Method for the termination of living polymers, and compounds suitable for the purpose

Coupling agents of general formula ##STR1## and their use in a method for the termination of living polymers obtained by anionic polymerization of diene and/or vinylaromatic monomers.

If effected under suitable conditions and with suitable monomers (M. SZWARC 
Carbanions, Living Polymers and El. Transfer Processes, Interscience 
Publishers J. Wiley & Sons, New York 1968), anionic polymerisation enables 
living polymers to be obtained which are well suitable for appropriate 
transformations. Among these, the coupling reaction (coupling of two or 
more polymer segments by a coupling agent to give a polymer having a 
molecular weight of nPM, where PM is the molecular weight of the polymer 
segment and n the functionality of the coupling agent) is certainly one of 
the most investigated, in that by a simple approach it enables important 
variations to be obtained, even in terms of the properties of the treated 
polymers. For example, in the polymerisation of dienes it is possible in 
this manner to increase the Mooney viscosity, decrease the cold flow, 
increase the green tensile strength and modify the molecular weight 
distribution at will. 
In the synthesis of block polymers constitued by linear or branched 
conjunctions of elements A and B (where A is a polyvinyl and/or 
polyisopropanyl aromatic sequence and B is a diene sequence, which can 
also be hydrogenated), the use of efficient coupling agents is a factor of 
essential importance in that it is a known fact that the possible presence 
of the unreacted substances A and B in the final product depresses the 
technological properties thereof. Numerous examples of coupling agents are 
reported in the literature [H. L. HSIEH, Rubber Chem. and Techn. 49 (5), 
1305 (1976)]. We have now found that polystyryl derivatives, as 
exemplified hereinafter, can be conveniently used as new coupling agents 
in that in addition to possessing the typical properties of the best 
coupling agents described in the literature (see H. L. Hsieh, ibid) they 
have the following advantages: 
(i) the coupling reaction can also be effected without the use of 
activators 
(ii) the coupling reaction can be effected at a lower temperature than that 
usually used for conventional coupling agents, for equal reaction times 
(iii) by-products are not formed as the coupling reaction is a reaction of 
addition rather than elimination. 
The products which we have found to be efficient coupling agents are those 
of the following general formula 
##STR2## 
where X is an organic radical of the following structures, or a 
multivalent derivative thereof: 
##STR3## 
n is a whole number between 2 and 6 and preferably 2, 3 or 4; R can be 
hydrogen, an alkyl radical which preferably has a tertiary carbon atom 
directly attached to the aromatic ring, or a cycloalkyl, alkoxy, 
dialkylamino or aromatic radical. 
R contains between 0 and 18 C atoms. 
Said coupling agents are prepared in a simple manner and with high yields 
by the method of A. E. Siegrist and colleagues, [Helvetica Chimica Acta 52 
(8), 2521 (1969), ibid 63 (5), 1311 (1980)] starting for example from the 
methyl derivatives of the structures exemplified heretofore by X: 
##STR4## 
Typical non-limiting examples of methyl compounds used are: 
2,6-dimethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 
2,3-dimethylnaphthalene, 1,5-dimethylnaphthalene, 
2,3,6-trimethylnaphthalene, 1,3-dimethylbenzene, 1,3,5-trimethylbenzene, 
p-ditolylether, 4,4'-dimethyldiphenylethyne. 
The compounds according to the present invention can be used in processes 
for the polymerisation of monomers susceptible to anionic initiation under 
living conditions, and in particular for the polymerisation of diene 
and/or vinylaromatic monomers. 
The conjugated dienes used contain between 4 and 12 carbon atoms, and 
preferably between 4 and 8. 
Said monomers comprise: 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, 
piperylene, 3-butyl-1,3-octadiene and 2-phenyl-1,3-butadiene. 
The vinylaromatic monomers contain between 8 and 20 carbon atoms, and 
preferably between 8 and 14. Typical examples are: styrene, 
.alpha.-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 
2-isopropanylnaphthalene, p-phenylstyrene, 3-methylstyrene, 
.alpha.-methyl-p-methylstyrene and p-cyclohexylstyrene. 
The conjugated dienes and/or vinylaromatic monomers can be polymerised 
alone, in mixture, or sequentially to form homopolymers, statistical 
copolymers or block copolymers. 
The polymerisation is effected in solution at a temperature of between 
-100.degree. and +200.degree. C. and preferably between 0.degree. and 
110.degree. C., and at a pressure which is that of the system under the 
temperature conditions used, but higher or lower pressures are non 
contra-indicated. 
Suitable solvents include paraffin, cycloparaffin and aromatic 
hydrocarbons. Typical examples are cyclohexanol, hexane, pentane, heptane, 
isooctane, benzene, toluene and mixtures thereof. 
