1. Field of the Invention
The present invention relates to a process for producing hydrophilic polymers. More particularly, the present invention relates to a process for producing novel hydrophilic diene polymers having unsaturated double bonds in their molecular structure.
2. Description of the Prior Art
A great variety of water-soluble polymers have been known hitherto. The water-soluble polymers include, for example, water-soluble, naturally occurring polymers such as sugar, polysaccharide, and chemically-modified derivatives thereof, for example, alginic acid (sodium alginate), carboxymethyl cellulose (CMC), and methyl cellulose (MC), methyl etherified cellulose (degree of etherification: 25% to 32%); water-soluble polysaccharides produced under the action of microorganisms such as pluran, dextran, and xanthangum; and water-soluble synthetic polymers such as polyvinyl alcohol, polyethylene oxide, sodium polyacrylate, and polyacrylamide.
The above-mentioned water-soluble polymers are used in various fields of industry, utilizing the characteristic properties thereof. For example, these water-soluble polymers are used in large quantities in various fields of the chemical and textile industries, for items such as adhesives, paints, fiber processing agents, sizing agents, binders for making Japanese paper and paperboard, emulsifying agents, coagulating agents, agents for reducing the frictional resistance of a liquid, thickening agents, asphalt-emulsifying agents, spreading agents for agricultural chemicals, pigment dispersants, latex thickeners, soil conditioners, and printing agents, as well as in various fields of bioindustry, such as additives for ice cream, feed processing agents, medicines, cosmetics, stabilizers for sustaining froth on beer, diet foods, medicine tablet-forming agents, and serum-filling agents.
In Japan, the amount of water-soluble polymer used in these fields totals several tens of tons per year, and demands for water-soluble polymers having unique characteristics are increasing.
On the other hand, attempts have been made to render diene polymers containing unsaturated double bonds hydrophilic, so as to provide an electrodeposition resinous paint.
Diene polymers, of which polybutadiene is typical, are essentially insoluble in solvents having a high polarity; for example, water and alcohols. If these polymers could be modified to be water and/or alcoholsoluble, they would be able to be utilized in various ways.
In order to render the diene polymers water-soluble, a great variety of methods have been reported, which are classified as follows.
(1) A method wherein polybutadiene is modified with maleic acid or anhydride and, optionally, the resultant modified product is subjected to further modification, so as to increase the degree of water-solubility of the modified polybutadiene. This method is disclosed in Japanese Examined Patent Publication (Kokoku) No. 46-954 and Japanese Unexamined Patent Publication (Kokai) No. 55-120,604.
(2) A method wherein butadiene is copolymerized with other vinyl monomers, or butadiene monomers is modified and the resultant butadiene derivative monomer is polymerized, to prepare a hydrophilic butadiene polymer. These methods are disclosed in Japanese Unexamined Patent Publication (Kokai) No. 52-102,812 and German Unexamined Patent Publication No. 2,817,227.
(3) A method wherein polybutadiene is epoxidized and the resultant oxirane rings contained in the epoxidized polybutadiene are opened with carboxylic acids, secondary amines, or diamines, to provide a hydrophilic butadiene polymer. The method is disclosed in Japanese Examined Patent Publication (Kokoku) Nos. 44-26,671 and 47-25,131.
(4) A method for chemically modifying polybutadiene with a modifying agent other than those mentioned above, for example, the addition of a sulfonic acid group to the polymer. This method is disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 55-75,457 and 57-74,308.
The references relating to the above-mentioned methods describe that the polymers obtained by the above-mentioned conventional methods are water-soluble or can be diluted with water. However, most of these polymers are merely capable of being emulsified with water to form a latex and are not really water-soluble. Otherwise they can be diluted with water only in the presence of a large amount of organic solvents compatible with water, such as cellosolves. Thus, of these polymers, few are truly water-soluble.
Furthermore, in the above-mentioned conventional methods, most of the base polybutadienes to be chemically modified are those having a low molecular weight of less than 10,000 (liquid polybutadiene). Polymers having a high molecular weight of 10,000 or more are little used.
The inventors of the present invention made extensive studies in an attempt to provide water-soluble diene polymers having unsaturated double bonds and a high molecular weight. As a result, the inventors of the present invention discovered that when rubber polymers, for example, 1,4-polybutadiene, or crystalline 1,2-polybutadienes having a high molecular weight are subjected to epoxidization so as to epoxidize the unsaturated double bonds contained therein to a specific degree of epoxidization and the resultant epoxidized products are heated in the presence of tertiary amines and carboxylic acids so as to ring-open the epoxidized polymers, the resultant polymers exhibit satisfactory hydrophilicity. The inventors of the present invention also discovered that when the epoxidization is carried out with a carboxylic acid and a peroxide compound and the carboxylic acid used in the epoxidization reaction is the same as that used in the ring-opening reaction of the epoxy rings, the combination of these reactions becomes smooth, and, thus, the production process efficiency can be remarkably improved. The present invention was attained based on the above-mentioned discovery.