Free radical polymerization telomerization

Combes, J. R. Guan, Z. DeSimone, J. M. Homogeneous Free-Radical Polymerizations in Carbon Dioxide. 3. Telomerization of 1,1-Difluoroethylene in Supercritical Carbon Dioxide. Macromolecules 1994, 27, 865-867. 

DEP afforded the synthesis of telechelic oligomers [29]. With the telomerization process, DEP appeared to be the first free-radical polymerization leading to telechelic oligomers. Tobolsky [30] first stated the conditions of DEP, i.e., the half life of the growing species has to be equivalent to that of the initiator. These specific conditions result in an unusual high rate of termination, which allows for the synthesis of oligomers. The telechelic structure will be obtained by combining a termination mode exclusively by recombination with the use of a difunctional initiator. 

The propagation step in this free radical polymerization has been demonstrated to involve radical attack on episulfide sulfur (as depicted above) by telomerization studies with cyclohexane. From the structures of the two major products, 20 and 21, cyclohexyl radical attacks at the sulfur atom by displacing fluoroalkyl radical. This new radical, a prototype of the growing polymer chain, then abstracts hydrogen from cyclohexane to form 20 or attacks another molecule of 6 (n = 1) at sulfur to give 21. 

Chain-transfer polymerizations (telomerizations), which were developed to produce polymers of narrower molecular weight distributions than in conventional free-radical polymerization, of poly-N-isopropylacrylamide (PNIPAM), poly-N,N-dimethylacrylamide (PNDMAM), and poly-N- 3-(dimethylamino)propyl acrylamide... 

An illustration of a telomerization reaction can be free-radical polymerization of ethylene in the presence of chloroacetyl chloride ... 

Nylon 7 and nylon 9 are part of a process developed in Russia to form polyamides for use in fibers. The process starts with telomerization of ethylene [66]. A free-radical polymerization of ethylene is conducted in the presence of chlorine compounds that act as chain-transferring agents. The reaction is... 

The large transfer constants of many compounds are useful in the telomerization process. If, for example, the free radical polymerization of... 

The terms telogen and telomerization were defined many years ago to describe an innovative method for the free-radical polymerization of ethylene (49,50). The essence of telomerization, described in a 1942 patent (50), involves reaction of a telogen XY (also called a chain-transfer agent) with an ethylenic molecule to give a telomer of structure X—(A) —Y. In the product telomer, fragments of the chain-transfer agent are attached to the termini of the molecule (49,50). Figure 15 illustrates the method. 

Free radical polymerization in the presence of a chain transfer agent (telogen) is often called telomerization reaction. Many different telogens have been reported (57) the most studied and well-documented telogen is CCI4 (Fig. 5). 

The telomerization of vinyl monomers is another example of chain end-functionalization by transfer. In the latter case, both propagation and transfer exhibit comparable rates, which affords a,(o-difunctionalized chains of low degree of polymerization also called telomers. For instance, the free radical polymerization of vinyl monomers in halogenated solvents produces a,co-halogenated oligomers ... 

Telomerization was initially developed by the Du Pont Company for free-radical polymerization of ethylene [56-61] and defined as a process of reacting a molecule, called telogen, with two or more ethylenically unsaturated molecules, called taxogens ... 

Fluorinated radicals play a significant role in synthetic organo-fluorine chemistry, for example, in electrophilic radical addition to alkenes, single-electron transfer reactions (SET), telomerization of fluoroalkenes with perfluoroalkyl iodides, polymerization to fluoropolymers and copolymers, and thermal, photochemical and radiation destruction of fluorocarbons. Furthermore, such free radicals are of interest for studying structures, reaction kinetics and ESR spectroscopic parameters.38... 

The first reported polymerization of fluoroolefins in carbon dioxide was by Fukui and coworkers [39,40]. Tetrafluoroethylene, chlorotrifluoroethylene,and other fluoroolefins were polymerized in the presence of CO2 using ionizing radiation [39, 40] and free-radical initiators [40]. DeSimone and coworkers reported the homogeneous telomerization of tetrafluoroethylene [41] and vinylidene fluoride [42] in CO2 using AIBN as an initiator. The kinetics of AIBN decomposition in CO2 is well understood [4]. However, peroxide initiators are preferred over azo initiators for producing stable endgroups in fluoroolefins... 

Aqueous polymerization is carried out in either an emulsion or a suspension. In the emulsion polymerization, monomers are polymerized in an aqueous medium containing a water soluble free radical initiator and an emulsifier to obtain a polymer particle slurry. In the suspension polymerization, monomers are polymerized in an aqueous medium containing both a free radical initiator which is soluble in the monomer and a dispersion stabilizer inert to telomerization to achieve the dispersion of polymer particles, followed by precipitation of the dispersion. 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

Control by degenerative transfer (DT) involves perhaps the smallest change from a eonventional free radical process of all the controlled/living polymerization proeesses developed to date. A recent review of various methods of telomer synthesis [180] diseusses the different types of transfer agents and monomers and the contribution of the teehniques of telomerization to CRP (includes discussion of iodine transfer polymerization, RAFT, and macromolecular design through interchange of xanthates (MADIX)) [181,182]. 

The transfer of the chain to another monomer molecule is followed by the increase of next macroradical. In that case the pol5mierization reaction rate does not change. The transfer of the chain on a solvent molecule, able to create relatively persistent free radicals leads to the formation of oligomeric products terminated by large substituents, coming from the decomposition of solvent molecule. These substituents determine the properties of the resulting compounds, called telomeres. This issue will be discussed larger in the chapter devoted to the polymerization in solution. 

The polymerization mechanisms have been extended from the original free-radical reaction to anionic, cationic, and transition-metal-catalyzed telomerization. 

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