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Chain Transfer Reaction (chain + transfer_reaction)
Selected AbstractsBorane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2010Wentian Lin Abstract This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl-B-9-borabicyclononane (Me-B-9-BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]-catalyzed ethylene (Cp2ZrCl2 and rac -Me2Si(2-Me-4-Ph)2ZrCl2 as a catalyst) and styrene (Cp*Ti(OMe)3 as catalyst) polymerizations. The two trialkylboranes were found,in most cases,able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)-terminated PE and s -PS polymers after an oxidative workup process, suggesting the formation of the B-polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp2ZrCl2/MAO, whereas it became less effective when the catalyst changed to rac -Me2Si(2-Me-4-Ph)2ZrCl2. Both TEB and Me-B-9-BBN caused an efficient chain transfer in the Cp2ZrCl2/MAO-catalyzed ethylene polymerization; nevertheless, Me-B-9-BBN failed in vain with rac -Me2Si(2-Me-4-Ph)2ZrCl2/MAO. In the case of styrene polymerization with Cp*Ti(OMe)3/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as BH-bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane-terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534,3541, 2010 [source] Synthesis of ethylene/propylene elastomers containing a terminal reactive group: The combination of metallocene catalysis and control chain transfer reactionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005U. Kandil Abstract This article discusses a chemical route to prepare new ethylene/propylene copolymers (EP) containing a terminal reactive group, such as ,-CH3 and OH. The chemistry involves metallocene-mediated ethylene/propylene copolymerization in the presence of a consecutive chain transfer agent,a mixture of hydrogen and styrene derivatives carrying a CH3 (p -MS) or a silane-protected OH (St-OSi). The major challenge is to find suitable reaction conditions that can simultaneously carry out effective ethylene/propylene copolymerization and incorporation of the styrenic molecule (St-f) at the polymer chain end, in other words, altering the St-f incorporation mode from copolymerization to chain transfer. A systematic study was conducted to examine several metallocene catalyst systems and reaction conditions. Both [(C5Me4)SiMe2N(t -Bu)]TiCl2 and rac-Et(Ind)2ZrCl2, under certain H2 pressures, were found to be suitable catalyst systems to perform the combined task. A broad range of St-f terminated EP copolymers (EP- t -p-MS and EP- t -St-OH), with various compositions and molecular weights, have been prepared with polymer molecular weight inversely proportional to the molar ratio of [St-f]/[monomer]. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1858,1872, 2005 [source] Use of Hydroxyl Functionalized (Meth)acrylic Cross-Linked Polymer Microparticles as Chain Transfer Agent in Cationic Photopolymerization of Cycloaliphatic Epoxy Monomer, 1MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2003Ludovic Valette Abstract In the case of cationic-type photopolymerized epoxy networks, a new type of chain transfer agent based on hydroxyl functional acrylic cross-linked polymer microparticles (CPM, also called microgels) has been tested. The CPM functionality was obtained through hydroxyethyl acrylate (HEA) monomer, used as comonomer with butyl acrylate (BA) and hexane diol diacrylate (HDDA). Stabilizing monomers were also required for the synthesis of CPM. In order to compare their particular effects, 4 sets of CPM were synthesized with 4 different stabilizing agents, either hydroxyl functional or not. Consequently, two types of OH groups were present in the particles: primary groups coming from HEA and preferentially located in the particles, and optional hydroxyl groups due to the hydroxyl functional stabilizing agents which were mainly placed onto the particles' surface. The viscoelastic properties of the photopolymerized films have been used to obtain information about the chain transfer reaction and the network microstructure. In all cases, the rubber modulus, was improved because of the decrease of the number of dangling epoxy chains in the epoxy network. When hydroxyl groups were only present in the particles, the mobility of the linkages was assumed to be low, and the mechanical relaxation temperature, T,, strongly increased. However, CPM aggregation occurred at high CPM concentrations, lowering and T,. On the contrary, when OH groups were located both on the surface as well as inside the particles, no large CPM aggregation took place, even with [CPM],=,40 wt.