Polymerization Bulk polymerizations Cationic

Under free radical conditions, we found that the bulk polymerization of 4-allyloxystyrene gave an insoluble crosslinked polymer with AIBN. Similar results were previously reported for the polymerization with benzoyl peroxide (8). The cationic polymerization of /7-alkoxystyrene monomers have been shown to proceed at rates that are comparable to vinyl ethers (12,13). As expected from these studies, we found that alkenyloxystyrene monomers also have a high degree of cationic reac-... 

Ever since 1962, when Williams, Okamura, and their associates started to publish propagation rate-constants k+p for the cationic bulk polymerization of cyclo-pentadiene, isobutene, styrene, a-methylstyrene and isopropylvinyl ether by ionizing radiations, these constants have been accepted as the best, most likely, values for the k+p of unpaired cations in a medium of low-polarity, and those obtained subsequently by Stannett and his collaborators, using similar methods, enjoyed the same status, (The loci classici are Bates et al. (1962), Bonin et al. (1964), Taylor Williams (1969) and the three papers by Ueno et al. (1967), Hayashi et al. (1967) and Williams et al. (1967).)... 

This is not the first time that the kinetics of bulk polymerizations has been analysed critically. Szwarc (1978) has made the same objection to the identification of the rate constant for the chemically initiated bulk polymerization of tetrahydrofuran as a second-order rate constant, k, and he related the correct, unimolecular, rate constant to the reported by an equation identical to (3.2). Strangely, this fundamental revaluation of kinetic data was dismissed in three lines in a major review (Penczek et al. 1980). Evidently, it is likely to be relevant to all rate constants for cationic bulk polymerizations, e.g., those of trioxan, lactams, epoxides, etc. Because of its general importance I will refer to this insight as Szwarc s correction and to (3.2) as Szwarc s equation . 

Vinylethers are known to polymerize in a cationic mechanism in the conventional homopolymerization system (35). Williams et al. (36) and Naruse et al. (37) studied the radiation-induced polymerization of vinylethers and found that they polymerize in the cationic mechanism by ionizing radiations, too. The propagation rate constant of the polymerization of isobutylvinylether in bulk at 30° C was estimated to be 3 x 105 M l sec 1, much higher than that of the polymerization by... 

It has been reported that vinylferrocene is polymerized by using a radical, cationic, anionic, or Ziegler system initiator [29 — 34]. In particular, higher molecular weight products can be obtained using radical-initiated bulk polymerization [31]. Indeed, both bulk copolymerization and solution copolymerization (in benzene) of 18 with vinylferrocene by using a radical initiator (AIBN) afforded the chiral polymers 19a —e (Scheme 3-13), which were purified by reprecipitation of the benzene solution with methanol. The ratios of the two comonomers were varied in copolymerization. The composition data of the copolymers obtained revealed nearly the same reactivity between 18 and vinylferrocene, which suggests that 19a—e are random copolymers. 

In the case of photo-initiated polymerizations bimodal distributions can occur as a result of concurrent free-radical and cationic growth, these intermediates not being in chemical equilibrium. This arises in the bulk polymerizations of styrene photo-initiated in the presence of tetracyanobenzene and also in the radiation-induced polymerization of alkyl-substituted styrenes.In the former system the higher molecular weight fraction is attributed to a cationic... 

A seven-membered cyclic phosphonlte (a dloxaphosphepane, 6) has been polymerized using a cationic Initiator (28) A bulk polymerization of 6 using Mel as an Initiator (2.0 mol % for 6) at 100 C gave In 20 hr a polyphosphlnate 42 (molecular weight = 12000). This Is the... 

Stejskal that aniline radical cations adsorb on the substrate surface during an induction period before bulk polymerization is observed. The adsorbed species promote the formation of a dense film initially on the substrate surface. Once this film has formed, further growth occurs on the PAn surface in a manner similar to the growth of localized globules during electropolymerization. The surface roughness of in situ PAn films may be further increased by the incorporation of PAn precipitates from the bulk solution. 

Polymer processing can be of several types, including free radical, cationic, anionic, metal complex, or metal oxide catalyzed, as mentioned earlier [5], Polymers can be made by bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization techniques [5], The automotive chemist or design engineer working for an OEM should be aware of these various manufacturing processes, which polymers are made by which process, and what characteristics can be expected from the type of process. 

