A method for preparing tapered block copolymers in a polymerization process by charging an initiator and monomers sequentially with one or more charges of first one of the monomers, then with a mixture of the two monomers, and then with one or more charges of the second monomer alternating with one or more charges of the first monomer with subsequent coupling, to produce a polymodal tapered block copolymer. Suitable monomers include conjugated dienes and monovinylaromatic compounds. The copolymers are suitable for use in injection and blow molding equipment; the copolymers are particularly useful for shrink films, containers, tubes, fibers and other packaging applications.

This invention relates to tapered block copolymers of conjugated dienes and 
monovinylarenes. 
In another aspect, this invention relates to a method of preparing tapered 
block copolymers of conjugated dienes and monovinylarenes. 
Polymerization of styrene and butadiene with organolithium initiators to 
produce block copolymers in which one or more non-elastomeric polymer 
blocks are bonded to one or more elastomeric polymer blocks has been 
disclosed. Similarly, styrene and butadiene with terminal tapered blocks 
have been prepared by sequential charging of initiator and monomers to the 
polymerization zone to produce block copolymers suitable for manufacture 
of transparent colorless blister packages. 
There is a continuing need for transparent colorless material suitable for 
shrink wrap packaging applications. Having better shrinkage properties 
exhibited at lower temperatures would facilitate the use of block 
copolymer shrink wrap in packaging applications. 
There has also developed in the polymer field, and especially in the 
packaging and related industries, a need for thermoplastic polymers that 
can be formed into transparent articles having high impact strength with 
good environmental stress crack resistance. These should be suitable for 
use with conventional injection and blow molding equipment and also 
suitable for use in other methods of forming plastics into containers, 
tubes, films, fibers and the like. Polystyrene, high impact polystyrene, 
branched block copolymers, and the like have been developed to meet these 
criteria with various degrees of satisfaction. There is a continuing need 
for colorless transparent materials with high impact strength and good 
environmental stress crack resistance. 
SUMMARY OF THE INVENTION 
Thus, it is an object of this invention to provide a novel tapered block 
copolymer of conjugated dienes and vinyl-substituted aromatic hydrocarbons 
with improved shrink properties. 
A further object of this invention is to provide a novel process for making 
tapered block copolymers. 
The inventive copolymers are prepared by: 
(1) charging a monovinylaromatic monomer and an initiator and in the 
presence of a randomizer and allowing polymerization to occur until 
essentially no free monomer is present; thereafter 
(2a) charging additional monovinylaromatic monomer and initiator, and 
allowing polymerization to occur until essentially no free monomer is 
present; 
(2b) charging a mixture of monovinylaromatic monomer and conjugated diene 
monomer, and allowing polymerization to occur until essentially no free 
monomer is present; 
(2c) charging additional monovinylaromatic monomer and additional 
initiator, and allowing polymerization to occur until essentially no free 
monomer is present; thereafter 
(3) charging conjugated diene monomer and allowing polymerization to occur 
until essentially no free monomer is present; and finally 
(4) charging the reaction mixture with a coupling agent. 
Charges (2a), (2b) and (2c) can be made in any order. Also, optionally, a 
charge of conjugated diene can be made next preceeding or next succeeding 
either of charges (2a) or (2b).

DETAILED DESCRIPTION OF THE INVENTION 
The tapered block character of the polymer is produced by, after the 
initial charge or charges of monovinylaromatic monomer and initiator, 
charging with a mixture of monovinylaromatic monomer and conjugated diene. 
This is generally followed by a charge of monovinylaromatic monomer and 
initiator to give a low molecular weight component. Alternatively (as in 
Run 5 described hereafter in Table III) the last monovinylaromatic monomer 
charge and the mixture charge can be reversed with the monovinylaromatic 
charge preceeded by a conjugated diene charge. Finally, a charge of 
conjugated diene is introduced. In another embodiment of this invention 
the charges can be made in the sequence shown in the typical charging 
sequence shown in Table I. At each stage of charging, polymerization is 
allowed to continue until essentially no free monomer is present. 
With each subsequent charge which includes initiator a different molecular 
weight species will be produced as well as the opportunity for 
polymerization of part of the charge with each of the existing species. 
After virtually complete polymerization of the final monomer charge, the 
active living linear block copolymers are charged with a polyfunctional 
coupling agent to allow coupling of each of the living species with each 
of the other species or with others of the same species to form the 
desired polymodal tapered block polymers. 
A typical charging sequence, and the resulting polymers at each stage, is 
shown in the following table. 
