Butadiene polymers having terminal functional groups

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BACKGROUND OF THE INVENTION

This invention relates to manufacture of low viscosity hydrogenated butadiene polymers having terminal functional groups and use of the low viscosity polymers to make coatings and other high molecular weight polymers.

Anionic polymerization of conjugated dienes with lithium initiators, such as sec-butyllithium, and hydrogenation of residual unsaturation has been described in many references including U.S. Pat. No. Re. 27,145 which teaches a relationship between the amount of 1,2-addition of butadiene (35% to 55%) and the glass transition temperatures of the hydrogenated butadiene polymers.

The termination of living anionic polymers to form functional end groups is described in U.S. Pat. Nos. 4,417,029, 4,518,753, and 4,753,991. Of particular interest for the present invention are terminal hydroxyl, carboxyl, phenol, epoxy, and amine groups.

For unsaturated 1,3-butadiene polymers it is known that low 1,2-addition is necessary to obtain low viscosity as taught in U.S. Pat. Nos. 4,518,753 and 3,652,732. However, when these polymers are hydrogenated they are crystalline solids. Such a crystalline polymer is available from Mitsubishi and is designated POLYTAIL H polymer which has a melting point of 72.degree. C.

The hydrogenated butadiene polymers are non-crystalline when the 1,2-addition of butadiene is above 30% as described in U.S. Pat. No. 4,020,125. The non-crystalline hydrogenated butadiene polymers are viscous liquids at low molecular weights as described in U.S. Pat. Nos. 4,866,120 and 4,020,125. POLYTAIL HA polymer produced by Mitsubishi and NISSO GI-2000 polymer produced by Nippon Soda are commercial examples of low molecular weight hydrogenated butadiene polymers which have terminal functional groups and 1,2-addition of about of 84%.

It is an object of the present invention to provide hydrogenated butadiene polymers having terminal functional groups and low viscosity at room temperature. It is also an object of the invention to use the low viscosity polymers to make coatings and other high molecular weight polymers.

SUMMARY OF THE INVENTION

Applicants have discovered that varying the amount of 1,2-addition of butadiene in hydrogenated butadiene polymers having terminal functional groups significantly and unexpectedly impacts the viscosity of the polymers. The lowest viscosity for any given molecular weight of a hydrogenated butadiene polymer having terminal functional groups is achieved when the 1,2-addition is between 30% and 70%, preferably between 40% and 60%.

The hydrogenated butadiene polymers of the invention may be used without solvents at room temperature when the peak molecular weight, as measured by gel permeation chromatography, is between 500 and 20,000, preferably between 1,000 and 10,000.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of the relationship between vinyl content and viscosity of hydrogenated 1,3-butadiene polymers having terminal functional groups. The viscosity data are adjusted to remove molecular weight contributions by dividing the viscosity by the peak molecular weight raised to the 3.4 power.

DETAILED DESCRIPTION OF THE INVENTION

Anionic polymerization of conjugated diene hydrocarbons with lithium initiators is well known as described in U.S. Pat. Nos. 4,039,593 and Re. 27,145 which descriptions are incorporated herein by reference. Polymerization commences with a monolithium, dilithium, or polylithium initiator which builds a living polymer backbone at each lithium site. Typical living polymer structures containing polymerized conjugated diene hydrocarbons are:

X--B--Li

X--A--B--Li

X--A--B--A--Li

Li--B--Y--B--Li

Li--A--B--Y--B--A--Li

wherein B represents polymerized units of one or more conjugated diene hydrocarbons such as butadiene or isoprene, A represents polymerized units of one or more vinyl aromatic compounds such as styrene, X is the residue of a monolithium initiator such as sec-butyllithium, and Y is the residue of a dilithium initiator such as the diadduct of sec-butyllithium and m-diisopropenylbenzene. Some structures, including those pertaining to polylithium initiators or random units of styrene and a conjugated diene, generally have limited practical utility although known in the art.

The anionic polymerization of the conjugated diene hydrocarbons is typically controlled with structure modifiers such as diethylether or glyme (1,2-diethoxyethane) to obtain the desired amount of 1,4-addition. As described in Re 27,145 which is incorporated by reference herein, the level of 1,2-addition of a butadiene polymer or copolymer can greatly affect elastomeric properties after hydrogenation.

The 1,2-addition of 1,3-butadiene polymers having terminal functional groups significantly and surprisingly influences the viscosity of the polymers as described in more detail below. A 1,2-addition of about 40% is achieved during polymerization at 50.degree. C. with about 6% by volume of diethylether or about 1000 ppm of glyme.

