Tetraphenols and their use as polycarbonate branching agents

Branched polycarbonates having properties suitable for blow molding are prepared by equilibrating a linear or branched aromatic polycarbonate with certain tetraphenols, especially 2,2,5,5-tetrakis (4-hydroxyphenyl)hexane and 1,1-bis(p-hydroxyphenyl)ethyl!-phenyl ether.

CROSS REFERENCE TO RELATED APPLICATION 
This application claims priority from provisional application Ser. No. 
60/021,749, filed Jul. 15, 1996. 
BACKGROUND OF THE INVENTION 
This invention relates to the preparation of branched polycarbonates and to 
reagents suitable for use therein. 
Branched polycarbonates are becoming of increasing importance for many 
purposes, especially in blow molding operations as exemplified by the 
fabrication of water bottles. Their non-Newtonian properties are extremely 
important under blow molding conditions. Branched polycarbonates useful 
for this purpose are typically prepared by the incorporation of a 
hydroxyaromatic compound having more than two hydroxy groups into a 
conventional polycarbonate-forming reaction mixture. 
Thus, U.S. Reissue Pat. No. 27,682 describes the preparation of branched 
polycarbonates in a conventional interfacial reaction or from 
chloroformates. U.S. Pat. No. 4,415,725 describes a similar method which 
may employ a carbonyl halide such as phosgene (as in the interfacial 
procedure), a haloformate or a diarylcarbonate. U.S. Pat. No. 5,021,521 
describes the preparation of branched polycarbonates by reactive extrusion 
of a linear or branched polycarbonate with a branching agent of the type 
described above. 
Many of the branching agents considered useful for the preparation of 
branched polycarbonates are trisphenols. The most common of these is 
1,1,1-tris(4-hydroxyphenyl) ethane. Others are disclosed in the 
aforementioned patents with particular reference to Re Pat. No. 27,682. 
It has been found, however, that the branched polycarbonates obtained from 
trisphenols in a reactive extrusion procedure do not have optimum 
viscosity characteristics for blow molding. The key properties for this 
purpose are a relatively low viscosity during high shear melt mixing such 
as extrusion, and a high viscosity under low shear conditions such as 
those encountered by a parison before and during blow molding. 
The melt strengths and melt viscosities of trisphenol-branched 
polycarbonates prepared by equilibration are too low to permit their 
fabrication into parisons. Only by the employment of very high molecular 
weight polycarbonates, such as those having weight average molecular 
weights greater than 175,000 relative to polystyrene, is it possible to 
produce branched products which even approach the desired blow molding 
properties in viscosity characteristics at low shear. 
It has been thought that the use of tetraphenols rather than trisphenols in 
reactive extrusion processes might improve the viscosity characteristics 
of the branched products. However, many of the tetraphenols disclosed as 
useful for this purpose in the art previously identified have serious 
disadvantages. These include the presence of benzylic hydrogen atoms, 
which decrease their thermal and oxidative stability; the presence of 
ortho-substitution, which decreases reactivity; and a characteristic 
bright color due to a high degree of conjugation, which carries over into 
the polymeric product and makes it unattractive for use. 
The search continues, therefore, for tetraphenolic branching agents which 
afford polycarbonates with the desired viscosity characteristics and which 
do not suffer from other serious deficiencies. 
SUMMARY OF THE INVENTION 
In one of its aspects, the invention is a method for producing a branched 
polycarbonate which comprises contacting a linear or branched aromatic 
polycarbonate, in the presence of a carbonate equilibration catalyst, with 
a tetraphenol of the formula 
##STR1## 
wherein R.sup.1 is C.sub.1-4 primary alkyl, Z is C.sub.1-4 alkylene or 
--A.sup.2 --Q--A.sup.2 --, each of A.sup.1 and A.sup.2 is an unsubstituted 
or substituted p-phenylene radical and Q is a single bond or a divalent 
linking group. 
Another aspect is a branched polycarbonate comprising branching structural 
units of the formula 
##STR2## 
wherein each of A.sup.1 and A.sup.2 is an unsubstituted or substituted 
p-phenylene radical and R.sup.1 is C.sub.1-4 primary alkyl. 