Cationic polymerization proceeds faster with strained unsubstituted lactams 50% conversion is reached in bulk polymerization with 1 % of HC1 at 180 °C after 1 hour with 9-membered lactam and after more than 2 weeks with the less strained 13-membered lactam. With changing the ring size of lactams (e.g. 9 - 13) not only the ring strain is changed (AAHP = 7 kcal mol-1) but also their basicities and dielectric constant of the medium (Ae = 17)3). 

One of the primary factors slowing the growth of functional polymers has been the relative complexity and cost of their preparation. The synthesis of functional polymers is often made difficult because of chemical or phase incompatibilities or antagonisms. This chapter surveys the general methods for functional polj er syntheses. It reviews the scope and limtations of functionalization by direct polymerization (e.g. anionic, cationic, free radical and organometallic methods), as weU as post-polymerization bulk and surface modification of preformed backbones. 

ROP is carried out in solution, in the melt, in the bulk or in suspension. The involved mechanism can be ionic (anionic or cationic), coordination-insertion or free-radical polymerization [19].The cationic pol)rmerization is initiated by only two catalysts, trifluoromethane-sulphonic acid and its methyl ester [10, 15]. Initiators such as potassium methoxide, potassium benzoate, zinc stearate, n-, sec-, fer-butyl lithium or 18-crown-6-ether complexes are added for the anionic polymerization to induce a nucleophilic reaction on the carbonyl to lead to an acyl-oxygen link cleavage. According to Jedkinski et al. only the primary alkoxides, such as the first mentioned catalyst, can yield polymers with negligible racemization, transesterification and termination [10]. 

Polyoxymethylene (polyacetal) — sometimes known as polyformaldehyde — is the polymer of formaldehyde. It is obtained either by anionic or cationic solution polymerization of formaldehyde or cationic ring-opening bulk polymerization of trioxane. Highly purified formaldehyde is polymerized in the presence of an inert solvent such as hexane at atmospheric pressure and a temperature usually in the range of -50 to 70°C. The cationic bulk polymerization of trioxane is the preferred method of production of polyoxymethylene. 

Polyoxymethylene (polyacetal) is the polymer of formaldehyde and is obtained by polymerization of aqueous formaldehyde or ring-opening polymerization of trioxane (cyclic trimer of formaldehyde, melting point 60-60°C), the latter being the preferred method [52]. This polymerization of trioxane is conducted in bulk with cationic initiators. In contrast, highly purified formaldehyde is polymerized in solution using using either cationic or anionic initiators. 

Figure 16-2. Change in the polymer fraction with polymerization on temperature for the bulk polymerization of tetrahydrofuran with various cationic initiators (from date of three research groups). Solid line gives the curve progress calculated according to Equation (16-32) with Xmp = 0.5, AHl = -12.4 kJ moF and ASl = -40.8 J K moF. ...

Bulk polymerization initiated via more novel methods have also been used to form bulk PS-MMT nanocomposites. Zhang et al. [19] used gamma irradiation to initiate the polymerization of PS-MMT nanocomposites with different surface modifications (3, 34) and successfully prepared exfohated morphologies when reactive clay modifications were used. Uthirakumar et al. [51-54] modified MMT with a cationic radical initiator which was used to initiate the bulk polymerization of styrene. Because the polymerization was initiated from the clay surface and the monomer and the clay were suitably compatible, exfoliated morphologies were formed. 

Three events are involved with chain-growth polymerization catalytic initiation, propagation, and termination [3], Monomers with double bonds (—C=C—R1R2—) or sometimes triple bonds, and Rj and R2 additive groups, initiate propagation. The sites can be anionic or cationic active, free-radical. Free-radical catalysts allow the chain to grow when the double (or triple) bonds break. Types of free-radical polymerization are solution free-radical polymerization, emulsion free-radical polymerization, bulk free-radical polymerization, and free-radical copolymerization. Free-radical polymerization consists of initiation, termination, and chain transfer. Polymerization is initiated by the attack of free radicals that are formed by thermal or photochemical decomposition by initiators. When an organic peroxide or azo compound free-radical initiator is used, such as i-butyl peroxide, benzoyl peroxide, azo(bis)isobutylonitrile, or diazo- compounds, the monomer s double bonds break and form reactive free-radical sites with free electrons. Free radicals are also created by UV exposure, irradiation, or redox initiation in aqueous solution, which break the double bonds [3]. 

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