GB2147586A - Preparation of block copolymers based on pivalolactone - Google Patents

Abstract

A process for the synthesis of block copolymers of ABC type, in which: A is a homopolymeric sequence of a vinylic monomer such as e.g., styrene, alpha -methyl-styrene, vinylbiphenyl, isopropenylbiphenyl, vinylnapthalene, isopropenylnaphtalene; B is a homopolymeric sequence of a dienic monomer or of a hydrogenation product of it and C is a homopolymeric sequence of pivalolactone, comprises: 1) polymerization of the vinylic sequence; 2) addition of the dienic sequence to the vinylic sequence, by means of the subsequent polymerization of the diene; 3) carboxylation of the living AB section, treatment with a tetraalkylammonium salt and polymerization of the pivalolactone.

Description

SPECIFICATION Preparation of block copolymers based on pivalolactone This invention relates to a process for the preparation of block polymers of the type AXByCz in which Ax is a polyvinyl and/or polyisopropenyl sequence, By is a diene sequence (optionally hydrogenated) and Cz is a polypivalolactone sequence.

According to the present invention, there is provided a process for the preparation of a block polymer of the type AXByCz in which Ax is an aromatic polyvinyl and/or polyisopropenyl sequence, By is a dienic sequence (optionally hydrogenated), Cz is a polypivaloiactone sequence, and x, y, z are integers representing the number of monomer units in the respective sequences, which process comprises the following stages (a) polymerization of an aromatic vinyl and/or isopropenyi monomer, (b) addition of a diene to the product formed in stage (a), (c) addition of carboxyl functional groups to the living AB polymer obtained in stage (b) causing the living AB polymer to initially react with carbon dioxide, and (d) addition of pivalolactone to the polymer obtained in stage (c).

The preparation of block copolymers of the A-B-C type in which A = styrene, B = diene and C = PVL (pivalolactone) is known from US-A-3557255. These polymers possess thermoelastomeric properties which depend on their polyphasic nature, with the presence of "hard" phases as well as of "soft" phases. The polymers are characterized by a good separation of the hard and soft phases and by a good cohesion within the regions of the hard phases (which in the case of the ABC polymers can be of two different types), and show generally good thermoelastomeric properties. Also, the transition temperature of the hard regions is an important parameter, in the sense that high transition temperatures are necessary for the thermoelastomers to show their resilient properties, particularly at high temperatures.

The ABC polymers disclosed in US-A-3557255 possess interesting characteristics; however, the polymers have a relatively low transition temperature (about 90"C) of the glass hard phase consisting of the polystyrene blocks. In GB-A-2112002, there is disclosed the preparation of block polymers of the ABC type, in which A is a homopolymeric sequence of a vinyl- or isopropenyl-aromatic monomer, B is a sequence of a dienic monomer (or it is the hydrogenation product of the same sequence) and C is a homopolymeric sequence of PVL, by a stagewise process which can be schematically shown as follows:: Ist stage In the first stage the polymerization is effected of the vinylaromatic or isopropenylaromatic monomer in the presence or not of a non polar solvent and/or a polar cosolvent (this is not added if in the subsequent 2nd stage the polydienic block is desired with a prevailingly 1-4 structure).

The reaction scheme can be as follows: R-Li + n STYR-(STY'),Li + (n - x) STY in which: xsn, STY = vinyl- or isopropenylaromatic monomer, R = alkyl.

The polymerization can be, as is the case of a-methylstyrene, an equilibrium polymerization depending on the concentration and on the temperature.

2nd stage In the second stage the diene is added to the product formed in the 1st stage, according to the schematic reaction:

R -(STY),Li + y DienR-(STY,-(Diene)-Li The addition of the diene must be carried out in the early steps of the second stage, cautiously in order to avoiding the depolymerization of the first block (due to the dilution) and to arriving to an end state (complete conversion of the diene) in which the agitation of the solution is satisfactory to the purpose of making it possible the following stage to be performed.

The "livingness" of the polymer additionally must not to have been impaired.

The microstructure of the diene is conditioned by the presence or not of polar activators.

