VINYLIDENE FLUORIDE COPOLYMER AND PROCESS FOR PRODUCING THE SAME

Abstract: A vinylidene fluoride copolymer comprising as monomer units: (A) at least 50 mol% of vinylidene fluoride, and (B) at least 0.1 mol% of an organosilicon compound containing at least one group selected from the group con­ sisting of the acryloyloxy group, methacryloyloxy group and vinyloxy group, and at least one silicon-bonded vinyl group in the molecule, and a process for producing the same. The copolymer is useful for formation of a thin film or coating on various substrates.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a vinylidene fluoride copolymer and a process for producing the same. 2. Description of the Prior Art Since conventional vinylidene fluoride resins can be dissolved in a solvent with difficulty, they are not suited to formation of coating on various substrates. Therefore, it has been difficult to use their excellent properties such as weather resistance and chemical resistance as coating material. In EP-A-185 526 there is described a solvent soluble fluorine-containing polymer, which is (i) a copolymer consisting substantially of (a) a fluoroolefin, (b) vinyl ether, and (c) an organosilicon compound having an olefinically unsaturated bond and a hydrolysable group, (ii) said copolymer comprising, based on the total mole number of said (a)-(c) in the copolymer, 30-70 mol% of (a), 20-60 mol% of (b) and 1-25 mol% of (c), and (iii) said copolymer having a number average molecular weight (Mn) of 3000-200000 as measured by gel permeation chromatography, a fluorine containing coating composition as well as a process of coating the fluorine-containing coating composition. The present inventors have discovered that a copolymer of an organosilicon compound having an acryloyloxy, methacryloyloxy or vinyloxy group and a silicon-bonded vinyl group in the molecule and vinylidene fluoride provided by the present invention can dissolve the above prior art disadvantage. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a vinylidene fluoride copolymer which has not been known in the prior art. More specifically, the present invention provides a vinylidene fluoride copolymer comprising as monomer units: (A) at least 70 mol% of vinylidene fluoride, and (B) at least 0.1 mol% of an organosilicon compound which is represented by the formula (1) or (2) : CH₂=CH-O-R¹-Si(CH₃) 3-a R² a (2) wherein X represents a hydrogen atom or methyl group, R¹ represents a trimethylene group or a group represented by the formula: -CH₂CH₂-O-CH₂CH₂-, R² represents a group represented by the formula: -OSi(CH₃)₂CH=CH₂ , and a is an integer of 1, 2 or 3. The present invention also provides a process for producing a vinylidene fluoride copolymer, comprising the step of radical-copolymerizing a mixture of monomers containing: (A) at least 70 mol% of vinylidene fluoride, and (B) at least 0.1 mol% of an organosilicon compound which is represented by the formula (1) or (2) : CH₂=CH-O-R¹-Si(CH₃) 3-a R² a (2) wherein X represents a hydrogen atom or methyl group, R¹ represents a trimethylene group or a group represented by the formula: -CH₂CH₂-O-CH₂CH₂CH₂-, R² represents a group represented by the formula: -OSi(CH₃)₂CH=CH₂ , and a is an integer of 1, 2 or 3. Unlike the prior art vinylidene resins, the copolymer of the present invention can be dissolved in a fluorine-containing solvent such as trichlorotrifluoroethane and hydrocarbon solvents such as cyclohexane. Therefore, the copolymer can be used as a solution for formation of a thin film or coating having good weather resistance, chemical resistance .on various substrates. The copolymer has residual vinyl groups, which can be used in crosslinking reaction with silicone polymers. Hence, it is possible to modify the silicone polymers so as to enhance weather resistance and chemical resistance. It is also possible to form coating stably bound to silicone product substrates. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS (A) Vinylidene fluoride Vinylidene fluoride is one of monomers constituting the copolymer of the present invention. The copolymer contains, as monomer units, at least 70 mol %, preferably from 70 to 99.7 mol% of vinylidene fluoride. (B) Organosilicon compound The organosilicon compound of (B) is, for example, represented by the following formula (I) : wherein X represents a hydrogen atom or methyl group, R¹ represents a trimethylene group or a group represented by the formula: -CH₂CH₂-O-CH₂CH₂CH₂-, R² represents a group represented by the formula: -OSi(CH₃)₂CH=CH₂, and a is an integer of 1, 2 or 3. Specific examples of the organosilicon compound of the formula (I) may include, for example, 1-(3-methacryloyloxypropyl)-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane, 1-(3-acryloyloxypropyl)-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane, 1-[3-(2-methacryloyloxyethaoxy)propyl]-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane. Among these compounds, preferred is 