TABLE I 
______________________________________ 
Typical Charging Sequence 
______________________________________ 
1. initiator.sub.1 tetrahydrofuran 
S.sub.1 --Li.sub.1 
and styrene.sub.1 
2. initiator.sub.2 and styrene.sub.2 
S.sub.1 --S.sub.2 --Li.sub.1 
S.sub.2 --Li.sub.2 
3. butadiene.sub.1 and styrene, 
S.sub.1 --S.sub.2 --B.sub.1 /S.sub.3 --Li.sub.1 
S.sub.2 --B.sub.1 /S.sub.3 --Li.sub.2 
4. butadiene.sub.2 (optional) 
S.sub.1 --S.sub.2 --B.sub.1 /S.sub.3 --B.sub.2 
--Li.sub.1 
S.sub.2 --B.sub.1 /S.sub.3 --B.sub.2 --Li.sub.2 
5. initiator.sub.3 and styrene.sub.4 
S.sub.1 --S.sub.2 --B.sub.1 /S.sub.3 --B.sub.2 
--S.sub.4 --Li.sub.1 
S.sub.2 --B.sub.1 /S.sub.3 --B.sub.2 --S.sub.4 
--Li.sub.2 
S.sub.4 --Li.sub.3 
6. butadiene, S.sub.1 --S.sub.2 --B.sub.1 /S.sub.3 --B.sub.2 
--S.sub.4 --B.sub.3 --Li.sub.1 
S.sub.2 --B.sub.1 /S.sub.3 --B.sub. 2 --S.sub.4 
--B.sub.3 --Li.sub.2 
S.sub.4 --B.sub.3 --Li.sub.3 
7. Epoxidized Vegetable Oil 
polymodal tapered block 
polymers with styrene 
terminal blocks 
______________________________________ 
where S = styrene 
B = butadiene 
B/S = tapered block 
At each stage, polymerization is allowed to continue until essentially no 
free monomer is present. The third, fourth, sixth and seventh steps shown 
above in the table of a typical charging sequence are carried out in the 
absence of additional initiator. Similarly, in invention charging 
sequences such as those shown in Table III and in the examples, steps in 
which only conjugated diene or in which a blend of conjugated diene and 
monovinylaromatic monomer is charged, no additional initiator is charged. 
Tapered blocks in each of the growing polymer chains present are produced 
by simultaneously charging with both monomers as in the third step shown 
above in the table of a typical charging sequence. As can be seen from the 
intermediate products listed in the typical charging sequence table above, 
there are at least three distinct polymer chains before coupling. Thus, 
polymodal block copolymers comprising high, medium and low molecular 
weight species are produced. The randomizer causes random polymerization 
of the monovinylaromatic monomer and the conjugated diene, but the diene 
still enters into the chain faster than the monovinyl substituted aromatic 
so that the block tapers gradually from an essentially pure polydiene 
block, to a random copolymer block, to an essentially monovinyl 
substituted aromatic block. 
The process of this invention can be carried out with any of the 
organomonoalkali metal compounds of the formula RM wherein R is an alkyl, 
cycloalkyl or arylcarbanion containing 4 to 8 carbon atoms and M is an 
alkyl metal cation. The presently preferred initiator is n-butyllithium. 
The conjugated diene monomers which can be used contain 4 to 6 carbon atoms 
and include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 
2,3-dimethyl-1,3-butadiene and 1,3-pentadiene and mixtures thereof. 
Presently preferred is 1,3-butadiene. 
The monovinylaromatic monomers which can be used contain 8 to 12 carbon 
atoms and include styrene, alpha-methylstyrene, p-vinyltoluene, 
m-vinyltoluene, o-vinyltoluene, 4-ethylstyrene, 3-ethylstyrene, 
2-ethylstyrene, 4-tertbutylstyrene and 2,4-dimethylstyrene and mixtures 
thereof. Presently preferred is styrene. 
The polymerization process is carried out in a hydrocarbon diluent at any 
suitable temperature in a range of -10.degree. to 150.degree. C., 
preferably in the range of 0.degree. to 110.degree. C., at pressures 
sufficient to maintain the reaction mixture substantially in the liquid 
phase. Preferred hydrocarbon diluents include linear and cycloparaffins 
such as pentane, hexane, octane, cyclohexane, cyclopentane and mixtures 
thereof. Presently preferred is cyclohexane. Generally the temperature is 
such that the resulting polymer is in solution. 
Small amounts of polar compounds are used in the hydrocarbon diluent to 
improve the effectiveness of alkylmonoalkali metal initiators such as 
n-butyllithium and to effect partial randomization of the 
vinylarene/conjugated diene so as to increase the random portion of the 
tapered block. Examples of polar compounds which can be advantageously 
employed are ethers, thioethers (sulfides) and tertiary amines. It is 
usually preferred to use ethers and sulfides in which the radicals 
attached to the oxygen or sulfur atoms are hydrocarbon radicals. Specific 
examples of such polar materials include dimethyl ether, diethyl ether, 
ethyl methyl ether, ethyl propyl ether, di-n-propyl ether, di-n-octyl 
ether, anisole, dioxane, 1,2-dimethoxyethane, dibenzyl ether, diphenyl 
ether, tetramethylene oxide (tetrahydrofuran), dimethyl sulfide, diethyl 
sulfide, tetramethylethylenediamine, tetraethyldiamine, di-n-propyl 
sulfide, di-n-butyl sulfide, methyl ethyl sulfide, dimethylethylamine, 
tri-n-ethylamine, tri-n-propylamine, tri-n-butylamine, trimethylamine, 
triethylamine, 1,2-dimethoxybenzene, N,N-di-methylaniline, 
N-methyl-N-ethylaniline, N-methylmorpholine, and the like. It is to be 
understood also that mixtures of these polar compounds can be employed in 
the practice of the present invention. The amount of polar compounds used 
in admixture with the hydrocarbon diluent is usually in the range of 0.005 
to 50 weight percent of the total mixture. Presently preferred are either 
tetrahydrofuran or diethyl ether. Amounts of tetrahydrofuran to provide 
preferably from about 0.01 to 10 phm (parts per 100 parts of total 
monomer), and more preferably 0.02 to 1.0 phm are suitable. 
