CA1040794A - Random ethylene/alkyl acrylate copolymers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Random copolymers of ethylene, alkyl acrylate and 1,4-butene-dioic acid esters whose vulcanizates exhibit both low brittle point and low oil swell characteristics.

Description

Back~round of the Invent~on A wide variety of industrial applications require vulcanized elastomeric articles which exhibit a combination of mechanical toughness, low brittle point, low oil swell, a high level of heat aging resistance, all at moderate cost. Hereto~ore, this particular combination of attributes has not been available in a single elastomeric material.
SummarY of the Invention The instant invention provides random elastomeric copolymers having a particularly desirable resistance to oil and low temperatures that renders them suitable for a wide variety of industrial applications.
Specifically, the instant invention provides a random copolymer comprising ethylene, alkyl acrylate se~ecLed from methyl and e~hyl acry'ate, a~d a~out f,om 0.0025-0.077 moles/100 gm. of polymer of a monoe~ter of 1,4-butene-dloic acit in which the alkyl group of the ester h-~ 1 to 6 carbon atom~. The copolymar ha~ about from 0.64-0.80 moles/100 gm. polymer of (-CO2-) unlts. The copolymer has a melt index at 190C. of about 0.3 to about 100 grams/
10 min., and preferably of 0.3 to 10 gram~/10 min. The copol-y~er when vulcanized is elastomeric and ha~ a brittle point of less than about -40C. and an oil swell of le~ than about 115% after immersion in ASTM $3 oil for 70 hours at 150C.

Detailet Description of the Invention The alkyl acrylate used in the preparation of the instant terpolymers can be selected from methyl acrylate and ethyl acrylate. Generally, methyl acrylate is pre-.

- 2 -~1, ferred, and comprises about from 48 to 63 weight percent of the terpolymer, preferably 52-58 weight percent.
The monoalkyl ester of 1,4-butene-dioic acid functions as a cure-site monomer and comprises about from 0.0025-0.077 moles/100 gm. of the terpolymer. 1,4-Butene-dioic acid exists in cis and trans forms, i.e., maleic and fumaric acid. Mono alkyl esters of either are satisfactory.
Methyl hydrogen maleate, ethyl hydrogen maleate, and propyl hydrogen maleate are particularly satisfactory.
Ethylene is the third component of the terpolymer.
Polymerized ethylene is present in the terpolymer in a complemental amount The terpolymers of this invention can be readily prepared by copolymerizing ethylene, an alkyl acrylate, and the mono alkyl ester cure-site monomer in the presence of a free-ratical polymerization initiator. Free-radical polymerization initiators that can be uset include peroxygen compounds such as lauryl peroxide, t-butyl peracetate, -butylperoxypivalate, and di-t-butylperoxide, or an azo bis compound, such as azobisisobutyronitrile.
The quantities of alkyl acrylate and ester cure-site monomer are ad3usted to provide the required amount of (-C02-) units in the final copolymer. The total (-CO2-) unlts in the polymer is the sum of the ester groups in the acrylate monomer and in the 1,4-butene-dioic acid mono ester, and the acid groups in the mono ester. It has been found that when the moles of (-CO2-) units per 100 grams of copolymer exceed 0.80, the brittle point of the copolymer is greater than the desired -40C. Conversely, when less than 0.64 moles of (-CO2-) units are present, the i04()79~
oil swell characteristics are depreciated.
Within the meaning of the present invention, the Brittle Point is measured by ASTM Method D-476-70 on peroxide press cured vulcanizates or amine press and post cured vulcanizates. The oil swell is measured on the same cured w lcanizates by ASTM Method D-471-68 (% volume swell in ASTM #3 oil after 70 hours at 150C.).
The copolymerization can be carriet out in a pressure reactor at moderately elevated temperatures, e.g., 90C. to 250C., preferably 145 o 155C, and pressures of 1600 to 2200 atms., preferably 1800 to 2000 atms.
The polymerization is run as a continuous process, and ethylene, acrylate, ester cure-site monomer and optionslly a solvent such as benzene are fed continuously into a stirret autoclave of the type tis-closed in U. S. Patent 2,897,183 to Christl et al together with initiator. The rate of addition will depend on variables such as the polymerization temperature, pres~ure, monomers employed, and concentration of the monomers in the reaction mixture. In some cases it may be desirable to use a telogen such as propane, to control molecular weight. The reaction mixture is contin-uously removed from the autoclave. After the reaction mixture leaves the reaction vessel, the terpolymer is separated from unreacted monomers and solvent, if solvent was used, by conventional means., e.g., vaporizing the unpolymerized materials and solvent under reduced pressure and at an elevated temperature.

