NO169445B - STAR-BLOCKED COPOLYMERS, THE PROCEDURES FOR THE PREPARATION AND THEIR USE IN BITUMEN MIXTURES - Google Patents

Description

The present invention relates to star-shaped block copolymers, optionally mixed with linear two-block copolymers and homopolymers, and the distinctive feature of the star-shaped block copolymers according to the invention is that they exhibit the following structure:

in which:

Z stands for a residue originating from a tetrafunctional

coupling agent,

A stands for a polystyrene block with a molecular weight in the range

15,000 to 40,000, preferably from 15,000 to 25,000,

B stands for a polybutadiene block with a molecular weight in the range of 20,000 to 70,000, preferably from 40,000 to

50,000, and

m, n, p and q are either 1 or zero, with the proviso that their sum is in the range from 1 to 4, preferably from 1 to 3.

The invention also relates to a method for producing the aforementioned star-shaped block copolymers, and the peculiarity of the method according to the invention is that it comprises the following steps carried out in the specified order: (a) polymerization of the styrene according to the technique with living polymers at a temperature from 35° to 65°C using catalysts consisting of metal alkyl or metal aryl compounds, to form a polystyrene block with a molecular weight of from 10,000 to 40,000 containing a metal atom linked to the end of the polymeric chain A-M (where "M" constitutes the metal in the metal alkyl or metal aryl catalyst, and "A" is the polystyrene block), (b) polymerization of 1,3-butadiene to form a diblock copolymer A-B-M wherein "M" is the metal atom, "A" is the polystyrene block and "B" is the polybutadiene block with one

molecular weight of 20,000 to 70,000,

(c) heating the reaction mixture obtained in step (b) to a temperature above 100°C for 10 to 20 minutes, to obtain grafted and metal-containing structures of formula

where A, B and M have the above meaning,

(d) coupling the metal-containing structures formed in step (c) by means of a tetrafunctional coupling agent, (e) isolating the polymers resulting from the coupling reaction in step (d), and optionally f) separating the star-shaped block copolymers from the polymers obtained in step (e).

The invention also relates to the use of the aforementioned star-shaped block copolymers in an amount of 2-30 parts by weight, preferably 8-13 parts by weight, per 100 parts by weight of bitumen to improve the mechanical properties of bitumen mixtures.

These and other features of the invention appear in the patent claims.

It is known that suitable monomers are anionically polymerized in the presence of metal-alkyl or metalaryl catalysts, whereby "living" polymers are obtained and which are then suitable for being subjected to further conversions, such as e.g. be-written by M. Shwarc, "Carbanions, Living Polymers and El. Transfer Processes", Interscience Publishers, J. Wiley & Sons, New York, 1968.

With the technique of "living" polymers, it is possible to produce linear or radial block copolymers. Among linear block copolymers, e.g. polymers of the A-B-A type, where "A" is a polystyrene block with non-elastomeric thermoplastic properties and "B" is an elastomeric polybutadiene block.

The radial block copolymers can be obtained by reacting the living polymer with a suitable coupling agent.

In the case where e.g. silicon tetrachloride is used as coupling agent, polymers are obtained which can be represented by formula

in which B and A may have the meaning indicated above.

The use of both linear and radial such block copolymers is known in the art, for addition to bituminous mixtures, to improve the general properties of bitumens, especially their properties of elasticity, adhesion and anti-shrinkage.

In e.g. BE patent 738,281 deals with bituminous mixtures containing about 15% by weight of a linear block copolymer A-B-A, where "A" is a thermoplastic block (generally a polystyrene block) and "B" is an elastomeric block, generally a polybutadiene block.

The use of radial block copolymers of the polystyrene-polybutadiene type in bituminous mixtures is discussed in e.g. BE patent document 853.210.

Finally, US Patent 4,464,427 teaches bituminous mixtures containing both a linear block copolymer and a radial block copolymer belonging to the above types.