Small quantities of polar compounds can be added in known manner to the 
solvent in order to obtain a 1,2 configuration in diene polymerisation, or 
in order to increase the efficiency of the initiator in the polymerisation 
of vinylaromatic monomers. 
The initiators are the typical anionic initiators used for this purpose. 
Organometal compounds of formula R--Me are preferably used, where R is an 
aliphatic, cycloaliphatic or aromatic hydrocarbon radical, and Me is an 
alkaline metal, preferably lithium. 
The quantity of initiator used is relative to the molecular weight of the 
polymer to be obtained. The polymerisation is conducted under conditions 
such as to ensure the living state of the polymer obtained (M. SZWARC 
Carbanions, Living Polymers and El. Transfer Processes, Interscience 
Publishers, J. Wiley & Sons, New York 1968). 
The coupling agent can be introduced into the reaction environment in any 
manner, either by a single addition or by partial additions, at the 
required time. 
It is preferably introduced in the required quantity on termination of the 
polymerisation. 
The molar quantity of coupling agent (m.sub.AC) to be added is given by the 
formula 
EQU m.sub.AC =m.sub.CA /f.sub.AC 
where m.sub.CA is the moles of active centres in the living polymer 
f.sub.AC is the functionality of the coupling agent. 
The amount of coupling agent used influences the coupling yield. 
Obviously a stoichiometric ratio of the polymer active centre to the 
coupling agent active centre (taking its functionality into account) 
favours maximum yield. 
The temperature at which the coupling reaction is carried out depends on 
the type of agent used, the type of polymer undergoing reaction, and other 
factors such as the reaction medium. Generally it can vary between 
20.degree. and 150.degree. C., but is preferably between 40.degree. and 
80.degree. C. The contact time is between some minutes and some hours, 
preferably being between 10 minutes and 2 hours. 
Sometimes polar activators can be used to increase the coupling rate. 
In the case of the more active coupling compounds claimed herein, the use 
of these activators is not required. 
The solvents are those used in polymerisation. 
The coupling reaction is conducted at the natural pressure of the system at 
the operating temperature, but higher or lower pressures are not 
contra-indicated.

EXAMPLE 1 
The polymerisation and coupling are carried out in a 1 liter reactor fitted 
with an agitator, pressure indicator, thermocouple well and a passage for 
introducing the reagents and inert gas. 
500 cm.sup.3 of anhydrous cyclohexane, 12 g of styrene and 1.0 mmoles of 
Li-sec.butyl are fed in that order, and are allowed to polymerise at 
60.degree. C. for about 1 hour. After this time, 30 g of butadiene are 
added and the polymerisation is completed at 60.degree. C. within 1 hour. 
A very small quantity of this polymer is withdrawn and fed to the various 
analyses. 0.45 mmoles of a solution of 2,6-distyrylpyridine in 
benzene-cyclohexane (50--50 v/v) are then injected at 60.degree. C. 
After 15 minutes the polymer, to which 1 g of antioxidant is added, is 
coagulated with an excess of methanol to obtain 42 g of product, which is 
dried at 60.degree. C. for 15 hours under vacuum. 
The properties of the polymers before and after the coupling reaction are 
given in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Composition % weight.sup.(a) 
Molecular weight, g/mole.sup.(b) 
Sample 
STY BUT 
##STR5## 
##STR6## 
Polydispersity index.sup.(c) 
Gel % 
Coupling efficiency 
%.sup.(d) 
__________________________________________________________________________ 
A--B 30 70 55000 50000 1.1 0 -- 
A--B--A 
30 70 127000 98000 1.3 0 &gt;90 
__________________________________________________________________________ 
NOTES: 
.sup.(a) by N.M.R. 
.sup.(b) by G.P.C. measurements in accordance with the procedure describe 
by L. H. Tung, J. Appl. Polym. Sci. 24, 953 (1979) 
##STR7## 
.sup.(d) as the ratio of the area of the polymer peak after the coupling 
reaction (A--B--A) to the area of the polymer peak before the coupling 
reaction (A--B), these areas being determined by G.P.C. 
The polymer A-B-A of Example 1 has the following technological 
properties: 
elongation: 915% 
ultimate tensile stress: 32 MPa 
whereas the corresponding polymer A-B shows an ultimate tensile stress of 
about 3 MPa for equal elongation. 
If the 2,6-distyrylpyridine is replaced by dichlorodiphenylsilane as the 
coupling agent, then under the same experimental conditions the coupling 
efficiency is less than 10%. 
EXAMPLE 2 
Example 1 is repeated, but using 2,4,6-tristyrylpyridine (0.30 mmoles), and 
polymers (A-B and A-B-A) are isolated having the properties given in Table 
2. 
