Vinyl fluoride, bulk polymerization

Continuous polymerization of VF was based on the modified suspension process in another work. In the bulk polymerization, vinyl fluoride was polymerized by a peroxide initiation. In an example, a glass ampoule was filled with VF containing 6.5 x Ifr mol/L of di-tert-butyl peroxide. The ampoule was irradiated by UV light from a mercury lamp below 25°C. Highly porous polymers, insoluble in vinyl fluoride, at conversions over 90%, were obtained. 

Polymerization of Styrene Solutions of Volatile Hydrocarbons. Addition of Hydrocarbon before Polymerization. Bulk Polymerization. Expandable polystyrene was prepared inadvertently in 1945 in an attempt to bulk copolymerize 10% isobutylene with styrene. The product formed a low density foam when heated (96). An early method (1950) for rendering polystyrene expandable by petroleum ether was to dissolve 6 parts of petroleum ether in a 40% solution of polystyrene in benzoyl peroxide-catalyzed styrene and to hold the mass for 28 days at 32 °C. (124). In a recent version of this process, the monomer (chlorostyrene) and blowing agent (trichlorofluoromethane) in a poly (vinyl fluoride) bag were irradiated with y-rays (105). 

Vinyl fluoride imdergoes free-radical polymerization.The first polymerization involved heating a saturated solution of VF in toluene at 67° C under 600 MPa for 16 hr. A wide variety of initiators and polymerization conditions have been explored. Examples of bulk and solution polymerizations exist however, aqueous suspension or emulsion method is generally preferred. Copolymers of VF and a wide variety of other monomers have been prepared. More recently, interpolymers of VF have been reported with tetrafluoroethylene and other highly fluorinated monomers, such as hexafluoropropylene, perfluorobuty-lethylene, and perfluoroethylvinylether. 

Bulk Polymerization of Vinyl Fluoride Benzoyl Peroxide Initiated. 338... 

As mentioned before, the monomer has a low boiling point ( - 72.2°C) and a relatively low critical temperature (54.7°C). For comparison, vinyl chloride has a boiling point of - 13.8°C and a critical temperature of 147°C (cf. this series, Vol. 11, 2nd ed., p. 358). Therefore the polymerization of vinyl fluoride is usually carried out under high-pressure conditions which probably resemble the polymerization of ethylene more than that of the other vinyl halides. The monomer is soluble in a variety of solvents. At room temperature, the homopolymer is insoluble. Therefore the neat subdivision of polymerization techniques into bulk, solution, suspension, and emulsion procedures which we have used in many other sections in this series becomes blurred. Most procedures seem to lead to blocks of polymer or some sort of dispersions from which... 

In one series of experiments on the polymerization of vinyl fluoride in bulk and in solution using tributylborane monoperoxide as the initiator, a difference between the two polymerization techniques was illustrated. In the bulk pol3mier-ization, the reaction order was 0.61 with respect to the initiator. In the solution polymerization, the reaction order with respect to the initiator was 1.24. The activation energy for the bulk polymerization of vinyl fluoride was found to be 10.1 kcal/mole [13]. 

With chemical initiators, examples of true bulk or solution polymerizations are rare. This may simply be a reflection of practical considerations. The monomer is a gas at ordinary temperatures and pressures, therefore work has to be carried out in some sort of pressure vessel. Bulk polymers generally are difficult to remove from reactors. They usually do not exhibit the optimum properties of the polymer. Poly(vinyl fluoride) is quite insoluble in most solvents at temperatures below approximately 100°C. It probably is also insoluble in its liquified monomer. Therefore, bulk polymerization processes would probably be strongly influenced by the precipitation of polymer from liquified monomer. A similar difficulty is found in attempts to prepare solution polymers. While the monomer may be soluble in many solvents, the polymer is not. As a result solution processes usually lead to precipitation or dispersion polymers, or some sort of swollen particles or gels. 

Procedure 2-1 is an example of a bulk polymerization of vinyl fluoride. It should be noted that the conversion is quite low. At 62°C benzoyl peroxide has a half-life of approximately 35 hr. Consequently heating the reaction mixture for 112 hr represents only a little over 3 half-life periods. From the literature [37] no estimate of the pressure inside the reactor could be made. Table II does indicate that in the presence of acetone or of aqueous acetone the conversion increased substantially. In fact, the procedure of the sixth experiment was found to be highly reproducible. Acetone was thought to enhance the solubility of the initiator in the monomer [37]. 

