KR20030038937A - Process for the polymerization of cardanolic polymer - Google Patents

Abstract

PURPOSE: A method for preparing a cardanol polymer, a molded product prepared by using the polymer and a thermosetting coating composition containing the polymer are provided, to make a cardanol polymer massively and economically which is useful as the anticorrosive coating. CONSTITUTION: The method comprises the step of polymerizing cardanol in the presence of 5 wt% or less of a cationic initiator. Preferably the polymerization is carried out by bulk polymerization; and the cationic initiator is at least one selected from the group consisting of a strong acid, a Lewis acid and a Lewis acid complex. The cardanol is derived from the cashew-nut shell liquid(CNSL) generated massively as a by-product in the process of cashew nut food; and the obtained cardanol polymer has a number average molecular weight of 10,000-100,000.

Description

PROCESS FOR THE POLYMERIZATION OF CARDANOLIC POLYMER

FIELD OF THE INVENTION The present invention relates to a process for preparing a cardenol polymer, and more particularly, to a process for preparing a high molecular weight cardenol polymer by chain polymerization of a cardenol monomer in the presence of a cationic initiator.

Cardenol, one of the representative low-cost natural raw materials, is one of the main components of the cashew-nut shell liquid (CNSL), a by-product that occurs in large quantities during the production and processing of nuts, a kind of cashew nut. The main components of CNSL include cardenol, cardol, and anacardic acid as shown in the following structural formula.

In particular, anacardic acid, which accounts for 70 to 80% by weight of the total CNSL, can be substituted with cardenol through a decarbonation reaction through a heat treatment of about 140 ° C., and the mixture can also be used as a cardenol in a yield of 90% or more through simple distillation. Only selectively can be separated.

Since such cardenol is very inexpensive and is a natural raw material, it has been attempted to be used for various applications such as brake friction agents and surface coating agents.

For example, there is a method of applying a condensation polymer with formaldehyde in an attempt to apply cardenol as a coating and a coating. Such condensation polymers include a resol type resin obtained by condensation of cardenol and formaldehyde in a molar ratio of 1: 2 under a basic catalyst and a novolak type resin obtained by condensation polymerization at a molar ratio of 0.8: 1 under an acid catalyst (see below). The resulting cardenol-formaldehyde condensation polymer is finally crosslinked by a curing agent such as hexamethylenetetramine and applied to various coatings and paints.

However, in the case of coatings and coatings using cardenol-formaldehyde condensers, there is a toxicity problem due to odor and inhalation due to volatilization in the use environment after coating of unreacted formaldehyde in the paint. There is a limit to the application to the unavoidable use due to the elution of the unreacted formaldehyde in the paint contact with the solution. Third, due to the poor mechanical and chemical properties of the formed coating film after coating, There is a limit to the application to the use.

Therefore, in order to solve the environmental and ecological risks that are strongly demanded in the coating and paint markets and to develop paints having properties suitable for various applications, it is urgent to develop high-functional cardenol natural paints that solve the above problems.

In order to realize this, instead of the conventionally used condensation polymerization method, the study is to use the chain polymerization method and the self-condensation polymerization method in which the content of additives other than cardenol can be limited to 50-100% compared to the condensation polymerization method. Proceeded. At this time, in the obtained chain polymer, it is difficult to obtain a cardenol polymer having a certain molecular weight or more, because of the characteristics of the molecular structure of the cardenol, the radical stabilization by the resonance phenomenon of the phenol ring, the chain growth is continuously It is a feature on the preparation of cardenol polymers that does not occur.

Japanese Patent Laid-Open Publication No. Hei 11-323258 discloses a liquid resin formed by polymerizing CNSR or its polymerizable component with an enzymatic catalyst and a metal drier. A curable composition consisting of is disclosed. The present invention has difficulties in mass production due to problems such as insufficient oxygen transfer due to mass transfer resistance, problems with reactor capacity control, and high cost of enzymes used.

SUMMARY OF THE INVENTION The object of the present invention is to provide a method for economically preparing a large molecular weight cardenol polymer without the above-mentioned problems, and to have mechanical and chemical properties suitable for use without harming the environment and ecosystem by using the obtained cardenol polymer. To provide a high performance cardenol natural paints.

