The present invention provides polycarbonates stabilized against .gamma.-radiation and their use for the production of medical equipment.

The present invention provides thermoplastic aromatic polycarbonates based 
on diphenols of the formula (I) 
##STR1## 
wherein 
X is a single bond, C.sub.1 -C.sub.5 alkylene, C.sub.2 -C.sub.5 alkylidene, 
C.sub.5 -C.sub.6 cycloalkylene, C.sub.5 -C.sub.12 cycloalkylidene, --S--, 
--O--, 
##STR2## 
--SO.sub.2 --, --SO-- or a residue of the formula 
##STR3## 
and 
R is H and/or C.sub.1 -C.sub.3 alkyl 
with a content of sulphonamides of the formula (II) 
##STR4## 
wherein 
R.sup.1 is a C.sub.1 -C.sub.8 alkyl, C.sub.5 -C.sub.6 cycloalkyl or a 
C.sub.6 -C.sub.10 aryl residue, 
R.sup.2 and R.sup.3 are the same or different and are H, a C.sub.1 -C.sub.8 
alkyl, phenyl or a C.sub.5 -C.sub.6 cycloalkyl, 
in amounts of from 0.001 wt. % to 5 wt. %, preferably from 0.005 wt. % to 1 
wt. % and in particular from 0.01 wt. % to 0.8 wt. %, in each case based 
on 100 wt. % of aromatic polycarbonate and optionally with a content of 
aliphatic or cycloaliphatic mono- or polyalcohols or derivatives thereof 
in amounts from 0.001 to 2 wt. %, preferably from 0.001 wt. % to 1.5 wt. 
%, again based in each case on 100 wt. % of aromatic polycarbonate. 
The polycarbonates according to the invention are stabilized against 
.gamma.-radiation by the additives and are thus suitable in various ways 
for medical applications, in particular for producing equipment or 
equipment parts which can be sterilized by ionizing radiation before or 
after use without excessive yellowing of the equipment taking place. 
The present invention thus also provides the use of the polycarbonates 
stabilized according to the invention for producing medical equipment or 
parts of medical equipment. 
Thermoplastic aromatic polycarbonates within the scope of the present 
invention comprise both homopolycarbonates and copolycarbonates; the 
polycarbonates may be linear or branched in a known manner. 
Some, up to 80 mol %, preferably from 20 mol % to 50 mol %, of the 
carbonate groups in the polycarbonates suitable according to the invention 
may be replaced by aromatic dicarboxylic acid ester groups. Polycarbonates 
of this kind, which contain both acid residues of carbonic acid and acid 
residues of aromatic dicarboxylic acids incorporated in the molecular 
chain are, accurately designated, aromatic polyester carbonates. For the 
sake of simplicity, in the present application they are subsumed under the 
heading of thermoplastic aromatic polycarbonates. 
Polycarbonates to be stabilized according to the invention are produced in 
a known manner from diphenols, carbonic acid derivatives, optionally chain 
terminators and optionally branching units, a portion of the carbonic acid 
derivatives being replaced by aromatic dicarboxylic acids or derivatives 
of aromatic dicarboxylic acids for the production of the polyester 
carbonates--specifically by aromatic dicarboxylic acid ester structural 
units determined by the carbonate structural units to be replaced in the 
aromatic polycarbonates. 
Details of the production of polycarbonates have been specified in hundreds 
of patent specifications for approximately 40 years. By way of example, 
reference is only made here to "Schnell" Chemistry and Physics of 
Polycarbonates", Polymer Reviews, Volume 9, Interscience Publishers, New 
York, London, Sydney 1964, to D. C. PREVORSEK, B. T. DEBONA and Y. KESTEN, 
Corporate Research Center, Allied Chemical Corporation, Morristown, N.J. 
07960, "Synthesis of Poly(ester Carbonate) Copolymers" in Journal of 
Polymer Science, Polymer Chemistry Edition, Vol 18, 75-90 (1980), to D. 
Freitag, U. Grigo, P. R. Muller, H. Nonvertue, BAYER AG, "Polycarbonates" 
in Encyclopedia of Polymer Science and Engineering, Volume 11, Second 
Edition, 1988, pages 648-718 and finally to Dres. U. Grigo, K. Kircher and 
P. R. Muller "Polycarbonate" in Becker/Braun, Kunststoff-Handbuch, Volume 
3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser 
Verlag Munchen, Vienna 1992, pages 117-299. 