It was observed that the block copolymers of the radial type give the bituminous mixtures in which they are incorporated properties with regard to adhesion, elasticity and anti-shrinkage which are generally better than those which can be obtained by using linear block copolymers.

The greater the number of polymer segments in the radial copolymer, the more meaningful this improvement is.

It would therefore be desirable to have available block copolymers of the radial type with a large number of polymeric segments linked to the polyfunctional coupling agent.

As a practical fact, however, such a realization is limited by difficulties and/or high costs that occur when radial block copolymers are produced, containing more than four segments connected to the said coupling means.

With the present invention, it has now been found that it is possible to surpass the current state of the art by producing block copolymers of the radial type, containing four polymeric segments linked to the tetrafunctional coupling agent, where the said polymeric segments exhibit a controlled degree of branching.

The radial and branched block copolymers in accordance with the invention can give the bituminous mixtures in which they are incorporated mechanical technological properties that are unexpectedly improved in comparison with the corresponding radial block copolymers that do not contain such branches.

Polymer mixtures that can be produced from the present invention contain at least 50% by weight and preferably at least 60% by weight of the above-mentioned radial and branched block copolymers, the rest being made up of two-block copolymers "B-A" and of "A" homopolymer, wherein "A" and "B" have the above meanings.

The method for producing such polymer mixtures comprises the previously mentioned steps carried out in sequence using the technique of living polymers.

After the production of the polystyrene block in the indicated manner, polymerization of 1,3-butadiene monomer is carried out by the technique of living polymers, in the presence of the polystyrene block in which the metal atom is linked to the end of the polymer chain coming from the previous step, by working at a temperature of from about 60 to 100°C, to give a diblock copolymer in which the metal atom is attached to the end of the polystyrene chain: A-B-M, where "A" is the polystyrene block, "B" is the polybutadiene block with a molecular weight of from 20,000 to 70,000, and "M " has the above meaning.

Next, heating of the reaction mixture obtained in the previous step is carried out at a temperature in the range of more than 100°C up to about 140°C, generally in the range of 110 to 125°C, for a sufficient time to effect a grafting of two- the block copolymer B-A, and obtain grafted and metal-containing structures that can be represented by the formula:

wherein A, B and M have the above-mentioned meaning, and finally the aforementioned coupling of the metal-containing structures resulting from the previous step is carried out by means of a tetrafunctional coupling agent, and

isolation of the polymer components from the mixture resulting from the coupling reaction, and optionally

a separation is made of the obtained radial and branched block copolymers of the polymer constituents.

According to a preferred practical embodiment of the invention, the styrene polymerization (step (a)) and the subsequent copolymerization with butadiene (step b) are carried out adiabatically, so that at the end of (step (b)) a temperature higher than 100 °C, up to a maximum of 140°C. The fact that the temperature at the end of the copolymerization with butadiene is more than 100°C is of significant importance for obtaining radial and branched block copolymers in accordance with the invention.

In fact, if the final temperature of the copolymerization with butadiene is below 100°C, and a heating to increase this temperature to the above values is not carried out, the reaction with grafting of the B-A copolymer on the polybutadiene-B blocks will not take place, and the final products after coupling will not be branched radial copolymers.

In practice, the styrene polymerization step (step (a)) is carried out under anhydrous conditions, as this is necessary to obtain living polymers, in solution in inert hydrocarbon solvents, such as e.g. cyclohexane and n-hexane, at an initial temperature of about 50°C, using an alkyl metal or an aryl metal compound, in particular n-butyl lithium or sec-butyl lithium, as catalyst, in a molar ratio of styrene/ catalyst in the range from 1,000 to 5,000 and preferably in the range from 1,500 to 2,500.

The reaction is allowed to continue for approximately 60 min. until the conversion of the styrene is complete or almost complete, and polymer blocks with a molecular weight in the range from 10,000 to 40,000 and preferably in the range from 15,000 to 25,000 have been obtained.

