WO1986000082A1

WO1986000082A1 - Polyblends of aromatic/isopropenyl aromatic copolymers with grafted rubber concentrates

Info

Publication number: WO1986000082A1
Application number: PCT/US1985/001055
Authority: WO
Inventors: Douglas E. Beyer; Edward T. Carrington
Original assignee: The Dow Chemical Company
Priority date: 1984-06-07
Filing date: 1985-06-04
Publication date: 1986-01-03
Also published as: EP0185734A1; EP0185734A4; CA1231484A; BR8506767A; AU4493385A; AU570332B2; KR860700127A; KR900002532B1

Abstract

Blends of: (A) copolymer(s) of styrene/-alpha-methylstyrene and equivalents thereof with (B) grafted rubber concentrates of an elastomeric substrator backbone having graft-interpolymerized styrene components. The polyblends involved exhibit superior thermal stability, environmental stress crack resistance, hardness and so forth.

Description

POLYBLENDS OF AROMATIC/ ISOPROPENYL AROMATIC COPOLYMERS WITH GRAFTED RUBBER CONCENTRATES

This invention pertains to improved poly- blends which are an admixed product of a copolymer of styrene and a-methylstyrene with a grafted interpoly- merizate of polystyrene on an elastomeric polybutadiene substrate or backbone.

The preparations of various homo- and copoly- mers of α-methylstyrene including styrene/α-methylstyrene copolymers and many sorts of α-methylstyrene-containing graft and block interpolymers on elastomeric or rubber substrates are well known and are exemplified in such references as U.S. Patents Nos. 2,658,058, 3,036,053, 3,069,405, 3,367,995, 3,463,833, 3,825,623, 3,952,512, 3,956,426, 4,075,253, 4,097,557, 4,104,327 and 4,294,.946; and British Patent No. 1,264,741. The theory and practice of polymer com¬ patibility and blending is set forth by D. R. Paul and Seymour Newman in Polymer Blends, Vols. 1 and 2, Academic Press 1978.

A number of rubber-reinforced plastics products, including polyblends, have been provided and are more or less well known, some of these including inter- polymers of α-methylstyrene. Some of these are charac¬ terized in ABS Plastics by Costas H. Baskekis published in 1964 as part of its Plastics Application Series by Rheinhold Publishing Corporation of New York City, Toughened Plastics by C. B. B cknell, Applied Science Publishers Ltd., London (1977); and United States Letters Patent 4,371,663 (Russell).

Many of the of synthetic resinous thermo¬ plastic polymerizates and/or polyblends of the prior art have acceptable tensile strengths, impact resis¬ tances and heat distortion values. However, they are often found to have less than desirable degrees of other significant properties such as and including thermal stability, hardness and environmental stress crack resistance; especially when the plastics are prepared from conventional interpolymerizates of styrene, including the polyblends of various styrene polymers with differing rubber-modifiers.

It would be advantageous if a polyblend of a rubber graft copolymer in intimate admixture with an α-methylstyrene or isopropenyl aromatic copolymer were available which exhibited not only satisfactory pro- perties of tensile strength, impact resistance and high heat distortion values but at the same time also dis¬ played characteristics of superior thermal stability, outstanding hardness and environmental stress crack resistance to a superior degree.

These outstanding benefits and other advan¬ tages in accordance with the present invention can be understood from a consideration of the following speci¬ fication and illustrations.

The present invention is an impact resistant and heat distortion resistant and tough polyblend composition that is comprised of an admixture of:

A. 40 to 95 percent by weight, based on total weight of the polyblend, of a copolymeric product of copolymerization of:

(a' ) at least one isopropenyl aromatic monomer of the Formula:

CH,

. -3

CH₂=C-Ar (I)

wherein Ar is an aromatic radical, and

(a") at least one vinyl aromatic monomer of the Formula:

CH=CH-AR (II)

wherein Ar is an aromatic radical; said copolymer containing 10 to 70 mole percent based on total copolymer weight of at least one copolymerized monomer of said Formula (I); and (B) 5 to 60 percent by weight based on total weight of the polyblend of a graft-copolymer, grafted rubber concentrate material dispersed in Component (A) in the form of particles having a core/shell structure comprised of:

(b') 10 to 75 weight percent based on total weight of Component (B), grafted in an exterior shell portion of its structure, of an interpolymer of at least one monomer of the Formula:

G

CH₂=C-Ar (III)

wherein G is hydrogen or methyl and Ar is an aromatic radical; said interpolymer (b') being formed upon a substrate or backbone core portion of said graft-copolymer of:

(b") 90 to 25 weight percent based on total weight of Component (B) of an elastomeric, graftable rubber which provides the core in said grafted rubber concentrate material of said Component (B).

