Styrenes, -alkoxy

In cationic polymerization the active species is the ion which is formed by the addition of a proton from the initiator system to a monomer. For vinyl monomers the type of substituents which promote this type of polymerization are those which are electron supplying, like alkyl, 1,1-dialkyl, aryl, and alkoxy. Isobutylene and a-methyl styrene are examples of monomers which have been polymerized via cationic intermediates. 

The reactions of alkyl hydroperoxides with ferrous ion (eq. 11) generate alkoxy radicals. These free-radical initiator systems are used industrially for the emulsion polymerization and copolymerization of vinyl monomers, eg, butadiene—styrene. The use of hydroperoxides in the presence of transition-metal ions to synthesize a large variety of products has been reviewed (48,51). 

Other miscellaneous compounds that have been used as inhibitors are sulfur and certain sulfur compounds (qv), picryUiydrazyl derivatives, carbon black, and a number of soluble transition-metal salts (151). Both inhibition and acceleration have been reported for styrene polymerized in the presence of oxygen. The complexity of this system has been clearly demonstrated (152). The key reaction is the alternating copolymerization of styrene with oxygen to produce a polyperoxide, which at above 100°C decomposes to initiating alkoxy radicals. Therefore, depending on the temperature, oxygen can inhibit or accelerate the rate of polymerization. 

A number of thermosetting acrylic resins for use as surface coatings have appeared during recent years. These are generally complex copolymers and terpolymers such as a styrene-ethyl acrylate-alkoxy methyl acrylamide... 

A chiral bis(oxazolinyl)phenylrhodium complex was found to catalyze the asymmetric hydrosilylation of styrenes with hydro(alkoxy)silanes such as HSiMe(OEt)2 (Scheme 7).47 Although the regioselectivity in forming branched product 27 is modest, the enantiomeric purity of the branched product 27 is excellent for styrene and its derivatives substituted on the phenyl group. The hydrosilylation products were readily converted into the corresponding benzylic alcohols 29 (up to 95% ee) by the Tamao oxidation. 

Without the alkoxy substituent on the olefin, steric effects prevail. The Heck adduct 164 was isolated when 2-chloro-3-pivaloylamidopyridine (163) was allowed to react with an excess of styrene [129], Steric effects can play a major role in the regioselectivity of these reactions. 

Styrene and indene derivatives (Scheme 2, Y = Ph) are dimerized to l,4-dimethoxy-l,4-diphenylbutanes or 1,4-diphenylbutadienes (Table 7, numbers 1 and 2) [52]. The product distribution is in some cases strongly dependent on the anode potential and the supporting electrolyte. Dimerization is promoted by a-substituents that stabilize the intermediate radical cation, for example, phenyl, vinyl, alkoxy, dialkylamino groups. IJ-Alkyl substituents strongly decrease the yield of dimers and favor formation of dimethoxy-lated monomers. 

The intramolecular coupling of enolethers with enolethers, styrenes, alkyl-substituted olefins, allylsilanes, and vinylsilanes was systematically studied by Moeller [69]. Many of these coupling reactions turned out to be compatible with the smooth formation of quaternary carbon atoms (Eq. 11) [70], which were formed diastere-oselectively and led to fused bicyclic ring skeletons having a ds-stereochemistry [71]. The cyclization is compatible with acid-sensitive functional groups as the allylic alkoxy group. Moeller has demonstrated in some cases that these reactions can be run without loss of selectivity and yield in a simple beaker with either a carbon rod or reticulated carbon as anode without potential control and a 6-V lantern battery as power supply [71]. 

Satisfactory to good yields of adducts have been found for styrenes (Scheme 5, Y = phenyl), conjugated dienes (Y = vinyl), enamines (Y = NR2), and enol ethers (Y = alkoxy), particularly if they are... 

Inverse type hetero-Diels-Alder reactions between p-acyloxy-a-phenylthio substituted a, p-unsaturated cabonyl compounds as 1-oxa-1,3-dienes, enol ethers, a-alkoxy acrylates, and styrenes, respectively, as hetero-dienophiles result in an efficient one step synthesis of highly functionalized 3,4-dihydro-2H-pyrans (hex-4-enopyranosides). These compounds are diastereospecifically transformed into deoxy and amino-deoxy sugars such as the antibiotic ramulosin, in pyridines having a variety of electron donating substituents, in the important 3-deoxy-2-gly-culosonates, in precursors for macrolide synthesis, and in C.-aryl-glucopyranosides. 

The alkoxy substituent allows a delocalization of the positive charge. If the substituent were not present (e.g., in ethylene), the positive charge would be localized on the single a-carbon atom. The presence of the alkoxy group leads to stabilization of the carbocation by delocalization of the positive charge over two atoms—the carbon and the oxygen. Similar delocalization effects occur with phenyl, vinyl, and alkyl substituents, for example, for styrene polymerization ... 

Scheme 6.27 Typical P-alkoxy alcohols obtained from the highly regioselective alcoholysis of styrene oxides catalyzed by thiourea 9 and mandelic acid 20 in a cooperative organocatalytic system.

