Novel block copolymers containing benzocyclobutene units

Novel, reactive block copolymers are claimed having the structures AB, ABA, (AB).sub.m Y, (AB).sub.n Y--A).sub.o and (AB).sub.n Y--B).sub.p where each A block is a copolymer block of a monoalkenyl arene monomer and a benzocyclobutene monomer of the formula ##STR1## where R is H or CH.sub.3 and each B block is a polymerized conjugated diene hydrocarbon block.

FIELD OF THE INVENTION 
The present invention is directed to novel block copolymers of monoalkenyl 
arenes and/or conjugated dienes. More particularly, the present invention 
is related to novel block copolymers of monoalkenyl arenes, conjugated 
dienes and derivatives of benzocyclobutene, which polymers may be 
crosslinked at elevated temperatures. 
BACKGROUND OF THE INVENTION 
Block copolymers have been developed rapidly within the recent past, the 
starting monomers usually being monoalkenyl arenes such as styrene or 
alphamethyl styrene block polymerized with conjugated dienes such as 
butadiene and isoprene. A typical block copolymer of this type is 
represented by the structure polystyrene-polybutadiene-polystyrene. When 
the monoalkenyl arene blocks comprise less than about 55% by weight of the 
block copolymer, the product is essentially elastomeric. Moreover, due to 
their peculiar set of physical properties they can be referred to more 
properly as thermoplastic elastomers. By this is meant polymers which in 
the melt state are processable in ordinary thermoplastic processing 
equipment but in the solid state behave like chemically vulcanized rubber 
without chemical vulcanization having been effected. Polymers of this type 
are highly useful in that the vulcanization step is eliminated and, 
contrary to scrap from vulcanized rubbers, the scrap from the processing 
of thermoplastic elastomers can be recycled for further use. 
These block copolymer have enjoyed broad commercial success. Nevertheless, 
improvements in such polymers are desired. In particular, for particular 
applications such polymers require greater solvent resistance and higher 
use temperatures. Still further, such polymers also need improved adhesion 
to polar materials when used in certain blend compositions. What has now 
been discovered is a new block copolymer that overcomes these 
deficiencies. 
SUMMARY OF THE INVENTION 
The present invention relates broadly to novel copolymers of monoalkenyl 
arenes and/or conjugated dienes with a benzocyclobutene derivative. In 
particular, the present invention relates to a block copolymer selected 
from the group consisting of AB block copolymers, ABA block copolymers, 
(AB).sub.m Y block copolymers, (AB).sub.n Y--A).sub.o block copolymers, 
(AB).sub.n Y--B).sub.p block copolymers and mixtures thereof where each 
"A" is a copolymer block of a monoalkenyl arene monomer and a 
benzocyclobutene monomer of the formula 
##STR2## 
where R is H or CH.sub.3, each "B" is a polymerized conjugated diene 
hydrocarbon block, "m", "n", "o" and "p" are each 1 to about 30 and Y is 
the residue of a multifunctional coupling agent or multifunctional 
initiator. 
The invention also relates to a process for preparing such polymers. 
ADVANTAGES OF THE INVENTION 
The polymers of the present invention possess a number of advantages over 
prior art block copolymers. When the polymers of the present invention are 
crosslinked at elevated temperatures, the resulting polymers possess 
improved solvent resistance along with higher use temperatures. In 
addition, it is possible to functionalize such non-crosslinked polymers to 
obtain polymers having improved adhesion to polar materials. 
DETAILED DESCRIPTION OF THE INVENTION 
The block copolymers of the present invention have idealized structures as 
follows: 
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Structure Type 
______________________________________ 
AB 2 block copolymer 
ABA linear block copolymer 
(AB) .sub.mY radial block copolymer 
(AB) .sub.nY(A).sub.o 
assymetric radial block copolymer 
(AB .sub.nY(B).sub.p 
assymetric radial block copolymer 
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Mixtures of the above structures are also contemplated. 
