United States Patent Office Patented June 8, 1965
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3,188,304 United States Patent Office Patented June 8, 1965 2 3,188,304 Now, however, it has been found that mercaptain modi CBL RUBBER POLYMERZAION PRO CESSES fiers are not equivalent in “hot” and “cold' rubber emul USNG AMCXTURE OF DECYL AND UNECYL sion polymerization systems. Surprisingly, in accord with MERCAPANSAS MODEFERS this invention, significant improvements are obtained in Roland H. Goshon, Fort Washington, Harry E. Alert, "cold' polymerization recipes for a styrene-butadiene sys Lafayette Hil, Bernard Bachholz, Fiorigwin, and tem when a modifier is employed which is a mercaptain Alfred C. Whiton, Norristown, Pa., assignors to containing 9, 10 or 11 carbon atoms in its molecule (i.e., Penasalt Chemicals Corporation, Philadelphia, Pa., a nonyl, decyl, and undecyl mercaptans) and these improve corporation of Penasylvania ments result also when the modifier used is a mixture of No Drawing. Fied July 17, 1961, Ser. No. 24,318 O these mercaptains. 6 Clains. (C. 260-84.3) One particular advantage found in using nonyl, decyl This invention deals with the preparation of synthetic or undecyl mercaptain as a modifier in “cold' rubber. rubber as obtained from styrene and butadiene and is par polymerization recipes is that improved modifier efficiency ticularly concerned with the use of certain mercaptans as is obtained. Modifier efficiency can be empirically meas modifiers in those polymerization processes carried out 5 ured in a synthetic rubber polymerization system by meas below about 50 F. (e.g. cold rubber processes). uring the Mooney viscosity of the dry polymer produced It is old in the art to use mercaptans as modifiers in the from such a system. At a given concentration level in emulsion polymerization of olefinic monomers such as the System, a modifier which produces a soft (low Mooney styrene and butadiene to obtain elastomeric products. viscosity) polymer is classified as more efficient than a Such polymerization modifiers are substances which are 20 modifier which produces a stiff (high Mooney viscosity) included in a polymerization recipe to make possible the polymer. The processability of a polymer is dependent production of a plastic, workable polymer. With no mod upon its viscosity and an efficient modifier is desired in ifier present in the recipe a tough, unworkable polymer is Synthetic rubber recipes, since less of it will be required produced. The exact role which the modifier plays in a to produce a polymer of specified Mooney viscosity. An free-radical initiated polymerization has been the subject 25 of much study, especially in butadiene-styrene emulsion other specific advantage obtained from this invention is copolymerization systems and it has been established that that the use of the decyl and undecyl mercaptans or their the modifier functions primarily as a chain transfer agent mixture is not adversely affected by the presence of resid in a free radical mechanism, and in this manner it controls ual olefin which is often present in the mercaptain from the molecular weight (and hence the processability) of the 30 its process of manufacture. This is particularly important polymer. where unreacted styrene used in the “cold" rubber manu Wolthan, in his U.S. Patent 2,281,613, disclosed that facture is recycled for further polymerization with the control of the polymerization is provided and plasticity butadiene component. As this recycle occurs, the olefin of the polymers obtained by incorporating in the aqueous contaminant from the mercaptain builds up in the styrene emulsion an aliphatic mercaptain having at least six carbon 35 monomer. With dodecyl mercaptain, for example, the atoms in an aliphatic linkage. In U.S. 2,378,030 Olin dis presence of Small amounts of the olefin from which the closed his improvement in the use of aliphatic mercaptains mercaptain is derived can build up to an amount on the having between 8 and 16 carbon atoms and pointed out order of 0.1 to 0.2 part per hundred parts of monomer the particular advantage of achieving high efficiency in and this significantly reduces modifier efficiency and causes the use of tertiary-dodecyl mercaptain as obtained by con 40 the rubber obtained to be stiff and undesirable. On the densation of triisobutylene with hydrogen sulfide. Addi other hand, use of decyl and undecyl mercaptains contam tional study in the use of mercaptan modifiers resulted in inated with starting, unreacted olefin (e.g. decenes and additional advances. For example, Crouch and Mashofer described in U.S. Patents 2,549,961 and 2,549,962 the ad undecenes) causes no adverse effects and actually results vantage of using blends of tertiary alkyl mercaptains hav 45 in a slight improvement in efficiency. ing 8 to 16 carbon atoms per molecule. In all of the above Still another unexpected advantage in the use of nonyl, disclosures the research was directed to and the disclosures decyl and undecyl mercaptains or their mixtures is that they are specific to the use of such mercaptain modifiers in enable a high conversion rate to be achieved. It has been styrene-butadiene polymerization recipes carried out at observed that the conversion rate is adversely affected about 50° C. or higher. 