LOW MOLECULAR WEIGHT ETHYLENE-ALPHAOLEFIN COPOLYMER INTERMEDIATES

Abstract: Low molecular weight copolymers comprised of ethylene, an alphaolefin and (optionally) a nonconjugated polyene, which copolymers have a viscosity index of at least about 75 and vinylidene-type unsaturation, possess unexpected advantages as intermediates in epoxy-grafted electrical encapulation compositions.

Description: FIELD OF THE INVENTION This invention is directed to low molecular weight ethylene/alphaolefin/(optionally) nonconjugated polyene copolymers possessing vinylidene-type unsaturation, which copolymers are useful as intermediates for epoxy-grafted electrical encapsulation compositions. BACKGROUND OF THE INVENTION Electronic circuitry is frequently employed in situations wherein it is subjected to adverse environmental conditions and/or to physical stress including shock and mechanical abuse, as well as to severe point pressure and abrasion. In order to protect such sensitive circuitry, it has become known to embed circuitry in an encapsulation composition. The materials employed in such encapsulation compositions must possess high electrical resistivity and should exhibit high arc resistance and track resistance in order to protect circuitry from moisture, physical shocks, and the like. Among the materials which have been found to exhibit highly desirable properties for encapsulation purposes are copolymers of ethylene, propylene and a nonconjugated diene (i.e., "EPDM"). Thus, U.S. Patent 3,974,132 to Valdiserri discloses the insulation and coating of electrically conducting wire with EPDM which is crosslinked with a trialkyl phosphate. However, several disadvantages are associated with the use of EPDM polymers such as those disclosed in this patent. Primary among these disadvantages is that in order to cure such EPDM compositions a curing agent (typically a peroxide) is required, and, consequently, heat must be applied to cause curing to be initiated. Because much electronic circuitry is temperature sensitive, the thermal shock encountered by the curing of such polymers may damage the circuitry to be protected. Moreover, the EPDM employed in the Valdiserri and other similar processes is a high molecular weight material which must be pelletized. Consequently, in order to adapt the embedding composition to the configuration of the circuitry to be protected, such pelletized EPDM must be simultaneously subjected to heat and pressure. The thermal and mechanical shocks resulting from such heat and pressure may cause damage to sensitive electrical circuitry. In addition, such pressure and temperature requirements prohibit the accomplishment of on-site encapsulation, e.g., for the protection of splices or other on-site repairs. In order to overcome these difficulties, copending U.S. Patent Application No. 787,870, filed October 16, 1985, discloses certain liquid epoxy-modified embedding compositions which are pourable and which, due to the presence of such epoxy groups, may be cured at ambient temperature. Moreover, because such compositions are liquids (i.e., they have a definite volume and will assume the shape of their container) the application of pressure to cause them to adapt to the conformation of the circuitry to be encapsulated is not necessary. The most preferred of these compositions are those which exhibit a low Brookfield viscosity (and which are thus more readily poured and formed into appropriate configuration at room temperature) and those exhibiting a high viscosity index (which are thus more readily pourable at low temperatures). It has now been found that those encapsulation compositions which are formed employing the ethylene/alphaolefin/(optionally) nonconjugated diene polymers disclosed herein as intermediates (which copolymers possess vinylidene-type unsaturation) will exhibit a desirably high viscosity index (of at least 75), coupled with an unexpectedly low Brookfield viscosity relative to identical compositions formed from other polymers having a similar composition and molecular weight but not exhibiting vinylidene-type unsaturation. Moreover, it has also been unexpectedly found that encapsulation compositions based upon copolymers having vinylidene-type unsaturation exhibit increased adhesion to wire relative to compositions based on similar copolymers not possessing vinylidene-type unsaturation. South