The "A" blocks are copolymer blocks of a monoalkenyl arene monomer and a 
benzocyclobutene monomer of the formula 
##STR3## 
where R is H or CH.sub.3. When R is H, the benzocyclobutene monomers are 
4-vinylbenzocyclobutene or 3-vinylbenzocyclobutene. When R is CH.sub.3, 
the benzocyclobutene monomers are 4-isopropenylbenzocyclobutene or 
3-isopropenylbenzocyclobutene. The preferred benzocyclobutene monomer is 
4-vinylbenzocyclobutene. Preferably the monoalkenyl arene is styrene. 
Other useful monoalkenyl arenes include alphamethyl styrene, tertbutyl 
styrene, paramethyl styrene and the other ring alkylated styrenes as well 
as mixtures of the same. 
The relative amounts of benzocyclobutene monomer and monoalkenyl arene 
monomer in the A blocks depends upon the desired functionality or degree 
of crosslinks. The table below shows suitable ranges in mole percent: 
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Preferred 
More Preferred 
______________________________________ 
Benzocyclobutene monomer 
0.01 to 20 
0.1 to 10 
Monoalkenyl arene monomer 
99.99 to 80 
99.9 to 90 
TOTAL 100 100 
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The B blocks are polymer blocks of conjugated dienes. Preferred dienes 
include butadiene and isoprene. A much preferred diene is butadiene. 
Mixtures of conjugated dienes may also be employed. 
The Y moiety stands for the residue of a multifunctional coupling agent. 
Linear polymers (ABA) are formed by employing coupling agents having two 
reactive sites or by sequential polymerization. One type of coupling agent 
employed in the forming linear polymers is a dihalo alkane such as 
dibromoethane. See G.B. Pat. No. 1,014,999. Another coupling agent 
employed in making linear polymers is phenyl benzoate as disclosed in U.S. 
Pat. No. 3,766,301. Radial polymers are formed by employing coupling 
agents having more than two reactive sites. Examples of such coupling 
agents include among others: SiCl.sub.4 --U.S. Pat. No. 3,244,664; 
Polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones, 
polyanhydrides, polyesters, polyhalides--U.S. Pat. No. 3,281,383; 
Diesters--U.S. Pat. No. 3,594,452; Methoxy silanes--U.S. Pat. No. 
3,880,954; Divinyl benzene--U.S. Pat. No. 3,985,830; 
1,3,5-benzenetricarboxylic acid trichloride--U.S. Pat. No. 4,104,332; and 
glycidoxy-methoxy silanes--U.S. Pat. No. 4,185,042. 
The linear and radial block polymers may also be formed by sequential 
polymerization using multi-functional initiators having .gtoreq.2 reactive 
carbon-lithium bonds. The dilithium initiators are represented by the 
formula LiRLi. Examples of these dilithium initiators are 
1,1,6,6-tetraphenyl-1,5-hexadiene, 1,3-divinylbenzene, 
1,3-bis(1-methylvinyl)benzene, 1,4-bis(2-phenylvinyl)benzene, 
1,3-bis(1-phenylvinyl)benzene, 1,4-bis(1-phenylvinyl)benzene, 
4,4'-bis(1-phenylvinyl)biphenyl, 2,7-diphenyl-1,7-octadiene, 
2,7-di-4-tolyl-1,7-octadiene, 1,2-bis(4-(1-phenylvinyl)phenyl)-ethane, and 
1,4-bis(4-(1-phenylvinyl)phenyl)butane. Initiators with more than two 
lithium-carbon bonds can be formed by the reaction of RLi and DVB. 
The letters "m", "n", "o" and "p" stand for the relative number of arms in 
each polymer molecule. Accordingly, m, n, o and p are integers when 
referring to a single polymer molecule. However, a polymer mass will 
generally contain molecules of varying functionality. When referring to 
the polymer (AB).sub.m Y, it is preferred that m be 1 to 15, preferable 2 
to 8. When referring to the polymers (AB).sub.n Y--A).sub.o and (AB).sub.n 
Y--A).sub.p, it is preferred that the sum of n+o be greater than 3, 
preferably 3 to 15 and that the sum of n+p be greater than 3, preferably 3 
to 15. Accordingly n is preferably 2 to 8 for both polymers. 
