Process for Producing Polymers of Monoallylamine

The present invention relates to a process for producing polymers of monoallylamine (CH.sub.2 .dbd.CHCH.sub.2 NH.sub.2).

As is well known in the art, allyl compounds are polymerized with usual radical initiators only with difficulty and at best, polymers of a low polymerization degree are formed generally in a low yield.

It may be explained because self-termination would occur due to the reaction of hydrogen atoms present in the allyl group and the radical. This reaction is generally called "allylic degradative chain transfer".

This fact is common knowledge to chemists in the field of high molecular chemistry, as is acknowledged in many papers and textbooks (for example, C. E. Schildknecht, "Allyl Compounds and their Polymers"; Wiley-Interscience; 1973, pages 29-30 and R. C. Laible, Chem. Rev., 58(5), 807-843 (1958)).

This phenomenon also occurs unexceptionally on monoallylamine which is a sort of allyl compounds. Monoallylamine is scarecely polymerized with usual radical type initiators or ion type initiators; only a few reports are published on polymerization of monoallylamine under special conditions as described below:

1. A process for producing a brown, resinous poly-monoallylamine (hereafter simply referred to as "polyallylamine") comprising gas phase polymerization using tetrafluorohydrazine as a catalyst (U.S. Pat. No. 3,062,798);

2. A process for producing a resinous (black-brown) polyallylamine hydrochloride having a molecular weight of 950 to 1000 which comprises adding a small quantity of water to monoallylamine hydrochloride and, heating the mixture at 80.degree. to 85.degree. C. to bring the system in a melt state followed by polymerization while adding hydrogen peroxide thereto in small quantities (V. V. Zykova, et al., Tr. Inst. Khim Nauk, Akad. Nauk Kaz. SSR, 11, 89-94 (1964), Chem. Abst., 61, 14855 (1964));

3. A process which comprises dissolving monoallylamine hydrochloride in a tert-butyl alcohol-chlorobenzene solvent mixture in the presence of diethyl phosphite and then polymerizing at a reflux temperature of the solvent using azobisisobutyronitrile as an initiator (German Offenlegungsschrift No. 2,946,550 and the corresponding Japanese patent application KOKAI (the term "KOKAI" refers to an application which has yet been unexamined but published and is thus open to public inspection) No. 82807/81).

Processes 1, 2 and 3 described above are concerned with polymerization of monoallylamine using catalysts such as radical initiators, etc. In Processes 1 and 2, the obtained polymers are all viscous and resinous, but no polymer having a high polymerization degree is obtained.

Process 3 described in the German Offenlegungsschrift is concerned with homopolymerization and copolymerization of monoallylamine hydrochloride. However, the examples described therein are all directed to copolymerization of monoallylamine with easily polymerizable vinyl monomers (acrylamide, acrylic acid, acrylic acid esters, acrylonitrile, etc.), except for one example. In the only one example involving homopolymerization described at page 36 of the German Offenlegungsschrift, polyallylamine hydrochloride is obtained in a yield of 85%. However, the so obtained polymer is not described either by its form or by polymerization degree; it is merely stated that the polymer is water soluble over the whole pH range. The present inventors have repeated the example and as the result, they have noted that a hygroscopic product having a lower molecular weight was obtained merely in a yield of about 0.6% (refer to Comparison Example 2 later described). In this connection, no example for any homopolymerization of allyl ammonium salt is included in the corresponding Japanese patent application (Japanese patent application KOKAI No. 82807/81).

