Note: Descriptions are shown in the official language in which they were submitted.
~ 1087t793
.~
.
O.Z. 31,89
BRANCHED BLOCK COPOLYMERS AND THEIR MANUFACTURE
The present invention relates to selectively hydrogenated, non-
elastomeric branched block copolymers which prior to hydrogenation
comprise a predominant proportion of units of a monovinylaromatic com-
pound and a lesser proportion of units of a conjugated diene, and which
possess high transparency and clarity, as well as ~ood mechanical pro-
perties, in particular high impact strength.
The manufacture by polymerization of styrene and butadiene with
lithium-hydrocarbons as initiators, of block copolymers in which one
or more non-elastomeric polymer blocks are bonded to one or more
elastomeric polymer blocks, has been disclosed. Depending on the con-
tent of polymer blocks in the total polymer, these thermoplastic block
copolymers exhibit non-elastomeric or elastomeric properties.
Successive polymerization of the monomers gives block copolymers
having a linear structure. If such linear block copolymers are cou~led
to one another by means of polyfunctional reactive compounds,
branched block copolymers having a star-shaped structure resu7t. Such
branched block copolymers, described, for example, in British
Patent 985,614, have a symmetrical structure and in general exhibit
better processability than the linear block copolymers.
It has also been disclosed t~lat styrene-butadiene block copoly-
- 1 - ~
~sm3 o.%. 31,~n~
mers ~laving a high styrene content are clear thermoplastic products
having a high impact strength. Even though the block copolymers of
this type hitherto developed and proposed have satisfactory properties
in some respects, they nevertheless fail to fulfil many practical
requirements. In particular, their physical and mechanical properties,
such as their impact strength, leave much to be desired, or the pro-
ducts do not have the transparency desirable for many applications.
German Laid-Open Application DOS 1,959,922 discloses branched
block copolymers having a star-shaped structure, comprisin~ a pre-
dominant proportion of styrene and a lesser proportion of a conjugated
diene, which are stated to combine good impact strength, clarity,
good processability and resistance to external factors in one and the
same polymer. These branched block copolymers are obtained by coupling
styrene-diene two-block copolymers in which the terminal polystyrene
blocks have different lengths. It is true that they exhibit better
mechanical properties than branched block copolymers in which the
polymer blocks of the branches all have the same structure, but they
are not entirely satisfactory, especially in respect of their tensile
strength.
It is an object of the present invention to improve the mechani-
cal properties of styrene-diene block copolymers which contain a pre-
dominant proportion of styrene, and in particular to produce products
having improved tensile stren~th. In addition, the products should he
transparent and as glass-clear as possible, and should be readilv
processable and very stable.
We have found, surprisingly, that this object is achieved and
that the mechanical properties of non-elastomeric, branched block co-
polymers comprising a predominant proportion of a monovinyl-aromatic
compound and a lesser proportion of a conju~ated diene can be improved
if such branched block copolymers, which have a quite specific com-
position and structure of the blocks at the hranch points, are hydro-
genated selectively.
Accordingly, the present invention relates to selectively hydro-
-- 2 --
1 ~ ~ 3 0-~ 3l,8~6
genated, non-elastomeric branched block copolymers of the general
formula
(A-B)n-X
where
A is a non-elastomeric polymer segment, exhibiting polymodal
distribution, based on a monovinyl-aromatic compound,
B is a hydrogenated elastomeric polymer segment based on a con-
jugated diene of 4 to 8 carbon atoms and having a crystallinity of
less then 5%,
X is the radical of a poly~unctional coupling agent by means of
which the polymer blocks (A-B) which form the branches are chemically
bonded to one another at the polymer segments B and
n is an integer not less than 3,
the proportion of the monovinyl-aromatic compounds in the branched
block copolymer being from 60 to 95% by weight and the content of
olefinic double bonds in the branched block copolymer having been
reduced by selective hydrogenation to a residual content of less than
5%.
