ACID SCAVENGED POLYMER HALOGENATION

Abstract: A process for halogenating polymers by contacting a polymer either in solution or in bulk with a halogenating agent in the presence of an acid scavenger. Halogenated polymer, e.g., butyl rubber, with a particular structure is obtained and the product suffers less molecular weight loss. Combinations of acid scavengers can also be used and the scavenger can be dispersed in the polymer prior to halogenation and/or added to the reaction zone during halogenation.

Description: ACID SCAVENGED POLYMER HALOGENATION BACKGROUND OF THE INVENTION This invention relates to a method of modifying polymers with a halogen or halogens; specifically to a process for the production of halogenated polymers. More specifically, it is directed to a continuous process for the manufacture of halogenated polymers such as butyl (a copolymer of a major proportion of an isoolefin and a minor proportion of a mul i-olef in) EPM (a copolymer of ethylene and propylene), EPDM (a terpoly er of ethylene, propylene and a noncon j ugat ed diene) , SBR (styrene- butadiene rubber), BR (polybutadiene rubber), polyisoprene rubber, various types of polyethylene, including linear low density polyethylene, ethylene vinyl acetate copoly- mer, etc.; in particular halogenation wherein a substitu- tion reaction results in the generation of hydrogen halide as a by-product or where hydrogen halide may be formed. Numerous references teach methods for halogenat- ing various polymers, for example the halogenation of butyl rubber. An early reference, U.S. Patent 2,944,578, teaches that chlorinated butyl rubber can be produced in a batch process by dissolving butyl rubber in a suitable, nonreactive solvent, e.g., hexane, and introducing chlorine or a chlorinating agent. By suitable control of the temperature, concentrations of chlorinating agent and rubber, and reaction time, chlorinated rubber containing the desired level of chlorine is produced. An improved, continuous solution process for chlorination or bromination of butyl rubber was sub- sequently disclosed in U.S. Patent 3,099,644. The halogenation of ethylene-propy lene noncon jugated diene elastomers (EPDM) has also been disclosed; such processes are analogous to those for halogenating butyl rubber. For example, U.S. 4,051,083 describes the solution bromination and chlorination of EPDM using N-halosuccinimide; additionally, the "neat" halogenation of EPDM is also described. In the latter disclosure the halogenating agent is dispersed in the EPDM by blending on a cool rubber mill and halogenation is effected by heating the mixture in a hydraulic press. Halogenation of EPDM in an aqueous batch process is disclosed in U.S. 3,896,095. The process employs the addition of an excess of CI2 or Br2 to a polymer slurry to effect halogenation and avoid the expense of solvent recovery systems previously disclosed for solution halogenation processes. Chlorobromination of polymers such as poly- butadiene, butadiene-isoprene copoly ers and natural or synthetic polyisoprene is disclosed in British 1,483,063 and 1,483,064. The reaction is described as taking place at a low temperature of 0-15 β C, preferably in an inert solvent, and the halogenated products are described as containing high levels, e.g., * at least 5555 by weight of halogen. The possibility of producing a halogenated rubber such as halogenated butyl rubber continuously in an e truder-reactor has been recognized, see, e.g., U.S. Patent 4,185,057. However, the generalized disclosure of that reference does no more than acknolwedge the desir- ability of such a process, but does not teach one how to accomplish such a process. The reference suggests that only enough chlorine be introduced into the extruder to react with the butyl rubber so that no chlorine remains after reaction. It then goes on to suggest that another gas, e.g., nitrogen, be introduced to effect the produc- tion of gas filled pores in the finished rubber, which is the primary object of the invention. No examples are disclosed in the patent and no conditions disclosed which would enable one to actually conduct such a butyl halogen- ation process. Chlorination of butyl rubber using dichloramine-T and a calender has been reported by Bulgarian workers (Kh. Tenchev. et al, Che Abstracts 50756u) . The disclosed process was not intended to produce neat chlorinated butyl since calendering is carried out on a mixture of butyl rubber, accelerators, prevulcanization inhibitors as well as variable amounts of carbon black and dichloramine-T . The halogenation, in a kneader or extruder, of polymers containing carboxylic acid groups using reagents that differ from those disclosed herein is described in U.S. Patent 3,364,187. The polymers are converted to the acyl halide derivatives using specific halogenating agents. The patent suggests that the kneading step may be carried out in an extruder, a Banbury mixer, a roll mill or any other apparatus that yields the described kneading action. A British Patent, 1,257,016, discloses a process for treating pointers with halogenating