Influence of the kind of crown ether on the anionic polymerization of (phenoxymethyl)oxirane initiated by potassium tert-butoxide

The propagation rate constant, k_p, was determined for the polymerization of (phenoxymethyl)oxirane (2,3-epoxypropyl phenyl ether) initiated by potassium tert-butoxide in the presence of various crown ethers: 12-crown-4, 15-crown-5, 18-crown-6, dicyclothexano-18-crown-6, dicyclohexano-24-crown-8, dibenzo-18-crown-6 and dibenzo-24-crown-8. The equation correlating k_p with complexation constants, K_c, of the crown ethers was derived.     

Anionic polymerization of carbazolyl-substituted oxiranes initiated by potassium alkalide,potassium tert-butoxide and potassium hydride

The influence of the kind of initiating system and the addition of a crown ether on the anionic polymerization of oxiranes with a carbazoyl substituent is described. Potassium alkalide, potassium tert-butoxide and potassium hydride were used as initiators. Selecting a suitable initiator and crown ether concentration, carbazolyl-containing polymers with polymerization degrees from 4 to 60 can be produced. Using a suspension of potassium hydride in tetrahydrofuran, polymers with relatively high molar masses were obtained.     

Influence of the kind of crown ether on the heterogeneous polymerization of propylene oxide in the presence of potassium hydride

The influence of 12-crown-4, 15-crown-5, 18-crown-6, dicyclohexano-18-crown-6 and dicyclohexano-24-crown-6 on the propylene oxide polymerization with potassium hydride was studied. The highest reaction rate was obtained in the presence of 18-crown-6 or dicyclohexano-18-crown-6. The use of dicyclohexano-18-crown-6 was found to enhance the molecular mass of polymers more than other ligands. The observed effects were related to the heterogeneity of the reaction mixture and the structure of the crown ether complexes with the potassium cation.     

Polymerization of lactams, 24. Effect of impurities on the non-activated polymerization of 2-pyrrolidone initiated with potassium tert-butoxide

The effect of tert-butyl alcohol, lower alcohols, and water on the non-activated polymerization of 2-pyrrolidone initiated with potassium tert-butoxide at 40°C was investigated. It was proved that the alcoholytic activity of alcohols decreased with the steric hindrance of the hydroxyl group; the effect of water is distinctly more pronounced.     

Anionic polymerization of oxiranes and cyclic siloxanes initiated with potassium salt-crown ether systems

Potassium carboxylates and 18-crown-6 form initiator systems for the anionic polymerization of oxiranes to afford polyethers with an acyloxy group at one of the chain ends. Because of the slow initiation as compared to the propagation step, the resulting polymers have wide molecular weight distributions (M _w/M _n ≈ 4,0). The presence of a small amount of water in the catalysts accelerates the initiation to give polymers with narrow molecular weight distributions (M _w/M _n ? 1,2). The polymerization of methyloxirane is accompanied by a significant chain-transfer reaction to the monomer, especially at high temperatures. Hexamethylcyclotrisiloxane is also polymerized by the same initiators. Furthermore, potassium salts of carboxylic acids initiate the polymerizations in the presence of a crown ether.     

Mechanisms and kinetics of the anionic polymerization of acrylates, 3. Effect of lithium chloride and lithium tert-butoxide on the oligomerization of tert-butyl acrylate

The influence of lithium tert-butoxide (tBuOLi) and of lithium chloride on the oligomerization of tert-butyl acrylate (tBuA) initiated by tert-butyl α-lithioisobutyrate (tBiB-Li) was investigated. These additives affect both the kinetics and the product distribution. Whereas the addition of LiCl leads to a narrower molecular-weight distribution (MWD) the presence of tBuOLi induces broader MWD's, characterized by a very high fraction of the dimer. Both additives decrease the rates of propagation to different degrees. These effects are discussed on the basis of the formation of aggregates and adducts, the lithiated dimer having a higher tendency to form aggregates than the other oligomers. The stability of the growth centres in this oligomerization is increased in the presence of these additives, tBuOLi exhibiting a much stronger effect than LiCl. The interaction of the lithiated dimer with the additives could not be demonstrated in the IR spectra of these mixtures.     

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

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-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.     

