BACKGROUND OF THE INVENTION (Co) polymers of conjugated dienes such as butadiene, isoprene and the like possess physical properties that make them suitable for many important applications such as synthetic rubbers and additives to other polymer systems.

One such system, high impact polystyrene (HIPS), can be manufactured by polymerization of styrene in the presence of 5 to 10% dissolved homo-or co- polymer of butadiene or butadiene copolymer rubber. Early in the polymerization, phase separation begins because of the immiscibility of the rubber in the polystyrene being formed and the depletion of the styrene phase. Grafting of polybutadiene with the polystyrene then takes place. Toughness, and other mechanical and rheological properties of HIPS are affected strongly by the nature of the rubber phase. In this regard, some of the characteristics of the rubber that may be modified to control the overall HIPS performance include concentration, volume, particle size, grafting and crosslinking ability, molecular weight, and viscosity.

One focus of the present invention is use of polybutadiene as an additive in HIPS or ABS resins. Specifically, the present invention relates to providing conjugated diene (co) polymers having useful molecular weight and viscosity ranges. In this regard, strictly linear polybutadiene of low molecular weight typically has a low Mooney viscosity, which makes it difficult to handle ; conversely, a tetra- coupled version of the same low molecular weight polymer typically has a viscosity that is too high to allow for processing. One mechanism to achieve a desired molecular weight and viscosity is to use a blend of tetra-coupled and linear polymer chains.

One method for manufacturing (co) polymers having linear and branched segments provides a blend of from 40-94 parts by weight (pbw) Component A and from 60-66 pbw Component B. Component A includes rubbery (co) polymer (s) of conjugated dienes, and at least 60% by weight of the components in the A portion are branched polymers. Component B is generally the same as Component A, but

consists of linear (co) polymer (s). The process of manufacture involves forming Component A in a one step, forming Component B in a another step, and then blending the two components.

Another known process is directed to polymerizing at least one diene monomer to a conversion between 30 and 70% to produce low molecular polydiene chains; joining from 20 to 70% of those chains with a suitable branching agent; and allowing the polymerization to continue to produce a polydiene rubber blend.

However, by failing to perform sufficient conversion in the first step, insufficient solution viscosity is produced.

SUMMARY OF THE INVENTION The present invention provides a continuous process for manufacturing a polymer composition. The process provides a polymer that includes branched and linear segments by polymerizing diene monomers in the presence of an organo- metallic initiator to a conversion of at least 90%, preferably 99%. To the resulting polydiene chains, a coupling agent is added to obtain a polymer of mixed branched and linear polydiene units. The coupling agent is added at a ratio of about 0.3 to about 0.6 equivalents per organometallic initiator equivalents. The resulting polymer mixture has a solution viscosity in the range of about 150 to 190 cP (0.15 kg/m-s to 0.19 kg/ms) and a Mooney viscosity (ML4) in the range of about 60 to 85.

This process advantageously produces a mixture of linear and branched polymers, thereby gaining the benefits of the individual polymers without requiring separate production segments to make the individual components. Moreover, the process is performed continuously, not requiring separate polymerization stages and a subsequent blending of components. The present invention limits the coupled polymer percentage in the overall mixture to produce a high molecular weight fraction that otherwise would be difficult to process by itself.

The resultant polymer is particularly suited for use as an additive in the manufacture of HIPS and ABS resins.

DETAILED DESCRIPTION OF PREFFERED EMBODIMENTS Feedstocks used to provide starting materials for the process of the present invention include one or more conjugated diolefin monomers. Typically, the feed- stock is an admixture of the conjugated diolefin (s) with low molecular weight hydro- carbons. Such admixtures, termed low concentration diene streams, are obtained

from a variety of refinery product streams such as, e. g., naptha cracking operations.