The thermoplastic polycarbonates, including thermoplastic aromatic 
polyester carbonates have mean molecular weights M.sub.W (determined by 
measurement of the relative viscosity at 25.degree. C. in CH.sub.2 
Cl.sub.2 and a concentration of 0.5 g per 100 ml of CH.sub.2 Cl.sub.2) of 
from 12 000 to 120 000, preferably from 18 000 to 80 000 and in particular 
from 22 000 to 60 000. 
Diphenols suitable for the production of the polycarbonates to be 
stabilized according to the invention are, for example, hydroquinone, 
resorcinol, dihydroxydiphenyls, bis(hydroxyphenyl)alkanes, 
bis(hydroxyphenyl) cycloalkanes, bis(hydroxyphenyl)sulphides, 
bis(hydroxyphenyl)ethers, bis(hydroxyphenyl)ketones, 
bis(hydroxyphenyl)sulphones, bis(hydroxyphenyl) sulphoxides, 
.alpha.,.alpha.'-bis(hydroxyphenyl) diisopropylbenzenes, and 
ring-alkylated compounds thereof. 
Preferred diphenols are 4,4'-dihydroxydiphenyl, 
2,2-bis(4-hydroxyphenyl)propane, 2,4-bis(4-hydroxyphenyl)-2-methylbutane, 
1,1-bis(4-hydroxyphenyl)-p-diisopropylbenzene, and 
1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. 
Particularly preferred diphenols are 2,2-bis(4-hydroxyphenyl)propane, 
1,1-bis(4-hydroxyphenyl) cyclohexane and 
1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. 
These and other suitable diphenols are described, for example, in U.S. Pat. 
Nos. 3,028,635, 2,999,835, 3,148,172, 2,991,273, 3,271,367, 4,982,014 and 
2,999,846, in German laid-open patent applications 1 570 703, 2 063 050, 2 
036 052, 2 211 956 and 3 832 396, in the French Patent 1 561 518, in the 
monograph "H. Schnell, Chemistry and Physics of Polycarbonates, 
Interscience Publishers, New York 1964" and in the Japanese laid-open 
patent applications 62039/1986, 62040/1986 and 105550/1986. 
In the case of homopolycarbonates, only one diphenol is used, in the case 
of copolycarbonates, a plurality of diphenols are used. 
Suitable chain terminators are both monophenols and monocarboxylic acids. 
Suitable monophenols are phenol itself, alkylphenols such as cresols, 
p-tert. butylphenol, p-n-octylphenol, p-iso-octylphenol, p-n-nonylphenol 
and p-iso-nonylphenol. 
Suitable monocarboxylic acids are benzoic acid and alkylbenzoic acids. 
Preferred chain terminators are phenols of the formula (III) 
##STR5## 
wherein 
R is a branched or unbranched C.sub.8 - and/or C.sub.9 -alkyl residue. 
The amount of chain terminator to be used is 0.5 mol % to 10 mol %, based 
on moles of the diphenols respectively used. The chain terminator may be 
added before, during or after the phosgenation. 
Suitable branching units are the tri- or higher functional compounds known 
in polycarbonate chemistry, in particular those with three or more than 
three phenolic OH groups. 
Suitable branching units are, for example, phloroglucinol, 
4,6-dimethyl-2,4,6-tris(4-hydroxyphenyl)hepten-2, 
4,6-dimethyl-2,4,6-tris(4-hydroxyphenyl)heptane, 
1,3,5-tris(4-hydroxyphenyl)benzene, 1,1,1-tris(4-hydroxyphenyl)ethane, 
tris(4-hydroxyphenyl)phenylmethane, 
2,2-bis[4,4-bis(4-hydroxyphenyl)cyclohexyl]propane, 
2,4-bis(4-hydroxyphenylisopropyl)phenol, 2,6 
bis(2-hydroxy-5'-methylbenzyl)-4-methylphenol, 
2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane, 
hexa(4(4-hydroxyphenylisopropyl)phenyl)orthoterephalate, 
tetra(4-hydroxyphenyl)methane, 
tetra(4-(4-hydroxyphenylisopropyl)phenoxy)methane and 
1,4-bis(4',4"-dihydroxytriphenyl)methyl)benzene and 2,4-dihydroxybenzoic 
acid, trimesic acid, cyanuric chloride and 
3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindol. 