The initial monovinylaromatic charge is made with the randomizer present 
for the additional effect of causing the monovinylaromatic component 
resulting from each initiator charge to be of relatively narrow molecular 
weight distribution. Surprisingly, it has been found that superior results 
are obtained by having a polymodal molecular weight distribution of the 
total polymer chain lengths as a result of the addition of initiator at 
least three times and yet having the terminal monovinyl substituted 
aromatic component portions of the molecules resulting from each initiator 
addition be of relatively narrow molecular weight distribution. 
The polymerization is carried out in a substantial absence of oxygen and 
water, preferably under an inert gas atmosphere. Prior to the coupling 
step, the reaction mass contains a very high percentage of molecules in 
which an alkali metal cation is positioned at one end of each polymer 
chain. Impurities in the feed such as water or alcohol reduce the amounts 
of monoalkali metal polymer in the reaction mass. 
After virtually complete conversion of the last monomer added to the 
polymer, a suitable polyfunctional coupling agent is added. As used here, 
the term "coupling" means the bringing together and joining, by means of 
one or more central coupling atoms or coupling moieties, two or more of 
the living monoalkali metal-terminated polymer chains. A wide variety of 
compounds for such purposes can be employed. 
Among the suitable coupling agents are the di- or multivinylaromatic 
compounds, di- or multiepoxides, di- or multiisocyanates, di- or 
multiimines, di- or multialdehydes, di- or multiketones, di- or 
multihalides, particularly silicon halides and halosilanes, mono-, di-, or 
multianhydrides, mono-, di-, or multiesters, preferably the esters of 
monoalcohols with polycarboxylic acids, diesters which are esters of 
monohydric alcohols with dicarboxylic acids, lactones, and the like, 
including combination type compounds containing two or more groups and 
mixtures. 
Examples of suitable vinylaromatic coupling agents include, but are not 
limited to, divinylbenzene, 1,2,4-trivinylbenzene, 1,3-divinylnaphthalene, 
1,3,5-trivinylnaphthalene, 2,4-divinylbiphenyl, diisopropenylbenzene and 
the like. Of these, the divinylaromatic hydrocarbons are preferred, 
particularly divinylbenzene in either its ortho, meta, or para isomer. 
Commercial divinylbenzene which is a mixture of the three isomers and 
other compounds is satisfactory. 
Epoxidized hydrocarbon polymers such as epoxidized liquid polybutadiene and 
the epoxidized vegetable oils such as epoxidized soybean oil and 
epoxidized linseed oil, and epoxy compounds such as 1,2; 5,6; 
9,10-triepoxydecane, and the like, can be used. 
Examples of suitable multiisocyanates include benzene-1,2,4-triisocyanate, 
naphthalene-1,2,5,7-tetraisocyanate, and the like. Commercially available 
products known as PAPI-1, a polyarylpolyisocyanate having an average of 3 
isocyanate groups per molecule and an average molecular weight of about 
380 are suitable. 
The multiimines, also known as multiaziridinyl compounds, such as those 
containing 3 or more aziridine rings per molecule, are useful. Examples 
include the triaziridinyl phosphine oxides or sulfides such as 
tri(1-aziridinyl)phosphine oxide, tri(2-methyl-1-aziridinyl)-phosphine 
oxide, tri(2-ethyl-3-decyl-1-aziridinyl)phosphine sulfide, and the like. 
The multialdehydes are represented by compounds such as 
1,4,7-naphthalenetricarboxyaldehyde, 1,7,9-anthracenetricarboxyaldehyde, 
1,1,5-pentanetricarboxyaldehyde, and similar multialdehyde-containing 
aliphatic and aromatic compounds. The multiketones are represented by 
compounds such as 1,4,9,10-anthracenetetrone, 2,3-diacetonylcyclohexanone, 
and the like. Examples of the multianhydrides include pyromellitic 
dianhydride, styrene-maleic anhydride copolymers, and the like. Examples 
of the multiesters include diethyladipate, triethylcitrate, 
1,3,5-tricarbethoxybenzene, and the like. 
