Thermal mediated polymerizations

Catala and coworkers167JuiS made the discovery that the rate of TEMPO-mediated polymerization of S is independent of the concentration of the alkoxyamine. This initially surprising result was soon confirmed by others.23 69 Gretza and Matyjaszewski169 showed that the rate of NMP is controlled by the rate of thermal initiation. With faster decomposing alkoxyamines (those based on the open-chain nitroxides) at lower polymerization temperatures, the rate of thermal initiation is lower such that the rate of polymerization becomes dependent on the alkoxyamine concentration, Irrespective of whether the alkoxyamine initiator is preformed or formed in situ, low dispersities require that the alkoxyamine initiator should have a short lifetime. The rate of initiation should be as fast as or faster than propagation under the polymerization conditions and lifetimes of the alkoxyamine initiators should be as short as or shorter than individual polymeric alkoxyamines. 

Various stable radicals such as nitroxide, triazolinyl, trityl, and dithiocarbamate have been used as the mediating or persistent radical (deactivator) for SFRP. Nitroxides are generally more efficient than the others. Cyclic nitroxide radicals such as 2,2,6,6-tetramethyl-l-piper-idinoxyl (TEMPO) have been extensively studied. SFRP with nitroxides is called nitroxide-mediated polymerization (NMP). Polymerization is carried out by two methods that parallel those used in ATRP [Bertin et al., 1998 Georges, 1993 Flawker, 1997 Flawker et al., 2001], One method involves the thermal decomposition of an alkoxyamine such as... 

Nitroxide mediated polymerization (NMP) [56, 57]. This consists in a thermally reversible termination reaction by a homolytic cleavage of a C-ON bond of an alkoxyamine, giving rise to an initiating alkyl radical (active species) and a nitroxyl radical, which brings control to the reaction [58]. 

Nitroxide mediated polymerization (NMP) is another type of controlled radical polymerization technique used to synthesize polymer hybrids. It relies on the reversible trapping of growing macro-radicals by nitroxide to form dormant species in which the C-ON covalent bond is thermally cleavaged (Fig. 19). At a polymerization temperature, the equilibrium between dormant and active species is strongly shifted to the dormant side, which Emits the irreversible chain termination reaction. 

In an attempt to overcome the low infusible character and low solubility of aniline, dispersion polymerization of aniline was conducted in water-dispersible colloidal particles that can be cast as films or blended with other materials to prepare composites. HRP mediated polymerization of aniline in a mixture of phosphate buffer and organic solvent resulted in polyaniline composed of ortho-directed units and para-directed units. Increasing the pH or adopting an organic solvent with a high dielectric constant, enhanced the production of ortho-directed units [54]. These ortho-directed polyanilines were more thermally flexible and electrically conductive. 

Since polystyrene is one of the oldest commercial polymers with over 9 million tonnes/yr of sales, there have been thousands of patents issued covering all aspects of its manufacture and property enhancement. The styrene monomer readily polymerizes to polystyrene either thermally or with free-radical initiators (see Chapter 6 on free-radical polymerization and Chapter 8 on nitroxide-mediated polymerization). Commercial processes for the manufacture of polystyrene are described in Chapter 3 while process modelling and optimization of styrene polymerization is examined in Chapter 5. Styrene also can be polymerized via anionic and Ziegler-Natta chemistries using organometallic initiators. Using free radical and anionic polymerization chemistries, the... 

Batch polymerizations of styrene, MMA, and 2-hy-droxyethyl methacrylate carried out in the presence of either dodecanethiol or 9c indicate that the overall rates of polymerization do not differ significantly in the two systems.438 The molecular weight distribution of the polymer formed in the presence of the thiol becomes increasingly broad, whereas the 9c-mediated polymerization produces a relatively uniform product during the course of the reaction. The polymer product formed with 9c was found to be slightly less stable thermally than the product formed by the thiol, presumably a result of the unsaturated end groups. 

