The present invention relates to nitroxyl containing compounds and their use in the production of rubber modified polymers. Rubber modified polymers have been produced from vinyl aromatic monomers by a number of processes for the purpose of improving impact resistance.

Typically, a rubber is blended with a polymerized vinyl aromatic monomer, or alternatively, the vinyl aromatic monomer is polymerized in the presence of a rubber.

In the latter method, the vinyl aromatic monomer is partially graft polymerized onto the rubber. However, the amount of grafting and molecular weight of the grafting chain is difficult to control, which can negatively influence the gloss and impact properties.

Rubber modified copolymers of vinyl aromatic monomers have also been produced, such as acrylonitrile-butadiene-styrene (ABS). ABS copolymers have been produced using polymerization processes such as bulk-suspension, continuous bulk, and emulsion. Emulsion polymerization processes typically produce products having the best balance of gloss and impact strength, however bulk processes are favored due to lower cost.

Other rubbers are also used in bulk polymerization processes to improve the gloss and/or impact properties, including styrene-butadiene block copolymer rubbers.

However, these rubbers are typically more expensive and are needed in higher amounts than conventional polybutadiene rubbers.

Therefore, there remains a need for a more efficient and cost effective process for producing rubber modified polymers from vinyl aromatic monomers, having excellent balance of gloss and impact properties. Additionally, there is a need to produce transparent rubber modified polymers.

A free radical process for producing a rubber modified polymer having excellent balance of gloss and impact strength from a vinyl aromatic monomer which is more efficient and cost effective when compared to the prior art is disclosed in a copending U.S. application filed from provisional 60/014,616 which was filed

March 29, 1996 by Priddy et al. The process of Priddy comprises polymerizing a vinyl aromatic monomer in the presence of a diene rubber which has been modified with at least one stable free radical group, such that vinyl aromatic diene block and/or graft copolymer rubber particles are formed and dispersed within the vinyl aromatic polymer. The diene rubber is typically terminated using a compound which contains

a nitroxyl group However, there are few known nitroxyl containing compounds which would act as polydiene terminators.

US-A- 4,581 ,429 by Solomon et al. discloses nitroxy containing free radical initiators for use in polymerizations However, the compounds disclosed would not act as polydiene terminators Therefore, there remains a need to develop further nitroxyl containing compounds which would act as polydiene terminators

The present invention is directed to new nitroxyl containing compounds which can be used as polydiene terminators

The present invention is a compound of the formula:

wherein T is a group which will either 1) react with a polydienyl lithium such that the polydiene will be terminated with the compound of formula I, or 2) be displaced by a polydienyl anion placing the molecule attached to T on the polydiene chain-end, Ar is an aromatic group having 1 or 2 aromatic πngs, R, R ¹ and R ² are each independently hydrogen or a C ₆ alkyl group, and R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ are each independently phenyl, Cι-C ₆ alkyl, or alternatively, 2 groups selected from R ³ -R ⁸ may combine such that a 5 or 6 membered ring containing the N of the nitroxyl group is formed These compounds can be used to terminate polybutadienyl lithium to produce block and/or graft copolymers in situ during the polymerization of the vinyl aromatic monomer and allows for the production of rubber reinforced polymers without the high cost of block or pregrafted diene rubbers. The present invention is a compound of the formula:

wherein T is a group which will either 1) react with a polydienyl lithium such that the polydiene will be terminated with the compound of formula I, or 2) be displaced by a polydienyl anion placing the molecule attached to T on the polydiene chain-end A group which will react with a polydienyl lithium such that the polydiene is terminated with the compound of formula I includes but is not limited to a glycidyl or aldehyde group The reaction of polydienyl lithium ( Lι ⁺ ) with such a group is exemplified in the following

A group which will be displaced by a polydienyl anion, thus placing the molecule attached to T on the polydiene chain end includes but is not limited to bromine, chlorine, tosylate, mesylate or any group typical of an SN ₂ displacement reaction A reaction showing the displacement of T with a polydiene is exemplified in the following scheme:

T cannot be a group such as hydroxy, an ether (O-R) or ester (0-C(=0)-R), as these groups are not good leaving groups for SN ₂ displacement reactions and will not react with polydienyl lithium to form a bond resulting in the attachment of a nitroxyl compound to the polydiene.

Ar can be any aromatic group having 1 or 2 aromatic rings. The aromatic rings can optionally contain additional substitution such as halogen, and alkyl, for example methylphenyl or t-butylphenyl.