Among the multihalides are the silicon tetrahalides such as silicon 
tetrachloride, silicon tetrabromide, and silicon tetraiodide; the 
trihalosilanes such as trifluorosilane, trichlorosilane, 
trichloroethylsilane, tribromobenzylsilane, and the like; and the 
multihalogen-substituted hydrocarbons, such as 
1,3,5-tri(bromomethyl)benzene, 2,5,6,9-tetrachloro-3,7-decadiene, and the 
like, in which the halogen is attached to a carbon atom which is alpha to 
an activating group such as an ether linkage, a carbonyl group, or a 
carbon-to-carbon double bond. Substituents inert with respect to lithium 
atoms in the terminally reactive polymer can also be present in the active 
halogen-containing compounds. Alternatively, other suitable reactive 
groups different from the halogens as described above can be present. 
Examples of compounds containing more than one type of functional group 
include 1,3-dichloro-2-propanone, 2,2-dibromo-3-decanone, 
3,5,5-trifluoro-4-octanone, 2,4-dibromo-3-pentanone, 
1,2,4,5-diepoxy-3-pentanone, 1,2; 4,5-diepoxy-3-hexanone, 1,2; 
11,12-diepoxy-8-pentadecanone, 1,3; 18,19-diepoxy-7,14-eicosanedione, and 
the like. 
Other metal multihalides, particularly those of tin, lead, or germanium, 
can be employed as coupling and branching agents. Silicon or other metal 
multialkoxides, such as silicon tetraethoxide, are also suitable coupling 
agents. 
The presently preferred coupling agent is epoxidized vegetable oil. Most 
preferred is epoxidized soybean oil. 
Any effective amount of the coupling agent can be employed. While the 
amount is not believed to be particularly critical, a stoichiometric 
amount relative to the active polymer-alkali metal tends to promote 
maximum coupling as a generality. However, less than stoichiometric 
amounts can be used for lesser degrees of coupling where desired for 
particular products of broadened molecular weight. 
Typically, the total amount of coupling agent is in the range of about 0.1 
to 20 mhm (gram millimoles per 100 grams of total monomers employed in the 
polymerization, presently preferably about 0.1 to 1 mhm (or about 0.1 to 1 
phm). 
At the conclusion of the coupling process, the system is treated with an 
active hydrogen compound such as water, alcohol, phenols or linear 
saturated aliphatic mono- and dicarboxylic acids to remove the lithium 
from the polymer. Preferably, the polymer cement, i.e. the polymer in the 
polymerization solvent, is treated with terminating agents such as water 
and carbon dioxide and then antioxidants. 
The resins are then stabilized with a combination of a hindered phenol and 
an organophosphite, specifically, octadecyl 
3-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate and 
tris-nonylphenylphosphite. After stabilization, the hydrocarbon diluent is 
then flashed off the polymer solution to increase the solids content. 
The polymers prepared according to this invention are polymodal, resinous 
block copolymers and contain from about 55 to 95, preferably 60 to 87, and 
more preferably 70 to 80, weight percent of polymerized monovinyl 
substituted aromatic hydrocarbon monomer based on the weight of total 
monomers employed. 
In charges (1), (2a), (2b) and (2c) referred to in the Summary of the 
Invention above, the weight percentages of monovinylaromatic monomer as a 
percent of the total monovinylaromatic monomer charged are as shown in the 
following Table II. 
TABLE II 
______________________________________ 
Amounts of Monovinylaromatic Monomer in Each Charge 
More 
Charge.sup.a 
Broad Range Preferred Range 
Preferred Range 
______________________________________ 
(1) 15-60, wt. %.sup.b 
20-55, wt. %.sup.b 
24-50, wt. %.sup.b 
(2a) 5-35, wt. %.sup.b 
10-29, wt. %.sup.b 
15-23, wt. %.sup.b 
(2b) 4-25, wt. %.sup.b 
5-20, wt. %.sup.b 
7-18, wt. %.sup.b 
(2c) 6-40, wt. %.sup.b 
12-36, wt. %.sup.b 
15-31, wt. %.sup.b 
______________________________________ 
.sup.a These charges (1), (2a), (2b) and (2c) correspond to the 
likenumbered charges in the Summary of the Invention above. 
.sup.b Based on total weight of styrene in the copolymer. 
The weight ratio of monovinyl substituted aromatic monomer to conjugated 
diene monomer in charge (2b) is from about 5:1 to about 1:10, preferably 
from about 1:1 to about 1:2, and more preferably from about 1:0.7 to about 
1:1.4. 
The amount of inititiator in the first initiator charge is from about 0.005 
mhm to about 10 mhm, preferably from about 0.1 mhm to about 1.0 mhm, and 
more preferably from about 0.03 mhm to about 0.04 mhm. 
The amount of inititiator in the second initiator charge is from about 
0.005 mhm to about 10 mhm, preferably from about 0.1 mhm to about 1.0 mhm, 
and more preferably from about 0.03 mhm to about 0.04 mhm. 
