Method of preparing water soluble silated polyvinyl alcohol

Abstract: A silated polyvinyl alcohol with a degree of substitution (D.S.) between 0.005 and 0.5 is prepared by reacting polyvinyl alcohol with a silating agent. Preferred silating agents are 3-glycidoxypropyltrimethoxysilane or vinyltrimethoxysilane. An alkali metal or ammonium salt of the silated polyvinyl alcohol can self-crosslink in the presence of atmospheric carbon dioxide to form a water resistant film which is soluble in caustic.

Description: Field of Invention : The invention relates to a method for preparing chemically modified, in alkaline water solution soluble polymers. In particular the invention relates to a method for preparing a class of silated polyvinyl alcohols with useful properties. Background of the Invention : U.S. Patents 4,097,436 and 4,219,591 describe a saponified vinyl acetate-vinyl alkoxysilane polymer produced by contacting a solution of vinyl acetate-vinyl alkoxysilane copolymer with an alcoholic solution of an alkali metal hydroxide and recovering a precipitated product. Further described is a process for contacting an acidified solution of a vinyl acetate-vinyl alkoxysilane copolymer with a substrate to form a water insoluble film. U.S. Patent 4,425,403 describes a lens coating composition prepared by reacting an acid hydrolyzed silane coupling agent with an aqueous solution of polyvinyl alcohol (91 to 94% saponification) and silica gel. U.S. Patent 3,959,242 describes a silane grafted polyvinyl alcohol polymer prepared by stepwise reaction of polyvinyl alcohol (87-89% saponified) with a silane coupling agent in the presence of an acid catalyst. These graft polymers are suitable for a mold release surface for preparing cast articles. U.S. Patent 4,489,117 discloses a magnetic tape abrasion coating produced by coating a melt extruded polyethylene terephthalate film with an aqueous solution of a water soluble polymer such as polyvinyl alcohol and a silane coupling agent and heat stretching the film. A water soluble polymer with a molecular weight of 100,000 to 1,000,000 is preferred along with a dimethoxysilane or trimethoxysilane. Silane coupling agents were disclosed in U.S. Patent 4,480,072 as a useful means to crosslink between organic and inorganic materials. A common feature of this and other references is crosslinking organic polyvinyl alcohol polymers and copolymers with an inorganic silane coupling agent without forming a new composition of matter containing nonhydrolyzable covalent bonds. Yet in spite of what was known in the art, it remained for the present invention to introduce a new class of water soluble silated polyvinyl alcohols and alkali salts useful for preparing water resistant films. EP-A-305 833 discloses poly(vinyl alcohol) polymers with organo-linked pendant silanes having reactable alkoxy and/or hydroxy groups. Due to the reaction conditions it is likely that it is more a mixture of the reactants than a reaction product. Summary of the Invention : A new method for the preparation of an in alkaline water solution soluble silated polyvinyl alcohol is disclosed which has nonhydrolyzable covalent bonds useful in the form of a film or powder for industrial, pharmaceutical, medical and cosmetic applications. The water soluble polymer obtainable by the method comprises an organosilyl modified polyvinyl alcohol homopolymer or copolymer having a silyl substituent covalently bonded to the polymer or copolymer wherein the number of silyl species per monomeric unit ranges from 0.005 to 0.5. Particularly useful for film forming applications is the preparation of an anionic polymer salt, especially the salt of an alkali metal or ammonium ion, comprising a silated polyvinyl alcohol homopolymer or copolymer wherein an organosilyl species is covalently