The polyblends according to the invention contain 40 to 95 percent by weight based on the total weight of the polyblend of Component A. Advantageously, the polyblends in accordance with the present invention contain 60 to 90 percent by weight of Component (A), more preferably 60 weight percent. The isopropenyl aromatic monomers utilizable in the preparation of the copolymer Component (A) in the polyblends of the invention are of the Formula:

CH₃ CH₂=C-Ar (I)

wherein Ar is an aromatic radical (including various alkyl- and halo-ring-substituted aromatic units) of from 6 to 10 carbon atoms. The preferable monomer of the Formula (I) is or-methylstyrene although such specific varieties as isopropenyltoluene and isopropenylnaph- thalene may also be utilized. Formula (I) monomers in mixtures may be employed.

Styrene is generally preferred as the vinyl aromatic Formula II monomer employed for copolymeri- zation with the Formula (I) monomers for preparation of the Component (A) constitutent. The monomeric materials (including styrene) which may be utilized in various mixtures with one another are of the Formula II:

CH₂=CH-Ar (II)

wherein Ar is an aromatic radical of the same defi¬ nition as employed in the description of Formula (I). Species of Formula (II) monomers besides styrene that may, be employed include: vinyltoluene; vinylnaph- thalene, the dimethylstyrenes; t-butylstyrene; the several chlorostyrenes (such as the mono- and dichloro- variants); and the several bromostyrenes (such as the mono-and dibromo-variants) . Generally, the (A) component has compoly- merized therein 10 to 70 mole percent of at least one Formula I monomer(s) and 90 to 30 mole percent Formula II monomer(s). It is often advantageous for the Formula (I)/Formula (II) copolymers employed as the Component

(A) constituents in the polyblends of the present invention to contain 20 to 70 weight percent of copoly¬ merized Formula (I) monomer. It is frequently pre¬ ferred for this proportion of the copolymerized Formula (I) monomer to be 50 to 70 weight percent. The heat distortion characteristics are substantially improved as the proportion of the Formula (I) monomer in the copolymers used as the Component (A) constituents is increased; particularly when α-methylstyrene is the included comonomer and especially so when such copolymer is comprised substantially of copolymerized α-methylstyrene and styrene.

The Formula (I)/Formula (II) copolymers perform well when their weight average molecular weight (M W) is in the range of from 50,000 to 500,000, with associated molecular weight distribution values of 1 to 3. There is usually achieved a most beneficial effect when the Component (A) copolymers have M W values in the range between 100,000 and 200,000 with M distribution values of 1 to 2.5.

The "shell/core" type graft-interpolymerized grafted rubber concentrates employed as the Component

(B) constituents of the polyblended compositions of the invention preferably have a core portion of normally- solid, elastomer. Any elastomeric material that can be obtained in emulsion or latex form is suitable for use in the present invention. Such elastomeric material may be prepared by free radical polymerization in an emulsion or alternatively an elastomer is dissolved in a solvent, the solution mechanically emulsified, agglomer¬ ated and grafted as described by component (B). Some such elastomers include butadiene polymers, isoprene polymers, acrylate polymers, ethylene propylene copoly¬ mers with a diene. Such elastomers include copolymers and terpolymers employing materials such as styrene, acrylonitrile and the like. Other of the rubbers and elastomers are disclosed in U.S. Patent 4,371,663.

This is especially the case when the synthetic rubber involved is a polymer or copolymer (besides polybutadiene) of butadiene-1,3 and/or isoprene and/or 2,3-dimethyl- butadiene-1,3.