-%. Nevertheless, the presumably higher mobility of the linkages on the particles' surface prevented any T, increase. The water absorption of all systems based on CPM was very low, around 2% whatever the concentration of chain transfer agent. Schematic description of the transfer reaction between a propagating cationic-type epoxy chain and a hydroxyl functional CPM. [source] On the Cascade Polymerization Process Consisting of Metallocene Polymerization and ATRP to Prepare i -PP-Based Polar Block CopolymersMACROMOLECULAR REACTION ENGINEERING, Issue 2-3 2009Qingfeng Yi Abstract Isotactic poly(propylene)s bearing a terminal hydroxyl group (i -PP- t -OH) with high degrees of end-group functionality were synthesized by a metallocene/methylaluminoxane (MAO)-mediated propylene polymerization process via a preferential aluminium chain transfer reaction assisted by a hydroalumination process at the end of polymerization. Despite the highly isotactic configuration and relatively high molecular weight ( as high as 60,800 g,·,mol,1) of the polymers, the hydroxyl group located at the i -PP chain terminal was efficiently transformed to an atom transfer radical polymerization (ATRP) initiator moiety of i -PP- t -Br via a reaction with 2-bromopropionyl chloride at 60,°C in toluene. Well-defined i -PP- b -PMMA and i -PP- b -PS block copolymers of controllable structure and compositions were then prepared with efficient ATRPs of MMA and St using i -PP- t -Br. [source] Alkyl exchange reaction between dialkylzinc compounds and methylaluminoxane and the effect on propylene polymerizationAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2010Chuanhui Zhang Abstract Alkyl exchange reaction between dialkylzinc compounds and vacuum-dried methylaluminoxane (MAO) was investigated. 1H NMR shows a clear and direct proof of alkyl exchange reaction between ZnEt2 and trimethylaluminum associated with MAO. Detailed analysis of polymers produced in the presence of dialkylzinc compounds gave other indirect but equally strong evidence of alkyl exchange. Therefore, care must be taken to investigate dialkylzinc-based chain transfer reaction in combination with a precatalyst and MAO. Copyright © 2010 John Wiley & Sons, Ltd. [source] Methacryloxyethyl phosphate-grafted expanded polytetrafluoroethylene membranes for biomedical applicationsPOLYMER INTERNATIONAL, Issue 12 2005Edeline Wentrup-Byrne Abstract Expanded polytetrafluoroethylene (ePTFE) membranes were modified by graft copolymerization with methacryloxyethyl phosphate (MOEP) in methanol and 2-butanone (methyl ethyl ketone (MEK)) at ambient temperature using gamma irradiation. The effect of dose rate (0.46 and 4.6 kGy h,1), monomer concentration (1,40 %) and solvent were studied and the modified membranes were characterized by weight increase, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XPS was used to determine the % degree of surface coverage using the CF (ePTFE membrane) and the CC (MOEP graft copolymer) peaks. Grafting yield, as well as surface coverage, were found to increase with increasing monomer concentration and were significantly higher for samples grafted in MEK than in methanol solution. SEM images showed distinctly different surface morphologies for the membranes grafted in methanol (smooth) and MEK (globular), hence indicating phase separation of the homopolymer in MEK. We propose that in our system, the non-solvent properties of MEK for the homopolymer play a more important role than solvent chain transfer reactions in determining grafting outcomes. Copyright © 2005 Society of Chemical Industry [source] Benzoyl peroxide,p -acetylbenzylidenetriphenyl arsoniumylide initiated copolymerization of citronellol and styrenePOLYMER INTERNATIONAL, Issue 8 2001K Srivastava Abstract Alternating copolymers, containing styrene and citronellol sequences, have been synthesized by radical polymerization using benzoylperoxide (BPO),p -acetylbenzylidenetriphenyl arsoniumylide (pABTAY) as initiator, in xylene at 80,±,1,°C for 3,h under inert atmosphere. The kinetic expression is Rp , [BPO]0.88 [citronellol]0.68 [styrene]0.56 with BPO and Rp , [pABTAY]0.27 [citronellol]0.76 [styrene]0.63 with pABTAY, ie the system follows non-ideal kinetics in both cases, because of primary radical termination and degradative chain transfer reactions. The activation energy with BPO and pABTAY is 94,kJ,mol,1 and 134,kJ,mol,1, respectively. Different spectral techniques, such as IR, FTIR, 1H NMR and 13C NMR, have been used to characterize the copolymer, demonstrating the presence of alcoholic and phenyl groups of citronellol and styrene. The alternating nature of the copolymer is shown by the product of reactivity ratios r1 (Sty),=,0.81 and r2 (Citro),=,0.015 using BPO and r1 (Sty),=,0.37 and r2 (Citro),=,0.01 using (pABTAY), which are calculated by the Finemann,Ross method. A mechanism of copolymerization is proposed. © 2001 Society of Chemical Industry [source] | ||||||||||