Vinylidene fluoride suspension polymerization

The most common methods of producing homopolymers and copolymers of vinylidene fluoride are emulsion and suspension polymerizations, although other methods are also used.55... 

Polymerization of vinylidene fluoride by emulsion or suspension polymerization in water is conducted at conditions of 10-130 °C and 10-200 bar. In the emulsion polymerization, either water-soluble peroxides or monomer-soluble peroxy or organic peroxides are used as initiators [ 17]. Fluorinated surfactants, such as ammonium perfluorooctanoate, are used as dispersing agents. Chain transfer agents, such as acetone, chloroform, or trichlorofluoromethane, may be... 

Commercial process for the production of PCTFE is essentially polymerization initiated by free radicals at moderate temperatures and pressures in an aqueous system at low temperatures and moderate pressures. It is reported that it is possible to polymerize CTEE in bulk, solution, suspension, and emulsion. According to some reports the emulsion system produces the most stable polymer [65]. The tendency of PCTFE to become brittle during use can be reduced by incorporating a small amount (less than 5%) of vinylidene fluoride (VDF) during the polymerization process [67]. 

PVDF is correctly named poly(l,l-difluoroethylene) and represented by (-CF2CH2-)n- It is a hard, tough thermoplastic fluoropolymer. PVDF is prepared by free-radical initiated polymerization, either in suspension or (usually) in emulsion systems. The basic raw material for PVDF is vinylidene fluoride (CH2=CF2), a preferred synthesis of which is dehydrochlorination of chlorodifluoroethane. 

Vinylidene fluoride, CH2=CF2, is obtained by the pyrolysis of 1,1-difluoro- 1-chloroethane, which in turn is produced from acetylene, vinylidene chloride, or 1,1,1-trichloroethane by reaction with hydrogen fluoride. Because of its low boiling temperature, —84°C, vinylidene fluoride is suspension or emulsion polymerized under pressure. Considerable head-head linkage quantities are produced in these polymerizations. 

Vinylidene fluoride (b.p. — 84°C) is free-radically polymerized in suspension or emulsion at 10-300 bar and 10-150°C. Suspension-polymerized material contains less branching and consequently a narrower molecular-weight distribution than the emulsion-polymerized material. For this reason, the suspension-polymerized material has higher crystallinity, greater mechanical strength, and better chemical stability. Materials from both polymerization methods contain a considerable proportion of head-to-head linkages. 

Obtained by the polymerization of vinylidene fluoride by two methods (a) Suspension polymerization producing S-PVDF (Typell PVDF)- Solef is of this type and is more crystalline with fewer structural defects (b) Emulsion polymerization producing E-PVDF (Type I PVDF) PVDF can be co-polymerized... 

Recently, also the synthesis of VF2 from 1,1-difluorethane on contact with Cr203/ AI2O3 based catalysts in the presence of oxygen has been reported [527]. Vinylidene fluoride is usually stored and shipped without polymerization inhibitors. If desired, terpenes or quinones can be added to inhibit polymerization. Before use the monomer has to be distilled and degassed several times to remove impurities [528]. Since vinylidene fluoride is a gas under normal conditions, most of the polymerization processes are carried out under pressure. The advantage of poly(vinylidene fluoride) is its good solubility in solvents such as dimethylacetamide (DMA), dimethylformamide (DMF), or dimethyl sulfoxide (DMSO). This fact allows its commercial processing without any problems. Industrially, polymerization is usually accomplished in suspension or emulsion as described in several patents [529-533]. Vinylidene fluoride can also be polymerized with... 

Water is commonly used as the polymerization medium, with peroxy compounds serving as the initiators for both suspension and emulsion polymerizations. In most cases reaction temperature is between 10 and 150 °C and pressure between 10 and 300 atm [541]. In the polymerization of vinylidene fluoride, proper selection of the radical initiator, the emulsifier, and the reaction medium is important. 

