Anionic polymerization of acrylates. III. Polymerization of 2-ethylhexyl acrylate initiated by lithium-tert-butoxide (original) (raw)
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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.
2002
Ligated anionic polymerization of methyl methacrylate (MMA) and tert-butyl acrylate (t-BuA) initiated either with 1,1-diphenyl-3methylpentyllithium (DPMPLi) or a-methyl styryllithium (a-MStLi) or methyl 2-lithioisobutyrate (MIB-Li) stabilized with lithium tertbutoxide (t-BuOLi) was studied at 260 8C. In combination with DPMPLi, or a-MStLi, stabilizing efficiency of the alkoxide is negligible; MMA polymerizes with high reaction rate, but the chains self-terminate after all the monomer has been consumed, which was tested in twodose experiments. Ageing of mixed DPMPLi/t-BuOLi solutions as well as an excess of the alkoxide over the initiator have no effect on the stability of the growing chain-ends. In the presence of ten-fold excess of t-BuOLi, MIB-Li initiates slow polymerization of MMA with high stability of active centers. Three MMA doses were successively polymerized producing polymers with narrow MWDs in all steps, so that the active centers remained living for more than 4 h. t-BuA also polymerized in a living manner with the same system. q
Macromolecules, 1998
Interactions of lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM) with the model dimer ditert-butyl 2-lithio-2,4,4-trimethylglutarate (A) and the living poly(tert-butyl methacrylate) oligomers (B) were studied in tetrahydrofuran-d 8 at 203-273 K using 1 H, 13 C, 7 Li, and 6 Li, 1D and 2D, NMR and ab initio SCF 3-21G and MNDO quantum chemical calculations. LiOEEM is shown to have a strong tendency to self-aggregation, producing dimeric, trimeric, and tetrameric aggregates and competing with its mixed aggregation (or complexation) with A and, in particular, B. When dissolved in THF, LiOEEM as well as its mixtures with A form metastable systems which relax in several days at 258 K into equilibrium. Interaction of LiOEEM with A leads to a system of mixed aggregates LiOEEM 1A1, LiOEEM3A1, and possibly LiOEEM2A1 along with the original components, in relative populations depending on the LiOEEM/A molar ratio, temperature, time, and probably other factors of preparation. Probable structures of these complexes are proposed, and the nature of the prevalent bonding is suggested. Experimental results indicate that LiOEEM is unable to convert A completely at moderate excess (up to 4/1 mol/mol). Interaction of LiOEEM with B leads to quite analogous complexes but with even lower yields. There appear to be traces of uncomplexed B even at the LiOEEM/B ratio of 10 mol/mol. This is suggested to produce at least two different kinds of active growth centers in the corresponding ligated anionic polymerization of tert-butyl methacrylate and, consequently, the observed bimodality of the polymeric product. The difference with respect to methyl methacrylate, where LiOEEM ensures an almost ideal living polymerization, is suggested to be due to the steric hindrance of efficient complexation exerted by the tert-butyl group.
Journal of Polymer Science Part A: Polymer Chemistry, 2011
Thermal frontal polymerization is a process in which a localized reaction propagates through an unstirred system by the coupling of the thermal diffusion and the Arrhenius kinetics of an exothermic polymerization. With multifunctional acrylates, such as trimethylolpropane triacrylate (TMPTA-n), front temperatures can reach 250 C, resulting in smoke from unreacted peroxide. Addition of a thiol lowers the front temperature and the front velocity due the copolymerization between the thiol and the acrylate, with some formulations not sufficiently reactive to sustain frontal polymerization. The effects of molecular weight per thiol and functionality of thiol on front temperature and velocity were studied in the frontal copolymerization of TMPTA-n/trimethylolpropane ethoxylate triacrylate and different thiols. We also investigated the front temperature and velocity for a system containing triacrylate and dodecyl acrylate. Finally, the effects of lithium chloride in the presence of thiol on the front velocity and front temperature were studied. V
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.
Studies on high conversion polymerization of n-alkyl acrylates
Polymer, 1994
The effect of initiator [I] and monomer [M] concentration on the molecular weight and molecular weight distribution in behenyl acrylate polymerization is presented. Gel formation was observed at high [I] and [M]. The effect of solvents in the polymerization of behenyl, octadecyl and butyl acrylates is discussed. The gel effect is prominent in non-polar solvents and in solvents with lower transfer constants. The viscosity of the reaction medium appears to control the polymerization rate and molecular weight distribution.
Macromolecules, 2010
Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS 2 ) was employed for the characterization of three poly(n-butyl acrylate)s. These polymers were produced at high temperature using the same initiator, tert-butyl peroxy-3,5,5-trimethylhexanoate, but in different solvents, viz. pentyl propionate, xylene and butyl acetate. Exact mass experiments performed on these polymers in an Orbitrap instrument supplied valuable information on the end group structures. Study of the data allowed identification of many reactions during the polymerization such as beta-scission and chain transfer to solvent or radical transfer to solvent from the initiator. Different fragmentation pathways were observed from the same precursor mass on MS/MS experiments, indicating the presence of isomers. The comprehensive assignment of the peaks in the LC-MS data allowed us to describe the end group distribution in a semiquantitative way. The results clearly show that the relatively reactive solvents used for polymerization have strong influences on the polymer composition.
Macromolecules, 1999
The kinetics of the anionic polymerization of methyl methacrylate in the presence of lithium perchlorate (LiClO4) 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 LiClO4 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 LiClO4 does not effectively perturb the aggregation of the enolate ion pair. The formation of various mixed aggregates is proposed. The polydispersity index of the obtained PMMA is lower than that obtained in the absence of salt indicating faster aggregation-deaggregation equilibria than in the absence of salt. The rate constants of termination in absence and presence of salt are comparable. Thus, LiClO 4 does not affect termination reactions, again similar to LiCl.