bonded through an organofunctional group such as ester, ether or carbamyl linkage and the degree of silyl substitution of the polymer or copolymer is between 0.005 and 0.2. In particular, an alkali metal or ammonium salt cast or coated from an aqueous solution can self-crosslink in the presence of atmospheric carbon dioxide to form a water resistant film which is soluble in caustic. In a preferred embodiment of the present invention the polymer used in the method is a copolymer of vinyl alcohol and vinyl acetate. The polymer as used in the present invention may be substituted with hydroxyethyl. A method of preparing an in alkaline water solution soluble silated polyvinyl alcohol polymer comprises the steps: (1) optionally preparing and/or employing in step (2) a polyvinyl alcohol homopolymer or copolymer with a degree of hydrolysis between 90 and 100%; (2) reacting the homopolymer or copolymer as a slurry in an alkaline environment at a temperature above 50°C in the presence of a silating agent according to claim 1; and (3) recovering a silated polyvinyl alcohol homopolymer or copolymer with a degree of silyl substitution between 0.005 and 0.5. A silated polymer obtained by the method may comprise a copolymer of vinyl alcohol and vinyl acetate reacted with 3-glycidoxypropyltrimethoxysilane (GPTMS), isocyanatopropyltrimethoxysilane or vinyltrimethoxysilane (VTMS). Preferably the method as described above is carried out wherein in step (2) a Lewis acid catalyst such as dibutyltin dilaurate is present. The water soluble silated polyvinyl alcohol polymer produced by the method as described above has preferably a degree of substitution between 0.005 and 0.2. Detailed Description of the Invention : Polyvinyl alcohols are synthetic polymers which can be modified and substituted to vary chemical and physical properties. Modification can be accomplished through the hydroxyl groups on the polyvinyl chain. Similarly, it was known that silane coupling agents could react with these hydroxyl groups such that the polymer could be crosslinked. Now a new method for preparing water soluble silated polyvinyl alcohols has been discovered to further expand on previously known modifications and substitutions. It was surprising to find that reactions and methods not found in the prior art gave useful compositions of matter when hydrolyzed polyvinyl alcohol (PVA) was directly modified with organosilanes to a particular degree of substitution. Organosilanes for the practice of the invention have the following general structure: where, Y = A hydrocarbyl spacer group (composed of at least one methylene group) between X and the silicon atom. R₁, R₂ and R₃ are groups attached to the silicon. These groups could be either hydrocarbyl or hydrolyzable such as halogen, alkoxy, aryloxy, acyloxy, siloxy or amine. They could also constitute a combination of hydrocarbyl and hydrolyzable groups just mentioned. However, at least one of them must be hydrolyzable. X = a functional group capable of reacting with the hydroxyl function of the polymer. The following X groups could be used to incorporate the silyl substituent into the polymer. i) Cl,Br,I (halide) ii) -N=C=O (isocyanate) iii) iv) v) vi) vii) where Z = Cl,Br,I. viii) ix) It has been found that polyvinyl alcohol reacts with 3-glycidoxypropyltrimethoxysilane (GPTMS) in the presence of NaOH to form the following silated PVA (SIL-PVA): The SIL-PVA was soluble in hot water at 60 - 97°C depending on the molecular weight of the PVA used. These materials are soluble in alkaline solution (pH ∼ 10-12). Under acidic environment, these polymers are insoluble. However, addition of an acid to a dilute solution(1-3 wt %) of SIL-PVA does not lead to solution viscosity enhancement or precipitation of the polymer. One of the interesting properties of SIL-PVA is