R, R ¹ and R ² are each independently hydrogen or a C^Ce alkyl group, and R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ are each independently a phenyl group which optionally contains additional substitution such as halogen, or alkyl, for example methylphenyl or t-butylphenyl; d-C ₆ alkyl, or altematively, 2 groups selected from R ³ -R ⁸ may combine such that a 5 or 6 membered ring containing the N of the nitroxyl group is formed.

Preferably T is Cl, R, R ¹ and R ² are each H, two R groups selected from R ³ -R ⁸ combine to form a six membered ring and the remaining R groups selected from R ³ - R ⁸ are each methyl. The compounds of this invention can be used as terminators for a polydienyl lithium. The compounds terminate the polydienyl lithium resulting in the attachment of a labile nitroxyl group to the end of the polydiene chain.

Examples of compounds of the present invention include:

Tos = tosylate = p-toluenesulfonate

= trifloromethanesulfonate = CF SO ₃

Nitroxy containing compounds can be prepared from the desired precursors, by forming carbon centered radicals in the presence of a nitroxy containing compound which traps the carbon centered radical intermediates as they form. Methods of making carbon centered radicals are well known in the art and include techniques such as 1 ) H-abstraction from activated hydrogen compounds as discussed in ACS Polym. Prepr. 1995, 36, 469 by I. Li, B.A. Howell; A. Ellaboudy; P. Kastl; and D.B. Priddy; 2) radical addition to activated double bonds as discussed in Macromolecules 1993, 26, 2987 by M.K. Georges, R.P.N. Veregin, P.M. Kazmaier, and G.K. Hamer; 3) electron transfer as disclosed in J. Organic Chemistry 1975, 40, 3448 by G. M. Whitesides and T.L Newirth; and 4) thermolysis of an activated azo compound as discussed in U.S. Patent Number 4,581 ,429 by Solomon et al., EP- 304756 by Solomon et al., and Chemistry in Australia, Jan-Feb. 1987, 32, by E. Rizzardo.

Compounds II, V, and VI can be prepared by exposing a solution of nitroxyl radicals dissolved in styrene (or a substituted styrene) to halogen (chlorine or bromine) radicals such that the halogen radicals are trapped by styrene and the resulting styryl radicals are trapped by nitroxyl radicals.

Compounds III, IV, VII, and VIII can be prepared from 2-Phenyl-2-(2,2,6,6- tetramethyl -piperidinyl-1-oxy)ethanol (CJ. Hawker and J.L. Hedrick, Macromolecules, 1995, 28, 2993) by reaction with p-toluene sulfonyl chloride, epichlorohydrin, mesityl chloride or trifluoromethanesulfonyl chloride, respectively.

These compounds can be used to produce nitroxyl terminated diene rubbers which are useful in producing rubber modified polymers from vinyl aromatic monomers. Suitable vinyl aromatic monomers include but are not limited to vinyl aromatic monomers previously known for use in polymerization processes, such as those described in US-A-4,666,987, US-A_4,572,819 and US-A-4,585,825. Preferably, the monomer is of the formula:

Ar-C=CH ₂

wherein R is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyi substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyi refers to a halo substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include: styrene, alpha-

methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, or vinyl naphthalene, and mixtures thereof. The vinyl aromatic monomers may also be combined with other copolymerizable monomers. Examples of such monomers include, but are not limited to acrylic monomers such as acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, acrylic acid, and methyl acrylate; maleimide, phenylmaleimide, and maleic anhydride.

The nitroxyl terminated diene rubbers produced using the compounds of the present invention will have at least one nitroxyl group attached to a chain-end. The rubber is prepared from a diene monomer component and is terminated using a nitroxyl containing compound of the present invention. Typically, the diene monomer is polymerized under anionic or free radical polymerization conditions and terminated in the presence of the nitroxyl containing compound. Preferably, the diene monomer component is a 1 ,3-conjugated diene such as butadiene, isoprene, piperylene, or chloroprene. Most preferably, the diene monomer component is 1 ,3-butadiene. The nitroxyl containing compounds of the present invention can form a stable free radical which are storage stable in pure form, that is nonreactive with itself at temperatures of up to 120°C.

