CA1038535A - Process for the preparation of novel block polymers - Google Patents

Abstract

Inventor: Robert E. Cunningham Invention: PROCESS FOR THE PREPARATION OF NOVEL BLOCK
POLYMERS

Abstract of the Disclosure There is disclosed a method of preparing a five-mem-bered block polymer, said block polymer exhibiting superior properties than would be expected from copolymers made from similar blocks.

Description

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This lnvention relates to a method o~ preparing block polymers and to the novel polymers produced thereby.
More specifically, this invention relates to the preparation of a five-membered block polymer using a di-- 5 lithium initiator.
The use of alkali metals as initiators to make ' ~ "living polymers" has been described in the prior art for '~5 the preparation of certain block copolymers. Many of the ., prior art block copolymers have limited tensile strengkh at -elevated temperatures, have low tensile at room temperature `~ and in many cases require several laboratory manipulations i to achleve the desired product and thus are costly to pro- ~
duce ~ ;
~' In the present invention, a five-membered block ;~
polymer i5 made with the resulting block polymer having - superior properties than would be expected from other ~ ~
copolymers made from similar blocks. A polymethacrylo- ;
nitrile-polybutadiene-polymethacrylonitrile block polymer had a maximum tensile strength of 200 psi at 160 percent elongation. A polystyrene-polybutadiene-polystyrene block polymer had a tensile strength of 1800 psi at 1120 percent q O
elongatlon at 75 F.
The pol~Jmer described in the present invention ~ -is a polymethacrylonitrile-polystyrene-polybutadiene-' 25 polystyrene-polymethacrylonitrile block which has a ten- ;
.:~ , ; .~ sile strength of 2300 psi at 750F. with a solvent resistant `' characteristic. One would expect the tensile value of the '~ block polymer described in this invention to fall somewhere ~ in between the previously described three-membered block , . -~ .

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polymers, but it unexpectedly showed sUperior tensile pro~
per-ties and these -types of five-membered block polymers ;
have no-t previously been described.
j Thus, according to the invention, an A-B-C-B-A
block polymer consisting of polymethacrglonitrile-poly~
,3~ styrene-poly(conjugated diene)-polystyrene-polymethacrylo-~ nitrile can be prepared by (1) polymerizing a conjugated ;~ diene (C) and a styrene or alkyl substituted styrene (B), ~,~ by contacting with an organodilithium catalyst wherein a B-C-B bloc~ polymer is formed, and (2) injecting a meth~
~ acryloni-trile (A) into the polymerizing zone and continuing~
`j! the polym~rization whereby block polymer A-B-C-B-A is ~ f`ormed , ,.
,.f The initiatoxs which are useful for this inven-1~ tion are dil:Lthium organo compounds. These compounds are characterized as having two lithium atoms on each organic ".1 radical so that polymerization proceeds from each lithium ;~
site. They are characteriæed by the formula Li-R-Li, wherein R may be selected from the group consisting of alkyl~ cycloalkyl, aryl, alkaryl and arylalkyl. The ini~
~ tiators themselves are not the thrust of this invention, ~ ~;
:~, so khat any dilithium organo initiator which will promote polymerization would fall within the scope and spixit of ~; this invention~
The amount of dilithium organo initiators used in the practice of this invention cannot be specifically set down since the amount of initiator used depends on the molecular weight of polymer desired. What can be said is that a catalytic amount is necessary for polymerization.~
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As ai general rule, the molecular weight of the polymer is ;~
equal to the grams of polymer formed, divided by the mo7es - of ini-tiator employed. Thùs, one sk:illed in the art can adj-ust the catalyst level to get any desired molecular weigh-t polymer.
By the term "living polymex" is meant that the polymcrization has no termination or transfer reactions so ~
i -that the polymer chains have lithium atoms attached to the ~`
` ! ' ~, chain end when all the monomer is consumed. If additional monomer is added, the polymerization will continue with thé
~ new monomer adding on to the already existing chains until -, it is consumed.
The blocks may have different molecular weights -depending upon a specifically desired physical or chemical ; ~ ;
:L~ characteristic of the final product. For example, the molecular weight of the polystyrene block may be varied so -~
that an increased polystyrene molecular weight will impart ~ -~
a stiffness to the resul-ting block polymer. Not only dG
~, the molecular weights of the individual blocks have an "5~, 20 effect on the final block polymer, but also the weight :,. . .
;~' ratios of the molecular weights between the individual .; , ~ .. .
~j blocks affect the properties of -the final polymer. For :~., .
example, if the polystyrene block comprises a majority of the polymer, then the product would have a plastic charac-ter. ~ ;~
In the present invention, the polystyrene or alkyl substituted polystyrene molecular weight can range from about 10,000 to abou~ 50,000, the poly(conjugated i diene) molecular weight can range from about ~0,000 to ".~i :
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- abOIlt 150,000 and the polymethacrylonitrile molecular weight -~
can range from about 1,000 to about 20,000. The minimum `~
and maximum could be lower and higher but then other dis-- advarlta~es such as lower physical properties and difficult ; :
~j processing of the polymers become substantial. A more preferred range of molecular weights would be from about ~ 10,000 to about 20,000 for the polystyrene or alkyl sub~
`7~ stituted polystyrene block, from about 50,000 to about 80,000 for the polytconjugated diene) block and from about ~ 10 1,000 -to about 10,000 for the polymethacrylonitrile block i An op-timum composition for an elastomeric type block poly- `
mer would have about a 3/2 weight ratio o~ polytconjugated J, cl:ione)/polystyrene or alkyl substituted polystyrene with the polymethacrylonitr~le comprising about 5 to 20 percent :Lj by weight of the total polymer.
Although preferred ranges are set down in this invention~ this is not to preclude o-ther molecular weights ~ of the blocks, and also not to preclude other weight ratios ." ~ ,.
i of the blocks to be within the scope and spirit o:~ this invention. The preferred ranges set down within this speci-~i fication are only for the type of rubbery block polymer or which the final polymers will be utilized and are not to be used as a restriction on the scope of this invention.
, Represen-tative of the compounds which can be used as initiators in this invention are dilithiomethane, 1,4-dilithiobutane, 1,4-dilithiocyclohexane, l,~-dilithio~