Dilithium initiation with the diadduct of sec-butyllithium (s--BuLi) and m-diisopropenylbenzene also requires presence of a non-reactive coordinating agent such as diethyl ether, glyme, or triethyl amine, otherwise monolithium initiation is achieved. Ether is typically present during anionic polymerization as discussed above, and the amount of ether typically needed to obtain specific polymer structures has been sufficient to provide dilithium initiation.

Anionic polymerization is often terminated by addition of water to remove the lithium as lithium hydroxide (LiOH) or by addition of an alcohol (ROH) to remove the lithium as a lithium alkoxide (LiOR). For polymers having terminal functional groups, the living polymer chains are preferably terminated with hydroxyl, carboxyl, phenol, epoxy, or amine groups by reaction with ethylene oxide, carbon dioxide, a protected hydroxystyrene monomer, ethylene oxide plus epichlorohydrin, or the amine compounds listed in U.S Pat. No. 4,791,174, respectively.

Termination with ethylene oxide results in release of fine particles of lithium bases as described in U.S. Pat. application Ser. No. 07/785,715, now U.S. Pat. No. 5,166,277 which is incorporated by reference herein. The lithium bases interfere with hydrogenation of the polymer and preferably are removed.

Termination with carbon dioxide results in carboxylate salt groups that reduce hydrogenation catalyst activity as described in U.S. Pat. No. 4,970,254 which disclosure is incorporated by reference herein. Improved hydrogenation is obtained by converting the carboxylate salt groups to ester groups prior to hydrogenation and then reconverting to carboxylate salt or carboxylic acid groups after hydrogenation.

Hydrogenation of at least 90%, preferably at least 95% of the unsaturation in low molecular weight butadiene polymers is achieved with nickel catalysts as described in U.S. Pat. No. Re. 27,145 and 4,970,254 and U.S. Pat. application Ser. No. 07/785,715 which are incorporated by reference herein. The preferred nickel catalyst is a mixture of nickel 2-ethylhexanoate and triethylaluminum described in more detail in Example 1 below.

Butadiene polymers having two or more terminal functional groups selected from hydroxyl, carboxyl, phenol, epoxy, and amine groups can be used without solvents when the viscosity of the polymer is less than about 500 poise. These functional groups do not exhibit significant atomic attractions that would otherwise solidify the functionalized polymers. Hydrogenated butadiene polymers having a lower viscosity than 500 poise are produced by limiting the peak molecular weight to a range from 500 to 20,000 and by limiting the 1,2-addition to an amount between 30% and 70%, preferably between 40% to 60%.

It is well known that the viscosity of higher molecular weight polymers is proportional to molecular weight raised to the 3.4 power as described by D. W. Van Krevelen, "Properties of Polymers" Elsevier Scientific Pub Co., New York, 1976, pp. 337-339, and J. D. Ferry, "Viscoelastic Properties of Polymers" John Wiley & Sons, New York, 1970, pp 267-271. For low molecular weight polymers having no functional groups, viscosity is proportional to molecular weight to the first power. Low molecular weight polymers having terminal functional groups behave like higher molecular weight polymers. Therefore, in comparing the viscosity of low molecular weight polymers having terminal functional groups, viscosity data must be adjusted for molecular weight variations by dividing measured viscosity by molecular weight raised to the 3.4 power.

The polymers of the invention have the conventional utilities such as forming coatings, sealants, and binders. In addition, the butadiene polymers having about two or more terminal hydroxyl groups can be co-polymerized with conventional compounds during production of polycarbonates, polyesters, and polyamides as described in U.S. Pat. No. 4,994,526 which is incorporated herein by reference.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hydrogenated 1,3-butadiene polymers having about two terminal groups per molecule and unexpectedly low viscosity have been produced by controlling the 1,2-addition of the butadiene. Such polymers are low viscosity liquids at room temperature when the peak molecular weight of the polymer ranges between 1,000 and 10,000, as measured by gel permeation chromatography using polybutadiene standards, and the 1,2-addition ranges from 40% to 60%. The examples below show that 1,2-addition of the hydrogenated butadiene polymers has an unexpected effect on viscosity.

The peak molecular weights were measured using gel permeation chromatography calibrated with polybutadiene standards having known peak molecular weights. The solvent for all samples was tetrahydrofuran.

The 1,2-additions vinyl contents was measured by C.sup.13 NMR in chloroform solution.

The viscosities were measured at room temperature on a Rheometrics Dynamic Mechanical Spectrometer in dynamic oscillatory mode at a frequency of 10 radians per second. Viscosity measurements were adjusted for comparison by division with peak molecular weight raised to the 3.4 power. Peak molecular weights are believed to best indicate molecular weight variations in the polymers of this invention and are determined from standards having known peak molecular weights rather than by approximation.