The polyblends according to the invention generally contain 5 to 60 percent by weight based on the total weight.of the polyblend of Component (B), more preferably 40 percent by weight. The shell portion of the grafted rubber concentrates included in the Component (B) is preferably interpolymerized poly¬ styrene grafted upon the substrate backbone elastomeric core. The shell portion of the grafted rubber concen¬ trate (b' ) is generally from 10 to 75 weight percent of the grafted rubber concentrate. It is often times of greater advantage for the shell portion of the grafted rubber concentrate to be between 20 and 30 weight percent of the graft-interpolymerized component; with optimum benefit often being when the shell portion is 25 weight percent of the grafted rubber concentrate material (within ±3 weight percent) .

In the preparation of the grafted rubber concentrate about half the Formula III polymerized monomer forms graft and about an equal amount of homo- polymer is formed.

Equivalents of styrene interpolymers for the shell portion of the grafted rubber concentrate include polymers which may include styrene, or any combination of monomers of the Formula:

CH₂=C-Ar, (HI)

wherein G is hydrogen or methyl and Ar has the same description as in the Formulae (I) and (II). Other than styrene, monomers of the Formula (III), which may be employed include those specifically identified in connection with said Formulae (I) and (II). Unless specilized graft-interpolymerization techniques are utilized, it is ordinarily prudent to employ none or only minor proportions of isopropenyl aromatic monomers for the Formula (III) monomer to be grafted as a shell portion onto the substrate elastomeric core.

In considering suitable particle sizes of the grafted rubber concentrate materials used for the Component (B) in polyblends of the present invention, it is usually desirable for the individual particles (whether monodisperse or polydisperse to be relatively large such as in the range of from 0.05 to 3 microns (μ); more frequently to be 0.3μ to 2μ .

When a latex of a polymer of 10 weight per¬ cent acrylic acid and 90 weight percent ethyl acrylate is utilized as an agglomerating agent, generally not more than 0.4 parts by weight based on solids of material is utilized per 100 parts of the elastomer to be agglom¬ erated. A shell/core agglomerating agent has been found to be of better properties than the acrylic acid acrylate combination. The shell/core agglomerating agent contains a shell of about 8 weight percent methacrylic acid and 92 percent ethyl acrylate and about 2 parts of the agent are used for 100 parts of the elastomer to be agglomerated. In both cases, 30 to 50 weight percent of the original elastomer having a particle diameter of 0.1 micron is agglomerated to a size of 0.3 to 2.5 microns.

Isopropenyl aromatic monomers of the Formula (I), particularly α-methylstyrene, are difficult and sometimes impossible to polymerize by thermal or free- radical-catalyst-initiated polymerization whether done in mass or by solution or suspension polymerization. Such difficulty is also experienced when conventional polymerizing techniques are used to make random copoly¬ mers and/or graft copolymers of isopropenyl aromatic monomers with other mono- or ethylenicallyunsaturated monomers and polymers which normally are readily polymer- izable by thermal or free-radical mechanisms.

The indicated copolymers and graft copolymers of component A, utilizing α-methylstyrene and/or other Formula (I) monomers, are readily made by anionic, solution polymerization using an organometallic initiator, such as sec-butyl-lithium, n-butyl-lithium as in U.S. Patents Nos. 3,322,734 and 3,404,134. A good procedure for co- and interpolymerization of isopropenyl aromatic monomers is as disclosed in EPO Publication 135,168. To make the polyblends of the present inven¬ tion, the desired proportions or Components (A) and (B) are physically admixed to provide a mixture which appears homogeneous to the unaided eye. Any suitable plastics compounding apparatus may be employed. Batch- wise blendings may be done using such equipment as a Brabender "PLAS ICORDER" (Reg. TM); while continuous blending may be made with ordinary extruders, including twin-screw extruders. In many instances, the poly- blends are prepared by melt blending of the Components (A) and (B) by mechanical admixture thereof on or in intensive compounding equipment (such as, extruders; compounding rolls, and Banbury mixers) at a temperature adequate to heat plastify the components being mixed but lower than that which might cause significant polymer decomposition thereof. If the polymers are in latex form, the latexes can be blended, the blend coagulated and dried to recover the polymer.