2-ethyl cyclohexane, 1,3-dilithio-~-phenyl butane, 1,10-dilithiodecane, l,l-dilithiodiphenylene, dillthionaphtha-lene, dilithioisoprene, dilithiohexane and the like.

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The conjugated dienes which can be utilized in ,~ , this inve~tion are those that are already kno~n in the prior art. The conjugated dienes that can be utilized .. ~:
: in this invention contain from about ~ to about 8 carbon ..
5 atoms. Representative of the conjugated dienes that can be utilized are butadiene, isoprene, 2,3-dimethyl-1,3 . butadi ne, 1,3 hexadiene, 1~3-butadienea 1?3-octadiene, .
~ . piperylene? 2-methyl-1,3-hexadiene, 2-ethyl-1,3-hexadiene, ~ 2,l~-octadiene~ and the like.
:L0 Styrene as well as some Qf the alkyl substituted - .
; styrenes may be utilized in this invention. Representative of the alkyl substituted styrenes which can be utilized . ;~
:in thls invention are vinyl toluenes~ p(t-butyl) st~rene~
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., p(-ethyl) styrene and the like. .
.j 15 The temperature at which the polymerizations of ' this invention may be conducted is not critical. The ~; temperature may range from about 0OCo to about 100C. and -~
more preferred is 20C. to 70C.
The polymerization condltions and techniques ., ,j , .
should be tho9e characterized as air and moisture-~ree so as not to hinder the polymerizatlon reactions. These ..
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techniques are well known to one skilled in the art~ :
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~ The.polymerizations are us~ally conducted in .. ~ . the presence Or a solventO The pol~merizations may be " ... . . . .
~ 25 run in any o~ the known aliphatic and aromatic hydrocarbon .i solvents as long as they do not adversely affect the poly- ; .
~;;1; merization rate or the final product. Representative of , ,,.j ,: : i-such solvents are toluene~ benzene, pentane, hexane, cyclo- :-hexane and the like.
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The prac-tice of this invention is further illustrated by reference to the followin~ examples which are intended to be represen-ta-tive rather than restrictive of the scope of the invention. Unless otherwise indicated, all par-ts and percentages are by weigh-t.
EXAMPLE I
A solution was prepared to con~ain 4 grams (gm) of styrene and 6 gm of butadiene in 160 millili-ters (ml) total of a benzene solution. The solution was passed through silica gel, sparged with nitrogen, then cha~ed - to a polymerization bottle. To this solution was added 0.90 ml of a 0.20 molar (M) benzene solution o~ diiso~
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prenyl dilithium. The bottle was tightly capped and the solution polymerized a-t 50C. ~or 4-1/2 hours. A block polymer of polys-tyrene-polybutadiene-polystyrene was formed.
A solution containing 4 gm of methaerylonitrile ~
in 10 ml of a benzene solution was passed through silica ' gel and sparged with nitrogen. Gas chromatographic analy--, 20 sis of this solution showed 3.4 gm of methacrylonitrile , per 10 ml of~solution after sparging.
The polymerization bottle was cooled -to 25C. and ~ 7.5 ml of the methacrylonitrile solution were syringed into 'l , the polymerization mixture. The polymerization solution was thoroughly mixed and allowed to stand for about 18 ~;~
hours. Two ml of an acidic methanol solution containing :
a phenolic antioxidant were syringed into the polymeriza-tion bottle to terminate polymerization and stabilize the polymer. The polymer was coagulated and dried at 50C.