EXAMPLE 1

A linear hydrogenated butadiene polymer having about two terminal hydroxyl groups per molecule, a peak molecular weight of 2900, as determined by Gel Permeation Chromatography (GPC) using polybutadiene standards, and a 1,2-addition of 40%, as determined by a Nuclear Magnetic Resonance (NMR) technique, was prepared as described below. The linear butadiene precursor polymer was synthesized using a diinitiator for the polymerization of 1,3-butadiene. The living polymer chain ends were capped using ethylene oxide to afford the precursor polymer having terminal, primary hydroxyl functionality. This polymer was hydrogenated using a Ni/Al catalyst.

To synthesize the diinitiator moiety, 100 pounds of cyclohexane, 6 pounds of diethyl ether, and 1564 g of m-diisopropenylbenzene (DIPB) (97% wt DIPB, 9.6 moles) were combined with stirring in a sealed, steel reactor vessel under an inert, nitrogen atmosphere. Impurities that might interfere with anionic polymerization were removed by titration with a solution of s--BuLi in cyclohexane (0.09 g of s--BuLi/ml). The purified solution was then treated with 2 equivalents of s--BuLi (23.5 pounds of s--BuLi solution, 19 moles) for each equivalent of DIPB that was present. Reaction at 50.degree. C. for 30 minutes gave a solution of the expected diinitiator. The structure of the diinitiator was verified by analyzing a methanol quenched aliquot of the solution using a gas chromatography-mass spectroscopy (GC-MS) technique.

In a separate vessel, 162 pounds of cyclohexane, 15 pounds of diethyl ether, and 42 pounds of polymerization grade 1,3-butadiene were combined under a nitrogen atmosphere at 20.degree. C. As described above, the solution was titrated with. s--BuLi reagent to remove impurities that would interfere with the anionic polymerization of butadiene. The purified solution of monomer was transferred to the vessel containing the diinitiator and polymerization ensued. The polymerization exotherm was controlled by cooling the reactor to keep the temperature of the reaction mixture below 50.degree. C. After 30 minutes, the polymerization reaction was essentially complete. An alpha, omega-polymer lithium species (Li--B--Y--B--Li) had been synthesized.

The solution containing the diinitiated polymer was treated, at 50.degree. C., with 7.5 pounds of ethylene oxide (77 moles) to insert --C--C--O-- at the polymer chain ends to form alkoxide polymer chain ends, --C--C--C--O--Li. Reaction was allowed to proceed for 3 hours. At this point, the reaction mixture was a solid rubbery mass resulting from the formation of an ionic gel derived from association of the alkoxide polymer chain ends. Treatment of the gel with 610 g of methanol afforded a free flowing solution of a polybutadiene diol having --C--C--O--H end caps and a precipitate of lithium methoxide (LiOMe). The precipitate was allowed to settle in the reactor overnight.

A LiOMe slurry was drained from the bottom of the vessel and discarded. An aliquot of the clear solution of the butadiene polymer having terminal hydroxyl groups was analyzed via GPC and found to contain a single polymeric species having a peak molecular weight of 2900. Average molecular weights were calculated from the GPC data as M(n)=2470 and M(w)=2940.

Analysis by C(13)NMR found the 1,2-addition to be 40% and the ethylene oxide end capping efficiency was 82% (100 times the ratio of moles of --C--C--O--H end caps to moles of s--BuLi initiator).

A 10 gallon aliquot of the solution of the butadiene polymer having terminal hydroxyl groups was transferred to a high pressure reactor for hydrogenation using a Nickel/Aluminum catalyst. The catalyst was prepared in advance by reacting nickel 2-ethylhexanoate with triethylaluminum in cyclohexane in amounts sufficient to give a ratio of 2.6 moles of aluminum to 1 mole of nickel. The polymer solution was sparged with hydrogen at 65.degree. C. The reactor was then filled with hydrogen to a pressure of 810 psig. An initial aliquot of the Ni/Al catalyst solution was then pressured into the reactor in such a volume as to afford a Ni concentration of 100 ppm in the reaction mixture. An exothermic hydrogenation reaction ensued.

When the temperature of the reaction solution had stabilized, an aliquot of the solution was analyzed by ozonolysis to check the degree of hydrogenation of the polybutadiene diol. As hydrogenation was incomplete, another aliquot of catalyst was added which lead to an additional exotherm. This process was repeated until the ozonolysis test showed essentially complete hydrogenation of the polybutadiene diol (final reaction conditions - [Ni]=1900 ppm, 95.degree. C., 6 hr). An aliquot of the polymer solution was analyzed by C(13)NMR; by this method of analysis, 95% of the carbon-carbon unsaturation (--C.dbd.C--) had been hydrogenated and there was no evidence of hydrogenolysis of the terminal hydroxyl groups.