The polyblended products of the present invention can contain other additives that are often¬ times utilized in plastics compositions, such as anti- oxidants; pigments; dyes; fillers; stabilizers; mineral oil and other plasticizers and lubricants; and blowing agents.

The polyblends of the present invention have a combination of very good toughness with high heat distortion values. As shown in Table I, a typical polyblend pursuant to the present invention surpri¬ singly exhibits good heat distortion while still main- taining high tensile strength and acceptable impact resistance. The tensile strengths are given in mega pascals (MPa) and in pounds per square inch (psi). The Izod impact strengths are given in Joules per meter of notch (J/m) and foot pounds per inch of notch (ft-lb/in.) The heat distortion values are given in degrees Celsius (°C) and farenheit (°F). The gloss is given in percent

Table I - Physical Property Comparisons of Some Styrenic Plastics

Izod Vicat

.Tensile Impact Heat Yield Strength Dis¬ Strength in J/m tortion

Product (T ), in (ft-lb/in.) Value in Tested MPa (psi) of Notch °C (°F) Gloss

(a) HIPS¹* 21 (3,000) 117 (2.2) 94 (202) 20

(b) ABS² 41 (5,900) 320 (6.0) 106 (222) 38

(c) GRC/PS³ * 31 (4,500) 278 (5.2) 100 (212) 90

(d) GRC/SAN⁴* 40 (5,800) 267 (5.0) 104 (219) 92

(e) GRC/S-αMS⁵ 31 (4,500) 203 (3.8) 126 (259) 90

Comparative experiments, not examples of the present invention.

A typical rubber-modified high-impact polystyrene plastic composition made with about 5 weight percent of polybutadiene.

A typical ABS product of polymerized acrylo- nitrile/butadiene/styrene having a rubber content of about 13.5 weight percent with a soluble fraction containing about 23.5 weight percent acrylo- nitrile, the product having properties about equivalent to such commercially available ABS resins.

A polyblend of about 50 percent by weight of general purpose polystyrene with a grafted rubber concentrate of the "shell/core" type having about 49 weight percent of polymerized styrene shell upon its polybutadiene core this being the same grafted rubber concentrate as prepared in the third experiment below. ⁴ A polyblend of about 50 percent by weight of a styrene/acrylonitrile copolymer containing about 29.7 weight percent of acrylonitrile copolymerized therein admixed with a grafted rubber concentrate which contains about 50 weight percent polybuta¬ diene and having styrene-acrylonitrile copolymer grafted thereon and a particle size range of about 0.1 to 1 micron.

⁵ A polyblend of about 50 percent by weight of an α-methylstyrene/styrene copolymer containing about

50 weight percent of each of the comonomers copolymer¬ ized therein admixed with the same grafted rubber concentrate material employed for Product (c).

The polyblends of the present invention are useful for heat fabrication (by injection and com¬ pression molding, extrusion, thermoforming and the like) into articles that are both tough and withstand higher service temperatures. Such applications, include hot-fill containers, dishes, cups, reusable containers for microwave heating and/or cooking; electronic com¬ ponent parts; television cabinets; automotive parts and like uses where high temperature performance is desir¬ able. Shaped articles produced from polyblends in accordance with the present invention can be made to have an attractive attractive smooth and glossy surface which cleans readily when subjected to ordinary washing procedures. They are also readily paintable and weldable.

The following examples show the benefits of reduction to practice of the present invention. All parts and percentages are given on a weight basis and all temperature readings (unless otherwise specified) are in degrees Centigrade, °C. Experiment 1 - Preparation of a Grafted Rubber Concentrate

The general teaching of U.S. Patent 4,419,496 (Henton and O'Brien) was employed.

A grafted rubber concentrate of the "shell/core" type of graft copolymer of a polystyrene shell portion on a polybutadiene core was prepared in the following manner. Minor proportions of monomeric materials other than styrene and butadiene were employed. These materials were used for the preparation of an agglom¬ erating agent used to produce relatively large-sized and largely monodispersed particles of the poly¬ butadiene core backbone. In adaptation of the Henton and O'Brien technique for preparation of grafted rubber concentrate materials, the steps involved include:

(i) preparation of a polybutadiene latex rubber; (ii) partial rubber agglomeration; and (iii) grafting of the rubber. The agglomerating agent is separately prepared for use in Step (ii).

