Anionic Polymerization Of Acrylates Research Articles

Anionic polymerization of acrylates. XIV. Synthesis of MMA/acrylate block copolymers initiated with ester-enolate/ tert-alkoxide complex

Diblock copolymers of methyl methacrylate (MMA) with 2-ethylhexyl, butyl, ethyl or tert-butyl acrylate (EtHA, BuA, EtA, t-BuA) have been prepared by the ligated anionic polymerization initiated with methyl 2-lithioisobutyrate (MIB-Li) in the presence of an excess of Li tert-butoxide ( t-BuOLi) in toluene/THF mixture at −60 or −78 °C. The copolymers, prepared at −60 °C, show MWD with a hint of bimodality, indicating partial deactivation of the living PMMA upon addition of acrylic monomer. At −78 °C, the extent of this deactivation is distinctly lower, the formed block copolymers, in particular, poly(MMA- b-EtHA), have unimodal MWD and exhibit tails only in the lower-molecular-weight region. Poly(MMA- b-EtHA)s were extracted with acetonitrile dissolving PMMA; very small parts of the crude products dissolved, whereas prevailing parts remained as solids documenting thus formation of block copolymer in a high yield. Surprisingly, the highest amount of self terminated PMMA was found in block copolymerization of MMA with t-BuA at both the temperatures, the products of which had clearly bimodal MWDs. This finding is shortly discussed on the basis of relatively slow propagation of t-BuA in comparison with EtHA, BuA and EtA.

Anionic Polymerization of Acrylates. Synthesis of (Meth)acrylate Di- and Triblock Copolymers Using the Li Ester−Enolate/tert-Alkoxide Initiating System

Methacrylate di- and triblock copolymers composed of methyl (MMA), butyl (BuMA), 2-(dimethylamino)ethyl (DMAMA), and 2-ethylhexyl (EtHMA) methacrylates and tert-butyl acrylate (t-BuA) blocks were prepared by ligated anionic polymerization and characterized by SEC and NMR. The process was initiated with the system methyl 2-lithioisobutyrate/lithium tert-butoxide (MIB-Li/t-BuOLi) at the 1/10 mole ratio, which was recently described as the optimum composition, at THF at -60 °C. The monomers were added to the reaction mixture successively after chosen polymerization intervals and products of the individual polymerization steps were isolated and analyzed. Molecular weights of methacrylate copolymers increased with increasing total amount of the monomers added, and the products of the two-or three-step polymerizations were not detectably contaminated with the products of the foregoing steps, so that the corresponding MWD curves were unimodal and symmetric. The product of MAIA/t-BuA block copolymerization exhibited bimodal MWD, originating probably by the self-termination proceeding at the beginning of the second polymerization step after addition of an acrylate monomer to the living polymethacrylate. A possible mechanism of self-termination and reactions of polymethacrylate chains bearing a few terminal acrylate units are briefly discussed.

Anionic polymerization of acrylates. XII. Polymerization of methyl methacrylate and tert-butyl acrylate initiated with alkyllithiums or methyl 2-lithioisobutyrate in the presence of lithium tert-butoxide

Ligated anionic polymerization of methyl methacrylate (MMA) and tert-butyl acrylate ( t-BuA) initiated either with 1,1-diphenyl-3-methylpentyllithium (DPMPLi) or α-methyl styryllithium (α-MStLi) or methyl 2-lithioisobutyrate (MIB-Li) stabilized with lithium tert-butoxide ( t-BuOLi) was studied at −60 °C. In combination with DPMPLi, or α-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 two-dose 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.