The addition of anilines to styrene oxide was reported to also proceed in the presence of 10mol% 37 affording the corresponding P-amino alcohols 1-5 in yields ranging from 75% to 92% (Scheme 6.37). Additionally, urea derivative 37 (20mol% loading) was found to catalyze the addition of aniline (2.0 equiv.) to ( )-stilbene oxide (92% yield 5.9 d 30°C), the addition of thiophenol (2.0 equiv.) to 2-methoxy styrene oxide (85% 20h rt), and the alcoholysis of 4-methoxy styrene oxide with benzyl alcohol (2.0 equiv.) affording the respective P-alkoxy alcohol (82% 20h rt). 

The DnPont photopolymeric system consists of polymeric binder resins, e.g. PVA, PMMA, cellnlose acetates and styrene-acrylates, reactive acrylic monomers, e.g. aryloxy or alkoxy acrylates, a dye sensitiser and a radical or charge transfer photoinitiator, e.g. DEAW and HABI respectively (see Chapter 4, section 4.5.2), and plasticisers. The process for producing the refractive index structures is as follows ... 

Much less attention has been focused on carbonylation reactions in ionic liquids. The biphasic palladium-catalyzed alkoxy carbonylation of styrene. Scheme 2, in [bmim][BF4]—cyclohexane has been reported. ... 

Alkyl alkoxy silanes have been found to be very effective in reducing alkali-aggregate expansion [11] (Fig. 6.4). Of the silanes used in the study, hexyl trimethyl siloxane and decyl trimethoxyl silane were found to be more effective in decreasing the expansion than the others. In the same study, Ohama et al. [11] investigated the effect of sodium silicofluoride, alkyl alkoxy silane, lithium carbonate, lithium fluoride, styrene-butadiene rubber latex and lithium hydroxide on compressive strength and the expansion of mortar containing cement with 2% equivalent Na20. The reduction of the level of expansion shown in Fig. 6.4 with the siloxanes was attributed to... 

This asymmetric end has the alkoxy group of alkyl vinylethers by cationic polymerization, phenyl group of styrene when either anionically or cationicaiiy polymerized, the vinyl group of butadiene under anionic catalysts to poly-1,2-butadiene, the ester and methyl of methylmethacrylate under anionic catalysis and the methyl of propylene by cationic catalysis. 

Essentially the same substituents as listed above may be present in the alkene being substituted, with the possible exception of chloro, alkoxy and acetoxy groups on vinyl or allyl carbons. These groups, especially chloro, may be lost or partially lost with palladium when the final elimination step occurs. For example, vinyl acetate, iodobenzene and triethylamine with a palladium acetate-triphenylphosphine catalyst at 100 C form mainly (E)-stilbene, presumably via phenylation of styrene formed in the first arylation step (equation 21 ).6 ... 

Trimethylsilyl groups also may be lost from vinylic or allylic positions in the arylation reaction.70 Halide ion facilitates die desilylation as well as the loss of alkoxy and acetoxy groups. Inclusion of soluble silver salts in reactions where trimethylsilyl groups are lost prevents this reaction.70 The reaction in the absence of silver ion is useful for preparing styrene derivatives. However, they also may be prepared directly from aryl halides and ethylene in fair to good yields.71... 

The generation of alkyl-substituted monomeric metaphosphoric acid esters (254) has been described using two different methods and the metaphosphate produced spontaneously self-condensed to give polymeric P—O—P bonds, hi the presence of styrene polymerization is avoided and happing occurs instead to give a diastereomeric mixture of 2-alkoxy-l,3,2-dioxophospholane-2-oxides with (254 R = Me).232 Pyridine A -oxidc-tricthylaminc mixtures individually or together catalyse the phosphorylation of... 

PC PE PES PET PF PFA PI PMMA PP PPO PS PSO PTFE PTMT PU PVA PVAC PVC PVDC PVDF PVF TFE SAN SI TP TPX UF UHMWPE UPVC Polycarbonate Polyethylene Polyether sulfone Polyethylene terephthalate Phenol-formaldehyde Polyfluoro alkoxy Polyimide Polymethyl methacrylate Polypropylene Polyphenylene oxide Polystyrene Polysulfone Polytetrafluoroethylene Polytetramethylene terephthalate (thermoplastic polyester) Polyurethane Polyvinyl alcohol Polyvinyl acetate Polyvinyl chloride Polyvinyl idene chloride Polyvinylidene fluoride Polyvinyl fluoride Polytelrafluoroethylene Styrene-acrylonitrile Silicone Thermoplastic Elastomers Polymethylpentene Urea formaldehyde Ultrahigh-molecular-weight polyethylene Unplasticized polyvinyl chloride... 

A formal iron-catalyzed [3 + 2]-cycloaddition of styrene derivatives with benzoqui-none was reported by Itoh s group [96]. The process is believed to proceed via electron-transfer reactions mediated by a proposed Fe3+/Fe2+ couple, which generates a styrene radical cation and a semiquinone. These intermediates undergo stepwise addition to yield the benzofuran product 51 (Scheme 9.38). The reaction seems to be limited to electron-rich alkoxy-functionalized styrenes, as the Fe3+/Fe2+ redox couple is otherwise unable to transfer the electrons from the styrene to the quinone. 

S)-3-sec-Butylpyridine, which interacts with the cobalt catalytic system (as shown by the increase of the reaction rate), does not cause asymmetric induction when styrene is used as the substrate17). Alkoxyalkylidenetricobaltmonocarbonyl cluster complexes bearing chiral alkoxy groups used as catalyst precursors do not give optically active aldehydes either18). 

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