1 is a schematic diagram of a polymerization reactor used in the process of the present invention,

2a and 2b are the results of nuclear magnetic resonance spectroscopy analysis of the cardenol and the polymer thereof obtained according to the present invention, respectively,

3A and 3B show the results of infrared spectroscopy analysis of cardenol and its polymers obtained according to the present invention, respectively.

* Brief description of the reference numbers

A: Three-necked flask B: Rubber stopper

C: nitrogen filled balloon D: thermostirrer

E: three-way valve

In order to achieve the above object, according to the present invention, there is provided a method of chain polymerization of a cardenol polymer, characterized in that the cardenol is polymerized in the presence of 5% by weight or less of the cationic initiator compared to the cardenol.

According to the present invention, there is also provided a cardenol polymer obtained by the above method, a molded article prepared therefrom and a coating composition comprising the polymer.

The configuration and effect of the present invention will be described in more detail below.

The method of the present invention adopts a chain polymerization method for preparing a cardenol polymer through the use of a polymerization initiating additive only within 5% by weight of the cardenol, thereby eliminating the use of a large amount of formaldehyde as in the prior art to prepare the polymer. It is characterized by preventing environmental pollution in the process and coating process.

In the present invention, as a starting material, a cardenol may be preferably used as a product obtained by treating and separating a cashew-nut shell liquid (CNSL), which is a large amount of by-product when processing cashew nut (cashew nut), which is a kind of nut. .

The chain polymerization method according to the present invention is carried out by applying bulk polymerization, solution polymerization, dispersion polymerization, and the like at room temperature, and cationic initiators that can be used include strong acids such as sulfuric acid and hydrochloric acid, boron trifluoride, boron trichloride, Lewis acids such as titanium tetrachloride, aluminum trichloride, tin tetrachloride, and Lewis acid complexes such as boron trifluoride diethyl ether complex.

According to the present invention, as a result of the chain polymerization, a cardenol polymer having a molecular weight of 10,000 or more and usually 100,000 is obtained. In this case, one or three double bonds of an alkyl group attached to a benzene ring remain, thereby preventing the use of a curing agent. It becomes the reaction place of the crosslinking reaction through.

After the chain polymerization, the obtained cardenol polymer can be molded into a suitable shape through direct heat addition, and can be used for all conventional phenolic resin applications including PCB substrates, brake linings, and regenerated products thereof.

In addition, after dissolving the obtained cardenol polymer in an organic solvent, it is possible to obtain a coating composition according to the present invention by adding 1 to 5% by weight of a curing agent, which provides a coating film of the crosslinked form under any heat addition during coating. Can be formed. Coatings are usually used for rust prevention, where the coating thickness can range from about 10 to 100 μm, preferably from 30 to 50 μm.

The cardenol in the present invention is very similar to urushiol, which is a main component of natural lacquer, and its molecular structure as follows. When the polymer is applied as a natural paint, various mechanical properties such as high coating strength of the natural lacquer are obtained. Of course, it is possible to form a coating film having excellent chemical properties such as chemical resistance, corrosion resistance, and antifouling property:

The cardenol polymer according to the present invention, such as bisphenol A and heavy metals, which are becoming a social problem by replacing anti-corrosive paints such as food and beverage cans, transparent food containers, infant goods, and iron articles in which epoxy resins and polycarbonates are used. It can be used as an alternative paint to eliminate the problem of producing environmental hormones.

The curing agent added for coating film formation in the cardenol polymer-containing coating composition according to the present invention is zinc-octoate, manganese-naphthenate, cobalt-octoate, cobalt-naphthenate, calcium- Naphthenate, calcium-octoate, tin-octoate, zirconium-octoate, copper-naphthenate, lead-naphthenate, lead-octoate, iron-naphthenate, and the like, preferably cobalt- Any curing agent may be used as long as it provides a function capable of causing a crosslinking reaction by using a double bond remaining in the alkyl group of the naphthenate or the cardenol polymer prepared by the chain polymerization.

