Free radically cured thermoplastic vulcanizates of a polyolefin and a acrylate modified paraalkylstyrene/isoolefin copolymer

A thermoplastic vulcanizate composition containing a thermoplastic and a functionalized copolymer of para-alkylstyrene-isoolefin is free radically cured, as for example, with a peroxide to yield a product having low impurities and good clarity. The thermoplastic typically can be a polyolefin.

FIELD OF THE INVENTION
 The present invention relates to the vulcanization of functionalized
 para-alkylstyrene/isoolefin copolymers in the presence of thermoplastics
 with a free radical curing agent such as a peroxide. Some of the alkyl
 groups of the copolymer are functionalized with an unsaturated compound
 such as an unsaturated acid.
 BACKGROUND OF THE INVENTION
 Heretofore, the curing of thermoplastic vulcanizates generally utilize cure
 systems such as sulfur or various resins. Such curatives generally
 discolored upon ultraviolet light exposure and did not yield compositions
 having good ultraviolet light resistance.
 SUMMARY OF THE INVENTION
 The thermoplastic vulcanizate composition generally has a continuous phase
 of a thermoplastic and a discontinuous rubber phase comprising a
 functionalized copolymer of para-alkylstyrene/isoolefin so that the rubber
 can be cured by a free radical mechanism. Cure can be obtained utilizing
 any free radical cure source such as radiation, electrical, microwave, or
 desirably decomposition of various organic peroxides. The various
 components are dynamically vulcanized at a temperature above the melting
 point of the thermoplastic or the thermoplastic elastomer.

DETAILED DESCRIPTION
 The thermoplastic polymer is a polyolefin having a melting point of at
 least 120.degree. C., and preferably at least 160 or 200.degree. C. up to
 about 220.degree. C. The one or more polyolefin thermoplastic polymers are
 made or derived from .alpha.-olefin monomers having from 2 to 8 carbon
 atoms. Such polymers are desirably crystalline, high molecular weight
 solid polymers made in accordance with conventional processes. Moreover,
 such polymers are generally isotactic and syndiotactic resins. Examples of
 suitable polyolefin thermoplastic polymers include polyethylene,
 polypropylene, poly(1-butene), poly(1-pentene), poly(1-hexene),
 poly(2-methyl-1-propene), poly(3-methyl-1-pentene),
 poly(4-methyl-1-pentene), poly(5-methyl-1-hexene), and mixtures thereof,
 with syndiotactic polypropylene being preferred.
 A preferred rubber is a functionalized copolymer of
 para-alkylstyrene/isoolefin wherein the olefin is derived from monomers
 containing a total of from 4 to 7 carbon atoms with isobutylene being
 preferred. The functionalized copolymer is generally made from a
 para-alkylstyrene/isoolefin copolymer wherein the alkyl group and contains
 a primary or secondary alkyl halide such as a primary or a secondary
 C.sub.1 to C.sub.5 alkyl bromide. The halide group is subsequently
 displaced via nucleophilic substitution by a nucleophilic molecule,
 oligomer or polymer. These grafting reactions are taught in U.S. Pat. No.
 5,162,445 herein fully incorporated by reference. The copolymer repeat
 units derived from isobutylene can be from about 10 to about 99.8 wt. % of
 the copolymer before halogenation and/or grafting, desirably from about 50
 to about 99.6 weight percent, and preferably from about 80 to about 99.5
 wt. percent. The repeat units of para-alkylstyrene are thus from about 0.2
 to about 90 wt. percent, desirably from about 0.4 to about 50 weight
 percent, and preferably from about 0.5 to about 20 wt. percent. The
 polymer before grafting can have a number average molecular weight from
 about 500 to about 25,000, 30,000 or 40,000.
