Polymerization, mechanism radical

A living radical polymerization mechanism was proposed for the polymerization of MMA23 -240 and VAc241 initiated by certain aluminum complexes in the presence of nilroxides. It was originally thought that a carbon-aluminum bond was formed in a reversible termination step. However, a more recent study found the results difficult to reproduce and the mechanism to be complex.242... 

Influence of Reactor Type on the MWD of the Product of a Free Radical Polymerization Mechanism. 

The polymerization rate equations are based on a classical free radical polymerization mechanism (i.e., initiation, propagation, and termination of the polymer chains). 

Our acrylic polymerization model was developed to meet the need for solving these problems. Kinetics used are based on fairly well accepted and standard free radical polymerization mechanisms. 

Block copolymerization was carried out in the bulk polymerization of St using 18 as the polymeric iniferter. The block copolymer was isolated with 63-72 % yield by solvent extraction. In contrast with the polymerization of MMA with 6, the St polymerization with 18 as the polymeric iniferter does not proceed via the livingradical polymerization mechanism,because the co-chain end of the block copolymer 19 in Eq. (22) has the penta-substituted ethane structure, of which the C-C bond will dissociate less frequently than the C-C bond of hexa-substituted ethanes, e.g., the co-chain end of 18. This result agrees with the fact that the polymerization of St with 6 does not proceed through a living radical polymerization mechanism. Therefore, 18 is suitably used for the block copolymerization of 1,1-diubstituted ethylenes such as methacrylonitrile and alkyl methacrylates [83]. 

When R-X and NiX have high reactivities for chain transfer and/or primary radical termination (Eqs. 36 and 37), and the C-X bond at the chain end further reacts with Ni° by redox reaction (Eq. 38), the polymerization proceeds via a living radical polymerization mechanism. In this polymerization, the polymerization which has R and X groups at both chain ends is produced ... 

Tetraethylthiuram disulfide (13) induces St polymerization by the photodissociation of its S-S bond to give the polymer with C-S bonds at both chain ends (15). The C-S bond further acts as a polymeric photoiniferter, resulting in living radical polymerization. Eventually, some di- or monosulfides, as well as 13, were also examined as photoiniferters and were found to induce polymerization via a living radical polymerization mechanism close to the model in Eq. (18), e.g., the polymerization of St with 35 and 36 [76,157]. These disulfides were used for block copolymer synthesis [75,157-161] ... 

It was confirmed that the resulting polymers obtained from the St polymerization with 13 induced further photopolymerization of MMA to produce a block copolymer, and the yield and molecular weight increased as a function of the polymerization time, similar to the results for the polymerization of MMA with 13, indicating that this block copolymerization also proceeds via a living radical polymerization mechanism [64]. Similar results were also obtained for the photoblock copolymerization of VAc. Thus, various kinds of two- or three-component block copolymers were prepared [157,158]. 

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 living radical polymerization of some derivatives of St was carried out. The polymerizations of 4-bromostyrene [254], 4-chloromethylstyrene [255, 256], and other derivatives [257] proceed by a living radical polymerization mechanism to give polymers with well-controlled structures and block copolymers with poly(St). The random copolymerization of St with other vinyl... 

While there have been several studies on the synthesis of block copolymers and on the molecular weight evolution during solution as well as bulk polymerizations (initiated by iniferters), there have been only a few studies of the rate behavior and kinetic parameters of bulk polymerizations initiated by iniferters. In this paper, the kinetics and rate behavior of a two-component initiation system that produces an in situ living radical polymerization are discussed. Also, a model that incorporates the effect of diffusion limitations on the kinetic constants is proposed and used to enhance understanding of the living radical polymerization mechanism. 

However, it was not until the appearance in 1953 of an important group of papers from the laboratories of Du Pont that any satisfactory evidence became available concerning the nature of the branches in polyethylenes of this type, the low-density polyethylenes (LDPE). Roedel (6) showed that the free-radical polymerization mechanism could be expected to lead not only to short branches containing a few carbon atoms (with which this review is not concerned) but by a mechanism first proposed by Flory (4) and involving the... 

Vmyl ethers can also be formulated with acrylic and unsatiiraterl polyesters containing maleate or fumarate functionality. Because of their ability to form alternating copolymers by a free-radical polymerization mechanism, such formulations can be cured using free-radical photoinitiators With acrylic monomers and oligomers, a hybrid approach has been taken using both simultaneous cationic and free-radical initiation. 

A classical radical polymerization mechanism has been applied to butadiene polymerization with azo initiators32). Transfer reactions are absent. 

PTFE is produced by free-radical polymerization mechanism in an aqueous media via addition polymerization of tetrafluoroethylene in a batch process. The initiator for the polymerization is usually a water-soluble peroxide, such as ammonium persulfate or disuccinic peroxide. A redox catalyst is used for low temperature polymerization. PTFE is produced by suspension (or slurry) polymerization without a surfactant to obtain granular resins or with a perfluori-nated surfactant emulsion polymerization) to produce fine powder and dispersion products. Polymerization temperature and pressure usually range from 0 to 100°C and 0.7 to 3.5 MPa. 

