Radical cation polymerization phase system

There are two problems in the manufacture of PS removal of the heat of polymeriza tion (ca 700 kj /kg (300 Btu/lb)) of styrene polymerized and the simultaneous handling of a partially converted polymer symp with a viscosity of ca 10 mPa(=cP). The latter problem strongly aggravates the former. A wide variety of solutions to these problems have been reported for the four mechanisms described earlier, ie, free radical, anionic, cationic, and Ziegler, several processes can be used. Table 6 summarizes the processes which have been used to implement each mechanism for Hquid-phase systems. Free-radical polymerization of styrenic systems, primarily in solution, is of principal commercial interest. Details of suspension processes, which are declining in importance, are available (208,209), as are descriptions of emulsion processes (210) and summaries of the historical development of styrene polymerization processes (208,211,212). 

The evidence for this mechanism is based on mass spectroscopy of the gas-phase radiolysis of isobutylene, which may not be applicable to the typical liquid-phase polymerization system. Initiation in condensed systems may follow the same course as electroinitiation— coupling of radical-cations to form dicarbocations. 

To minimize the indane, 99, formation, dimerization was conducted in two-phase systems containing toluenesulfonic acid,354 sulfuric acid,355 356 electrophilic transition-metal complexes,357 the polymeric solid-state acid Nafion,358 359 metal oxide solid-state catalysts such as tungstophosphoric acid,360 various zeolites,361 362 mixed oxides,363 and montmorillonite clay in the presence of organic solvents.364 365 The major limitation of the cationic approach, however, is the unavoidable formation of internal isomer 100. Since isomer 100 is inert in radical polymerization, the lower the content of isomer 100, the higher activity of the 98 mixture. Even in the very best cases, its presence is never less than 5—15%. 

Currently, there are few applications of step and non-radical polymerization (except for cationic polymerization by Yoshida s group (see Chapter 14) in the solution phase to microreactor systems. In this section, we focus on controllable amino add polymerization using a microreador. 

To synthesize water-soluble or swellable copolymers, inverse heterophase polymerization processes are of special interest. The inverse macroemulsion polymerization is only reported for the copolymerization of two hydrophilic monomers. Hernandez-Barajas and Hunkeler [62] investigated the copolymerization of AAm with quaternary ammonium cationic monomers in the presence of block copoly-meric surfactants by batch and semi-batch inverse emulsion copolymerization. Glukhikh et al. [63] reported the copolymerization of AAm and methacrylic acid using an inverse emulsion system. Amphiphilic copolymers from inverse systems are also successfully obtained in microemulsion polymerization. For example, Vaskova et al. [64-66] copolymerized the hydrophilic AAm with more hydrophobic methyl methacrylate (MMA) or styrene in a water-in-oil microemulsion initiated by radical initiators with different solubilities in water. However, not only copolymer, but also homopolymer was formed. The total conversion of MMA was rather limited (<10%) and the composition of the copolymer was almost independent of the comonomer ratio. This was probably due to a constant molar ratio of the monomers in the water phase or at the interface as the possible locus of polymerization. Also, in the case of styrene copolymerizing with AAm, the molar fraction of AAm in homopolymer compared to copolymer is about 45-55 wt% [67], which is still too high for a meaningful technical application. 

While not strictly considered emulsions, two other systems may be classified in this category, both of which comprise very small particles of silicone fluids in aqueous dispersions. The first method of preparing these microdroplets involves in situ polymerization of a water-soluble vinyl monomer or mixtures of said monomer and acryl comonomers. The silicone fluids are first dispersed into microdroplets in the water phase by means of high-speed agitation and then the vinyl monomers or cationic polymers are added at elevated temperatures in the presence of free-radical catalysts. The resulting aqueous polymer matrix contains stable, discreet microdroplets of the silicone fluids. The second method utilized to prepare such a fine dispersion is very-high-pressure injection of silicone into the aqueous phase. These microdroplets have been referred to as nanoparticles, but they are actually nanometer-sized fluid droplets as opposed to nanometer-sized sihcone resin particles, which are referred to by the same term (86). Both of the systems described above have been claimed to readily deposit onto hair and skin, and to increase ease of formulation (87,88). 

In order to study the mchanism of micellar polymerization, they used a variety of initiators and inhibitors having different water solubilities. It was concluded that most of the time the radicals are produced in the water phase and have to enter the micelles before the polymerization can take place. The authors have studied three systems in the first, a hydrophobic acrylamido monomer swelling SDS micelles was copolymerized with acrylamide in the second, they used their styrenic cationic surfmer N16 and in the last, they used mixed micelles of N16 and a similar but nonpolymeriz-able surfactant B16. 

No phase changes or segregation phenomena occurred up to ca. 20 % conversion of the UV-curable system, in a wide temperature range The LC phase does not affect the free radical polymerization rate Unlike cationic photopolymerization, the free-radical mechanism promotes rate accelerations at conversions related to compositions, for which changes in medium opacity are observed... 

The features and detail of the IPN kinetics were also studied in other works [274-276]. The kinetics of thermally initiated cationic epoxy polymerization and free radical acrylate photopolymerization were investigated in [277]. It was found that the preexistence of one polymer has a significant effect on the polymerization of the second monomer. The reaction kinetics and phase separations were studied for sequential IPNs in [278]. The kinetics of IPN formation was studied for IPNs based on PDMS-cellulose acetate butyrate [279]. All these and other works [280-282] confirm the general regularities of the reaction kinetics and its connection with phase separation in forming systems. 

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