3rd stage The third stage comprises a chain of reactions (said), which can be described as follows:

R-(STY)x-(Diene)yLi + CO2 > (1 a) R-(STY)x-(Diene),-COO-Li R-(STY)X-(Diene)y-COO- Li + H + > (1 .b) R-(STY)x-(Diene)y-COOH + Li+ R-(STY)x-(Diene)v-COOH + N R'4-O H (1 ) (1.c) R-(STY)x-(Diene)y-COONR14 + H20 R-(STY)K-(Diene)y-COON R'4 + z PVL ) (1.d) 0 rl R-(STY)x-(Diene)y-C-O-(PVL)z-N R'4 The Applicant has now surprisingly found that, by using, in the third step of the above described process, a salt of tetraalkylammonium having the formula NR'4S, the same step can be modified according to the following chain of reactions (2.a-2.c):

R-(STY)x-(Diene)y-Li + CO2 > (2.a) > R-(STY)X-(Diene)y-COO-Li R-(STY)x-(Diene)y-COO-Li + NR'4S z (2.b) R-(STY)x-(Diene)y-COONR'4 + LiS R-(STY)x-(Diene)y-COONR'4 + z PVL - > (2.c) 0 R-(STY)x-(Diene)y-C-O-(PVL),-NR14 The notable advantages of such an alternative are evident from the remarkable simplifications of the process which they allow: i) the grafting stage is effected with one reaction less; i.e., the reaction (1.b) is eliminated of formation of the -COOH function bearing polymer and correspondingly: ii)-the expensive and complex operations are avoided of purifying and drying of the -COOH function bearing polymer, needed to the purpose of removing the impurities harmful for the subsequent polymerization of PVL; iii) the reactions of introducing the -COOH function and of polymer grafting (2.a-2.c) are carried out in one single reaction vessel instead of two different reactors (1.a-1.b separated from 1.c-1.d); iv) special materials for the reactors and accessories are not needed, such as those required for acidic treatments (such as for the reaction 1 .b).

The allternative processes claimed and the resulting operational simplifications do not involve negative changes of the properties of the thus produced ABC copolymers.

The synthesis of the products of the present invention is shown in details hereinafter.

1. Synthesis of the A sequence According to the type of monomer used, the polymerization is carried out with or without using polymerization activators, in view of the type of product which is to be obtained.

As initiators alkyl or amide or hydride derivatives of the alkali metals can be used.

The usually used initiator is the Li-sec.-butyl, but also other initiators can be conveniently used such as e.g. Li-ethyl, Li-n.-propyl, Li-iso-propyl, Li-tert.-butyl and Na-amyl.

The use or not of aliphatic, cycloaliphatic, aromatic, alkylaromatic and polar aprotic solvents which allows the living polymerization to be effected, can be conditioned by the value of Tc of the monomers used (Tc = ceiling temperature, typical of each monomer, is the temperature above which a given monomer cannot be converted to a polymer).

Also the polymerization temperature for the various used monomers is conditioned by the value of their Tc: the polymerization reaction is generally carried out in the range of from -- 80"C to + 150"C, and preferably from - 30"C to + 80"C.

In particular cases, such as for a-methylstyrene, the polymerization is carried out as a mass reaction at room temperature, or in solution at lower temperature.

The types of monomers used are chosen among the vinylic and alkenylaromatic compounds.

In particular, styrene, a-methyístirene, vinylbiphenyl, isopropenylbiphenyl, vinylnaphtalene and isopropenylnaphtalene are used, their various possible isomers being comprised within the class of useful monomers. The polymerization degree, variable as desired (living polymer) is chosen in relation to the type of product which is to be obtained so as to obtain a desired ratio between the hard and the soft phases (see paragraph 2).

2. Synthesis of the B sequence The diene is added to the living polymer of the preceding paragraph, with the Li, Na or K counter-ion according to the type of initiator used, and the AB block is obtained in which the structure of the diene is a function of the type of counter-ion and of solvent used.

The addition must be done under such conditions as not to modify the living nature of the A block and the monomer-polymer equilibrium of the same A block (if A consists of monomer with low values of Tc).

In the absence of chain terminating products the conversion of the diene is complete.

The molecular weight of the B sequence is proportional to the quantity of dienic monomer and to the number of living A chains present in the system.

