POLYMER HAVING A FLUORINE-CONTAINING END GROUP AND PRODUCTION OF THE SAME

Abstract: A polymer having a fluorine-containing end group which is produced by polymerizing a monomer capable of radical polymerization in the presence of a fluorine-containing thiol; a vinyl ester polymer having a fluorine-containing end group which is produced by polymerizing vinyl ester in the presence of a fluorine-containing thiol; and vinyl alcohol polymer hav­ ing a fluorine-containing end group which is produced by saponifying the said vinyl ester polymer; and processes for producing the same are provided. The polymers of this invention are superior in water repel­ lency, oil repellency, heat resistance, chemical resistance, and surface activity which are characteristic of fluorocarbon com­ pounds, and are expected to find use in various application areas.

Description: The present invention relates to partially saponified vinyl ester polymers having a fluorine-containing end group and to a process for producing said polymers. It is well known that fluorocarbons provide characteristic surfaces which are hard to get wet and to become dirty and are slippery, on account of the extremely low surface energy they have. They are also superior in heat resistance and chemical resistance. Because of these characteristic properties, fluorocarbons have recently come into use for surface finish, and the surface finish with fluorocarbons is finding use in many application areas. Fluorocarbon surfactants are superior in interfacial properties to hydrocarbon surfactants. They draw public attention because they produce a good effect even when used in small quantities. However, since fluorocarbon compounds are generally expensive, it is expected that they will find use more in the area where their characteristic surface properties are of importance, than in the area where their bulk properties are utilized. Typical examples of their use include the soil-resistant finishing that imparts water repellency and oil repellency to textiles and film. For example, Japanese Patent Laid-open No. 139679/1979 discloses a process for producing surface-treated polyvinyl alcohol film. According to this process, a dispersion or solution of fluoroplastic such as tetrafluoroethylene is applied, followed by drying, to the surface of polyvinyl alcohol film. The surface treatment of a material with a fluorocarbon compound, as in the above case, has a disadvantage that sufficient adhesion is not achieved between the substrate material and the fluorocarbon compound coated because the characteristic surface properties of the fluorocarbon compound interfere with adhesion, in other words, the superior surface properties of the fluorocarbon compound do not last for a long time of period. Thus there is a demand for a new technology that overcomes this disadvantage. One way of improving the durability is to chemically bond the fluorine-containing compound to the surface of a polymeric substrate through graft polymerization which is usually achieved by irradiation or electrical discharge. Graft polymerization by irradiation is not generally used because irradiation severely deteriorates the polymeric substrate. Graft polymerization by electrical discharge is in limited use as disclosed in Japanese Patent Laid-open No. 56671/1979 which claimes a fluorinated polymeric substrate having the surface layer formed by graft polymerization of a fluorine-containing unsaturated monomer by electrical discharge. US-A-3 758 447 discloses polymers containing perfluoroalkyl groups lowering the free surface energy of the polymer. The formation of the polymers involves free radical polymerization in the presence of the perfluoroalkyl mercaptans which function as chain transfer agents and are incorporated into the polymer chain. Graft polymerization by electrical discharge is achieved by any one of the following ways, which all require complex processes and operation. (1) The surface of the substrate is activated by electrical discharge and then exposed to a vapor of fluorine-containing monomer. (This is suitable for a fluorine-containing monomer of high vapor pressure.) (2) The surface of the substrate is activated by electrical discharge and then brought into contact with a solution of fluorine-containing monomer. (This