The hydrogenation catalyst was removed from the polymer cement by contacting with an excess of 1% by weight aqueous sulfuric acid solution (organic/aqueous=1/3(vol/vol)). The organic phase was washed repeatedly with water to remove excess sulfuric acid. Ammonia gas was bubbled through the organic phase to ensure complete neutralization. An antioxidant, Irganox 1076, was added to the cement in an amount to afford a concentration of 0.1% by weight in the final product. The solvent was removed from the polymer under vacuum affording a clear, low viscosity liquid, hydrogenated butadiene polymer having about two terminal hydroxyl groups per molecule. The properties of this sample are listed in Tables 1 and 2 which follow the description of Examples 2-5 below. Several commercial hydrogenated polybutadiene diols are included for comparison.

EXAMPLES 2-5

The procedure of Example 1 was modified to prepare a series of hydrogenated butadiene polymers having about two terminal hydroxyl groups per molecule, different peak molecular weights, and different amounts of 1,2-addition. The molecular weight of the diol was adjusted by varying the diinitiator to monomer ratio during polymerization of the butadiene. The 1,2-addition was varied by adjusting the diethyl ether content of the solvent before polymerization and by adjusting the temperature at which the butadiene polymerization was conducted. Higher levels of 1,2-addition were favored by higher levels of diethyl ether and lower reaction temperatures. Synthesis in this way afforded products with the structures of Table 1 and properties of Table 2.

TABLE 1 ______________________________________ 1,2- EO Capping Hydro- Example MW Addition Efficiency genation Number (Peak) (%) (%) (%) ______________________________________ 1 2900 40 82 95 2 3900 41 95 98 3 5060 40 92 99 4 3500 52 87 98 5 3970 48 85 99 POLYTAIL HA.sup.1 2300 84 NA .sup. 99.sup.3 NISSO GI-2000.sup.2 2380 84 NA .sup. 98.sup.3 POLYTAIL H.sup.1 3720 22 NA NA ______________________________________ .sup.1 Polymer produced by Mitsubishi. .sup.2 Polymer produced by Nippon Soda. .sup.3 Measured by ozonolysis.

TABLE 2 ______________________________________ 1,2- Example MW Addition Viscosity Adj. Viscosity Number (Peak) (%) (poise) (poise/MW.sup.3.4) ______________________________________ 1 2900 40 155 0.26 .times. 10.sup.-9 2 3900 41 836 0.52 .times. 10.sup.-9 3 5060 40 2322 0.59 .times. 10.sup.-9 4 3500 52 353 0.32 .times. 10.sup.-9 5 3970 48 760 0.44 .times. 10.sup.-9 POLYTAIL HA.sup.1 2300 84 1650 6.1 .times. 10.sup.-9 NISSO GI-2000.sup.2 2380 84 1480 4.9 .times. 10.sup.-9 POLYTAIL H.sup.1 3720 22 Solid.sup.3 -- ______________________________________ .sup.1 Polymer produced by Mitsubishi. .sup.2 Polymer produced by Nippon Soda. .sup.3 Infinite viscosity at room temperature.

The relationship between viscosity and 1,2-addition for the hydrogenated butadiene polymers is plotted in FIG. 1 wherein the viscosity data is adjusted to remove molecular weight variations as described above.

For many applications such as coatings it is desirable to have polymers that have terminal functional groups and have low viscosity at room temperature to allow application without any solvent, preferably at the highest possible solids content. While it is known in the art that hydrogenated butadiene polymers having less than 30% 1,2-addition are crystalline solids, Table 2 and FIG. 1 show that 1,2-addition between 30 and 70% provides suprisingly low viscosities at room temperature for hydrogenated butadiene polymers having terminal groups. The polymers of the invention preferably have a ratio of viscosity (poise) to peak molecular weight raised to the 3.4 power of at most 2.0.times.10.sup.-9, most preferably less than 1.0.times.10.sup.-9.

Results for Examples 2 and 3 validate the theoretical relationship between viscosity and peak molecular weight. The ratios of viscosity to peak molecular weight raised to the 3.4 power for Examples 2 and 3 are almost identical although the polymers have significantly different molecular weights and significantly different viscosities.

EXAMPLE 6 (HYPOTHETICAL)

A hydrogenated butadiene polymer having terminal hydroxyl groups is prepared as described in Example 1 except that the ratio of diinitiator to butadiene monomer is adjusted to provide a peak molecular weight of 10000.

EXAMPLE 7 (HYPOTHETICAL)

A hydrogenated butadiene polymer having terminal hydroxyl groups is prepared as described in Example 1 except that the ratio of diinitiator to butadiene mo