Difunctional, radical cations

Polystyrene is imusual among commodity polymers in that we can prepare it in a variety of forms by a diversity of polymerization methods in several types of reaction vessel. Polystyrene may be atactic, isotactic, or syndiotactic. Polymerization methods include free radical, cationic, anionic, and coordination catalysis. Manufacturing processes include bulk, solution, suspension, and emulsion polymerization. We manufacture random copolymers by copolymerizing styrene directly vith comonomers containing vinyl groups. In addition, we can polymerize styrene in the presence of polymer chains containing unsaturation in order to create block copolymers. Crosslinked varieties of polystyrene can be produced by copolymerizing styrene vith difunctional monomers, such as divinyl benzene. 

Initiation sites, in VDC polymer degradation, 25 714-715 Initiator bonds, breaking, 14 278 Initiators. See also Anionic initiators Cationic initiators Free-radical initiators alkoxide, 14 259 copolymerization, 14 252 difunctional and trifunctional, 14 252— 254... 

Acrolein is a very reactive monomer with a high tendency to polymerize. Free-radical and cationic polymerizations lead to Insoluble polymers even if the conversions are low. On the other hand, anionic polymerization gives soluble polyacroleins under well-adapted conditions. Because of the difunctional nature of this monomer, the chains of polyacroleins contain different types of units ... 

Ethylenic cation radicals are also capable of rotating around the double bond. At the same time, the main specificity of ethylenic cation radical reduction consists of the high selectivity of the reaction. One-electron oxidation was developed as a strategy for selective and efficient reduction of relatively ionizable functionalities, including conjugated dienes, styrenes, and vinyl sulfides (Mirafzal et al. 1993). Reduction is highly sensitive to substrate ionizability and permits selective reduction of the more ionizable function in a difunctional compound. 

An excess (5 1 mole ratio) of ethyl diazoacetate is used in these reactions to suppress cyclobutadimerization or Diels-Alder cyclodimerization. In difunctional molecules which have non-equivalent ionizable functionalities, cyclopropanation is highly selective for the more easily oxidized functionality. The latter selectivity is perhaps the most attractive aspect of the reaction. In contrast to transition metal (e.g. rhodium) catalyzed cyclopropanations, cation radical additions to electron deficient alkene moieties do not occur at all. The reaction is relatively sensitive to... 

The compositions of materials photocrosslinkable by cationic mechanism consist of mixtures of various vinyl ethers, or epoxides, or both. Difunctional cycloaliphatic epoxides have been used extensively in some UV curable systems, often as diluents for the various epoxy resins described in Chapter 6. Use of various divinyl ethers is also extensive. Because some cationic photoinitiators also generate free radicals, some compositions may contain mixtures of both types of materials, those that cure by cationic and those that cure by free-radical mechanisms. 

Pathway (1) is mainly encountered in chain polymerization (anionic, cationic, and controlled radical polymerizations) the second one refers essentially to polycondensation and polyaddition. There is no strict distinction between these two sets of techniques, e.g., the difunctional oligoethers used in poly(ether-6-ester)s or poly(ether-6-amide)s can be prepared by ring-opening polymerization and then polycondensed with the other oligomer (Scheme 2) [39]. 

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