Chain transfer applications

Wolf, C., Burchard, W. Branching in free radical polymerization due to chain transfer, application to poly(vinyl acetate). Makromol. Chem. 177, 2519-2538 (1976)... 

In solution polymerization, an organic solvent dissolves the monomer. Solvents should have low chain transfer activity to minimize chain transfer reactions that produce low-molecular-weight polymers. The presence of a solvent makes heat and viscosity control easier than in bulk polymerization. Removal of the solvent may not be necessary in certain applications such as coatings and adhesives. 

The major applications of catalytic chain transfer are in molecular weight control and in synthesis of macromonomcrs based on methacrylate esters. However, they have also been shown effective in polymerizations and copolymerizations of MAA, MAM, MAN, AMS, S and some other monomers. 

Many Co11 porphyrins (87)110 131 and phthalocyanine complexes (102)110 have been examined for their ability to function as catalytic chain transfer agents and much mechanistic work has focused on the use of these catalysts. The more widespread application of these complexes has been limited because they often have only sparing solubility and they are highly colored. 

The effect of the initiation and termination processes on compositional heterogeneity can be seen in data presented in Figure 7.3 and Figure 7.4. The data come from a computer simulation of the synthesis of a hydroxy functional oligomer prepared from S, BA, and HEA with a thiol chain transfer agent. The recipe is similar to those used in some coatings applications. 

The theory of radiation-induced grafting has received extensive treatment [21,131,132]. The typical steps involved in free-radical polymerization are also applicable to graft polymerization including initiation, propagation, and chain transfer [133]. However, the complicating role of diffusion prevents any simple correlation of individual rate constants to the overall reaction rates. Changes in temperamre, for example, increase the rate of monomer diffusion and monomer... 

C. H. Bamford and H. Tompa, J. Polymer Sci.j 10, 345 (1953), first derive the moments of the distribution for the case of chain transfer to polymer. They then obtain the molecular weight distribution from these moments by appropriate mathematical methods. Their procedure should be applicable to a wide variety of polymerization mechanisms. 

Amine sulfide terminal moieties can be imparted into vinyl polymers by using aminethiols as chain transfer agents in aqueous radical polymerization [1182]. The polymers are useful as mineral dispersants. Other uses are as water-treatment additives for boiler waters, cooling towers, reverse osmosis applications, and geothermal processes and oil wells and as detergent additives... 

In 1988, Terry and coworkers attempted to homopolymerize ethylene, 1-octene, and 1-decene in supercritical C02 [87], The purpose of their work was to increase the viscosity of supercritical C02 for enhanced oil recovery applications. They utilized the free radical initiators benzoyl peroxide and fert-butyl-peroctoate and conducted polymerization for 24-48 h at 100-130 bar and 71 °C. In these experiments, the resulting polymers were not well studied, but solubility studies on the products confirmed that they were relatively insoluble in the continuous phase and thus were not effective as viscosity enhancing agents. In addition, a-olefins are known not to yield high polymer using free radical methods due to extensive chain transfer to monomer. 

Our review of the use of organoboron compounds in radical chemistry will concentrate on applications where the organoborane is used as an initiator, as a direct source of carbon-centered radicals, as a chain transfer reagent and finally as a radical reducing agent. The simple formation of carbon-heteroatom bonds via a radical process is not treated in this review since it has been treated in previous review articles [3,9]. 

The polymerization of other fluoroolefins such as TFE with hexafluoropro-pylene (HFP), TFE with ethylene, and vinylidine difluoride - " further demonstrates the broad applicability of liquid and supercritical CO in the production and processing of fluorinated polymers. Many of the aforementioned advantages associated with CO2, including tunable solvent properties, integrated synthesis, separation and purification processes, negligible chain transfer in the presence of highly electrophilic species, and relative ease of recycling, make it an ideal solvent for fluoroolefm polymerization. 

Investigations conducted by the same group using laser flash photolysis techniques elucidated details of the PET-reductive activation of selenosilanes and the application of this chemistry to a bimolecular group-transfer radical reaction and intermolecular radical chain-transfer addition [59], Based on this new concept, a catalytic procedure utilizing PhSeSiRs for radical reactions such as cycliza-tion, intermolecular addition and tandem anellation was designed (Scheme 39) [60],... 

Transfer to polymer cannot, however, be neglected for the practical situation where polymerization is carried to complete or high conversion. The effect of chain transfer to polymer plays a very significant role in determining the physical properties and the ultimate applications of a polymer [Small, 1975], As indicated in Chap. 1, branching drastically decreases the crystallinity of a polymer. 

Immortal polymerization of epoxides with la and an alcohol is also accelerated by co-use of bulky Lewis acid 2a. The polymerization of PO with la/2-propanol system ([PO]/[la]/[2-propanol] = 1000/1/49) in the presence of 2a ([PO]/[2a] = 1000/1) proceeds rapidly to achieve 86% conversion in 1.5 h, while the polymerization in the absence of 2a requires 380 h to reach 84% conversion (Table 1). The polyether produced in the presence of 2a has an of 900 gmoP and an MJM of 1.10, which indicates that almost all of la and 2-propanol participate in the initiation of the polymerization. Other protic chain-transfer reagents, such as methanol, benzyl alcohol, and 4-/ r/-butylphenol, are also applicable to the high-speed immortal polymerization to give similar results as 2-propanol. As a substrate, ECH is also employable. Polymerization of ECH ([EGH]/[la]/[2-propanol]/[2a] = 1000/1/49/1) gives a polymer with and/n of 1100gmol close to the value estimated from the conversion and [PO]/([la] + [2-propanol]) ratio, and a narrow M IM of 1.10, while the conversion is lower than the case of PO. 

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