Preferred diene monomers utilized in the preparation of the linear polydiene chains contain from 4 to 12 carbon atoms, with those containing from 4 to 8 carbon atoms being most commonly used. Isoprene and 1, 3-butadiene are the most common conjugated diolefin monomers used in this process. Additional monomers that can be utilized include, but are not limited to, 1,3-pentadiene, 2-methyl-1, 3- pentadiene, 4-butyl-1, 3-pentadiene, 1,3-hexadiene, 1,3-octadiene, 2,3-dimethyl- 1,3-butadiene, piperylene, 2,3-dibutyl-1,3-pentadiene, 2-ethyl-1, 3-pentadiene, 2- ethyl-1, 3-butadiene, 3-butyl-1, 3-octadiene, 2-phenyl-1, 3-butadiene, styrene and the like. These can be used alone or in combinations.

Some examples of low molecular weight hydrocarbons that can be admixed with the monomers in the polymerization feed include propane, propylene, iso- butane, n-butane, 1-butene, isobutylene, trans-2-butene, cis-2-butene, vinylacetyl- ene, cyclohexane, ethylene, propylene, hexane, heptane, octane, and the like.

Polydiene rubbers that are co-or terpolymers of one or more diolefin monomers with one or more other ethylenically-unsaturated monomers also can be prepared from the process of this invention. Some representative examples of potentially useful ethylenically-unsaturated monomers include vinylidene mono- mers; vinyl aromatic such as styrene, a-methylstyrene, bromostyrene, chloro- styrene, fluorostyrene and the like ; a-olefins such as ethylene, propylene, 1-butene, and the like ; vinyl halides, such as vinylbromide, chloroethane (vinylchloride), vinyl- fluoride, vinyliodide, 1,2-dibromethene, 1,1-dichloroethane (vinylidene chloride), 1,2-dichloroethane, and the like ; vinyl esters, such as vinyl acetate; and a, ß- olefinically unsaturated nitriles, such as acrylonitrile amides, such as (meth) acryl- amide, N-methyl acrylamide, N, N-dimethylacrylamide, methacrylamide, and the like.

The polymerization normally is carried out in a hydrocarbon solvent which can be one or more aromatic, paraffinic, or cycloparaffinic compounds. The solvents normally contain from 4 to 10 carbon atoms per molecule and are liquids under the conditions typically used for such polymerizations. Representative exam- ples of potentially useful organic solvents include one or more of pentane, cyclo- hexane, n-hexane, benzene, toluene, xylene, ethyl benzene, and the like. In solution polymerizations which utilize the process of this invention, the polymeri- zation medium can include 5 to 35 weight percent monomers, preferably from 10 to

30 weight percent monomers, and more preferably 20 to 25 weight percent monomers.

In addition to an organic solvent and reactant monomers, the polymerization mixture contains at least one initiator selected from organometallic compounds of the general formula M (R) x wherein M is Group I or il metal and R is an organic group (described in more detail below). Organometallic initiators include the mono-and multi-functional types known for polymerizing the monomers described herein. Generally, monofunctional organometallic initiators are preferred. Preferred metals include lithium, potassium, sodium, zinc, magnesium, and aluminum. Of these, organolithium initiators are particularly preferred.

The term"organolithium compounds", as employed herein, refers to those materials which correspond to the formula LiR, wherein R is a C1-C20 hydrocarbyl radical, preferably C3-C6, advantageously an aliphatic radical, but also may be C6- C20, preferably C6-C12, cycloaliphatic or aromatic radical. Preferred R groups include n-butyl and sec-butyl, although other suitable R groups include but are not restricted to ethyl, n-propyl, isopropyl, n-amyl, sec-amyl, sec-hexyl, n-hexyl, n- heptyl, octyl, nonyl, decyl, dodecyl, octadecyl, phenyl, tolyl, dimethylphenyl, ethylphenyl, naphthyl, cyclohexyl, methylcyclohexyl, ethylcyclohexyl, cycloheptyl, allyl, 2-butenyl, 2-methyl butenyl, cyclopentylmethyl, methycyclopentylethyl, pohenylethyl, cyclopentadienyl, naphthyl, penylcyclohexyl, and the like.

