Stabilized polycarbonate compositions

Polycarbonates are heat stabilized by the incorporation of a dioxolane compound having a boiling point greater than about 250.degree. C. The amount of dioxolane compound used is from 100 to 10,000 parts per million.

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 2-keto-1,3-dioxolane 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 (2-keto-1,3-dioxolane) 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 also 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. 
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 
2-keto-1,3-dioxolane compound having a boiling point greater than about 
250.degree. C. 
The amount of the dioxolane compound used herein can range from 100 to 
10,000 parts per million with the preferred amount being 500 to 5,000 
parts per million. 
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 oxyalkyl 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(4-hydroxyphenyl)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 dihydrocydiphenyls: 
3,3',5,5'-tetrabromo-4-4'-dihydroxydiphenyl 
3,3'-dichloro-4,4'-dihydroxydiphenyl 
3,3'-diethyl-4,4'-dihydroxydiphenyl 
3,3'-dimethyl-4,4'-dihydroxydiphenyl 
p,p'-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 carbonate 
polymers of the invention. 
Examples of known 2-keto-1,3-dioxolane compounds which are useful in this 
invention are 
##STR3## 
R is H or an alkyl group of 1-4 carbons. 
##STR4## 
R is aryl or alkyl groups R' is the same or different aryl or alkyl 
groups. 
##STR5## 
R is H or an alkyl group of 1-4 carbons. 
##STR6## 
R is phenylene, --(CH.sub.2).sub.n, where n is 1 to 10. 
##STR7## 
where n is 0 to 10 
R is H or CH.sub.3. 
##STR8## 
where n is 1 to 10.

EXAMPLE 1 
1 gram of 2,2-bis[p-(2-keto-1,3-dioxolanyl-4-methoxy) phenyl] propane (BDP) 
was dissolved in 100 ml of heptane and mixed with 500 grams of a powdered 
bisphenol A polycarbonate having a weight average molecular weight of 
about 30,000. 
The treated powder was dried in a vacuum oven at 125.degree. C. for 16 
hours. The dried powder was extruded and chopped in a conventional twin 
screw extruder having a barrel temperature of 316.degree. C. (600.degree. 
F.) and a die temperature of 196.degree. C. (385.degree. F.). 
A sample of the pellets from the extruder was molded into optical disks 2 
inches (5.08 cm) in diameter by 1/8 inch (0.317 cm) thick at 301.6.degree. 
C. (575.degree. F.). A control sample without the additive was given the 
identical treatment. The discs were measured for light transmittance and 
yellowness index. The results are given in Table I. 
TABLE I 
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% Light ASTM D-1925 
Sample Transmittance 
Yellowness Index 
______________________________________ 
Control I 88.5 5.0 
(no additive) 
Ex. 1 (BDP) 89.2 4.2 
2,000 ppm 
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EXAMPLES 2 AND 3 
Following the procedures of Example 1, 908 grams of the same polycarbonate 
was treated with 1.816 grams of the additives of Table II and pelletized. 
Samples of pellets were molded after one extrusion and after three 
extrusions. The results are set forth in Table II. 
TABLE II 
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ASTM D-1925 
Yellowness Index of Test Discs 
After 1 After 3 
Sample Extrusion 
Extrusions 
______________________________________ 
Ex. 2 BDP 2,000 ppm 
4.0 6.2 
Ex. 3 4-p-toluyloxy 
4.3 8.4 
methyl-2-keto- 
1,3-dioxolane 
2,000 ppm 
Control 1 (no additive) 
5.2 9.0 
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EXAMPLE 4 
A powdered commercial polycarbonate resin containing no additives (NOVAREX) 
in the amount of 3,300 grams was mixed with 132 ml of a heptane solution 
containing 2.5 weight percent of 
2,2-bis[p-(2-keto-1,3-dioxolanyl-4-methoxy) phenyl] propane to give a 
polycarbonate resin containing 1,000 parts per million of the additive. 
The resin mixture was vacuum dried at 120.degree. C. for 6 hours. The 
resin was then extruded eight times at 600.degree. F. (316.degree. C.) at 
30 rpm through a one-inch (2.54 cm) extruder. After each extrusion, 300 
gram samples were injection molded into test disks at 575.degree. F. 
(301.5.degree. C.) and 12,000 psi. (82.68 MPa) 
The resin without stabilizer had a yellowness index of 2.9 before 
extrusion. The resin with stabilizer had an yellowness index of 2.8 before 
extrusion. The results after eight extrusions for both are given in Table 
III. 
TABLE III 
______________________________________ 
% Light ASTM D-1925 
Sample Transmittance 
Yellowness Index 
______________________________________ 
Control 72.7 31.25 
Example 4 77.05 20.75 
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