is suitable for a fluorine-containing monomer of low vapor pressure.) (3) The surface of the substrate is activated by electrical discharge and exposed to oxygen or an oxygen-containing gas and finally brought into contact with a heated solution of fluorine-containing monomer. In addition, graft polymerization by electrical discharge does not form a uniform layer on a polymeric substrate having an intricate, irregular surface. In order to overcome the above-mentioned disadvantages, the present inventors carried out a series of researches on the process for modifying the plastics surface with a fluorocarbon compound. As the result, it was found that an improved surface is obtained by the aid of a polymer having a fluorine-containing end group which is produced by polymerizing monomers capable of radical polymerization in the presence of a fluorinated thiol. The present inventors also investigated the method for improving the surface of polyvinyl ester and polyvinyl alcohol obtained by hydrolyzing said polyvinyl ester. This investigation led to the following findings. When a vinyl ester such as vinyl acetate undergoes radical polymerization in the presence of a fluorine-containing thiol, there is obtained a polyvinyl ester such as polyvinyl acetate having a fluorine-containing end group. This polymer, upon saponification, provides polyvinyl alcohol having a fluorine-containing end group. These polymers thus obtained have the surface characteristic of fluorocarbon compound. The present invention is based on these findings. Accordingly, it is an object of this invention to provide partially saponified vinyl ester polymers having a fluorine-containing end group which are produced by polymerizing a vinyl ester in the presence of a fluorine-containing thiol and partially saponifying the above polymer. It is still further another object of this invention to provide a process for producing the aforesaid polymers. The polymers of this invention are superior in water repellency, oil repellency, heat resistance, chemical resistance, and surface activity which are characteristic of fluorocarbon compounds. The polymers having a fluorine-containing end group are represented by the formula R f -(X) m -S-P (m is 0 or 1), wherein R f is a fluorinated alkyl group represented by the formula (1) below or a fluorinated alkyl ether group represented by the formula (2) or (3) below. Formula (1) A(CF₂) q wherein q is 2 to 20, and A is hydrogen, fluorine, wherein q is 2 to 20. wherein t is 1 to 10. Examples of R f include H(CF₂)₂, H(CF₂)₄, H(CF₂)₆, H(CF₂)₈, F(CF₂)₂, F(CF₂)₃, F(CF₂)₄, F(CF₂)₅, F(CF₂)₆, F(CF₂)₇, F(CF₂)₈ F(CF₂)₉, F(CF₂)₁₀, X is an alkylene group of formula (4), an alkylene ether group of formula (5), an alkylene amide group of formula (6), an alkylene thioether of formula (7), an alkylene imine group of formula (8), and and alkylene ester group of formula (9) or (10) shown below. Formula (4) (CH₂) n (wherein n is 1 to 5.) Formula (5) (CH₂) p O(CH₂) n (wherein p is 1 to 5 and n is 1 to 5.) Formula (6) -CONH(CH₂) n (wherein n is 1 to 5.) Formula (7) -(S) r (CH₂) p -B(CH₂) n (wherein p is 1 to 5, n is 1 to 5, B is Sulfur or Oxygen, and r is 0 or 1 when B is Sulfur, and r is 1 when B is Oxygen.) (wherein p is 1 to 5, n is 1 to 5, and R₈ is a C₁₋₅ alkyl group.) Formula (9) (CH₂) p COO(CH₂) n (wherein p is 1 to 5, and n is 1 to 5.) Formula (10) -COO(CH₂) n ( wherein n is 1 to 5.) Typical examples of X include CH₂O(CH₂)₃, (CH₂)₂, (CH₂)₄, -S(CH₂)₂, (CH₂)₂S(CH₂)₃, -S(CH₂)₂O(CH₂)₂, -S(CH₂)₂S(CH₂)₂, -CONH(CH₂)₂, ( CH₂ )₂COO(CH₂)₃, and -COO(CH₂)₃. m is 0 or 1, S means sulphur, and P is a polymer unit containing the structural units Y and Z, wherein R₅ is hydrogen or a C₁₋₆ alkyl group, and R₆ is hydrogen or a C₁₋₁₉ alkyl group and the content of Y being 50 mol% to 99.1 mol% based on the total amount of Y and Z. Examples for the monomers yielding the structural unit Z, which can be saponified to the structural unit Y, are vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, Versatic acid vinyl ester ("VeoVa® 10", a product of Shell), vinyl laurate, vinyl stearate, and α-substituted compounds thereof. The polymer having a fluorine-containing end group covered in this invention is not restricted in the degree of polymerization and the molecular weight