Polymerization, anionic poly lithium

The difficulties encountered in the early studies of anionic polymerization of methyl methacrylate arose from the unfortunate choice of experimental conditions the use of hydrocarbon solvents and of lithium alkyl initiators. The latter are strong bases. Even at —60 °C they not only initiate the conventional vinyl poly-addition, but attack also the ester group of the monomer yielding a vinyl ketone1, a very reactive monomer, and alkoxide 23). Such a process is described by the scheme. 

Hyperbranched polymers have also been prepared via living anionic polymerization. The reaction of poly(4-methylstyrene)-fo-polystyrene lithium with a small amount of divinylbenzene, afforded a star-block copolymer with 4-methylstyrene units in the periphery [200]. The methyl groups were subsequently metalated with s-butyllithium/tetramethylethylenediamine. The produced anions initiated the polymerization of a-methylstyrene (Scheme 109). From the radius of gyration to hydrodynamic radius ratio (0.96-1.1) it was concluded that the second generation polymers behaved like soft spheres. 

Remarkably few systematic studies have been made of the kinetics of anionic polymerization in non-polar solvents containing small amounts of ethers in contrast, studies of bulk ether systems abound. Several studies have appeared 156 158) in which the propagation reactions involving styryllithium were measured in mixtures of benzene or toluene with ethers. The kinetic orders, in some cases, of the reactions were identical to those observed in the absence of the ether. Thus, in part, the conclusion was reached 157,1581 that the ethers did not disrupt the dimeric degree of aggregation of poly(styryl)lithium. The ethers used were tetrahydrofuran 156), anisole 157), diphenyl ether 158), and the ortho and para isomers of ethylanisole157). 

Rossi has synthetized block copolymers polyisoprene-poly(vinyl-2-pyridine) and polyisoprene-poly(vinyl-4-pyridine) of various composition and molecular weight by anionic polymerization under high vacuum205, 208. The polymerization in THF dilute solutions with Cumylpotassium as initiator yielded a 1,2 + 3,4-microstructure of the polyisoprene block. The polymerization in toluene solutions with sec-butyl-lithium as initiator yielded a 1,4-c/s-microstructure of the polyisoprene block. 

Living anionic polymerization of 4-vinylphenol was performed after transformation of the phenolic hydroxy group into trialkybilyl ether group and removal of the protection group after polymerization [125]. n-Butyl lithium was used for the synthesis of poly[2-hydroxy-4-methacryloyloxybenzophenone] [61] (102) or HALS terminated poly(methyl methacrylate) [126]. 2-Hydroxy-4-methacryloyl-... 

Poly(amino acids)2892 and polypeptides2893 can also be grafted onto starch. Starch was first alkylated in the presence of lithium naphthalene, and then the alkoxy derivatives were reacted with /V-carboxy anhydrides. Poly(amide amines) were produced by reacting amines with dioic acids on starch and then crosslinking with epichlorohydrin or 1,2-dichloroethane 2894 Grafting of starch with a synthetic polymer chain, for instance, polystyryl carboxylate anions prepared by an anionic polymerization, can be carried out on a blend of starch and cellulose functionalized by sulfonation, mesylation, or tosylation. In this manner, cellulose-starch graft copolymers were prepared.2895... 

Hydrocarbon Solvents One of the most important synthetic and commercial aspects of anionic polymerization is the ability to prepare polydienes [poly(l,3-dienes)] with high 1,4-microstructure using lithium as the counterion in hydrocarbon solutions [3, 156]. The key discovery was reported in 1956 by scientists at the Firestone Tire and Rubber Company that polyisoprene produced by lithium metal-initiated anionic polymerization had a high (>90%) cm-1,4-microstructure similar to natural rubber [47], In general, conjugated 1,3-dienes [CH2=C(R)-CH=CH2] can polymerize to form four constimtional isomeric microstructures as shown below. The stereochemistry of the anionic polymerization of isoprene and... 

