Approaches to controlled polymerization of methyl acrylate through functional anionic initiators (original) (raw)
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Living/controlled copolymerization of acrylates with nonactivated alkenes
Journal of Polymer Science Part A-polymer Chemistry, 2004
The living/controlled copolymerization of methyl acrylate with 1-alkenes and norbornene derivatives through several radical polymerization techniques has been achieved. These techniques include atom transfer radical polymerization, reversible addition–fragmentation transfer polymerization, nitroxide-mediated polymerization, and degenerative transfer polymerization. These systems display many of the characteristics of a living polymerization process: the molecular weight increases linearly with the overall conversion, but the polydispersity remains low. Novel block copolymers have been synthesized through the sequential addition of monomers or chain extension. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6175–6192, 2004
Macromolecules, 1992
It has been previously shown that p-coordinating inorganic salts, such as LiC1, were effective in preventing the anionic polymerization of methacrylic esters and hindered alkyl acrylates from being disturbed by secondary transfer and termination reactions. That strategy has opened the way to the "living" polymerization of these monomers and their controlled sequential polymerization with monomers lacking a carbonylconjugated group. That control is however limited to THF at low temperatures for methyl methacrylate and tert-butyl acrylate. It is reported now that the polymerization mechanism remains strictly controlled in apolar solvents, such as toluene, and at temperatures as high as 0 "C, when crown ethers are used in relation to their capability of chelating the alkali-metal counterion and surrounding it with a steric barrier blocking a large enough space area around the metal-containing ion pair.
2005
ATRP of methyl methacrylate (MMA), initiated with 1,3-bis{1-methyl-1-[(2,2,2-trichloroethoxy)carbonylamino]ethyl}benzene as a bifunctional initiator (BI) under CuCl catalysis was studied in the presence of 2,2 0 -bipyridine (bpy) or hexamethyltriethylenetetramine (HMTETA) ligands, in bulk or in toluene. With the bpy, the polymerization reaches only limited monomer conversions and products have broad MWDs. In contrast, polymerization in the presence of HMTETA is a well-controlled process, affords virtually quantitative conversion, giving PMMAs with narrow MWDs and predictable molecular weights within a range of more than one order of magnitude. NMR analysis of the prepared PMMA proved formation of linear polymers with im-measurable extent of chain branching or b-scission as undesired side reactions. The prepared a,u-dichloro-PMMAs were used as macroinitiators for ATRP of tert-butyl acrylate (t-BuA), giving the corresponding triblock copolymers with narrow MWDs and molecular weights controllable in a wide range. Block copolymerizations were performed in dimethyl formamide (DMF) or acetone in the presence of pentamethyldiethylenetriamine (PMDETA) as ligand and could be accelerated by addition of metallic copper. q
Die Makromolekulare Chemie, 1993
In the anionic polymerization of 2-ethylhexyl acrylate the possibility of controlling the molecular weights of the resulting polymers by varying the initial stoichiometric conditions was studied. The starting concentrations of monomer and initiator, tert-butyl2-lithioisobutyrate, were varied in the range 0,24-1,20 mol/L and 0,006-0,017 mol/L, respectively, so that the mole ratio [MI, /[I], spanned the range from 14 to 160. The mole ratio tert-butyl2-lithioisobutyrate: Li ieributoxide was 1 : 3 in all experiments. A mixture toluene/tetrahydrofuran (volume ratio 9 : 1) was used as reaction medium. The molecular weights of the polymers formed (3 700-55000) depend linearly on the ratio [M],/[I],. All products have narrow molecular-weight distributions. The efficiency of the initiator is not quantitative, but in the range investigated it does not depend markedly on the concentration conditions. NMR analysis of the polymers indicates that the polymerization is initiated by Li ester-enolate and any metal transfer from the initiator to the monomer can be neglected. The polymerization is shown to proceed by the mechanism which is close to the ideal "living" process.
Comparison of living polymerization mechanisms. Acrylates and carbocationic polymerization
Makromolekulare Chemie. Macromolecular Symposia, 1993
The concept of a living polymerization is critically discussed. A system ranking various classes of "livingness" is proposed, and the importance of determining the real values of ktr/kp and kt/kp ratios is expounded. New living systems, including carbocationic polymerization and group transfer polymerization of acrylates are compared with classic ionic systems. The mechanism of propagation and the nature of the true active species are similar in both new and classic polymerizations. The role of various components which improve the "livingness" of the polymerizations is discussed and explained by dynamic equilibration between dormant and active species and suppression of side reactions.
Macromolecules, 1999
Metal-free anionic polymerizations of alkyl (meth)acrylates using tetrabutylammonium salts of diethylphenylmalonate, fluorene, and 9-ethylfluorene as initiators were performed in THF at 30°C. A poor control of molecular weights, inconsistent initiator efficiencies, and broad or bimodal molecular weight distributions were obtained. The effect of counterion nature was studied from the polymerization of methyl methacrylate using the 1,1-diphenylhexyl anion with tetrabutylammonium, tetramethyldiethylguanidinium, and lithium as counterions under otherwise identical conditions. Metal-free initiators resulted in incomplete initiation which is attributed to the fact that the initiation is an equilibrium reaction. In conjunction with possible side reactions such as Hofmann elimination and transfer reactions, this leads to broad and bimodal molecular weight distributions of the resulting polymers.
Macromolecules, 2009
N-Heterocyclic carbenes (NHCs), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2) were employed as neutral organocatalysts to bring about the group transfer polymerization (GTP) of both methacrylic and acrylic monomers, including methyl methacrylate (MMA), tert-butylacrylate (tBA), and n-butylacrylate (nBA). This could be achieved at room temperature using 1-methoxy-2-methyl-1-trimethylsiloxypropene (MTS) as initiator in polar or apolar medium. In this way, polymethacrylates and polyacrylates with molar masses in the range 10 000-300 000 g 3 mol-1 , corresponding to the initial [monomer]/[MTS] ratio and with polydispersities lower than 1.2, were obtained in quantitative yields. The kinetics of GTP of MMA catalyzed by 1 or 2 was further investigated. Though the first-order kinetic plot ln[M] 0 /[M] versus time deviated from linearity at high monomer conversion, no inhibition period was noted at low monomer conversion. Moreover, the polymerization rate dramatically increased as the concentration of initiator increased, with first-order dependence in initiator. When mixed in 1/1 molar ratio, MTS and NHC 1 did not reveal the formation of enolate-type species by 29 Si or 13 C NMR spectroscopy. Based on these observations, we propose that NHCs activate the silyl ketene acetal initiator and further propagate GTP via an associative mechanism. The fact that ln[M] 0 /[M] does not evolve linearly with time in the terminal phase of the polymerization can be understood by a reduced diffusion of the catalyst to the trimethylsilyl end groups. The proposed associative mechanism can also account for the successful control of NHC-catalyzed GTP of acrylates during which termination reactions such as backbiting or internal isomerization could be drastically minimized. Next, was described the synthesis of all acrylic block copolymers based on polyacrylates and polymethacrylates (e.g., PMMA-b-PnBA-b-PMMA), utilizing the same NHC as catalyst in sequential GTP. It is again argued that such block copolymer formation is favored by an associative mechanism forming highly unstable activated silicon intermediates.