African Patent Application 824,858 discloses one process by which the polymers of this invention may be prepared. However, the copolymers actually disclosed in this Application are all of too high a molecular weight to be liquid materials. While low molecular weight (Mn = 5,000) polypropylene homopolymer was prepared, polypropylene is comparatively undesirable for use in such pourable encapsulation compositions because (as is indicated by its relatviely low viscosity index of about 50) such material is difficult to pour at low temperatures. Sinn et al, in US Patent No 4,404,344, disclose the use of a halogen-free catalyst which may be employed to produce the compounds of this invention, but show only the production of solid, unpourable high molecular weight polymers. John A Ewen, "Mechanisms of Stereochemical Control in Propylene Polymerisations with Soluble Group 4B Metallocene/Methylalumoxane Catalysts", Journal American Chemical Soc, Vol 106, pp 6355-6364 (1984) discloses that polypropylene made by a dicyclopentadiene zirconium dichloride/methylalumoxane polymerisation catalyst exhibits some vinylidene unsaturation (in Table XII). However, as is noted above, polypropylene is less desirable as a base polymer due to its comparatively low viscosity index. European Patent No 69951 discloses copolymerisation of polyolefins using dicyclopentadiene zirconium dichloride/alumoxane catalysts. The molecular weight of products are very high. The polymers would have little or no vinylidene unsaturation. Thus, it is to be noted that none of the above publications disclose the actual making of the compounds of this invention nor do they provide any motivation for doing so. The lower Brookfield viscosities and increased adhesion to wire exhibited by electrical encapsulation compositions based upon the intermediates of this invention (relative to compositions based on similar copolymers not having vinylidene-type unsaturation) is completely unexpected from such disclosures. DESCRIPTION OF THE INVENTION In one aspect, this invention is directed to a copolymer comprised of ethylene and an alphaolefin having the formula H₂C=CHR wherein R is an alkyl radical containing from 1 to 10 carbon atoms; said copolymer having: (a) a number average molecular weight of between 250 and 20,000 and; (b) a viscosity index of at least 75; said polymer exhibiting vinylidene-type unsaturation, such that one end of the polymer will be of the formula P-CR=CH₂ wherein P represents the polymer chain and R is as defined above, and wherein at least 30% of the polymer chains possess vinylidene-type unsaturation. In another respect, this invention is directed to a composition incorporating the copolymer of the first aspect of the invention. The copolymers of this invention are useful intermediates in the production of epoxy-grafted electrical encapsulation compoositions. Such grafted compositions exhibited unexpectedly lower Brookfield viscosities -- and thus greater pourability -- as well as greater adhesion to wire, relative to compositions based on copolymers not possessing vinylidene-type unsaturation. The copolymers of this invention are copolymers of ethylene, an alphaolefin having the formula H₂C=CHR wherein R is an alkyl radical comprising 1 to 10 carbon atoms and (optionally) a nonconjugated polyene. The alphaolefins which may be employed in the practice of this invention are compounds of the formula CH₂=CHR wherein R is an alkyl radical containing from one to ten carbon atoms. When R contains more than 2 carbon atoms such radical may be straight chain or branched. Preferred alphaolefins include propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-pentene, 1-heptene, 1-octene and 1-decene. The polyenes which may be employed in the practice of this invention are nonconjugated. Illustrative of such nonconjugated polyenes are aliphatic dienes such as 1,4-hexadiene, 1,5-hexadiene, 1,4-pentadiene, 2-methyl-1,4-pentadiene, 3-methyl-1,4-hexadiene, 4-methyl-1,3-hexadiene, 1,7-octadiene, 1,9-decadiene, exo and endodicyclopentadiene and the like; exo- and endo-alkenylnorbornenes, such as 5-propenyl-, 5-(buten-2-yl)-, and 5-(2-methylbuten-[2']-yl)norbornene and the like; alkylalkenylnorbornenes, such as 5-methyl-6-propenylnorbornene and the like; alkylidenenorbornenes, such as 5-methylene-, 5-ethylidene-, and 5-isopropylidene-2-norbornene, vinylnorbornene, cyclohexenylnorbornene