Generally hydrocarbon aliphatic, cycloaliphatic, aromatic and alkylaromatic solvents are used.

If the A sequence consists of monomers with low Tc values, as it has already been said at the beginning of this paragraph, before diluting with a solvent a blocking reaction must be effected, e.g. of the poly-a-methylstyrene at the end of the chain with butadiene, in order to avoiding that the monomer-polymer equilibrium, due to the dilution, be shifted towards the monomer. The dilution can then be done without any troubles.

In general the reaction is carried out at a temperature within the range of from - 50"C to + 150"C and preferably of from 0" to 60'C.

The generally used dienes are those containing up to 1 2 carbon atoms and preferably are 1,3butadiene, isoprene, 2,3-dimethyl-1 ,3-butadiene, 1,3-pentadiene (piperylene), 2-methyl-3-ethyl1,3-butadiene, 3-methyl-1 ,3-pentadiene, 1,3-hexadiene, 2-methyl-1 ,3-hexadiene-and 3-butyl1,3-octadiene.

3. Synthesis of the C sequence Starting from the living AB polymer resulting from the 2nd stage and applying the reactions 2.a, 2.b, 2.c in the order as described, products are obtained in which the distribution of C segments of PVL in all chains is homogeneously attained.

The introduction in the AB polymer of carboxyl functional groups according to the equation (2.a) is carried out by placing the living AB polymer in contact with an excess of CO2 dissolved within aliphatic, cycloaliphatic, aromatic, polar solvents and/or mixtures thereof, operating at a temperature comprised within the range of from - 50"C to + 100"C and preferably from - 5"C to + 25"C for a time of some hours. In order to speeding up the carboxylating reaction also operating under pressure of CO2 is possible. According to the experimental conditions adopted, a pollution in the functional groups bearing polymer can be obtained by ABBA coupling.

The functional groups bearing AB polymer can be used as such in the following grafting stage (see hereunder) of the pivalolactone block, or it can be preliminarly hydrogenated. In this case, if the diene is butadiene, the microstructure of the butadienic block must be suitably chosen in such a way, as to obtain, after the hydrogenation, a hydrogenated block still having elastomeric characteristics. In the hydrogenating process catalysts can be used indeed which operate in homogeneous or in heterogeneous phase; also compounds of the type of the tosylhydrazide which act in a stoichiometric ratio relatively to the unsaturations present give satisfactory results.

The AB-f-COO-Li compound dissolved in tetrahydrofuran and/or mixtures of it with aromatic, aliphatic and cyclo-aliphatic solvents, after that the excess of CO2 has been removed, is reacted with tetraalkylammonium salts (2.b) of the type NR'R2R3R4-S in which R1, R2, R3 and R4, equal to or different to each other are alkyl groups containing from 1 to 8 carbon atoms, and S is: Cl-, Br-, J-, CH3COO- HS04-, NO2-, NO3-, OCN-, SCN-, BF4-, and CH3-CsH4-SO3-.

The reaction is preferably carried out with a stoichiometric ratio of the -COO-Li to the NR4-S, taking into account the -COO-Li functions really present, at a temperature comprised within the range of from 20"C to 80 C, and preferably of + 60"C, the reaction being effected for variable times (from some minutes up to some hours) relatively to the adopted experimental conditions, to the reactivity and to the solubility of the used salts.

The addition of pivalolactone (reaction 2.c) in different quantities according to the type of product to be obtained, takes place with quantitative yields operating at temperatures comprised within the range of from + 20"C to + 80"C for a time of some hours. A homogeneous distribution of PVL in all chains is thus obtained. These copolymers show the typical properties of the products of the thermoelastomeric type.

Examples All the operational details will be evident from the reading of the following Examples which, however, must not be considered as to be limitative of the invention.

The products of the present invention are block copolymers of the A,ByC, type in which: A = aromatic polyvinyl and/or polyisopropenyl sequence; B = polydienic sequence and/or hydrogenated derivate thereof; C = polypivalolactone sequence.

x, y, z = integers representing the monomer units in the respective sequences, and which can assume the following values: 25(at750 200 < y. < 3000 5 < z < 200 The polymers of the AxByC, type have generally a molecular weight comprised within the range of from 20,000 to 200,000 The structures of the various sequences can be represented by the following formulas: Sequence of the A type:

and the possible different isomers.