The amount of the branching units to be optionally used is 0.05 mol % to 2 
mol %, again based on moles of the respective diphenols used. 
The branching units may be either initially charged together with the 
diphenols and the chain terminators in the aqueous alkaline phase, or be 
added dissolved in an organic solvent, before the phosgenation. 
All these measures for producing polycarbonates are known to the person 
skilled in the art. 
Aromatic dicarboxylic acids suitable for producing polyester carbonates 
are, for example, orthophthalic acid, terephthalic acid, isophthalic acid, 
tert. butylisophthalic acid, 3,3'-diphenyldicarboxylic acid, 
4,4'-diphenyldicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 
3,4'-benzophenonedicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 
4,4'-diphenylsulphonedicarboxylic acid, 2,2-bis(4-carboxyphenyl)propane, 
trimethyl-3-phenylindane-4,5'-dicarboxylic acid. 
Of the aromatic dicarboxylic acids, terephthalic acid and/or isophthalic 
acid are particularly preferably used. Derivatives of dicarboxylic acids 
are dicarboxylic acid dihalides and dicarboxylic acid dialkyl esters, in 
particular dicarboxylic acid dichlorides and dicarboxylic acid dimethyl 
esters. 
The replacement of the carbonate groups by the aromatic dicarboxylic acid 
ester groups takes place substantially stoichiometrically and also 
quantitatively, so that the molar ratio of the coreactants is also 
reproduced in the final polyester carbonate. The aromatic dicarboxylic 
acid ester groups may be incorporated either randomly or in blocks. 
Preferred methods of producing the polycarbonates to be stabilized 
according to the invention are the known interface method and the known 
melt transesterification process. 
The carbonic acid derivative used is preferably phosgene in the first 
method, in the latter method preferably diphenylcarbonate. 
Catalysts, solvents, working up, reaction conditions etc. are adequately 
described and known in both cases. 
Preferred residues R.sup.1, R.sup.2 and R.sup.3 of the formula (II) are 
phenyl, methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl and cyclohexyl. 
Suitable sulphonamides of the formula (II) are, for example, 
triphenylsulphonamide, N,N-diphenyl methyl sulphonamide, N-methyl N-phenyl 
phenylsulphonamide and N,N-dimethyl phenyl sulphonamide. 
The aliphatic or cycloaliphatic mono- or polyalcohols suitable as additives 
are preferably C.sub.1 -C.sub.20 monoalcohols, aliphatic C.sub.2 -C.sub.20 
dialcohols, aliphatic C.sub.3 -C.sub.20 trialcohols and aliphatic C.sub.4 
-C.sub.20 tetraalcohols, cycloaliphatic C.sub.3 -C.sub.12 monoalcohols and 
cycloaliphatic C.sub.3 -C.sub.12 dialcohols. 
These mono- and polyalcohols are known in the literature (see, for example, 
Houben-Weyl, "Methoden der organischen Chemie", Volume 6/1a/1 "Alkohole 
I", Band 6/1a/2, "Alkohole II" and Volume 6/1b, "Alkohole III" Georg 
Thieme Verlag Stuttgart-New York, 1979, 1980 and 1984). 
Preferred monoalcohols are dodecanol, hexadecanol-(1), hexadecanol-(2), 
stearyl alcohol, octadecanol and eicosanol. 
Preferred polyalcohols are diols, triols, tetraols, pentaols and hexaols, 
in particular diols of the formula (IV) 
##STR6## 
wherein R.sup.3 .dbd.R.sup.4 .dbd.H, R.sup.5 .dbd.H or C.sub.1 -C.sub.4 
alkyl, n is an integer of from 1 to 36 and m is an integer of from 1 to 
1500, preferably from 2 to 1200 and in particular from 3 to 1000. 
Examples of this are ethylene glycol, 1,2-propane diol, 1,3-propane diol, 
1,2-butane diol, 1,3-butane diol, 1,4-butane diol, 2,3-butane diol, 
1,2-pentane diol, 1,5-pentane diol, 2,4-pentane diol, 1,2-hexane diol, 
1,6-hexane diol, 3-methyl-1,5-pentane diol, 2,5-hexane diol, 
1,2-cyclohexane diol, 1,4-cyclohexane diol, cyclohexyl-1,4-dimethanol, 2 
-methyl-2,4-pentane diol, 1,8-octane diol, 1,10-decane diol, 1,2-undecane 
diol, 1,2-dodecane diol, 1,12-dodecane diol, 1,2-hexadecane diol, 
1,2,5-pentane triol, 1,2,3-hexane triol, 1,2,6-hexane triol, 
2-(hydroxymethyl)-2-methyl-1,3-propane diol and 2,3,4,5,6,7-octane hexaol. 