Mechanisms and kinetics of the anionic polymerization of acrylates, 2. Polymerization of tert-butyl acrylate in a flow tube reactor and effect of lithium chloride and lithium tert-butoxide

The kinetics and the molecular weight distributions (MWD) in the anionic polymerization of tert-butyl acrylate (tBuA) in tetrahydrofuran at 23 ± 3°C were investigated. Tert-butyl α-lithioisobutyrate (tBiB-Li) was used as the initiator in the absence and presence of the additives lithium chloride and lithium tert-butoxide (tBuOLi). A flow tube reactor was used which allowed very rapid mixing of reagents, within milliseconds. The polymerization is extremely fast, half-lives being 0,01 s for the system without additive, 0,05 s for LiCl and 3 s for tBuOLi as an additive. The rate of termination was estimated from the strong UV absorption of the enolized β-oxoester end group formed. The number-average degree of polymerization is a linear function of conversion, the absolute values, however, demonstrate initiator efficiencies of only ca. 30%. The MWD's of the polymers formed are narrow (M _w/M _n = 1,35 without additive, M /M _n = 1,08 in the presence of LiCl and M _w/M _n = 1,77 in the presence of tBuOLi). After precipitation these values are reduced to 1,17; 1,06 and 1,32, respectively. Experiments in a stirred tank reactor and in ampoules lead to much broader MWD's. This shows that the rate of mixing has a strong effect on the MWD and is of substantial importance in these rapid polymerizations.     

Synthesis of poly(ethylene oxide) with a terminal amino group by anionic polymerization of ethylene oxide initiated by aminoalcoholates

Poly(ethylene oxide)s having a primary or secondary amino group at one chain end have been synthesized by direct anionic polymerization of ethylene oxide initiated by aminoalcoholates. The ring opening reaction of ethylene oxide by the amino group could be avoided when the alcoholate was reactive enough, that is, with potassium alcoholates in dry aprotic medium (THF). In this case, a living anionic polymerization of ethylene oxide occurred, with full conversion of the monomer. This is shown by the NMR and molecular weight characterizations of the polymers and kinetic studies of the polymerization.     

The counterion effect on the steric course of the cationic polymerization of tert-butyl vinyl ether

The cationic polymerization of tert-butyl vinyl ether was carried out at ?76°C with a variety of triphenylmethyl salts as initiator. The microtacticity of the polymer was determined by ¹H NMR spectroscopy after conversion to poly(vinyl alcohol). The fraction of isotactic units, P_m, increased with decreasing polarity of the polymerization medium, in consistence with the published data for metal halide initiators. The P_m value decreased gradually from 0,85 to 0,72–0,75 in 7 : 3 (v/v) CH₂Cl₂-toluene by increasing the counteranion radius from 2,4 Å (BF^?₄) to ca. 4 Å (AlCl^?₄). A further increase in the counteranion size, however, did not notably influence the steric structure of the polymer. These structure variations are discussed in terms of the steric course of cationic propagation. In the case of pentacoordinate counteranions (SnCl^?₅ and ZrCl^?₅), the steric structure depended also on the counteranion concentration, as already reported for other monomers.     

Equilibria in the anionic polymerization of methyl methacrylate, 2. Effect of lithium tert-butoxide on rate and equilibrium constants

The effect of lithium tert-butoxide (t-BuOLi) on rate constants and equilibrium constants of reactions involved in the initial stage of the anionic polymerization of methyl methacrylate (MMA) in tetrahydrofuran, initiated by methyl α-lithioisobutyrate (P) was investigated at 23 ± 3°C. Addition of t-BuOLi decreases the rate constants of initiation and propagation by one order of magnitude; the rate constants of termination by cyclization decrease by two orders of magnitude. This leads to an overall tenfold higher preference of propagation with respect to termination and explains the favourable effect of alkoxide in the polymerization reported earlier. Within experimental error, the equilibrium constant for initiation is independent of alkoxide. The infrared spectra prove the interaction of lithiated MMA-dimer with t-BuOLi and show the changed properties of the Li-enolate group as well as the increased extent of the γ-ester group coordination to lithium.     

Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 4 NMR and quantum chemical study of the initiation systems containing tert-butyl 2-lithioisobutyrate and lithium tert-butoxide or lithium 3-methylpentan-3-olate

In contrast to methyl 2-lithioisobutyrate ( I ), tert-butyl 2-lithioisobutyrate ( A ) in tetrahydrofuran (THF) appears to have one form only, irrespective of concentration (0,1-0,8 mol/L) or temperature (203–273 K). According to its relaxation characteristics, this form probably is a tetramer. The results indicate, however, that about 20% of A do not provide well-developed NMR signals and may be present as a partly organized pseudophase. A is shown to form 2:2 and 1:3 complexes with lithium tert-butoxide ( B ) and lithium 3-methylpentan-3-olate (C) in THF in dependence on their mole ratio and partly on storage time. The ⁷Li, ¹H and ¹³C NMR relaxation behaviour of these complexes support their essentially tetrameric nature. Although intramolecular exchange of Li atoms in a complex appears to be rapid, intermolecular exchange of any of the components is vanishingly slow on the NMR time scale. The complexes of A with either B or C exhibit remarkable stability above 273 K, in contrast to that of A itself. The quantum chemical analysis of the complexes shows that they are held together by a cooperative system of polycentric bonds and electrostatic interactions. Thus they are not easily destroyed by thermal activation but they react readily with monomer. Implications of the results for anionic polymerization of (meth)acrylates are discussed.     

