Grignard reagent polymerization initiator

Braun et al. [258] used a combination of tert-butyllithium (t-BuLi) and tetramefhy-lethylenediamine to create initiator sites at the surface of carbon black for the LASIP of styrene. Schomaker et al. [259] first immobilized a methyl methacrylate derivative on colloidal silica and after activation by a Grignard reagent polymerized MMA. 

Polymerization of racemic 1-phenylethyl methacrylate (PEMA) using a chiral complex of a Grignard reagent with a diamine as an initiator may proceed by reaction of only one of the two enantiomers to give an optically active polymer. 

The isoselective polymerization of acetaldehyde has been achieved using initiators such as zinc and aluminum alkyls, Grignard reagents, and lithium alkoxides [Kubisa et al., 1980 Pasquon et al., 1989 Pregaglia and Binaghi, 1967 Tani, 1973 Vogl, 2000], The isoselectivity is high in some systems with isotactic indices of 80-90%. Cationic initiators such as BF3... 

In the case of sihca and sihcalike particles, Schomaker et al. [48] immobilized a methylmethacrylate (MMA) derivative onto sihca (Aerosil) particles, initiated polymerization using a Grignard reagent, and added additional MMA. 

Nucleophilic substitution of the chlorine atom present in 2-chlorothiepane (132) using Grignard reagents has provided a synthetic route to 2-methyl- (133) or 2-phenyl- (134) thiepanes (equation 27) (69JHC115). An a-sulfinyl carbanion (114), generated by alkyllithium attack on thiepane 1-oxide (115), was found to act as nucleophile in the synthesis of cis and trans sulfoxides of thiepane (133 equation 28) (78TL5239). Polymerization of 2-thiepanone (135) has been initiated by attack of the f-butoxide anion and concomitant liberation of a thiolate anion (Scheme 26) (64MI51700). 

Yerusalimskii has demonstrated a similar mechanism for acrylonitrile polymerization initiated by Grignard reagents (13). We were unable at the time to investigate the isotactic polymerization initiated by t-BuMgBr in toluene as it was too fast for classical techniques. We have now developed techniques which can follow this reaction. 

Dehydration of isochromanols has to be carried out with care because of the relative ease with which the resulting isochromenes undergo polymerization under acidic conditions. Potassium hydrogen sulfate is a suitable reagent in some cases, and p-toluenesulfonic acid has also been used (71MI22400). The initial hydroxy compounds are available from iso-chromanones by reduction or by the action of a Grignard reagent. 

Coupling to produce dimeric product was a side reaction in these systems also, e.g. 75 % dimer formation was reported for poly(styryl)lithium and 23 % dimer formation with the poly(styryl)-Grignard reagent 326). However, it should be noted that the only reported characterizations of these reactions were size exclusion chromatography traces and silver catalyzed polymerization of tetrahydrofuran using the polymeric halogen compounds as co-initiator. 

The initiation of methyl methacrylate polymerization by alkyl- and aryl-lithium compounds is a very complex process which has not been completely elucidated so far. Even less information is available on the efects of or-ganometals not containing lithium. Recently, the interest of some authors has centred on the application of Grignard reagents for the initiation of anionic polymerizations, especially of MMA [171, 172],... 

For the initiation of caprolactam polymerization, Grignard reagents [173] have been used as a source of lactamate salt. Tsuchiya and Tsuruta have described an interesting case of methyloxirane polymerization initiated with... 

As in free radical polymerization, there are initiation and propagation steps. Various initiators, such as organometallic compounds, alkali metals, Grignard reagents, or metal amides, like sodium amide, shown in Figure 3-31, can be used. Propagation proceeds in the usual manner, but there is no termination... 

Additions occur more easily if a carbanion with resonance or inductive stabilization is formed in the addition. Thus, fulvenes are very reactive, vinylsilanes and highly fluorinated alkenes somewhat less so. Styrene, 1,3-dienes, and enynes are more reactive than isolated alkenes, and Grignard reagents may be used to initiate anionic polymerization of styrenes, dienes, and acryhc monomers. Strained alkenes such as norbomenes and cyclopropenes are also more reactive. Examples of additions facilitated by resonance or substitution are shown in Scheme 8. 

Most Grignard reagents are inert toward styrene (up to the temperature of spontaneous thermal polymerization). This is a significant difference from lithium alkyls, which are readily able to initiate styrenic monomers [123]. The only reported exception is p-vinylbenzyl magnesium chloride, which polymerized styrene in THF at O C, but not at — 78X [50,51]. Substitution at the puru-position of a phenyl ring may stabilize the benzyl anion, owing to the delocatlization of electrons, and favor ionic dissociation of... 

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