Abstract:
Compositions containing a relatively low equivalent weight epoxy resin and an advancement catalyst for reacting said epoxy resin with a polyhydric phenol are stable at high storage temperatures when the advancement catalyst is a phosphonium salt of phosphoric acid, phosphorous acid or polyphosphoric acid.

Description:
BACKGROUND OF THE INVENTION 
     Precatalyzed epoxy resin compositions containing a relatively low equivalent weight epoxy resin and a phosphonium compound have been employed to prepare relatively high molecular weight resins by reacting with a polyhydric phenol. Such compositions are subject to storage over prolonged periods of time and in many instances, the composition loses its catalytic activity after such storage at elevated temperatures, which results in an epoxy resin having a significantly different epoxide content than expected from a ratio of epoxy to phenolic hydroxy groups as well as detrimental increases in viscosity. 
     These problems have been overcome by the present invention which pertains to a precatalyzed epoxy resin which is relatively stable at elevated temperatures. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to an improvement in a precatalyzed epoxy resin composition containing a mixture of (A) a relatively low equivalent weight epoxy resin having an average of more than one glycidyl ether group per molecule and (B) a phosphonium compound as a catalyst for the reaction between said liquid epoxy resin and a phenolic-hydroxyl containing compound which is subsequently blended with said precatalyzed epoxy resin composition; wherein the improvement is that which provides a stable precatalyzed epoxy resin composition as evidenced by 
     (1) after subjecting said precatalyzed epoxy resin composition to a temperature of about 200° F. (93.3° C.) for about 48 hours; 
     (a) not more than 50% of the phosphonium groups originally present in said mixture are deactivated; 
     (b) the viscosity has not increased by more than 30% of the original value; and 
     (2) after subjecting said precatalyzed resin composition to a temperature of 200° F. (93.3° C.) for about 63 hours, the product resulting from its reaction with a phenolic hydroxyl-containing compound having an average of more than one phenolic hydroxyl group per molecule, has a % epoxide value not greater than the value obtained by dividing the theoretical % epoxide value by 0.9; 
     by employing as the catalyst, a phosphonium salt of phosphoric acid, phosphorous acid, polyphosphoric acid or mixture thereof, which salts are represented by the formula ##STR1## wherein each R is independently a hydrocarbyl group having from 1 to about 20, preferably from about 2 to about 8, carbon atoms or the group R 1  Y wherein R 1  is a aliphatic hydrocarbon group having from 1 to about 20, preferably from about 2 to about 8, carbon atoms and Y is Cl, Br, I, NO 2  or OH and Z is a phosphate ##STR2## a phosphite ##STR3## or a polyphosphate group or mixture thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Suitable relatively low equivalent weight epoxy resins which can be employed in the compositions of the present invention include those represented by the formulas: ##STR4## wherein A is independently a divalent hydrocarbon group having from one to about 8 carbon atoms, --O--, --S--, ##STR5## each A&#39; is independently a divalent hydrocarbon group having from one to about 8 carbon atoms; each X is independently hydrogen, bromine, chlorine or a hydrocarbon group having from one to about 8 carbon atoms; n has a value of zero or 1; n&#39; has an average value less than about 0.9, preferably less than about 0.2, most preferably from about 0.01 to about 0.15 and m has an average value of from about 0.1 to about 4, preferably from about 0.8 to about 2. 
     Suitable phosphonium compounds which can be employed in the compositions of the present invention include, for example, those represented by the formula ##STR6## wherein each R is independently a hydrocarbyl group having from 1 to about 20, preferably from about 2 to about 8, carbon atoms or the group R 1  Y wherein R 1  is an aliphatic hydrocarbon group having from 1 to about 20 carbon atoms and Y is Cl, Br, I, NO 2  or OH and Z is a phosphate ##STR7## a phosphite ##STR8## or a polyphosphate group. Mixtures of such catalysts can also be employed. 
     Particularly suitable phosphonium catalysts which can be employed include, for example, ethyltriphenyl phosphonium phosphate, ethyltriphenyl phosphonium phosphite, tetrabutyl phosphonium phosphate, tetrabutyl phosphonium phosphite, mixtures thereof and the like. 
     Suitable aromatic hydroxyl containing compounds which can be reacted with the compositions of the present invention to prepare epoxy resins which are relatively high in molecular weight include, for example, those represented by the formulas: ##STR9## wherein each A, X and n are as defined above. 