agents such as N-bromσsuccinimide under mechanical shear and at high temperature (120-180°C) for the purpose of producing unsaturation . The patent mentions that halogenation may possibly occur in an intermediate step followed by dehydrohalogenation , but production and isolation of a useful halogenated product is not an objective, nor is it achieved. The reference also discloses the use of scavenging amounts of a metal oxide or carbonate such as magnesium oxide, zinc oxide or calcium carbonate in addition to the halogenating agent and -olefin polymer. The patent discloses, as an alternate method, the pre- blending of the halogenating agent with a solution of the polymer followed by solvent removal. It is stated that very little, if any, reaction occurs during such an operation. The reference does not disclose that scaveng- ing agent can be used to produce halogenated polymers nor that the absence of such scavengers can affect the configuration of the halogenated polymer. An extensive disclosure of polymer modifications conducted in an extruder can be found in U.S. Patent No. 3,862,265. This patent is directed to modification of polyolefins using heat, shear and controlled pressure to induce degradation in the polyolefin and to combine the polyolefin with a free-radical initiator and/or one or more monomers. The broad disclosure is of value for its teachings directed to the modification of polyolefins with. various monomers especially to form novel grafted poly- mers. U.S. Patent 3,510,416 (Vaccari et al) teaches an improved method of halogenating PVC particles by using gaseous hydrogen in combination with a swelling agent (chlorination carrier). Following reaction, the PVC particles are transferred to another piece of equipment (a dryer) in which the chlorination carrier is stripped and gaseous by-products are separated. This reference discloses a process based on particle fluidization which relies on diffusion to accomplish drying; in addition, such a process requires separate pieces of equipment and relatively long times for drying. A recent U.S. Patent, 4,384,072, and pending applications U.S. serial no. 481,366 (filed April 1, 1983) and serial no. 481,320 (filed April 1, 1983) disclose methods for halogenating neat polymers, i.e., not requir- ing the use of solution techniques. These disclosures are incorporated herein by reference for the benefit of their teachings and their relevance to this process generally, but they do not disclose the advance herein. in 1979 Van Tongerloo et al disclosed a bromin- ated butyl rubber which was low in conjugated diene content (if any) and in which the halogen was incorporated as primary allylic halogen as well as secondary and tertiary allylic halogen. (Van Tongerloo, A. and Vukov, R. , Proceedings, International Rubber Conference, Milan, Italy, 1979, p. 70 ff) . The reference states that the polymer was produced by a proprietary method and discloses only that rearrangement to the more stable primary configuration can be accomplished in brominated butyl rubber "under a variety of conditions — for example, in the presence of acid, free radicals, bases or heat." Stabilized halogenated butyl rubber described in U.S. Patent No. 4,130,519 discloses stabilizing agents which are added to the halogenated rubber following halogenation, i.e., in order to protect the rubber during further processing or during storage. Some polymers, e.g., butyl rubber, are particu- larly sensitive when exposed to shear and elevated temperatures in the presence of a halogenating agent. The halogenation reaction of butyl rubber in solution is described in "Encyclopedia of Chemical Technology", Kirk-Othmer, Third Edition (1979) , Volume 8 at page 476 ff. It is noted that the halogenation reaction carried beyond one halogen atom per olefin unit is complicated by chain fragmentation. Indeed, such fragmentation or degradation is a persistent problem when halogenation of butyl rubber is attempted; that problem is aggravated under conditions of heat and shear. A method of preparing halogenated butyl rubber in solution is described in U.S. Patent No. 3,099,644 which is incorporated herein by reference. SUMMARY OF THE INVENTION In accordance with the present invention, an improved process has been discovered for the halogenation of polymers, the process comprising adding an effective amount of an acid scavenger to said polymer wherein said scavenger is present during halogenation. In preferred alternative embodiments, the scavenger is added to bulk polymer prior to halogenation in an extruder or the scavenger is added to a solution of the polymer as it is being fed to a halogenation contactor. The products of this process are useful for a wide range of applications including tires, innertubes, mechanical goods, hoses, and electrical products. Halogenated products containing reactive halogen, e.g., halogenated butyl rubber, are capable of being vulcanized with sulfur-free cure systems, for example, zinc oxide in combination with stearic acid; this halogenated rubber can also be vulcanized by standard sulfur and