The amount of inititiator in the third initiator charge is from about 0.01 
mhm to about 50 mhm, preferably from about 0.05 mhm to about 10 mhm, and 
more preferably from about 0.07 mhm to about 1.0 mhm. 
The following examples will describe in more detail the experimental 
process used and the polymodal tapered block copolymers with vinylarene 
terminal blocks obtained as a result of the process. 
EXAMPLE I 
In one run there was prepared a polymodal block copolymer of styrene, 
1,3-butadiene monomers and a tapered styrene/butadiene copolymer. While 
not wishing to be bound by theory, applicants believe the copolymer 
prepared is comprised primarily of species having at least the following 
general formulas: 
##STR1## 
where S=polystyrene block polymer 
taper=random tapered block copolymer of butadiene and styrene 
B=polybutadiene block 
x=residual coupling agent 
This block copolymer was prepared in a six-step sequential charging process 
as follows. In a first step, cyclohexane, 1.63 phm; tetrahydrofuran, 0.5 
phm; n-butyllithium, 0.035 phm; and styrene, 36 phm (where phm is parts 
per 100 parts total amount) were charged at 50.degree. C. to a two-gallon 
reactor provided with a stirrer. The temperature peaked at about 
95.degree. C. while the styrene polymerized substantially adiabatically to 
completion in about 5 minutes. The pressure was about 30 psig. 
Then a second charge of 0.035 phm n-butyllithium, 15.8 phm styrene and 13.2 
phm cyclohexane was added to the stirred reactor at 69.degree. C. The 
polymerization was allowed to proceed substantially adiabatically with 
polymerization temperature peaking at 80.degree. C. Total reaction time 
was 5 minutes. 
In a third step, 6.9 phm butadiene, 6.9 phm styrene and 13.2 phm 
cyclohexane were added to the stirred reactor and contents at 68.degree. 
C. The polymerization was allowed to proceed substantially adiabatically 
peaking at 91.degree. C. The total reaction time was 10 minutes. 
In a fourth step, 0.08 phm n-butyllithium, 16.8 phm stryene and 13.2 phm 
cyclohexane were charged to the reactor and contents at 67.degree. C. The 
reaction proceeded substantially adiabatically peaking at 88.degree. C. 
Total polymerization time was 5 minutes. 
In the fifth and final polymerization step, 17.7 phm butadiene and 6.6 phm 
cyclohexane were added to the reactor and contents at 84.degree. C. The 
polymerization was allowed to proceed substantially adiabatically with 
temperature peaking at 105.degree. C. Pressure was 60 psig. The total 
polymerization time was 10 minutes. 
After polymerization was complete, in a sixth final coupling step, the 
contents of the reactor were heated to 93.degree. C., and 0.4 phm 
epoxidized soybean oil was added. This was allowed to react for 15 
minutes. A small amount of water and carbon dioxide was added in a post 
treatment. After 5 minutes a phenolic stablizer, 0.25 phm, and a phosphite 
stabilizer, 1.0 phm, were added. After another 5 minutes, the polymer 
solution, 33.2 weight percent concentration, was heated to 176.degree. C. 
The cyclohexane was removed by flashing at ambient pressure. The isolated 
polymer, still containing some 15 to 20% residual cyclohexane, was dried 
further in a vacuum oven. 
The polymerization product mixture just prior to the final coupling step 
has the following three species of monoalkali living polymers: 
##STR2## 
where S=polystyrene block 
taper=random tapered block copolymer of butadiene and styrene 
B=polybutadiene block 
Li=active lithium 
The final polymodal tapered block copolymer is a result of various 
combinations of each of these three species with itself and with each of 
the others. 
Several additional resins were prepared in which the tapered block location 
and monomer were varied following essentially the same polymerization, 
coupling, and isolation procedure. The runs are shown in Table III. All of 
the polymerizations were done in a final solvent of approximately 201 phm. 
Polymerizations were usually initiated at or near 50.degree. C. and 
allowed to proceed adiabatically. Polymerization time was 5 minutes for 
styrene and 10 minutes for butadiene and butadiene/styrene mixtures. 