50 When certain mercaptans (particularly those containing Immediately after World War II, however, it was less than nine carbon atoms) are used in “cold" rubber learned that rubber having improved properties for tire polymerization recipes. treads was obtained when polymerization was carried out In order to facilitate discussion of the mercaptains they at temperatures of about 50 F. or lower and in the pres Will be referred to as C. mercaptains where C refers to a ence of an organic peroxide or hydroperoxide initiator. 55 hydrocarbon radical and x is the number of carbon atoms This development lead to the well-known “cold' rubber per molecule. Thus, Co is nonyl mercaptan, Co is decyl of commerce. In using modifiers for the cold polymeriza mercaptan, C11 is undecyl mercaptan, etc. The C, Co, tion recipes the industry logically used the same mercaptain and C11 mercaptains used in accord with the invention modifiers employed for the previously known “hot” rubber 60 have highly branched alkyl chains and are predominantly recipes and these were found to work quite well. Of Secondary and tertiary mercaptains. These compounds are particular value and predominantly used were tertiary readily prepared in accord with the known methods for dodecyl mercaptain and a mixture of tertiary mercaptains the addition of H2S to olefins. Because mixtures of olefins containing 12, 14 and 16 carbon atoms. are normally used for the HS addition, rectification of 3,188,804 s 3 A. the mercaptain mixture is carried out to isolate the C9, In the actual polymerization procedure, normal polym Co, and C1 mercaptains. Reference is made to U.S. erization ingredients and the usual operating techniques 2,392,554 for details of the mercaptain preparation process. will be employed except that the mercaptain modifier will In that patent it is pointed out that these mercaptain mix be a C9, Co, or C11, or a mixture of these mercaptains. tures are made by the method which comprises the re As indicated, peroxides or hydroperoxides will be used action of hydrogen sulfide with an olefinic polymer selected as catalysts (e.g. p-menthane hydroperoxide, cumene hy from the group consisting of polymers of propylene, butyl droperoxide, phenylcyclohexyl hydroperoxide, etc.) and ene, amylene and their mixtures. such recipes for “cold' rubber recipes are discussed by it will be understood that the C3, Co, and C1 mer G. S. Whitby in his book "Synthetic Rubber, John Wiley captains are not discrete compounds, but comprise isomer 0 & Sons, 1954. The amount of modifier used will be in mixtures. As indicated above, however, the compounds accord with usual practice and will vary from about are predominantly secondary and tertiary mercaptains and 0.05-0.50 part per hundred parts of monomer. Less than the purity of the rectified fractions will be on the order this annount of modifier results in too stiff a polymer of 90-100% mercaptain by weight. It will also be under product whereas more than about 0.50 phm. causes too stood, for example, that the term "Co mercaptan' re 5 great a softening of the polymer. Preferably, from about fers to a fraction consisting essentially of decyl mer 0.10 to 0.3 phin. will be used. captan, but there will also be present small amounts of C11 mercaptain and probably traces of other mercaptains. EXAMPLE 1. Likewise the term 'C mercaptain” refers to a fraction Butadiene-styrene copolymers were prepared by polym consisting essentially of undecyl mercaptain with decyl 20 erization at 43 F. according to the following SBR-1500 and other mercaptains present in small amounts. "Ca recipe. mercaptain' is likewise predominantly nonyl mercaptain ingredients: Parts by weight with trace amounts of other mercaptains. The C9, C10 and Butadiene --------------------------- 72 C1 mercaptain mixtures will also be of a comparable purity Styrene ----------------------------- 28 and will contain the C9, C10, and C11 mercaptain com 25 Water ------------------------------ 200 ponents in weight ratios ranging from about 10:90 to Mercaptain -------------------------- Variable 90:10 for two component systems and for three com Rosin soap ("iDresinate” 214) ---------- 4.50 ponent systems the lowest concentration of a single con Sodium sulfonate dispersant ("Daxad' ponent will be about 5% by weight. Because of avail 11) ------------------------------ 0.10 ability, the preferred modifier will be a Co and C11 mix 30 Sequestrant (Versene Fea Specific) ------ 0.04 ture which will consist essentially of approximately equal FeSO47H2O ------------------------ 0.12 amounts by weight of Co and C11 mercaptan. When K4P2O7 ----------------------------- 0.15 using the C component, it will be used preferably in a Na3PO4'12H2O ---------------------- 0.30 mixture with the Co and/or C11 mercaptain because of p-Menthane hydroperoxide ------------ 0.04 its tendency to lower conversion rates.