The preparation of the agglomerating agent was done in a 0.76 cubic meter (200 U.S. gallon) glass-lined jacketed Pfaudler kettle equipped with an agitator. The following mixtures were prepared. All numerical weight quantities are indicated kilograms (kg) and the quantity in pounds is given in parenthesis:

1. Reactor Charge:

366 (807) - deionized water 0.82 (1.8) - sodium bicarbonate 0.49 (1.08) - sodium persulfate 1.02 (2.25) - "CALSOFT L-40" (Reg. TM) of 40% activity grade 0.60 (1.32) - acrylic acid

2. Monomer Mix:

245 (540) - ethyl acrylate 27.2 (60) - acrylic acid

3. Aqueous Mix:

122 (270) - deionized water 12.9 (28.4) - "CALSOFT L-40", a dispersing detergent ingredient

The reactor charge (1) was added to the

Pfaudler reactor at 30°C. The reactor contents were deoxygenated using nitrogen and vacuum. After oxygen was removed, 6.12 kilograms (13.5 pounds) of Mixture (2) was added to the reactor and the contents were heated to 65°C. Fifteen (15) minutes after the reactor contents had reached 65°C, a concurrent-addition or "con-add" of Monomer Mix (2) was begun and continued for five hours at a rate of 53.21 kilograms (117.3 pounds) per hour. Ten (10) minutes after commencement of the Monomer Mix (2) addition, the Aqueous Mix (3) was fed to the reactor for 5 hours at a rate of 27.1 kilograms (59.7 pounds) per hour. When all the addi¬ tions were completed, the reaction mixture was main¬ tained for an additional 3 hours at 65°C. After cool- ing, the resulting agglomerating agent mixture was filtered for subsequent use. In order to prepare the grafted rubber con¬ centrate material for preparation of polyblends in accordance with the present invention, a second set of preformulated mixtures was prepared most being in the form of aqueous solutions or dispersions where the below-indicated percent activity or percent solids concentrations were used. Manufacture of the grafted rubber concentrate material was done in a 13.25 cubic meters (3,500 U.S. gallon) glass lined jacketed reactor. The mixtures used were as follows where quantities are in kilograms and (pounds):

4. Reactor Charge for Graft Copolymer Formation: 2486 (5,480) - deionized water

69.0 (152) - 34.5 percent active polybutadiene seed latex

754 (1,663) - 0.467 percent active sodium bicarbonate 59.0 (130) - 1.13 percent solids "VERSENE"

(Reg. TM) chelating agent (tetrasodium ethylenedinitriol tetr acetate)

5. Rubber Reaction Aqueous Mix:

433 (954) - deionized water

142 (314) - 43.9 percent solids "CALSOFT L-40" (a sodium alk larylsulphonate)

6. Agglomerating Agent Mix:

1690 (3,720) - deionized water

22.7 (50) - 42.9 percent solids "CALSOFT L-40"

94.4 (208) - agglomerating agent from the above-described pre-preparation

7. Aqueous Mix for Graft Reaction Accomplishment: 1480 (3,260) - deionized water

22.7 (50) - 42.9 percent solids "CALSOFT L-40" 376 (829) - 2.46 percent active sodium persulfa catalyst

Reactor Charge (4) was added to the reactor and deoxygenated by vacuum after which the reactor was heated to 65°C. During the heat-up period, 33 kg (73 pounds) of acrylonitrile was added to the reaction mass in the reactor. After the reactor contents had reached 65°C there were then charged: 1.8 kg (4 pounds) acrylo¬ nitrile; 4.1 kg (9 pounds styrene); 78.9 kg (174 pounds) butadiene-1,3; .32 kg (0.7 pounds) n-dodecylmercaptan; and 138 kg (304.3 pounds) of an aqueous solution of 2.46 percent active sodium persulfate. After that charging, the following additives were then begun:

Addition Addition Total Rate in Duration Additions kg/hr in in kg

Material (lbs/hr) hrs (lbs)