1-(3-methacryloyloxypropyl)-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane. Another example of the organosilicon compound of (B) is represented by the general formula (II) : CH₂=CH-O-R¹-Si(CH₃) 3-a R²a (II) wherein R¹, R² and a are as defined above. Specific examples of the organosilicon compound of the general formula (II) may include, for example, 1-(3-vinyloxy)propyl-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane, 3-(3-vinyloxy)propyl-1,5-divinyl-1,1,3,5,5-pentamethyl-1,3,5-trisiloxane, 3-(3-vinyloxy)propyl-3-dimethylvinylsiloxy-1,5-divinyl-1,1,5,5-tetramethyl-1,3,5-trisiloxane, 1-[3-(2-vinyloxyethoxy)propyl]-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane. Among these compounds, preferred is 1-[3-vinyloxypropyl]-3-vinyl-1,1,3-tetramethyl-1,3-disiloxane. The copolymer of the present invention contains at least 0.1 mol%, preferably from 0.3 to 30 mol% of the organosilicon compound of (B). Other monomers Alternatively, the copolymer of the present invention may contain a monomer other than vinylidene fluoride of (A) and the organosilicon compound of (B), in addition to these monomers (A) and (B). The other monomer must be copolymerizable with vinylidene fluoride of (A) or the organosilicon compound of (B). Examples of such other monomers may include fluorine-containing monomers such as tetrafluorethylene, hexafluoropropylene, chlorotrifluoroethylene; α-olefinic monomers such as ethylene, propylene; acrylic monomers such as methyl methacrylate. These may be used either singly or in combination of two or more. The amount of these monomers in the copolymer is preferably not more than 49.9 mol%, and more preferably not more than 29.7 mol% based on all the monomer units. Other polymerization conditions In practicing the process mentioned above, copolymerization can be performed according to any polymerization system such as suspension polymerization, emulsion polymerization, solution polymerization, and mass polymerization. According to the process, a mixture of 70 mol % or more, preferably from 70 to 99.7 mol%, of vinylidene fluoride, 0.1 mol% or more, preferably from 0.3 to 30 mol%, of the organosilicon compound of (B), and optionally the other monomer as described above preferably in an amount of not more than 49.9 mol%, is subjected to polymerization. Where the copolymer is prepared by suspension polymerization, the radical polymerization initiator to be used may be those generally used. For example, there may be included organic peroxides such as diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, isobutyryl peroxide; fluorine-containing organic peroxides such as heptafluorobutyryl peroxide, trichloroperfluorohexanoyl peroxide; axo compounds such as azobisisobutyronitrile. As the polymerization solvent, water is generally employed, but a hydrophobic halogenated hydrocarbon solvent such as trichlorotrifluoroethane, 1,2-dichlorotetrafluoroethane may be also optionally used in combination as desired. Also, if necessary, a chain transfer agent such as acetone, isopropyl alcohol, and t-butyl alcohol; a pH buffering agent; a pH controller. may be also used as desired. As the suspending stabilizer, water-soluble polymer compounds such as methyl cellulose, and polyvinyl alcohol known in the art may be available. Where the copolymer is prepared by emulsion polymerization, as the water-soluble radical polymerization initiator to be used, those which have been used in the prior art may be employed, including, for example, persulfates such as potassium persulfate and ammonium persulfate. As the emulsifier, conventional fluorocarbon emulsifiers such as ammonium perfluorooctoate may be used. As for halogenated hydrocarbon solvents, chain transfer agents, pH buffering agents, pH controllers, the same are applicable as in the case of the above-mentioned suspension polymerization. Where the copolymer is prepared by solution polymerization, polymerization solvents to be used may include the halogenated hydrocarbon solvents as mentioned above, alcoholic solvents and ester solvents. Other components similar to those in the case of suspension polymerization are available. Polymerization temperature may be suitably selected depending on the polymerization system employed, and may be, for example, about 0 to 100°C. The pressure during polymerization may be suitably selected depending on the polymerization system, the ratio of monomers charged, the polymerization temperature, etc. Practically a pressure of about 1 to 100 atm is normally employed. The polymerization time may be also suitably selected depending on the polymerization system, the ratio of the monomers charged, the polymerization temperature, etc. and may be normally about 1 to 50 hours. In the process of the present invention, the respective components may be charged into a polymerization vessel by charging initially all the amounts of vinylidene fluoride and the organosilicon compound and optionally, other various components used as required, or alternatively by charging a part or all of either