COMPOSITIONS AND METHODS FOR INHIBITING VINYL AROMATIC MONOMER POLYMERIZATION

Abstract: Compositions and methods for inhibiting the polymerization of vinyl aromatic monomers in oxygen-free processing systems are disclosed. The compositions comprise a hydroxylamine compound, a phenylenediamine compound and a vinyl aromatic monomer. The methods comprise adding to the monomer bis-N,N'(hydroxypropyl)hydroxylamine.

Description: COMPOSITIONS AND METHODS FOR INHIBITING VINYL AROMATIC MONOMER POLYMERIZATION TECHNICAL FIELD The present invention relates to compositions and methods for inhibiting the undesirable polymerization of vinyl aromatic monomer compounds. BACKGROUND ART Polystyrene is a thermoplastic with many desirable characteristics It is clear, transparent, readily colored and easily fabricated. The family of styrene polymers includes polystyrene itself, copolymers of styrene with other vinyl monomers, polymers of derivatives of styrene and mix¬ tures of polystyrene and styrene-containing copolymers with elastomers. Pure polystyrene is glass-like, transparent, hard, and rather brittle. ABS (acrylonitrile, butadiene, styrene) and SAN (styrene, acryloni¬ trile) resins have enjoyed tremendous commercial popularity for many years as durable, temperature and solvent resistant elastomers. On the other hand, styrene plastics are commonly used for packaging, including foams and films, coatings, in appliance fabrication, for housewares and toys, lighting fixtures and in construction materials. Common industrial methods for producing vinyl aromatic mono¬ mers, such as styrene, include a variety of purification processes, the most common one being distillation. It is well known that vinyl aromatic monomers readily polymerize when heated and that rate of polymeriza¬ tion increases rapidly as the temperature increases. Thermal polymeri¬ zation during distillation results not only in loss of product, but it could render the finished monomer unsuitable for using without further treat- ment. To prevent polymerization of vinyl aromatic monomers under distil¬ lation conditions, various inhibitor compositions have been employed Unfortunately, although several compounds are effective against vinyl aromatic monomer polymerization under storage conditions, only some of these compounds have proved to be effective against polymerization under distillation conditions. Dinitrophenol compounds are generally used commercially to inhibit polymerization of vinyl aromatic monomers. U.S Patent No. 4,105,506, Watson et al., teaches the use of 2,6-dinιtro-ρ-cresol as a polymerization inhibitor of vinyl aromatic compounds U.S. Patent No 4,466,905, Butler et al., teaches that a combination of 2,6-dinitro-p-cresol and p-phenylene- diamine compounds will inhibit polymerization in distillation columns when oxygen is present. U.S. Patent No. 4,774,374, Abruscato et al., teaches compositions and processes for inhibiting the polymerization of a vinyl aromatic monomer employing the oxygenated reaction product of oxygen and N-aryl-N'-alkyl-p-phenylenediamine compound. U.S. Patent No. 4,720,566, Martin, teaches methods and composi¬ tions of a hydroxylamine compound and a phenylenediamine compound used for inhibiting the polymerization of acrylonitrile in a quench tower. This system differs from a vinyl aromatic purification process in the type of monomer involved, but also in that oxygen is readily present in an acryloni¬ trile quench column, the quench tower reactor effluent is cooled by contact with a recirculating water stream and sulfuric acid is added to the quench column. U.S. Patent No. 4,929,778, Roling, teaches compositions of a phenylenediamine compound and a hindered phenol compound for inhibiting the polymerization of vinyl aromatic monomers. U.S. Patent No. 4,956,020, Nakajima, teaches methods for the in- hibition of popcorn polymer, such as styrene, growth in an olefin appara¬ tus. The methods comprise treating the inner surface of an olefin produc¬ tion apparatus with a popcorn polymer growth inhibitor while the operation of the apparatus is suspended and olefins are substantially removed from the apparatus. The popcorn polymer growth inhibitor is selected from the group which can include N.N'-di-sec-butyl-p-phenylenediamine and hydroxylamine. While these uses may inhibit vinyl aromatic monomer polymeriza¬ tion, it would be advantageous to possess polymerization inhibitors that avoid the use of highly toxic compounds such as dinitrophenol com¬ pounds and function in