In addition, when forming a coating film without the use of a curing agent is possible through the addition of heat in the range of 30 ℃ to 150 ℃, through a low temperature heat addition to produce a coating film having a mechanical strength of a suitable degree for the experimental use For a long time, a short time is required through the addition of high temperature heat, and the curing temperature and time can be mutually corrected for use.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

Example

Example 1 Separation and Purification of Cardenol from CNSL Using Vacuum Distillation

100 ml of CNSL stock solution was placed in a 250 ml 1-neck round flask and installed in a rotary distillation machine. The flask was heated for several hours to maintain a temperature of 130 ° C to 140 ° C, and after replacing the anacardic acid contained about 70 to 80% in the CNSL stock with cardenol through a decarbonation reaction, a reduced pressure of 1 to 3 mmHg After maintaining at 245 ℃ to 250 ℃ to collect the gas to be distilled and condensed and recovered. The liquid obtained by repeating this method twice was diluted in deuterium-substituted chloroform (CDCl ₃ ) to obtain a spectrum using a 300 MHz hydrogen nuclear magnetic resonance spectrometer (Bruker AVANCE BPX-300). In addition, the liquid was placed in a liquid cell, and an infrared spectrum was obtained by using an infrared spectrometer (Spectrum GX I model of Perkin-Elmer). Analysis of the structure of the material obtained using the two spectra confirmed that pure cadenol was obtained with a high yield of 90% or more (see FIGS. 2A and 3A).

Example 2 Preparation of Cardenol Chain Polymers Using Boron Trifluoride Diethyl Ether Complex

In the reactor as shown in FIG. 1, 100 ml of cardenol and 100 ml of benzene obtained in Example 1 were placed in a three-necked flask (A) in a constant temperature stirrer (D), and one place was a rubber stopper with a syringe needle inserted therein. Sealed with (B), the other one is sealed with a three-way valve (E) connected with a nitrogen-filled balloon (C), and the other one is sealed with a normal glass stopper, stirred for 1 hour, and with nitrogen flowed through the air in the reactor. Was substituted with nitrogen containing no moisture. Thereafter, the balloon and the needle were removed, and in a sealed state, 5 ml of a boron trifluoride diethyl ether complex, a cationic chain polymerization initiator, was injected through a rubber stopper (B) and stirred for 3 hours to produce a polymer.

The polymerization product was washed with distilled water, separated into a water layer and a reactant layer, and then a reaction layer was collected to remove the remaining activity of the initiator and the chain polymerization initiator, and then the obtained polymer was distilled to separate the remaining solvent and distilled water. To obtain a cardenol polymer.

The polymer thus obtained was a liquid phase with a very high yellow viscosity.

In the polymerization reaction, the reaction mixture was collected by a syringe during the reaction, and the polymerization progress was confirmed by nuclear magnetic resonance spectroscopy in the same manner as in Example 1, and the nuclear magnetic resonance spectroscopy analysis of the obtained cardenol polymer was performed. Is shown in Figure 2b. The analysis revealed that between 0.5 and 3 ppm were peaks by protons attached to saturated carbon, between 4.8 and 6 ppm were proton peaks by unsaturated carbon and between 6.5 and 7.5 ppm by protons attached to benzene rings. . There was no difference in the position of the peak on the spectra of the cardenol polymer after the reaction and the cardenol polymer after the reaction, and only the peaks were widened. Macromol. Rapid Commun. 21 , 496-499 (2000)], the difference between the ratio of the integral of the peaks of the single bond moieties between 0.5 and 3 ppm and the peaks of the double bond moieties between 4.8 and 6 ppm, ie 0.5 to 3 ppm peaks. The integral value of the 6 ppm peak at the integral value of / 4.8 gives a value of 4.52 for the cardenol and 10.70 for the cardenol polymer, which can be concluded through the polymerization to reduce double bonds and increase single bonds. It was found that the polymerization was a reaction using a double bond.

About the cardenol polymer obtained above, molecular weight was measured using the gel permeation chromatography method. Molecular weight measurement was performed by dissolving the obtained viscous polymer in chloroform and injecting and passing a Styragel column connected to a Waters 2410 RI detector using a syringe (using polystyrene as a standard). The number average molecular weight showed a peak corresponding to approximately 34,000.

In addition, the spectrum was obtained by infrared spectroscopy in the same manner as in Example 1 of the obtained cardenol polymer is shown in Figure 3b. As a result, the relative intensity of the absorption peak by aliphatic CC single bond site CH bond stretching at 3000 cm ⁻¹ relative to the intensity of absorption peak due to stretching of C = C bond at wavenumber 1600cm ⁻¹ to 1700cm ⁻¹ was determined. Compared to knol, the polymerized cardenol appears to be larger, indicating that the polymerization takes place at the aliphatic double bond of cardenol. In addition, the absorption peak due to the stretching of the OH bond of phenol, which appears widely from 3300 cm ^{−1 to} around 3500 cm ⁻¹ , demonstrates that the cardenol polymerization in this experiment is mainly due to aliphatic double bonds.