its ability to undergo self-crosslinking when its aqueous solutions are air dried. The films formed by air drying the SIL-PVA are water- and acid-resistant but alkali-soluble. Besides self-crosslinking, SIL-PVA can also crosslink other water-soluble polymers, such as hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), carboxymethylcellulose (CMC), carsboxymethylhydroxyethylcellulose (CMHEC), polyvinyl alcohol (PVA) and polyethyloxazoline. Since SIL-PVA is anionic, it crosslinks with polyvalent metal ions, such as Ti⁺⁴ to form viscoelastic gels. Solution-cast SIL-PVA films are clear and flexible. They are water-resistant despite their ability to imbibe a significant amount of water. These hydrated films are transparent, elastic and tacky. Although insoluble in water and acids, they dissolve in alkali. SIL-PVA exhibits good adhesive strength to various cellulosic materials and substrates containing surface hydroxyls. Unlike the prior art, the degree of hydrolysis of PVA is critical to form the SIL-PVA of the invention. Only 100% hydrolyzed PVA, i.e. PVA containing no residual acetate groups reacts with GPTMS under alkaline environment to yield a completely soluble SIL-PVA. PVA's having about 94-98% degree of hydrolysis react with GPTMS to form water-soluble SIL-PVA containing some insolubles. The higher the degree of PVA hydrolysis the lower the amount of insolubles. The following examples illustrate the practice of the invention. Example 1 Preparation of SIL-PVA by the Reaction of PVA With GPTMS To a one-liter resin kettle reactor equipped with a reflux condenser and an overhead stirrer and containing hexane (300 g) and caustic solution (4 g of NaOH dissolved in 30 g of water) was added PVA powder (50 g "as is") (Aldrich; 100% hydrolyzed; molecular weight ∼14,000). The resulting mixture was vigorously mixed for 30 minutes at room temperature in a nitrogen atmosphere. Then GPTMS (5 g) was added to the PVA slurry and the resulting reaction mixture was heated at 69°C for 5 h. The reaction mixture was cooled to room temperature, treated with glacial acetic acid (2 g) and filtered. The residue was washed twice with acetone/water (80:20 w/w) mixture. After dehydration with acetone, the polymer was dried in a fluid bed drier at 50°C for 30 minutes. Properties The SIL-PVA was soluble in hot water (95-97°C). The pH of a 1% (w/w) solution was 12.7. A solution-cast film was insoluble in boiling water. Analytical Moisture - 7.15% Ash (Na₂SO₄) - 11.85% Silicon - 0.92% Example 2 Preparation of SIL-PVA in t-Butyl Alcohol Example 1 was repeated using the following reagents in a stainless steel sealed reactor. (1) t -Butyl alcohol - 600 g (2) Sodium hydroxide - 8 g (3) Water - 60 g (4) Polyvinyl alcohol (Aldrich - 100 g ("as is") (100% hydrolyzed; mol. wt. ∼14,000) (5) GPTMS - 15 g (6) Glacial acetic acid - 4 g Properties The SIL-PVA was insoluble in hot water at 90°C. The pH of a 1% (w/w) slurry was 11.7. After adjusting the pH to 12.2 with NaOH solution and heating the SIL-PVA slurry at 98°C for several hours, the polymer completely dissolved. A solution-cast film was insoluble in hot water. Analytical Moisture -2.56% Ash (Na₂SO₄) - 12.24% Silicon - 1.08% Example 3 Preparation of SIL-PVA in t-Butyl Alcohol Example 2 was repeated using 9.5 g of GPTMS. Properties The SIL-PVA was soluble in hot water (90°C). A solution-cast film was hot water insoluble. Analytical Moisture - 4.86% Ash (Na₂SO₄) -7.38% Silicon -1% Examples 4 to 10 The preparation and properties of various SIL-PVA's under different conditions are summarized in Table 1 Examples 8 and 9 illustrate the importance of having a PVA with a degree of hydrolysis at 90% or higher in order to form a soluble SIL-PVA. Example 11 Preparation of SIL-PVA in Dimethylformamide (DMF) in the Presence of NaOH Polyvinyl alcohol (Aldrich) (10 g; 88% hydrolyzed; mol. wt. ∼96,000) was dissolved in dimethylformamide (400 g) at 60°C in a one-liter round-bottomed flask. To the polymer solution were added NaOH powder (0.5 g) and GPTMS (0.5 g). The resulting reaction mixture was heated at 60°C for 4h and cooled to room temperature when a dark brown product separated out. The product was insoluble in boiling water and caustic. Example 12 Preparation of SIL-PVA in Hexane Using Vinyltrimethoxysilane (VTMS) Example 1 was repeated using vinyltrimethoxysilane (3 g). The silation was carried out at 60°C for 5 h. Analytical Moisture - 5.18% Ash (Na₂SO₄) - 5.24% Silicon - 0.6% Properties The product was soluble in hot water (65-70°C). A solution-cast film was insoluble in hot water. Example 13 Preparation of SIL-PVA in Hexane Using VTMS in the Presence of Less Caustic Example 1 was repeated using the following reagents. The silation was carried out at 60°C for 6 h. 1. Hexane - 600 g. 2. Sodium hydroxide - 7.3 g. 3. Water - 40 g. 4. Polyvinyl alcohol (Aldrich) - 75 g ("as is") (100% hydrolyzed; mol. wt. ∼14,000) 5. VTMS - 9 g. Properties The SIL-PVA was soluble in hot water (65-70°C). A solution-cast film was insoluble in hot water. Analytical Moisture - 9.02% Ash (Na₂SO₄) - 13.02% Silicon - 1.66% Example 14 Preparation of Silated Hydroxyethyl PVA (SIL-HEPVA) To a mixture of hexane (600 g) and caustic solution (8 g NaOH dissolved in 60 g of water) was added polyvinyl alcohol (100 g "as is") (Aldrich; 100% hydrolyzed; mol. wt. ∼115,000). The resulting mixture was mixed at 20°C for 30 minutes to alkalize the PVA. To the alkalized PVA slurry were added GPTMS (10 g) and ethylene oxide (80 g). The resulting reaction mixture was heated at 68°C for 5 h, cooled to room temperature and treated with glacial acetic acid (4 g). After filtering the reaction mixture, the residue was washed three times with acetone/water (80/20 w/w) mixture and finally dehydrated with acetone. The dehydrated polymer was dried in a fluid bed drier at 50°C for 30 minutes. Properties The SIL-HEPVA was partially (∼90%) soluble in water. A solution-cast film was water-resistant. Analytical Moisture - 7.89% Ash (Na₂SO₄) - 9.07% Silicon - 0.9% Example 15 Preparation of Silated Carboxymethyl PVA (SIL-CMPVA) The SIL-CMPVA was made in two stages as described below. a. Preparation of Carboxymethyl PVA (CMPVA) . To a mixture of t -butyl alcohol (588 g) and caustic solution (27 g of NaOH dissolved in 70 g of water) in a stainless steel pressure reactor was added PVA (100 g "as is") (Aldrich; 100% hydrolyzed; mol. wt. ∼86,000). The resulting mixture was vigorously agitated at room temperature for 30 minutes to alkalize the PVA. To the alkalized PVA slurry was added a solution of monochloroacetic acid (30 g) in t -butyl alcohol (50 g) over a period of 15 minutes and the resulting reaction mixture heated at 68°C for 3 h. After cooling to room temperature, the reaction mixture was neutralized with 70% nitric acid (3 g), filtered and the residue washed three times with methanol/water (80:20 w/w mixture). The purified CMPVA was dried in a fluid bed drier at 50°C for 30 minutes. Analytical Moisture - 4.2% Ash (Na₂SO₄) - 7.31% Carboxymethyl Degree of Substitution - 0.06 b. Silation of CMPVA The above CMPVA was silated with GPTMS according to the procedure described in Example 2. The reagents used were as follows: 1. t -Butyl alcohol - 588 g. 2. Sodium hydroxide - 10 g. 3. Water - 60 g. 4. CMPVA - 80 g ("as is"). 5. GPTMS - 15 g. Properties The SIL-CMPVA was soluble in water. A solution-cast film was water-resistant. Analytical Moisture - 7.22% Ash (Na₂SO₄) - 17.07% Silicon - 0.97% Example 16 Preparation of SIL-PVA by the Reaction of PVA with 3-glycidoxypropylmethyldimethoxysilane Example 1 was repeated using the following reagents. 