Polymerization process

#This invention relates to a method for the production and treatment of stereoregular propylene polymers and more particularly to the treatment of isotactic propylene polymers involving the incorporation of ethoxylated amines as processing aids.

#Thermoplastic olefin polymers, such as linear polyethylene, polypropylene, and olefin copolymers, such as ethylene propylene copolymer, are conveniently formed in continuous loop-type polymerization reactors and thermoformed to arrive at granules or pellets of the polymers. For example, polypropylene and/or propylene/ethylene copolymers are polymerized in continuous polymerization reactors in which the monomer stream is introduced into a reactor and circulated with an appropriate catalyst to produce the olefin homopolymer or copolymer. The polymer is withdrawn from the catalyst reactor and subjected to appropriate processing steps and then extruded as a thermoplastic mass through an extruder and die mechanism to produce the polymer as a raw material in particulate form, usually as pellets or granules. The polymer particles are ultimately heated and processed in the formation of the desired end products.

#Polypropylene and propylene copolymers, as used in various applications involving production of films, fibers, and similar products in the polymers, are thermo-processed and shaped or oriented by one unidirectional or bidirectional stresses. Such polymers are thermoplastic crystalline polymers. Polymers of this nature are subject to degradation due to high temperatures and photochemical action induced by electromagnetic radiation in the visible light range and in the ultraviolet region. In order to retard the degradation of such polymeric objects, the base polymer system, which is molded or extruded to form the desired object, e.g. fiber or film, may be treated with hindered amine light stabilizers, identified by the acronym “HALS,” which function to protect the film, fiber, or other object against degradation due to electromagnetic radiation by radiation in the visible light spectrum.

#FIG. 1 is a schematic illustration of a process for the polymerization of polypropylene in which the present invention is implemented.

#FIG. 2 is a schematic illustration of a film orienting process which can be used to implement the present invention.

#The present invention involves the use of a particular class of tertiary amines which are incorporated in the formation of a propylene polymer product to provide a product which is especially suitable for use in the formation of film products, particularly oriented film products. The tertiary amine is added as a processing aid to the propylene polymer fluff in the course of the polymer recovery process. That is, the tertiary amine is incorporated into the polymer prior to the extrusion of the polymer to produce pellets as contrasted with adding it during the use of the polymer pellets to produce a film. The tertiary amine processing agent which is incorporated into the fluff in a small concentration, no more than 0.08 wt. % to facilitate processing when using the subsequently-formed polypropylene particles, can be characterized by the following formula: 6

#In Formula (5), R is an aliphatic group containing 8-18 carbon atoms (including mixtures of C8 to C18 aliphatic groups) and R′ and R″ are each independently a hydroxyalkyl group containing from 1 to 3 carbon atoms. As described in greater detail below, the tertiary hydroxyalkyl amine can be incorporated with a minor amount of a polymer carrier, such as polypropylene, in the manner as disclosed in the aforementioned patent to Castro. In addition, the tertiary amine additive can be expected to provide anti-static properties to films which may be ultimately produced from the polymer pellets arrived at by the initial extruding step. However, the tertiary amine additive is employed not in the course of forming films or fabricating products as in the case of the aforementioned patent to Castro but instead is added to the fluff prior to pelletizing.

#The invention will be described with reference to a loop-type reactor used in the production of stereoregular polypropylene, specifically isotactic polypropylene, although it will be recognized that the invention may be carried out with respect to syndiotactic polypropylene or other propylene polymers or copolymers which may incorporate other olefin polymers such as polyethylene. Referring to FIG. 1, there is illustrated a loop-type polymerization reactor 10 which is supplied with propylene monomer through an input line 12 and a catalyst system through an input line 14. The continuous loop-type reactor is, as will be understood by those skilled in the art, equipped with an impeller 15 which functions to circulate the polymerization reaction mass continuously through the loop-type reactor under controlled temperature and pressure conditions. The polymerization reactor may be operated under any suitable conditions. Liquefied propylene preferably is used as the carrier medium in the course of the polymerization reaction within reactor 10. Alternatively, an inert solvent such as hexane can be used.