~040794 If desired the polymer may be branched to modify its processing characteristics by including a minor amount of ethylene glycol dimethacrylate in the charge to the reactor.
After the continuous operation has reached a steaty state, the total conversion of monomers to polymer varies from 5 to 12 weight percent. The melt index (M.I.) of a polymer is well recognized as being related to its molecular weight, the lower the M.I. the higher the molecular weight. The M.I. values are determined at 190C as described in tentative ASTM test method D 1238-52T (ASTM Standards, lg55, Part 6, page~ 292-295), and these varied from about 0.3 to 100 g/10 min. or more depending on polymerization conditions or the use of a telogenic attitive. The percent by weight incorporation of the e8ter ~u~e-site ~onomer can be measur~d by potentiometric titration with aqueous sotium hydroxide of a solution of the polymer in tetrahydrofuran.
The weight percent acrylate is determined by proton nuclear magnetic resonance and/or oxygen analysis after correcting for the amount of mono ester present.
From these, the moles of carboxyl unit content per gram of copolymer can be determined by routine calculation.
The vulcanizates of terpolymers of the instant invention exhibit an oil swell of less than 115%, a brittle point of less than -40C., and excellent heat aging resistance. These desirable properties permit the use of the instant terpolymers in automobile engine and heavy indu~trial equipment applications where good resistance to oil and low and high temperatures are required ~0407.94 In contrast to the ethylene/alkyl acrylate co-polymers of the prior art the instant copolymers exhibit 8ignific~ntly lower brlttle points for a given level of acrylate monomer incorporated in the polymer composition;
consequently, the instant copolymer compositions offer a marketly superior combination of oil resistance and low temperature performance.
Vulcanizates of the elastomeric copolymers of the instant invention can be used in a wide variety of industrial applications, includlng ignition wire ~acketing, sp~rk plug boots, hose, belts, miscellaneous molded boots, seals, and gaskets. The good low and high temperature physical properties and excellent oil resistance make these elastomers particularly well suited for automotive applications The pre6ent elastomeric co~pos~t~ons can be cured and compounded according to the followlng procedures.
The compositions of the present invention can be w 1-canized in the presence of peroxide curing systems com-posed of a peroxide and optionally a coagent. Theperoxides used should be those that decompose rapidly within the range of lS0 to 250C. These include, for xample, dicumyl peroxide, 2,5-bis(t-butyl-peroxy)-2,5-d~methylhexane, and a,a-bis(t-butylperoxy)-diisopropyl-benzene. In a typical w lcanizate composition there will be about 0.5-5 parts by weight of peroxide per 100 parts of polymeric blend. The peroxide may be adsorbed on an lnert carrier such as calcium carbonate, carbon black or Rieselguhr; however, the weight of the carrier is not included in the above range.