It is true that German Laid-Open Application DOS 2,125,344 has
already proposed the selective hydrogenation o~ unsymmetrically
branched block copolymers of styrene and a conjugated diene which
possess a homopolymer block in at least one branch. This is intended
not only to increase the maximum use temperature of the polymers
obtained but also to improve their thermal and oxidative stability
and to modi~y their solubility properties i~o~ever, the products dis-
closed in German ~aid-Open Application DOS 2,125,344, which, according
to the Example given, contain a predominant proportion Or the con-
jugated diene, do not exhibit the desired combination o~ properties,
i.e. high transparency coupled with good mechanical properties,
especially high tensile strength~ U.S Patents 3,5~,9~2 and
3,700,633 also disclose the hydrogenation o~ elastos~eric, rubbery,
branched block copolymers. Here again, the hydrogenation only
improves the oxidation resistance and processa~ility of the hranched
-- 3 --
10~93 ~ . . 31,896
rubbery block copolymers. Accordingly, it was entirely sur~rising
and unforeseeable that the selective hydrogenation Or non-elastomeric,
branched block copolymers comprising a predominant proportion of a
monovinyl-aromatic compound and a lesser proportion of a conjugated
diene, which have a quite specific composition and structure of the
blocks, gives products which are not only transparent and substantially
glass-clear, and are easily processable, but which also exhibit
increased tensile strength.
Examples of monovinyl-aromatic compounds which may be used to
synthesize the branched block copolymers of the invention are styrene,
styrenes which are alkylated in the side chain, e.g. ~-methylstyrene,
and nuclear-substituted styrenes, e.g. vinyltoluene or ethylvinyl-
benzene. The monovinyl-aromatic compounds may be employed individually
or as mixtures with one another. ~owever, the use of st~rene alone
is preferred. Examples of conjugated dienes which, according to the
invention, may be used individually, or as mixtures with one another,
for the manufacture of the branched block copolymers are butadiene,
isoprene and 2,3-dimethyl-butadiene. Butadiene or isoprene give
particularly advantageous results, and of the two butadiene is pre-
ferred.
The non-elastomeric, branched block copolymers of the invention
comprise a predominant proportion of the monovinyl-aromatic compound
and are manufactured by successive polymerization of the monovinyl-
aromatic compound and of the conjugated diene in solution in the
presence of a monolithium-hydrocarbon as the initiator, monomer and
initiator being added stepwise, followed by coupling of the resulting
living linear block copolymers with a polyfunctional, reactive com-
pound as the coupling agent, and in turn followed by selective
hydrogenation of the resulting branched block copolymers. Prior to
hydrogenation, the block copolymers of the invention should comprise
from 65 to 95~0 by weight, especially from 70 to 90% by weight, of the
- monovinyl-aromatic compound and from 40 to 5% by weight, preferably
from 30 to 10~ by weight, of the conjugated diene. ~he intrinsic
1~ _
7. 31,8~6
1 ~ ~ 3
viscosity of the selectively hydrogenated, non-elastomeric, branched
block copolymers (which is a measure of the molecular weight) is as
a rule from 60 to 180 cm3/g and preferably from 70 to 140 cm3/g. It
is determined by measuring the viscosity in an 0.5~, strength by weight
solution in toluene at 25C.
The manufacture of the non-hydrogenated branched block copoly-
mers which exhibit a polymodal distribution in the non-elastomeric
polymer segments A made up of the monovinyl-aromatic compounds is
essentially known and is, for example, largely described in German
Laid-Open Application DOS 1,959,922. Specifically, the branched block
copolymers are manufactured as follows:
First, the non-elastomeric polymer segments A exhibiting a poly-
modal distribution are manufactured from the monovinyl-aromatic com-
pounds. For this purpose, a substantial portion of the total amount
of the monovinyl-aromatic compound is polymerized in a first process
stage, under conventional conditions, by means of a relatively small
amount of the monolithium-hydrocarbon initiator, in an inert solvent.
From 50 to 80% by weight, preferably from 60 to 75% by weight, of
the total amount of the monovinyl-aromatic compound employed, overall,
for the manufacture of the branched block copolymers should be used
in this first process stage. The total amount of monovinyl-aromatic
compound used for the manufacture of the branched block copolymers is
from 60 to 95% by weight, especially from 70 to 90% by weight, of
the total monomers used for the manufacture of the polymer.
