Unified approach to living and non‐living cationic polymerization of alkenes

Matyjaszewski, Krzysztof; Sigwalt, Pierre

doi:10.1002/pi.1994.210350101

Cited by 77 publications

(44 citation statements)

References 107 publications

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“…However, such a scenario was realized by the development of controlled/''living'' systems in which the active propagating radicals are intermittently formed. This concept, originally applied to cationic ring-opening polymerization [21], was successfully extended to carbocationic systems [22] and later to anionic and other polymerizations where growing centers are in equilibrium with various dormant species [23].…”

Section: General Conceptsmentioning

confidence: 99%

Radical Polymerization

Matyjaszewski

2009

Controlled and Living Polymerizations

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Approximately 50% of all synthetic polymers are currently made via radical polymerization (RP) processes. The commercial success of RP can be attributed to the large range of radically polymerizable monomers, their facile copolymerization, the convenient reaction conditions employed (typically room temperature to 100 • C, ambient pressure), and very minimal requirements for purification of monomers and solvents. RP is not affected by water and protic impurities and can be carried out in bulk, solution, aqueous suspension, emulsion, dispersion, etc. The range of monomers is larger for RP than for any other chain polymerization because radicals are tolerant to many functionalities, including acidic, hydroxy, and amino groups. In conventional RP, high molecular weight (MW) polymers are formed at the early stages of the polymerization, and neither long reaction times nor high conversions are required, in sharp contrast to step-growth polymerization.However, RP has some limitations, especially in comparison with ionic processes that provide facile routes to living polymers. For a polymerization to be considered ''living,'' the contribution of chain breaking reactions such as termination and transfer should be negligible. While transfer is not a major issue in RP when the appropriate conditions are applied, termination is much less avoidable and is a major limitation of RP. In contrast to ionic reactions, in which cations or anions do not react via bimolecular termination, radicals terminate with a diffusion controlled rate. To form high MW polymers, the relative probability of such termination must be minimized. This is accomplished by running RP at very low concentrations (from ppb to ppm) of propagating radicals. The concentrations of growing species are thus much lower in RP than in carbanionic or ring-opening polymerizations. In RP, a steady concentration of radicals is established by balancing the rate of termination with that of initiation. The rate of propagation is much faster than the rate of initiation/termination (as required to keep radical concentration low). Therefore, Controlled and Living Polymerizations. Edited a Measurements in bulk at 40 • C and ambient pressure, unless otherwise stated. b k t reported at 1000 bar. c Solvent = chlorobenzene. E p and A p represent the Arrhenius activation energy for propagation and frequency factor for propagation, respectively. Typical Features of Radical Polymerization 107coefficients of termination depend on chain length and conversion (viscosity), the values in Table 3.1 are given for low conversion and DP ≈ 100. CopolymerizationFacile statistical copolymerization is one of the main advantages of RP. In contrast to ionic polymerization, the reactivities of many monomers are relatively similar, which makes them easy to copolymerize statistically. For monomers with opposite polarities, there is a tendency for alternation (r A r B < 1, where r A = k AA /k AB and r B = k BB /k BA ). Electrophilic radicals (i.e., those with -CN, -C(O)OR, or Cl groups) prefer to react ...

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Section: General Conceptsmentioning

confidence: 99%

Radical Polymerization

Matyjaszewski

2009

Controlled and Living Polymerizations

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“…Originally, such control was reported for anionic polymerization of non‐polar monomers and subsequently extended to cationic ring‐opening polymerization (CROP),3 carbocationic systems4 and eventually to controlled/living radical polymerization (CRP) 5, 6. Most of these systems employ formation of a dynamic equilibrium between active and dormant species to attain controlled polymerization 7–9…”

Section: Introductionmentioning

confidence: 99%

The synthesis of functional star copolymers as an illustration of the importance of controlling polymer structures in the design of new materials

Matyjaszewski

2003

Polymer International

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Several different methods for the synthesis of star copolymers employing atom transfer radical polymerization are presented. They include core‐first and arm‐first methods, and a combination of both to prepare mikto‐arm stars. Stars with a well‐defined number of arms were prepared by using a core with a precise number of functional groups, and ill‐defined stars were prepared from hyperbranched cores. In addition, end‐functional stars were prepared by either displacing end‐functional halogens or through radical addition with unreactive functional alkenes. Another approach to end‐functional stars employs functional initiators and the subsequent coupling of the end‐functional arms with difunctional vinyl monomers. Star‐like backbones were also used to grow star‐like macromolecular brushes that were visualized by AFM. The polydispersities of individual arms and entire stars followed Schulz–Flory statistics. Copyright © 2003 Society of Chemical Industry

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“…This situation is rather typical for living polymerization processes;25–30 therefore the systems in which these processes occur may be regarded as ‘living systems with reversible chain termination’, according to the classification proposed by Quirk and Lee 31. (The recomendations of IUPAC concerning living polymerizations are published in refs 32 and 33). Apparently, electron donor additives play an important role in the reversibility of the halogenation reaction.…”

Section: Resultsmentioning

confidence: 99%