and the like; alkylnorbornadienes, such as methyl-, ethyl-, and propylnorbornadiene and the like; and cyclodienes such as 1,5-cyclooctadiene, 1,4-cyclooctadiene and the like. The molar ethylene content of the copolymers of this invention is preferably in the range of between 20 and 80 percent, is more preferably between 30 and 70 percent, and is most preferably between 35 and 65 percent, although higher or lower ethylene contents may be present. The nonconjugated polyene molar percent (when present) generally ranges between 0 and 25 percent. The remaining mole percent of such copolymers (up to 100%) is comprised of alphaolefin. The copolymers of this invention generally possess a number average molecular weight of between 250 and 20,000, preferably of between 500 and 15,000, most preferably of between 1,000 and 10,000. Consequently, such copolymers generally possess an intrinsic viscosity (as measured in tetralin at 135°C) of between 0.025 and 0.6 dl/g, preferably of between 0.05 and 0.5 dl/g, most preferably of between 0.075 and 0.4 dl/g. Moreover, the copolymers of this invention generally possess a viscosity index of at least 75, more preferably of at least 100, and most preferably of at least 125. The viscosity index of a compound is determined according to ASTM method D2770-74 wherein the viscosity index is related to kinematic viscosities measured at 40°C and 100°C. The polymers of this invention preferably exhibit a degree of crystallinity such that, when grafted, they are essentially amorphous. The copolymer of this invention is further characterized in that it possesses vinylidene-type unsaturation. Thus, one end of such polymer will be of the formula P-CR=CH₂ wherein R is as defined above (for the alphaolefins which may be employed) and P represents the polymer chain. The composition of this invention comprises copolymer chains, at least 30 percent of which possess vinylidene-type unsaturation. Preferably at least 50 percent, more preferably at least 60 percent, and most preferably at least 75 percent, of such polymer chains exhibit vinylidene-type unsaturation. The percentage of polymer chains exhibiting vinylidene-type unsaturation may be determined by FTIR spectroscopic analysis or titration. The copolymer and the composition of this invention may be prepared employing a Group 4 (of the Periodic Table as is defined on the inside cover of the Handbook of Chemistry and Physics , CRC Press, 66th Ed., 1985-1986) catalyst and an aluminoxane cocatalyst. The catalysts which may be employed are generally of the formula Q n MX 4-n wherein Q is cyclopentadiene, cyclopentadiene substituted with up to five C₁-C₆ alkyl groups, or indene; M is zirconium, titanium or hafnium; X is C₁-C₄ alkyl, halogen, CH₂AlR"₂, CH₂CH₂AlR"₂ or CH₂CH(AlR"₂)₂ wherein R" is C₁-C₆ alkyl or OAl(C₁-C₆ alkyl)₂, and n is 1, 2 or 3. Preferably Q is cyclopentadiene, methylcyclopentadiene or indene; M is zirconium or titanium; X is methyl, ethyl, Cl or Br; and n is 2 or 3. Most preferably Q is cyclopentadiene; M is zirconium; X is methyl or chlorine and n is 2. Representative catalysts include: (C₅H₅)₃TiC₂H₅; (C₅H₅)₂TiCl₂; (CH₃C₅H₄)₂HaCl₂; (C₅H₅)₂ZrCH₃Cl; (C₅H₅)₃ZrC₂H₅; (C₅H₅)₂Zr(CH₃)₂; (C₅H₅)₂ZrCl₂ and (C₅H₅)₂ZrBr₂. The cocatalysts which are typically employed to produce the polymer intermediates of this invention are aluminoxanes either having the linear formula (a) R'₂AlO -(AlR'O) n -AlR'₂ or the cyclic formula (b) (-AlR'O-) n+2 wherein R' is linear or branched C₁-C₆ alkyl and n is an integer of 2-40; preferably R' is methyl or ethyl and n is 6-20. Most preferably cocatalysts have the formula (b) wherein R' is methyl and n is 10-20. Preferred cocatalysts include linear or cyclic methaluminoxane ethylaluminoxane and butylaluminoxane. The catalyst system is employed so that the Al/m molar ratio (wherein M is as defined above) is between about 10 and about 10,000, is preferably between about 20 and about 5,000, and most preferably between about 40 and about 2,000. Polymerization is generally conducted at temperatures ranging between about 20° and about 100°C, preferably between about 30° and about 80°C. Reaction time is not critical and may vary from several hours or more to several minutes or less, depending upon factors such as reaction temperature, the monomers to be copolymerized, and the like. One of ordinary skill in the