Abstract:
Polycarbonates are heat stabilized by the incorporation of a carbonate compound having a boiling point greater than about 250° C. and an organophosphorous compound such as a phosphonite or a phosphite. The amount of the additive compound used in each instance is from 100 to 10,000 parts per million.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to heat stabilized aromatic polycarbonate compositions which are resistant to yellowing during heating due to the incorporation of cyclic carbonates or 1,2-carbonate compounds and organophosphorous compounds. 
     It is known from U.S. Pat. No. 3,888,817 dated June 10, 1975 that polyester resins can be stabilized against the loss of molecular weight by adding a cyclic carbonate and an antioxidant such as a phenol, phosphite or an amine. However, the reference does not suggest the application of these cyclic carbonates to polycarbonate resin nor does it indicate any reduction in the yellowing of the resins. 
     It is known from U.S. Pat. Nos. 4,066,611 and 4,076,686 that polycarbonates can be heat stabilized with additives which include epoxy compounds. 
     It is also known from Ser. No. 370,698, filed Apr. 22, 1982 that polycarbonate resins can be heat stabilized by the addition of cyclic carbonates or 2-keto-1,3-dioxolane compounds. The compositions of the instant invention are rendered more heat stable by the incorporation of organophosphorous compounds. 
     SUMMARY OF THE INVENTION 
     It now has been found that aromatic polycarbonates can be heat stabilized and made resistant to yellowing by blending the polycarbonates with a carbonate compound having a boiling point greater than about 250° C. and an organophosphorous compound. 
     The amount of the carbonate compound used herein can range from 100 to 10,000 parts per million with the preferred amount being 500 to 3,000 parts per million. The amount of the organophosphorous compound used herein can range from 100 to 10,000 ppm and is preferably in the range from 500 to 3000 ppm. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The aromatic polycarbonates that are useful in this invention are made from dihydroxy compounds having the following general formula: ##STR1## wherein A is a divalent hydrocarbon radical containing 1-15 carbon atoms, ##STR2## X is independently hydrogen, chlorine, bromine, fluorine, or a monovalent hydrocarbon radical such as an alkyl group of 1-4 carbons, an aryl group of 6-8 carbons such as phenyl, tolyl, xylyl, an oxylalkyl group of 1-4 carbons or an oxyaryl group of 6-8 carbons and n is 0 or 1. 
     One group of suitable dihydric aromatic compounds are those illustrated below: 
     1,1-bis(4-hydroxyphenyl)-1-phenyl ethane 
     1,1-bis(4-hydroxyphenyl)-1,1-diphenyl methane 
     1,1-bis(4-hydroxyphenyl)cyclooctane 
     1,1-bis(4-hydroxyphenyl)cycloheptane 
     1,1-bis(4-hydroxyphenyl)cyclohexane 
     1,1-bis(4-hydroxyphenyl)cyclopentane 
     2,2-bis(3-propyl-4-hydroxyphenyl)decane 
     2,2-bis(3,5-dibromo-4-hydroxyphenyl)nonane 
     2,2-bis(3,5-isopropyl-4-hydroxyphenyl)nonane 
     2,2-bis(3-ethyl-4-hydroxyphenyl)octane 
     4,4-bis(4-hydroxyphenyl)heptane 
     3,3-bis(3-methyl-4-hydroxyphenyl)hexane 
     3,3-bis(3,5-dibromo-4-hydroxyphenyl)hexane 
     2,2-bis(3,5-difluoro-4-hydroxyphenyl)butane 
     2,2-bis(4hydroxyphenyl)-propane(Bis A) 
     1,1-bis(3-methyl-4-hydroxyphenyl)ethane 
     1,1-bis(4-hydroxyphenyl)methane. 
     Another group of dihydric aromatic compounds useful in the practice of the present invention include the dihydroxyl diphenyl sulfoxides such as for example: 
     bis(3,5-diisopropyl-4-hydroxyphenyl)sulfoxide 
     bis(3-methyl-5-ethyl-4-hydroxyphenyl)sulfoxide 
     bis(3,5-dibromo-4-hydroxyphenyl)sulfoxide 
     bis(3,5-dimethyl-4-hydroxyphenyl)sulfoxide 
     bis(3-methyl-4-hydroxyphenyl)sulfoxide 
     bis(4-hydroxyphenyl)sulfoxide. 
     Another group of dihydric aromatic compounds which may be used in the practice of the invention includes the dihydroxyaryl sulfones such as, for example: 
     bis(3,5-diisopropyl-4-hydroxyphenyl)sulfone 
     bis(3,5-methyl-5-ethyl-4-hydroxyphenyl)sulfone 
     bis(3-chloro-4-hydroxyphenyl)sulfone 
     bis(3,5-dibromo-4-hydroxyphenyl)sulfone 
     bis(3,5-dimethyl-4-hydroxyphenyl)sulfone 
     bis(3-methyl-4-hydroxyphenyl)sulfone 
     bis(4-hydroxyphenyl)sulfone. 
     Another group of dihydric aromatic compounds useful in the practice of the invention includes the dihydroxydiphenyls: 
     3,3&#39;,5,5&#39;-tetrabromo-4-4&#39;-dihydroxydiphenyl 
     3,3&#39;-dichloro-4,4&#39;-dihydroxydiphenyl 
     3,3&#39;-diethyl-4,4&#39;-dihydroxydiphenyl 
     3,3&#39;-dimethyl-4,4&#39;-dihydroxydiphenyl 
     p,p&#39;-dihydroxydiphenyl. 
     Another group of dihydric aromatic compounds which may be used in the practice of the invention includes the dihydric phenol ethers: 
     bis(3-chloro-5-methyl-4-hydroxyphenyl)ether 
     bis(3,5-dibromo-4-hydroxyphenyl)ether 
     bis(3,5-dichloro-4-hydroxyphenyl)ether 
     bis(3-ethyl-4-hydroxyphenyl)ether 
     bis(3-methyl-4-hydroxyphenyl)ether 
     Other dihydric aromatic compounds of interest include the phthalein type bisphenols which are disclosed in U.S. Pat. Nos. 3,035,021; 3,036,036; 3,036,037; 3,036,038; and 3,036,039. 
     It is, of course, possible to employ a mixture of two or more different dihydric aromatic compounds in preparing the thermoplastic carbamate polymers of the invention. 
     Examples of known carbonate compounds which are useful in this invention are ##STR3## 
     Suitable organophosphorous compounds useful in this invention are exemplified by the following formulas: 
     
