Preparation of peroxide terminated polycarbonate

Peroxy-terminated polycarbonates are prepared by the reaction of an aromatic dihydroxy compound, preferably a bisphenol, with phosgene in one or two steps, in the presence of a peroxy ester such as the mono-t-butyl perester of maleic acid. The peroxy-terminated polycarbonates may be employed to initiate vinyl polymerization of ethylenically unsaturated monomers or to react with polymers containing ethylenically unsaturated groups, to form copolymers which are useful as compatibilizers for blends of polycarbonates with said polymers.

This invention relates to the preparation of polycarbonates having 
functional end groups, suitable for the preparation of compatibilizing 
copolymers. More particularly, it relates to peroxide-terminated 
polycarbonates. 
Polycarbonates, particularly aromatic polycarbonates, have long been 
recognized as a class of resins with valuable and advantageous properties. 
In recent years, the improvement of such properties of polycarbonates as 
ductility, solvent resistance and barrier properties has been of interest. 
One potential method of improving such properties in polycarbonates is by 
blending them with other polymers which have the desired properties. 
However, this is frequently difficult and the resulting blends may be 
deficient by reason of the incompatibility of polycarbonates with the 
other polymers in the blend. 
It has also been recognized that polymer blends of this type can be 
compatibilized by the incorporation therein of a copolymer of the two 
polymers. The preparation of polycarbonate copolymers of this type 
requires the presence of a reactive functional group on the polycarbonate. 
Thus, for example, U.S. Pat. No. 4,732,934 describes the preparation of 
polycarbonate-polyamide copolymers from an anhydride-terminated 
polycarbonate, the latter in turn being prepared by the reaction of a 
compound such as trimellitic anhydride acid chloride with a 
hydroxy-terminated polycarbonate. 
It will be apparent that the type of functionality required on a 
polycarbonate for reactions of this type is dependent in large part on the 
nature of the polymer with which copolymer formation is desired. In many 
instances, said polymer will be an addition polymer formed by a free 
radical reaction involving one or more ethylenically unsaturated monomers, 
illustrated by such commonly used and commercially important polymers as 
polystyrenes, aliphatic olefin polymers, polyvinyl halides, acrylic 
polymers and polymerized dienes. Provided the proper functionality is 
present on the polycarbonate, copolymer formation could then take place by 
initiation of the corresponding free radical polymerization reaction 
involving the unsaturated monomer(s) or by free radical-induced grafting 
through an olefinic bond present in the polymer. 
Several varieties of functional polycarbonates capable of inducing free 
radical reactions are known in the art, but most of them require the 
presence of relatively exotic carbonate structural units. For example, 
Japanese Kokai 84/27908 describes the preparation of a 
copolyestercarbonate from bisphenol A and 5,5'-azobis(5-cyanovaleroyl 
chloride), a reagent which is not readily available at a reasonable price. 
Therefore, there is a continuing need for polycarbonates containing free 
radical reaction-inducing moieties which can be prepared by relatively 
simple means from inexpensive and readily available materials. 
The present invention provides a method for preparing such polycarbonates. 
The products are peroxide-terminated polycarbonates which react readily 
with ethylenically unsaturated monomers and with polymers containing 
olefinic bonds, to produce copolymers capable of compatibilizing blends of 
the polycarbonate with the other polymer. 
In one of its aspects, therefore, the present invention includes 
peroxide-terminated polycarbonates characterized by the presence of end 
groups having the formula 
##STR1## 
wherein A.sup.1 is a divalent aliphatic, alicyclic or aromatic radical, 
R.sup.1 is a divalent aliphatic or alicyclic radical and R.sup.2 is a 
tertiary aliphatic or alicyclic radical. 
Other than in their end group structure, the polycarbonates of the present 
invention are conventional. Thus, they may be considered as comprising 
structural units of the formula 
##STR2## 
wherein A.sup.1 is as previously defined. Most often, A.sup.1 is an 
aromatic radical, particularly a radical having the formula 
EQU -A.sup.2 -Y A.sup.3 - (III) 
wherein each of A.sup.2 and A.sup.3 is a monocyclic divalent aromatic 
radical and Y is a bridging radical in which one or two atoms separate 
A.sup.2 from A.sup.3. The free valence bonds in formula III are usually in 
the meta or para positions of A.sup.1 and A.sup.2 is relation to Y. 