3-Glycidoxypropylmethyldimethoxysilane was used in place of GPTMS and the silation was done at 68°C for 6 h. 1. Hexane - 900 g. 2. Sodium hydroxide - 12 g. 3. Water - 90 g. 4. Polyvinyl alcohol (Aldrich - 150 g "as is"). (100% hydrolyzed; mol. wt. ∼14,000). 5. 3-Glycidoxypropylmethyldimethoxysilane (Petrarch) - 23 g. 6. Glacial acetic acid - 8 g. Properties The SIL-PVA was soluble in hot water (90°C). The solution-cast film was insoluble in boiling water. Analytical Moisture - 4.98% Ash (Na₂SO₄) - 9.74% Silicon - 0.84% Example 17 Preparation of SIL-PVA by the Reaction of PVA with Bis(3-glycidoxypropyl)tetramethyldisiloxane Example 16 was repeated using the following reagents: 1. Hexane - 900 g. 2. Sodium hydroxide - 12 g. 3. Water - 90 g. 4. Polyvinyl alcohol (Aldrich) - 150 g ("as is") (100% hydrolyzed; mol. wt. ∼14,000) 5. Bis(3-glycidoxypropyl)tetramethyldisiloxane (Petrarch) - 17 g. 6. Glacial acetic acid - 10 g. Properties The SIL-PVA was soluble in hot water (90°C). A solution-cast film was insoluble in water at room temperature but dissolved in hot water at 90°C. Analytical Moisture - 5.02% Ash(Na₂SO₄) - 9.54% Silicon - 0.027% Example 18 Preparation of SIL-PVA in (DMF) in the Presence of Pyridine Example 8 was repeated using pyridine (1 g) in place of NaOH. The product isolated was soluble in water. A solution-cast film was water-soluble.

Claims: A method of preparing an in alkaline water solution soluble silated polyvinyl alcohol polymer comprising the steps: (1) optionally preparing and/or employing in step 2 a polyvinyl alcohol homopolymer or copolymer with a degree of hydrolysis between 90 and 100%; (2) reacting the homopolymer or copolymer as a slurry with a silating agent having the general formula: where, Y = a hydrocarbyl spacer group (composed of at least one methylene group) between X and the silicon atom; R₁, R₂ and R₃ are groups attached to the silicon and the groups can be either hydrocarbyl or hydrolyzable such as halogen, alkoxy, aryloxy, acyloxy, siloxy or amine and they can also constitute a combination of hydrocarbyl and hydrolyzable groups just mentioned, but at least one of them must be hydrolyzable; X = a functional group capable of reacting with the hydroxyl function of the polymer, in an alkaline environment at a temperature above 50°C; and (3) recovering a silated polyvinyl alcohol homopolymer or copolymer with a degree of silyl substitution between 0.005 and 0.5. The method of Claim 1 where the degree of silyl substitution is between 0.005 and 0.2, Y contains two or three methylene groups; at least one of R₁, R₂ or R₃ is a methoxyl group; and where X is an organofunctional group selected from epoxy,halide, isocyanate or vinyl. The method of Claims 1 or 2 where the silating agent is 3-glycidoxypropyltrimethoxysilane, isocyanatopropyltrimethoxysilane or vinyltrimethoxysilane. The method of Claims 1 to 3 where the polymer is a copolymer of vinyl alcohol and vinyl acetate. The method of Claims 1 to 4 where the polymer is substituted with hydroxyethyl. The method of Claims 1 to 5 above where step (2) is carried out in the presence of a Lewis acid catalyst such as dibutyltin dilaurate. The method of claims 1 to 6 where an anionic polymer salt of an alkali metal or ammonium ion is recovered which comprises a silated polyvinyl alcohol homopolymer or copolymer wherein the silyl substituent is covalently bonded through an ester, ether or carbamyl linkage, wherein the degree of substitution of the polymer is between 0.005 and 0.2 with a degree of silyl substitution sufficient to effect crosslinking and produce water resistance in a film cast from a water solution of the salt and dried.

Inventors: SAU ARJUN CHANDRA, SAU, ARJUN CHANDRA
Applicants: AQUALON CO, AQUALON COMPANY
Application year: 1990
Main classification: C08F8
IPC codes: C08F8, C08F216, C08F16