High temperature process for the production of atactic, amorphous,tacky propylene polymers

#The present invention relates to the production of atactic or amorphous poly-alpha-olefins. More particularly it relates to a high temperature process for the production of non-crystalline or low crystallinity polymers and copolymers.

#In the early processes for the production of isotactic or crystalline polypropylene, the initial catalyst systems (brown or violet titanium trichloride) were not very stereospecific and appreciable amounts of amorphous or atactic polypropylene were coproduced along with the desired isotactic polymer. These atactic or amorphous polymers were low melting non-crystalline or low crystallinity polymers with poor physical properties compared to isotactic polypropylene. The atactic or amorphous polymer had to be removed by solvent extraction so that the properties of the isotactic polymer were not degraded. At first, this material was burned or discarded by burial. Gradually, means were found to purify this material by removing the catalyst residues and solvent, and the resulting tacky, low molecular weight solid material found applications as an ingredient in hot melt adhesives, sealants, and bituminous formulations. However, the product quality was variable, with no two batches of material being exactly the same. The situation was further complicated by the fact that some material resulted from copolymer production and other material resulted from homopolymer production. The market for the amorphous material developed nicely. However, as the catalysts were improved, the amorphous polymer content was reduced to such a low value that it was not necessary to remove the atactic or amorphous polymer from the isotactic polypropylene. Producers found the demand for atactic or amorphous polymers outstripping the supply. Material which had been discarded earlier was mined from atactic pits and purified by acid washing and steam distillation. One polypropylene producer's catalyst system for isotactic polymer was very poor and large quantities of atactic were produced, giving that producer a reasonable supply of amorphous poly-alpha-olefins (APAO). Another producer converted an isotactic polypropylene line to amorphous production and used a magnesium chloride (MgCl2) supported titanium catalyst minus the stereoregulator to produce “on purpose” APAO. This approach increased the quality and consistency of the amorphous product and allowed production of copolymers and terpolymers which had properties which were appreciably different from the coproduct atactic produced with isotactic polypropylene. This approach also opened up a potential for different materials which might have new applications.

#U.S. Pat. No. 4,736,002 (issued Apr. 5, 1988 to G. Allen et al.) describes a process for preparing amorphous polypropylene and copolymers at relatively low temperatures of 150° F. in liquid propylene, utilizing a converted isotactic polypropylene polymerization line. The disadvantages of this process are the necessity to operate the polymerization at low temperatures due to the inherent tackiness of the amorphous polymers and copolymers and the resulting low polymerization rates.

#The organoaluminum solution was prepared by mixing an equimolar amount of triethyl aluminum and diethyl aluminum chloride in a heptane solution. This solution was fed to the tubular reactor to maintain an Al/Ti mole ratio of 300/1. The solid titanium component of the catalyst is prepared by (1) co-comminuting 8 moles of magnesium chloride with 1.25 moles aluminum trichloride for 12 hours. The product of this step (1) is then co-comminuted with 0.5 moles of titanium tetrachloride for 15 hours in the absence of any electron donor. The resulting solid catalyst has a titanium content of about 2.5 wt %. This catalyst is then pumped continuously to the tublar reactor as a 10 wt % mixture in a 50/50 weight ratio blend of mineral oil and petrolatum, at a rate which maintains the polymerization rate and reactor temperature and yields very high catalyst efficiencies.

#An alternate brown TiCl3 catalyst system is prepared by mixing 5 liters of 0.1 molar diethyl aluminum chloride with 5 liters of 0.1 molar titanium tetrachloride TiCl4 (both in heptane) in a 2/1 molar ratio of aluminum to titanium Al/Ti and allowing them to prereact for 15 minutes at ambient temperature, The resulting brown slurry is then slowly added to the tubular reactor at the required rate to maintain a constant temperature and polymerization rate. Any of the indicated monomers may be used with this catalyst system.

#Another catalyst system is prepared by suspending 40 pounds of a violet powder composed of ball-milled 3TiCl3.AlCl3 in 60 pounds of mineral oil to form a 40 wt. % slurry. This slurry is added to the reactor with the monomer(s) after mixing with aluminum triethyl in an Al/Ti molar ratio of 10/1.