To the solution containing the polystyrene blocks containing the metal atom at one end of their polymer chain, the solution having a temperature of approximately 60 to 65°C, 1,3-butadiene is added and over a period of approximately 40 min. linear polymers B-A are obtained, in which the "B" block has a molecular weight in the range from 20,000 to 70,000 and preferably in the range from 40,000 to 50,000.

The solution resulting from the copolymerization with butadiene is allowed to stand at a temperature above 100°C and preferably in the range from 110°C to 125°C for a time of from 10 to 20 minutes.

After this time period, a tetrafunctional coupling agent is added to the mixture, as this can then be selected from esters of aliphatic and aromatic dicarboxylic acids, chlorine derivatives of aliphatic or aromatic hydrocarbons, chlorine derivatives of aliphatic or aromatic silanes, substituted unsaturated arenes, such as e.g. divinylbenzene, further tetrachloro derivatives of tin, silicon, germanium and preferably SiCl4, in a molar ratio SiCl4/styrene equivalent to the stoichiometric or nearly stoichiometric ratio.

The coupling reaction is carried out at a temperature in the range from 100 to 140°C and preferably in the range from 110 to 125°C for a time of from 5 to 25 min., and the yield generally reaches a value of approximately 90%.

An amount of from 1 to 1.5% by weight of an antioxidant is added to the polymer components contained in the solution and the aforementioned polymer components are recovered from the reaction mixture by solvent stripping and drying in a vacuum oven at 60°C.

The polymer mixture thus obtained can be added as such to the bituminous mixtures, or as an alternative, the radial and branched copolymers can be separated from the other polymer components.

The polymer mixture resulting from step (e) comprises at least 50% by weight and preferably at least 60% by weight of the radial and branched copolymers, with the rest being 100% of the linear styrene-butadiene copolymer, or of polybutadiene.

The radial and branched block copolymers according to the invention can lead to a considerable improvement in the mechanical and technological properties of the bituminous mixtures in which they are incorporated compared to the corresponding non-branched, radial polymers.

It is further possible to obtain bituminous mixtures which are given the same properties as obtained previously, but by using the aforementioned copolymers in quantities which are much smaller than those known from prior art.

Such radial and branched block copolymers in accordance with the invention can be used in quantities in the range from 2 to 30 parts by weight for every 100 parts by weight of bitumen and preferably in the range from 8 to 13 parts by weight for every 100 parts by weight of bitumen.

The following examples illustrate the invention.

Example I

100 ml of anhydrous cyclohexane and 15 g (0.144 mol) of styrene distilled over calcium hydride are added to a 1 liter reactor from which moisture has been removed by means of a hot nitrogen stream, equipped with a stirrer, thermometer and cooling jacket. The cyclohexane contains 0.035 g of THF.

The mixture is stirred at 50°C and kept stirred.

0.047 g (0.73 mmol) of sec-butyllithium is added as polymerization initiator and the reaction is allowed to continue for 60 min. the temperature being kept at 50°C until the styrene conversion is complete.

At the end of this time period, 35 g (0.648 mmol) of 1,3-butadiene are added and the polymerization is allowed to continue for 40 min.

The end temperature of the polymerization is 95°C. The block copolymer, a living copolymer, which is formed, is left for 1 min. at 100°C and 0.028 g (0.165 mmol) SiCl4 is then added to the reactor.

The reaction is allowed to continue for 15 min. at 97°C and at the end of this time period, the obtained polymer mass is emptied from the reactor into a glass flask containing 45 g of BHT and "Polygard" (Phosproportional stabilizer).

The polymer solution is stripped in a stream of steam and dried in a vacuum oven at 60°C for two hours.

The polymer mixture was characterized by gel permeation chromatography and the results are shown in Table I.