sulfur-donor-containing cure systems. DESCRIPTION OF THE PREFERRED EMBODIMENTS Polymers useful in the practice of this inven- tion can be categorized in various ways and include: (a) olefin polymers, such as the various forms of polyethylene, ethylene-propylene co-polymers, other ethylene copolymers with comonomers such as 1-butene, isobutylene, vinyl acetate, maleic anhydride, ethyl acrylate, methyl acrylate; generally alpha-olefin and cyclic olefin homopolymers and copolymers; (b) polymers from dienes, such as styrene-butadiene rubber, polychloropreπe (Neoprene), butyl, polybutadiene, polyisoprene, butadiene- acrylonitrile (Nitrile), ethylene-propylene- diene; (c) vinyl and vinylidene polymers, such as polyvinyl chloride and its family of copolymers, polyvinyl esters such as polyvinyl acetate, acrylic polymers such as polymethylmethacrylate, polystyrene and its family of copolymers such as butadiene-styrene, styrene-acrylonitrile, styrene-isoprene, aerylonitrile-butadiene- styrene; (d) heterochain thermoplastics, such as polyamides polyesters, polyethers, polysulf ides, poly ur ethanes, polycarbonates. Unsaturated polymers useful in the present in- vention include ethylenically unsaturated elastomers, e.g., the several rubbers of commercial significance, for exam pie, butyl rubber, EPDM rubber, styrene butadiene rubbe (SBR), polyisoprene rubber and poly (butadiene-isoprene) copolymer rubbers. The butyl rubber copolymers useful in th present invention contain a major proportion, preferably a least 70 wt.%, of isoolefins and a minor proportion, pref erably not more than about 30 wt.%, of multi-olef ins. Co polymers of this general type, especially where the copoly er contains about 85-99.5% (preferably 95-99.5%) of C4-C7 isoolefin, such as isobutylene, with about 15-0.5 (preferably about 5-0.5 wt.%) of a multi-olefϊn of abou 4-1 carbon atoms, are commonly referred to in patents an literature as "butyl rubber"; see, for example, the ' text book "Synthetic Rubber" by G. S. Whitby (1954 edition b John Wiley and Sons, Inc.), pages 608-609, "Encyclopedia o Chemical Technology", Third Edition, Volume 8, (1979) pages 470-484, etc. The expression "butyl rubber" as ea ployed in the specification and claims is intended to in elude copolymers containing about 80-99% by weight of a isoolefin of about 4-7 carbon atoms and about 20-1% o conjugated multi-olef in of about 4-10 carbon atoms. Th preparation of butyl-type rubbers is amply described in th literature. In general, it consists of the reaction produc of a C4-C7 isoolefin (preferably isobutylene) with a C4-C^ (preferably a C4-C5 conjugated diolefin, such as isoprene butadiene, dimethyl butadiene, piperylene, etc. The reac 1 tion product of isobutylene and isoprene is preferred. The 2 preparation of butyl rubber is described in U.S. Patent 32,356,128 which is incorporated herein by reference. 4 Conventional high molecular weight butyl rubber 5 generally has a number average molecular weight of about 625,000 to about 500,000, preferably about 80,000 to about 7300,000, especially about 100,000 to about 250,000; and a ' 8 Wijs Iodine No. of about 0.5 to 50, preferably 1 to 20. ' 9 More recently low molecular weight polymers have also been* 10 prepared which have number average molecular weights of! 11 from 5,000 to 25,000 and unsaturation expressed as mole %,; 12 of 2-10. 13 The term "EPDM" as used in the specification d! 14 claims is used in the sense of its ASTM definition and is^ 15 intended to mean a terpolymer containing ethylene and 16 propylene in the backbone and diene enchainment " with 17 residual unsaturation in the sidechains.' .Illustrative 18 methods for producing these terpolymers are found in O.S. 19 Patent 3,280,082, British Patent 1,030,989 and. French. 20 Patent 1,386,600 which are incorporated herein by 21 reference. 22 The preferred polymers contain about 45 to about 23 80 wt.% ethylene and about 1 to about 10 wt.% diene 24 monomer. The balance of the polymer is propylene. Prefer- 25 ably, the polymer contains 45 to 70 wt.% ethylene, most 26 preferably 50 to 60 wt.% ethylene, e.g., 56 wt.%, and about 27 2 to about 9 wt.% diene monomer, more preferably about 2 to 28 about 6 wt.% diene monomer, most preferably 2.6 to 4 wt.% 29 diene monomer. The diene monomer is a non-conjugated 30 diene. Illustrative of -these non-conjugated diene monomers 31 which may be used in the terpolymer (EPDM) are hexadiene, 32 dicyclopentadiene, ethylidene norbornene, methylene nor- 33 bornene, propylidene norbornene and ethyltetrahydroindene. 34 A typical EPDM containing ethylidene norbornene as a diene 1 monomer is Vistalon 4608 (Exxon Chemical Company, U.S.A.), 2 a polymer .having a Mooney viscosity at 260 * F of about 62, 3 and an ethylene content of about 56 wt.%. ..The polyisoprene. rubber referre to in this 5 invention may be natural rubber or synthetic polyisoprene 6 prepared , by processes well known in the art, and, in 7 -general, has a molecular weight of from about 500 to abou 8 500,000, preferably about 1500 to about 200,000. 