A stable free radical nitroxyl group is formed upon activation of the nitroxyl containing compound. For activation of the nitroxyl containing compound to occur, the radical forming atom of the nitroxyl containing compound is typically bonded to the diene rubber through an activated carbon. The nitroxyl containing compound- activated carbon bond is typically stable at temperatures up to 50°C. An activated carbon atom is defined as a carbon atom which is bonded to an aromatic ring. At temperatures above approximately 60°C, the nitroxyl containing compound activates to form a stable free radical. For example, a compound containing -C -0-N< as the nitroxyl containing compound, wherein the C ^' atom is activated or bonded to an aromatic ring, will activate at temperatures above 60°C to form a O-N< and carbon radical pair. If activation of the nitroxyl containing compound occurs during the polymerization of a vinyl aromatic monomer, the vinyl aromatic monomer will react with the carbon radical and become inserted between the O of the nitroxyl and the activated carbon, resulting in the formation of a vinyl aromatic polymer segment, for example -C -(poly(vinyl aromatic monomer))-0-N<.

Anionic polymerization methods of polymerizing dienes are well known in the art and any method may be utilized in preparing the diene rubbers used in the process of the present invention.

A rubber reinforced polymer can be prepared by dissolving the diene rubber containing a nitroxyl group in a vinyl aromatic monomer and polymerizing the rubber/monomer mixture. This process can be conducted using conventional techniques known in the art for preparing rubber reinforced polymers such as high impact polystyrene (HIPS) and ABS, which are described in US-A-2,646,418, US-A-4,31 1 ,819 and US-A-4,409,369. The amount of rubber added to the vinyl aromatic monomer is typically from 3 to 20 percent, preferably from 5 to 15 percent and more preferably from 7 to 12 percent based on the total weight of the vinyl aromatic monomer and the rubber.

During the polymerization of the rubber/monomer mixture, the vinyl aromatic monomer polymerizes to form a matrix phase and also grafts onto the diene rubber as well as add vinyl aromatic blocks to the nitroxyl functional chain-ends.

The weight average molecular weight (Mw) of the grafted polymer inserted between the nitroxyl containing compounds and the activated carbon atom is typically less than half of the Mw of the matrix phase, preferably less than 25 percent, more preferably less than 20 percent, and most preferably less than 15 percent. Typically, the Mw of the grafted polymer is from 15,000 to 150,000, preferably from 25,000 to 100,000, more preferably from 25,000 to 75,000, and most preferably from 30,000 to 60,000.

The Mw of the matrix phase can vary greatly dependent upon the applications of the rubber modified polymer. Typically, the Mw can vary from 50,000 to 300,000. The compounds of the present invention are particularly useful in preparing high impact polystyrene and acrylonitrile-butadiene-styrene polymers wherein the rubber is typically dispersed throughout the polystyrene or polystyrene-acrylonitrile matrix phase. These polymers can be used in a variety of applications including injection molding and thermoforming of refrigerator liners, household appliances, toys, and furniture.

Additionally, the compounds of the present invention can be used to produce transparent rubber reinforced polymers. These polymers typically contain dense rubber particles having a volume average particle size of less than 0.1 μ. Methods of particle sizing are well known by those skilled in the art. The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and they should

not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.

EXAMPLES

Example 1

2-Phenyl-2-(2,2,6,6-tetramethylpiperidinyl-1-oxy)ethanol (A) is prepared according to the method of Hawker (CJ. Hawker and J.L. Hedrick, Macromolecules 1995 28, 2993). Epichlorohydrin (2.8 g) is added dropwise to a 100 mL round-bottomed flask containing a mixture of 50 percent aqueous sodium hydroxide (4.3 mL) and Bu NHS0 ₄ (0.085 g)and the mixture is stirred vigorously at approximately 25°C for 2 hours. Compound (A) (1.7 g) is then added dropwise over 1 hour while stirring is continued for 16 hours. Water (30 mL) is added and the resulting mixture is extracted with methylene chloride. Evaporation of the methylene chloride provides an oil which is crystallized from methanol to give 1.5 g of white crystal (mp = 35-36°C). The product is confirmed to have structure (B) using NMR spectroscopy.

Example 2 Preparation of Polybutadiene Terminated with (B)

Anionic polymerization of butadiene is carried out using sec.-butyllithium as initiator by combining butadiene (17.4 mmol) with 10 mL cyclohexane and sec- butyllithium (0.29 mmol). The mixture is stirred under dry nitrogen for 24 hours at approximately 25°C The polybutadienyl lithium is terminated by the addition of (B) (3.4 mmol) which has been dissolved in 20 mL cyclohexane. Stirring is continued for an additional 24 hours and methanol is added to precipitate the polybutadiene. Analysis of the polymer using gel permeation chromatography shows that the Mw =

3930 and Mn = 3840. Analysis of the polymer using ¹ H-NMR confirms that >95 percent of one of the polybutadiene chain-ends possesses fragment (C).