distribution. In view of the fact that the polymer of this invention has the fluorine-containing group only at the end of the molecule, the effect of introducing the fluorine-containing group lessens when the degree of polymerization is excessively high. Hence, the degree of polymerization should preferably be lower than 3500, and more preferably lower than 2000, with the lower limit being about 10, although not mandatory. Examples of the monomers yielding the structural unit Y include vinyl alcohol, α-methylvinyl aclohol, α-ethylvinyl alcohol, α-propylvinyl alcohol, α-butylvinyl alcohol, and α-hexylvinyl alcohol. The partially saponified vinyl ester polymers having a fluorine-containing end group are not restricted in the degree of polymerization, and the molecular weight distribution. In view of the fact that these polymers have the fluorine-containing group only at the end of the molecule, the effect of introducing the fluorine-containing group lessens when the degree of polymerization is excessively high. Hence, the degree of polymerization should preferably be lower than 3500, and more preferably lower than 2000, with the lower limit being about 10, although not mandatory. The vinyl alcohol polymer should preferably have the degree of saponification higher than 70 mol% from the standpoint of water solubility. A detailed description is given below of the process for producing the partially saponified vinyl ester polymers having a fluorine-containing end group. The feature of the process of this invention resides in the radical polymerization of vinyl ester monomers capable of radical polymerization which is performed in the presence of a fluorinated thiol represented by the formula R f -(X) m -SH (m is 0 or 1). A variety of fluorinated thiols represented by the formula R f -(X) m -SH (m is 0 or 1) can be used. (R f and X are defined as above.) Examples of fluorinated thiols represented by the formula R f -(X) m -SH wherein m is 1 include H(CF₂)₂CH₂O(CH₂)₃SH, H(CF₂)₄CH₂O(CH₂)₃SH, H(CF₂)₆CH₂O(CH₂)₃SH, H(CF₂)₈CH₂O(CH₂)₃SH, H(CF₂)₃CH₂O(CH₂)₃SH, F(CF₂)₅CH₂O(CH₂)₃SH, F(CF₂)₇CH₂O(CH₂)₃SH, F(CF₂)₉CH₂O(CH₂)₃SH, F(CF₂)₆CH₂CH₂SH, F(CF₂)₇CH₂CH₂SH, F(CF₂)₈CH₂CH₂SH, F(CF₂)₉CH₂CH₂SH, F(CF₂)₁₀CH₂CH₂SH, F(CF₂)₈(CH₂)₄SH, F(CF₂)₈SCH₂CH₂SH, F(CF₂)₁₀SCH₂CH₂SH, F(CF₂)₈CH₂CH₂S(CH₂)₃SH, F(CF₂)₈SCH₂CH₂OCH₂CH₂SH, F(CF₂)₈SCH₂CH₂SCH₂CH₂SH, F(CF₂)₃CONHCH₂CH₂SH, F(CF₂)₇CONHCH₂CH₂SH, F(CF₂)₉CONHCH₂CH₂SH, and Examples of fluorinated thiols represented by the formula R f -(X) m -SH wherein m is 0 include C₂F₅SH, C₄F₉SH, and The selection of the proper thiol should be made according to the desired surface properties which are obtained when the polymer of this invention is formed into film or fiber. For example, in the case where lowering the surface energy is an objective, R f in the formula R f -(X) m -SH (m is 0 or 1) is preferably F(CF₂) q rather than H(CF₂) q , wherein q is preferably greater than 2, with the maximum being about 20, although not mandatory. According to the process of this invention, there are no restrictions in the quantity and method of addition of the fluorinated thiol (represented by the formula R f -(X) m -SH (m is 0 or 1)) to the polymerization system for the polymerization of a vinyl ester in the presence of the fluorinated thiol. In the polymerization system, the fluorinated thiol functions as a chain transfer agent. The quantity and method of addition of it to the polymerization system affects the degree of polymerization and the molecular weight distribution. The quantity and method of addition are properly selected according to the desired physical properties of the polymer; but they are not essential problems. According to the process of this invention, the polymerization can be carried out by known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. The solution polymerization that employs methanol or toluene is industrially preferable. In addition, the polymerization can be performed batchwise, semibatchwise, or continuously. The process for polymerization employs a generally known radical polymerization initiator such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), benzoyl peroxide, diisopropylperoxy dicarbonate, and potassium persulfate. The polymerization temperature is 10 to 90°C depending on the initiator employed. The