TABLE III 
__________________________________________________________________________ 
Run 2 Run 3 Run 4 Run 5 
__________________________________________________________________________ 
Step 1 
tetrahydrofuran, 
tetrahydrofuran, 
tetrahydrofuran, 
tetrahydrofuran, 
Charges 
0.5 phm 0.5 phm 0.5 phm 0.5 phm 
n-butyllithium, 
n-butyllithium, 
n-butyllithium, 
n-butyllithium, 
0.035 phm 0.030 phm 0.030 phm 0.0325 phm 
styrene, styrene, styrene, styrene, 
37 phn 32 phm 32 phm 37 phm 
Step 2 
n-butyllithium, 
n-butyllithium, 
butadiene, n-butyllithium, 
Charges 
0.035 phm 0.035 phm 5 phm 0.035 phm 
styrene, styrene, styrene, styrene, 
16 phm 16 phm 5 phm 16 phm 
Step 3 
butadiene, butadiene, n-butyllithium, 
butadiene, 
Charges 
7 phm 7 phm 0.035 phm 7 phm 
styrene, styrene, styrene, 
10 phm 5 phm 16 phm 
Step 4 
n-butyllithium, 
n-butyllithium, 
butadiene, n-butyllithium, 
Charges 
0.080 phm 0.080 phm 7 phm 0.08 phm 
styrene, styrene, styrene, 
12 phm 22 phm 17 phm 
Step 5 
butadiene, butadiene, n-butyllithium, 
butadiene, 
Charges 
18 phm 18 phm 0.08 phm 5 phm 
styrene, styrene, 
22 phm 5 phm 
Step 6 butadiene, butadiene, 
Charges 13 phm 13 phm 
Products 
S--S--B/S--S--B--Li 
S--S--B/S--S--B--Li 
S--B/S--S--B--S--B--Li 
S--S--B--S--B/S--B--Li 
Going S--B/S--S--B--Li 
S--B/S--S--B--Li 
S--B--S--B--Li 
S--B--S--B/S--B--Li 
into Final 
S--B--Li S--B--Li S--B--Li S--B/S--B--Li 
Coupling 
Step 
__________________________________________________________________________ 
where S = styrene polymer block 
B = butadiene polymer block 
B/S = tapered butadiene/styrene copolymer block 
Note: 
Run 1 is given as EXAMPLE I above. 
A comparative run in which no tapered blocks were made is shown in Example 
II. 
EXAMPLE II 
______________________________________ 
Run 6 
______________________________________ 
Step #1 Tetrahydrofuran 0.5 phm 
n-Butyllithium 0.035 phm 
Styrene 37 phm 
Step #2 n-Butyllithium 0.035 phm 
Styrene 16 phm 
Step #3 Butadiene 7 phm 
Step #4 n-Butyllithium 0.08 phm 
Styrene 22 phm 
Step #5 Butadiene 18 phm 
______________________________________ 
Intermediate products of this charging sequence resulted in the following 
polybutadienyllithium-terminated living molecules: 
##STR3## 
Coupling of this polymer lithium with epoxidized soybean oil and isolation 
of the resulting polymodal polymer was done in a manner identical to that 
used for the inventive runs described above. While not wishing to be bound 
by theory, applicants believe that the resulting polymodal polymer 
primarily comprised six species from the six possible coupling 
combinations: 
##STR4## 
where S=styrene block polymer 
B=butadiene block polymer 
x=residual coupling agent 
EXAMPLE III 
An invention run was done using the sequence of charges represented by 
charges (1), (2b), (2a), (2c) and (3) as listed in the Summary of the 
Invention above with an additional butadiene charge made next succeeding 
charge 2a. This invention run (designated Run 7 in the Tables) was carried 
out in the manner generally described in Example I for Runs 1 through 5. 
Invention Run 7 differed in that the following steps and amounts were 
used. 
______________________________________ 
Run 7 
______________________________________ 
Step #1 Tetrahydrofuran 0.5 phm 
n-Butyllithium 0.03 phm 
Styrene 32 phm 
Step #2 Butadiene 5 phm 
Styrene 5 phm 
Step #3 n-Butyllithium 0.035 phm 
Styrene 16 phm 
Step #4 Butadiene 7 phm 
Step #5 n-Butyllithium 0.08 phm 
Styrene 22 phm 
Step #6 Butadiene 13 phm 
Step #7 Epoxidized Vegetable Oil 
0.4 phm 
______________________________________ 
Intermediate products of the charging sequence of Run 7 are believed to 
have resulted in the following polybutadienyllithium-terminated living 
molecules: 
##STR5## 
Coupling of this polymer lithium with epoxidized soybean oil and isolation 
of the resulting polymodal polymer was done in a manner identical to that 
used for the inventive runs described above. While not wishing to be bound 
by theory, applicants believe that the resulting polymodal polymer 
primarily comprised six species from the six possible coupling 
combinations: 
##STR6## 
where S=styrene block polymer 
B=butadiene block polymer 
x=residual coupling agent 
EXAMPLE IV 
A comparative run (Run 8) was done using the same procedure and 
experimental conditions under which inventive Run 7 was made with the 
exception that no coupling step was done. The following steps and amounts 
were used. 
______________________________________ 
Run 8 
______________________________________ 
Step #1 Tetrahydrofuran 0.5 phm 
n-Butyllithium 0.029 phm 
Styrene 32 phm 
Step #2 Butadiene 5 phm 
Styrene 5 phm 
Step #3 n-Butyllithium 0.03 phm 
Styrene 16 phm 
Step #4 Butadiene 7 phm 
Step #5 n-Butyllithium 0.08 phm 
Styrene 22 phm 
Step #6 Butadiene 13 phm 
______________________________________ 
After termination of the polymerization and product recovery, it is 
believed that the following species are present in the polymodal block 
copolymer made in Run 8; 
##STR7## 
EXAMPLE V 
A comparative run (Run 9) was done using the same procedures and 
experimental conditions under which inventive Run 7 was made with the 
exception that the charge which would produce a tapered block was made 
just prior to the coupling step. 