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'~, 'I'il:i', polymer was polyme-thacrylonitrile-polystyrene~poly~
bu~adienc-polystyrene-polymethacryIonitrile. The molecular wci~rhts were about 18,000 for. the polystyrene blocks, about ,o~o for the polybutadiene block and about ~700 ~`or -the polymethacrylonitrile blocks. The 10 gm of polymer con~
ta:ined 9~1~ percent by weight of methacrylonitrile. The polymer had a DSV of 1.72 and contained 20 percent gel .~
i measured in toluene at 30C ; however, the five-membered :.. ` `~:
.; bl.ock polymer was completely soluble in a 50-50 mixture . `
of toluene and dimethylformamide~ indicating that the poly~
j mer h^Ld resistance to aromatic solvents but was not a .~ c~ocslinked polymer. At 750F. khc five-membered block ..
-~ polymer had an ult.imate tensile of 2300 pounds per square ~.
:i.nch (psi) at 720 percent elongation. The control. block ~.
~ polymer to which no methacrylonitrile had been added had ;~ a DSV o~ 1.6~ and 2.4 percent gel in toluene at 30C. The ~ .`
control polymer had ultimate tensile of 1600 psi at 83Q ~:

percent elongation.
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;~J, EXAMPLE II
20. A polystyrene-pol~butadiene-polystyrene block ~ -:
]. polymer was prepared using similar procedures as Example ~`
1 :L except that 1.l~ ml of a 0.20 M solution of dilithio~
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polyisoprene was the initiator.
The methacrylonitrile solution was prepared 2~ similar to Example I except that 2 gm of methacrylonitrile , were used in the 10 ml solution and the gas chromato- :
:'1 ,, ~, graphic analysis showed the sclution contained 1.12 gm .
~l~ of methacrylonitrile after sparging. :~
~ To the polymerization bottle was added 20 ml o~ - ~
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the methiacrylonitrile solution. ~ ;
~` The isolated five-membered block polymer had a DSV of 1.52 and ~7 percent gel in toluene at ~0C. The ;~
molecular weights were about 11,000 for the polystyrene blocks, about 32,000 for the polybutadiene block and about , 4,200 ~or the polymethacrylonitrile blocks. The polymier -~ was completely soluble in an equivolume mixture of di~
methylformamide, methyl ethyl ~etone and toluene. The ! polymer had an ultimate tensile of 2350 psi at 710 percent elongation. ~ ;
s The control polymier to which no methacrylonitrile -~
was added had a DSV of 1.36 and 2.6 percent gel in toluene at 30C. The control polymer had an ultimate tensile of i ;~
1860 psi at 1120 percent elongation. ' EXAMPLE III
~! Thie example shows that the polymethacrylonitrile-~ polybutadiene-polymethacrylonitrile can be made but does j not possess good physical properties. It would not be expected that the polystyrene-polybutadiene-polystyrene 20~ polymers made in Examples I and II, when coupled with ; ~ the polymer made in this example, would result in such 1 superior properties.
'A,.'~ ' A solution was prepared to contain 6 gm of buta-diene in 160 ml o~ benzene solution. The solution was passed through silica gel and charged to a reaction bottle.
The solution was sparged with nitrogen and 1.1 ml of a 0.20 M benæene solution of dilithiodiisoprene was added.
;~, The reaction bottle was capped and tumbled in a water ~ ~
bath at 50C. for about 3.5 hours. The bottle was allowed ~;
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to cool -to abou-t 25C.
A solution was prepared to contain 2 gm o~
methacrylonitrile in every 10 ml benzene solution. This -~
solution was passed through silica gel column and sparged ~;
i 5 with nitrogen. Fifteen ml of -the met;hacrylonitrile solu~
' tion were syringed into the "livingl' polybutadiene solu~
. .. . tion. The solutions were allowed to s-tand at 25C. ~or about 16 hours.
The polymer cement was coagulated in acidi~ied methanol containing a phenolic an-tioxidant. me polymer was dried in vacuo at 50C. The block polymer had a DSV
of 1.47 and a gel con-tent of 58.1 percent in toluene at 30C. The block polymer had a tensile strength of 202 ', psi at 160 percent elongation. The polymer was analyzed , ;
to contain 21.5 percent by weight o~ methacr~loni-trile.
While certain represéntative embodiments and details have been shown for the purpose o~ illustratin~
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the invention, it will be apparent to those skilled in this art that various changes and modi~ications may be made therein without departing from the splrit or scope o~ the invention.
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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the preparation of novel block polymers comprising the steps:
(1) polymerizing a conjugated diene (C), and a styrene or alkyl substituted styrene (B), by contacting with an organodilithium cata-lyst wherein a B-C-B block polymer is form-ed, and (2) injecting a methacrylonitrile (A) into the polymerizing zone and continuing the poly-merization whereby block polymer A-B-C-B-A
is formed.

2. A process according to claim 1 in which the conjugated diene contains from 4 to 8 carbon atoms.

3. A process according to claim 1 in which the alkyl substituted styrene is selected from the group consist-ing of vinyl toluene, p(t-butyl) styrene, vinyl xylene and p(-ethyl) styrene.

4. A block polymer prepared according to the process of claim 1.

5. A block polymer according to claim 4 wherein the (C) block molecular weight is from about 40,000 to about 150,000, the (B) block molecular weight is from about 10,000 to about 50,000 and the (A) block molecular weight is from about 1,000 to about 20,000.