Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

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. ... [Pg.265]

Tables. Styrene monomer reactivity ratios for copolymerizations of styrene (Mi) with 1,1-diphenylethylene using w-butyllithium as initiator [126]... 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... [Pg.512]

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. [Pg.530]

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... [Pg.98]

Table7. Monomer reactivity ratios (ri) for the copolymerization of dienes (Mi) and 1,1-diphenylethylene using n-butyllithium as initiator [125, 133-136]... 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. [Pg.100]

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... [Pg.122]

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. [Pg.290]


See other pages where Reactivity ratios butyllithium copolymerizations is mentioned: [Pg.40]    [Pg.696]    [Pg.507]    [Pg.8994]    [Pg.458]    [Pg.26]    [Pg.97]    [Pg.100]    [Pg.498]   
See also in sourсe #XX -- [ Pg.336 ]




SEARCH



Butyllithium

Butyllithiums

Copolymerization ratios

Copolymerization reactivity ratios

Reactivity copolymerization

Reactivity ratios

© 2024 chempedia.info