Still another aspect is tetraphenols of the formula 
##STR3## 
wherein A.sup.1, A.sup.2 and R.sup.1 is C.sub.1-4 are as previously 
defined. 
DETAILED DESCRIPTION 
Preferred Embodiments 
The tetraphenols used to prepare branched polycarbonates by reactive 
extrusion, in accordance with the method of this invention, have formula I 
in which each of A.sup.1 and A.sup.2 is an unsubstituted or substituted 
p-phenylene radical. Typical substituents on the substituted radicals are 
halogen and especially chlorine atoms and alkyl groups, normally C.sub.1-4 
primary alkyl groups and especially methyl. The preferred compounds, 
however, are those in which Al and A.sup.2 are unsubstituted. 
The R.sup.1 radicals are also primary alkyl. Most often, they are methyl or 
ethyl and especially methyl. 
The Z radical may be a C.sub.1-4 alkylene radical or a bisphenol-derived 
radical of the formula --A.sup.2 --Q--A.sup.2 --. Q may be a single bond 
or a linking group such as oxygen, sulfur, SO.sub.2, methylene or 
ethylene. 
Various compounds of formula I in which Z is alkylene are known, being 
disclosed, for example, in the aforementioned U.S. Pat. No. 4,415,725. The 
preferred compound of this type is 
2,2,5,5-tetrakis(4-hydroxyphenyl)hexane, in which A.sup.1 is unsubstituted 
phenylene, R.sup.1 is methyl and Z is ethylene. 
The compounds of formula I in which Z is a bisphenol-derived radical are 
novel compounds. They may be prepared by the acylation of a compound of 
the formula HA.sup.2 --Q--A.sup.2 H under Friedel-Crafts conditions to 
yield a 4,4'-diacylated compound, which may then undergo reaction with a 
phenol of the formula HA.sup.1 OH. The second of these reactions is 
similar to the reaction of phenol with acetone to produce 
2,2-bis(4-hydroxyphenyl) propane, also known as "bisphenol A". The 
acylation reaction is carried out under typical Friedel-Crafts conditions 
as disclosed, for example, in Soviet Union Patent 643,492. 
The preparation of the novel tetraphenols of this invention is illustrated 
by the following example.

EXAMPLE 1 
A 500-ml three-necked flask equipped with a 100-ml addition funnel having 
an equalizer side arm and an overhead mechanical stirrer was charged with 
65 g (500 mmol) of aluminum chloride and 170 ml of 1,2-dichloroethane. The 
resulting slurry was cooled to 20.degree. C. under nitrogen and stirred 
while 17 g (100 mmol) of phenyl ether was added dropwise over several 
minutes, whereupon the slurry turned orange in color. Acetic anhydride, 24 
g (240 mmol), was then added dropwise over 1 hour with continued stirring, 
while the temperature was maintained at about 20.degree. C. The resulting 
purple solution was stirred for an additional 30 minutes while warming to 
room temperature, and was poured over ice. The organic phase was separated 
and washed with water, 2% aqueous sodium hydroxide solution and water, and 
was dried over magnesium sulfate. Upon filtration, concentration and 
purification by recrystallization from ethanol, the desired 4-acetylphenyl 
ether was obtained in 94% yield. 
A 100-ml three-necked flask equipped with an overhead stirrer was charged 
with 57 g (610 mmol) of phenol, 7.7 g (300 mmol) of 4-acetylphenyl ether, 
4.3 g (310 mmol) of boron trifluoride-ethyl ether complex and 280 mg of 
3-mercaptopropionic acid. The mixture was heated under vacuum (about 20 
torr) at 55.degree. C. for 8 hours, with stirring, after which the 
reaction was shown by liquid chromatography to be about 85% complete. 
Stirring under vacuum was continued for 14 hours. 
