Search results for "Solution polymerization"

Controlled radical polymerization of alkyl acrylates and styrene using a half-sandwich molybdenum(III) complex containing diazadiene ligands

2003

Abstract The half-sandwich molybdenum(III) complex CpMoCl 2 ( i Pr 2 -dad) ( i Pr 2 -dad= i Pr–NCH–CHN– i Pr) proved to be an effective metal catalyst for the controlled radical polymerization of methyl acrylate, butyl acrylate, and styrene. In conjunction with an alkyl iodide [R–I: CH 3 CH(COOEt)I] as an initiator and in the presence or absence of Al(O– i -Pr) 3 as a co-catalyst, the molybdenum-based system gave polymers with narrow molecular weight distributions. The in situ addition of styrene to a macroinitiator of poly(methylacrylate) afforded an AB-type block copolymer.

Effect of Lithium Perchlorate on the Kinetics of the Anionic Polymerization of Methyl Methacrylate in Tetrahydrofuran

1999

The kinetics of the anionic polymerization of methyl methacrylate in the presence of lithium perchlorate (LiClO 4 ) are investigated in THF using 1,1-diphenylhexyllithium as initiator in a flow-tube reactor between -30 and 0 °C. The rate constants of propagation determined in the presence of LiClO 4 are lower than those obtained in the absence of the salt, similar to the effect observed for LiCl. For propagation, the reaction order with respect to active center concentration is found to be 0.5 in both cases, which indicates that LiClO 4 does not effectively perturb the aggregation of the enolate ion pair. The formation of various mixed aggregates is proposed. The polydispersity index of the…

Kinetic Analysis of “Living” Polymerization Systems Exhibiting Slow Equilibria. 3. “Associative” Mechanism of Group Transfer Polymerization and Ion P…

1996

The averages of the molecular weight distribution are derived for a “living” polymerization process which proceeds via active and “dormant” species and where the active species are formed by addition of a catalyst to a “dormant” species. Such a mechanism is applicable to group transfer and “living” cationic polymerizations (assuming that ion pairs are formed exclusively in the latter case). Both equilibrium and nonequilibrium initial conditions are used for the calculation. The results are very similar to those obtained for degenerative transfer (i.e., direct exchange of activity between active and “dormant” species). The dominating parameter is β = k2/(kpI0), where k2 and kp are the rate c…

Mechanism of Anionic Polymerization of (Meth)acrylates in the Presence of Aluminium Alkyls IV. Formation of a Co-ordinative Polymer Network via the L…

1996

The polymerization of methyl methacrylate in the presence of aluminium alkyls in toluene deviates from conventional kinetics. This results predominantly from the formation and precipitation of a co-ordinative polymer gel or network. Due to the lower reactivity and accessibility of the living chains in the gel, they are regarded as ’dormant’ and thus the concentration of active species decreases during polymerization. The network formation occurs via co-ordination of the living aluminate chain end group with in-chain ester carbonyl groups. Part of the chains are deactivated by a termination process but they are free of cyclic β-ketoesters which would result from the common ’back-biting’ reac…

Ring-opening polymerization of lactides using heterobimetallic yttrocene complexes

1999

Structurally characterized, chiral heterobimetallic yttrocene derivatives Li[Y(η 5 :η 1 -C 5 R 4 Si-Me 2 NCH 2 CH 2 OMe) 2 ] (R = Me, H) have been shown to be active in the controlled ring-opening polymerization of L-lactide to give poly(L-lactide)s with high molecular weights and moderately narrow molecular weight distributions (M w /M n < 1.50). Both transesterification and racemization appear to be less prominent. 'H NMR spectroscopic tetrad analysis of copolymers prepared using a mixture of L- and D-lactide demonstrates the absence of any preference for one enantiomer during the polymerization.

Synthesis of multiarm star poly(glycerol)-block-poly(2-hydroxyethyl methacrylate).

2006

Well-defined multiarm star block copolymers poly(glycerol)-b-poly(2-hydroxyethyl methacrylate) (PG-b-PHEMA) with an average of 56, 66, and 90 PHEMA arms, respectively, have been prepared by atom transfer radical polymerization (ATRP) of HEMA in methanol by a core-first strategy. The hyperbranched macroinitiators employed were prepared on the basis of well-defined hyperbranched polyglycerol by esterification with 2-bromoisobutyryl bromide. Polydispersites M(w)/M(n) of the new multiarm stars were in the range of 1.11-1.82. Unexpectedly, with the combination of CuCl/CuBr(2)/2,2'-bipyridyl as catalyst, the polymerization conversion can be driven to maximum values of 79%. The control of CuCl cat…

Lanthanides benzimidinates: initiators or real catalysts for theɛ-caprolactone polymerization

2000

On the anionic polymerization of dialkylaminoisoprenes, 3. A nuclear magnetic resonance study of the structure of oligo[5-(N,N-diisopropylamino)isopr…

1995

The structure of oligo[(5-N,N-diisopropylamino)isoprenyllithium] (number-average degree of polymerization Pn = 1-2) prepared by reaction of alkyllithium with 5-(N,N-diisopropylamino)-isoprene1 in nonpolar (benzene) and polar (tetrahydrofuran) solvents has been studied by 1H and 13C NMR spectroscopy. In tetrahydrofuran, as expected, the negative charge at the terminal chain unit is more delocalized than in benzene and, consequently, the carbon-lithium bond has a more ionic character. In both solvents the living chain end shows a cisoid-4, 1-structure. No cistrans isomerization could be detected. This independence of the carbanion structure of the solvent polarity is explained by the complexa…

Mechanism of anionic polymerization of (meth)acrylates in the presence of aluminium alkyls, 2. Kinetic investigations with methyl methacrylate in tol…

1995

The kinetics of the polymerization of methyl methacrylate initiated by lithium alkyls (tert-butyllithium or ethyl α-lithiobutyrate) was investigated in the presence of aluminium alkyls (triethylaluminium or triisobutylaluminium) in toluene at −78°C. The rate of polymerization decreases considerably once the living dimer is formed. This suggests that the aluminate end-group coordinates with the penultimate ester group of the polymer chain, thus decreasing reactivity. The results are at variance with an activated monomer mechanism.

Kinetic analysis of "living" polymerization processes exhibiting slow equilibria. 6. Cationic polymerization involving covalent species, ion pairs, a…

1996

The kinetics of cationic polymerization is studied theoretically in accordance with a three-state mechanism which consists of two successive equilibria:  the ionization/ion collapse equilibrium between covalent species and ion pairs, and the subsequent dissociation/association equilibrium between ion pairs and free ions. The number- and weight-average degrees of polymerization and the polydispersity index (PDI), Pw/Pn, are derived. The molecular weight distribution of the polymer generated from this mechanism is generally broader than that of polymers formed via a two-state mechanism, i.e. with only one equilibrium either between covalent species and ion pairs or between covalent species an…