The polymers of the present invention are produced by anionic 
polymerization employing an organomonolithium initiator. (The following 
description refers only to mono-lithium initiators, though it is 
appreciated, as stated above, that multi-functional initiators may also be 
used.) The first step of the process involves contacting the monoalkenyl 
arene monomer benzocyclobutene monomer and the organomonolithium compound 
(initiator) in the presence of an inert diluent therein forming a living 
polymer compound having the simplified structure A-Li. The monoalkenyl 
arene is preferably styrene. The inert diluent may be an aromatic or 
naphthenic hydrocarbon, e.g., benzene or cyclohexane, which may be 
modified by the presence of an alkene or alkane such as pentenes or 
pentanes. Specific examples of suitable diluents include n-pentane, 
n-hexane, isooctane, cyclohexane, toluene, benzene, xylene and the like. 
The organomonolithium compounds (initiators) that are reacted with the 
polymerizable additive in step one of this invention are represented by 
the formula R.sup.1 Li; wherein R.sup.1 is an aliphatic, cycloaliphatic, 
or aromatic radical, or combinations thereof, preferably containing from 2 
to 20 carbon atoms per molecule. Exemplary of these organomonolithium 
compounds are ethyllithium, n-propyllithium, isopropyllithium, 
n-butyllithium, sec-butyllithium, tertoctyllithium, n-decyllithium, 
n-eicosyllithium, phenyllithium, 2-naphthyllithium, 4-butylphenyllithium, 
4-tolyllithium, 4-phenylbutyllithium, cyclohexyllithium, 
3,5-di-n-heptylcyclohexyllithium, 4-cyclopentylbutyllithium, and the like. 
The alkyllithium compounds are preferred for employment according to this 
invention, especially those wherein the alkyl group contains from 3 to 10 
carbon atoms. A much preferred initiator is sec-butyllithium. See U.S. 
Pat. No. 3,231,635. The concentration of the initiator can be regulated to 
control molecular weight. Generally, the initiator concentration is in the 
range of about 0.25 to 50 millimoles per 100 grams of monomer although 
both higher and lower initiator levels can be used if desired. The 
required initiator level frequently depends upon the solubility of the 
initiator in the hydrocarbon diluent. These polymerization reactions are 
usually carried out at a temperature in the range of -75.degree. to 
+150.degree. C. and at pressures which are sufficient to maintain the 
reaction mixture in the liquid phase. 
Next, the living polymer in solution is contacted with a conjugated diene. 
Preferred dienes include butadiene and isoprene. A much preferred diene is 
butadiene. The resulting living polymer has a simplfied structure 
A--B--Li. The predominantly cis-1,4 microstructure of the polybutadiene 
blocks obtained from polymerization in cyclohexane can be modified to a 
random mixture of 1,4- and 1,2-structures by the addition of a small 
amount of ether modifiers such as Et.sub.2 O, THF, etc. 
The B-Li polymer arms may be formed in a separate reactor employing an 
inert solvent, organomonolithium initiator and conjugated diene monomer. 
In an alternative embodiment, the B-Li arms may be formed in the same 
reactor as the AB-Li polymer arms. In that case, after the A-Li arms are 
formed, additional initiator is added. Then the conjugated diene monomer 
is added. In this alternative embodiment, the B arms and the B portion of 
the AB arms will necessarily be similar in composition and molecular 
weight. 
The molecular weights of the living polymer arms (A and B) may vary between 
wide limits. Suitable number average molecular weights are: 
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Preferred More Preferred 
______________________________________ 
A 300 to 30,000 
3,000 to 20,000 
B 15,000 to 100,000 
25,000 to 60,000 
______________________________________ 
The living AB-Li and B-Li or A-Li polymer arms are then reacted with a 
multifunctional coupling agent. Exemplary coupling agents are listed 
above. The AB and ABA polymers do not require use of coupling agents. 