9 The polybutadiene and poly(butadiene-isoprene) 0 copolymer rubbers referred to in this invention include th 11 geometric isomers thereof, all of which may be prepared b 12 processes well known in the art. In general, such polymer 13 and copolymers have a molecular weight of from about 500 t 14 about 500,000, preferably from about 1500 to about 200,000 I- 5 Generally, polybutadiene rubbers have Mooney viscosit 15 values, measured at 212 * F, of from about 25 to about 65 17 preferably from about 35 to about 55, most preferably fro 18 about 40 to about . 50. 19 The styrene butadiene rubber referred to in thi 20 invention * is also, known as poly(butadiene-co-styrene) , an 21 typically abbreviated SBR, and includes rubbers prepared b 22 the emulsion (hot and cold) and solution processes wel 23 known in the art. Bound styrene levels are from about 3 t 24 about 50 wt.%, preferably from about 10 to about 45 wt.% 2*5 most preferably from about 12 to about 30 wt.%, fo 6 example, 23.5 wt.%. Generally, such polymers have Moone 7 viscosity values, measured at 212 * F, of from about 20 t 28 130 and above, preferably from about 35 to about 80, mos 29 preferably from about 40 to about 70, for Example 52. .9 The butadiene in such copolymers is present a 31 all three geometric isomers, cis-1,4, trans-1,4 and 1,2 o 3 ' 2 vinyl and the copolymer can be random, block or graft. 33 The elastomers or rubbers referred to above an 34 processes for their preparation are generally described i 35 the Xirk-Othmer "Encyclopedia of Chemical Technology" 36 Third Edition, Volume 8, (1979), butyl p. 470 ff, EP p.492 ' ff, polybutadiene p. 546 ff, polyisoprene p. 582 : ff and _ pojL (butadiene-co-styrene) p. 608 ff, incorporated herein by reference. * Some forms of halogenated butyl rubber, prepared in solution according to processes described above, are commercially available, e.g., chlorinated butyl rubber and brominated butyl rubber. One method used to prepare hal- ogenated butyl rubber is that of halogenating butyl rubber in a solution (butyl rubber cement) containing between 1 to 60% by weight of butyl rubber in a substantially inert C5-C8 hydrocarbon solvent such as pentane, hexane, heptane, etc., and contacting this butyl rubber cement with a halo- gen for a period of up to about 25 minutes. There is the formed the halogenated butyl rubber and a hydrogen halide, the polymer containing up to one or somewhat more haloge atoms per double bond initially present in the polymer. Generally, halogenated butyl rubber comprises a copolyme of 85 to 99.5 wt.% of a C4 to Cg isoolefin, e.g..', isobuty lene, with 15 to 0.5 " wt.% of a C4 to C14 multi-olef in e.g., isoprene, containing at least about 0.5 wt.% ".combine halogen in its structure. For example, where butyl i halogenated with bromine, the bromine can be present in th brominated butyl in an amount of from about 1.0 to abou 3.0 wt.%, preferably from about 1.5 to about 2.5 wt.%. method of preparing conventionally halogenated butyl rubbe is described in U.S. Patent 3,099,644, which is incorpo rated herein by reference. The preparation, in solution, of halogenate butyl rubber containing both bromine and chlorine, i.e. bromochlorinated butyl rubber, is described in U.S. Paten 4,254,240, incorporated herein by reference. The potentia for molecular weight breakdown of the butyl rubber, note -earlier, is present even where bromine chloride is used a the halogenating agent, as disclosed in this referenc (column 4, lines 24-32). The invention disclosed herein is also particu- larly useful for the halogenation of saturated polymers. Such polymers include rubbers such as ethylene-propylene copolymers (EPM), generally known in the art and similar in their preparation and composition to EPDM terpolymers with the exception of the presence of residual unsaturation; -also included is polyisobutylene rubber, produced com- ercially in grades varying as to molecular weight. Other saturated polymers useful in the practice of the instant invention include olefin polymers such as high- and low density polyethylene (HDPE and LDPE) and linear low density polyethylene ( DPE), ςo- polymers of ethylene such as et ylene-vinyl acetate, and "polyvinyl "and vinyl polymers, for example, polyvinyl chloride. HDPE has a density of about 0.941 to about 0.965 g/cc. .High density polyethylene is an established product of commerce and its manufacture and general properties are well known in the. art. Typically, HDPE has a -relatively broad molecular weight distribution, characterized- y the ratio of ' weight average to number average molecular weight, of from about 20 to about 40. LDPE is, similarly, an ite of commerce, and typically includes products with densities in the range of about 0.910 to about 0.925 g/cc. Mediu density polyethylene should not be excluded as a useful polymer, e.g., about 0.925 to about 0.940 g/cc. Linear low density polyethylene (LLDPE) is relatively new class of low density polyethylene character ized by little, if any, long chain branching, in contras to conventional low density polyethylene. The processe for producing LLDPE are well known in the art and