Anionic polymerization alkali metal complexes

Bifunctional Initiation. The bifunctional initiators like alkali metal complexes of polycyclic aromatic compounds can be used to produce ABA triblock copolymers even when the A anion is not sufficiently basic to initiate polymerization of B monomers. In these cases polymerization would be started with monomer B to produce a polymeric dianion which could initiate polymerization of the A monomer which is added later. These initiators can be prepared only in aliphatic ethers, however. This precludes their use for the synthesis of useful styrene-diene ABA copolymers because polydienes made anionically in such solvents have low 1,4 contents and are not good rubbers. 

In case the anion is the polymeric species (anionic polymerization) a carbanion or an alkoxide anion forms the active chain end. Initiation is achieved by direct attack of organometaUic compounds, or by electron transfer from alkali metals, alkali metal complexes, or ionizing radiation. In case the cation is the polymeric species (cationic polymerization) a... 

Anionic polystyrene can be prepared by polymerizing styrene with butyl lithium, alkali metals, or soluble alkali metal complexes such as sodium naphthalene ... 

The polymerization of acrylate esters by organomagnesium reagents is best described as pseudo-anionic monomer is complexed to a magnesium atom covalently bonded to carbon. The anionic polymerization of methyl methacrylate in benzene yields the syndiotactic polymer when the initiator is an alkali metal complexed with 18-dicyclohexyl-6-crown. When a solution of methyl methacrylate in toluene is placed below a solution of butyl-lithium in the same solvent at —78 °C so as to avoid any mechanical mixing, the polymer obtained has a higher isotacticity than that observed if the solutions are stirred. ... 

Interest in the synthesis and structural characterisation of less common metalloorganophosphide systems has continued. A range of alkali metal complexes of the phosphide anion (48) has been prepared from the lithio-phosphide by simple metathesis with alkali metal alkoxides. The lithio-phosphide exists as a dimer, but crystallisation of the sodium and potassium drivatives in the presence of TMEDA results in the formation of monomeric species. The caesium triphosphenide (49), involving a phosphorus analogue of the allyl anion, has been prepared from the previously described sodium complex. Unlike the sodium and potassium complexes, which are monomeric, the caesium complex has a polymeric structure. A variety of arylphosphide complexes of magnesium, calcium, strontium and barium have been prepared and their solid state structures characterised. Cop-per(I)-, silver(I)- and gold(I)-complexes of the cyclo-(P ion have also... 

The following are commonly nsed initiator systems for anionic polymerization 1. Alkali metals and alkali metal complexes (e.g., Na, K, Li, and their... 

Block copolymers of (R,S)-(3-butyrolactone and eCL have been synthesized by combining the anionic ROP of the first monomer with the coordinative ROP of the second one (Scheme 15) [71]. The first step consisted of the synthesis of hydroxy-terminated atactic P(3BL by anionic polymerization initiated by the alkali-metal salt of a hydroxycarboxylic acid complexed with a crown ether. The hydroxyl end group of P(3BL could then be reacted with AlEt3 to form a macroinitiator for the eCL ROP. 

The purpurate anion (53) has a mononegative charge delocalized over more than one donor atom.30 The kinetics of its complexation with alkali metal cations have been reviewed.290 The structures of several purpurates have been solved and the ligand consistently acts as a tridentate ligand. However, a variety of bonding modes are exhibited with the cation and polymeric structures resulting.30... 

Enolate Initiators. In principle, ester enolate anions should represent the ideal initiators for anionic polymerization of alkyl methacrylates. Although general procedures have been developed for the preparation of a variety of alkali metal enolate salts, many of these compounds are unstable except at low temperatures (67,102,103). Useful initiating systems for acrylate polymerization have been prepared from complexes of ester enolates with alkali metal alkoxides (104,105). 

Synthetic routes include anionic, cationic, zwitterionic, and coordination polymerization. A wide range of organometallic compounds has been proven as effective initiators/catalysts for ROP of lactones Lewis acids (e.g., A1C13, BF3, and ZnCl2) [150], alkali metal compounds [160], organozinc compounds [161], tin compounds of which stannous octoate [also referred to as stannous-2-ethylhexanoate or tin(II) octoate] is the most well known [162-164], organo-acid rare earth compounds such as lanthanide complexes [165-168], and aluminum alkoxides [169]. Stannous-2-ethylhexanoate is one of the most extensively used initiators for the coordination polymerization of biomaterials, thanks to the ease of polymerization and because it has been approved by the FDA [170]. 

Although most alkali metal compounds have M—C a bonds, cyclopentadienyl 7r-complexes are known for Li, Na, and K. These are commonly polymeric but solvation can break the chains and even result in cation-anion separation.44... 

The fi-diketonates have been extensively studied, particularly since some of the fluorinated derivatives give complexes that are volatile and suitable for gas-chromatographic separation. The preparation of /3-diketonates by conventional methods invariably gives hydrated or solvated species such as [Ln(acac)3]-QHsOH SHzO. Anhydrous species obtained by vacuum dehydration appear to be polymeric, not octahedral. The neutral /3-diketonates can complex further to give anionic species such as the eight-coordinate thenoyltrifluoroacetate [Nd(TTA)4] The alkali metal salts of [Ln(/3-dike)4] are sometimes appreciably volatile and can be sublimed. 

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