     Particularly suitable aromatic hydroxyl-containing compounds are the bisphenols such as bisphenol A. 
     CATALYST A was the reaction product of a 70% solution of ethyltriphenyl phosphonium acetate.acetic acid complex in methanol and phosphoric acid in a molar ratio of one to one. The resultant product was diluted to 30% by weight with methanol. 
     CATALYST B was the reaction product of a 70% solution of ethyltriphenyl phosphonium acetate.acetic acid complex in methanol and phosphoric acid in a molar ratio of one to one. The by-product acetic acid was removed by recrystallization from methanol. The recrystallized ethyltriphenyl phosphonium phosphate was then diluted with methanol to provide a 30% by weight solution. 
     CATALYST C was the reaction product of a 70% solution of ethyltriphenyl phosphonium acetate.acetic acid complex and 118% phosphoric acid (polyphosphoric acid) in a molar ratio of one to one. The resultant product was diluted to 30% by weight with methanol. 
     CATALYST D was the reaction product of a 70% solution of ethyltriphenyl phosphonium acetate.acetic acid complex in methanol and phosphorous acid in a molar ratio of one to one. The resultant product was diluted to 30% by weight with methanol. 
     CATALYST E was the reaction product of a 70% solution of tetrabutyl phosphonium acetate.acetic acid complex in methanol and phosphoric acid in a molar ratio of one to one. The resultant product was diluted to 30% by weight with methanol. 
     CATALYST F was a 20% solution of ethyltriphenyl phosphonium iodide in the methyl ether of ethylene glycol. 
     CATALYST G was a 30% solution of ethyltriphenyl phosphonium acetate.acetic acid complex in methanol. 
     CATALYST H was the reaction product of Catalyst F with phosphoric acid in a molar ratio of one to one. The resultant product was diluted to 30% by weight with methanol. 
     CATALYST I was the reaction product of ethyl triphenyl phosphonium bicarbonate with diethyl phosphate in a molar ratio of one to one. The resultant product was diluted to 30% by weight with methanol. 
     CATALYST J was a 70% solution of tetrabutyl phosphonium acetate.acetic acid complex in methanol. 
     EPOXY RESIN A was a diglycidyl ether of bisphenol A having an average epoxide equivalent weight of about 188. 
     EPOXY RESIN B was a diglycidyl ether of bisphenol A having an average epoxide equivalent weight of about 189. 
     EPOXY RESIN C was a mixture of 85% by weight of Epoxy Resin A and 15% by weight of an epoxy novolac resin having an average epoxide equivalent weight of about 181 and an average functionality of about 3, the resultant mixture having an average epoxide equivalent weight of about 192. 
     EPOXY RESIN D was a mixture of 98.5% by weight of Epoxy Resin A and 1.5% by weight of the hydrolysis product of the diglycidyl ether of bisphenol A and an EEW of about 188 prior to hydrolysis; the resultant mixture having an EEW of about 192. 
     HEAT AGING 
     The storage stability of precatalyzed epoxy resin compositions was provided by placing the following compositions in a 200° F. (93.3° C.) oven for various periods of time. 
     300 g epoxy resin 
     12.5 g xylene 
     0.313 g catalyst (solvent free basis) 
     The epoxy resin, catalysts employed and results, active catalyst remaining, are given in Table I. 
     ACTIVE CATALYST DETERMINATION 
     (1) 0.5 g of precatalyzed resin is dissolved in methylene chloride and brought to a 25 ml volume; (2) a 5 ml aliquot is taken, to which 15 ml of methylene chloride and 1 ml of 0.1% aqueous solution of methyl orange indicator are added all in a 2 oz. bottle; (3) this mixture is shaken for one minute, then allowed to stand for 5 minutes; (4) a 10 ml aliquot is then taken and filtered into a Klett tube, which is placed in the Klett colorimeter. The colorimeter measures the color intensity which is directly proportional to active catalyst (phosphonium cation) levels. Catalyst concentration is then taken based on the PPM active catalyst per Klett unit. 
     ADVANCEMENT AFTER AGING 
     (1) After the aging period, a new EEW is calculated; (2) bisphenol A is added to theoretically provide a final product having a 3000 EEW (1.43% epoxy); (3) the n-butyl ether of ethylene glycol is added to bring the system to 85% solids, with this dilution, system should reach 1.27% epoxy if no solvent is lost. The epoxy resin, bisphenol A and n-butyl ether of ethylene glycol are added at room temperature and heated at 2°-3° C./min. to 175° C., where the heating means is cut off and the system allowed to exotherm. The resin is cooked for four hours after exotherm to acquire the finished product. 