104(~794 The coagent can be, for example, N,N'-(m-phenyl-ene)-dimaleamide, trimethylolpropane trimethacrylate, tetrasllyloxyethane, triallyl cyanurate, tetramethylene di-acrylate, or polyethylene oxide glycol dimethacrylate. The amount of the coagent is about 0-5 parts by weight per 100 parts of polymeric blend, about 1-3 parts per 100 J
bein8 preferret.
The coagents u~ually contain multiple unsaturated groups such as allyl or acrylic esters. While their mode 10 of act~on i8 not known with certa~nty, it is believed that they react with the in~tial radical formed on the polymer backbone to form a more stable radical, which untergoes coupling reactions to form crosslinks more readily than chain scission reactions.
Other vulcanizing agents that can be u~ed with the instant copolymers ~nclude Amine curing systems, ~uch as hexamethylenetiamine, hexamethylenediamine car-b~mate, tetramethylenepentamine, hexamethylenediamine-cinnamaldehyde adduct, as well as hexamethylenediamine-dibenzoate ~alt. Aromatlc amines can also be used as curing agcnts.
The vulcanlzates o~ the present lnvent~on may al~o contaln an antloxldant ~ystem based on a phosphorus ester ~ntloxldant, a hindered phenollc antloxldant, an amlne antl-oxldant, or a mlxture o~ two or more Or the~c compounds. The phosphoru~ ester compound can be, ~or example:
trltmlxed mono- and dlnonylphenyl) phosphlte, tris(3,5-di-t-butyl-4-hydroxyphenyl) phosphate, high molecular welght poly(phenollc phosphonates)~
and i~40794 6-(3,5-di-t_butyl-4-hydroxy~benzyl~H-dibenz-Lc~e~ 2]oxaphosphorin-6-oxide.
The hindered phenolic compounds include~ for example, the following:
4,4-butylidenebis(6-t-butyl-m-cresol), 1,3,5-trimethyl-2,4,6-tris_(3,5-di-t_butyl-4_hydroxy-benzyl)benzene, 2,6-di-t-butyl-~-dimethylamino-~-cresol, and 4,4'-thiobis-(3_methyl-6-t_butylphenol).
Suitable amine antioxidants include, among others, the followings polymerized 2~2,4-trimethyl-1~2-dehydro-quinoline; N-phenyl-N'_(p-toluenesulfonyl)-~-phenylene-diamine; N,N'-ditp-naphthyl)-~-phenylenediamine; low tem-perature reaction product of phenyl (~-naphthyl)amine and acetone; and 4,4'-bis(c,c-dimethylbenzyl)diphenylamine, The proportion of the antioxidant compound in the w lcanizing composition is 0.1-5 parts per 100 parts of polymer, the preferred proportion being 0.5-2.5.
The antioxidant improves the heat aging of the compositions. The antioxidant effect is usually quite low below theepreferred range and impractically low below the broad range recited above. Above the higher limits, little additional improvement is observed, and theremay be adverse effects on the state of cure. The weight ratio of the phenolic or,a~ne antioxidant to the phosphorus compound in the mixtures is about 0.5-3, the preferred ratio bein8 about 1.
The preferred antioxidant conpositions contain tri(mixed mono and dinonylphenyl) phosphite in mixture with either 4,4'-bis(~,~-dimethylbenzyl)diphenylamineor 4,4~_butylidenebis(6-t-butyl-m_cresol).

It is often desirable to add fillers to reduce ccst and to improve mechanical properties. A typical vulcanized composition will usually contain about 15-40 volume percent of fillers, for example, carbon black, barium sulfate, magnesium silicate, or s$1ica. Other conventional fillers can also be used. The preferred proportion of the fillers is 20-25 volume percent~ and also depends on the reinforcing effect of the individual fillers, Below the lower limit, the improvement of tensile properties is quite low; while above thelupper limit, the heat aging reslstance of the polymer is adversely affected.
The present lnventlon is further illustrated by the following speclfic examples.

ExamPles 1-5 In examples 1-5 mixtures of ethylene, an alkyl arcrylate, and a monoalkyl ester of maleic acid were co-polymerized in the presence of a free-radial polymerization initiator and in a pressure reactor at 125-175C. and a pressure of 1700-1900 atm. The alkyl acrylate used was methyl-, or ethylacrylate containing 530-1200 ppm of a stabilizer. the mononethyl ether of hydroquinone. The monoalkyl ester of ~aleic acid contained less than 3 weithy percent maleic acid and less than 2 weight percent maleic anhydride. The free-radical polymerization initia-tor used was t-butylperoxypivalate.
me polymerization was run as a continuous pro-cess, and ethylene, acrylate, monoalkyl ester of maleic acid, and benzene solvent were fed continuously into a 325 or 720 cc stirred autocalve at rates of 7-18 lbs/hr, 0.4-1.5 lbs/hr, 0.02-0.06 lbs/hr, and 1.1-2.5 lbs/hr, 104~794 respectively. Initiator was introduced continuously at a rate of about 1 0-5.5 lb~/1000 lbs of polymer. The reaction mixture was continuously removed from the auto-clave and wa~ ~tripped of unpolymerized monomers and solvent und r reduced pre~ure and at elevated temPerature.
The melt lntices of the resulting polymers were t-t-nmlned at 190C. a8 descrlbed ln tentative ASTM test method D 1238-52T (ASTM Standards, 1955, Part 6, pages 292-295). The percent by weight incorporation of the monoalkyl ester of maleic acid was measured by potentio-metrlc tltration with aqueous sotium hydroxide of a solu-tion of the polymer ln tetrahydrofuran. The weight percent of alkyl acrylate is determined by proton nuclear magnetic rosonance and/or oxygen analysis after correcting for the amount of monoalkyl maleate present. The various physlcal properties are summarlzed ln Table I. In the Control Example, the quantity of (-C02-) units in the copolymer below that required for the present invention.
The copolymers were then vulcanized by the 2n following procedure. On a 2-roll rubber mill at about 25C. were m~xed 100 parts of terpolymer, 50 parts of Fa~t Extruding Furnace (FEF) carbon black, 1.5 parts of hexa-methylenediamine carbamate (HMDAC), antioxldants ant other additives as indicated in Table II. The compositions were sheetet off the mill and specimens for physical testing were preparet. Vulcanizate slabs 0.075 in. thick were prepared by press-curing for 30 minutes at 180C. at about a total pressure of 40,000 lb~. Modulus, tensile strength, ant elongation values were obtained at room temperature by ASTM Method D-412-66 on press-cured samples.