______________________________________ 
Run 9 
______________________________________ 
Step #1 Tetrahydrofuran 0.5 phm 
n-Butyllithium 0.029 phm 
Styrene 32 phm 
Step #2 n-Butyllithium 0.03 phm 
Styrene 21 phm 
Step #3 Butadiene 20 phm 
Step #4 n-Butyllithium 0.08 phm 
Styrene 17 phm 
Step #5 Butadiene 5 phm 
Styrene 5 phm 
Step #6 Epoxidized Vegetable Oil 
0.4 phm 
______________________________________ 
Intermediate products of the charging sequence used for Run 9 resulted in 
the following polystyryllithium-terminated living molecules: 
##STR8## 
Coupling of this polymer lithium with epoxidized soybean oil and isolation 
of the resulting polymodal polymer was done in a manner identical to that 
used for the inventive runs described above. While not wishing to be bound 
by theory, applicants believe that the resulting polymodal polymer 
primarily comprised six species from the six possible coupling 
combinations: 
##STR9## 
where S=styrene block polymer 
B=butadiene block polymer 
B/S=tapered block polymer 
x=residual coupling agent 
EXAMPLE VI 
A comparative run (Run 10) was done using the same procedures and 
experimental conditions under which inventive Run 7 was made with the 
exception that no step which would produce a tapered block was made. Run 
10 is dintinguishable from Run 6 in that the following steps and amounts 
were used. 
______________________________________ 
Run 10 
______________________________________ 
Step #1 Tetrahydrofuran 0.5 phm 
n-Butyllithium 0.029 phm 
Styrene 32 phm 
Step #2 n-Butyllithium 0.03 phm 
Styrene 21 phm 
Step #3 Butadiene 5 phm 
Step #4 n-Butyllithium 0.08 phm 
Styrene 22 phm 
Step #5 Butadiene 20 phm 
Step #6 Epoxidized Vegetable Oil 
0.4 phm 
______________________________________ 
Intermediate products of this charging sequence resulted in the following 
polybutadienyllithium-terminated living molecules: 
##STR10## 
Coupling of this polymer lithium with epoxidized soybean oil and isolation 
of the resulting polymodal polymer was done in a manner identical to that 
used for the inventive runs described above. While not wishing to be bound 
by theory, applicants believe that the resulting polymodal polymer 
primarily comprised six species from the six possible coupling 
combinations: 
##STR11## 
where S=styrene block polymer 
B=butadiene block polymer 
x=residual coupling agent 
SHRINK TEST PROCEDURE 
The rsins to be tested for shrink were extruded as 20 mil sheets using a 
1.25" extruder with a 6" wide die and a 0.020" die gap. 
Samples were die cut from the 20 mil extruded sheets and conditioned at 
205.degree.-210.degree. F. The samples were stretched by an A.M. Long film 
stretcher at 205.degree.-210.degree. F. at a rate of 1000%/min. The amount 
of stretch was 2X in the machine direction (MD) and 3X in the transverse 
direction (TD). 
A standard test method, ASTM-D2732-70, was used to measure unrestrained 
linear thermal shrinkage. The specimens were die cut to 2.5".times.2.5" by 
the normal thickness. Three specimens of each were tested. The test 
specimens were conditioned at 23.degree..+-.2.degree. C. and 50.+-.5 
percent relative humidity for not less than 40 hours prior to testing. The 
specimens were placed in a free shrink holder. The holder did not restrain 
the specimens from floating in the bath medium, glycerine. The bath 
temperature was maintained for 10 minutes. The specimens were then removed 
from the bath and quickly immersed in water at room temperature. The 
specimens were set aside to cool for one hour, and then both the machine 
and transverse linear directions were measured. 
The percent of free shrinkage for each direction was calculated as follows: 
##EQU1## 
where L.sub.1 =initial length of side 
L.sub.2 =length of side after shrinkage 
The results of the shrink tests of the polymers made in Runs 1-6 given in 
Table IV. 
TABLE IV 
__________________________________________________________________________ 
Percent Shrink, Machine Direction/Transverse Direction 
Run 1 
Run 2 
Run 3 
Run 4 
Run 5 
Run 6 
__________________________________________________________________________ 
Butadiene/Styrene 
1:1 1:1.4 
1:0.7 
1:1 1:1 -- 
Monomer weight ratio 
in blend charge 
Tested at 60.degree. C. 
0.4/3.0 
0.8/1.6 
0.4/2.2 
0.4/1.2 
1.4/3.0 
0-/0.8 
Tested at 70.degree. C. 
3.4/8.4 
1.4/4.0 
3.8/8.8 
4.0/12.0 
3.2/10.2 
0.8/3.8 
Tested at 80.degree. C. 