Examples 3 to 8: Preparation of Cardenol Chain Polymers Using Various Cationic Polymerization Initiators

The polymerization reaction was carried out in the same manner as described in Example 2, using the components as shown in Table 1 as the cationic chain polymerization initiator.

NMR analysis and infrared spectroscopy of the obtained polymer were the same as in Example 2, and their properties and molecular weights are also shown in Table 1.

Example Initiator Statue Molecular Weight 2 5 ml of boron trifluoride diethyl ether complex Yellow high viscosity liquid 31,000 3 5 ml concentrated sulfuric acid Yellow high viscosity liquid 18,000 4 10 ml concentrated hydrochloric acid Yellow high viscosity liquid 17,500 5 5 ml of aluminum trichloride Light brown liquid with very high viscosity 28,000 6 5 ml of titanium tetrachloride Brown Viscous Liquid 25.000 7 5 ml of tin tetrachloride Brown Viscous Liquid 26,000 8 5 ml of boron trichloride Pale yellow high liquid phase 22,000

Example 9 Preparation of Molded Article Using Cardenol Polymer

After 100 g of the cardenol polymer obtained in Example 2 was evaporated in a vacuum drying furnace for 48 hours, the solvent was evaporated, and 3 g of cobalt-naphthenate was added thereto and stirred again. The mixed product was placed in a round mold (mold) and heated sequentially for 30 minutes at 100 ℃, 30 minutes at 120 ℃, 30 minutes at 140 ℃ and then cooled to room temperature to obtain a molded product.

Example 10 Preparation of Cardenol Polymer Coatings by Thermal Addition

100 g of the cardenol polymer obtained in Example 2 and 10 g of the acetone solvent were added to a 250 ml beaker, and stirred and mixed for 10 minutes. The mixture was applied to the slide glass to a thickness of 50 μm using a film maker and left at 120 ° C. for 70 hours to maintain 70% relative humidity to form a yellowish transparent film. After the coating film was heated at 150 ° C. for 1 hour, the strength of the coating film obtained by using a micro hardness tester was measured. As a result, the coating film obtained after being left at room temperature for 21 days showed 80 N / mm ² coating strength. It was.

Example 11 Formation of Cardenol Polymer Coatings through Addition of Curing Agents

100 g of the cardenol polymer obtained in Example 2 and 10 g of the acetone solvent were added to a 250 ml beaker, and stirred and mixed for 10 minutes. Then, 3 g of cobalt-naphthenate was added thereto and mixed with vigorous stirring for 3 minutes. The mixture was applied to the slide glass to a thickness of 50 μm using a film maker, and left for 1 hour while maintaining a relative humidity of 70% at room temperature to form a yellowish transparent film. After the coating film was heated at 150 ° C. for 1 hour, the strength of the coating film obtained by using a micro hardness tester was measured. As a result, the coating film obtained after being left at room temperature for 7 days showed 100 N / mm ² coating strength. It was.

Example 12 Physical Properties of Cardenol Polymer Coating Films

The following test was performed about the coating film obtained in Example 11 above.

(1) flex resistance

When the test tin plate was cut to about 7 × 12 cm and completely bent into a U-shaped arch on a mandrel having a diameter of 0.317 cm, 1.27 cm, and 2.54 cm, there was no swelling or cracking.

(2) salt water resistance (KS M 5424)

The steel sheet manufactured according to Test Method 1111 of KS M 5000 was coated to have a dry coating film of 25 to 30 μm, heated and dried at 150 ° C. for 1 hour, and then further coated 25 to 30 μm to heat and dried at 150 ° C. for 1 hour. After the test, the periphery of the test plate was painted with molten paraffin (melting point: 55-65 ° C.), and after immersion in 3 (w / v%) saline for 96 hours, the test was taken out and observed.