The A.sup.2 and A.sup.3 values may be unsubstituted phenylene or 
substituted derivatives thereof. Unsubstituted phenylene radicals are 
preferred. Both A.sup.2 and A.sup.3 are preferably p-phenylene, although 
both may be o- or m-phenylene or one o- or m-phenylene and the other 
p-phenylene. 
The bridging radical, Y, is one in which one or two atoms, preferably one, 
separate A.sup.2 from A.sup.3. It is most often a hydrocarbon radical and 
particularly a saturated C.sub.1-12 aliphatic or alicyclic radical such as 
methylene, cyclohexylmethylene, [2.2.1]bicycloheptylmethylene, ethylene, 
ethylidene, 2,2-propylidene, 1,1-(2,2-dimethylpropylidene), 
cyclo-hexylidene, cyclopentadecylidene, cyclododecylidene or 
2,2-adamantylidene, especially an alkylidene radical. Aryl-substituted 
radicals are included, as are unsaturated radicals and radicals containing 
atoms other than carbon and hydrogen; e.g., oxy groups. Substituents may 
be present on the aliphatic, alicyclic and aromatic portions of the Y 
group. 
Both homopolycarbonates and copolycarbonates may be employed, as well as 
copolyestercarbonates. Most preferably, they are bisphenol A homo- and 
copolycarbonates, in which, in at least a portion of the structural units, 
each of A.sup.2 and A.sup.3 is p-phenylene and Y is isopropylidene. The 
bisphenol A homopolycarbonates are often especially preferred by reason of 
their availability and excellent properties. 
The end groups of the polycarbonates of this invention have formula I. In 
that formula, R.sup.1 is a divalent aliphatic or alicyclic radical, 
ordinarily containing about 2-6 carbon atoms. It is usually aliphatic and 
contains about 2-4 carbon atoms. It may be saturated or may contain double 
or triple bonds, most often double bonds. Especially preferred are the 
--CH.sub.2 CH.sub.2 -- and --CH.dbd.CH-- radicals. 
The R.sup.2 value is a tertiary aliphatic or alicyclic radical, most often 
aliphatic and generally containing about 4-10 carbon atoms. The t-butyl 
radical is especially preferred by reason of its availability. 
The peroxide-terminated polycarbonates of this invention may be prepared by 
the reaction of an organic dihydroxy compound, preferably a 
dihydroxyaromatic compound such as a bisphenol, with phosgene in the 
presence of a peroxy ester of the formula 
##STR3## 
wherein R.sup.1 and R.sup.2 are as previously defined, as a chain 
termination agent (hereinafter sometimes "chainstopper"). This method is 
another aspect of the invention. In most instances, the preferred compound 
of formula IV is the mono-t-butyl perester of maleic acid, since it is 
commercially available at relatively low cost. 
Preparation of the peroxide-terminated polycarbonate is ordinarily most 
conveniently conducted under conventional interfacial conditions, 
employing as an organic solvent a substantially water-immiscible liquid 
such as methylene chloride. Said reaction occurs in an alkaline medium, in 
the presence of a tertiary amine such as triethylamine as catalyst. It may 
be conducted in one step, employing phosgene in combination with the 
dihydroxy compound and the peroxy ester. It is often preferred, however, 
to first prepare a bischloroformate oligomer composition by reaction of 
the bisphenol with phosgene under alkaline conditions, and subsequently to 
add the catalyst and convert said bischloroformate composition to a 
polycarbonate, as described, for example, in U.S. Pat. Nos. 4,737,573 and 
4,743,676, the disclosures of which are incorporated by reference herein. 
Introduction of the chainstopper prior to conversion to the polycarbonate, 
as disclosed in the aforementioned U.S. Pat. No. 4,743,676, is often 
particularly preferred. 
The proportion of chainstopper is selected so as to produce a polycarbonate 
of the desired molecular weight, and can be readily determined on that 
basis by routine experimentation. It is usually found that somewhat higher 
proportions of peroxy ester must be employed to produce a polycarbonate of 
a specific molecular weight than is the case with conventional 
chainstoppers such as phenols. Thus, about 1-10 and preferably about 2-8 
mole percent of peroxy ester, based on bisphenol, is generally employed.