 The molecules, oligomers or polymers grafted onto the benzylic carbon atom
 by nucleophilic substitution need to have a nucleophilic group which can
 displace the halogen. The molecules, oligomers, or polymers desirably have
 more favorable blending characteristics with the thermoplastic phase of
 the thermoplastic vulcanizate than the rubber of the thermoplastic
 vulcanizate and thus act as a compatibilizing agent. Preferred
 functionalizing molecules, oligomers, or polymers include those derived
 from an unsaturated acid or a salt thereof. Suitable acids include acrylic
 or methacrylic acid, or unsaturated acids having a total of from 4 to 1 5
 carbon atoms. As known to the art, the acid is first reacted to form a
 salt and the salt acrylate, etc., subsequently reacted with the alkyl
 styrene wherein the alkyl group contains a halogen. This approach is set
 forth in U.S. Pat. No. 5,473,017, hereby incorporated by reference, and as
 set forth in Example A thereof, small amounts of a benzophenone can also
 be incorporated. Preferred functionalizing agents are acrylate and/or
 methacrylate modified para-alkyl/isoolefin copolymers. Such acrylate
 modified para-alkylstyrene/isoolefin copolymers are commercially available
 from Exxon such as XP-50-16924, XP-50-15870, and the like. The number of
 styrene groups that are substituted or modified to contain unsaturation
 thereon so that the copolymer can be crosslinked is generally less than 12
 percent, desirably less than 1 percent, and preferably less than 0.5
 percent based upon the total number of styrene groups in the copolymer.
 The amount of the one or more thermoplastic polymers to the total amount of
 one or more rubbers is generally from about 15 to about 75, desirably from
 about 20 to about 70, and preferably from about 25 to about 65 parts by
 weight per 100 parts by weight of total rubber.
 The rubber is cured utilizing generally any type of free radical cure
 source, such as radiation, electrical or microwave, various organic
 compounds, with organic peroxides being preferred. Examples of suitable
 organic peroxides include diacyl peroxides, dialkyl peroxides, ketone
 peroxides, peroxydicarbonates, peroxy esters, and peroxy ketals. Examples
 of ketone peroxides include methyl ethyl ketone peroxide, benzoyl
 peroxide, cumene hydroperoxide, and 2,4-pentanedione peroxide. Examples of
 peroxydicarbonates include di-sec-butyl peroxydicarbonate, di-n-propyl
 peroxydicarbonate, di-2-ethyl hexyl peroxydicarbonate. Examples of peroxy
 esters include t-butyl and t-amyl peroxy neoesters (e.g., t-butyl
 peroxyneodecanoate, t-amyl peroxyneodecanoate, and t-butyl
 peroxypivalate). Other peroxy esters include t-butyl peroxy 2-ethyl
 hexanoate, t-butyl peroxyisobutyrate, t-butyl peroxyacetate, and t-butyl
 peroxybenzoate. Still other peroxides include di-benzoyl peroxide, dicumyl
 peroxide, 2,5-dimethyl-2,5-bis-(2-ethyl hexyl peroxy) hexane,
 t-amylperoxyoctoate, t-butyl peroxyoctoate, lauroyl peroxide, t-butyl
 peroxybenzoate, 1,1-bis-t-butyl peroxy cyclohexane, 1,1-bis-t-amyl peroxy
 cyclohexane, and dicumyl peroxide. Still other peroxides include 2,2'-bis
 (t-butyl peroxy) diisopropyl benzene, 2,5-dimethyl-2,5-di (t-butyl peroxy)
 hexane, ethyl 3,3-bis (t-butyl peroxy) butyrate, n-butyl 4,4-bis(t-butyl
 peroxy) valerate, and 2,5-dimethyl-2,5-di (t-butyl peroxy) hexene-3.
 Organic peroxides which are generally preferred in the present invention
 include 2,2'-bis (t-butyl peroxy) diisopropyl benzene, 2,5-dimethyl-2,5-di
 (t-butyl peroxy) hexane, and other high temperature decomposing peroxides.
 The amount of the peroxide generally depends upon the amount of the rubber
 such as XP-50 and is typically from about 0.1 to about 3.0 parts by weight
 and preferably from about 0.2 to about 1.0 parts by weight per 100 parts
 by weight of the rubber.
 The curatives effect crosslinking by reacting the functionalized or
 unsaturated group on the styrene repeat units with a similar unit on an
 adjacent polymer chain. Inasmuch as peroxide cures occur rapidly, there is
 little degradation, i.e., chain scission, of the various polymers. A clear
 blend can be produced since conventional curatives which often contain
 impurities need not be utilized. High clarity blends are desired for
 numerous medical applications such as tubing, hosing, clear liners, and
 the like. The thermoplastic elastomers of the present invention also
 generally have good UV stability or resistance and thus, if necessary,
 require only small amounts of additional UV stabilizers.