vinyl ester that can be used in this invention includes vinyl acetate, vinyl formate, vinyl propionate, Versatic acid vinyl ester (VeoVa 10, a product of Shell), vinyl laurate, and vinyl stearate. For the production of vinyl alcohol polymer by saponification after polymerization, it is preferable to use vinyl acetate as the principal monomer. In the polymerization process, the above-mentioned vinyl ester can be copolymerized with the above-mentioned comonomers. The vinyl ester polymer having a fluorine-containg end group can be saponified by the known method to give vinyl alcohol polymer. The known method includes alkali saponification and acid saponification. Saponification with NaOH or CH₃ONa in methanol is industrially preferable. The saponification temperature is not specifically limited; but it is preferably 20 to 60°C from the stand-point of preventing the discoloration of the resulting vinyl alcohol polymer. NaOH or CH₃ONa is used in an amount of 0.001 to 0.2 mol per 1 mol of vinyl ester unit, so that the discoloration of vinyl alcohol polymer is prevented and the quantity of sodium acetate in the polymer can be reduced. In the case where the polymer contains acidic comonomer units which consume alkali, the quantity of NaOH or CH₃ONa should be increased accordingly. The polymer having a fluorine-containing end group obtained in this invention has the same bulk properties as the ordinary polymer. However, a cast film formed from a solution of the polymer exhibits greater water repellency and oil repellency than the ordinary polymer. When a fluorinated alkyl chain is introduced into the terminal of water-soluble polymer polyvinyl alcohol, its aqueous solution exhibits great surface activity. The polymer having a fluorine-containing end group obtained in this invention exhibits the characteristic properties of surface chemistry. In addition, the water-soluble polymer polyvinyl alcohol incorporated with a fluorine-containing end group can be used as a new fluorocarbon surfactant. The partially saponified vinyl ester polymer having a fluorine-containing end group has the same bulk properties as the ordinary partially saponified vinyl ester polymer. However, a cast film formed from a solution in an organic solvent such as methanol, acetone, and toluene exhibits greater water repellency and oil repellency than the ordinary vinyl ester polymer. This phenomenon is pronounced in the case of vinyl alcohol polymer. A cast film formed from an aqueous solution of ordinary polyvinyl alcohol has no oil repellency. Being naturally water-soluble, polyvinyl alcohol is poor in water repellency. Contrary to this, a cast film obtained from an aqueous solution of the vinyl alcohol polymer having a fluorine containing end group of this invention exhibits both great water repellency and oil repellency. This is attributable to the fact that the chains containing fluorine atoms migrate to the film surface, forming thereon a thin layer rich with the fluorine-containing group, at the time of film forming. A similar phenomenon is observed in the case of polyvinyl alcohol having hydrocarbon chains in place of fluorine-containing groups; but oil repellency is very low (although a little higher than the ordinary polyvinyl alcohol). These results reflect the generally known difference between the fluorinated alkyl chain and the hydrocarbon chain. Because of the above-mentioned characteristic propertis or surface chemistry, the vinyl ester polymer and vinyl alcohol polymer, both having a fluorine-containing end group, of this invention are very useful in various application areas. The vinyl ester polymer can be used as a surface modifier of various resins because of its good compatibility and miscibility with various resins. The vinyl alcohol polymer can be applied to the surface treatment of paper, film, sheet, and textile. It exhibits both water repellency and oil repellency. The polymer can be used as vinylon yarn having a low coefficient of friction. Such vinylon yarn requires no or only a little oiling. The aqueous solution of the vinyl alcohol polymer of this invention exhibits an extremely low surface tension, and it can be used as a new fluorocarbon surfactant. The invention is now described in more detail with reference to the following examples, in which quantities are expressed as parts by weight unless otherwise noted. (a) Example of synthesis of fluorinated thiol: The fluorinated thiol was synthesized from a fluoro-alcohol represented by the formula R f (CH₂) n OH through the reactions shown below. (wherein R f denotes H(CF₂) q or F(CF₂) q , q is an integer of 2 to 20, and n is 1 or 2.) A detailed description is given below of the synthesis of a fluorinated thiol from H(CF₂)₄CH₂OH. 