Method for preparing a flame-retardant triallyl isocyanurate prepolymer

Abstract: A flame-retardant TAIC is polymerized in the presence of a polymerization modifier and a polymerization initiator. As the polymerization modifier, 6H-dibenz (c,e ) (1,2 ) oxaphosphorine-6-oxide is used in an amount of 1 to 200 % by weight on the basis on the weight of triallyl isocyanurate.

Description: Background of the Invention The present invention relates to a method for preparing a new flame-retardant triallyl isocyanurate prepolymer having a relatively low molecular weight. Triallyl isocyanurate (referred to as "TAIC" hereinafter) is a chemical compound also called chemically triallyl ester of isocyanuric acid or allyl isocyanate trimer and is also a tautomer of triallyl cyanurate. Since TAIC is superior in chemical and thermal stability to the latter, it has attracted special interest recently as a vinyl monomer which can be used as a crosslinking agent for various thermosetting resins and synthetic rubbers or a modifier for their thermal resistances, mechanical properties, hydrolysis resistances and the like. Although it is widely practised that TAIC is added in a form of monomer to various synthetic resins or rubbers to be modified to crosslink them, it is often used in a form of prepolymer of relatively low molecular weight depending on the applications including electronic materials, synthetic resins, paints, adhesives and other industrial materials as described, for example, in Japanese Laid-Open Patent Publications No. 74245 of 1981 and No. 16911 of 1986. In these applications, flame retardancy is required. Accordingly, the development of a flame-retardant TAIC prepolymer is of high industrial importance. Various methods for the preparation of a TAIC prepolymer have been proposed. For example, Japanese Patent Publication No. 26586 of 1963 and Japanese Laid-Open Patent Publication No. 54192 of 1973 disclose a method of reacting TAIC with an aliphatic aldehyde having 2 to 8 carbon atoms in the presence of a polymerization initiator. However, the TAIC prepolymer prepared by this method shows no flame retardancy and the final product tends to discolor on standing. Japanese Laid-Open Patent Publication No. 77294 of 1978 describes a method for the preparation which improves yield and purity and in which the solid TAIC prepolymer is separated and then the methylcarbonylpropyl group containing residue included in the mother liquor is recovered for use. Even this method cannot solve the above problem. Further, it is disadvantageous for industrial manufacturing because of requiring an autoclave as the reactor. On the other hand, as a method for flame retarding the TAIC prepolymer, Japanese Patent Publication No. 198739 of 1982 describes that diallyl tetrabromophthalate is used as a reactive flame retarding agent to the TAIC-diallyl phthalate copolymerized prepolymer. This method lowers the content of TAIC moiety naturally and thus the deterioration of physical properties possessed originally by TAIC cannot be avoided. Furthermore, a method is well known in which, as a method for the preparation of a flame retardant prepolymer having a low molecular weight, TAIC is polymerized in a halogenated hydrocarbon and a portion of the solvent is combined with the prepolymer molecule by utilizing the chain transfer reaction to the solvent in order to synthesize a halogenated TAIC prepolymer. According to the inventors' experience, however, not only a coloured product is prepared but also the lowering of molecular weight that is, the chain transfer effect, is insufficient when the selected halogenated hydrocarbon is unsuitable and, in some cases the polymerization reaction is inhibited. Accordingly, this method is also unsuitable as a method for the preparation of a TAIC prepolymer of high quality. Therefore, an object of the invention is to solve the above problems and to provide a method for industrial preparation of a flame retardant TAIC prepolymer which has not only excellent flame retardancy but also good physical properties. Summary of the Invention In the method of the invention, a flame retardant triallyl isocyanurate is prepared by a method wherein TAIC is polymerized in the presence of a polymerization modifier, a polymerization initiator and an organic solvent. As the polymerization modifier, 6H-dibenz [c,c] [1,2] oxaphosphorine-6-oxide is used in an amount of 1 to 200% by weight on the basis of the weight of triallyl isocyanurate. The organic solvent is such that both triallyl isocyanurate and the polymerization modifier are dissolved in the organic solvent. Detailed Description of the Invention Raw Material TAIC has a melting point of 23 to 27°C and is a colorles or pale yellow liquid or a crystalline odorless nontoxic substance. Its grades range from industrial to reagent and one of 95 % pure or higher is preferably used in the present invention. Polymerization modifier 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide is a compound also known as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide or 3,4,5,6-dibenzo-1,2-oxaphosphane-2-oxide and having a structure represented by the following formula: An industrial grade product commercially available as a discoloration inhibitor or stabilizer for resin can be used in the present invention. The added amount of the agent may be varied according to the desired degree of flame retardancy, the yield of TAIC prepolymer and the molecular weight of it. The object of the present invention can be usually attained with an amount of 1 to 200 %, preferably 5 to 150 %, based on the weight of TAIC. An amount not higher than 1 % shows poor effect on lowering molecular weight, while that higher than 200 % also shows no additional effect on control of molecular weight and is also not economical. Polymerization initiator 1 ○ Type: The most preferable polymerization initiators in the present invention are radical polymerization initiators. They include, for example, organic peroxides such as benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, dicumyl peroxide, α, α′-bis(t-butyl peroxy-m-isopropyl)benzene and t-butyl peroxybenzoate and azo compounds such as 2,2′-azobis(2,4-dimethylvaleronitrile), azobis-isobutylonitrile, 2,2′-azobis(2,4,4-trimethyl pentane and 2-phenyl-azo-2,4-dimethyl-4-methoxyvaleronitrile. Any compound having similar structure to the above can be also used. 2 ○ Amount of the polymerization initiator: It may be used within the range of 0.1 to 10 %, preferably 0.5 to 8 %, based on the weight of TAIC. 3 ○ Time of adding the polymerization initiator: It may be added at a time before the polymerization reaction, or continuously or dividedly added during the polymerization reaction. Solvent 1 ○ Type: The polymerization modifier used in the present invention, 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide, is a solid having a melting point of 115 to 119 °C. Accordingly, it is necessary to use an organic solvent to obtain a marked effect on control of molecular weight, to control the viscosity of the produced prepolymer and further to make the reaction mild. As the organic solvent, there are preferably used common solvents dissolving both TAIC and 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide. Such solvents include, for example, an aromatic hydrocarbon such as benzene, toluene and xylene, lower aliphatic alcohols such as methanol, ethanol, isopropanol, n-butanol and isobutanol, an amphoteric solvents such as DMF and dimethylacetamide. Although halogenated aliphatic hydrocarbons such as carbon tetrachloride and chloroform do not inhibit especially the effect of the present invention, they tend to color the product and hence it is preferred to avoid their use. 2 ○ Amount of the solvent: The solvent is preferably used within the range of 1 to 10 parts by weight, preferably 1.2 to 8 parts by weight, per 1 part by weight of the total amount of TAIC and 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide. Not more than 1 part by weight of the solvent shows poor diluting effect and gives difficulty on smooth polymerization reaction and thus may cause undesirable gelation, while not less than 10 parts by weight of it is economically disadvantageous. Reaction temperature and reaction period Preferred reaction temperature and reaction period correlate closely to the concentration of TAIC and the amounts of the polymerization initiator and the polymerization modifier. Further, it affects the yield and the molecular weight of the objective prepolymer as a result. Accordingly, their relationship cannot be easily defined wholly. However, it is preferred for a smooth control of the reaction that the temperature is selected from the range of 40 to 200 °C, preferably 50 to 150°C and the period is selected from the range of 1 to 10 hours, preferably 2 to 8 hours. Care must be taken when polymerization is carried in such a condition as increasing the polymerization rates, for example at high reaction temperature, at high amount of the initiator and at high monomer concentration, because the yield of the reaction product may exceed the estimated level in a short period or the whole reaction mixture may gel. Reaction Method TAIC, 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide and the polymerization initiator are dissolved in the organic solvent and reacted together under heating in an atmosphere of an inert gas such as nitrogen gas. The polymerization reaction is controlled by such a procedure that a part of the reaction mixture is successively sampled during the reaction and then the molecular weight of the product is determined by a gel permeation chromatography or the consumption of