Monomers, vinyl aromatic substituted

Grant et a/.397 examined the reactions of hydroxy radicals with a range of vinyl and a-methylvinyl monomers in organic media. Hydroxy radicals on reaction with AMS give significant yields of products from head addition, abstraction and aromatic substitution (Table 3.8) even though resonance and steric factors combine to favor "normal tail addition. However, it is notable that the extents of abstraction (with AMS and MMA) arc less than obtained with t-butoxy radicals and the amounts of head addition (with MMA and S) are no greater than those seen with benzoyloxy radicals under similar conditions. It is clear that there is no direct correlation between reaclion rale and low specificity. 

Danusso extended the above work with various substituted vinyl aromatic monomers (304) and discussed the reaction mechanisms based on these results (277). Some of the conclusions which are pertinent to this discussion are summarized below. 

However, styrene is the simplest vinyl aromatic with the fewest production and purification problems and an adequate supply of benzene was soon assured by the development of a new process to convert toluene to benzene (9). Construction of larger scale plants and growing production experience accelerated the cost advantage of styrene over its rivals, and, as a result, styrene/poly-styrene became the dominant vinyl aromatic monomer/polymer in the marketplace For three decades that situation has remained virtually unchallenged by a substituted styrene. 

Styrene has enjoyed a special position among vinyl aromatic monomers because of its lack of isomers and consequent ease and simplicity of production Additional steps are normally required to make substituted styrene derivatives, and separation and purification of isomers are usually difficult Our discovery of novel technology to produce p-ethyltoluene is a unique departure from this situation A highly selective catalyst enables the manufacture of a substituted vinyl aromatic monomer without coproducing undesirable and dlfflcult-to-separate Isomers Furthermore, direct use of toluene eliminates the need for hydrodemethylation by which much of the benzene starting material for styrene is produced ... 

We now report an extension of this chemistry to a new and apparently general route for the synthesis of a wide variety of Ti -vinyl-cyclopentadienyl organometallic monomers.This method provides a convenient means of introducing vinyl substituents onto n cyclo-pentadienyl rings in systems which are incapable of undergoing electrophilic aromatic substitution. 

Aryl radicals are produced in the decomposition of alkylazobenzenes and diazonium salts, and by f)-scission of aroyloxy radicals (Scheme 3.73). Aryl radicals have been reported to react by aromatic subsitution (e.g. of Sh) or abstract hydrogen (e.g. from MMA10) in competition with adding to a monomer double bond. However, these processes typically account for <1% of the total. The degree of specificity for tail vs head addition is also very high. Significant head addition has been observed only where tail addition is retarded by sleric factors e.g. methyl crotonate10 and -substituted methyl vinyl ketones 79, 84). 

A factor that affects the kinetics of the polymerization, and, more critically, the utility of the monomer in copolymerizations with other monomers, e.g., methyl methacrylate, is the stability of the radical formed from addition of the growing polymer chain to the vinyl terminus. In order to gauge the stabilizing effect of the phcnylethynyl group, and the sensitivity of the stabilization to substitution at the para position of the aromatic ring, Ochiai and co-workers carried out calculations at the UHF/3-21G level to evaluate... 

The latter mechanism is met in amine-vinyl monomer systems [41-46] (see Scheme 4). Due to the small n-acceptor ability of normal substituted vinyl monomers, an interaction in the ground-state level does not take place. The exciplexes assumed are detectable in aromatic amine-acrylonitrile (AN) systems by their emission spectra, as is shown in Fig. 1 for typical examples. The emission bands at 350 nm (by JV,JV-dimethyl-p-toluidine (DMT)) and 370 nm (by p-phenylene diamine (TMPD) result from the normal fluorescence of the isolated amine. As can be seen, the intensity of the exciplex emission is much higher in the DMT-AN system. This corresponds to the higher polymerization efficiency of that system (<)>[, by A. = 313 nm and 80 K 0.6 for DMT 0.15 for TMPD [46]). Mainly, the much higher dipole moment of DMT (1.1 D) is responsible for this result. The cation radicals [46] or neutral radicals [42] of the amines formed after PET and proton transfer have been detected by ESR measurements. As expected, the rate of photopolymerization of the systems discussed increases with increasing... 

A series of at least 14 papers [200-208] have been published dealing with the synthesis of telechelic polymers or block copolymers from the radical polymerization of various vinyl monomers with substituted 1,1,2,2-tetraphenyl ethanes. These aromatic compounds, known for over a century [209], are efficient in radical polymerization [201,210], They behave as both initiators and terminating agents [200] that can be involved in living radical polymerization as illustrated in the following reaction ... 

Various substituted styrenes also anionically polymerize readily. These include methyl, methoxy, dimethylamino, t- butyl and other groups which are electron donating to the benzene ring and do not themselves react with carbanion centers. Substituents such as chloro or nitro can be anionically polymerized only at imder very carefolly controlled conditions. 2,3, or 4 vinylpyridine can also be anionically polymerized. Any aromatic or condensed aromatic compounds with a vinyl substituent is potentially anionically polymerizable, or co polymerizable with any other anionically polymerizable monomer. 

A novel polyfunctional initiator has been prepared by the reaction of a copolymer of styrene and methyl methacrylate with polytetrafluoroethylene (PTFE) radicals generated photochemically from the monomer and manganese carbonyl. These radicals react with aromatic rings by addition and substitution so that the product copolymer from this reaction carries short PTFE chains with Mn(CO)6 end groups of, for example, structures (12). At 100 °C, scission of the CFj— Mn(CO)s bonds occurs with formation of active radicals, and the copolymer behaves as a polyfunctional macroinitiator. On heating this material with styrene or JV-vinyl-2-pyrrolidone a network structure and a graft copolymer respectively are formed. 

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