Suitable derivatives of the mono- or polyalcohols suitable according to the 
invention are ethers, carboxylic acid esters, acetals, alkyl carbonates, 
epoxides, urethanes, phosphates, phosphonates, phosphites, phosphonites 
and siloxanes. 
These derivatives are also known in the literature, or are obtainable by 
processes known in the literature (see the relevant volumes of 
Houben-Weyl), "Methoden der organischen Chemie", Georg Thieme Verlag). 
Preferred derivatives are the ethers, carboxylic acid esters, acetals and 
alkyl carbonates of mono- or polyalcohols; examples of these are 
diethylene glycol, diethylene glycol diethyl ether, dipropylene glycol, 
tripropylene glycol, 1,3-diethoxy-2-propanol, 3,3'-oxibis(1,2-propane 
diol), 2,2'-oxibisbutane, the alkyl esters of undecanoic acid, dodecanoic 
acid, hexadecanoic acid, stearic acid and dodecanoic acid, glycerine 
monostearate, glycerine distearate, glycerine tristearate, 
1,1-bis(2,3-dioctadecanyloxypropyloxy)hexadecane, 
2,2-dicyclohexyloxypropane, 
acetoxy(4-(2-tetrahydropyranyloxy)pentyloxy)methane, 
acetoxydodecyloxymethane, 
acetoxy(3-(2-methyl-1,3-dioxolan-2-yl)-propyloxy) methane, ethylene 
carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, 
diisopropyl carbonate and dineopentylcarbonate. 
Derivatives particularly preferred are those of the Formula (IV) 
##STR7## 
wherein 
R.sup.3 and R.sup.4 may be the same or different, and may be C.sub.1 - to 
C.sub.30 -alkyl, either branched or unbranched, or acyl, silyl and/or 
pyranyl, 
R.sup.5 may be H or C.sub.1 - to C.sub.4 -alkyl, 
n may be an integer from 1 to 36 and 
m may be an integer from 1 to 1500, preferably from 2 to 1200 and in 
particular from 3 to 1000. 
The compounds of the formula (IV) may preferably have molecular weights of 
between 106 g/mol and 100 000 g/mol, particularly preferably between 150 
g/mol and 12 000 g/mol, very particularly preferably between 500 g/mol and 
10 000 g/mol. 
The sulphonamides to be used according to the invention and optionally the 
mono- or polyalcohols, or derivatives thereof, to be optionally used may 
be incorporated into the polycarbonates either simultaneously or 
successively at temperatures between 260.degree. and 380.degree. C. via 
the melts of the polycarbonates or via the solution of the polycarbonates 
in known solvents, such as CH.sub.2 Cl.sub.2 and/or chlorobenzene and 
subsequent evaporation of the solvent in a known manner. 
The present invention thus also provides a method for producing 
polycarbonates stabilized according to the invention which is 
characterized in that sulphonamides of the formula (II) 
##STR8## 
wherein 
R.sup.1 is a C.sub.1 -C.sub.8 -alkyl, C.sub.5 -C.sub.6 -cycloalkyl or a 
C.sub.6 -C.sub.10 -aryl residue, 
R.sup.2 and R.sup.3 are the same or different, and are H, a C.sub.1 
-C.sub.18 -alkyl, phenyl or a C.sub.5 -C.sub.6 -cycloalkyl, 
and optionally the aliphatic or cycloaliphatic mono- or polyalcohols or 
derivatives thereof are mixed with polycarbonates at temperatures between 
260.degree. and 380.degree. C. in the mixing devices conventional for 
this, for example kneaders or extruders, or in that the sulphonamides of 
the formula (II) and optionally the aliphatic or cycloaliphatic mono- or 
polyalcohols or derivatives thereof are dissolved together with 
polycarbonate in the known solvents, such as CH.sub.2 Cl.sub.2 and/or 
chlorobenzene and the mixtures thus obtained, of sulphonamides of the 
formula (II) and optionally aliphatic or cycloaliphatic mono- or 
polyalcohols or derivatives thereof, with the polycarbonates are isolated 
by subsequent evaporation of the solvent in a known manner. 