As other processes for polymerizing monoallylamine, the following processes for polymerization using rediations have also been proposed. According to these processes, polymers of monoallylamine having a high polymerization degree are obtained as compared to that using radical catalysts. Namely;

4. A process which comprises polymerizing monoallylamine by gamma rays irradiation or by UV irradiation in the presence of hydrogen peroxide in a protonic acid (phosphoric acid, sulfuric acid, hydrochloric acid) (V. A. Kabanov, et al., Vysokomol. Soed., 18, No. 9, 1957-1962 (1976) and 18, No. 10, 2233-2238 (1976));

5. A process which comprises polymerizing monoallylamine, allylcyanide or allyl mercaptan with a variety of irradiation of various radiations (gamma rays, electron rays, X rays, UV rays) in the presence of an inorganic acid or an inorganic acid salt of a metal belonging to Group I or II of the Periodic Table (L. S. Polak, V. A. Kabanov et al., U.S.S.R. Pat. No. 296,423);

In the U.S.S.R. patent supra, polymerization using a radical catalyst is included; however, the examples merely mention polymerization of allyl cyanide using benzoyl peroxide in the presence of zinc chloride and polymerization of allyl mercaptan using hydrogen peroxide in the presence of calcium chloride. Nothing is disclosed on polymerization of monoallylamine using a radical catalyst therein.

The foregoing process directed to polymerization of monoallylamine all fail to obtain polyallylamine in a high yield in a simple manner.

On the other hand, polyallylamine is an extremely interesting polymer for practical purpose and, attempts to produce polyallylamine or N-alkyl-substituted derivatives thereof have also been made by chemically modifying other vinyl polymers. Examples of such attempts are shown below:

6. A process for producing polyallylamine which comprises hydrogenation of polyacrylonitrile latex (U.S. Pat. No. 2,456,428);

7. A process for synthesis of polyallylamine which comprises reducing polyacrolein oxime (Yoshikazu Hatsuhama, et al., Kogyo Kagaku Zasshi, 64, No. 3, 595 (1961));

8. A process for obtaining a polymer of trimethyl allyl ammonium chloride which comprises reacting a polymer (molecular weight, about 900) of allyl chloride with trimethylamine (U.S. Pat. No. 4,053,512);

9. A process for producing poly-(N,N-dimethylallylamine) which comprises reducing a polymer of N,N-dimethylacrylamide (U.S. Patent supra).

Of the 9 processes for producing polymers of monoallylamine or N-substituted derivatives thereof described above, relatively preferred are radiation polymerization using gamma rays in protonic acids as described in Processes 4 and 5. As is well known in the art, however, radiation polymerization is not an excellent method for producing large quantities of polymers. As a matter of fact, no polymer is produced in an industrial scale according to these processes involving radiation polymerization. Thus, polyallylamines have not been produced yet in an industrial scale.

Only recently, one (Harada) of the present inventors has found that when inorganic acid salts of monoallylamine are polymerized in a polar solvent using an azo type radical initiator containing a group having a cationic nitrogen atom in the molecule thereof, polymers can easily be obtained and based on the finding, a patent application was filed (Japanese patent application No. 54988/83, now open to public inspection as Japanese patent application KOKAI No. 20181/83). In Japanese patent application KOKAI No. 20181/83, it is disclosed that it is important that both monomer and initiator have electric charges in polymerization system, as a requirement for smooth proceeding in polymerization of inorganic acid salts of monoallylamine. In this case, in terms of the initiator, the disclosure obviously refers to the nitrogen atom having a cationic charge.

The present inventors have investigated to develop more effective polymerization initiators and polymerization system, upon polymerization of inorganic acid salts of monoallylamine in a polar solvent, which can provide polymers of a high polymerization degree in a high yield. As a result, the present inventors have discovered that inorganic acid salts of monoallylamine can easily be polymerized using an azo type initiator selected from azo compounds represented by formula (I), (II), (V) and (VI): ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each represents, which may be the same or different, a hydrocarbon group; R.sub.1 and R.sub.2 or/and R.sub.3 and R.sub.4 may be combined to complete a ring together with the carbon atom attached thereto; R.sub.5 represents a hydrogen atom or an alkyl group; and m represents 0 or 1.

That is, the present invention relates to a process for producing polymers of monoallylamine which comprises polymerizing inorganic acid salts of monoallylamine in a polar solvent in the presence of the azo type radical initiator selected from the azo compounds represented by the general formula (I), (II), (V), (VI) described above, wherein R.sub.1 through R.sub.5 and m have the same significances as defined above; hereafter the same.