Styrene 11.3 (24.9) 8 107 (235)

Acrylonitrile 5.72 (12.6) 8 45.8 (101)

Butadiene 253 (557.5) 8 2020 (4,460) n-Dodecylmercaptan 105 (2.32) 7.75 8.2 (18) Aqueous Mix (5) 0.93 (2.06) 6 562 (1,238)

Upon completion of all of the above-indicated additions, temperature of the reaction mass was held at

5 65°C until a 1.4 x 10 pascal (20 psig) pressure was reached in the reactor. The reactor was then vented and purged with about 101 m³ (3,600 ft³) of nitrogen.

After purging, 1950 grams of this latex was placed in a 4-liter cylindrical reactor. The reactor and contents were heated to 80°C. The contents were agitated with a paddle agitator on a shaft rotating at about 300 revolutions per minute. 130 Grams of agglom¬ erating mix (6) were added to the reactor at a rate of 4.83 grams per minute. The latex particles, initially having an average particle size of about O.lμ, were 41.6 weight percent agglomerated to form a group of larger particles having an average particle size of about 0.83μ On completion of the addition of the agglomerating mix, the reactor temperature was reduced to 70°C and the following graft copolymerization reaction additions were added to the reactor.

Addition Addition Total

Rate Duration Additions

Material gm hr) (hrs) (qm)

Aqueous Mix (7) 85.1 7 595.8

Styrene Monomer 100.3 7 702 n-Dodecylmercaptan 0.155 6.75 10

The graft copolymerization reaction was allowed to proceed for an hour after completion of all above-indicated additions. The reactor contents were then cooled.

The resulting grafted rubber concentrate converted from latex to a dry powder. A plurality of dried samples were prepared by a charging of 3.8 liters (1 U.S. gallon) of the grafted rubber concentrate latex into a steam-stripping unit, adding to the latex prior to the stripping about 3-5 grams of a commercial silicone antifoam agent obtained from Dow Corning Corporation of Midland, Michigan 48640, under the trade-designation "DOW CORNING FG-10". For each 3.8 liter portion converted, the steam stripping was continued until 350 ml of condensate had been collected. After that, 0.6 percent (based on the rubber content) of "TOPANOL CA" (Reg. TM; TOPANOL CA is 1,l,3-tris(2' methyl 4' hydroxy-5' tertiary-butyl phenyl) butane), and 0.2 percent (also based on the involved rubber content) of dilaurylthiodipropanoate were added to each steam- stripped sample. The product was then freeze-coagulated, centrifuged and dried overnight at 50°.

The resultant pulverulant grafted rubber concentrate material was used below in the preparation of polyblends according to the present invention.

Experiment 2 - Preparation of a Grafted Rubber Concentrate The general procedure of Experiment 1 was used to prepare a second grafted rubber concentrate.

The following mixes were employed:

Mix 1. 35 parts of polybutadiene latex rubber com¬ bined with 65 parts of deionized water;

Mix 2. An agglomerating agent mix of 1.8 parts of Mix 6 of Experiment 1 plus 0.6 parts of

"CALSOFT L-40" and 97.6 parts of deionized water;

Mix 3. An aqueous mix of 0.4 parts sodium persulfate with 2.2 parts of "CALSOFT L-40" and 97.4 parts of deionized water; and

Mix 4. A monomer mix of 0.15 parts of n-octyl mer- captan and 99.85 parts of monomeric styrene. A 38 liter (10 U.S. gallon) stirred jacketed reactor was employed. The reactor was charged with 16,150 grams of Mix 1 which was first deoxygenated and then heated to 70°C. Following that, 1,100 grams of Mix 2 was added into the reactor at a uniform rate over a 28 minute period. The latex particles which initially had an average particle size of about O.lμ were partially agglomerated to form a group of particles having a larger average particle size. Then, 5,040 grams of Mix 3 and 5,880 grams of Mix 4 were charged, to the reactor over a 7 hour period at a temperature of 70°C; the reaction mixture was maintained at 70°C for one hour after addition was complete. Prior to steam-stripping of the completed product, 21 grams of "TOPANOL CA" and 7 grams of dilaurylthiodipropanoate were added to the resultant latex. The grafted rubber concentrate was then, as in Experiment 1, freeze-coagulated, centrifuged and dried.