com er cial grades of this polyolefin plastic are available Generally, it is produced in gas-phase fluidized bed reac tors or liquid-phase solution process reactors; the forme process can be carried out at pressures of about 100 to 30 psi and temperatures as low as 100 * C. Polymers can be mad - I 2 - 1 in the gas phase with melt indices and densities over the 2 full commercial range and with molecular weight distribu- 3 tions from very narrow to very broad. • 4 : . ' Polyethylene copolymers include copolymers of 5 ethylene and alpha-olef ins having 3 to 16 carbon atoms, for 6 example, propylene, 1-butene, etc. Also included are 7 copolymers of ethylene with an unsaturated ester of a lower 8 carboxylic acid. In particular, copolymers of ethylene 9 with vinyl acetate or alkyl acrylates, for example, methyl 10 acrylate and ethyl acrylate, are employed. For the pur- 11 poses of this invention, polyethylene copolymers are also 12 considered to include blends of polyethylene and poly- 13 ethylene copolymers. Many such ethylene copolymers are 14 available as items of commerce and their composition and 15 methods for producing them are well known in the art.* 16 ; ' Polyvinyl chloride (PVC) is the -most . . com 17 mercially significant member of the polyvinyl and vinyl 1 * 8 copolymer family which comprises various polymers based o 19 the vinyl radical or vinyl idene radical. Vinyl, chlorid 20 has been copolymerized with materials such as vinyl ace 21 tate, acrylic esters and vinylidene chloride. Mor 22 recently other polymers have been grafted to polyvinyl 23 chloride including ethylene vinyl acetate and EPDM. PVC i 24 manufactured commercially using various well known poly 25 erization processes: suspension, mass, e ulsion/disper 26 sion and solution; the first is the dominant method. Th 27 product is available in several forms including particles, 28 fine powders and latexes. 29 In the halogenation of the polymers suitable for 30 use in this invention, hydrogen halide is often formed as 31 a by-product. It is the objective of this invention to 32 remove the hydrogen halide by reaction with an effective 33 amount of an acid scavenger. Such removal precludes the 1 acid from being available to participate in further 2 addition and/or rearrangement and/or degradation reac- 3 tions. In addition, the acid will not be available to 4. cause corrosion problems, particularly if an aqueous 5 stream is present. 6 Several types of scavengers are useful in this 7 process. Generally suitable is any scavenger that is 8 capable of reacting with the hydrogen halide, but does not 9 interfere with the subsequent utility of the polymer, or 0 can be removed from the polymer prior to its eventual end 1 use. Useful scavenging agents include alkali metal or 2 alkaline earth metal carboxylates, epoxides, metal oxides, 3 metal hydroxides inorganic salts of strong bases and weak 4 acids and mixtures thereof. 5 The metal portion of the metal carboxylate can 6 be an alkali or alkaline earth metal. Thus, particularly 7 suitable carboxylates are those of sodium, magnesium, and 8 calcium. The carboxylic acid from which the carboxylate 9 is derived can be mono- or poly-carboxylic. Thus, 0 suitable mono-carboxylic acids are the C to C20 mono-car- 1 boxylic acids such as caproic, caprylic, pelargonic, 2 myristic, palmitic, oleic, stearic and 2-ethyl hexanoic 3 acids. Also suitable is naphthenic acid. The preferred 4 metal carboxylate is calcium stearate. 5 Suitable epoxides are the products formed by 6 epoxidizing esters and glyceride.s of unsaturated fatty 7 acids of about C3 to C2 , such esters as soybean oil, 8 castor oil, linseed oil, safflower oil, etc. The pre- 9 ferred specific polyethers of this class include 0 epoxidized soybean oil and epoxidized linseed oil (sold 1 under the trademarks Drapex 6.8 and Drapex 10.4, respec- 2 tively). Other suitable epoxides are monomeric low 3 molecular weight, e.g., C2 - C7, moπofunctional epoxides, 4 such as ethylene epoxide, propylene epoxide, butylene epoxide, etc.; preferred are ethylene, propylene and butylene epoxide. Also suitable are aryl substituted alkyl epoxide, for example 1 , 2-epoxyethylbenzene, i.e, styrene epoxide. The metal oxides or hydroxides suitable for use in this invention include those wherein the metal is selected from Group HA of the Periodic Table. Particu- larly suitable are Ca(0H)2, CaO, Mg(0H)2 and MgO. Suitable examples of inorganic salts of strong bases and weak acids include bicarbonates of sodium, potassium and calcium. The acid scavenger should be present in an amount which is effective to react with the hydrogen halide by-product formed during halogenation, taking into consideration reaction kinetics, e.g., temperature in the region in which the scavenger must react, the time available for the reaction compared to the potential for the acid halide to cause an undesirable side reaction (e.g. addition or degradation or isomerization) , the use of additional means to remove hydrogen halide from the process (e.g.., gas scrubbing, particularly in a process for halogenation of neat