In the formulae above, R.sub.1 through R.sub.4 each represent, which may be the same or different, a hydrocarbon group, preferably a straight or branched alkyl group having 1 to 4 carbon atoms or, a cycloalkyl group having 3 to 6 carbon atoms (cyclopentane ring, cyclohexane ring, etc.), a phenyl group or a benzyl group or, R.sub.1 and R.sub.2 or/and R.sub.3 and R.sub.4 are combined to complete a ring together with the carbon atom attached thereto.

The azo type radical initiators represented by formulae (I), (II), (V) and (VI) are disimilar to the azo type radical initiator used in the process of Japanese patent application KOKAI No. 201811/83 supra in the following point. Namely, the azo type initiator of the Japanese patent application KOKAI No. 201811/83 contains a nitrogen group which constitutes a strongly basic moiety such as an amidino group or an alkylamino group. In contrast, the nitrogen atom contained in the amidoxime group (formula (I)) or the hydroxamic acid moiety (formula (II)) is markedly weak in its basicity, as compared to the nitrogen atom of the amidino group or the alkylamino group contained in the initiator of the Japanese patent application KOKAI No. 20,811/83.

More obviously, the azo type radical initiators represented by formulae (V) and (VI) contain no nitrogen atom other than the azo group; these azo type radical initiators are completely neutral substances and insoluble in water, an aqueous solution of ordinary alkalis or an aqueous solution of ordinarly inorganic acids. In fact, even though it is attempted to cause polymerization by adding the azo type initiator representd by formula (V) or (VI) to, e.g., monoallyamine hydrochloride, no polymerization substantially occurs (cf. Comparison Example 1 later described). However, when inorganic acid salts, e.g., zinc chloride, etc., are added to and dissolved in the reaction system described above, a marked effect is obtained.

On the other hand, it is well known in the art that acrylonitrile is polymerized in a concentrated solution of zinc chloride, using azobisisobutyronitrile as an initiator. When this is attempted to apply to polymerization of monoallylamine hydrochloride as it is, that is, even though it is attempted to cause polymerization by adding an aqueous solution of zinc chloride of monoallylamine hydrochloride to azobisisobutyronitrile as a radical initiator, no effect is obtained (cf. Comparison Example 1 later described).

Taking the foregoing facts or properties into account in combination with the technical background, it is quite surprising that marked effects are attained by the use of the azo type radical initiators represented by formulae (I), (II), (V) and (VI), notwithstanding that it was expected that no effect would be obtained even if these azo compounds were used as initiators for polymerization of inorganic acid salts of mono allylamine.

Other conditions for polymerization are explained below.

Preferred examples of inorganic acid salts of monoallylamine which can be employed in the present invention include hydrochloride, sulfate, sulfite, phosphate, etc. Of these salts, the hydrochloride is particularly preferred.

Polymerization is carried out in a polar solvent, namely, in water, inorganic acids (hydrochloric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, etc.) or an aqueous solution thereof, organic acids (formic acid, acetic acid, propionic acid, lactic acid, etc.) or an aqueous solution thereof, or an alcohol, dimethyl sulfoxide, dimethylformamide, formamide, an aqueous solution of inorganic acid salts (zinc chloride, calcium chloride, magnesium chloride, etc.).

Upon polymerization, the aforesaid inorganic acid salts (e.g., hydrochloride) of monoallylamine may be generally used in the form of isolated crystals. Alternatively, a predetermined amount of monoallylamine is added to an aqueous inorganic acid (e.g., hydrochloric acid) solution and then, if necessary the aforesaid inorganic acid salts (e.g., zinc chloride) is directly added to the mixture and, the resulting solution may be provided for polymerization as it is. In case that inorganic acids or an aqueous solution thereof are used as media for polymerization, needless to say, a predetermined amount of monoallylamine is polymerized as it is by adding the same to inorganic acids or an aqueous solution thereof (e.g., hydrochloric acid). Particularly in the case of using the azo type initiator represented by the formula (V) or (VI), polymerization is carried out in an aqueous solution containing inorganic acid salts, for example, zinc chloride, calcium chloride or magnesium chloride. An aqueous solution of zinc chloride is particularly preferred.