True bulk polymerizations of vinyl fluoride are rare since PVF is insoluble at room temperature in all common solvents as well as in its liquefied monomer. Thus, the bulk polymerization is greatly influenced by the precipitation of the polymer from the monomer. 

The first photopolymerization of VF was reported by Newkirk in 1946 [453]. By irradiation with UV light of a wavelength of 253.7 nm in a quartz capillary at 27 °C for 2 days, a yield of 36% polymer was obtained. Later [482], the photopolymerization of vinyl fluoride, in the presence of peroxide, was studied in bulk as well as in DMSO or in t-butanol solution (50% by volume of the total liquid monomer composition) within a temperature range of —20 to +30 °C. The monomer mixture was irradiated with a mercury UV lamp. It was found that high reaction rates could be obtained despite the fact that the polymer precipitated at an early stage. In DMSO, the precipitate was a gel that was partially transparent to light, and by continuous supply of monomer to the polymerization, a transparent bulk polymer was formed. 

Apart from the fluoro monomers vinyl fluoride (VF), vinylidene fluoride (VF2), and tetrafluoroethylene (TFE), only chlorofluoroethylene has found commercial use as homopolymer. It is applied as thermoplastic resin based on its vapor-barrier properties, superior thermal stability (Tdec > 350 °C), and resistance to strong oxidizing agents [601]. Chlorofluoroethylene is homo- and copolymerized by free-radical-initiated polymerization in bulk [602], suspension, or aqueous emulsion using organic and water-soluble initiators [603,604] or ionizing radiation [605], and in solution [606]. For bulk polymerization, trichloroacetyl peroxide [607] and other fluorochloro peroxides [608,609] have been used as initiators. Redox initiator systems are described for the aqueous suspension polymerization [603,604]. The emulsion polymerization needs fluorocarbon and chlorofluorocarbon emulsifiers [610]. 

The rate data in radiation-induced bulk polymerization of vinyl fluoride revealed a heterophase process.Polymerization was conducted aty-ray dosage rates of 13-100 rad/s using Co. The rate of polymerization at 3 8°C was proportional to the dosage rate to the power 0.42. Gas-phase polymerization of VF with y-rays has been studied in the range of 10-100 rad/s. Polymerization rate increased sharply with the increase in dosage, leading to generation of active sites in the polymer chain and branches. Radiation polymerization of vinyl fluoride dissolved in solvents such as tetrachloromethane lead to chain transfer and incorporation of solvent in the polymer. Vinyl fluoride can also be polymerized in plasma. 

A process for continuous polymerization of VF in aqueous medium has been described in the litera-A mixture of vinyl fluoride, water, and a water-soluble catalyst was stirred at 50-250°C and 15-100 MPa. A small amount of a monoolefin (Cj—C3) was continuously introduced into the reactor to inhibit the bulk polymerization of vinyl fluoride to low molecular weight polymers. The water-soluble catalyst generated free radieals, which initiated the polymerization. Catalysts ineluded ammonium persulfate, organie peroxides, and water-soluble azo initiators. In a two-stage eontinuous polymerization, the polymer partieles formed in the first stage aeted as nucleation sites for the second reaction zone. l... 

The formation of some structure units in head-to-head or tail-to-tail position is an unavoidable phenomenon of the radical polymerization of vinyl monomers. In the ease of poly(vinylidene fluoride) these chain defects are of particular importance because they affect the crystallization and thus the properties of the polymer [521]. In general, the percentage of monomer inversion in PVF2 appears to be a function of the temperature of polymerization The number of H H and T-T units increase from 3.5% at 20 °C to 6.0% at 140 °C. A polymer with a very low content of chain defects has been prepared by Butler et al. [579]. The authors carried out the polymerization in bulk at 0 °C using trichloroacetyl peroxide as the initiator and obtained high-molar-mass PVF2 with only 2.85% of reversed monomer units and low content of branches. 

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