polymer), etc. Some limited experimentation, well within the skill of those in the art, will readily determine the effective amount of scavenger to be used in the particular circumstances at hand. As a general guide it will be recognized that in the absence of other means of removing hydrogen halide (e.g., gas scrubbing), one equivalent of scavenger is required at equilibrium per equivalent of hydrogen halide generated, but that as a practical matter up to about two to three times the theoretical amount can be used effectively. Where supplementary means are provided for hydrogen halide removal or where the effect of the hydrogen halide on the polymer is not particularly negative, as little as one-half or one-quarter the theoretical amount can be used effectively. As noted above, certain polymers are particu- larly sensitive to the presence of hydrogen halide, and polymer changes can be accelerated at elevated tempera- tures. For example, although bromination of butyl rubber at moderate temperature (e.g. 25°C) can result in a brominated polymer with a high proportion of secondary allylic bromine, and minor amounts of tertiary, isomeriza- tion to a primary allylic structure increases at elevated temperatures; i somerizat ion at elevated temperature is also increased in an acidic environment. Use of an acid scavenger reduces such isomerization, as where the polymer is present during the halogenation process at a tempera- ture of from about 50-190°C, particularly 60-175'C, more particularly 65-140°C, most particularly 70-125°C, for example at 75-115°C. In one preferred embodiment the polymer and halogenating agent are contacted, or reacted, in a nonsolution, continuous flow device; a neat or bulk process. Suitable devices include kneaders, extruders (employing single or multiple screws, e.g., twin screws, continuous mixers and a recently disclosed blending/ extrusion device referred to as a cavity transfer mixer (see, e.g., European Rubber Journal, July-August, 1982, pages 29-32 and G.M. Gale, U.K. Patent Application 8030586, 1980). Although such polymers can attain very high viscosities, even at relatively high temperatures, such devices are capable of subjecting polymers to deformation. The continuous flow device should be capable of initially forming the polymer feed into a cohesive mass and then deforming the polymer, disrupting the polymer surface, thereby exposing fresh, i.e., unreacted, polymer to the halogenating agent. The exposure of new surface does not necessarily require the use of high speeds where, e.g., an extruder is used. However, surface disrupting means are preferably employed (as will be described in detail below), for example, pins, reverse flow sections, a "Maillefer" screw design, the cavities of a cavity transfer mixer, multiple flight screw section, interrupted flight sections, e.g., slotted flights, and combinations thereof. A process for the neat halogenation (non- solution) of polymers is described in detail in U.S. Patent applications, serial numbers, 481,320 and 481,366 incorporated herein by reference. When carrying out the present invention in such processes, the acid scavenger can be added to the polymer feed. This can be achieved, e.g., by preblending the scavenger with the polymer or by feeding the scavenger with the polymer as the polymer is fed to the halogenating device. In both cases, the amount of scavenger is controlled so as to achieve the desired efect of reacting with by-product hydrogen halide; excessive amounts are not beneficial as they add to the cost of the process and can be residual additives in the polymer. If the scavenger is intended to serve an additional purpose in the finished polymer, e.g., further stabilization against dehydrohalogenation or heat, the amount used can be adjusted for that purpose. In another preferred embodiment halogenation is conducted in a solution process, i.e., a solution of the polymer in a suitable, non-reactive solvent (a "cement") is halogenated. Such a process is well known in the art and has been referred to previously. In such a process, the acid scavenger can be added to the cement prior to contact with the halogenating agent. Alternatively, the scavenger can be added to the reactor to which the halogenating agent is being added. In order to improve the efficiency of the scavenger suitable means should be provided for thorough mixing or dispersion of the scaven- ger in the reaction medium. As described in the cited references incorpor- ated herein, the halogenating agent can be gaseous, liquid or solid and may be further diluted with a suitable inert fluid, e.g., organic or inorganic liquids as well as gases such as inert gases, CO2 and air. Suitable halogenating agents include chlorine, bromine, sulfuryl halide, etc. Gaseous chlorine and bromine are preferred, particularly when mixed with nitrogen. Following reaction in either a neat or solution process, the process features normally employed can be utilized, e.g. , neutralization to insure that unwanted by-products and unreacted halogenating agent are reduced or eliminated, stabilizer