It is generally preferred that the inorganic acid salts be added in a large amount; however, the solubility is different depending upon the solubility of a salt in water or in a solution containing various concentrations of monoallylamine hydrochloride and, it is thus difficult to uniformly define the addition amount in all cases. In any case, however, it is preferred that the inorganic acid salt be contained in an amount of 5 to 500 wt % based on monoallylamine hydrochloride.

The thus obtained polymers of inorganic acid salts of monoallylamine may be converted, if necessary and desired, to polymers of monoallylamine or polymers of organic acid salts of monoallylamine, in a conventional manner.

Particularly preferred azo type initiators are given below: ##STR2##

The amount of the azo type initiator employed in the present invention is generally in a range of 0.1 to 10 wt %, preferably in a range of 1 to 6 wt %, based on the inorganic acid salt or monoallylamine.

Polymerization temperature varies depending upon chemical structure of the initiator but generally ranges from 30.degree. to 100.degree. C., preferably 40.degree. to 70.degree. C. A time required for polymerization is generally within 100 hours.

It is desired that the concentration of the starting monomer be as high as possible within its solubility; however, the concentration is generally in a range of 10 to 85 wt %.

Polymerization is more or less inhibited by the oxygen in the air. It is thus desired that polymerization be carried out in an inert gas such as nitrogen, etc.

Hereafter the present invention will be described more in detail with reference to the examples and comparison examples, wherein as monoallylamine (hereafter simply referred to as "MAA") used as the starting monomer, a fraction having a boiling point of 52.5.degree. to 53.degree. C. obtained by drying MAA made by Shell Chemical Co., U.S.A. over sodium hydroxide particles and rectifying it in a nitrogen flow was used. Examination by gas chromatography indicates that this fraction contained neither diallylamine nor triallylamine.

The present invention will be described in more detail with reference to the examples and comparison examples below.

FIG. 1 shows representative one .sup.1 H-NMR spectra of polymers of monoallylamine obtained using various azo type radical initiators in accordance with the process of the present invention.

This example shows a process for producing a polymer of monoallylamine comprising polymerization of monoallylamine in phosphoric acid using as an initiator 2,2'-azobis-(2-methyl-propioamidoxime) (hereafter referred to as Initiator I-1).

To a solution of 14 g (0.35 mol) of sodium hydroxide in 250 ml of water 30 g (0.18 mol) of hydroxylamine sulfate was added under ice-cooling while stirring. In the system 12.3 g (0.075 mol) of 2,2'-azoisobutyronitrile was added and the mixture was reacted at 35.degree. to 45.degree. C. for 40 hours. After completion of the reaction, the precipitates were taken out by filtration, thoroughly washed with a water-acetone (10:1 in a weight ratio) solvent mixture and dried at 40.degree. C. under reduced pressure. Yield 14.1 g (81.5%). From the results of elementary analysis, IR analysis and .sup.1 H-NMR analysis, the product was identified to be Initiator I-1.

In a 2 liter-round bottomed flask equipped with a stirrer, a thermometer, a reflux condenser and a dropping funnel, 1150 g (10 mols) of 85% phosphoric acid was charged and 285 g (5 mols) of MAA was dropwise added thereto while stirring. During the addition, the temperature was kept at 10.degree. to 30.degree. C. After completion of the dropwise addition, the system was warmed to 50.degree. C. A solution of 13.8 g of Initiator I-1 in 50 g of 85% phosphoric acid was added to the thus obtained solution of MAA-phosphate in phosphoric acid. Then, polymerization was carried out at 50.degree..+-.2.degree. C. for 72 hours. After completion of the polymerization, a colorless, transparent viscous solution was obtained. The solution was poured into a large quantity of water to precipitate a polymer (polyallylamine-phosphate) in a rice cake form. After thoroughly washing the precipitates with water, the precipitates were dissolved in 550 ml of conc. hydrochloric acid to convert the polyallylamine-phosphate into the hydrochloride. The solution was added to a large quantity of methanol and the formed precipitates were taken out by filtration. The precipitates were extracted with methanol using a Soxhlet's extractor to remove the unpolymerized monomer and phosphoric acid. The precipitates were dried at 50.degree. C. under reduced pressure to obtain 320 g (about 65%) of a polymer. By elementary analysis, IR spectrum analysis and .sup.1 H-NMR analysis, the polymer was identified to be polyallylamine hydrochloride (PAA-HCl).