The radiation-initiated polymerization of vinylidene fiuoride is used on a laboratory scale only. The effect of polymerization conditions on the chain defects, content, and changes in the crystalline phases have been studied [528,536,537,544]. Doll and Lando [544] used a °Co source with an average dose rate of 0.33 Mrad/h. The polymerization was carried out between 0 and 400 °C at a pressure equal to the vapor pressure of the solvent-vinylidene fluoride mixture. Esters and ketones (acetone, methyl ethyl ketone, ethyl acetate, acetophenone), DMF, DMSO, and y-butyrolactone were used as solvents. All these solvents are good chain-transfer agents for vinylidene fluoride. The molding characteristics of the resulting polymers were very poor and the intrinsic viscosity of the sample polymerized in acetone solution was low (0.183 dL/g) compared to that of a suspension-polymerized polymer (1.68 dL/g) [544]. 

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]. 

Oils and waxes with excellent chemical inertness are obtained from low-molar-mass poly(chlorotrifluoroethylene). They are prepared by polymerization of the monomer in the presence of suitable chain transfer agents [601]. Furthermore, chlorotrifluoroethylene has been copolymerized with vinylidene fluoride to elastomeric polymers by suspension and emulsion polymerization [601,611]. 

Other fluoroearbon polymers result from the eopolymerization of vinylidene fluoride with fluorine-eontaining aerylates [e.g., F2C=CH—COOR, F2C=CF—COOCH3, F2C=C(CF3)—COF] and are mentioned mainly in the patent literature [615]. An interesting thermoplastie fluoropolymer from Allied Chemical Corp., called CM-1, is reported [616]. This eopolymer from hexafluoroisobutylene and vinylidene fluoride can be radically polymerized in suspension or emulsion at a pressure of 10 to 20 bar and a temperature of 20 °C. The properties of the eopolymer are comparable or even better than those of poly (tetrafluoroethylene). 

Poly(vinylidene fluoride), PVDF or PVF2, is usually manufactured from radical initiated batch polymerization process in aqueous emulsion or suspension of CH2=CF2 monomer. PVDF is a thermoplastic that exhibits interesting properties, such as piezoelectric, pyroelectrical, and ferroelectric behaviors. PVDF has even superior dielectric permittivity arising from the strong polymerization originating from C—F bonds, and the spontaneous orientation of dipoles in the crystalline phases makes it a polar polymer with good compatibility with polar chemicals. 

The first successful aqueous polymerization of vi-nylidene fluoride was reported in 1948 [83] using a peroxide initiator in water at 50-150°C and 30 MPa. No surfactants or suspending agents were present in the polymerization recipe. PVDF has been polymerized by a number of methods including emulsion, suspension, solution, and bulk. Later, copolymers of vinylidene fluoride with ethylene and halogenated ethylene monomers were also produced [84]. In 1960, a manufacturing process was developed and PVDF was introduced to the market. 

Reaction temperature ranges between 10 and 150°C at pressure of 1 MPa or higher. Similar to TFE, emulsion polymerization of vinylidene fluoride requires a stable fluorinated surfactant and an initiator such as peroxide or persulfate. Suspension polymerization is conducted in an aqueous medium, sometimes in the presence of a colloidal dispersant like hydroxy cellulose. Solution polymerization of VDF in solvents uses free radical initiators. PVDF is commercially produced by aqueous emulsion or suspension processes [72]. 

Vinylidene fluoride (VDF) can be polymerized by a variety of methods such as suspension, dispersion, and solution polymerization. It can be copolymerized with a number of fluorinated and non-fluorinated comonomers. Examples of these two groups include perfluoroolefin monomers and acrylic compounds. VDF polymers and copolymers are fabricated by melt processing as well as coating techniques. 

The main objective of batch suspension polymerization of vinylidene fluoride is to limit the formation of polymer scale on the walls of the reactor, A... 

Table 5.45. Results for Suspension Polymerization of Vinylidene Fluoride using Different Initiators ...

Several patents, including some recent cases, have described modifications of the suspension polymerization process of vinylidene fluoride.f lf fif ll l Saito, et al.,[ ] reported a process in which vinylidene fluoride and another vinyl monomer have been copolymerized to produce a polymer with excellent water repel-lency and release properties (as a film). 

---