art may readily obtain the optimum reaction time for a given set of reaction parameters by routine experimentation. The polymerization may be conducted employing liquid monomer, such as liquid propylene, as the reaction medium. Alternatively, polymerization may be accomplished in the presence of a hydrocarbon inert to the polymerization such as butane, pentane, isopentane, hexane, isooctane, decane, toluene, xylene, and the like. If so desired, the polymerization may be carried out in the presence of hydrogen to further lower polymer molecular weight. Care should be taken to assure that vinylidene-type unsaturation is not reduced to less than about 30 percent of the polymer chains. When carrying out the polymerization in a batch-type fashion the reaction medium (if any), alphaolefin, ethylene and (optionally) polyene are charged at appropriate ratios to a suitable reactor. Care must be taken that all ingredients are dry, with the reactants typically being passed through molecular sieves or other drying means prior to their introduction into the reactor. Subsequently, either the catalyst and then the cocatalyst, or first the cocatalyst and then the catalyst are introduced while agitating the reaction mixture, thereby causing polymerization to commence. Alternatively, the catalyst and cocatalyst may be premixed in a solvent and then charged to the reactor. As polymer is being formed, additional monomers may be added to the reactor. Upon completion of the reaction, unreacted monomer and solvent are either flashed or distilled off, if necessary by vacuum, and the low molecular weight copolymer withdrawn from the reactor. The polymerization may be conducted in a continuous manner by simultaneously feeding the reaction medium (if employed), monomers, catalyst and cocatalyst to a reactor and withdrawing solvent, unreacted monomer and polymer from the reactor so as to allow a residence time of ingredients long enough for forming copolymer of the desired molecular weight and separating the copolymer from the reaction mixture. The copolymers of this invention possess several unobvious advantages when employed as intermediates for epoxy-grafted electronic encapsulation compositions. As is shown in Table II below, such grafted copolymers unexpectedly exhibit a lower Brookfield viscosity than do graft copolymers produced from copolymer intermediates of the same composition and weight which do not possess vinylidene-type unsaturation. Because of such lower Brookfield viscosity, encapsulation compositions produced from the copolymers of this invention are more pourable at room temperature and are thus more easily employed. Moreover, because of the high viscosity indexes exhibited by the copolymers of this invention, they retain their fluidity at lower temperatures to a much greater degree than do compounds of similar molecular weight (such as low molecular weight atactic polypropylene). Further, as is shown in Table III below, electrical encapsulation compositions based upon these copolymers exhibiting vinylidene-type unsaturation exhibit unexpectedly high adhesion to wires. Consequently, the compounds of this invention are unexpectedly superior intermediates for epoxy-grafted encapsulation compositions. A further embodiment of the invention can be found in claim 19. Examples The following Examples are intended to further illustrate the invention and are not intended to limit the scope of the invention in any manner whatsoever. Examples 1-4 Ethylene/propylene copolymer was prepared in the following manner. To a 37.2 liter reactor equipped with thermometer, stirrer, monomer inlet tubes for sub-surface addition, catalyst/cocatalyst addition means and a compressor-condenser ebullient cooling system, were added 5000 grams propylene, 655 grams of a 1.16 molar solution of methylaluminoxane in toluene and 200 grams ethylene. The initial reactor temperature was 27°C. The agitator was started and the reactor was open to the cooling system. Ethylene was introduced to reset the reactor pressure to between 170 and 173 psi (1.17-1.19 MPa) at 27°C. The reactor temperature was then increased to 46°C causing the pressure to rise to 182 psi (1.25 MPa). Subsequently, 64.5 ml of a 0.0384 molar solution of (C₅H₅)₂ZrCl₂ in toluene were charged over a period of 15 minutes, which addition produced an exothermic reaction. The reaction temperature was