Commercially, it is polymerized by free-radical polymerization mechanism, usually in an aqueous (or nonaqueous) media via addition polymerization of TFE and hexafluoropropylene. The initiator for the polymerization is usually water-soluble peroxide, such as potassium persulfate. Chain transfer agents could be used to control the molecular weight of the resin. In general, the polymerization regime and conditions resemble those used to produce PTFE by emulsion polymerization. For melt fabrication processes, FEP is recovered, dried, and melt-extruded into cubes. It is also available in dispersion form. 

This plastic is a partially fluorinated straight-chain polymer with a very high molecular weight. It is produced by free-radical polymerization mechanism in a solvent or a hybrid (a solvent/aqueous mixture) media, using an organic peroxide initiator. Copolymerization of tetrafluoroethylene and ethylene (CH2=CH2, molecular weight 28, CAS number 74-85-1) proceeds by an addition mechanism. 

A free-radical polymerization mechanism can be excluded on the basis of the polymer microstructure and experiments with radical inhibitors. Rhodium(I)-spe-cies, formed by reduction of Rh " salts used as catalyst precursors by butadiene monomer, have been suggested as the active species. The catalyst is stable during the aqueous polymerization for over 30 h [23]. Catalyst activities are moderate with up to ca. 2x10 TO h [24, 25]. By contrast to industrially important free-radical copolymerization, styrene is not incorporated in the rhodium-catalyzed butadiene polymerization [26]. Only scarce data is available regarding the stability and other properties of the polymer dispersions obtained. Precipitation of considerable portions of the polymer has been mentioned at high conversions in butadiene polymerization [23, 27]. 

Poly(2-methyl-1-pentene sulfone) (PMPS) is an alternating copolymer of 2-methyl-l-pentene (2MP) and sulfur dioxide. The formation of PMPS occurs only by a free radical polymerization mechanism and is complicated to a degree by ceiling temperature considerations. For all exothermic addition polymerization reactions there is a critical temperature called the ceiling temperature (Tc) above which no reaction occurs. The precise Tc depends upon the monomer concentration according to the expression (i)... 

N-p-(methoxy-o-hydroxybenzylidene)-p-aminostyrene], in the isotropic, nematic and oriented nematic states [30]. In addition, Hsu and Blumstein observed no change in the radical polymerization mechanism of another Schiff base [N-(p-cyanobenzylidene)-p-aminostyrene]... 

At high temperatures, [Ru(CH3)(Tp)(CO)(NCMe)] acts as catalyst for the production of polystyrene. The dependence of polystyrene molecular weight on benzene/cumene molar ratios suggests a radical polymerization mechanism. The polymerization of methyl methacrylate, in the presence of [Ru(CH3)(Tp)(CO)(NCMe)j with carbon tetrachloride or methyl dichloroacetate, has been observed at 90°C.31... 

The anomalies observed in the GPC traces of the early fractions implicate GTP mechanisms rather than SCF extraction efficiencies. Unlike anionic and free-radical polymerization mechanisms, GTP is catalyzed, and a silicon atom is central to the catalysis mechanism. It is plausible that the presence of nonfunctional PDMS may interfere with the normal rate of propagation (Hellstern, 1989) since silicon atoms in the PDMS chain may act as alternative catalyst sites. Hellstern (1989) compared the extent of MMA polymerization in the presence of nonfunctional PDMS with the extent of MMA-PDMS... 

The term "ionic polymerization" basically involves the chemistry of heterolytic cleavage of chemical bonds, as opposed to the homolytic reactions that characterize the well-known free-radical polymerization mechanism. Hence, essential and profound differences exist between these two mechanisms of polymerization. Although these differences are also found between radical and ionic mechanisms in ordinary reactions, they exert a much more drastic influence on the result, that is, the growth of a long chain molecule to macro dimensions. Thus, one would expect that the two mechanisms could lead to quite different results in most simple reactions, in terms of rate, yield, or mode of the reaction. In the case of polymerization, however, such differences, can, in fact, decide whether any high polymer is obtained at all. 

Emulsion polymerization is the process of choice for the commercial production of many polymers used for coating and adhesive applications, especially for those products that can be used in latex form. Emulsion polymerization uses free-radical polymerization mechanisms with unsaturated monomers. The heterogeneous nature of the reaction mixture, however, has a significant influence on the chemical and physical reaction mechanisms and on the nature of the final product. 

Figure 4.1 Controlled radical polymerization mechanisms via (a) NMRP, (b) ATRP, and (c) RAFT.

A free radical polymerization mechanism was proposed by Singer ... 

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