The .sup.1 H-NMR spectrum (in D.sub.2 O, 270 MHz, TSP internal standard) of this polymer is shown in FIG. 1.

The number average molecular weight Mn of PAA-HCl determined by measurement of osmotic pressure in an aqueous saline solution was 22000.

The thus obtained PAA-HCl is freely soluble in water and an aqueous acid solution but insoluble in an organic solvent. The viscosity of an aqueous solution of PAA-HCl shows a typical behavior of a polyelectrolyte.

When heated in the air, PAA-HCl decomposes at temperatures of 300.degree. C. or higher without melting.

Next, free polyallylamine (PAA) was produced from PAA-HCl. That is, 30 g of PAA-HCl was dissolved in 270 g of distilled water and the solution was passed through a strongly basic ion exchange resin (Amberlite IRA-402) to remove hydrochloric acid. Freeze-drying of the filtrate gave 16.5 g of white PAA. PAA is readily soluble in water and in methanol and swells with dimethylsulfoxide and pyridine but is insoluble in ordinary organic solvents. When allowed to stand in the air, PAA absorbs carbon dioxide and moisture to form the carbonate.

This example shows a process for producing a polymer of monoallylamine comprising polymerization of monoallylamine hydrochloride in an aqueous solution thereof using as an initiator 2,2'-azobis-(2-methylpropionhydroxamic acid) (hereafter referred to as Initiator II-1).

To 6.91 g (0.03 mol) of 2,2'-azobis-(2-methylpropioamidoxime) (Initiator I-1, which synthesis is shown in Example 1), 30 g of cold, conc. hydrochloric acid was added. While stirring the mixture was reacted at 0.degree. C. for 20 minutes. After completion of the reaction, the reaction mixture was poured into 900 ml of acetone. The formed precipitates were taken out by filtration and dried under reduced pressure to obtain 4.7 g (67.5%) of white powders. The powders were subjected to elementary analysis, IR spectrum analysis and .sup.1 H-NMR analysis and identified to be Initiator II-1.

Next, 570 g (10 mols) of MAA was dropwise added to 1.1 kg of conc. hydrochloric acid (35 wt %) at 5.degree. to 10.degree. C. while stirring. After completion of the dropwise addition, water and excess hydrogen chloride were removed by distillation at 60.degree. C. under reduced pressure of 20 mmHg using a rotary evaporator to obtain white crystals. The crystals were dried on silica gel for drying at 80.degree. C. under reduced pressure of 5 mmHg to obtain 980 g of MAA-HCl. MAA-HCl contained about 5% of adsorbed water.

In a 500 ml round bottomed flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet tube, 98 g of the aforesaid MAA-HCl and 36 g of distilled water were charged. The mixture was stirred to dissolve the reactants, which was made a 70% aqueous solution of MAA-HCl. While introducing nitrogen gas therein, the system was warmed to 50.degree. C. Then, a solution of 4.5 g of Initiator II-1 in 10 ml of water was added to the system, the mixture was allowed to stand at 48.degree. to 52.degree. C. for 70 hours to effect polymerization. The thus obtained colorless, transparent viscous solution was added to a large quantity of methanol to precipitate a white polymer. The precipitates were taken out by filtration, washed with methanol and then dried at 50.degree. C. under reduced pressure to obtain 66 g (about 68%) of PAA-HCl. The number average molecular weight Mn of PAA HCl determined by the measurement of osmotic pressure in an aqueous saline solution was 5500.

This example shows a process for producing a polymer of monoallylamine comprising polymerization of monoallylamine hydrochloride in an aqueous solution of zinc chloride using as an initiator 2,2'-azobis-(methyl 2-methylpropionate) thereafter referred to as Initiator V-1).

