Radical polymerization ideal living

In conventional radical polymerization, the chain length distribution of propagating species is broad and new short chains are formed continually by initiation. As has been stated above, the population balance means that, termination, most frequently, involves the reaction of a shorter, more mobile, chain with a longer, less mobile, chain. In living radical polymerizations, the chain lengths of most propagating species are similar (i.e. i j) and increase with conversion. Ideally, in ATRP and NMP no new chains are fonned. In practice,... 

Most reviews on living radical polymerization mention the application of these methods in the synthesis of end-lunctional polymers. In that ideally all chain ends are retained, and no new chains are formed (Section 9.1.2), living polymerization processes are particularly suited to the synthesis of end-functional polymers. Living radical processes are no exception in this regard. We distinguish two main processes for the synthesis of end-functional polymers. 

These are two possibilities for the polymerization of MA deviated from the ideal living radical polymerization (i) the chain end of poly(MA) formed primary radical termination with a DC radical does not dissociate or dissociates at an unfavorable position like 41 (ii) bimolecular termination leading to the deactivation of the iniferter sites occurs preferentially to the primary radical termination with the DC radical which reproduces the iniferter site. 

The polymerization of MA with 7 was carried out in the presence of 13, i.e., 7 and 13 were used as two-component iniferters [175]. When an identical amount of 13 to 7 was added to the system, the polymerization proceeded according to a mechanism close to the ideal living radical polymerization mechanism. Similar results were also obtained for the polymerization of VAc. These results indicate that the chain end of the polymer was formed by the competition of primary radical termination and/or chain transfer to bimolecular termination, and that it could be controlled by the addition of 13. 

The nature of free-radical polymerization has traditionally hindered attempts to produce an ideal living free radical polymerization technique. It is very difficult to prevent chain transfer and termination reactions in free-radical polymerizations and although several methods have afforded polymers with very low polydispersities < 1.1), these approaches are often referred... 

Additional well-defined side-chain liquid crystalline polymers should be synthesized by controlled polymerizations of mesogen-ic acrylates (anionic or free radical polymerizations), styrenes (anionic, cationic or free radical), vinyl pyridines (anionic), various heterocyclic monomers (anionic, cationic and metalloporphyrin-initiated), cyclobutenes (ROMP), and 7-oxanorbornenes and 7-oxanorbornadienes (ROMP). Ideally, the kinetics of these living polymerizations will be determined by measuring the individual rate constants for termination and... 

The living radical polymerization (LRP) approach was first introduced in the 1980s. LRP is a type of polymerization in which a chain can only propagate and not undergo irreversible termination or chain transfer. Hence, LRP is an ideal system to produce monodisperse polymers of known molecular weights, architectures and compositions. Reversible addition-fragmentation chain transfer polymerization (RAFT), atom transfer radical... 

CRP (also referred to as living radical polymerization ) is a family of promising techniques for the synthesis of macromolecules with well-defined molecular weight, low polydispersities (often close to unity) and various architectures under mild conditions at 20-120°C, with minimal requirements for purification of monomers and solvents. A common feature of the variants is the existence of an equilibrium between active free radicals and dormant species. The exchange between active radicals and dormant species allows slow but simultaneous growth of all chains while keeping the concentration of radicals low enough to minimize termination. The ideal CRP is achieved if all chains are initiated... 

There are two main changes to this mechanism that are required for an ideal living radical polymerization process ... 

A. -C. Shi, M. K. Georges, H. K. Mahabadi, Kinetics of controlled living free radical polymerization 1. Ideal case, Polym. React. Eng. 1999, 7, 283-300. 

The three main requirements for an ideal SNR-mediated living/controlled free-radical polymerization are (i) essentially simultaneous initiation (ii) reversible reaction of SNR given in Eq. (11.10) and (iii) no important degree of irreversible termination, if any. Under these conditions, one would expect the system to be described by a simple kinetic scheme, as described below. 

FIGURE 12.13 M versus conversion, /from ACOMP for several BA polymerization reactions by RAFT ( 1 ) and a free radical polymerization reaction ( 5). For high [DoPAT]/[AIBN] ( 1-3), the reactions exhibit typical CRP behavior with nearly linear increase of mass versus /. The downward curvature in reaction 4 indicates significant deviations from the ideal living mechanism. Reaction 5 shows classical uncontrolled radical polymerization behavior of with conversion. Reprinted (adapted) with permission from Alb AM, Serelis AK, Reed WF. Kinetic trends in RAFT homopolymerization from online monitoring. Macromolecules 2008 41 332-338. 2008 American Chemical Society. 

An example of monomer linkage with termination is free radical polymerization. An example of monomer linkage without termination is ionic living polymerization or (in the ideal case) controlled radical polymerization. 

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