maintained at between 45° and 50°C while feeding ethylene and propylene at a 1/1 weight ratio into the reactor. After 2.25 hours, i.e., after a total of 6660 grams ethylene and 8000 grams propylene had been fed to the reactor, unreacted monomer was vented off, and 14,800 grams of copolymer were isolated. The results of this copolymerization are summarized in Table I below. Following essentially the procedure of Example 1, several additional polymerizations (Examples 2, 3 and 4) were performed. The conditions and results of these polymerizations are summarized in Table I. Analysis indicated that in all the above Examples, a major amount of the polymer chains exhibited vinylidene unsaturation. Examples 5 and 6 and Comparative Experiments A and B Several ethylene/propylene copolymers were modified by grafting onto them allyl glycidyl ether utilizing an organic peroxide following a process similar to that described in United States Patent 4,245,061 to Tachi et al. Two of these copolymers (Comparative Experiments A and B) were prepared using a VOCl₃-based Ziegler-Natta catalyst system and two (Examples 5 and 6) were made according to this invention (employing a zirconium catalyst as described in Example 1). The resultant polymers were analyzed, which analyses are summarized in Table II below. The polymers of Comparative Experiments A and B do not exhibit vinylidene-type unsaturation whereas analysis reveals that a major percentage of the polymer chains of Examples 5 and 6 possess vinylidene unsaturation. Example or Comp. Experiment A B 5 6 VOCl₃-catalyzed yes yes - - Zr-catalyzed - - yes yes Molecular weight, initial 2500 2500 2500 2500 Molecular weight, after grafting 2340 2760 2460 2820 No. epoxy groups/Chain 2.2 2.4 2.6 3.0 Brookfield viscosity (25°C) 178,000 126,000 33,000 112,000 The above data clearly indicate the lower viscosities observed for epoxy-grafted ethylene/propylene copolymers having vinylidene unsaturation relative to similar grafted copolymers produced from ethylene/propylene copolymer intermediates of identical molecular weight not exhibiting vinylidene-type unsaturation. It should be noted that the Brookfield viscosity is influenced by molecular weight as well as by the epoxy functionality per chain. It is, therefore, surprising that Example 6 (this invention) exhibits a lower viscosity than Comparative Experiment B (based on copolymer not exhibiting vinylidene unsaturation) although both the molecular weight and the epoxy functionality of the composition of this invention are higher. Example 7 and Comparative Experiment C Additional low molecular weight ethylene/propylene copolymers were prepared employing (in Example 7) a catalyst composition comprising (C₅H₅)₂ZrCl₂ and (Comparative Experiment C) employing a catalyst composition comprising VOCl₃. The zirconium-catalyzed copolymers exhibited vinylidene unsaturation whereas the vanadium-catalyzed copolymers did not exhibit vinylidene-type unsaturation. These copolymers were grafted with allyl glycidyl ether by reacting such copolymers and ethers with dicumyl peroxide. The physical properities of the graft copolymers are shown in Table III. These graft copolymers were formulated (as described in Table III) into electronic encapsulation compositions. The initial Brookfield viscosities of such compositions and the gel times (i.e., the minutes until a viscosity of 10⁵ centipoise was measured) were determined. In addition, the adhesion of said encapsulation compositions to a length of polyethylene insulated copper wire coated with a cable filling compound was measured by inserting a length of said wire into a 5 inch test tube; pouring in the encapsulation composition to be tested until it filed 4.5 inches of such test tube; allowing the encapsulation composition to cure; and measuring the force required (in pounds) to withdraw the 4.5 inch length of wire. The results of said testing are summarized in Table III. The above data once again indicate the unexpectedly low Brookfield viscosities exhibited by epoxy-grafted copolymers formed from the vinylidically unsaturated copolymers of this invention vis-a-vis similar copolymers not exhibiting vinylidene-type unsaturation. Moreover, such data indicate the unexpectedly high adherence to wires exhibited by electronic encapsulation compositions based upon the vinylidenically unsaturated copolymers of this invention.