TABLE 2 
__________________________________________________________________________ 
Composition % weight.sup.(a) 
Molecular weight, g/mole.sup.(b) 
Sample 
STY BUT 
##STR8## 
##STR9## 
Polydispersity index.sup.(c) 
Gel % 
Coupling efficiency 
%.sup.(d) 
__________________________________________________________________________ 
A--B 30 70 57000 52000 1.1 0 -- 
A--B--A 
30 70 196000 145000 1.35 0 about 
__________________________________________________________________________ 
95 
Notes: 
see Table 1 
EXAMPLE 3 
50 g of .alpha.-methylstyrene and 1 mmole of Li-sec.butyl are fed into the 
reactor described in Example 1, and polymerised at 20.degree. C. for 1 
hour and 15 minutes. At the end of this time, 5 g of butadiene are added 
and allowed to interact for 15 minutes, after which 500 cm.sup.3 of 
cyclohexane and 25 g of butadiene are added, allowing polymerisation to 
continue at 60.degree. C. for 1 hour. A small sample is withdrawn, and 
0.45 mmoles of 2,6-distyrylpyridine are then injected, the coupling 
reaction being conducted at a temperature of 60.degree. C. for 15 minutes. 
A polymer is isolated in the usual manner (43 g) and has the properties 
shown in Table 3, which also gives the properties of the product A-B. 
TABLE 3 
__________________________________________________________________________ 
Composition % weight.sup.(a) 
Molecular weight, g/mole.sup.(b) 
Sample 
.alpha.STY 
BUT 
##STR10## 
##STR11## 
Polydispersity index.sup.(c) 
Gel % 
Coupling efficiency 
%.sup.(d) 
__________________________________________________________________________ 
A--B 30 70 63000 55000 1.15 0 -- 
A--B--A 
30 70 139000 99000 1.40 0 about 
__________________________________________________________________________ 
90 
Notes: 
see Table 1 
EXAMPLE 4 
Example 1 is repeated but using 2,3-distyrylnaphthalene as the coupling 
agent. The relative data are given in table 4. 
TABLE 4 
__________________________________________________________________________ 
Composition % weight.sup.(a) 
Molecular weight, g/mole.sup.(b) 
Sample 
STY BUT 
##STR12## 
##STR13## 
Polydispersity index.sup.(c) 
Gel % 
Coupling efficiency 
%.sup.(d) 
__________________________________________________________________________ 
A--B 30 70 53900 49000 1.1 0 -- 
A--B--A 
30 70 128000 95000 1.35 0 about 
__________________________________________________________________________ 
85 
Notes: 
see Table 1 
EXAMPLE 5 
The polymerisation test described in Example 3 is repeated, but using 
1,3,5-tristyrylbenzene as the coupling agent. The data relative to the 
isolated polymers are shown in Table 5. 
TABLE 5 
__________________________________________________________________________ 
Composition % weight.sup.(a) 
Molecular weight, g/mole.sup.(b) 
Sample 
.alpha.STY 
BUT 
##STR14## 
##STR15## 
Polydispersity index.sup.(c) 
Gel % 
Coupling efficiency 
%.sup.(d) 
__________________________________________________________________________ 
A--B 29 71 50600 46000 1.1 0 -- 
A--B--A 
29 71 186000 133000 1.4 0 &gt;90 
__________________________________________________________________________ 
Notes: 
see Table 1 
EXAMPLE 6 
Example 1 is repeated, but polymerising isoprene instead of butadiene. 
2,6-distyrylpyridine is used as the coupling agent, the reaction being 
conducted at 90.degree. C. for 30 minutes. 
The data relative to the isolated polymer (about 42 g) and the 
corresponding product A-B are given in Table 6. 
TABLE 6 
__________________________________________________________________________ 
Composition % weight.sup.(a) 
Molecular weight, g/mole.sup.(b) 
Sample 
STY BUT 
##STR16## 
##STR17## 
polydispersity index.sup.(c) 
Gel % 
Coupling efficiency 
%.sup.(d) 
__________________________________________________________________________ 
A--B 30 70 52800 48000 1.1 0 -- 
A--B--A 
30 70 124000 92000 1.35 0 about 
__________________________________________________________________________ 
80 
Notes: 
see Table 1 
EXAMPLE 7 
About 40 g of butadiene are polymerised with 1 mmole of Li-sec.butyl in 
about 400 cm.sup.3 of cyclohexane for about 1 hour at 60.degree. C., in 
the apparatus heretofore described. At the end of this time, a mixture of 
2,6-distyrylpyridine (0.225 mmoles) and 2,4,6-tristyrylpyridine (0.5 
mmoles) is added, and the reaction allowed to proceed for 15 minutes at 
60.degree. C. The G.P.C. diagram of the isolated polymer shows the 
presence of peaks of products with a different degree of coupling and with 
a wider molecular weight distribution than that of the polymer A-B.