(3) Water resistance (KS M 5705)

Using three glass plates (150 × 70 × 2 mm) made in accordance with Test Method 1121 of KS M 5000, the sample is coated to a thickness of 20 to 30 μm, and the coating surface is placed horizontally upward and heated at 150 ° C. for 1 hour. The test piece was used. The material of the container to be tested with the specimen was made of glass. Deionized water was added to the container to a depth of about 150 mm and maintained at 20 ± 1 ° C. After placing two specimens soaked about 120 mm, they were left for 18 hours, then removed, shaken off and immediately observed by visual observation. Observed after standing for 2 hours at. The observation object range was made into the surface of the coating film except width 10mm from the test piece periphery and the liquid level. In the initial observation, there should be no wrinkles, swelling, cracking or peeling, and after 2 hours, the degree of gloss change, cloudiness, whitening, and discoloration were not large compared to the original test specimens.

(4) Acid resistance (KS M 5705)

Using three glass plates (150 × 70 × 2 mm) made according to Test Method 1121 of KS M 5000, the samples are coated to a thickness of 20 to 30 μm and heated at 150 ° C. for 1 hour by laying the coating surface horizontally upward. The test piece was used. Two test pieces except the original test piece were coated with molten paraffin (melting point of 60 ° C. or more) of about 5 mm. In accordance with Test Method 3411 of KSM 5000, a sufficient amount of immersion liquid is placed in a container without a lid so that the test plate is immersed to a depth of 1/2 to 1/3, and the test plate is placed almost vertically with the painted side up. Built up. And, when the coated test plate is upright and dried, it was immersed so that the upper end at the time of drying submerged in the immersion liquid. The acid solution was diluted sulfuric acid in deionized water at a weight ratio of 1: 1 and maintained at 50 ± 1 ° C. After immersion for 96 hours, the test piece was taken out and the coating film was visually observed. There was no clouding and the degree of coloring and turbidity of the immersion solution was not large.

(5) basic resistance (KS M 5705 and KS M 5307)

Using three glass plates (150 × 70 × 2 mm) made according to Test Method 1121 of KS M 5000, the samples are coated to a thickness of 20 to 30 μm and heated at 150 ° C. for 1 hour by laying the coating surface horizontally upward. The test piece was used. Two test pieces except the original test piece were coated with molten paraffin (melting point of 60 ° C. or more) of about 5 mm. In accordance with Test Method 3411 of KSM 5000, a sufficient amount of immersion liquid is placed in a container without a lid so that the test plate is immersed to a depth of 1/2 to 1/3, and then the test plate is placed almost vertically with the painted surface up. Built up. And, when the coated test plate is upright and dried, it was immersed so that the upper end at the time of drying submerged in the immersion liquid. The immersion base solution was diluted to 30% by weight of sodium hydroxide in deionized water and maintained at 50 ± 1 ° C. After immersion for 96 hours, the test piece was taken out and observed with the naked eye, without any swelling or peeling of the test plate. In comparison with the test piece, there was no clouding and the coloration and turbidity of the immersion solution was not large.

(6) Petrol resistance (KS M 5705)

Samples were coated to a thickness of 20 to 30 μm using three iron plates (150 × 70 × 0.8 mm) prepared according to Test Method 1111 of KS M 5000, and the coating surface was placed horizontally up and heated at 150 ° C. for 1 hour. The test piece. Test method 3411 (immersion resistance test method of paint dry coating film) of KS M 5000 was followed. The test gasoline was mixed with petroleum benzene (reagent) and toluene (reagent) in a volume ratio of 9: 1, maintained at 20 ± 1 ° C, immersed for 30 minutes, and then taken out of the test specimens to observe the coating film immediately. There was no discoloration, cloudy.

(7) Cold repeatability (KS M 5705)

Iron plate (200 × 100 × 1mm) manufactured according to 4.4 of Test Method 1111 of KS M 5000 was coated to a thickness of 20 ~ 30㎛, and the coating surface was placed horizontally and heated at 150 ℃ for 1 hour. It was set as the test piece. The test pieces were placed in a high temperature bath maintained at 80 ± 2 ° C., heated for 2 hours, and immediately cooled in a low temperature bath maintained at −20 ± 2 ° C. for 2 hours. After repeating this heating and cooling operation, it was left to stand at normal temperature for 16 hours. After repeating 3 cycles with 1 cycle as the above procedure, it was visually observed under diffused daylight, and there was no crack, peeling, swelling or whitening phenomenon.