an oxygen-free environment. DISCLOSURE OF INVENTION The present invention relates to compositions for inhibiting the polymerization of vinyl aromatic monomer compounds under processing conditions comprising adding to said monomer an inhibitor composition comprising a hydroxylamine compound and a phenylenediamine compound. The present invention also relates to a method for inhibiting the polymerization of vinyl aromatic monomer compounds under processing conditions comprising adding to said monomer bis-N,N'(hydroxypropyl) hydroxylamine. The compositions of the present invention prove efficacious at inhibiting the polymerization of vinyl aromatic monomers, particularly styrene, during their processing. These processing conditions include but are not limited to purification and distillation of vinyl aromatic monomers. The hydroxylamine compounds useful in this invention generally have the formula: R N — OH wherein R and R^ are the same or different and are hydrogen, alkyl, aralkyl, or hydroxyalkyl groups and preferably have about 3 to about 20 carbon atoms, except when R is H, then R 1 is a Ce to C2 0 alkyl group The preferred hydroxylamine compounds are N,N'-dιethylhydroxylamιne (DEHA), isopropylhydroxylamine (IPHA) and bιs-N,N'(hydroxypropyl)hy- droxylamine (HPHA) The phenylenediamine compounds useful in this invention generally have the formula. wherein R 2 , R3, R4, and R 5 are the same or different and are hydrogen, alkyl, aryl, alkaryl or aralkyl groups having from 1 to about 20 carbons The preferred phenylenediamine compound is N,N'-dι-sec-butyl-p- phenylenediamine (PDA) The total amount of hydroxylamine compound and phenylenedia¬ mine compound used in the methods of the present invention is that amount which is sufficient to inhibit polymerization and will vary according to the conditions under which the vinyl aromatic monomer is being proc¬ essed and exposed to high temperatures At higher temperatures and higher monomer contamination, larger amounts of the polymerization inhibiting composition are required Preferably, the total amount of polymerization inhibiting composi¬ tion added to the vinyl aromatic monomer ranges from a total of 1 to about 10,000 parts per million parts of monomer More preferably, the range is about 5 parts to about 500 parts of the composition per million parts of monomer The weight ratio of hydroxylamine compound to phenylenediamine compound present in the vinyl aromatic monomer ranges from 1 9 to 9 1 with a weight ratio of 1 1 preferred The amount of bιs-N,N'(hydroxypropyl)hydroxylamιne added to the vinyl aromatic monomer will vary as per the earlier described conditions This amount generally ranges from about 1 to about 10,000 parts per million parts of vinyl aromatic monomer Preferably, this amount ranges from about 100 parts to about 1000 parts per million parts of vinyl aromatic monomer The compositions of the present invention can be added to the vinyl aromatic monomer by any conventional method, either as individual components or as a combination It is preferred that the individual ingre¬ dients are added to the monomer as a single treatment The compositions of the present invention may be added to the vinyl aromatic monomer as either a dispersion or as a solution using a suitable liquid carrier or solvent Any solvent that is compatible with the individual ingredients of the composition and the vinyl aromatic monomer may be employed Accordingly, it is possible therefor to produce a more effective vinyl aromatic monomer polymerization inhibition treatment than is ob¬ tainable by the use of any one ingredient alone when measured at com- parable treatment levels This enhanced activity allows for the concen¬ tration of each of these ingredients to be lowered and the total quantity of polymerization inhibitor required, particularly at higher processing tem¬ peratures, may be reduced MODES FOR CARRYING OUT THE INVENTION This invention will now be further described with reference to a number of specific examples which are to be regarded solely as illustra¬ tive and not as restricting the scope of the invention Examples In order to evaluate the improved polymerization inhibition of the inventive combinations and to demonstrate the enhanced activity of the combination, styrene polymerization testing was performed Uninhibited styrene (5 ml) was placed in a test tube and the ap¬ propriate amount of treatment was added. The tube was capped with a septum and argon was bubbled through the liquid at 15 ml/min for 3 min¬ utes. Then, the tubes were placed in an oil bath heated to 100°C for 2 hours. The amount of polystyrene formed was determined by methanol precipitation. Results of this testing are summarized in Table I. TABLE I Styrene Polymerization Test Uninhibited styrene at 100°C Treatment Dose (ppml Polymer formed (mα/5 ml Blank „-— ,, 271 IPHA 25 232 IPHA 50 150 IPHA 100 96 IPHA/PDA 25/25 89 IPHA/PDA 50/50 38 Blank 239 DEHA 25 192 DEHA 50 149 DEHA 100 98 DEHA/PDA 25/25 94 DEHA/PDA 50/50 54 PDA 100 86 IPHA is isopropylhydroxylamine DEHA is N,N'-diethylhydroxylamine PDA is N,N'-di-sec-butyl-p-phenylenediamine The results of this testing indicate that the composition of hydroxyl¬ amine compound and phenylenediamine compound, particularly IPHA/PDA and DEHA PDA, provides enhanced activity over either hydroxylamine compound at inhibiting the polymerization of styrene. These results are particularly indicative of the compositions enhanced activity at inhibiting the polymerization of styrene under oxygen free conditions and high tempera¬ tures which are present when styrene is undergoing processing such as distillation or purification. The procedure described to generate the examples of Table I was repeated. The results of this testing are presented in Table II. TABLE II Treatment Dose (ppm) Polymer (mq/5 ml) Blank 174 PDA 100 33 PDA 50 114 PDA 25 130 HPHA 100 70 HPHA 50 105 HPHA 25 141 PDA/HPHA 50/50 22 PDA/HPHA 25/25 60 PDA is N,N'-di-sec-butyl-p-phenylenediamine HPHA is bis-N,N'(hydroxypropyl)hydroxylamine These results demonstrate that the HPHA is effective by itself at inhibiting the polymerization of styrene. These results further demonstrate that HPHA is more effective than either the DEHA or IPHA reported in Table I. INDUSTRIAL APPLICABILITY The present invention relates to compositions and methods for inhibiting polymerization of vinyl aromatic monomers during monomer processing conditions such as distillation of the vinyl aromatic monomers. The compositions of the present invention are added as a combi¬ nation of a phenylenediamine compound and a hydroxylamine compound to the vinyl aromatic monomer undergoing processing. The combination is particularly effective at inhibiting polymerization of styrene during its distillation under oxygen-free conditions. While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modi¬ fications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover ail such obvious forms and modifications which are within the true spirit and scope of the present invention.

Claims: Having thus described the invention, what we claim is: 1. A composition comprising a vinyl aromatic monomer, a hydroxylamine compound and a phenylenediamine compound. 2. The composition as claimed in claim 1 wherein said vinyl aromatic monomer is styrene. 3. The composition as claimed in claim 1 wherein said hydroxylamine compound has the formula: N — OH / Ri wherein R and R^ are the same or different and are hydrogen, alkyl, ar¬ alkyl, or hydroxyalkyl groups and preferably have about 3 to about 20 carbon atoms. 4. The composition as claimed in claim 3 wherein R is H and R- is a Ce to C2 0 alkyl group. 5. The composition as claimed in claim 3 wherein said hy¬ droxylamine compound is N,N'-diethylhydroxylamιne. 6. The composition as claimed in claim 3 wherein said hy¬ droxylamine compound is isopropylhydroxylamine 7. The composition as claimed in claim 1 wherein said phenyl¬ enediamine compound has the formula: wherein R 2 , R3, R4 and R 5 are the same or different and are hydrogen, alkyl, aryl, alkaryl, or aralkyl groups having from 1 to about 20 carbon atoms. 8. The composition as claimed in claim 7 wherein said phenyl¬ enediamine compound is N.N'-di-sec-butyl-p-phenylenediamine. 9. The composition as claimed in claim 1 wherein the weight ratio of hydroxylamine compound to phenylenediamine compound ranges from 1 :9 to 9:1. 10. A method for inhibiting the polymerization of vinyl aromatic monomers undergoing processing comprising adding to said monomers an effective polymerization inhibiting amount of bis-N,N'(hydroxypropyl) hydroxylamine. 11. The method as claimed in claim 10 wherein said bιs-N,N'(hy- droxypropyl) hydroxylamine is added to said monomer in an amount rang¬ ing from about 1 parts to about 10,000 parts per million parts of monomer

Inventors: ARHANCET GRACIELA B, HENRICI INGE K, ARHANCET, GRACIELA, B., HENRICI, INGE, K.
Applicants: BETZDEARBORN INC, BETZDEARBORN INC.
Application year: 1997
Main classification: C07C7
IPC codes: C07B63, C07C7