         R.sub.1 -P(OR.sub.2)OR.sub.3                               I. 
    
     
         R.sub.1 O-P(OR.sub.2)OR.sub.3                              II. 
    
     
         R.sub.3 O(R.sub.2 O)P-R.sub.4 -P(OR.sub.2)OR.sub.3         III. 
    
     where 
     R 1 , R 2 , R 3  are selected from the group consisting of alkyl, cycloalkyl, aralkyl, and alkaryl radicals having 1 to 10 carbon atoms; 
     R 4  is an alkylene, cycloalkylene or an arylidene group having 1-12 carbon atoms. 
     Examples of compounds within the scope of the foregoing formulas are: 
     tetrakis (2,4-ditertiarybutylphenyl) 4,4&#39;-biphenylylenediphosphonite, 
     tris(2,4-di-tertiary-butylphenyl)phosphite, diphenyl benzene phosphonite, 
     dinonylphenyl benzene phosphonite, 
     didecyl benzene phosphonite, 
     di(4-tertiary butyl phenyl) 2 nonylphenyl phosphite, 
     octyl di(4-tertiary butyl phenyl) phosphite, 
     diisopropyl phenyl phosphite, 
     butyl diphenyl phosphite, 
     didecyl phenyl phosphite, 
     tris(4-tertiary butyl phenyl) phosphite, 
     tris phenyl phosphite, and 
     tris octyl phosphite. 
    
    
     EXAMPLE 1 
     (DB 22872 pg. 4 &amp; 10) 
     To 908 grams of a 2,2-bis(4-hydroxyphenyl)propane (Bisphenol-A) polycarbonate resin was added the following solutions of additives in 100 ml of acetone. 
     1. 0.908 grams of tetrakis-(2,4-di-tert-butylphenyl)-4,4&#39;-biphenylylenediphosphonite. (Control B). 
     2. 1.816 grams of 3,3&#39;-isopropylidene bis(p-phenyleneoxy) di-1,2-carbonato propane. (Control C.) 
     3. The combination of No. 1 and No. 2. (Example 1) 
     The formulated powder was dried in a vacuum oven at 125° C. for approximately 16 hours. The dried powder is extruded at 600° F. into a strand which is comminuted into pellets. A portion of the sample is molded at 575° F. into optical test discs two inches in diameter by one-eighth inch in thickness. As a control, an unformulated sample of the same lot of polycarbonate powder is taken through the same procedures. The discs are tested for yellowness in accordance with ASTM Method D-1925. The remainder of the sample is reextruded @ 600° F. into a strand and comminuted into pellets for two additional runs. This is again followed by making of the samples into test discs at 575° F. The samples are then re-tested for yellowness. 
     All additive amounts in Table I are based on the weight of the polycarbonate resin. In each case, the Yellowness Index Test is run at room temperature. The results are shown in Table I: 
     