Mv = weight average molecular weight

Ma = number average molecular weight

The polymer mixture was used to produce a bituminous mixture by mixing 13 parts of the polymer mixture into 100 parts of bitumen (SOLEA 180/200).

The properties of the bituminous mixture are given in Table II, in accordance with ASTM D5-65 and ASTM D36-66T standards.

Example II

The same amounts of reaction components as in ex. I is used, but the reactions are carried out under diabatic conditions in that the initial temperature during the styrene polymerization is 60°C,

and during a time of 20 min. the reaction temperature rises to 65°C where the monomer conversion is complete.

At the end of the copolymerization with 1,3-butadiene, the temperature rises due to the effect of the exothermic heat development in the reaction, to 120°C.

The polymer solution is left at the end of the reaction with butadiene for 15 min. at 120°C and then the process is continued by adding silicon tetrachloride, as referred to in ex. IN.

The properties of the polymer mixture are given in Table III.

The resulting polymer mixture is used to produce a bituminous mixture by mixing 100 parts of the polymer mixture into 100 parts of bitumen (SOLEA 180/200).

The properties of the thus obtained bituminous mixture are reproduced in Table IV, in accordance with ASTM D5-65 and ASTM D36-66T standards.

Claims (7)

1. Star-shaped block copolymers, optionally mixed with linear two-block copolymers and homopolymers, characterized in that they display the following structure: wherein: Z stands for a residue originating from a tetrafunctional coupling agent, A stands for a polystyrene block with a molecular weight in the range of 15,000 to 40,000, preferably from 15,000 to 25,000, B stands for a polybutadiene block with a molecular weight in the range 20,000 to 70,000, preferably from 40,000 to 50,000, and m, n, p and q are either 1 or zero, provided that their sum is in the range from 1 to 4, preferably from 1 to 3. 2. Star-shaped block copolymers as stated in claim 1, characterized in that the residue "Z" is silicon. 3. Process for the production of the star-shaped block copolymers specified in claim 1 or 2, characterized in that it comprises the following steps carried out in the specified order: (a) polymerization of the styrene according to the technique with living polymers at a temperature from 35° to 65°C using catalysts consisting of metal alkyl or metal aryl compounds, to form a polystyrene block with a molecular weight from 10,000 to 40,000 containing a metal atom linked to the end of the polymeric chain A-M (where "M" is the metal in the metalalkyl or metalaryl catalyst, and "A" is the polystyrene block), (b) polymerization of 1,3-butadiene to form a diblock copolymer A-B-M wherein "M" is the metal atom, "A" is the polystyrene block, and "B " is the polybutadiene block having a molecular weight of 20,000 to 70,000, (c) heating the reaction mixture obtained in step (b) to a temperature above 100°C for 10 to 20 minutes, to obtain grafted and metal-containing e structures with formula wherein A, B and M have the above meaning, (d) coupling the metal-containing structures formed in step (c) by means of a tetrafunctional coupling agent, (e) isolating the polymers resulting from the coupling reaction in step (d), and optionally f) separation of the star-shaped block copolymers from the polymers obtained in step (e). 4. Method as stated in claim 3, characterized by ati step (c), the heating is carried out at a temperature of 110° to 125°C. 5. Method as stated in claim 3, characterized in that the tetrafunctional coupling agent used in step (d) is selected from esters of aliphatic and aromatic dicarboxylic acids, chlorine derivatives of aliphatic or aromatic hydrocarbons, chlorine derivatives of aliphatic or aromatic silanes, doubly ethylenically unsaturated aromatics, and tetrachloro derivatives of tin, silicon and germanium. 6. Method as stated in claim 5, characterized in that SiCl4 is used as tetrafunctional coupling agent. 7. Use of the star-shaped block copolymers as stated in claim 1 or 2 in an amount of 2 to 30 parts by weight, preferably 8 to 13 parts by weight per 100 parts by weight of bitumen to improve the mechanical properties of bitumen mixtures.