 The thermoplastic vulcanizate compositions of the present invention,
 whether clear or not, can generally be used in any TPV applications such
 as seals, gaskets, boots and the like. They are also utilized for many
 automotive parts. Inasmuch as TPV compositions have fairly good air and/or
 water vapor barrier properties, they can be utilized whenever such is
 desirable.
 Generally, when high clarity vulcanizates are desired, processing aids are
 generally not utilized. However, when clarity is not a factor,
 conventional additives can be utilized such as reinforcing and
 non-reinforcing fillers, extenders, antioxidants, stabilizers, rubber
 processing oil, extender oils, lubricants, plasticizers, anti-blocking
 agents, anti-static agents, waxes, foaming agents, pigments, flame
 retardants and other processing aids known in the rubber compounding art.
 Such additives can comprise up to about 60 weight percent of the total
 composition, and can be in the plastic phase, the rubber phase or both.
 Fillers and extenders which can be utilized include conventional
 inorganics such as calcium carbonate, clays, silica, talc, titanium
 dioxide, carbon black, and the like. The rubber processing oils generally
 are paraffinic, or naphthenic oils derived from petroleum fractions. The
 type that can be used in conjunction with the specific rubber or rubbers
 present in the compositions, and the quantity based on the total rubber
 content may range from zero to about 100 phr and preferably from about 10
 to about 40 phr.
 Partial or preferably complete cross-linking can be achieved by adding one
 or more of the above-noted rubber curatives to the blend of a
 thermoplastic and rubber and vulcanizing the rubber to a desired degree of
 cure under conventional vulcanizing conditions. The degree of cure of the
 elastomer or rubber of the present invention is generally at least 50,
 desirably from about 75 to about 100, and preferably 90 to 100 percent. By
 degree of cure, it is meant that the above indicated percent by weight of
 the rubber does not dissolve in cyclohexane at room temperature, i.e.,
 20.degree. C.
 It is preferred that the rubber be cross-linked by the process of dynamic
 vulcanization. As used in the specification and claims, the term "dynamic
 vulcanization" means a vulcanization or curing process for a rubber
 contained in a thermoplastic vulcanizate composition, wherein the rubber
 is vulcanized under conditions of shear at a temperature above the melting
 point of the thermoplastic component. The rubber is thus simultaneously
 cross-linked and dispersed as fine particles within the thermoplastic
 matrix although other morphologies may also exist. Dynamic vulcanization
 is effected by mixing the thermoplastic vulcanizate components at elevated
 temperature in conventional mixing equipment such as roll mills, Banbury
 mixers, Brabender mixers, continuous mixers, mixing extruders, and the
 like. The unique characteristic of dynamically cured compositions is that,
 notwithstanding the fact that the rubber component is partially or fully
 cured, the compositions can be processed and reprocessed by conventional
 plastic processing techniques such as extrusion, injection molding, blow
 molding and compression molding. Scrap or flashing can be salvaged and
 reprocessed.
 The thermoplastic vulcanizate compositions of the present invention
 generally has good physical properties as other conventional dynamically
 vulcanized thermoplastic elastomers such as good tensile strength, good
 elongation, ultimate elongation as well as hardness. A notable property,
 as indicated above, is good clarity when a minimum or nil amount of
 various additives such as oils, plasticizers, and antioxidants were
 utilized.
 The invention will be better understood by reference to the following
 examples, which serve to illustrate, but not limit, the present invention.
 The following recipes set forth in Tables 1, 2, and 3 were prepared
 utilizing a Brabender mixer heated to a temperature of about 180.degree.
 C. and 100 RPM. The acrylate modified XP-50 was charged to the mixer along
 with the polyolefin. The various additives noted in the table can be added
 at the same time. After 2 to 3 minutes of mixing, when the blend is fully
 homogenized as indicated by the torque leveling off, the curatives were
 added and the Brabender speed increased to 220 RPM. An increase in torque
 normally occurs and the blended compounds were mixed for an additional 4
 to 6 minutes. The blend is then removed from the Brabender and pressed
 into a cold press to cool it and to obtain a sheet which is then molded
 and tested.
