Initiator-transfer agents

Such functionality can also be of great practical importance since functional initiators, transfer agents, etc. are applied to prepare end-functional polymers (see Section 7.5) or block or graft copolymers (Section 7.6). In these cases the need to maximize the fraction of chains that contain the reactive or other desired functionality is obvious. However, there are also well-documented cases where weak links formed by initiation, termination, or abnormal propagation processes impair the thermal or photochemical stability of polymers. 

In each of the sections below, we will consider the initiation process separately. For each system, various initiation methods have been applied. In some cases the initiator is a low molecular weight analog of the propagating species, in other cases it is a method oT generating such a species. The initiators first used in this form of living radical polymerization were called iniferters (initiator - transfer agent - chain terminator) or initers (initiator - chain terminator). 

Analytical expressions have been derived for calculating dispcrsitics of polymers formed by polymerization with reversible chain transfer. The expression (eq. 17) applies in circumstances where the contributions to the molecular weight distribution by termination between propagating radicals, external initiation, and differential activity of the initial transfer agent are negligible.21384... 

New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator-Transfer Agents (Inifers) End Reactive Polyisobutylenes by Semicontinuous Polymerization... 

J.P. Kennedy and R.A. Smith, New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers). II. Synthesis and characterization of a, a>-di(ferf-chloro)polyisobutylenes,. Polym. Sci., Part A Polym. Chem., 18(5) 1523-1537,1980. 

The alkoxyamines work as iniferters (initiator, transfer agent, chain terminator). Their C-0 bond undergoes reversible homolysis on heating to... 

One more option for increasing time scale tj of the formation of macromolecules in the processes of radical polymerization is the employment of nontraditional initiators, such, as iniferters. The term "iniferter," introduced by Otsu and Yoshida (1982), is a result of the fusion of three words initiator, transfer agent, and terminator. A special feature of an iniferter is its participation in each of the three reactions mentioned. 

Polymerization is only rarely limited to the interaction of a monomer with the initiator, transfer agent or impurity. Each component of the system, including the so-called inert materials, participates in polymer formation. The mutual interaction of various components with the monomer may vary from a simple physical process to a complicated chemical reaction. In all cases intermolecular forces are involved, as manifested by the formation of solvates, associates and complexes. Sometimes it is difficult to determine the poorly defined boundary between physical and chemical processes. 

With 2-methylpropene as M, both linear and star macromers have been prepared [92-94]. Many kinds of inifers may, of course, be used. For example Kress and Heitz prepared macromers from poly(oxytetramethylene) chains with acrylate or methacrylate end groups, by THF polymerization initiated by superacids with anhydrides as co-initiators - transfer agents [95]. 

Fundamental studies directed toward the elucidation of the mechanism of olefin i.e.f isobutylene, polymerizations yielded a new method for the synthesis of novel linear and tri-arm star telechelic polymers and oligomers [1,2]. The synthesis involves the use of bi- or tri-functional initiator/transfer agents, so called inifers (binifers and trinifers), in conjunction with BCI3 coinitiator and isobutylene, and gives rise to polyisobutylenes carrying exactly two or three terminal -CH2-C(CH3)2Cl groups. These liquid telechelic polyisobutylene chlorides can be readily and quantitatively converted to telechelic polyisobutylene di- or tri-olefins [2,3] which in turn can quantitatively yield by hydroboration/oxidation telechelic polyisobutylene di- and triols [4,5]. 

In regard to Step 1, the principle of the inifer synthesis is that certain bifunctional initiator/ transfer agents (inifers) induce polymerizations and subsequently control the termini of the polymers that are formed by chain transfer to inifer steps. Scheme II shows a simplified inifer mechanism (XRX = inifer,... 

MIPs can be synthesized in the pores and on the surface of pre-made porous particles. Porous silica particles have been applied for this purpose. To ensure that the imprinted polymer is attached firmly to the particle, the particles are often chemically modified by coupling of polymerizable groups or initiator molecules to the particle surface prior to the MIP polymerization [100-102]. The use of immobilized initiators is often referred to as the iniferter (initiator-transfer agent-terminator) approach [103]. The method has been applied to the imprinting of a range of templates [104—107]. 

One of the most common technologies for the synthesis of polymer polyols by a radical mechanism is based on the stepwise addition of a mixture of vinylic monomers (polyether polyol, initiator, transfer agent (mixture I)) to a second mixture (mixture II) of polyether polyol (identical with the polyether used for mixture I) and NAD (macromer or nonreactive NAD) under a nitrogen protective atmosphere, in the polymerisation reactor at 115-... 

Thermoresponsive HAs were prepared by graft polymerization of A-isopropyla-crylamide (NIPAM) on HA using dithiocarbamate. The dithiocarbamate acted as an initiator, transfer agent, and terminator in the reaction. These... 

Controlled/ living radical polymerization (CLRP) processes are well-established synthetic routes for the production of well-defined, low-molecular weight-dispersity polymers [99]. The types of CLRP processes (initiator-transfer agent-terminator (INIFERTER), atom transfer radical polymerization (ATRP), nitroxide-mediated radical (NMRP) polymerization, reversible addition-fragmentation transfer (RAFT)) and their characteristics are described in Section 3.8 of Chapter 3 and in Section 14.8 of Chapter 14. 

Georgiev has reported a photoiniferter ability for [bis(acyloxy)iodo]arenes during the bulk polymerization of methyl methacrylate, styrene and A-vinylpyrrolidone [44]. The term photoiniferter refers to a chemical compound that has a combined function of being a free radical initiator, transfer agent and terminator in photolytically induced polymerization [47]. Under visible light [bis(acyloxy)iodo]arenes initiate... 

Otsu, T. Masatoshi,Y. Role of initiator-transfer agent-terminator (iniferter) in radical polymerizations pol5nner design by organic disulfides as iniferters. Makromol. Chem. Rapid. Commun. 1982, 3, 127-132. 

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