Sequence of the B type:

in which Ra, Rb, Rc, Rd, Re, and Rf are equal or different to each other, and can be hydrogen and/or alkyl radicals.

Sequence of the C type:

In relation to the different values of x, y and z, products are obtained with different technological properties. In particular, the value of z can also be very reduced and as small as some units (25).

Example 1 In a tubular perfectly sealable glass reaction vessel of the capacity of 1 litre, equipped with stirring means, inlet for the nitrogen, pressure and temperature gouges and feeding inlet for the reagents, 50 cm of a-methylstyrene and 0,65 mmoles of Li-sec-hutyl are introduced The polymerization is effected for a 1 h and 45' time at room temperature and then 2 y of butadiene are charged, allowing the reaction to proceed, always at room temperature, for a 15' time. 300 cm3 of cyclohexane and 34 g of butadiene are then introduced, the reaction being continued at 60"C for 1 hour.

At the end this polymeric solution is slowly transferred into a reactor with nitrogen blanket containing 300 cm3 of CO2 saturated (in a stream of CO,,. tetrahydrofuran at 0 C).

After 1 hour the reaction mixture is left to reach the room temperature and by a slight depression the excess of carbon dioxide is completely removed. A small portion of this product, isolated and purified, shows (H-NMR analysis from CDCI3) the following composition: amethylstyrene (a-Sty) = 29% by weight (15.8 molar); butadiene (BUT)= 71% by weight (1-2 = 8.5 molar; 1-4 = 75.6 molar).

Its molecular weight is 75,000 g/mole. To the residual polymeric solution 0.5 meq are added of tetra-butylammonium iodide and the mixture is allowed to react for 1 h at 60"C. The pivalolactone (PVL; 3 ml) is at last charged and the reaction is allowed to proceed at the said temperature for further 3 hours.

By addition of a few cm3 of hydrochloric acid and precipitation with methanol, 52 g are isolated of product having the following composition: PVL 6% by weight, a-Sty = 28% and BUT = 66%.

The differential thermal analysis shows three transitions at - 91 'C, at + 160"C and at + 209"C (melting), attributable to respectively polybutadiene with high 1-4 linking rate, sharp; to poly-a-Sty, not very defined; and to poly-PVL, sharp. The polymer results to be completely soluble in cyclohexane after 16 hours of boiling.

The test pieces for the technological tests have been prepared from plates, compression moulded between two aluminum surfaces treated with a silicone anti-adhesive agent.

The moulding conditions can be summarized as follows: Temperature: 240"C Pressure: 30 kg/cm2 Preheating: 10 minutes Moulding: 10 minutes Cooling: running water at room temperature, which allows a maximum initial cooling rate of 40"C/minute.

Pressure release: when the temperature has reached the value of 30"C.

The test pieces for the tensile tests have been prepared by shearing 1 mm thick plates with the punching tool DIN S 3 A. The tensile tests have been effected by means of an INSTRON dynamometer according to the DIN 53504 standard at the rate of 200 mm/minute. The stress has been measured at strain intervals of 50%. The resulting curve is shown in Fig. 1 (o).

Example 2 The reaction is carried out as described in Example 1, polymerizing the a-methylstyrene for 1 h and 20', the remaining steps being the same; to the COO Li functions bearing polymer (amethylstyrene = 23% by weight, butadiene = 77% from NMR, molecular weight = 69,000 g/mole from GPC) tetrabutylammonium bromide is added, and the mixture is made to react for 1 h at 60"C. The pivalolactone is then added (2.8 ml) and the polymerization is allowed to proceed for some hours at the same temperature. By the same treatment as described in Example 1 a product is isolated, which has the following composition: PVL = 6% by weight, a Sty= 21% and BUT = 73%.The differential thermal analysis shows three transitions at - 90"C, at + 160"C and at + 208"C (melting) easily attributable.

The polymer is completely soluble in boiling cyclohexane.

The technological data on test pieces prepared as previously described are shown in Fig. 1 (*).