The preparation of the peroxide-terminated polycarbonates of this invention 
is illustrated by the following example. 
EXAMPLE 1 
A 500-ml. Morton flask fitted with a phosgene dip tube, an overhead 
stirrer, a Friedrich condenser, a 50-ml. pressure equalizing addition 
funnel and a pH probe was charged with 3.01 grams (56 mmol.) of bisphenol 
A, 60 ml. of water and 100 ml. of methylene chloride, and the pH thereof 
was adjusted to between 9 and 10 by the addition of 50% aqueous sodium 
hydroxide solution. Phosgene was added at the rate of 0.32 grams per 
minute, with stirring, as the pH was maintained at 9.5-10.0 by addition of 
sodium hydroxide solution as necessary. Phosgene addition was stopped 
after 20 minutes and the mixture was sparged with nitrogen and stirred for 
5 minutes after nitrogen sparging ceased. 
There was then added 0.75 gram (2.8 mmol.) of the mono-t-butyl perester of 
maleic acid, and stirring was continued for another 30 minutes. After the 
addition of 1 ml. of 0.56 M triethylamine solution in methylene chloride, 
phosgene addition at 0.32 gram per minute was resumed for 10 minutes, with 
maintenance of the pH in the range of 9.0-9.5. The mixture was again 
sparged with nitrogen for 5 minutes and was allowed to stand until a 
negative reading was obtained with phosgene detection paper. The organic 
layer was separated, washed three times with aqueous hydrochloric acid 
solution and once with deionized water (whereupon a negative chloride test 
was obtained with silver nitrate) and poured into acetone in a blender. 
The peroxide-terminated polycarbonate precipitated as a white powder and 
was removed by vacuum filtration and dried for 60 hours in a vacuum oven 
at 45.degree. C. It was shown to have the desired molecular structure by 
proton nuclear magnetic resonance and Fourier transform infrared 
spectroscopy. Gel permeation chromatographic analysis showed the product 
to have a weight average molecular weight of 61,200 and a number average 
molecular weight of 30,000. 
The peroxide-terminated polycarbonates of this invention undergo reaction 
with ethylenically unsaturated compounds, initiating free radical reaction 
thereof which is followed by coupling with the polycarbonate to yield 
copolycarbonates which are another aspect of the invention. The 
ethylenically unsaturated compounds which may be employed include 
polymerizable monomers such as ethylene, propylene, styrene, vinyl 
chloride, acrylic acid, acrylonitrile, ethyl acrylate, methyl 
methacrylate, maleic anhydride, butadiene and isoprene. They may be 
employed singly or in admixture. The preferred compounds for many purposes 
are styrene, maleic anhydride and acrylic monomers, especially 
acrylonitrile. Ethylenically unsaturated polymers, such as polybutadiene 
and styrene-butadiene copolymers, may also be employed. 
The copolymer-forming reaction may be conducted in solution in a suitable 
solvent for the peroxide-terminated polycarbonate and the ethylenically 
unsaturated compound. Where appropriate, as when the ethylenically 
unsaturated compound is a polymer, it may also be conducted in the melt, 
typically in an extruder. The proportions of peroxide-terminated 
polycarbonate and ethylenically unsaturated compound are not critical but 
may be varied according to the properties of the desired product. 
In most instances, preparation of copolycarbonates by reaction of the 
peroxide-terminated polycarbonate with at least one ethylenically 
unsaturated monomer will also result in some homopolymerization of said 
monomer(s). The presence of homopolymer is frequently not detrimental. 
However, said homopolymer may be removed if desired, typically by 
dissolution in a solvent therefor which does not dissolve the 
copolycarbonate. 
The precise molecular structures of the copolycarbonates of this invention 
are not known with certainty. It is virtually certain that the 
peroxide-terminated polycarbonate generates an alkoxy free radical with 
the formation of a polymeric carboxy-terminated free radical; the latter 
may then decarboxylate to form an alkyl- or vinyl-terminated radical. In 
any event, the polymeric radical apparently initiates polymerization of 
the ethylenically unsaturated monomer, or reacts similarly with a polymer 
containing olefinic groups to form a graft copolymer. 
The preparation of the copolycarbonates of this invention is illustrated by 
the following examples. 