     
                                           TABLE I__________________________________________________________________________                                        RESIN ADVANCEMENT.sup.3EXAMP.                                                VALUE OFOR                         % PHOS- VISCOSITY HOURS                                             PER-                                                 THEORETICALCOMP.          HOURS               ACTIVE PHONIUM AT 25° C.                                    % OF                                        PAST CENT                                                 % EPOXIDEEXPT.CATA-     EPOXY          AT   CATALYST                      GROUPS  CENTI-                                    ORIG-                                        EXO- EPOX-                                                 DIVIDEDNO.  LYST RESIN          200° F.               PPM    REMAINING                              STOKES                                    INAL                                        THERM                                             IDE By__________________________________________________________________________                                                 0.91    A    A    0    1000   100     2600  N.A..sup.6   1.41          24   755    75.5    N.D.      1    1.60          48   650    65      3023  116 3    N.D..sup.4          63   545    54.5    N.D.      4    1.372    B    A    0    1000   100     2600  N.A.         1.41          24   840    84      N.D.      1    1.48          48   680    68      2966  114 3    1.20          63   670    67                4    1.14 3.sup.1A    A    0    1000   100     8115  N.A.         1.41          24   655    65.5    N.D.      1    1.42          48   575    57.5    10286 127 3    1.21          63   510    51      N.D.      4    1.164    A    B    0    1000   100     2114  N.A.         1.41          24   710    71      N.D.      1    1.41          48   645    64.5    2659  126 3    1.14          63   600    60                4    1.005    C    A    0    1000   100     2600  N.A.         1.41          24   655    65.5    N.D.      1    1.47          48   555    55.5    2889  111 3    1.16          63   505    50.5    N.D.      4    1.116    D    A    0    1000   100     2600  N.A.         1.41          24   1000   100     N.D.      1    1.22          48   1000   100     3373  130 3    0.95          63   975    97.5    N.D.      4    0.927    E    A    0    1000   100     2600  N.A.         1.41          24   1000   100     N.D.      1    1.25          48   1000   100     2966  114 3    0.98          63   985    98.5    N.D.      4    0.92A.sup.2F    A    0    1000   100     2600  N.A.         1.41          24   425    42.5    N.D.      1    3.65          48   210    21.0    2996  115 3    N.D.          63   185    18.5    N.D.      4    1.89B.sup.2G    A    0    1000   100     N.D.  N.D.          4    115    11.5    N.D.  N.D.                                        N.D. N.D. 8.sup.5A    A    0    1000   100     2939  N.A.         1.59          24   523    52.3    N.D.      1    1.53          48   538    53.8    3268  111 3    1.40          63   561    56.1    N.D.      4    1.379    A    C    0    1000   100     3367  N.A.         1.41          24   836    83.6    N.D.      1    1.46          48   627    62.7    3673  109 3    1.16          63   564    56.4              4    1.1210   H    A    0    1000   100     2600  N.A.         1.41          24   871    87.1    N.D.      1    1.45          48   803    80.3    2941  113 3    1.16          63   750    75.0    N.D.      4    1.12C.sup.2I    A    0    1000   100     2600  N.A.         1.41          24   351    35.1    N.D.      1    1.93          48   390    39.0    3371  130 3    1.67          63   357    35.7    N.D.      4    1.60D.sup.2I    D    0    1000   100     2940  N.A.         1.41          24   350    35.0    N.D.      1    1.79          48   343    34.3    3435  117 3    1.39          63   364    36.4    N.D.      4    1.33E.sup.2J    A    0    1000   100     2600  N.A.         1.41          24   1000   100               1    1.33          48   1000   100     8296  219 3    gelled                                             after          63   1000   100               4    1.5 hrs.__________________________________________________________________________ FOOTNOTES TO TABLE .sup.1 Xylene was omitted from the heat aging composition. .sup.2 Comparative Experiment .sup.3 The resincatalyst mixture was advanced with bisphenol A after agin at 200° F. for 63 hours. The % epoxide was measured after 1, 3 and 4 hours after exotherm was recorded and the % epoxide is based on total composition including solvent. The theoretical % epoxide was 1.27 %. .sup.4 N.D. = Not Determined. .sup.5 The epoxidation was conducted without solvent therefore the theoretical % epoxide was 1.43% instead of 1.27%. .sup.6 N.A. = Not Applicable.