50 g of H(CF₂)₄CH₂OH was dissolved in 100 ml of dimethyl sulfoxide (DMSO). 22.4 g of sodium hydroxide was added with stirring, and then 33 g of allyl chloride was added slowly at room temperature over 2 hours. Stirring was continued for 5 hours. After filtration of precipitates, the solution was heated on a water bath to remove unreacted allyl chloride. The solution was poured into a large amount of water to separate H(CF₂)₄CH₂OCH₂-CH=CH₂. A small quantity of BPO of the order of mg was added to H(CF₂)₄CH₂OCH₂-CH=CH₂, and then thiolacetic acid was added with stirring at room temperature over 2 hours. Unreacted thiolacetic acid was removed under reduced pressure. 100 cc of methanol and 10 g of sodium hydroxide were added, and reaction was carried out at 60°C for 3 hours. After cooling to room temperature, the reaction product was poured into a large amount of water to give crude H(CF₂)₄CH₂OCH₂CH₂CH₂SH. Upon distillation, there was obtained a purified product having bp. 57°C/3 mmHg. The structure of this compound was confirmed by ¹H-NMR. (b) Production of vinyl ester polymer and vinyl alcohol polymer, each having a fluorine-containing end group: EXAMPLE 1 Into a reactor were charged 960 parts of vinyl acetate (abbreviated as VAc hereinafter), 220 parts of methanol, and 0.086 parts of fluorinated thiol H(CF₂)₈CH₂OCH₂CH₂CH₂SH. The atmosphere of the reactor was replaced with nitrogen. The reactor was heated, and when the internal temperature reached 60°C, 20 parts of methanol containing 0.174 parts of 2,2'-azobisisobutyronitrile was added. Immediately, 60 parts of methanol containing 0.79 parts of fluorinated thiol H(CF₂)₈CH₂OCH₂CH₂CH₂SH was added evenly over 3 hours. Conversion to polymer after 3 hours was 37.6%. After cooling, unreacted VAc was removed together with methanol under reduced pressure by replenishing methanol. Thus there was obtained a methanol solution (42.3%) of vinyl acetate polymer having a fluorine-containing end group. To a portion of this solution a methanol solution of NaOH was added to a molar ratio of NaOH to VAc of 0.02. Upon saponification at 40°C, there was obtained polyvinyl alcohol (PVA) having a fluorine-containing end group. The degree of saponification was 99.0%. The degree of polymerization of the polymer was 1320. (measured for polyvinyl acetate obtained by re-acetifying the polyvinyl alcohol with an acetic anhydride-pyridine mixture.) (The degree of polymerization (P) was calculated according to Nakajima's formula [η] = 7.94 x 10⁻³ x P 0.62 , wherein [η] was measured in acetone at 30°C. According to elemental analysis, the content of fluorine in the PVA was 0.26 wt%. EXAMPLES 2 to 8 Polyvinyl acetate and polyvinyl alcohol (PVA), each having a fluorine-containing end group, were prepared in the same way as in Example 1, except that the fluorinated thiol was changed. Table 1 shows the recipes, the results of polymerization, and the degree of polymerization of the resulting polymers. EXAMPLE 8 Into a reactor were charged 768 parts of vinyl acetate, 192 parts of VeoVa 10 (a product of Shell), 220 parts of methanol, and 0.52 parts of fluorinated thiol F(CF₂)₉CH₂OCH₂CH₂CH₂SH. The atmosphere of the reactor was replaced with nitrogen. The reactor was heated, and when the internal temperature of the reactor reached 60°C, 20 parts of methanol containing 0.174 parts of 2,2'-azobisisobutyronitrile were added to start polymerization. The rate of polymerization after 3 hours was 39.2%. After cooling, the reaction product was poured into n-hexane to separate the polymer. The polymer was purified by reprecipitation twice with acetone-n-hexane. The degree of polymerization (P) was 1950. It was calculated according to Nakajima's formula [η] = 7.94 x 10⁻³ x P 0.62 , wherein [η] was measured in acetone at 30°C. CONTROLS 1 to 3 Vinyl acetate and polyvinyl alcohol were prepared in the same way as