The coupling agent should be aded to the living polymer after the 
polymerization of the monomers is substantially complete, i.e., the agent 
should only be added after substantially all of the monomer has been 
converted to living polymers. 
The amount of coupling agent added depends upon the structure of the 
coupling agent and on the desired number of arms, and the choice is within 
the skill of the average polymers chemist. 
The coupling reaction step may be carried out in the same solvent as for 
the polymerization reaction step. A list of suitable solvents is given 
above. The coupling reaction step temperature may also vary between wide 
limits, e.g., from 0.degree. to 150.degree. C., preferably from 20.degree. 
to 120.degree. C. The reaction may also take place in an inert atmosphere, 
e.g., nitrogen and under pressure e.g., a pressure of from 0.5 to 10 bars. 
Following the coupling reaction, the polymer product may be hydrogenated 
according to copending application Ser. No. 812,424, now U.S. Pat. No. 
4,687,815, or functionalized. 
Then the product is typically recovered such as by coagulation utilizing 
hot water or steam or both. 
A key aspect of the present invention is that the end product contains 
randomly distributed benzocyclobutene structures in the styrene end 
blocks. A schematic structure for an ABA block copolymer is shown below, 
where the monoalkenyl arene block is made from styrene (S) and the diene 
block is made from butadiene (B): 
##STR4## 
Accordingly, when such a polymer is molded at temperatures above about 
200.degree. C. (or otherwise heated above such temperatures), a 
crosslinked elastomer is obtained. 
To illustrate the instant invention, the following illustrative embodiments 
are given. It is to be understood, that the embodiments are given for the 
purpose of illustration only and the invention is not to be regarded as 
limited to any of the specific materials or conditions used in the 
specific embodiments.

ILLUSTRATIVE EMBODIMENTS I 
A key aspect of the present invention deals with the ring-opening of the 
benzocyclobutene monomers to reactive o-quinodimethanes. In this 
embodiment, half-life values for the parent benzocyclobutene are 
calculated and summarized in the following Table 1, based on activation 
parameters reported in W. R. Roth et al Chem. Ber. 111, 3892-3903 (1978). 
The results suggest that reactive oligomers and polymers containing 
benzocyclobutenes which are not substituted at the cyclobutene ring would 
have long shelf-life and good reactivity at 200.degree.-250.degree. C. 
TABLE 1 
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##STR5## 
T (.degree.C.) 
k (sec.sup.-1) 
t.sub.1/2 (hr) 
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25 2.5 .times. 10.sup.15 
7.6 .times. 10.sup.10 
100 1.7 .times. 10.sup.-9 
1.1 .times. 10.sup.5 
150 9.6 .times. 10.sup.-7 
2 .times. 10.sup.2 
200 1.4 .times. 10.sup.-4 
1.4 
250 7.8 .times. 10.sup.-3 
2.5 .times. 10.sup.-2 
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ILLUSTRATIVE EMBODIMENT II 
Preparation of 4-vinylbenzocyclobutene 
A solution of 4-chloromethylbenzocyclobutene (24.4 g, 160 mmol) and 
triphenylphosphine (41.9 g, 160 mmol) in 120 ml of chloroform was heated 
at reflux for 24 h. Addition of diethyl ether followed by filtration gave 
tripheny(4-benzocyclobutenyl)methyl phosphonium chloride as a white 
powder: .sup.1 H NMR (CDCl.sub.3) .delta.3.03 (m, 4H), 5.36 (d, 2H), 6.82 
(m, 3H), 7.6-7.8 (m, 15H). To a solution of the phosphonium salt in 500 ml 
of 37% formaldehyde in water was added dropwise 75 ml of 50% aqueous 
sodium hydroxide. The mixture was stirred at ambient temperature for 2 h 
and then extracted with diethyl ether. The ether extract was washed with 
brine and dried over magnesium sulfate. Fractional distillation gave 14.5 
g of 90% pure 4-vinylbenzocyclobutene: bp 63.degree.-66.degree. C. (6 
torr); .sup.1 H NMR (CDCl.sub.3) .delta.3.11 (s, 4 H), 5.11 (d, 1H), 5.63 
(d, 1H), 6.66 (dd, 1H), 6.95 (d, 1H), 7.10 (s, 1H), 7.18 (d, 1H); .sup.13 
C NMR (CDCl.sub.3) .delta.29.29, 29.44, 112.27, 119.87, 122.52, 125.70, 
136.72, 137.97, 146.66, 146.01. 