                       TABLE I______________________________________             Yellowness             Index of Test Discs               After 1 After 3               Sample  Sample               Extru-  Extru-  %RUNS WITH POLYCARBONATE               sion    sions   Increase______________________________________Control A (no additives)               5.2     9.0     73.07Control B1000 ppm tetrakis (2,4-di-               3.3     5.7     42.1tertbutylphenyl)4,4&#39;-bi-phenylylenediphosphonitewith PCControl C2000 ppm 3,3&#39;-Isopropylidene               4.0     6.2     35.4bis(p-phenyleneoxy)di-1,2-carbonato propane with PCExample 1 (with both additives)               3.4     4.5     24.4______________________________________ 
    
     EXAMPLE 2 
     (DB 22872 pg. 4 &amp; 10) 
     Example 1 was repeated except that 0.2% of 1,2-carbonato-3-toloxypropane is employed in place of the dicarbonate. The samples were subjected to ASTM test method D-1003 for determining light transmission of the sample. The higher the percent light transmittance, the better is the clarity of the sample. The results are shown in Table II: 
     
                       TABLE II______________________________________             % Light             Transmission             of Test Discs               After 1 After 3               Sample  Sample               Extru-  Extru-  %RUNS WITH POLYCARBONATE               sion    sions   Decrease______________________________________Control D100 ppm tetrakis (2,4-di-tert-               88.7    86.1    2.93butylphenyl)4,4&#39;-biphenylyl-enediphosphonite with PCControl E2000 ppm 1,2-carbonato-3-               88.9    85.6    3.71toloxypropane with PCExample 2 (with both additives)               89.1    87.5    1.79______________________________________ 
    
     EXAMPLE 3 
     (DB 22872 pg. 4 &amp; 10) 
     Example 2 was repeated except that 0.1% or 1000 ppm tris(2,4-di-t-butylphenyl)phosphite is employed in place of the diphosphonite. The results are shown in Table III: 
     
                       TABLE III______________________________________             % Light             Transmission             of Test Discs               After 1 After 3               Sample  Sample               Extru-  Extru-  %RUNS WITH POLYCARBONATE               sion    sions   Decrease______________________________________Control F1000 ppm of tris(2,4-di-               89.1    86.5    2.91t-butylphenyl)phosphiteControl E2000 ppm 1,2-carbonato-3-               88.9    85.6    3.71toloxypropane with PCExample 3           88.7    87.3    1.57(with both additives)______________________________________ 
    
     EXAMPLE 4 
     To 454 grams of a 2,2-bis(4-hydroxyphenyl) propane (Bisphenol-A) polycarbonate resin is applied any of the following solutions of additives in 100 ml of acetone: 
     1. 0.454 gm of tetrakis-(2,4-di-tert-butylphenyl)4,4&#39;-biphenylylenediphosphonite. (Control F). 
     2. 0.908 gm of 3,4-carbonate-cyclohexyl-methyl-3,4-carbonatecyclohexane carboxylate. (Control G). 
     3. The combination of No. 1 and No. 2. (Example 4). 
     The formulated resin is dried in a vacuum oven at 250 F. for approximately 16 hours. The dried resin is extruded at 575 F. into a strand which is comminuted into pellets. A portion of the sample is molded at 575 F. into optical test discs two inches in diameter by one-eighth inch in thickness. As a control, an unformulated sample of the same resin is taken through the same procedure. The discs are tested for yellowness in accordance with ASTM Method D-1925. After oven aging for 500 hours at 284 F., the samples are retested for yellowness. 
     The amount of the additives used is based on the weight of the polycarbonate resin. In each case, the Yellowness Index Test is run at room temperature. The results are as follows: 
     
                       TABLE IV______________________________________        Yellowness Index of Test Discs                After 500 hrs. at        Initial 284° F.______________________________________Control F0.1% tetrakis-(2,4-di-          4.1       12.5tert-butylphenyl)4,4&#39;-biphenylylene-diphos-phoniteControl G0.1% 3,4-carbonato-          7.3       25.8cyclohexylmethyl-3,4-carbonato cyclohexanecarboxylateExample 4 (with both          3.4       10.9additives)Control H (no additive)          5.8       18.2______________________________________