15.6/26.7 
11.0/19.2 
11.6/23.6 
15.8/27.8 
11.0/23.2 
4.2/17.6 
__________________________________________________________________________ 
Notes: 
The material tested in each of the runs, 1 through 6, in this table is th 
polymodal polymeric material produced in each of the correspondingly 
numbered runs described above in Example I, Table III and Example II. Run 
1 through 5 are tests of inventive polymers within the scope of this 
invention and Run 6 is a test of the control run material from Example II 
 
It can be seen from the shrink test results shown in Table IV that all the 
resins of the invention had greater shrink than the control resin. Shrink 
was greater in the transverse, cross direction of the extruded sheet. 
Although all the resins with tapered blocks had better shrink than the 
control resin, location of the tapered block and monomer ratio affected 
shrink. It can be noted from the above table that, in general, the greater 
the amount of butadiene relative to the amount of styrene in the polymodal 
tapered block copolymer, the better the shrink obtained. The butadiene to 
styrene monomer weight ratio was the same in the copolymers of Runs 4 and 
5, but because of the tapered block being located nearer the terminal 
polystyrene block, Run 4 exhibited better shrink than Run 5. 
Another set of runs was done in order to show distinctions between the 
invention polymers and polymers having some of the features not 
characteristic of the invention polymers. 
Tests of Runs 7, 8, 9 and 10 were done in the same manner as that described 
in the test procedures and with the same equipment used to evaluate Runs 
1, 2, 3, 4, 5 and 6, except that the resins to be tested were extruded as 
15 mil sheets. 
TABLE V 
__________________________________________________________________________ 
Properties of Polymers Made for Comparison Purposes 
Environmental 
Stress Crack 
Percent Shrink, 
Percent Shrink, 
Resistance 
Melt 
Machine Direction 
Transverse Direction 
Curl 
Curl 
Polymer 
Comparison Feature 
Flow.sup.a 
at 158.degree. F. 
at 176.degree. F. 
at 158.degree. F. 
at 176.degree. F. 
Up Down 
__________________________________________________________________________ 
Run 7 
inventive run 
5.5 8 40 0 19 .14 .10 
Run 8 
no coupling 
42 11 28 2 9 .22 .24 
Run 9 
tapered block 
1.8 17 39 5 15 1.2 1.5 
on end prior 
to coupling 
Run 10 
no taper 8.6 5 19 2 11 .86 1.5 
__________________________________________________________________________ 
.sup.a g/10 min. 
It can be seen from the shrink tests results shown in Table V that all of 
the non-inventive runs exhibited less shrink than any of the inventive 
Runs 1-5 and 7. 
EXAMPLE VII 
Three invention runs (designated Runs A, B and C) were made using the 
procedures described in Example I, but with the sequence of steps and 
amounts of charges shown in Table VI. These three runs were tested for 
environmental stress crack resistance potential by use of an accelerated 
test referred to as the Puncture Test. Test specimens about 2 inces square 
were cut from an interior layer about 0.015 inches thick from a coil or 
roll of extruded sheet. The side of the film or sheet facing away or 
furtherest from the center of the coil or roll, of course, must "stretch" 
or cover more distance than the side closest to the center of the coil or 
roll. Results obtained from the outside part of a rolled layer are termed 
"curl down" and those from the inside part are termed "curl up". 
Each specimen was clamped over a hole about 1 inch in diameter and 4 drops 
of soybean oil were placed on the specimen over the hole. A rounded tipped 
stainless steel rod about 1/2 inch in diameter was weighted with a 2 kg 
load and brought into contact with the specimen. The time to failure in 
minutes was recorded. Ten specimens of each run were tested and the 
results were averaged. 
TABLE VI 
______________________________________ 
Amounts of Styrene and Butadiene and Resultant Properties 
Compar- 
Invention 
Invention 
Invention 
ison 
Run A Run B Run C Material.sup.a 
______________________________________ 
Step 1 
Styrene 30 phm 30 phm 24 phm 
Step 2 
Styrene 16 phm 16 phm 16 phm 
Step 3 
Butadiene 6 phm 18 phm 12 phm 
Styrene 6 phm 18 phm 12 phm 
Step 4 
Styrene 18 phm 6 phm 18 phm 
Step 5 
Butadiene 24 phm 12 phm 18 phm 
Melt flow, g/10 min. 
8.7 6.4 6.3 
Environmental Stress 
Crack Resistance 
Curl up 114.7 156.1 205.9 5.2 
Curl down 128.0 161.6 155.7 8.0 
______________________________________ 
.sup.a For purposes of comparison KR05 KResin .RTM. polymer commercially 
available from Phillips Petroleum Company was tested. 
While the polymers and methods of this invention have been described in 
detail for the purpose of illustration, the inventive polymers and methods 
are not to be construed as limited thereby. This patent is intended to 
cover all changes and modifications within the spirit and scope thereof.