TAIC is traced by a chemical analysis (such as bromine value) and after reaching a little before the intended molecular weight or conversion of TAIC, the polymerization reaction is compulsorily terminated by quenching the reaction mixture or blowing air into it. Excessive progress of polymerization, that is gelation, can be avoided by such an operation. Isolation of TAIC prepolymer There is no special restriction on the method for isolating the objective product (TAIC prepolymer) from the reaction mixture. However, a method is usually used in which the reaction mixture is fed into a lower alcohol such as methanol, ethanol, isopropanol and the like, and the prepolymer is recovered as precipitate. In some cases, it is favorable to use a reaction solvent in which TAIC and the polymerization modifier are dissolved but the prepolymer is not dissolved, such as methanol and the like, to deposit TAIC prepolymer during the polymerization reaction. The prepolymer, according to the present invention, requires no isolation necessarily for some applications and the reaction mixture can be used as it is for the succeeding process in a form of a solution containing as the main components TAIC prepolymer, TAIC and the remaining polymerization modifier. Properties of TAIC prepolymer 1 ○ Appearance and molecular weight: The TAIC prepolymer prepared according to the present invention is resinous white powder or, in some cases, somewhat adhesive white powder having a molecular weight of 800 to 80,000. A molecular weight of not higher than 10,000 tends to give an adhesive powder having a melting point, while a molecular weight of 20,000 to 80,000 tends to give a powder. The molecular weight mentioned here means a weight average molecular weight measured by a gel permeation chromatography (GPC) using polystyrene as the standard. It is preferred the molecular weight is within the range of 800 to 80,000 for the purpose of the present invention. The product having a molecular weight of more than 80,000 is partly insoluble, that is, it tends to gel and thus it cannot be said to be a good prepolymer. 2 ○ Infrared spectrum: The TAIC prepolymer of the present invention shows adsorptions of P =0 stretching vibration and C=C stretching vibration (originated from benzene ring) based on the 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide segment at 1200∼1250 cm ⁻¹ and 1580 ∼1610 cm ⁻¹ respectively and is obviously different from the known TAIC prepolymer. Operation (1) 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide acts very efficiently as a chain transfer agent and prevents effectively the increase in the molecular weight. (2) The The TAIC prepolymer according to the present invention has 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide segment in the molecule, as apparent from its infrared spectrum and this segment gives the TAIC prepolymer flame retardancy. It has been known that derivatives of 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide act as flame retarding agents (See U.S. Patent No. 4,280,961 ( CA, 96, 86446S ).). Examples The embodiments and the effect of the present invention will be illustrated by Examples and Comparative Examples as follows. They are given for the purpose of illustration and not intended to be limitation of the present invention. Example 1 70 g of TAIC, 3.5 g of dicumyl peroxide, 120 g of toluene and 7 g of 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide were fed in a 300 ml reactor equipped with a stirrer, a reflux condenser, a nitrogen blowing tube and a thermometer. The atmosphere in the reaction system was replaced with nitrogen by nitrogen-bubbling and then the mixture was heated for 4 hours at 115 °C. Then, the reaction mixture was cooled and the reaction mixture was poured into 1500 ml of methanol. The deposited white precipitate was filtered and washed with a sufficient amount of methanol and then dried in vacuo at a temperature not higher than 50 °C to give 29.1 g of a white TAIC prepolymer. Yield: 41.6 % (based on TAIC). The number average molecular weight (Mn) was 3,690 and the weight average molecular weight (Mw) was 32,670 measured by GPC using polystyrene as the standard. Examples 2 to 5 TAIC prepolymers were prepared by the same procedure as in Example 1 using the polymerization initiators and the solvents shown in Table 1 under reaction conditions also shown in Table 1. The yields and the physical properties of the prepolymers are shown also in Table 1. Example No. 2 3 4 5 Amount of TAIC (g) 70 50 30 50 Amount of the polymerization modifier (g) 14 20 30 75 Polymerization initiator Type Cumene hydroperoxide Azobis-isobutyronitrile Dicumyl peroxide Benzoyl peroxide Amount (g) 4.7 1.0 0.7 0.8 Reaction solvent Type Xylene Benzene Toluene Benzene Amount (g) 110 130 140 150 Reaction condition Temp. (°C) 135 80 115 80 Period (hr) 4 3 3 2 Yield (g) 34.0 26.3 28.0 20.7 Yield (%) 48.6 52.6 93.4 103.5 Prepolymer property Mn 3360 2070 940 750 Mw 27480 9810 1390 1180 Example 6 50 g of TAIC, 2.0 g of azobis-isobutyronitrile, 200 g of methanol and 20g of 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxdide were fed in a same kind of reactor as in Example 1 and then the atmosphere in the reactor was replaced with nitrogen and the mixture was heated to the refluxing temperature of methanol for 7 hours. Formation of precipitated TAIC prepolymer was observed as the polymerization proceeds. After the reaction was completed, the precipitate was filtered and washed with a sufficient amount of methanol and dried in vacuo to give 24.4 g of white TAIC prepolymer. Yield was 48. 8 % based on TAIC. Mn=2,130 and Mw=11,150. Comparative Example 1 Example 1 was repeated except that 6H-dibenz [c,e ] [1, 2 ] oxaphosphorine-6-oxide was not used to synthesize TAIC prepolymer. Resultantly, TAIC prepolymer was obtained in a yield of 27.4 g (39.1 % based on TAIC ), but this prepolymer contained insoluble material in tetrahydrofuran showing apparently existence of gelation. Though temporal values of Mn=8,850 and Mw =317,750 were obtained by the molecular weight measurement, it was assumed that actual molecular weight was more than that. As the prepolymer has poor solubility in solvent, the product is of poor commercial value. Comparative Example 2 A same procedure was repeated as in Comparative Example 1 except that the reaction period was 3 hours. Yield: 21.4 g ( 30.6 % based on TAIC ). The molecular weight of the prepolymer was Mn =6,130 and Mw=34,580. It showed good solubility in tetrahydrofuran and was of reasonable in quality. Comparative Example 3 A same procedure was repeated as in Example 1 except that 7 g of carbon tetrachloride was used as the polymerization modifier instead of 6H-dibenz [c,e ] [1,2 ] oxaphosphorine-6-oxide. Yield: 28.1 g ( 40.1 % based on TAIC). The molecular weight of the resultant prepolymer was Mn =5,840 and Mw=78,700. Although the effect of decreasing molecular weight with carbon tetrachloride was observed, the resultant prepolymer had yellow color and was a poor commercial value. Comparative Example 4 A same procedure was repeated as in Comparative Example 3 except that carbon tetrabromide was used instead of carbon tetrachloride. The yield of TAIC prepolymer was only 5.3 g ( 7.6 % based on TAIC ). Obviously, the polymerization reaction was inhibited and the resultant prepolymer was brown in color. Reference Example 1 The TAIC prepolymers prepared by Examples and Comparative Examples according to the present invention were dissolved in toluene and then impregnated in a laminate paper (150 g/m²) to 100 % (same weight to the paper) in solid basis and dried and then the paper was carried out the burning test according to JIS K 7201. The results are shown in Table 2. Sample No. Examples Comparative Example 2 1 2 3 4 5 Oxygen index 23.0 23.5 24.0 26.5 28.0 19.0 It is clear from the above table that flame retardancy is provided by the TAIC prepolymer of the present invention. As described above, a flame retardant TAIC prepolymer, which has a low molecular weight and good quality, can be easily provided by the present invention.

Claims: A method for preparing a flame-retardant triallyl isocyanurate prepolymer having a molecular weight of 800 to 80,000, characterised in that polymerization of triallyl isocyanurate is carried out in the presence of a polymerization modifier, a polymerization initiator and and organic solvent, said polymerization modifier being 6H-dibenz [c,e] [1,2] oxaphosphorine-6-oxide and being used in a amount of 1 to 200% by weight on the basis of the weight of triallyl isocyanurate, both the triallyl isocyanurate and the 6H-dibenz [c,e] [1,2] oxaphosphorine-6-oxide being dissolved in the organic solvent. A method as defined in Claim 1, wherein said polymerization initiator is a radical polymerization initiator. A method as defined in Claim 1 or 2, wherein said polymerization initiator is used in an amount of 0.1 to 10% by weight on the basis of the weight of triallyl isocyanurate. A method as defined in any preceding claim, wherein said solvent is used in an amount of 1 to 10 parts by weight per part of the total weight of triallyl isocyanurate and 6H-dibenz [c,e] [1,2] oxaphosphorine-6-oxide. A triallyl isocyanurate prepolymer comprising 6H-dibenz [c,e] [1,2] oxaphosphorine-6-oxide moieties and exhibiting adsorption of P = O stretching vibration and C = C stretching at 1200 cm⁻¹ and 1580 to 1601 cm⁻¹ respectively.

Inventors: HAYASHI TOMOMI, HIRATSUNA SATOSHI, HOTTA HIROSHI, HAYASHI, TOMOMI, HIRATSUNA, SATOSHI, HOTTA, HIROSHI
Applicants: DAI ICHI KOGYO SEIYAKU CO LTD, DAI-ICHI KOGYO SEIYAKU CO., LTD.
Application year: 1990
Main classification: C08F226
IPC codes: C08F26, C08F2