The amount of initiator employed in the first process stage
depends above all on the desired molecular weight of the polymer and
is in general from 0.1 to ~ mmoles per mole of the monovinyl-aromatic
compounds employed in this first process stage. Preferably, the poly-
merization in the first process stage is carried out with from 0.4 to
2 mmoles of initiator per mole of the monovinyl-aromatic compounds
employed in this stage. The conv~ntional monolithium-hydrocarbons of
the general formula RLi, where R is an aliphatic, cycloaliphatic,
aromatic or mixed aliphatic-aromatic hydrocarbon radical, are used
- 5
10~779;~ o.z. 31,896
as initiators. The hydrocarbon radical may have rrom 1 to about 12
carbon atoms. Examples Or the lithium-hydrocarbon initiators to be
employed according to the invention are methyl-lithium, ethyl-lithium,
n-, sec.- or tert.-butyl-lithium, isopropyl-lithium, cyclohexyl-
lithium, phenyl-lithium or p-tolyl-lithium. Preferably, the mono-
lithium-al~yl compounds where alkyl is of 2 to 6 carbon atoms are
employed, n-butyl-lithium and sec.-butyl-lithium being particularly
preferred.
The polymerization of the monovinyl-aromatic compounds is carried
out in solution in a inert organic hydrocarbon solvent. Suitable
hydrocarbon solvents are aliphatic, cycloaliphatic or aromatic hydro-
carbons which are liquid under the reaction conditions and preferably
contain from 4 to 12 carbon atoms. Examples of suitable solvents are
isobutane, n-pentane, iso-octane, cyclopentane, cyclohexane, cyclo-
heptane, benzene, toluene, dixylenes and others. Mixtures of these
solvents may also be employed. Furthermore, the polymerization can be
carried out in the presence of small amounts, in general from 10 3 to
5% by weight, based on the total solvent, of ethers, e.g. tetrahydro-
furan, dimethoxyethane and anisole, thereby influencing the rate Or
polymerization, and the configuration of the diene polymer segment 8,
in the conventional manner. The concentration of the monomers in the
reaction solution is not critical and can be so chosen that any
desired apparatus can be used for the polymerization. In general, the
polymerization is carried out in a solution of from 10 to 30% strength
by weight in the inert solvent.
The polymerization is carried out under the conventional con-
ditions for anionic polymerization with lithium-organic compounds,
for example in an inert gas atmosphere, with exclusion of air and
moisture. The polymerization temperature may be ~rom 0 to 120C and
is preferably kept at from 40 to 80C.
In this first process stage, the polymerization is taken to
virtually complete conversion of the monovinyl-aromatic compounds
employed. This gives a solution of non-elastomeric, living polymers
i~ ~ 93 O.Z. 31,8~6
of the monovinyl-aromatic compounds, with active terminal lithium-
hydrocarbon bonds, to which further monomers can add.
In a second process stage, the remainder Or the monovinyl-aro-
matic compound, i.e. from 20 to 50% by weight, preferably from 25 to
40% by weight, of the total monovinyl-aromatic compound used for the
manufacture Or the branched block copolymer is added, in one or more
portions, to the above reaction solution of tbe non-elastomeric
living polymers based on the mono~inyl-aromatic compounds with
lithium-terminated chain ends capable Or undergoing further polymeri-
zation; each addition of a portion Or the monovinyl-aromatic compound
is accompanied by the addition of a further amount Or initiator. The
amount of fresh initiator added to the reaction solution in the
second process stage whenever adding a portion Or the monovinyl-aro-
matic compound should be as great or greater than the original amount
Or initiator employed in the first process stage Or the polymeri-
zation. Preferably, the amount of fresh initiator added with the
addition of each portion Or the monovinyl-aromatic compound in the
second process stage is from 1 to 15 times, and especially from 1 to
10 times, the amount Or initiator originally employed. It is particu-
larly advantageous if this factor is from 1 to 5, especially if, asdescribed in more detail ~elow, trifunctional or tetrafunctional
coupling agents are employed in the subsequent coupling reaction.
Suitable initiators are the monolithium-hydrocarbons which can also be
used in the firs~ process stage; preferably, the initiator used is the
same as in the first process stage. It is advantageous to introduce
the additional fresh initiator into the reaction solution in each -
case prior to adding a further portion of the monovinyl-aromatic com-
pound.