The amount of organometallic initiator utilized can vary according to the monomer (s) being polymerized and the molecular weight desired for the resultant polymer. However, as a general rule, from 0.01 to 1 phm (parts per 100 pbw of monomer) of initiator typically is used. In most cases, 0.025 to 0.07 phm of the organometallic initiator is sufficient.

The polymerization temperature can vary over a broad range from about- 20 to 150°C although, in most cases, a temperature within the range of about 30 to 120°C can is preferred. The pressure used will normally be sufficient to maintain the reaction mixture as a substantially liquid phase under the conditions of the polymerization reaction.

The polymerization reaction generally is conducted for a time sufficient to obtain a conversion of at least about 90% and preferably at least 99% conversion.

Accordingly, using 1, 3-butadiene as monomer and the preferred range of initiator, the first stage of the process typically yields polybutadiene having a weight average molecular weight (tv) in the range of about 70,000 to 250,000.

A coupling agent can be added to obtain the preferred mixture of linear and branched polydiene units. While many coupling agents are known in the art and may be used in the present invention, a multifunctional coupling agent that joins at least three polymer chains is preferred. Representative examples of suitable coupling agents include multi-vinyl aromatic compounds, multi-epoxides, multi- isocyanates, multi-amines, multi-aldehydes, multi-ketones, multi-halides, multi- anhydrides, multi-esters, and the like. Preferred coupling agents include multi- halides such as SiC14, SiBr4, and Sil4. In addition to these silicon multihalides, other metal multihalides, particularly those of tin, lead, or germanium also can be readily employed as the coupling agent. Preferred among these are SnC1 hexachloraldisilane, methyl trichlorosilane, CC14, and CH3SnCl3.

The coupling reaction can be terminated by any known method such as the addition of an active hydrogen-containing compound such as, e. g., water, lower alcohols, etc.

Coupling agent can be added in a ratio of about 0.2 to 0.8 coupling equivalents to initiator equivalents. More preferably, the ratio can be about 0.3 to about 0.6 equivalents of coupling agent to organometallic initiator. In this manner, the desired ratio of linear units to branched units can be achieved to provide a polymer having a solution viscosity in the range of 100 to 300 cP (0.10 to 0.30 kg/m's) and Mooney viscosity in the range of 30 to 120 (ML4). A Mw of between about 150, 000 and about 350,000, preferably from about 225,000 to about 275,000, can be obtained.

As recognized by the skilled artisan, a variety of modifications and/or additions to the basic process of this invention can be made without departing from the intention thereof. For example, various modifiers stabilizers and antioxidants may be employed.

To further illustrate the instant invention, the following exemplary embodiment is provided.

The system was first flushed and dried. Into a first mixing tank were combined approximately 285 phm hexane, approximately 100 phm 1,3-butadiene, approximately 0.02 phm 1,2-butadiene, a titrating agent and vinyl modifier. This blended mixture was transferred to a second reaction tank and approximately 0.067 phm butyllithium catalyst was added. The reaction raised the temperature to between approximately 93° and 104°C and proceeded until approximately greater than 98% monomer conversion was achieved. The resultant polybutadiene was

transferred to a third mixing tank to which approximately 0.02 phm SiC ! 4 was added (SiCI4/Li = 0.45 Cl/Li ; coupling agent to initiator equivalents). A stabilizer was added, and the reaction terminated by the addition of water. The resultant product was dried and baled. The polybutadiene had a solution viscosity of about 170 cP (0.170, Wm s), a Mooney viscosity of about 65 (ML4), and a Mw of 260,000.

Accordingly, mixed coupled and linear polybutadiene having the desired characteristics can be prepared via the inventive process.

While certain representative embodiments and details have been shown for purposes of illustrating the present invention, various modifications and changes to the process can be made without departing from the scope of the present invention.