Anionic polymerization of acrylates. XI. Effect of composition and ageing of the Li ester enolate/tert-butoxide initiating complex on the anionic polymerization of methyl methacrylate and 2-ethylhexyl acrylate

The article presents the results of (meth)acrylate polymerization in THF initiated with various complexes of methyl 2-lithioisobutyrate (MIB-Li) and lithium tert-buioxide (t-BuOLi), prepared from the components in mole ratios 1:3, 1:6 and 1:10 in THF and aged for various time periods and at various temperatures. In dependence on the component ratio, temperature and storage time, the mixtures form cubic cross-aggregates with MIB-Li/t-BuOLi mole ratios 3:1, 2:2 and 1:3 which exhibit different behavior when used as initiators. It was found that the way of synthesis of the complex and its structure not only affect the kinetics of polymerization but also distinctly change the microstructure of the formed polymers.

Anionic Polymerization of Acrylates. 10. Synthesis and Characterization of Block Copolymers with Acrylate Blocks

Block copolymers poly(styrene)-block-poly(tert-butyl acrylate), poly(tert-butyl acrylate)-block-poly(2-ethylhexyl acrylate), and poly(tert-butyl acrylate)-block-poly(butyl acrylate) were prepared by a successive anionic polymerization at -60 °C. As initiators, butyllithium/lithium tert-butoxide 1 :6 (mol/mol) and tert-butyl 2-lithioisobutyrate/lithium tert-butoxide 1 :3 or 1 :10 (mol/mol) complexes were used, in the mixed solvent toluene/THF 9 :1 or 19 :1 (v/v). Products were characterized by SEC, 13 C NMR, and DSC. The block character of poly(tert-butyl acrylate)-block-poly(2-ethylhexyl acrylate) was proved by the extraction test with hexane. Compared to corresponding homopolymers, all the block copolymers exhibit only a slightly broadened MWD, which documents the virtually negligible extent of self-termination under given experimental conditions.

Anionic polymerization of acrylates

The article presents preliminary results of the anionic polymerization of 2-ethylhexyl- and butyl acrylates initiated by ester enolate in the presence of Li 3-methylpentoxide-3. Compared with the Li t-butoxide which has been widely used earlier, this alkoxide is a more efficient stabilizer of active centers. Under selectively chosen reaction conditions, polymerizations of both monomers proceed quantitatively with a small extent of the selftermination event at-40 and-20°C producing polymers with narrow MWD's.

Anionic Polymerization of Acrylates. 8. Kinetics of the Anionic Polymerization of Butyl Acrylate Initiated with the Complex Initiator Lithium Ester Enolate/Lithium tert-Butoxide

The kinetics of the anionic polymerization of butyl acrylate initiated with the system tert-butyl 2-lithioisobutyrate (Li-t-BIB)/lithium tert-butoxide (t-BuOLi) in the mixed solvent toluene/THF was studied at -70 to -40°C. At -60°C, the external reaction order is unity with respect to the concentrations of both the monomer and propagating species. Semilogarithmic conversion curves indicate a certain extent of self-temination at higher degrees of conversion. The termination reaction process formally as a first-order reaction with respect to active centers. Kinetic calculations show that while the rate constant of propagation is concentration-independent, the rate constant of termination increases with the initial concentration of the monomer

Anionic polymerization of acrylates

The anionic polymerization of butyl acrylate initiated by the complex initiator tert-butyl 2-lithioisobutyrate/tBuOLi (mole ratio 1:3 or 1:10) was studied in toluene, THF and their mixtures (9:1 or 19:1 v/v) at -60°C. The extent of autotermination increases with increasing content of THF; in neat THF the limiting conversion is only ca 70%. In neat toluene, the prepared polymers have broad or even multimodal MWD; conversion curves indicate a slow initiation step. M w /M n , ratio of the polymers prepared in THF and in the mixed solvents was 1.7 and 1.12-1.35, respectively

The anionic polymerization of acrylates, 5. Controlling the molecular weights in the polymerization of 2‐ethylhexyl acrylate initiated by the mixed initiator lithium ester‐enolate/lithium tert‐butoxide

AbstractIn 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‐butyl 2‐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 [M]0/[I]0 spanned the range from 14 to 160. The mole ratio tert‐butyl 2‐lithioisobutyrate: Li tert‐butoxide 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 (37 00–55 000) depend linearly on the ratio [M]0/[I]0. 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.