addition, solvent removal where warranted, drying where required, etc. The halogenated polymers of this invention can be processed in standard equipment used for each such polymer, such as internal mixers, mills, extruders, calenders, etc. Said polymers are amenable to conven- tional compounding practice and various fillers and extenders can be incorporated, e.g., various carbon blacks, clays, silicas, carbonates, oils, resins, waxes, etc. As described previously, various halogenated polymers are produced by the process of this invention. Halogenated butyl rubber of this invention (e.g., chlorin- ated and/or brominated) may be cured or vulcanized by any of the prior art methods suitable for such halogenated rubbers, e.g., using sulfur, sulfur-containing curing agents (such as sulfenamide derivatives, benzothiazyl disulfide, tetramethylthiouram disulfide, alkyl phenol disulfide, etc.), zinc oxide alone or with various promoters, and mixtures thereof. Curing is usually accomplished at a temperature of from about 140°C to about 250°C, preferably 150°C to about 200°C, and usually takes from 1 to 150 minutes. Such rubber is useful in tires, e.g., innerliners and sidewalls; in innertubes; hoses; mechanical goods; sheeting; electrical insulation; plastic blends, etc. This invention will be further understood by reference to the following examples which describe equipment demonstrating the principles of this invention. EXAMPLE 1 This invention is particularly useful in the bromination of butyl rubber. In the bromination of butyl rubber, isoprene residues in the rubber (I) react with bromine to yield substituted structure II and by-product hydrogen bromide: C C A. -E-C - C = C - C -3-+ Br2 *→-t- C - C - C - C--+ HBr . Br I II Further reaction of structure II results in structure III via rearrangement, conjugated diene structure IV via elimination and conjugated diene structure V via elimina- tion and rearrangement: C Br B. II → - C - C = C - C *^- III C C. II +C - H - C = C 4- + HBr IV C D. IV *→ -E- C = C - C r C - V In commercial brominated butyl rubber made in solution, the reacted isoprene residues are primarily structure II, with minor proportions of structures III and V. It is also observed that some molecular weight degradation occurs during halogenation as measured by Mooney viscosity of the halogenated elastomer compared to the starting rubber, for example a decrease of about 5-10 points in a test conducted at 125 β C (one minute preheat, eight minute test). In a bulk or neat halogenation process the brominated product has been found to contain a different distribution of structures and somewhat greater molecular weight loss. This is summarized in the following table. TABLE I Typical Bromobutyl Comparison P:cior to This Invention M i ooney Loss Halogenation Proportion of Rιsacted I (1 • +8 » ) 125°C, Method II III V Points Solution 70-90 5-20 3-10 5-10 Bulk/neat 10-50 40-70 15-30 13-20 In the following experiments, the acid scaven- gers shown were first dispersed in the butyl rubber to be halogenated by mixing the scavenger and butyl in a Banbury mixer for about 2 minutes. The rubber was then halogen- ated in the bulk phase using an extrusion device as described in United States Patent application serial number 481 ,320, using a partially filled reaction zone, a mixture ' of bromine and nitrogen as the halogenating agent and nitrogen purging following reaction. The amount of scavenger shown is weight percent based on the polymer and the distribution of structures was determined using nuclear magnetic resonance spectroscopy (NMR). T ab le I I Effect of Acid Scavengers on Bulk .Bromination of Butyl Mooney Loss, Proportion of Reacted (1 * +8') 125°C, Scavenger Run II III V Points A 10 62 28 13 None B 43 43 15 19 C 37 41 22 13 1% CaSt 2 * D 50 42 8 15 0.1% MgO E 50 32 18 8 0.3% ESB0* E 68 17 15 5 *CaSt2 = calcium stearate ESB0 - Epoxidized soybean oil The acid scavengers had a significant effect on the structure of the rubber produced as well as generally resulting in less molecular weight los.s. As discussed previously, the acid scavengers can be effectively used in combination; Table III shows the results of several cominations. TABLE III Scavenger Combinations in Bulk Bromination of Butyl Mooney Loss, Propoi 'tion of Reacted I (1 ■ +8') 125°C, Scavenger Run I_I III _ Points None A 10 62 28 13 B 43 43 15 19 C 37 41 22 13 1% CaSt 2 D 78 17 6 - 1% ESB0 0.3% ESB0 F,G 80 10 10 0.1% MgO 0.4% ESB0 H 78 16 5 0.08% MgO - 2&a - Extruder conditions were as follows: Reactor Stripper Stabilizer Run Length, in. Length, in. Injection, in. Injection, in. A 55 19 3 B 55 19 9 C-H 49 25 9 15 In all runs bromine/nitrogen injection was 5 in. from the start of the reaction zone and the reaction zone screw configuration consisted of alternating forward triple slotted flights and forward single and double flights. Stripping was accomplished with 0.5-4 kg/hr. nitrogen; injection point is measured from the extruder exit. Stabilizer consisted of calcium stearate and expoxidized soybean oil; point of injection measured from extruder exit. Additional