one or both of vinylidene fluoride and the organosilicon compound consecutively into a polymerizer continuously or continuously. The copolymer obtained by the process of the present invention generally has an intrinsic viscosity [η] as measured at 30°C in dimethylformamide as the solvent preferably of 0.05 dl/g or more, more preferably 0.10 dl/g or more. If the intrinsic viscosity is too small, the copoymer may be formed into a thin film with difficulty. Uses The copolymer obtained by the process of the present invention is generally soluble in fluorine-containing solvents such as trichlorotrifluoroethane and the like, hydrocarbon solvents such as cyclohexane, and dimethylformamide, and can be easily formed into a thin film or coated onto various substrates. In the copolymer obtained by the process of the present invention, the vinyl group bonded to silicon atoms in the organosilicon compound of the component (B) has low reactivity in radical copolymerization, and therefore more or less vinyl groups remain in the copolymer obtained. Accordingly, since other silicone polymers can be crosslinked with the residual vinyl groups, the copolymer obtained by the process of the present invention can be used for uses such as various paints, coating materials, rubber materials. EXAMPLES In the following, the process of the present invention is described in more detail by referring to Examples. Example 1 Into a stainless steel ampoule of 100 ml inner volume were charged 0.6 g of 1-(3-methacryloyloxypropyl)-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane 0.2 g of n-propylperoxydicarbonate, and 50 g of trichlorotrifluoroethane. After replacement with nitrogen, the ampoule was internally evacuated to vacuum. Next, 20 g of vinylidene fluoride was charged by pressurization and polymerization was carried out with shaking at 60°C for 15 hours. After completion of polymerization, unreacted vinylidene fluoride was purged, and the reaction mixture was taken out of the ampoule and dried. The yield of the copolymer is shown in Table 1. The copolymer obtained was found to be soluble in tetrahydrofuran at normal temperature, and could be formed into uniform films by casting. The intrinsic viscositiy [η] of the copolymer was measured in dimethylformamide as the solvent at 30°C. The result is shown in Table 1. Example 2 A copolymer (6.7 g) was obtained in the same manner as in Example 1 except for using 1-(3'-vinyloxy)propyl-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane in place of 3-vinyloxypropylvinyldimethylsilane. The intrinsic viscosity of the copolymer obtained was measured at 30°C using dimethylformamide as the solvent, to be 0.18.

Claims: A vinylidene fluoride copolymer comprising as monomer units: (A) at least 70 mol% of vinylidene fluoride, and (B) at least 0.1 mol% of an organosilicon compound which is represented by the formula (1) or (2): CH₂=CH-O-R¹-Si(CH₃) 3-a R² a (2) wherein X represents a hydrogen atom or methyl group, R¹ represents a trimethylene group or a group represented by the formula: -CH₂CH₂-O-CH₂CH₂-, R² represents a group represented by the formula: -OSi(CH₃)₂CH=CH₂ , and a is an integer of 1, 2 or 3. The vinylidene fluoride copolymer according to Claim 1 essentially consisting of from 70 to 99.7 mol% of vinylidene fluoride (A) and from 0.1 to 30 mol% of said organosilicon compound (B). A process for producing a vinylidene fluoride copolymer, comprising the step of radical-copolymerizing a mixture of monomers containing: (A) at least 70 mol% of vinylidene fluoride, and (B) at least 0.1 mol% of an organosilicon compound which is represented by the formula (1) or (2): CH₂=CH-O-R¹-Si(CH₃)₃ -a R² a (2) wherein X represents a hydrogen atom or methyl group, R¹ represents a trimethylene group or a group represented by the formula: -CH₂CH₂-O-CH₂CH₂CH₂-, R² represents a group represented by the formula: -OSi(CH₃)₂CH=CH₂ , and a is an integer of 1, 2 or 3. The process according to Claim 3, wherein the compound of the general formula (1) is 1-(3-methacryloyloxypropyl)-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane. The process according to Claim 3, wherein the compound of the general formula (2) is 1-(3-vinyloxypropyl)-3-vinyl-1,1,3,3-tetramethyl-1,3-disiloxane. The process according to Claim 3, wherein said mixture of monomers contains from 70 to 99.7 mol% of vinylidene fluoride (A). The process according to Claim 3, wherein said mixture of monomers contains from 0.1 to 30 mol% of said organosilicon compound (B). The process according to Claim 3, wherein said mixture of monomers further comprises other monomers copolymerizable with vinylidene fluoride (A) or the organosilicon compound (B). The process according to Claim 8, wherein said other monomer is selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, ethylene, propylene and methyl methacrylate.

Inventors: WATANABE, JUNICHI, YAMAMOTO, YASUSHI
Applicants: SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1990
Main classification: C08F214
IPC codes: C08F214