In general, TEMPO-mediated polymerizations have been successfully used to prepare copolymers of St-based monomers however, attempts to incorporate other monomers have been difficult. The major reason behind this limitation is that radicals generated by the thermal self-initiation reaction of St are required to moderate the rate of polymerization by consuming the excess nitroxide produced by termination. When the ratio of St in the monomer feed is high, copolymerization with non-St based monomers is possible however, as the level of St... 

Nitroxide-mediated polymerization (NMP) [3] and atom transfer radical polymerization (ATRP) [4, 5] are the two main methods of CRP based on a reversible termination reaction. This corresponds to an equilibrium between the active macromolecular radical and a dormant covalent counterpart, which is either an alkoxyamine for NMP or an alkyl halide for ATRP (Fig. 1). Activation of the alkoxyamine is a thermal process and requires elevated temperatures, whereas in... 

Ring-opening polymerization (ROP) has seen broad utility for synthesizing main-chain organometallic polymers. Initially reported by Rauchfuss [9], and thoroughly developed by Manners and coworkers [10], the transformation from 10 to 11 (Schane 1.4) has been optimized to include various conditions for polymerization such as thermal, anionic, photo, and metal-mediated polymerizations Both solution and solid-state polymerization have also been reported. Molecular weights on the order of 10 Da have been achieved and the ability to prepare monomers of varying functionahty has assisted... 

While the SNR-mediated polymerization process comprises heating a mixture of monomer(s) and P-N adduct (that acts both as an initiator and a controlling agent), or a mixture of monomer(s), free-radical initiator, and SNR (or P-N adduct), the best temperature of polymerization, determined by experiments, is the one that leads to (i) a fast initiation rate as compared to the propagation rate (ii) a fast equilibrium between the active species and the dormant ones (iii) a low concentration of active species in order to minimize the termination and/or transfer reactions and (iv) a negligible thermal polymerization (of styrenic monomers). For example, the rate of formation of thermal radicals in styrene is equal to 1.6x10 mol L s at 100°C, 0.6x10 mol L... 

However, when the equilibrium constants are very small the polymerizations are slow, as in the classic case of the TEMPO mediated polymerization of styrene, Xgq at 130 °C. In that case, the rate can be increased to an acceptable level by increasing the number of radicals either from thermal initiation by the monomer or by adding a second conventional radical initiator, which has an appropriate lifetime at the polymerization temperature, such as dicumyl peroxide [68,80,81]. In that case, the concentration of radicals is defined by the balance between rates of initiation and termination ... 

Probably the most important factor for the future of NMP will be the development of new compounds that allow polymerization and copolymerization of a broader range of monomers under milder reaction conditions we should however note that nitroxide mediated polymerization has already been applied to styrene [92], acrylates [93], acrylamides [94], acrylonitrile [67], dienes [95], and recently polymerization of ethylene has been claimed to be controlled [96,97]. NMP has also been extended to functional monomers such as sodium styrene sulfonate [98], 2-vinylpyridine [99,100], 3-vinyl pyridine [101,102], and 4-vinylpyridine [103]. However, since a nitroxide residue ends up at the end of each chain, these new compounds should be inexpensive, and introduce no adverse properties (color, poor thermal stability, etc.) to the final material. 

MOR 15] Morris J., Telitel S., Fairfull-Smith K.E. et al, Novel polymer synthesis methodologies using combinations of thermally- and photochemically-induced nitroxide mediated polymerization . Polymer Chemistry, 2015. 

In the DC process, P-X is activated by a thermal or photochemical stimulus to produce P and the stable or persistent radical X, which is stable enough to undergo no reaction other than the combination with P (i.e., neither initiates polymerization or reacts with itself). Nitroxides such as 2,2,6,6-tetramethylpiperidinyl-l-oxy (TEMPO) are the typical X currently utilized (nitroxide-mediated polymerization (NMP)) [9,10]. 

According to Table 8, the DBN-mediated polymerization of tBA may be as well controlled as the TEMPO-mediated polymerization of styrene. Actually, however, the thermal degradation of the active chain end of PtBA-DBN occurs rather seriously at high temperatures, not allowing the polydispersity to be lowered as in the TEMPO/styrene system. Clearly, a large feact is a necessary but not a sufficient condition for a high-performance LRP. 

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