##STR6## 
ILLUSTRATIVE EMBODIMENT III 
Preparation of Styrene-Butadiene Triblock Polymers with 
4-vinylbenzocyclobutene in the Styrene Block 
To a solution of styrene (9.73 g, 93.6 mmol), 4-vinylbenzocyclobutene 164 
mg, 1.26 mmol), and 25 .mu.l of 1-.eta.-butoxy-2-t-butoxyethane in 233 g 
of cyclohexane was added 1.3 mmol of s-butyl lithium. After the mixture 
was heated at 50.degree. C. for 30 min under an inert atmosphere, 
butadiene (25.6 g, 474 mmol) was added and the heating was continued for 
an additional 2.5 h. The polymerization was terminated by the addition of 
0.5 mmol of methyl benzoate. GPC analysis showed the product to be a 
mixture of polystyrene (7.9% MW 7,500), styrene-butadiene diblock (35.4%, 
MW 28,000), styrene-butadiene-styrene triblock (54.4%, MW 58,000), and 
styrene-butadiene multiblock (2.3%, 106,000). .sup.1 H NMR showed the 
product to contain 28%W styrene, 1.2%m 4-vinylbenzocyclobutene in the 
styrene block, and 40%m vinyl in the butadiene block. 
ILLUSTRATIVE EMBODIMENT IV 
Various styrene-butadiene-styrene block copolymers with 
4-vinylbenzocyclobutene (VBC) in the styrene blocks were prepared in a 
manner similar to that used in Illustrative Embodiment III. 
Reactive styrene-butadiene-styrene block polymers containing VBC were 
prepared using styrene monomer containing 1.3%m of VBC. The 
polymerizations were carried out in glass bottles at 50.degree. C. in 
cyclohexane using s-BuLi as initiator and the results are summarized in 
Table 1. Styrene-butadiene-styrene triblock polymers were prepared by 
sequential anionic polymerization of styrene and butadiene using twice the 
theoretical amounts of BuLi followed by coupling the living diblock 
polymers with methyl benzoate. GPC analysis showed the products to be 
mixtures of diblock and triblock polymer whose experimental molecular 
weights were in good agreement with those calculated based on zero 
consumption of BuLi by impurities. The coupling efficiencies based of 
methyl benzoate were generally in the range of 70-80% (Table 2). 
The presence of benzocyclobutene in the products can be readily confirmed 
by the magnetic resonance of the ethylene protons in benzocyclobutene at 
.delta.3.1 ppm. Quantitative .sup.1 H NMR showed the 
styrene-butadiene-styrene triblock polymer to contain 1.2%m VBC based on 
styrene. This value agrees well with that of 1.3%m VBC in styrene monomer. 
TABLE 1 
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Comparison of Calculated and GPC Molecular Weights 
##STR7## 
SBBS MW (.times. 10.sup.3) 
17317-28-# Calculated Found 
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1 5.1-25.2-5.1 4.5-23.4-4.5 
2 5.1-26.8-5.1 4.6-25.5-4.6 
3 7.6-37.8-7.6 7.1-40.7-7.1 
4 7.6-39.4-7.6 7.5-43.1-7.5 
5 5.0-25.4-5.0 4.5-24.8-4.5 
6 7.6-40.0-7.6 7.3-44.4-7.3 
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TABLE 2 
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% SBBS 
17317-28-# 
Calculated Found Coupling Eff. (%) 
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1 78 58 73.4 
2 79 50 63.3 
3 77 62 80.5 
4 77 54 70.1 
5 79 61 77.2 
6 77 62 80.5 
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