(8) Pollution Resistance (KS M 5705)

Samples were coated to a thickness of 20 to 30 µm using four iron plates (200 × 100 × 1 mm) prepared according to 4.4 of Test Method 1111 of KS M 5000, and the coating surface was placed horizontally upward and heated at 150 ° C. for 1 hour. The test piece was used. Three sheets were used as test specimens for testing, and one sheet as a circular test specimen of the sample. The contaminated materials were black tea, soy sauce, and lipstick, and the settling time of contamination was 18 hours at room temperature. Place the test piece on the test surface horizontally, and apply the dropper to the liquid contaminant, dropping the contaminant to the center of the test piece so that the contaminant is about 15 to 20 mm in diameter, and cover it with a watch glass plate. Cut into 2 mm x 8 mm rectangular sections with a knife, press it on the painted surface, and move the wide part of the tip in the direction perpendicular to each other and draw three mutually parallel lines about 20 mm long and parallel to the long side at the center of the test piece. Tested by painting to cm 2. After the settling time of contamination, the liquid contaminated material should be removed from the watch glass dish, immediately washed with plenty of water, the lipstick wiped with clean gauze, each with ethanol and then gently wiped with clean dry gauze. The central part of the coated surface was visually observed under diffuse daylight and compared with the original specimen of the sample.

(9) Non-tackiness (KS M 5705)

Using three glass plates (100 × 100 × 2mm) made according to Test Method 1121 of KS M 5000, the samples were coated to have a thickness of 20 to 30 μm, and the coating surface was placed horizontally and heated at 150 ° C. for 1 hour. The test piece. The test piece was placed in a thermostat in which a desiccator containing saturated potassium sulfate solution was maintained at 50 ± 1 ° C. The paint surface was placed horizontally, and 50 × 50mm gauze was stacked in five layers on the center of the paint surface, and a flat cylindrical weight with a diameter of 40mm and a weight of 500g was placed on the center of the gauze. After 18 hours, the gauze was removed and the gauze marks on the painted surface and gauze were examined. The gauze was removed and examined using three test pieces. At this time, there was no hole formed by peeling the coating film.

(10) pencil hardness (KS M 5705)

Using iron plate (150 × 70 × 0.8mm) prepared in accordance with 4.4 of Test Method 1111 of KS M 5000, paint the sample to a thickness of 20 ~ 30㎛ and heat the coating surface horizontally for 150 hours at 150 ℃. It was set as the test piece. The test method was conducted according to 4.17 of KS M 5703, and the strength of the coating film was evaluated as HB.

(11) ozone cracking ability (KS M 5705)

Using three glass plates (100 × 100 × 2mm) made according to Test Method 1121 of KS M 5000, the samples were coated to have a thickness of 20 to 30 μm, and the coating surface was placed horizontally and heated at 150 ° C. for 1 hour. The test piece. Test method 3411 (immersion resistance test method of paint dry coating film) of KS M 5000 was followed. The test ozone solution is diluted with H ₂ O ₂ solution in deionized water at a weight ratio of 10ppm, maintained at 40 ± 1 ° C, immersed for 48 hours, and then taken out of the test specimens to observe the coating film and compared with the original test specimens. There was no blur.

According to the present invention, if a cardenol polymer is prepared by a continuous polymerization process in the presence of a cationic polymerization initiator using cardenol which is a low-cost natural raw material, a high molecular weight cardenol polymer can be economically produced without generating environmental pollution, This polymer can form a coating film having excellent physical properties by addition of a curing agent or heating, and can be used hygienically as a substitute in all fields to which a conventional phenolic resin is applied.

Claims (9)

A process for producing a cardenol polymer, characterized in that the cardenol is polymerized in the presence of up to 5% by weight of cationic initiator relative to cardenol. The method of claim 1, Cadenolic cashew nut (Cewew nut) A method characterized in that it is derived from cashew-nut shell liquid (CNSL), which occurs in large quantities as a by-product of food processing. The method of claim 1, The polymerization is carried out by a bulk polymerization method. The method of claim 1, And wherein the cationic initiator is at least one selected from strong acids, Lewis acids and Lewis acid complexes. A cardenol polymer prepared by the method according to any one of claims 1 to 4. The method of claim 5, Cardenol polymer, characterized in that it has a number average molecular weight in the range of 10,000 to 100,000. A molded article obtained by molding the cardenol polymer according to claim 5 in the presence of a curing agent. A thermosetting coating composition comprising the cardenol polymer according to claim 5 and 1 to 5% by weight of a curing agent thereon. The method of claim 8, Coating composition, characterized in that used for rust prevention.