The reaction mixture was poured into water and ethyl acetate was added. The 
organic layer was separated, washed with water, saturated aqueous sodium 
bicarbonate solution, 1% aqueous hydrochloric acid solution and water. The 
organic phase was separated and most of the unreacted phenol was removed 
by vacuum stripping, after which the residue was redissolved in ethyl 
acetate and stirred with 200 ml of 5% aqueous sodium hydroxide solution, 
resulting in precipitation of the sodium salt of the tetraphenol. The salt 
was collected by filtration, reslurried in water, acidified and extracted 
again with ethylacetate. The organic extracts were dried over magnesium 
sulfate and concentrated to yield a light brown gum, which was 
crystallized from a chloroform-acetonitrile mixture. The product was 11.2 
grams (75% of theoretical) of an off-white solid. Recrystallization from 
an acetone-hexane mixture yielded the desired pure 
1,1-bis(p-hydroxyphenyl)ethyl!phenyl ether having a melting point of 
172.degree.-174.degree. C. 
The aromatic polycarbonates employed in the branched polycarbonate 
preparation method of this invention generally comprise structural units 
of the formula 
##STR4## 
wherein R.sup.2 is an aromatic organic radical. Preferably, R.sup.2 is an 
aromatic organic radical and still more preferably a radical of the 
formula: 
EQU --A.sup.3 --Y--A.sup.4 --, (V) 
wherein each of A.sup.3 and A.sup.4 is a monocyclic divalent aryl radical 
and Y is a bridging radical in which one or two carbon atoms separate 
A.sup.3 and A.sup.4. Such radicals frequently are derived from 
dihydroxyaromatic compounds of the formula HO--A.sup.3 --Y--A.sup.4 --OH. 
For example, A.sup.3 and A.sup.4 typically represent unsubstituted 
phenylene or substituted derivatives thereof. The bridging radical Y is 
most often a hydrocarbon group and particularly a saturated group such as 
methylene, cyclohexylidene or isopropylidene. The most preferred 
dihydroxyaromatic compound is bisphenol A, in which each of A.sup.3 and 
A.sup.4 is p-phenylene and Y is isopropylidene. 
Previously branched polycarbonates may be employed in place of or in 
admixture with the linear polycarbonates. Such previously branched 
polycarbonates may be prepared as described earlier, using trisphenols or 
tetraphenols as branching agents in interfacial, melt or reactive 
extrusion polycarbonate-forming reactions. 
As carbonate equilibration catalysts, various bases and Lewis acids may be 
employed. Numerous compounds suitable for this purpose are disclosed in 
the aforementioned U.S. Pat. No. 5,021,521, the disclosure of which is 
incorporated by reference herein. Of those compounds, the ones preferred 
in most instances are the tetraphenylborate salts, and especially the 
quaternary ammonium and quaternary phosphonium tetraphenylborates. 
It is frequently more preferred, however, to employ catalysts more readily 
susceptible than the tetraphenylborates to decomposition under reactive 
exclusion conditions, so that residues which may promote degradation and 
discoloration do not remain in the polycarbonate. A class of compounds 
which meet this requirement is the genus of quaternary bisphenolates 
having the molecular formula 
EQU H.sub.3 Q(OA.sup.5).sub.2 Y!.sub.2, (VI) 
wherein A.sup.5 is unsubstituted p-phenylene, Q is a monocationic carbon- 
and nitrogen-containing moiety containing 9-34 atoms and Y is as 
previously defined. Such compounds are disclosed and claimed in copending, 
commonly owned application Ser. No. 08/768,871. Now U.S. Pat. No. 
5,756,843 
The Q radical in the quaternary bisphenolates of formula VI is a 
monocationic carbon- and nitrogen-containing moiety; i.e., a moiety having 
a single positive charge. It may be a tetraalkylammonium moiety wherein 
the alkyl groups contain 2-5 carbon atoms, as illustrated by 
tetraethylammonium, tetra-n-butylammonium and diethyldi-n-butylammonium. 
Preferably, however, it is a hexaalkylguanidinium moiety such as 
hexaaethylguanidinium, hexa-n-butylguanidinium or 
tetraethyldi-n-butylguanidinium. The atom content of 9-34 atoms includes 
both carbon and nitrogen atoms and its size is governed by the fact that 
the tetraethylammonium cation contains 8 carbon atoms and one nitrogen 
atom for a total of 9, while the hexapentylguanidinium cation contains 31 
carbon atoms and 3 nitrogen atoms for a total of 34. 