As initiator V-1, Reagent manufactured by Wako Junyaku Kogyo K.K. was used as it was.

570 g (10 mols) of MAA was dropwise added to 1.1 kg of conc. hydrochloric acid (35 wt %) at 5.degree. to 10.degree. C. while stirring. After completion of the dropwise addition, water and excess hydrogen chloride were removed by distillation at 60.degree. C. under reduced pressure of 20 mmHg using a rotary evaporator to obtain white crystals. The crystals were dried on silica gel for drying at 80.degree. C. under reduced pressure of 5 mmHg to obtain 980 g of MAA-HCl. MAA-HCl contained about 5% of moisture. Water was added to the thus obtained MAA-HCl to make a 85% aqueous solution of MAA-HCl, which was provided for use hereafter.

In a 500 ml round bottomed flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet tube, 100 g of the aforesaid 85% aqueous solution of MAA-HCl and 200 g of a 70% aqueous solution of zinc chloride were charged to make a homogenous solution. While introducing nitrogen gas therein, the solution was warmed to 60.degree. C. Then, 2.09 g of Initiator V-1 described above was added directly to the system to dissolve it. The resulting solution was allowed to stand at 58.degree. to 60.degree. C. for 48 hours to effect polymerization. The thus obtained colorless, transparent viscous solution was added to a large quantity of methanol to precipitate a white polymer. The precipitates were taken out by filtration and extracted with methanol using a Soxhlet's extractor to remove the unreacted monomer and zinc chloride. The precipitates were dried at 50.degree. C. under reduced pressure to obtain 62.5 g (about 73.5%) of PAA-HCl.

By elementary analysis, IR epectrum analysis and .sup.1 H-NMR analysis, the polymer was identified to be PAA-HCl.

The .sup.1 H-NMR spectrum (in D.sub.2 O, 270 MHz, TSP internal standard) is essentially similar to that shown in FIG. 1.

The number mean molecular weight Mn of PAA-HCl determined by the measurement of osmotic pressure in an aqueous saline solution was 9800.

The thus obtained PAA-HCl is freely soluble in water and an aqueous acid solution but insoluble in an organic solvent. The viscosity of an aqueous solution of PAA-HCl shows a typical behavior of a high molecular electrolyte.

When heated in the air, PAA-HCl decomposes at temperatures of 300.degree. C. or higher without melting.

Next, free PAA was produced from the thus obtained PAA-HCl. That is, 30 g of PAA-HCl was dissolved in 270 g of distilled water and the solution was passed through a strongly basic ion exchange resin (Amberlite IRA-402) to remove hydrochloric acid. Freeze-drying of the filtrate gave 16.5 g of white PAA. This PAA is readily soluble in water and in methanol and swells with dimethylsulfoxide and with pyridine but is insoluble in ordinary organic solvents. When allowed to stand in the air, this PAA absorbs carbon dioxide and moisture to form the carbonate.

This example shows a process for producing a polymer of monoallylamine hydrochloride comprising polymerization of monoallylamine hydrochloride in an aqueous solution of zinc chloride using as an initiator 2,2'-azobis-(2-acetoxypropane) (hereafter referred to as Initiator VI-1).

To a solution of 33.6 g of sodium acetate in 300 ml of acetic acid, 11.2 g of ketazine synthesized from hydrazine and acetone was added. While stirring the mixture at 10.degree. to 20.degree. C., chlorine gas was slowly introduced into the system. After an equimolar amount of chlorine gas was introduced, the mixture was stirred for further 30 minutes at 20.degree. C. The reaction mixture was poured into a 5- to 8-fold amount of an ice-water mixture and the product was extracted with ether. Ether was removed by distillation to obtain 17.3 g (about 75%) of a solid substance. From data on elementary analysis, IR spectrum analysis and NMR analysis, the product was identified to be Initiator VI-1.

(Other initiators represented by formula (VI) can be obtained using the corresponding ketone and hydrazine as the starting materials in a similar manner).

