Coinitiator

The polymerization system is of the cationic type, usiag coinitiators such as AlCl and water at very low temperatures (—100° C) and leading to an almost instantaneous polymeriza tion (see Elastomers, SYNTHETIC-BUTYL RUBBER). 

The first sulfur curable copolymer was prepared ia ethyl chloride usiag AlCl coinitiator and 1,3-butadiene as comonomer however, it was soon found that isoprene was a better diene comonomer and methyl chloride was a better polymerization diluent. With the advent of World War II, there was a critical need to produce synthetic elastomers in North America because the supply of natural mbber was drastically curtailed. This resulted in an enormous scientific and engineering effort that resulted in commercial production of butyl mbber in 1943. 

The production rate is 2—4 t/h, depending on the feed rate, monomer concentration in the feed, and conversion. The conversion of isobutylene and isoprene typically ranges from 75—95% and 45—85%, respectively, depending on the grade of butyl mbber being produced. The composition and mol wt of the polymer formed depend on the concentration of the monomers in the reactor Hquid phase and the amount of chain transfer and terminating species present. The Hquid-phase composition is a function of the feed composition and the extent of monomer conversion. In practice, the principal operating variable is the flow rate of the initiator/coinitiator solution to the reactor residence time is normally 30—60 minutes. 

Butyl slurry at 25—35 wt % mbber continuously overflows from the reactor through a transferline to an agitated flash dmm operating at 140—160 kPa (1.4—1.6 atm) and 55—70°C. Steam and hot water are mixed with the slurry in a nozzle as it enters the dmm to vaporize methyl chloride and unreacted monomers that pass overhead to a recovery system. The vapor stream is compressed, dried over alumina, and fractionated to yield a recycle stream of methyl chloride and isobutylene. Pure methyl chloride is recovered for the coinitiator (AlCl ) preparation. In the flash dmm, the polymer agglomerates as a coarse cmmb in water. Metal stearate, eg, aluminum, calcium, or zinc stearate, is added to control the cmmb size. Other additives, such as antioxidants, can also be introduced at this point. The polymer cmmb at 8—12 wt % in water flows from the flash dmm to a stripping vessel operated under high vacuum to... 

The following reaction scheme is suggested for methyl methacrylate monomer and CHBra halide as coinitiators ... 

A wide range of polymer networks are constructed in this manner. Poly(vinyltrichloacetate) was used as the coinitiator with styrene, MMA and chloroprene as cross-linking units. Polycarbonates, polystyrene, N-haloge-nated polyamide, polypeptides, and cellulose acetate, suitably functionalized, have been used as a coinitiator... 

The chlorinated surface of glass then acted as a coinitiator, and when photochemically treated with metal carbonyl in the presence of MMA monomer, a thin layer of 0.4 /Am thickness of poly(methyl methacrylate) was obtained. 

Polymers with an antiplatelet agent of 5-(6-carboxyl-hexyl) l-(3-cyclohexyl-3-hydroxyropyl) hydantoin as an end group were synthesized by esterifying the hydantoin molecule with a haloalcohol, such as CCI3CH2OH or BrCH2CH20H, and using the product as coinitiator with... 

Precooled coinitiator solution was rapidly added to precooled solution of monomer and initiator while shaking the culture tube. Polymerizations were terminated generally... 

In order to carry out these syntheses a key requirement was that the Si-G bond of the Si-Cl functional initiators should not react with the EtzAlCl coinitiator and the propagating carbenium ion, but be able to effect condensations. Synthetic possibilities obtainable with polymers having Si-Cl termini are shown in Scheme 1. 

The key requirements for using Si-Cl functional initiators to produce polymers carrying Si Cl termini by carbenium ion polymerization are i) Si-Cl should be inert toward aUcylaluminum coinitiators, ii) Si-Cl should not react with propagating carbenium ions, in) chain transfer to monomer should be negligible so as to end up with one Si-Cl head-group per polymer chain. 

Results of these orienting experiments compiled in Table 3 in regard to the effect of temperature, medium polarity, initiator concentration, monomer concentration, and coinitiator concentration are similar to those reported by others36"39 for cationic polymerization of a-methylstyrene. For example, decreasing temperature, the molecular weight increases and increasing medium polarity, the yield increases. 

According to these results the yields and E. F. decrease with the increasing number of Si-Cl bonds in the functional initiators. It is possible that Si-Cl bonds may slowly react with the diethylaluminum chloride coinitiator and thus reduce the expected E.F. as follows40 ... 

Having demonstrated that the Si-H bond is quite stable in the presence of Me3AI coinitiator and benzyl carbenium ion, further model experiments have been carried out to explore the stability of the Si-H bond in the presence of propagating carbenium ions. 

Effects of solvent polarity, counter-anion nucleophilidty, temperature, and monomer concentration on the carbenium ion polymerization chemistry have been extensively studied29,36 38,49. Based on previous knowledge26"29 Me3Al was chosen because with this coinitiator undesired chain transfer to monomer processes are absent. Preliminary experiments showed that Et3Al coinitiator did not yield PaMeSt, possibly because the nuc-leophilicity of the counter-anion Et3AlQe is too high and thus termination by hydrida-tion is faster than propagation36. ... 

This section concerns the synthesis of polyisobutylenes (PIB) bearing a Si-H head-group (HSi-PIB) by the use of Si-H containing functional initiator in conjunction with Me3Al coinitiator. First the effect of reaction conditions on the rate and molecular weight have been investigated and subsequently a H1 NMR method for the quantitative characterization of Si-H groups in HSi-PIB was developed. 

VIII. Effect of the Nature of Halogen in t-BuX Initiators, Et2AlX Coinitiators... 

Kennedy8,9 studied in detail aspects of initiation of isobutylene and styrene polymerization using Et2 A1C1 coinitiator. Subsequently, Kennedy and co-workers10 ... 

Although the history of isobutylene polymerization chemistry can be traced back to the nineteenth century12, systematic research began barely forty years ago. The introduction of alkylaluminum coinitiators took place at about the same time13. Since early work has been reviewed by Kennedy and Gillham14, only a comprehensive review of recent study of isobutylene polymerization using alkylaluminum coinitiators will be presented. 

In a series of seven recent publications, these Italian authors21-27 reported isobutylene homo- and copolymerizations using alkylaluminum coinitiators in the presence of halogen, interhalogen compounds and alkyl halide initiators. The following conclusions21 are reported in the first paper. 

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