Quaternary bisphenolates of formula VI may be prepared by the reaction of a 
bisphenol of the formula (HOA.sup.5).sub.2 Y with an alkali metal 
hydroxide and a quaternary salt of the formula Q.sup.+ X.sup.-. The X 
value in the quaternary salt is halide, preferably bromide or chloride and 
most preferably chloride. Typical reaction temperatures are in the range 
of about 10.degree.-125.degree. and preferably about 10.degree.-50.degree. 
C. An inert atmosphere such as nitrogen or argon may be employed. 
The quaternary bisphenolate-forming reaction takes place in an aqueous 
medium, most often also containing a C.sub.1-3 alkanol and preferably 
methanol. The quaternary bisphenolate is usually insoluble in water but 
soluble in the alkanol, and can be isolated by precipitation with an 
excess of water. 
It is generally found convenient to initially form an alcoholic mixture of 
bisphenol and alkali metal hydroxide, whereupon the bisphenol dissolves as 
the alkali metal salt, and to add thereto an aqueous-alcoholic solution of 
the quaternary salt. Another alternative is to combine the bisphenol and 
quaternary salt and gradually add aqueous alkali metal hydroxide solution 
thereto. In the water-alkanol embodiment, ambient temperatures in the 
range of about 20.degree.-30.degree. C. are generally preferred 
In still another procedure, a non-polar organic solvent such as toluene is 
employed. An aqueous alkaline solution of the quaternary salt is added 
gradually to a combination of the bisphenol and refluxing solvent. The 
product precipitates out and can be purified by washing with water. 
Further purification of product obtained by any of these methods can be 
achieved by recrystallization, most often from an alkanol and preferably 
methanol. 
Reactant proportions are not critical in the method for preparing the 
quaternary bisphenolates. This is apparent from the fact that their 
formation was initially discovered in mixtures comprising the 
non-stoichiometric proportions of 2 moles of alkali metal hydroxide, 2 
moles of hexaalkylguanidinium chloride and 1 mole of bisphenol. For 
optimum yield, however, a bisphenol:quaternary salt:alkali metal hydroxide 
molar ratio of 1:2:0.5-1.5 and especially 1:2:1 is preferred. 
The preparation of quaternary bisphenolates is illustrated by the following 
examples. "Catalyst solution" in this example is an aqueous solution of 
28.54% (by weight) hexaethylguanidinium chloride and 10.09% sodium 
chloride. 
EXAMPLE 2 
A 5-l round-bottomed flask was purged with nitrogen and charged with 228.29 
g (1 mole) of bisphenol A, 20.29 g (0.5 mole) of sodium hydroxide and 300 
ml of methanol. The resulting solution was magnetically stirred under 
nitrogen. A blend of 462.26 g of catalyst solution (0.5 mole of 
hexaethylguanidinium chloride) and about 175 ml of methanol was added 
rapidly, whereupon a solid immediately precipitated. Methanol, 900 ml, was 
added with stirring to redissolve all of the solids. 
Stirring was continued for 15 minutes, after which 1100 ml of water was 
added to reprecipitate the solids. The flask was cooled to 20.degree. C. 
in ice and vacuum filtered. The filter cake was washed with 1200 ml of 
water and dried in a vacuum oven at 75.degree. C., yielding 335.44 g 
(98.1% crude yield) of a white solid. Recrystallization from methanol 
followed by vacuum drying yielded 244.14 g (71.4% of theoretical) of 
purified product in the form of colorless crystals with a melting point of 
208.degree.-210.degree. C. The purified product was shown by elemental 
analysis, atomic adsorption analysis and proton nuclear magnetic resonance 
spectroscopy to be the desired hexaethylguanidinium bisphenolate, having 
the stoichiometric proportions of three hydrogen atoms, one 
hexaethylguanidinium cation moiety and two bisphenol A dianion moieties. 
The polycarbonate equilibration reaction takes place when an intimate 
mixture of the linear or branched polycarbonate and the catalyst is heated 
in the melt, as in a batch melt reactor or an extruder, at temperatures in 
the range of about 250.degree.-350.degree. C. The proportions of catalyst 
and branching agent are ordinarily about 10-500 ppm by weight and about 
0.1-2.0 mole percent, based on structural units in the polycarbonate, 
respectively. When the catalyst is a quaternary bisphenolate, it 
decomposes during the reaction to an olefin, a bisphenol and the 
relatively volatile pentaalkylguanidine. 