Studies on the mechanism of redox polymerization initiated by N-haloamines and iron(II)

The mechanism of the redox polymerization of methyl methacrylate in aqueous medium in the dark was studied for the redox initiator systems N-halodiethylamine + Fe(II) and triethylamine + halogen + Fe(II), by analysis of the polymer end groups using the dye partition method. In the case of chlorine, both these initiator systems incorporate only the amino group into the polymer to an extent of about one group per polymer molecule. The polymers are found to be free from chlorine. Furthermore, a large portion of the total amino groups introduced into the polymer, using the initiator system triethylamine + halogen + Fe(II) are quaternary in nature. In the case of bromine, both the initiator systems introduce only a bromine atom and no amino group into the polymer. The initiator systems containing chlorine prove to be useful for the preparation of polymers containing amino groups at the one end only.     

Anionic block polymerization initiated by potassium solutions, 2. Synthesis of poly(2-oxetanone)-block-polystyrene-block-poly(2-oxetanone)

The block polymerization of styrene with 2-oxetanone (β-propiolactone) proceeds fast with a yield of more than 90%, in the presence of potassium solutions in THF containing 18-crown-6. Poly(2-oxetanone)-block-polystyrene-block-poly(2-oxetanone) ABA triblock polymers having the expected molecular mass and composition are formed. Their glass transition and melting temperatures as well as their melting enthalpies determined by DSC show a strict correlation with block polymer composition. The mechanism of this block polymerization involving acyloxygen and alkyl-oxygen bond scission in 2-oxetanone is in good agreement with previous results of the homopolymerization of β-lactones by alkali metal solutions abounding in potassium anions.     

Influence of substituent on the polymerization of oxiranes by potassium hydride

The polymerization of butoxymethyl-, ethyl-, methyl-, phenoxymethyl-, phenyl- and 2-propen-1-yloxymethyloxirane in the presence of potassium hydride suspension in tetrahydrofuran with 18-crown-6 was studied. The influence of polar and steric effects of substituent on the reaction rate is described. The appropriate correlation equation is derived. The chain transfer reaction to the monomer, found to occur only in the polymerization of methyloxirane, results in lower molecular weight and higher polydispersity of poly(methyloxirane) as compared with other polymers obtained.     

Formation of macrozwitterions in anionic vinyl polymerization initiated by tertiary phosphines. 5th communication on macrozwitterions1

The temperature dependency of the thermal degradation of Nylon 6.6 and Nylon 6.10 was compared under different state conditions. The considerably more pronounced thermal instability of Nylon 6.6 can be understood from the ring closure tendency of the adipic-acid component. In the presence of water the thermolysis is predominantly determined by reactions of the endgroups and in dry high-molecular systems by reactions involving chain-amide-groups, where the primary reaction step consists in a break of an amide-bond forming an amino-endgroup and a neutral cyclopentanone endgroup. In both cases the secondary products of the breakdown are compounds resulting from the reaction of cyclopentanone with amines, and partly products from the reaction of NH₃ with ? COOH and ? NHCO? . Not in all cases the strong tendency for gelation and the amount of NH₃ can be understood from the formation of secondary amines. The origin of relatively large amounts of NH₃ and CO₂ found in Nylon 6.6-degradation can satisfactorily be explained on the basis of previous model investigations.     

Vinyl polymerization by metal complexes, 17. Effect of nitriles on the vinyl polymerization initiated by imidazole-copper (II) complex

Polymerization of vinyl monomers initiated by the imidazole-copper(II) complex was studied in dimethyl sulfoxide solution. Different from the case of acrylonitrile, the polymerization of styrene and methyl methacrylate did not proceed, even in the presence of various sort of nitriles. From these findings and the copolymerization behaviour of acrylonitrile with styrene and methyl methacrylate, together with the spectroscopic data, the presence of acrylonitrile monomer is essential for generating active species to initiate the polymerization.