104~79~
Percent volume swell after immersion in ASTM #3 oil for 70 hrs. at 150C. was determined according to ASTM
D-471-68 on press-cured and post-cured (24 hours at 150C.
in an air atmosphere) samples. The brittleness temperature (Brittle Point) was determined according ~o ASTM D-746-70, Examples 1-5 are within the scope of the application and have oil swell <115% and a brittle point ~-40C. The Control Example has oil swell ~115%.

104~)794 ~ ~ .
-'1' ~ ~
~1 ~ ~ ~
'~

o ~ o U~ o~ t~ ~ ~o ~ ~ oo 8 ~ ~ o co ~ ,, ~ ~ o .~" ' ,, O~q O~ O ~D O ~ O O ~ 00 ~o oOo, ~0 o~_~
P: ~o ,, ~ ~0~ O ~D O O~ ~ I~ ~ Cr~
~1 a ~ ~ Og~O~ ~ ~ O

~ ~ ~1 0~
0 ~ ~ ~ 0 U~ ~ ~ 0 ~O
2 o g ~ u~ uO~ 0 -4 ~
. ~ ~0 ~ ~1 0 ~ 0 ~ ~ 0 0 ~ o ~ ,~
X '' ~ ~ ~ ~ ' ~--' ~

., ~ 0~
0 q ~
e ;i ~ .co ~ ~ O <~ ~0 O ~ ,~ n ~ O ~ J- O
~ ~ ~ ~ æ ~ e ~
ol ~? ~
g o ~ g e ~:~
E ~ t~ ~ ~ o J~
O O
E~ ~ :~: 3 :~ ~ X

~04~794 ~1~, o, ,, o ~, o o .. . . . .
O O ,~ o o o ~ o o ~1 g ~ '' ~ ~ 2 ~ ~ ~ U, o U~ o o - o o ,i ,. ,. o ~ o ~o ,~

o o o o ,. ' ,. ~ ' ' o o ~ ' o 0 o !3 ,~ o o~o~ O

1 ~ ~ -r~

_ }3 -Example 6 ~040794 A random copolymer containing propyl hydrogen maleate can be produced by substituting an equal molar amount of this monomer for the ethyl hydrogen maleate of any of Examples 1-5, and carrying out the reaction under substantially the same conditions. The product will have similar properties.

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A random copolymer made by continuously feeding monomers and initiator to a stirred reaction zone and continuously withdrawing a reaction mixture containing the copolymer from the reaction zone, which copolymer when it contains 50 parts of fast extruding carbon black per 100 parts of copolymer and is cured with 1.5 parts of hexamethylene diamine carbamate per 100 parts of copolymer for 30 minutes at 180°C and 40,000 lbs. pressure has a brittle point of less than about -40°C, an oil swell of less than about 120%, a Shore A hardness at 25°C of less than 69, an elongation at break of greater than 260%, and a 100% modulus of less than 940 psi, comprising polymerized ethylene, alkyl acrylate selected from methyl and ethyl acrylate, and from about 0.5 to 10 weight percent of a mono alkyl ester of 1,4-butene-dioic acid in which the alkyl group of the ester has 1 to 6 carbon atoms, said copolymer having from about 20 to 35 grams of (-CO2-) units per 100 grams of copolymer, said copolymer having a melt index of about 0.3 to 100 g/10 min.

2. A copolymer of Claim 1 wherein the alkyl acrylate units consist essentially of methyl acrylate.

3. A copolymer of Claim 2 wherein the methyl acrylate units comprise about from 48 to 63% by weight of the copolymer.

4. A copolymer of Claim 1 wherein the ester of 1,4-butene-dioic acid is propyl hydrogen maleate.

5. A copolymer of Claim 1 wherein the ester of 1,4-butene-dioic acid consists essentially of ethyl hydrogen maleate.

6. A copolymer of Claim 1 wherein the ester of 1,4-butene-dioic acid is methyl hydrogen maleate.