polymer/mol Zn h).

Copolymerization of carbon dioxide and cyclohexene oxide catalyzed by aluminum porphyrin-quaternary ammonium salt in the presence of bulky lewis acid

Chloro( 5,10,15,20-tetraphenyl-porphyrinato)-aluminum/tetraethylammonium bromide ( Et4NBr) in combination with bulky Lewis acid was used for the copolymerization of CO2 and cyclohexene oxide ( CHO). Bulky Lewis acid having substituents at the ortho positions of the phenolate ligands, like methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate), significantly shortened the induction period and raised the catalytic activity, the corresponding turnover frequency reached 44.9 h(-1) in 9 h, which was 23.8% higher than that from ( TPP)AlCl/Et4NBr binary catalyst. The resulting polycarbonate has carbonate linkage over 93% with number average molecular weight of ( 4.5-6.5) x 10(3) and polydispersity index below 1.10.