Chain initiation group transfer polymerization

Haddleton, D. M., et al. (1997). Identifying the nature of the active species in the polymerization of methacrylates inhibition of methyl methacrylate homopolymerizations and reactivity ratios for copolymerization of methyl methacrylate/n-butyl methacrylate in classical anionic, alkyUithium/trialkylaluminum-initiated, group transfer polymerization, atom transfer radical polymerization, catalytic chain transfer, and classical free radical polymerization. Macromolecules, 30(14) 3992-3998. 

If the living ROMP of norbomene is terminated with a 9-fold excess of terephthalaldehyde, the chains formed carry an aldehyde end-group which, when activated by ZnCl2, can be used to initiate the aldol-group-transfer polymerization of tert-butyldimethylsilyl vinyl ether621. 

The triflated polysilanes were also used to initiate the polymerization of methyl methacrylate by group transfer polymerization. The initiation sites were prepared in-situ using equimolar amounts of triflic acid and arylsilanes, methyl-propionate and triethylamine. Tris(dimethylaminosulfonium) bifluoride was the catalyst. It was found by degradation studies that each polysilane chain contains on average 2.7 PMMA branches. No additional details were reported on the characterization of these graft copolymers. 

Difimctional initiators cause chain growth to proceed from each end. Because group-transfer polymerizations are living polymerizations, once all the monomer has been consumed a different monomer can be added and block copolymers can be formed. 

Other types of chain-growth polymerizations include (a) insertion polymerizations, such as the Ziegler-Natta process used in the preparation of polyethylene and metathesis polymerizations (27,28), and (b) group transfer polymerizations, a process in which an initiator molecule transfers its active group to a monomer molecule under the action of a catalyst. 

Obtain an expression for the number-average chain length at complete conversion in a group-transfer polymerization batch that contains I, M, and RH moles of initiator, monomer, and chain-transfer agent, respectively. 

Notably, low-molar-mass radicals are not formed and homopolymerization cannot occur. Moreover, metal atoms do not become bound to the polymer in these processes. Polymeric initiators with terminal halide groups can be prepared in different ways. Anionic polymerization [24,25], group transfer polymerization [26], metal carbonyl initiation [27], chain transfer reaction... 

The term acrylic apphes to a family of copolymers of monomers that are polymerized by a chain growth mechanism. Most often, the mechanism of polymerization is by free radical initiation. Other mechanisms of polymerization, such as ionic and group transfer polymerization, are possible but will not be discussed in this publication. For a description of other polymerization mechanisms, polymer textbooks are available (5,6). Technically, acrylic monomers are derivatives of acrylic or methacrylic acid. These derivatives are nonfunctional esters (methyl methacrylate, butyl acrylate, etc.), amides (acrylamide), nitrile (acrylonitrile), and esters that contain functional groups (hydroxyethyl acrylate, glycidyl methacrylate, dimethylaminoethyl acrylate). Other monomers that are not acryhc derivatives are often included as components of acryhc resins because they are readily copolymerized with the acryhc derivatives. Styrene is often used in significant quantities in acryhc copolymers. 

Lipases have also been used as initiators for the polymerization of lactones such as /3-bu tyro lac tone, <5-valerolactone, e-caprolactone, and macrolides.341,352-357 In this case, the key step is the reaction of lactone with die serine residue at the catalytically active site to form an acyl-enzyme hydroxy-terminated activated intermediate. This intermediate then reacts with the terminal hydroxyl group of a n-mer chain to produce an (n + i)-mer.325,355,358,359 Enzymatic lactone polymerization follows a conventional Michaelis-Menten enzymatic kinetics353 and presents a controlled character, without termination and chain transfer,355 although more or less controlled factors, such as water content of the enzyme, may affect polymerization rate and the nature of endgroups.360... 

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