Reactivity ratios butyllithium copolymerizations

On the other hand, butyllithium-aluminum alkyl initiated polymerizations of vinyl chloride are unaffected by free-radical inhibitors. Also, the molecular weights of the resultant polymers are unaffected by additions of CCI4 that acts as a chain-transferring agent in free-radical polymerizations. This suggests an ionic mechanism of chain growth. Furthermore, the reactivity ratios in copolymerization reactions by this catalytic system differ from those in typical free-radical polymerizations An anionic mechanism was also postulated for polymerization of vinyl chloride with t-butylmag-nesium in tetrahydrofuran. ... 

Tables. Styrene monomer reactivity ratios for copolymerizations of styrene (Mi) with 1,1-diphenylethylene using w-butyllithium as initiator [126]...

There are few studies of the effect of temperature on monomer reactivity ratios [Morton, 1983]. For styrene-1,3-butadiene copolymerization by r-butyllithium in rc-hexane, there is negligible change in r values with temperature with r — 0.03, r2 = 13.3 at 0°C and n = 0.04, r% = 11.8 at 50°C. There is, however, a signihcant effect of temperature for copolymerization in tetrahydrofuran with r — 11.0, r2 = 0.04 at —78°C and r — 4.00, r2 = 0.30 at 25° C. The difference between copolymerization in polar and nonpolar solvents is attributed to preferential complexing of propagating centers and counterion by 1,3-butadiene as described previously. The change in r values in polar solvent is attributed to the same phenomenon. The extent of solvation decreases with increasing temperature, and this results in... 

Relatively little information is available for the copolymerization of butadiene with isoprene. In an early paper by Rakova and Korotkov (8), it was concluded that in n-hexane with n-butyllithium as the initiator, the reactivity ratios for butadiene and isoprene were rg = 3.38 and rj = 0.47, respectively. 

Hatada and coworkers [130, 132] have investigated the copolymerization of divinylbenzenes with 1,1-diphenylethylene and the monomer reactivity ratios are listed in Tabled. Using ratios of DVB/DPE=0.5 in THF at -78°C, soluble copolymers could be obtained with compositions of DVB/DPE=1.2-1.4. The monomer reactivity ratios in Tabled suggest that a more highly alternating polymer structure will be obtained with mcfa-DVB compared to para-DVB. The resulting polymers were reacted with butyllithium at -78 °C in THF to... 

Table7. Monomer reactivity ratios (ri) for the copolymerization of dienes (Mi) and 1,1-diphenylethylene using n-butyllithium as initiator [125, 133-136]...

This lack of copolymerization reactivity of DPE was also observed for the copolymerization of 1,1-diphenylethylene and isoprene [125, 134]. As shown in Table 7, when isoprene was copolymerized with DPE in benzene using n-butyllithium as initiator, the monomer reactivity ratio was 37, which indicates that the addition of isoprene to the isoprenyllithium chain end is 37 times faster than the addition of 1,1-diphenylethylene. The unreactivity of isoprenyl carbanions toward DPE is unique to lithium the monomer reactivity ratios for isoprene in benzene were 0.38 and 0.05 with sodium and potassium as the counterions [125, 134]. When THE was used as the solvent at 0°C, ri decreased to 0.11 with lithium as counterion. 

It was anticipated that the copolymerization of substituted 1,1-dipheny-lethylenes with dienes such as butadiene and isoprene would be complicated by the very unfavorable monomer reactivity ratio for the addition of poly(-dienyl)lithium compounds to 1,1-diphenylethylene [133, 134]. Yuki and Oka-moto [133, 134] calculated values of ri=54 and ri=29 in hydrocarbon solutions for the copolymerization of 1,1-diphenylethylene (M2) with butadiene (Mi) and isoprene (Mi), respectively. Although the corresponding values in THE are ri(butadiene)=0.13 and ri(isoprene)=0.12, this would not be an acceptable solution since THE is known to form polymers with high 1,2-microstructures [3]. Anionic copolymerizations of butadiene (Mi) with excess l-(4-dimethyla-mino-phenyl)-l-phenylethylene (M2) were conducted in benzene at room temperature for 24-48 h using scc-butyllithium as initiator [189]. Anisole, triethy-lamine and ferf-butyl methyl ether were added in ratios of [B]/[RLi]=60, 20, 30, respectively, to promote copolymerization and minimize 1,2-enchainment in the polybutadiene units. Narrow molecular weight distribution copolymers with Mn=14xl0 to 32x10 (Mw/Mn=1.02-1.03) and 8, 12, and 30 amine... 

TMC and DTC can be used for the copolymerization with a less reactive six-membered cyclic carbonate such as 5,5-diphenyl-l,3-dioxan-2-one. The copolymerization proceeded according to an anionic mechanism to afford a polymer containing 5,5-diphenyl-l,3-dioxan-2-one units, but in lower ratio than that in the monomer feed. DTC was also copolymerized with other six-membered cyclic carbonates to furnish random as well as block copolymers upon addition of the initiator (sec-butyllithium) to a mixture of the monomers or upon consecutive addition of the monomers to the initiator, respectively. 

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