Though it is possible, in the second process stage, to add the
remaining portion of the monovinyl-aromatic compound to the reaction
solution in as many portions as desired, it is preferred to add it to
the polymerization solution in 1 or 2 portions, and adding it in one
portion has proved particularly advantageous. In the second process
1087793 o.z. 31,896
stage, the same polymerization conditions as in the first process
stage are maintained, and after each further addition Or monomer and
initiator sufficient time is allowed to elapse to enable the freshly
added monomer to polymerize virtually completely.
The monomers added in the second process stage undergo addition
to the active, lithium-terminated chain ends Or the previously formed
polymers, and also form new chains Or living polymers, as a result of
the fresh initiator added with each portion of monomer. Accordingly,
after complete polymerization of the monomers in the second process
stage, the solution obtained contains polymers of the monovinyl-aro-
matic compound with different average chain lengths, i.e. the non-
elastomeric polymer segments A formed from the monovinyl-aromatic com-
pounds have a polymodal distribution. The polymodality of the polymer
segments A corresponds to the total number Or additions of initiator
and monomer and is thus preferably 2 or 3, a bimodal distribution
being particularly advantageousO After completion of the polymeri-
zation Or the monovinyl-aromatic compounds in the second process
stage, the chain ends Or the polymodal non-elastomeric polymer seg-
ments A carry active, reactive lithium-carbon bonds to which further
r 20 monomers can add. The active living polymer segments are hereinafter
referred to as A-Li.
In a third proces B stage, the polymer segments B are then poly-
merized onto the active chain ends of the non-elastomeric polymer
segments A-Li, to form the polymer bloc~s (A-B) which form the
branches of the block copolymer of the invention. For this purpose,
the total amount Or the conjugated diene monomer is added to the
fully polymerized reaction solution from the second process stage.
The amount of conjugated diene is from 5 to 40% by weight, preferably
from 10 to 30% by weight, of the total monomers employed to manu-
facture the branched block copolymers of the invention. The conjugateddienes are polymerized under the same polymerization conditions as
~ in the first two process stages, and again the reaction is taken to
911~. ~r~mr~ nn~ q~nn n~ 1-.hP mnnr~mPt~q WhPn r~lvmerizin~
1~8~93 o.z. 31,8~6
the conjugated dienes, it is necessary to ensure that the number of
alkyl side chains of the linear diene polymer segments is sufficiently
great that, after hydrogenation, the polymer segments B have a
crystallinity of less than 5%. If only branched dienes, e.~. isoprene
or 2,3-dimethylbutadiene, are employed~this condition is as a rule
observed without taking any special measures. I~, however, butadiene,
by itself or as the predominant constituent, is employed as the con-
jugated diene, the polymerization in the third process stage must be
carried out in the presence of small amounts of ethers to give a
sufficiently high 1,2-vinyl content of the butadiene polymer segments.
I~ the ether, which is in general employed in amounts of rrom 10 3 to
5% by weight and preferably from 10 2 to 2% by weight, based on total
solvent, is not already present from the ~irst process stage, it can
be introduced into the reaction solution, in the third process stage,
together with the butadieneO If the conjugated diene employed is
butadiene, the 1,2-vinyl content of the butadiene polymer segments
should be from 25 to 50% by weight and preferably from 32 to 40% by
weight, if products having satisfactory properties are ultimately to
result.
As explained, elastomeric polymer segments B based on the con-
; jugated dienes are polymerized onto the polymodal, non-elastomeric
polymer segments A, produced from the monovinyl-aromatic compounds,
in the third process stageO A~ter completion of the polymerization o~
the monomers in the third process stage, the reaction solution thus
contains living, linear block copolymers comprising a non-elastomeric
polymer segment produced from the monovinyl-aromatic compounds and an
elastomeric diene polymer segment, and these linear block copolymers
have a polymodal distribution and possess an active, reactive
lithium-carbon bond at each free end Or the elastomeric diene polymer
segment.
These active linear block polymers are then reacted in a ~urther
- process stage, by adding a polyfunctional reactive compound as a
coupling agent. The polyfunctional couplin~ agent used should be at
_ q _
1~8~93 o.z. 31,896
least trifunctional, i.e. it should be capable of reacting with at
least 3 of the active living block copolymer chains, at their terminal
lithium-carbon bonds, to form a chemical bond, so that a single,
coupled and accordingly branched block copolymer is formed. The
coupling of lithium-terminated living polymers with polyfunctional
coupling agents is known in the art and disclosed, for example, in
the publications cited in the lntroductory section, especially in
British Patent 985,614.