 TABLE 1
 Material 1 2 3 4 5
 Functionalized Br (Control) 35.00 35.00 35.00 33.33
 XP-50 A* 35.00
 Polypropylene 23.30 23.30 23.30 23.30 22.33
 N,N'-m-phenylene- 0.07 0.07 0.07
 dimaleimide HVA-2
 2,5-dimethyl-2,5-di(t- 0.07 0.07 0.07
 butylperoxy)hexane
 (LUPERSOL L-101)
 Butyl Rubber (Exxon 4.46
 Butyl 268)
 TOTAL: 58.30 58.37 58.37 58.44 60.26
 Physical Properties
 SAMPLE ID:
 Property 1 2 3 4 5
 Hardness (shore A&D) 86/30 86/30 90/35 90/35 86/30
 UTS (psi) 877 1192 1629 1773 1449
 Elongation % 124 137 223 230 204
 M 100 (psi) 867 1115 1256 1338 1096
 Comp. Set 22 hrs @ 88.6% 59.4% 43.5% 44.7% 43.4%
 100.degree. C.
 Wt. Gain 72 hrs @ Failure 218.9 155.5 151.6 185.1
 125.degree. C.
 Tension Set 54.8% 38.2% 24.1% 26.1% 22.1%
 *Methacrylate ester 0.57% mole, hydroxybenzophenone 0.34 mole %
 Mooney ML.sub.1+8 @ 125.degree. C., 77.
 As apparent from Table 1, the thermoplastic vulcanizates which were cured
 with a peroxide curative, i.e., Examples 3, 4, and 5, had much better
 properties than Example 1, which did not utilize any peroxide cure, and
 Example 2, which utilized only a co-curative.
 TABLE 2
 A B C
 FUNCTIONALIZED Br XP-50 B* 100 100 100
 POLYPROPYLENE 67 67 67
 LUPERSOL L-101 .2 .2 .2
 HVA-2 -- .2 .2
 POLYGARD (antioxidant) -- .2 --
 PHYSICAL PROPERTIES
 SHORE 35D 31D 32D
 TENSION SET % 34 33 24
 UTS, PSI 1280 1430 2010
 M100, PSI 970 1110 1040
 M300, PSI -- -- 1750
 UE, % 280 290 380
 % UNCURED RUBBER CYCLOHEXANE 12.51 8.82 4.63
 *Contains acrylic acid 0.51 mole %, hydroxybenzophenone 0.14 mole %.
 TABLE 3
 Composition # H I J K L M N
 O P Q R
 Functionalized Br XP-50 B* 100 100 100 100 100 100
 100 100 100 100 100
 PP 67 67 67 67 67 67
 67 67 67 67 67
 HVA-2 0.25 0.25 0.25 0.25 0.25 0.25
 -- -- -- -- --
 ZnO -- -- -- 1 -- -- -- -- -- -- --
 Hercules S03765 (Accelerator) -- -- -- -- -- 0.3 -- -- -- -- --
 Sartomer 368 (Accelerator) -- -- -- -- -- -- 0.2 0.4 0.4
 -- --
 Saret 623 (Accelerator) -- -- -- -- -- -- -- -- -- 0.2 0.4
 Lupersol 101 0.1 0.2 0.4 0.4 0.05 -- 0.1
 0.1 0.2 0.1 0.1
 Shore D 33 35 35 34 30 31
 33 34 36 31 32
 Tension Set, % 33 27 28 28 73 72
 31 32 24 37 37
 UTS, psi 1490 2130 1770 1780 970 990
 1490 1560 2130 1230 1240
 M100, psi 1100 1130 1040 1040 950 1010
 910 940 1090 850 870
 M300, psi -- 1640 1510 1530 -- -- 910 1360
 1680 1180 1210
 UE, % 280 520 420 430 260 290
 400 440 420 370 370
 Table 2 shows the effect of using a co-agent, e.g., HVA-2, on the degree of
 crosslinking as determined by percent extractable rubber in cyclohexane
 solvent.
 Table 3 shows the effect of different amounts of peroxide with different
 types of co-agents.
 While in accordance with the Patent Statutes, the best mode and preferred
 embodiment have been set forth, the scope of the invention is not limited
 thereto, but rather by the scope of the attached claims.