Claims: A copolymer comprising of ethylene and an alphaolefin having the formula H₂C=CHR wherein R is an alkyl radical containing from 1 to 10 carbon atoms; said copolymer having: (a) a number average molecular weight of between 250 and 20,000 and; (b) a viscosity index of at least 75; said polymer exhibiting vinylidene-type unsaturation, such that one end of the polymer will be of the formula P-CR=CH₂ wherein P represents the polymer chain and R is as defined above, and wherein at least 30% of the polymer chains possess vinylidene-type unsaturation. A copolymer according to Claim 1 characterised in that said copolymer further comprises a nonconjugated polyene. A copolymer according to Claim 2 characterised in that said nonconjugated polyene is selected from 5-ethylidene-2-norbornene, 1,4-hexadiene and dicyclopentadiene. A copolymer according to any of the preceding claims characterised in that said copolymer has a number average molecular weight of between 500 and 15,000 A copolymer according to Claim 4 characterised in that said copolymer has a number average molecular weight of between 1,000 and 10,000. A copolymer according to any of the preceding claims characterised in that said copolymer has a viscosity index of at least 100. A copolymer according to any of the preceding claims characterised in that said copolymer has a viscosity inex of at least 125. A copolymer according to any of the preceding claims characterised in that said copolymer has a molar ethylene content of between 20 and 80 percent. A copolymer according to Claim 8 characterised in that said copolymer has a molar ethylene content of between 30 and 70 percent. A copolymer according to Claim 9 characterised in that said copolymer has a molar ethylene content of between 35 and 65 percent. A copolymer according to any of the preceding claims characterised in that said copolymer consists of ethylene and an alphaolefin having the formula H₂C=CHR wherein R is an alkyl radical containing 1 to 10 carbon atoms. A copolymer to any of the preceding claims characterised in that said alphaolefin is propylene. A composition including a copolymer as claimed in any preceding claim. A composition according to Claim 13 characterised in that at least 50 percent of said copolymer exhibits vinylidene-type unsaturation A composition according to Claim 14 characterised in that at least 60 percent of said copolymer exhibits vinylidene-type unsaturation. A composition according to Claim 15 characterised in that at least 75 percent of said copolymer exhibits vinylidene-type unsaturation. Use of a composition for encapsulation of electronic circuitry characterised in comprising a copolymer as claimed in any of claims 1 to 12. Use of a composition as claimed in claim 17, wherein the copolymer is epoxy-grafted. Use of a composition as claimed in Claim 18, wherein the copolymer comprises an initial backbone polymer comprising: ethylene and an alphaolefin having the formula H₂C=CHR wherein R is an alkyl radical containing from 1 to 10 carbon atoms; said polymer having: (a) a number average molecular weight of between 250 and 20,000 and; (b) a viscosity index of at least 75; said polymer initially exhibiting vinylidene-type unsaturation, such that i) one end of the polymer will be of the formula P-CR=CH₂ wherein P represents the polymer chain and R is as defined above; and ii) at least 30 percent of the polymer exhibits vinylidene-type unsaturation said backbone polymer having grafted thereto allyl glycidyl ether or a monoglycidyl ether of a C₁₂-C₁₄ alcohol; and wherein the graft polymer is crosslinkable.

Inventors: MATTHEWS, DEMETREOS N., RIM, YONG S.
Applicants: UNIROYAL CHEMICAL COMPANY, INC.
Application year: 1986
Main classification: C08F210
IPC codes: C08F255, C08F4, C08F10, H01B3, C08F210