In a 300 ml round bottomed flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet tube, 50 g of a 85% aqueous MAA-HCl solution and 150 g of a 70% aqueous solution of zinc chloride were charged to make a homogeneous solution. While introducing nitrogen gas therein, the solution was warmed to 60.degree. C. Then, 1.05 g of Initiator VI-1 described above was added directly to the system. The mixture was allowed to stand at 58.degree. to 60.degree. C. for 70 hours to effect polymerization. The thus obtained colorless, transparent viscous solution was added to a large quantity of methanol to precipitate a white polymer. The polymer was purified in a manner similar to Example 3 to obtain 28.9 g (about 68%) of PAA-HCl. The number average molecular weight Mn of PAA-HCl determined by the measurement of osmotic pressure in an aqueous saline solution was 8000.

In a 50 or 100 ml Erlenmeyer's flask with a stopper, 10 g of the 85% aqueous solution of MAA-HCl produced in Example 3 was charged and a predetermined amount of a 70% aqueous solution of zinc chloride was added to dissolve. Then, Initiator V-1 or Initiator VI-1 was added to the system. The mixture was allowed to stand at 60.degree. C. for 70 hours to effect polymerization. After completion of the polymerization, the product was treated in a manner similar to Example 3. Thus PAA-HCl was obtained. The results are summarized in Table 1 below.

For the purpose of comparative study, the results obtained with polymerization using Initiator V-1 or VI-1 but without adding zinc chloride (Comparison Examples 1a and 1b) and polymerization using azibisisobutyronitrile (AIBN) as an initiator (Comparison Example 1c) are also shown in Table 1.

As is evident from the results of Table 1, PAA-HCl was not obtained substantially in all of Comparison Examples 1a, 1b and 1c, whereas in Example 5, PAA-HCl having a high polymerization degree was obtained in good yield.

In an Erlenmeyer's flask with a stopper, 5 g of an aqueous solution of MAA-H.sub.3 PO.sub.4, in which the concentration of MAA in 85 wt % phosphoric acid was 19.85%, was charged and 5 g of a 70% aqueous solution of zinc chloride was added thereto to dissolve. Initiator V-1, 0.04 g (1 mol %) was added to the system. The mixture was allowed to stand at 60.degree. C. for 48 hours to effect polymerization. The thus obtained solution was poured into a large quantity of methanol to precipitate a polymer. The precipitates were taken out by filtration and dissolved in 5 ml of 2N HCl. Precipitation was further effected in methanol to isolate the product as PAA-HCl. The yield was 0.1 g (6.2%). The product showed intrinsic viscosity of .eta.inh 0.5 g/100 ml 1/10M NaCl being 0.1.

For the purpose of comparative study, an example of polymerization of MAA-HCl using 2,2'-azoisobutyronitrile in the presence of diethyl phosphite shown in German Offenlegungsschrift No. 2,946,550 was repeated by the present inventors. The details are shown below.

In accordance with the process described at page 36 of German Offenlengungsschrift No. 2,946,550, 100 ml of t-butanol was charged in a 1 liter round bottom flask while introducing nitrogen. The mixture was heated under reflux while stirring. A solution of 46.8 g of MAA-HCl and 0.5 g of diethyl phosphite in 500 ml of t-butanol and a solution of 0.3 g of azobisisobutyronitrile (AIBN) in 50 ml of chlorobenzene were dropwise added simultaneously to t-butanol in the aforesaid flask. A time period required for completion of the dropwise addition of the two solution was approximately 60 minutes. Then, the reaction mixture was refluxed for 3 hours. In initial 2 hours out of the 3 hours, a solution of 0.3 g of AIBN in 50 ml of chlorobenzene was further added to the system. The reaction mixture was cooled to 20.degree. C., filtered and washed with ethyl acetate. Thereafter the system was dried at 60.degree. C. under reduced pressure to obtain 0.25 g (yield 0.53%) of a yellow hygroscopic product. It was failed to determine the polymerization degree of the product because the amount of the product produced was small. However, the fact that the product was hygroscopic indicates that the product would have a relatively low polymerization degree.