Example 3 The preceding Example is repeated with the only difference that instead of the tetrabutylammonium bromide is now used tetraethylammonium acetate. A product is obtained having the following composition: PVL = 6%, a-Sty = 22% and BUT = 72%. The technological data are similar to those of the preceding Example.

Example 4 The Example 1 is repeated with the only difference that tetraoctylammonium chloride is used.

A product is obtained having the following composition: PVL = 6% by weight, a-Sty = 28% and BUT = 66%.

The technological data of this product are similar to the preceding.

Claims (20)

1. A process for the preparation of a block polymer of the type A,B,C, in which A, is an aromatic polyvinyl and/or polyisopropenyl sequence, By is a dienic sequence (optionally hydrogenated). Q is a polypivalolactone sequence, and x, y, z are integers representing the number of monomer units in the respective sequences, which process comprises the following stages (a) polymerization of an aromatic vinyl and/or isopropenyl monomer, (b) addition of a diene to the product formed in stage (a), (c) addition of carboxyl functional groups to the living AB polymer obtained in stage (b) causing the living AB polymer to initially react with carbon dioxide, and (d) addition of pivalolactone to the polymer obtained in stage (c).

2. A process as claimed in claim 1, in which stage (a) is carried out in the presence of hydrocarbonaceous aliphatic, cycloaliphatic, aromatic, alkylaromatic or aprotic polar solvent

3. A process as claimed in claim 1 or 2, in which stage (a) is carried out in the presence of, as an initiator, an alkali metal alkyl, hydride or amide.

4. A process as claimed in claim 3, in which the initiator is Li-sec-butyl.

5. A process as claimed in any of claims 1 to 4, in which stage (a) is carried out at a temperature of from - 80"C to 1 50 C.

6. A process as claimed in claim 5, in which stage (a) is carried out at a temperature of from - 30"C to 80 C

7. A process as claimed in any of claims 1 to 6, in which stage (b) is carried out in the presence of hydrocarbonaceous aliphatic, cyclo-aliphatic, aromatic, alkylaromatic or polar aprotic solvent.

8. A process as claimed in any of claims 1 to 7, in which stage (b) is effected in the presence of an alkali metal alkyl, hydride or amide.

9. A process as claimed in any of claims 1 to 8, in which stage (b) is carried out at a temperature of from - 50"C to 150"C.

10. A process as claimed in claim 9, in which stage (b) is carried out at a temperature of from 0 C to 60'C.

11. A process as claimed in any of claims 1 to 10, in which, in stage (c), the introduction of carboxyl functional groups in the AB polymer is carried out by means of a saturated solution of CO2.

1 2. A process as claimed in claim 11, in which the solvent of the solution of CO, is an aliphatic and/or cycloaliphatic solvent

1 3. A process as claimed in any of claims 1 to 12, in which, in stage (c), the reaction is carried out at a temperature of from - 50"C to 20by.

14. A process as claimed in claim 13, in which, in stage (c). the reaction is carried out at at temperature of from - 5"C to 5"C.

1 5. A process as claimed in any of claims 1 to 14, in which stage (d) is carried out in the presence of a mixture of toluene and tetrahydrofuran.

1 6. A process as claimed in any of claims 1 to 15, in which stage (d) is carried out in the presence of a tetraalkylammonium salt having the general formula NR1R2R3R4S in which Rt, R2, R3 and R4 are the same or different and each is an alkyl group containing from 1 to 8 carbon atoms and S is selected from Cl-, Br-, I-, CH3COO-, HSO4-, NO2-, NO3-, OCN-, SCN-, BR4- and CH3C6H4SO3-

17. A process as claimed in any of claims 1 to 16, wherein the aromatic monomer is styrene, a-methylstyrene, vinylbiphenyl, isopropenylbiphenyl, vinylnaphthalene or isopropenylnaphthalene.

1 8. A process as claimed in any of claims 1 to 17, wherein x is from 25 to 750, and/or wherein y is from 200 to 3000, and/or wherein z is from 5 to 200.

19. A process as claimed in claim 1, substantially as described in any of the foregoing Examples.

20. A block polymer prepared by a process as claimed in any of claims 1 to 1 9.