The microstructure of anionic polymerization of other poly(l,3-diene)s with lithium as counterion in hydrocarbon media is also predominantly 1,4 microstructure [3], However, higher amounts of cm-1,4-microstructures are obtained with more sterically hindered diene monomers. Thus, using conditions that provide polyisoprene with 70% cm-1,4, 22% trans-, A, and 7% 3,4 microstructure, 2-/-propyl-1,3-butadiene and 2-n-propyl-l,3-butadiene provide 86% and 91% cm-1,4 enchainment, respectively. Both... 

As an additional example, for the structure in Figure 16.13, Figure 16.14 shows the NMR spectrum for a sample of poly(dimethylsiloxane) (PDMS-H) obtained by anionic polymerization of hexadimethyl-trisiloxane (D3) initiated by butyl-lithium in the presence of chlorodimethylsilane [14],... 

Living polymerization of azo monomers is one of the most effective ways to prepare well-defined azo BCs. Generally, a monodispersed macroinitiator should be prepared first. It is then used as an initiator for the subsequent polymerization of azo monomers. Finkelmann and Bohnert (1994) first reported the synthesis of LC-side chain AB azo BCs by direct anionic polymerization of an azo monomer. As shown in Scheme 12.1, the polymerization of polystyrene (PS)-based diblock copolymers was carried out from a PS-lithium capped with 1,1-diphenylethylene (DPE), whereas the poly(methyl methacrylate) (PMMA)-based diblock copolymers were prepared by addition of methyl methacrylate (MMA) monomers to the living azo polyanion, obtained by reaction of l,l-diphenyl-3-methylpentylithium (DPPL) with the azo monomer in tetrahydrofuran (THF) at lower temperature. By this method, a series of well-defined azo BCs were obtained with controlled molecular weights and narrow polydispersities (Lehmann et al., 2000). 

Chloral, CChCHO, can be anionically or cationically polymerized. The polymerization is initiated above the ceiling temperature of 58° C and then allowed to proceed well below the ceiling temperature. Phosphines and lithium /-butoxide are especially suitable as anionic polymerization initiators, whereas tertiary amines only produce poly (chlorals) of low thermal stability. Anionic copolymerization of chloral with excess isocyanates produces alternating polymers, as is also the case for the cationic copolymerization of chloral with trioxan. 

A tadpole polybutadiene with two linear PS chains has been prepared by Quirck and Ma living anionic poly(styryl) lithium chains were first coupled by reacting the living ends with the double diphenylethylene. Then the resulting polymer bearing two reactive catbanionic centers located in the middle of the chain was used as a bifimcdonal macroinitiator to initiate the anionic polymerization of butadiene. The two... 

An alternative approach to preparing i-PP standard reference materials has been suggested by Fetters etal [37], using narrow-distribution atactic polypropylenes, a-PP. The anionic polymerization of 2-methyl-1, 3-pen-tadiene with s c-butyl lithium occurs exclusively by 1,4-addition to produce poly(l,3-dimethyl-l-butenylene). The polymers are monodisperse in molecular mass distribution. Hydrogenation transforms them into a-PP. Light scattering and osmometry were carried out, as well as viscosity measufements in tetrahydrofuran and 2-octanol, a 0-solvent, and the intrinsic viscosity were related to the mass average molecular mass ... 

Chloral, CCI3CHO, can be polymerized cationically or anionically. Phosphine and lithium t-butoxide are especially suitable initiators for anionic polymerization, whereas tertiary amines produce poly(chlorals) of lower thermal stability. The polymerization is first initiated above the ceiling temperature (58°C) and is subsequently allowed to proceed well below the ceiling temperature however, yields of only 75-80% are obtained because of the unfavorable polymerization equilibria. Since the unconverted monomer cannot be removed completely by heating, heating must be supplemented by extraction to remove the residual monomer. 

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