The complex viscosity ratio, R*, is an indication of the suitability of a 
polymer for blow molding. It is defined as the melt viscosity in poise of 
the polymer at a temperature T* under low shear conditions of 1 rad/sec, 
typical of a blow molding parison, divided by 20,000 poise which is the 
viscosity of said polymer at a high shear rate of 100 rad/sec at T* and 
which is assumed to be exemplary of extrusion conditions. R* is thus a 
measure of the shear thinning behavior of the polymer. Experience has 
shown that good blow molding performance is obtained if R* for a given 
polymer is approximately equal to or greater than 3.5; T* for that polymer 
is or approximates the ideal temperature for creating a parison. 
R* and T* values as listed hereinafter were obtained by determining melt 
viscosities on a Rheometrics Dynamic Spectrometer at shear rates of 1 and 
100 rad/sec during a heating scan over a range which included T*. Upon 
plotting viscosity against temperature, the value of T* was obtained by 
interpolation as that temperature at which the viscosity is 20,000 poise 
at 100 rad/sec. Then the viscosity at this temperature and a shear rate of 
1 rad/sec was determined by interpolation on the viscosity curve 
corresponding to that rate. R* is the viscosity at low shear divided by 
20,000 poise. 
The preparation of branched polycarbonates by the method of this invention 
is illustrated by the following examples. 
EXAMPLES 3-11 
Dry blends of a commercial bisphenol A polycarbonate having a weight 
average molecular weight of about 66,000 relative to polystrene, as 
determined by gel permeation chromatography, and various proportions of 
2,2,5,5-tetrakis(4-hydroxyphenyl)hexane as a branching agent and 
tetraethylammonium acetate as an equilibration catalyst were prepared by 
dry blending and extruded on a twin screw extruder at temperatures of 
about 280.degree. C., with vacuum venting. The values of R* and T* were 
determined and compared with those for two controls: Control 1 which was 
the reactant polycarbonate, and Control 2 which was an extruded blend of 
the reactant polycarbonate with tetraethylammonium acetate only. The 
results are provided in 
TABLE I 
______________________________________ 
Tetraphenol, 
Catalyst, 
Example mole % ppm R* T * 
______________________________________ 
3 0.20 100 3.14 265 
4 0.30 100 3.40 267 
5 0.40 100 3.80 267 
6 0.20 200 2.66 261 
7 0.30 200 3.48 263 
8 0.40 200 3.68 260 
9 0.20 300 2.46 261 
10 0.30 300 3.05 258 
11 0.40 300 3.46 255 
Control 1 -- -- 1.43 270 
Control 2 -- 200 1.64 266 
______________________________________ 
It will be seen that numerous products prepared by this method have 
viscosity properties making them suitable for blow molding. This is in 
contrast to products formed by branching with 
1,1,1-tris(4-hydroxyphenyl)ethane; even employing a reactant polycarbonate 
with a weight average molecular weight of 180,000, R* values below 3 were 
obtained in all instances. 
EXAMPLES 12-18 
The procedure of Examples 3-11 was repeated, employing the product of 
Example 1 in the amount of 0.28 mole percent as the branching agent and 
various compounds as equilibration catalysts. The results are given in 
Table II. 
TABLE II 
______________________________________ 
Example 
Identity Conc., ppm 
R* T (R*) 
______________________________________ 
12 Tetra-n-butylammonium 
380 3.71 272 
tetraphenylborate 
13 Tetra-n-butylphosphonium 
380 3.90 277 
tetraphenylborate 
14 Tetra-n-butylammonium 
29 3.20 266 
borohydride 
15 Tetra-n-butylphosphonium 
200 3.00 253 
acetate 
16 Sodium tetraphenylborate 
14 3.63 266 
17 Product of Ex. 2 
64 3.55 267 
18 Product of Ex. 2 
129 4.12 271 
______________________________________ 
Again, it will be seen that many of the products have excellent properties 
for blow molding. In particular, the products of Examples 17 and 18, 
prepared using the guanidinium bisphenolate as a catalyst, have 
extraordinarily good viscosity characteristics. In addition, they are free 
from catalyst decomposition residues since the catalyst by-products have 
been removed by volatilization.