Anionic polymerization of acrylates. II. Polymerization of 2‐ethylhexyl acrylate initiated by butyllithium/lithium‐tert‐butoxide system in tetrahydrofuran and its mixtures with toluene

AbstractThe anionic polymerization of 2‐ethylhexyl acrylate (EtHA) initiated with the complex butyllithium/lithium‐tert‐butoxide (BuLi/t‐BuOLi) was investigated at −60°C in a medium of various solvating power, i.e., in mixtures of toluene and tetrahydrofuran and in neat tetrahydrofuran. With increasing amount of THF in the mixture the attainable limiting conversion of polymerization decreases; the monomer can be polymerized quantitatively only in a toluene/THF mixture (9/1). Molecular weights of the polymers thus obtained, their distribution, and initiator efficiency are not appreciably affected by the polymerization medium. The molecular weight distribution of the products is medium‐broad (Mw/Mn = 2–2.4), with a hint of bimodality. The 1H‐13C‐NMR, and IR spectra suggest that during the polymerization there is neither any perceptible reesterification of the polymer with the alkoxide nor transmetalation of the monomer with the initiator. In a suitable medium, autotermination of propagation proceeds to a limited extent only, predominantly via intramolecular cyclization of propagating chains; in a medium with a higher content of polar THF, it prevails and terminates propagation before the polymerization of the monomer has been completed. © 1992 John Wiley & Sons, Inc.

Anionic polymerization of acrylates. III. Polymerization of 2‐ethylhexyl acrylate initiated by lithium‐tert‐butoxide

AbstractThe polymerization of 2‐ethylhexyl acrylate (EtHA) initiated with lithium‐tert‐butoxide (t‐BuOLi) in tetrahydrofuran (THF) and in the temperature range between −60 and 20°C was investigated. The reaction rate is distinctly temperature‐dependent and at −60°C is already very low, similarly to the polymerization of methacrylates. Molecular weights of the polymers thus formed, particularly at higher temperatures, are inversely proportional to conversion of the monomer due to the slow initiation reaction. This is documented by the low consumption of alkoxide even at long reaction times, which also depends on the reaction temperature. At higher temperatures the polymerization stops spontaneously, due to the greater extent of autotermination reactions. The weak initiating efficiency of the alkoxide decreases still more with decreasing concentration of the monomer during the polymerization, as confirmed by the concentration dependence of the reaction rate in toluene at −20°C. The results suggest a negligible initiating effect of alkoxides in complex bases, particularly at lower polymerization temperatures. © 1992 John Wiley & Sons, Inc.

The anionic polymerization of acrylates, 4 the polymerization of 2‐ethylhexyl acrylate initiated with a mixed initiator lithium ester‐enolate/lithium tert‐butoxide

The anionic polymerization of acrylates, 4 the polymerization of 2‐ethylhexyl acrylate initiated with a mixed initiator lithium ester‐enolate/lithium <i>tert</i>‐butoxide

Anionic polymerization of acrylates. I. Polymerization of 2‐ethylhexylacrylate in nonpolar solvents

AbstractInitiation with a combined initiator n‐butyllithium/lithium tert‐butoxide in the ratio 1:6 brings the anionic polymerization of 2‐ethylhexylacrylate (EtHA) in toluene and n‐heptane at temperatures between −78 and −20°C up to a quantitative conversion. In the initial stages of the process the molecular weight distribution (MWD) of the products is polymodal as a result of the stablizing function of the alkoxide; MWD of the final product after a complete consumption of the monomer is medium, being visibly dependent on the reaction temperature and without any distinct content of low‐molecular weight components, which suggests a sufficient activity of all growth centers, and thus an essential restriction of side termination reactions.