EXAMPLES 2-6 
A solution of 5.08 grams of the product of Example 1 and 18 grams of one or 
more vinyl monomers in 50 ml. of m-dichlorobenzene was purged with 
nitrogen and heated in a nitrogen atmosphere to 100.degree. C. for 10 
minutes, to 150.degree. C. for 1.5 hours and to 190.degree. C. for 15 
minutes. The solutions were cooled and poured into methanol in a blender, 
whereupon the copolycarbonates precipitated. They were removed by 
filtration, slurried three times in methanol and filtered, and dried 
overnight in a vacuum oven at 110.degree. C. 
Molecular weights were determined by gel permeation chromatography relative 
to polystyrene. In addition, proton nuclear magnetic resonance 
spectroscopic analysis was performed to confirm the molecular structures 
of the products, and Soxhlet extraction was performed to determine the 
proportion of vinyl homopolymer (unbound to polycarbonate) present. The 
results are given in the following table. 
TABLE I 
__________________________________________________________________________ 
% recovered 
Extraction 
after extraction 
% vinyl 
Example 
Monomer(s) solvent 
Example 
Control homopolymer 
Mw 
__________________________________________________________________________ 
2 Styrene Cyclohexane 
70 30 30 136,700 
3 Styrene (86%), 
maleic anhydride (14%) 
Ethyl acetate 
58 20 40 131,000 
4 Methyl methacrylate 
Acetone 
66 39 30 90,800 
5 Styrene (97%), 
divinylbenzene (3%) Product gelled 
6 Styrene (72%), 
Acetone 
68 31 30 144,000 
acrylonitrile (28%) 
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EXAMPLE 6 
A mixture of 300 grams of the product of Example 1 and 300 grams of a 
commercially available styrene-butadiene-styrene triblock copolymer was 
dry blended and extruded on a twin screw extruder at temperatures from 
120.degree. to 275.degree. C., at a screw speed of 400 rpm. Soxhlet 
extraction of the extrudate with toluene showed that 38% by weight of the 
triblock copolymer was bound to polycarbonate. 
The copolycarbonates of this invention are useful as compatibilizers for 
blends of homopolycarbonates with polymers of the vinyl monomers employed 
in copolycarbonate preparation, as well as chemically similar polymers 
(e.g., polyphenyene ethers which are miscible with polystyrenes in all 
proportions). Their effect is demonstrated under various circumstances by 
improved properties, including notched Izod impact strengths and tensile 
elongations, and improved blend morphologies as shown by inspection of the 
fracture surfaces of Izod test specimens. 
For example, inspection of the fracture surface of a blend comprising 70% 
of a commercially available polycarbonate and 30% polystyrene showed the 
presence of a dispersed phase containing relatively large polystyrene 
particles, typically on the order of 2 microns. By contrast, a similar 
blend compatibilized by the presence of the copolymer of Example 2 in the 
amount of 25% by weight contained much smaller polystyrene particles, 
typically on the order of 0.25-0.5 micron. 
Likewise, blends of equal weights of a commercially available polycarbonate 
and a commercially available poly(2,6-dimethyl-1,4-phenylene ether) were 
shown to have a dispersed polycarbonate phase with particles as large as 
15-20 microns. Particle sizes of the same order of magnitude were observed 
in blends which additionally contained 5% by weight of polystyrene. By 
contrast, polyphenylene ether-polycarbonate blends containing 25% by 
weight of the copolymer of Example 2 contained much smaller particle 
sizes, typically on the order of 1-2 microns, in the dispersed phase. 
Similar effects were observed in blends comprising bisphenol A 
polycarbonate and the triblock copolymer employed in Example 6. Much 
smaller particles in the discontinuous phase were observed when the 
copolymer of Example 6 was employed as a compatibilizer than when it was 
absent. 
In addition, notched Izod impact strengths and tensile elongations were 
improved by the use of the copolymer of Example 6 as a compatibilizer. 
This is shown in Table II. 
TABLE III 
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Izod 
Parts by weight impact 
Poly- Tri- Copoly- strength, 
Tensile 
carbonate 
block carbonate joules/m. 
elongation, % 
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-- 50 50 192 103 
50 50 -- 48 17 
60 20 20 150 104 
80 20 -- 11 6 
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