Examples of suitable coupling agents for the manufacture Or the
branched block copolymers Or the invention are polyepoxides, epoxi-
dized linseed oil, polyisocyanates, e~g. benzo-1,2,4-triisocyanate,
polyketones, polyanhydrides, eOg. pyromellitic dianhydride, or poly-
halides. Dicarboxylic acid esters, e.g. diethyl adipate or the like,
may also be used as coupling agents. A further preferred group Or
coupling agents comprises the silicon halides, especially silicon
tetrachloride, silicon tetrabromide, trichloroethylsilane or 1,2-bis-
(methyldichlorosilyl)-ethane. Polyvinyl-aromatics, especially divinyl-
benzene, may also be used as coupling agents, as disclosed, for
example, in U.S. Patent 3,280,084. In that case, a few divinylbenzene
units undergo addition, with crosslinking, to form a branching center,
by means of which the preformed polymer blocks are bonded to one
another.
The nature of the polyfunctional coupling agent employed is not
critical, provided it does not significantly impair the desired pro-
perties of the end product. The use of a trifunctional or tetra-
functional coupling agent of the type described, or Or divinylbenzene,
is preferredO In general, the polyfunctional coupling agent is added
to the reaction solution in amounts equivalent to the total amount Or
the living polymer blocks, i.e. equivalent to the number Or the
active lithium-carbon bonds in the previously formed linear copolymer
blocks. The reaction of the active, linear bloc~ copolymers with the
coupling agent is preferably carried out under the same reaction con-
ditions as the preceding polymerization of the monomers.
-- 10 --
1087793 o.z. 3l,8g~
Following the coupling reaction and, advantageously, prior to
isolating the reaction product from the reaction solution, the ole-
finic double bonds of the branched block copolymers obtained are
hydrogenated selectivelyO The selective hydrogenation can be carried
out in the conventional manner, using molecular hydrogen and catalysts
based on meta~.s, or salts of metals, of group 8 of the periodic table,
as described, for example, in U S. Patent 3,113,986, Oerman Published
Application DAS 1,222,260, German Laid-Open Application DOS 1,013,263
or U.S. Patent 3,700,6330 According to these publications, the selec-
~10 tive hydrogenation of the olefinic double bonds of the branched block - ~copolymer is preferably carried out in a homogeneous phase, using
catalysts based on salts, especially carboxylates, enolates or
alkoxides, of nickel, cobalt or iron, which have been reduced with
metal-alkyls, especially aluminum-alkyls, at hydrogen pressures of
. from 1 to 100 bars and at from 25 to 150Co The selective hydrogenation
is cont;nued until the content of olerinic double bonds in the
branched block copolymer has been reduced to less than 5% and pre-
ferably less than 2%. This residual content is determined by a Wijs
titration or by analysis by IR spectroscopy. In particular, the hydro-
- 20 genation is continued until the olefinic double bonds have been
reduced virtually completely. Preferably, the hydrogenation is carried
out under conditions such that the aromatic double bonds o~ the
branched block copolymer are not attacked. ~;
~ he process of manufacture determines the composition and
structure of the selectively hydrogenated, non-elastomeric branched
block copolymers of the invention~ The most probable structure Or
these corresponds to the general formula
(A-B)n-X
where
A is a non-elastomeric polymer segment, exhibiting polymodal
distribution, based on the monovinyl-aromatic compounds,
~ is an elastomeric polymer segment based on the conjugated
- 11 -
O Z. 31,8~6
~Q8779;~
dienes, the content of olefinic double bonds in the segment having
been reduced to less than 5%, and preferably less than 2%, by selec-
tive hydrogenation,
X is the radical of the polyfunctional coupling agent and
n is an integer not less than 3, in general from 3 to 10 and
preferably 3 or 4.