in Example 1, except that the fluorinated thiol was replaced by 1-dodecane thiol (n-C₁₂H₂₅SH). Table 2 shows the recipes, the results of polymerization, and the degree of polymerization of the resulting polymers. The effect of the terminal fluorinated group was investigated by using the vinyl ester polymer and vinyl alcohol polymer obtained in Examples 7 to 14 in comparison with the vinyl ester polymer and vinyl alcohol polymer having a termianl alkyl chain as obtained in Controls 7 to 9. The test items and test methods are given below, and the results are shown in Table 3. (1) Surface tension of aqueous solution: 0.2% aqueous solution of polyvinyl alcohol was prepared, and the surface tension of the solution was measured at 20°C. (2) Water repellency of film surface: 0.2 mm thick film was prepared by casting 3% aqueous solution of the polyvinyl alcohol onto a PET film and air-drying at room temperature. The film was heat-treated at 160°C for 10 minutes. A water drop was placed on the film surface (opposite to PET film) and the contact angle was measured. (3) Oil repellency of film surface: 0.2 mm thick film was prepared by casting 3% methanol solution of the vinyl ester polymer onto a PET film and air-drying at room temperature. The film was heat-treated at 80°C for 1 hour. A drop of n-octane was placed on the surface (opposite to PET film) of the cast film of polyvinyl alcohol (as obtained in (2) above) and the surface (opposite to PET film) of the cast film of vinyl ester polymer. "Wetting" of the film surface was rated as follows. 1 n-Octane remains as a drop on the film surface. 2 The film surface partly gets wet with n-octane. 3 The film surface completely gets wet with n-octane. The cast film of the vinyl ester polymer having a fluorine-containing end group as obtained in this invention was heat bonded to the cast film of the ordinary polyvinyl ester at 120°C under a load of 20 kg/cm² for 1 minute, with the PET side of the former being the adherend surface. Complete adhesion was obtained, and the surface of the former film exhibited oil repellency of the same degree as mentioned above.

Claims: Polymers of the general formula R f -(X) m -S-P, wherein R f is a fluorinated alkyl group represented by the formula (1) or a fluorinated alkyl ether group represented by the formula (2) or (3), Formula (1) A(CF₂) q (wherein q is 2 to 20, and A is hydrogen, fluorine, (wherein q is 2 to 20 ) (wherein t is 1 to 10 ) X is an alkylene group of formula (4), an alkylene ether group of formula (5), an alkylene amide group of formula (6), an alkylene thioether of formula (7), an alkylene imine group of formula (8), and an alkylene ester group of formula (9) or (10), Formula (4) (CH₂) n (wherein n is 1 to 5 ) Formula (5) (CH₂)pO(CH₂) n (wherein p is 1 to 5 and n is 1 to 5 ) Formula (6) -CONH(CH₂) n (wherein n is 1 to 5 ) Formula (7) -(S) r (CH₂) p -B(CH₂) n (wherein p is 1 to 5, n is 1 to 5, B is Sulfur or Oxygen, and r is 0 or 1 when B is Sulfur, and r is 1 when B is Oxygen ) (wherein p is 1 to 5, n is 1 to 5, and R₈ is a C₁₋₅ alkyl group ) Formula (9) (CH₂) p COO(CH₂) n (wherein p is 1 to 5, and n is 1 to 5 ) Formula (10) -COO(CH₂) n ( wherein n is 1 to 5 ) m is 0 or 1, S means sulphur, and P is a polymer unit containing the structural units Y and Z, wherein R₅ is hydrogen or a C₁₋₆ alkyl group, and R₆ is hydrogen or a C₁₋₁₉ alkyl group and the content of Y being 50 mol% to 99.1 mol% based on the total amount of Y and Z. Polymers according to claim 1 having a degree of polymerization lower than 3,500. Process for producing polymers according to claim 1 or 2 which comprises performing the radical polymerization of monomer composed mainly of vinyl ester in the presence of a fluorinated thiol represented by the formula R f -(X) m -SH, wherein R f , X and m have the meaning as described in claim 1, and subsequently saponifying the resulting polymer. The use of the vinyl ester polymer according to claim 1 or 2 as a surface modifier. The use of the vinyl alcohol polymer according to claim 1 or 2 for the surface treatment of paper, films, sheets and textiles and for preparing vinylon yarn.

Inventors: OKAYA, TAKUJI, SATO, TOSHIAKI, YAMAUCHI, JUNNOSUKE
Applicants: KURARAY CO., LTD.
Application year: 1984
Main classification: C08F2
IPC codes: C08F8, C08F2