Radical initiators, addition

In a simple free-radical-initiated addition polymerisation the principal reactions involved are (assuming termination by combination for simplicity)... 

Examples of perfluoroalkyl iodide addition to the triple bond include free radical addition of perfluoropropyl iodide to 1 -heptyne [28] (equation 21), thermal and free radical-initiated addition of lodoperfluoroalkanesulfonyl fluorides to acetylene [29] (equation 22), thermal addition of perfluoropropyl iodide to hexa-fluoro 2 butyne [30] (equation 23), and palladium-catalyzed addition of per-fluorobutyl iodide to phenylacetylene [31] (equation 24) The E isomers predominate in these reactions Photochemical addition of tnfluoromethyl iodide to vinylacetylene gives predominantly the 1 4 adduct by addition to the double bond [32] Platinum catalyzed addition of perfluorooctyl iodide to l-hexyne in the presence of potassium carbonate, carbon monoxide, and ethanol gives ethyl () per fluorooctyl-a-butylpropenoate [JJ] (equation 25)... 

Addition of P—H bonds to unsaturated systems also continues to be used as a route to heterocyclic systems. Thus base-catalysed cyclization of the phosphine (32) [prepared by the addition of methyl methacrylate (2 moles) to phenylphosphine], followed by subsequent hydrolysis and decarboxylation, affords the phosphorinanone (33). The phosphorinanone system is also directly accessible by the addition of phenylphosphine to divinyl ketones.28 The radical-initiated addition of phenylphosphine to dialkynyl systems (34) gives the heterocyclohexadienes (35).29 80 The stereochemistry of the addition of phenylphosphine to cyclo-octa-2,7-dienone to give... 

In addition to traditional radical initiated addition polymerizations, cation and/or anion catalyzed addition polymerizations are of great commercial importance, since PE, PP and PS are most frequently produced using this type of polymerization technique (Table 5). In addition to the vinyl monomers, vinyli-dene monomers, in which neither R nor R is hydrogen, can form commercially important polymers. PMMA is a typical example of this type of thermoplastics. 

Commercial products based on copolymers of ethylene and TEE are made by free radical-initiated addition copolymerization.69 Small amounts (1 to 10 mol%) of modifying comonomers are added to eliminate a rapid embrittlement of the product at exposure to elevated temperatures. Examples of the modifying comonomers are perfluorobutyl ethylene, hexafluoropropylene, perfluorovinyl ether, and hexafluoro-isobutylene.70 ETFE copolymers are basically alternating copolymers,70 and in the molecular formula, they are isomeric with polyvinylidene fluoride (PVDF) with a head-to-head, tail-to-tail structure. However, in many important physical properties, the modified ETFE copolymers are superior to PVDF with the exception of the latter s remarkable piezoelectric and pyroelectric characteristics. 

The radical-initiated addition of CBrCls or CBr4 to olefins followed by base-induced dehydrobromination of the adducts can be used to prepare a wide variety of RR C=C(Ii/,)CX3-type compounds whose reaction with dicobalt octacarbonyl will give the respective vinylic cluster derivatives. The reactions of the latter with appropriate reagents will extend further the number and types of organo-functional cluster complexes. Also, their... 

Although scheme (138) is the standard mechanism for the radical-catalyzed isomerization of isomeric alkenes, kinetic data for both substitution and isomerization are sparse. Using cis- or frcms-diiodo-ethene and labeled iodine atoms, Noyes et al. (1945) demonstrated that iodine atoms exchanged with predominant retention isomerization was the slower process, the barrier being <4 kcal/mole. Corresponding studies with dibromoethene and bromine atoms indicate a barrier of ca. 3 kcal/mole (Steinmetz and Noyes, 1952) in which bromine-atom departure from and isomerization of the intermediate were competitive. Qualitative selective or stereospecific radical-initiated additions to alkenes have since indicated that radical intermediates probably have stereostability, but the studies cited are definitive. The kinetic analysis provided the essential model for SS in mechanistic schemes such as (138), whether for SE, SH or SN processes. 

Ethylene (CH2=CH2) is the simplest monomer that will polymerize. Through free-radical-initiated addition polymerization at high pressures (1000 atm to 3000 atm) and temperatures (300°C to 500°C), it forms polyethylene ... 

The preparation and reactions of organotin phosphines continue to attract interest, and have been reviewed. Cyclodehydrogenation of the secondary phosphine (40) with azobenzene in the presence of AIBN gives the 1,2-stannaphospholans (41). Radical-initiated addition of di-n-butylstannane to the dialkynylphosphines... 

Free Radical Initiated Additions of Carbon Tetrachloride to a-Olefins. 

Alkyl phenyl thioethers RCH2SPh are available by radical-initiated addition of benzenethiol to a terminal olefin or by reaction of an alkyl bromide with thio-phenoxide ion. N -Chlorosuccinimide effects halogenation at the a-site, and the a-chloroalkyl thioether gives the corresponding aldehyde RCHO on treatment with mercury(ll) chloride and cadmium(ll) carbonate in aqueous carbon tetra-... 

Copolymer Formation through Radical Initiator Addition... 

Table 5.49 PO/PO blends copolymer formation through radical initiator addition...

So-called anaerobic polyurethane adhesives also belong to this category. This system combines urethane poly-addition chemistry with free-radical initiated addition polymerization. A polymerizable alcohol such as j -hydroxyethyl methacrylate is reacted with an equivalent amount of a diisocyanate such as TDI or with an isocyanate-terminated urethane prepolymer. An organic hydroperoxide is then added to such intermediates... 

Acrylic resin formulations have been used for outdoor, weather-resistant adhesives. Pressure-sensitive acrylic adhesives are common on decals, bumper stickers, decorative plates, etc. Two-part thermosetting acrylic formulations have been developed and packaged for encapsulating, potting, and structural adhesives. Thermosetting acrylics cure by free radical-initiated addition polymerization. These materials can be cured at room temperature with benzoyl peroxide and an amine promoter (dimethyl aniline). 

Synthesis of Vinyl Sulfides from Alkynes. The AIBN radical-initiated addition reaction of thiophenol to the terminal... 

The first relevant report of a selective cyclization toward the (Cy 5) radical from a diallylic substrate was made in 1964 by Brace in the free radical chain reaction of 1,6-heptadiene (Scheme 25, X = CHj) with 1-iodoperfluoropropane initiated by AIBN. Further work, mainly by this author, confirmed (Scheme 25) the high selectivity toward formation of the (Cy 5) radical, in complete agreement with the results obtained with the 5-hexenyl radical (Sections II. 1 and III.1). Thus all reports, particularly in the polymerization area, that assumed formation of (Cy6) compounds must be regarded as suspect For instance, Cadogan and Hey reported the formation of a Cy5/Cy6 mixture by radical-initiated addition of various addenda to ethyl diallylacetate (X = CHCOjEt) but had to recognize later that the two compounds were in fact the two stereoisomeric (Cy5) compounds. 

The polar addition of HBr to alkenes leads to the more substituted bromide, whereas the radical-initiated addition of HBr gives the less substituted bromide. Thus, you have the ability to make either regioisomer when the alkene is imsym-metrically substituted. The addition of HCl and HI always gives the more substituted halide. 

Polar or radical-initiated additions to the vinyl groups make vinylboranes of some importance as intermediates both in the preparation of other organofunctional boranes and in synthetic organic chemistry. Allyl-boranes CH2 CHCH2BR2 and alkynylboranes RC CBR 2 are also relatively reactive. 

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