conditions were as follows: Reaction Rubber Reactor Zone Feed Bromine Feed Pressure Rubber Run kg/hr kg/hr N2/Br2 RPM Bar ( absol . ) Temp., °C A 35 2.4 3 95 4-5 90 B 32 2 3-4 88 4.25 90 C 38 2.4 4 114 6 110 D 36 2.4 4-6 90 7.5 105 ε 35 2 4.5-5 90 7-8 95 F 38 1.8 6-8 92 7.2 90 G 36 2.7 4-5 92 7-8 95 H 36 2.5 3-5 90 4-5 95 - 21 - EXAMPLE 2 Solution bromination was conducted using butyl rubber with a commercial grade designation of 268 (Exxon Chemical Co.); Mooney viscosity of the rubber was 58 (125 β C) and unsaturation was 1.65 mole %. Halogenation was conducted in a 500 ml., 4 neck round bottom flask which was blackened to exclude light. The rubber was dissolved in U.V. grade hexane to prepare a 20 wt. % cement. The flask was fitted with a wet ice condenser, stirrer, sampling tube and nitrogen bubbler and immersed in a temperature controlled bath. (A) Control run: Bath temperature 55°C, no acid scavenger, 250g butyl (grade 278) in hexane, 2.453g bromine in 5g. hexane added for bromination. The polymer obtained after 245 sec. of reaction had the following features: Bromine, wt. % 2.1 Molecular Weight, vis. avg. 380,000 Type II Br, mole % ' 28 Type III Br, mole % 59 (B) Acid scavenged run: Bath temperature 55°C, acid scavenger -- epoxidized linseed oil, 10.4 wt. % epoxy oxygen (commercial designation Drapex 10.4), 271g butyl in hexane, 7.3g scavenger added to cement and stirred at 800 rpm for 20 min., 2.76g bromine in 20g hexane added. Samples removed at 160, 404 and 710 seconds neutralized with 15 ml. 0.5% NaOH and 10 ml hexane. Results: Time Bromine, wt. % Molecular Weight 160 2.22 426,000 404 2.69 419,000 710 2.48 413,000 Each of the samples had only trace amounts of Type III structure; 100% Type II. These results demonstrate the effectiveness of acid scavenging.

Claims: - 2Z - CLAIMS : 1. A process for halogenating polymer compris¬ ing adding an effective amount of an acid scavenger to said polymer wherein said scavenger is present during halogenation. 2. The process of claim 1 wherein said halogen¬ ation is conducted in solution. 3. The process of claim 1 wherein said halogen¬ ation is neat. 4. The process of claim 1 wherein said scaven¬ ger is added to said polymer prior to contacting with said halogenating agent. 5. The process of claim 1 wherein said scaven¬ ger is added during halogenation of said polymer. 6. The process of claim 1 wherein said scaven¬ ger is selected from the group consisting of alkali metal or alkaline earth metal carboxylates, epoxides, metal oxides or hydroxides, inorganic salts of strong bases and weak acids and mixtures thereof. 7. The process of claim 6 wherein said car¬ boxylate is a C to C20 mono-carboxylate. 8. The process of claim 7 wherein said car¬ boxylate is selected from the group consisting of sodium, magnesium and calcium carboxylate. 9. The process of claim 8 wherein said car¬ boxylate is calcium stearate. - 23 ' - 10. The process of claim 6 wherein said epoxide is selected from the group consisting of epoxidized esters and glycerides of unsaturated fatty acids of about Cβ to C 2 4- 11. The process of claim 10 wherein said epoxide is epoxidized soybean oil or epoxidized linseed oil. 12. The process of claim 6 wherein said metal oxide or hydroxide is selected from the metals of Group HA of the Periodic Table. 13. The process of claim 12 wherein said metal oxide or hydroxide is selected from the group consisting of Ca(0H) 2 , CaO, Mg(0H) 2 and MgO. 14. The process of claim 6 wherein said scavenger is a mixture of an epoxide and a metal oxide. 15. The process of claim 14 wherein said epoxide is epoxidized soybean oil and said metal oxide is magnesium oxide. 16. The process of claim 14 wherein said epoxide is epoxidized soybean oil and said organic base is calcium stearate. 17. The process of claim 1 wherein said acid scavenger is present in an amount of up to about three times the equivalent of said scavenger per equivalent of hydrogen halide by-product. 18. The process of claim 1 wherein said polymer is butyl rubber. - 24 - 19. The process of claim 18 wherein said halogenation is conducted at a temperature of from about 50-130°C. 20. The process of claim 18 wherein halogena¬ tion is conducted as a nonsolution or neat process. 21. The process of claim 6 wherein said inorganic salt is selected from the group consisting of bicarbonates of sodium, potassium and calcium. 22. The process of claim 1 wherein said polymer is selected from the group consisting of olefin polymers, polymers from dienes, vinyl and vinylidene polymers and heterochain thermoplastics. 23. The process of claim 22 wherein said polymer is styrene-butadiene rubber, polybutadiene, polyisoprene, butadiene-acrylonitrile, ethylene-propylene diene rubber or polychloroprene.

Inventors: DAVIS WILLIAM MYERS, FUSCO JAMES VINCENT, GARDNER IRWIN JEROME, KOWALSKI RONALD CHARLES, NEWMAN NEIL FREDERICK, DAVIS, WILLIAM, MYERS, FUSCO, JAMES, VINCENT, GARDNER, IRWIN, JEROME, KOWALSKI, RONALD, CHARLES, NEWMAN, NEIL, FREDERICK
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1985
Main classification: C08F8
IPC codes: C08F8