Suitable equipment for producing the polycarbonates stabilized according to 
the invention are, in the case in which incorporation is carried out via 
the polycarbonate melt, kneaders or extruders, in the case in which 
incorporation is carried out via the polycarbonate solution, boilers 
having mixing or stirring devices. 
The irradiation of polycarbonate mouldings by means of ionizing radiation, 
such as .gamma.-radiation or electron radiation is carried out in order to 
sterilize articles such as dialyzers for blood dialysis, disposable 
syringes etc. before their medical use. In the process, irreversible 
damage, for example in the form of yellowing of the polycondensate, always 
occurs. In order to reduce or avoid this damage, the polycondensates have 
to be stabilized before irradiation. 
According to U.S. Pat. No. 4,007,150 and U.S. Pat. No. 4,041,003, it is 
known to add perfluoroalkanesulphonamides to polycarbonates as demoulding 
aid. 
According to U.S. Pat. No. 4,477,637, it is known to add sulphonamides to 
special alkylated polycarbonates. The sulphonamides act as flame 
retardants. 
Polycarbonates with sulphonanilide end groups are known according to U.S. 
Pat. No. 4,471,104. These polycarbonates are distinguished by improved 
flame resistance. 
Polycarbonates with N-alkyl perfluoroalkylsulphonamide end groups which 
have improved processability are known according to U.S. Pat. No. 
4,503,213. 
Flame-resistant polycarbonates with co-condensed bissulphonylamide 
structural units are known according to EP-O 0 071 125. 
Colour-stable polycarbonates are known according to U.S. Pat. No. 
4,880,855, which contain as additives, inter alia, thiols, thioethers, 
cyclic thioethers and sulphones. 
The sulphonamides to be added according to the invention, however, have the 
technical advantage of remaining stable at high processing temperatures 
and producing no yellowing due to processing, with, at the same time, an 
outstanding colour-stabilizing effect with respect to ionizing radiation. 
According to U.S. Pat. No. 5,214,078, radiation-resistant polycarbonates 
are known which contain polyetherpolyols and aromatic disulphides. The 
sulphonamides to be added according to the invention, by contrast, have, 
by virtue of their considerably higher thermal stability, a significantly 
greater processing range as regards the height of the processing 
temperature and the colour stability in the melt in the event of machine 
stoppages during injection moulding. As a result, only a very small amount 
of reject material is produced on start up of the respective injection 
moulding machine after standstill in the melt. 
Radiation-resistant polycarbonates are also known according to EP-A-0 572 
889, which contain a multiplicity of sulphur compounds and optionally 
alcohols or derivatives thereof as stabilizers. The sulphonamides to be 
added according to the invention have the same advantages with respect to 
these as with respect to the aromatic disulphides described according to 
U.S. Pat. No. 5,214,078. 
The polycarbonates stabilized according to the invention are neither 
previously described nor made obvious by this prior art. 
Rather, it was surprising that the compounds of the formula (II), in 
particular in combination with mono- or polyalcohols or with derivatives 
thereof have an exceptional stabilizing effect on polycarbonates or on 
polyester carbonates against the effect of .gamma.-radiation, so that they 
cause yellowing of the particular polycondensate to be stabilized to a 
significantly less extent than the already known stabilizer systems of the 
current prior art, which fact can be demonstrated by determining the 
difference in the Yellowness Index of the polycondensate mixture according 
to the invention after and before .gamma. irradiation. 
The polycarbonates stabilized against .gamma.-radiation according to the 
invention may also contain conventional additives such as thermal 
stabilizers, UV absorbers, flow modifiers, demoulding aids, plasticizers, 
antistatic agents, flame retardants and/or colorants and, for special 
applications, also fillers such as glass fibres or glass beads. The 
additives are mixed in in the amounts conventional for polycarbonates, 
under conventional conditions and on conventional machines. They may be 
mixed in before, during or after the stabilization according to the 
invention by the sulfonamides and optionally alcohols or derivatives 
thereof. 
The processing of the polycarbonates stabilized according to the invention 
into mouldings of any kind, in particular medical equipment, is carried 
out on known injection moulding machines and extrusion machines. 
The mouldings made of polycarbonates stabilized according to the invention 
may, apart from in medicine, also be used in applications involving food 
contact, that is to say as packaging materials of any kind and in all 
other fields of application conventional for polycarbonates.