The non-elastomeric polymer segments A are, more particularly,
homopolystyrene segments. Their molecular weight and polymodality
depend primarily on the intended end use of the product. The molecular
weight is decided, in the conventional manner, by the amount of
initiator employed per mole of monomer; the polymodality depends, as
already described, on the frequency of addition of initiator and is
preferably 2 or 3 and especially 2D The elastomeric polymer segment B
based on the conjugated dienes should have a crystallinity of less
than 5% and preferably of less than 2% after hydrogenation. The
crystallinity Or the polymer segments B is determined by differential
calorimetry, using a Perkin-Elmer DSC calorimeter.
The selectively hydrogenated, non-elastomeric branched block co-
polymers of the invention possess not only high transparency and
20 clarity, but also good aging resistance and weathering resistance,
and are easily processable~ They are distinguished by their good
mechanical properties and are in particular superior in tensile
strength to the conventional products, as described in German Laid-
Open Application DOS 1,959,922. The branched block copolymers Or the
invention can readily be processed by conventional methods used for
thermoplastics, e.gO extrusion, deep-drawing or injection molding,
and are above all suitable for the manufacture of m~ldings and
packaging materials. They may be employed by themselves or as mixtures
with other thermoplastics.
- 30 The Examples which follow illustrate the invention. Parts and
percentages are by weight, unless stated otherwise. The intrinsic
viscosity, measured in 0.5% strength solution in toluene at 25C, is
given as a measure of the molecular weight. The tensile strength Z
- 12 -
OOZ. 31,86
793
was determined on a compression-molded half-dumb-bell according to
DIN 53,455.
EXAI/!PLE
4.3 kg of cyclohexane and 680 g of styrene are titrated with
sec.-butyl-lithium in a 10 1 pressure kettle, under an inert E~as
atmosphere and whilst excluding moisture, until the polymerization
startsO 17 mmoles of secO-butyl-lithium are then added and the poly-
merization is carried out at 50C for about 1 5 hours, by which time
conversion is virtually completeO The polystyrene formed has an
intrinsic viscosity of 28.7 E~m3/~. A further 17 mmoles Or sec.-
10 butyl-lithium are then added, followed by 340 g of styrene, and the
polymerization is continued for 1 hour at 50C. The polystyrene then
has an intrinsic viscosity of 30.3 ~cm3~g] 0 11 g of THF and 340 g of
butadiene are then added and the mixture is completely polymerized
in the course of 3 hours at 60Co The product has an intrinsic vis-
cosity Or 47.9 ~cm3~g~0 It is subjected to coupling with 8.5 mmoles
of SiCl4. The intrinsic viscosity Or the product is 81.8 ~cm3/g~.
The product is then hydrogenated for 6 hours at from 75 to 80C
under a hydrogen pressure of 10 atmospheres gauge, using 100 ml of a
nickel hydrogenation catalystD The finished product contains less
20 than 1% of olefinic double bonds (determined by a Wijs titration)
and has a glass transition temperature of -69C. The tensile strength
Z is found to be 333 kp~cm .
EXAMPLE II
2.7 kg of cyclohexane and 600 g of styrene were titrated with
sec~-butyl-lithium in a 6 l pressure kettle under an inert gas
atmosphere, and were then polymerized with 0.33 g of sec.-butyl-
lithium for 30 minutes. The temperature was initially 54C. 0.22 kg
of cyclohexane, 0.9 g of sec.-butyl-lithium and 225 g of styrene were
added to the reaction solution at 71C and polymerization was carried
out for one hour; 10 g of THF and 250 g of butadiene are then poly-
30 merized onto the product in the course of one hour at about 74C.Coupling was carried out with 10 ml of Epoxol 9-5 ~as marketed by
1087793 o~z. 31,~g~
Swift Chemical Corp.) in 150 ml of toluene. The intrinsic viscosity
Or the product was 91.9 ~cm3/ ~ O
The product was then hydrogenated for 6 hours at from 75 to 80C
under a hydrogen pressure of 10 atmospheres gauge, using 100 ml of a
nickel hydrogenation catalyst. The end product contained less than
1% of olefinic double bonds (determined by a Wijs titration) and had
a glass transition temperature of -63C. The tensile stren~th Z was
320 kp/cm2.
COMPARATIVE EXAMP~E
The procedure followed was as described in Example 2, with the
sole difrerence that after coupling the styrene-butadiene block co-
polymer was not hydrogenated. The tensile strength Or this product
was about 190 kpJcm20
- 14 -
