Cationic polymerization reactions

The most important reaction with Lewis acids such as boron trifluoride etherate is polymerization (Scheme 30) (72MI50601). Other Lewis acids have been used SnCL, Bu 2A1C1, Bu sAl, Et2Zn, SO3, PFs, TiCU, AICI3, Pd(II) and Pt(II) salts. Trialkylaluminum, dialkylzinc and other alkyl metal initiators may partially hydrolyze to catalyze the polymerization by an anionic mechanism rather than the cationic one illustrated in Scheme 30. Cyclic dimers and trimers are often products of cationic polymerization reactions, and desulfurization of the monomer may occur. Polymerization of optically active thiiranes yields optically active polymers (75MI50600). 

The controlled synthesis of polymers, as opposed to their undesired formation, is an area that has not received much academic interest. Most interest to date has been commercial, and focused on a narrow area the use ofchloroaluminate(III) ionic liquids for cationic polymerization reactions. The lack of publications in the area, together with the lack of detailed and useful synthetic information in the patent literature, places hurdles in front of those with limited loiowledge of ionic liquid technology who wish to employ it for polymerization studies. The expanding interest in ionic liquids as solvents for synthesis, most notably for the synthesis of discrete organic molecules, should stimulate interest in their use for polymer science. 

Only a few examples of the cationic polymerization reactions of organometallic monomers have been reported in the literature. 

Attempts to bring the benefits of ionic Hquid technology, drawing on this inherent ability of the chloroaluminate(lll) ionic liquids, to catalysis of cationic polymerization reactions, as opposed to their minimization, were patented by Ambler et al. of BP Chemicals Ltd. in 1993 [29]. They used acidic [EMlM][Cl-AlCl3] (X(AlCl3) =... 

Some common initiators for cationic polymerization reactions are protonic acids, Friedel-Crafts catalysts (Lewis acids), compounds capable of generating cations, or ionizing radiation. 

CHEC(1984) and CHEC-II(1996) discuss the acid-catalyzed transformations of oxetanes including ring expansion to THFs and formation of cyclic orthoesters <1984CHEC(7)363, 1996CHEC-II(1)721>. They also include many examples of the use of oxetane monomers in cationic polymerization reactions, giving ready access to polyethers. 

Discussion Point DP2 Olefin polymerization is an exothermic process. Estimate the heat of reaction released per day by a polymerization reactor with a typical production capacity of about 1000 t of PE or PP per day. Identify the means which can be used to remove this amount of heat from the reactor. What are their relative merits (and limits) in terms of energy use or recycling Some (e.g. cationic) polymerization reactions proceed rapidly and give products with excellent properties when conducted at temperatures below 0°C. What makes such processes uneconomical ... 

The narrow molecular weight distributions observed suggest the possibilities of the existence of "living polymers in these polymerization reactions, as has been suggested previously for other cationic polymerization reactions (7 ). Indeed, in at least one of these reactions, that of the polymerization of the isopropyl monomer initiated with TiCl and TPMC as the catalyst-... 

Many papers have been published concerning the structure of the active centers in anionic and cationic ring-opening polymerization reactions of oxacyclic monomers. Recently, attention has been paid in our laboratory to the influence of the structure of complex carbonium salt initiators, especially of the dioxolanyllum salts used for initiating the cationic polymerization reactions of trioxane, tetrahydrofuran and dioxolane, on the course of the polymerization ( ). 

A system that has recently been receiving attention Is radiation induced cationic curing. The interest in cationic curing has been Inspired by the development of onlum salt catalysts. Strong acids are liberated when the coatings are Irradiated In the presence of certain onlum salts. These acids are capable of catalyzing cationic polymerization reactions (7). Onlum salts have been used mostly In UV curable systems. However, It has been shown recently that they may also be used for electron beam Induced curing (8,9). 

One of the most promising techniques to overcome oxygen inhibition is to perform curing reactions in an inert atmosphere. It is also necessary to note that cationic polymerization reactions are less sensitive to oxygen and provide a rapid surface cure. Several additional methods have been reported to reduce O2 inhibition such as addition of O2 barriers (e.g., paraffin waxes) O2 scavengers, thiols, phosphines, acrylic amine and introducing surface active photoinitiators or mixed photoinitiators, 22,145... 

ESR evidence supports the presence of an Fe(lll) radical intermediate. Irradiation of the iron(ll) arene compound shown in Figure I9.40 leads to slippage of the linkage to the >74 bonding mode. The resulting compound is coordinatively unsaturated (16 e ). Continued irradiation leads to the loss of the arene li d and replacement by three solvent molecules. This species has been used as a photoinitiator for cationic polymerization reactions, as shown in Figure 19.40. 

Microfluidic systems (microreactors) provide great benefits, such as precise fluid-manipulation [1] and high controllability of rapid and difficult to control chemical reactions (see Part 2, Bulk and Fine Chemistry). Advantages of microreaction technology have been utilized in polymer chemistry notable examples include the synthesis of fine solid polymeric materials [2,3] and excellent control of exceptionally reactive polymerization through mainly radical and cationic polymerization reactions (see Chapters 13-15). Other polymerizations using microreaction technology are still in their infancy, vhich include step polymerization, that is, polycondensation and polyaddition and other non-radical polymerizations. 

XIA 14] Xiao P., Fouassier J.P., Lalevee J., Photochemical production of interpenetrating polymer networks simultaneous initiation of radical and cationic polymerization reactions , in Sperling L.H. (ed.), Photopolymerization of Acrylate/Epoxide Blends, Polymers, Special Issue Interpenetrating Polymer Networks , available at http //www.mdpi.com, 2014. 

---