The grafted rubber concentrate material was employed in the manufacture of polyblend products pursuant to the invention.

Experiment 3 - Preparation of an Example Composition

A 50:50 weight ratio copolymer of α-methyl- styrene and styrene was made by means of continuous anionic polymerization so as to have a 170,000 M W.

The procedure of Experiment 2 was used to prepare a grafted rubber concentrate material which had a 51 percent butadiene content with the group of large particles having an average particle size of 0.6μ. Blending of 608 grams of the described copolymer and 329 grams of the described grafted rubber concentrate was then accomplished by passing a mixture thereof through a 2 cm (0.8 inch) Welding Engineer Twin Screw Extruder. The polyblended product was then injection molded into test bars with which the physical pro¬ perties were then determined.

The results obtained, are set forth in the following Table II.

Table II - Physical Properties of Typical Polyblend

Made According to the Invention

Property Tested Result

Tensile Yield (T ) in

MPi (in psi) 31 (4,500) Tensile Rupture (T ) in MPa ^r (in psi) 26 (3,800)

% Elongation (at break) 27

Tensile Modulus in MP§

(in psi x 10^" ) 2200 (3.2) Izod Impact Value in J/m

(ft-lb/in) of notch . . .203 (3.8)

Vicat Heat Distortion Temperature in °C (in °F) . . .126 (258)

Melt Flow Rate at Condition "I" in gms/10 minutes 1.5

Experiment 4

Repeating the general procedure as set forth in Experiment 3, two (2) additional α-methylstyrene/styrene copolymers were prepared; one of which had a M W of

110,000 with a 1.5 value distribution thereof and the other of which had a Mw of 170,00 with 2.2 distribution. Both copolymers showed excellent results, commensurate with those in Table II, when blended with various grafted rubber concentrate materials containing about 50 percent polymerized polystyrene in the shell portions thereof (being similar to the grafted rubber concentrate of Experiment 3), so that equal weight proportions of the copolymers and the grafted rubber concentrates were present in the several samples which were tested, each of which was made into polyblends with the twin extruder of Experiment 3.

It is generally desirable to maximize the styrene polymer content of the shell of the to grafted rubber concentrate to maximize the percent Elongation at Break values in the polyblend products of the inven- tion.

Experiment 5

To demonstrate the effect of particle size control in the grafted rubber concentrates employed in the practice of the present invention, the procedure of the Experiment 3 was repeated excepting to utilize grafted rubber concentrate whose particle size did not exceed 1.8μ (GRC 2). This GRC is in contrast with the grafted rubber concentrate of the Experiment 3 (GRC 1) which contained some particles varying in size larger than 1.8μ.

Samples of polyblends with only the smaller particle size grafted rubber concentrates were then prepared in about the same homopolymer or copolymer (Component A) to grafted rubber concentrate (Component B) weight ratios as made in the Experiment 3 using in some, for comparative purposes, general purpose polystyrene in the mixtures and in the others α-methylstyrene/styrene copolymers. The test specimens of second grafted rubber concentrate materials with no particle size inclusions greater than 1.8μ were compared with samples of analogous homopolystyrene and α-methylstyrene/styrene copolymer polyblends containing the first grafted rubber concentrate material as used in the Experiment 3 which had some of the 1.8μ and larger particles.

The results are as set forth in Table III. The polyblends were formulated to contain 20 weight percent elastomer.

TABLE III

% Change in Properties Due to the Effect of the

GRC 1 GRC 2 Rubber Particle Size

Agglomerating Agent A shell/core

Agglomerated Rubber Particle 0.83 0.6 Average Size in Microns

Range of Particle Sizes 0.3-2.2 0.3-1.12

Unagglomerated Rubber 0.1 0.1

Particle Size in Microns

Weight Percent Agglomeration 41.6 39.5

Graft Weight/Rubber Weight 0.5 0.46

General Purpose Polystyrene (285,000M ) Tensile Yield in MPa Ypsi) 29.8 (4,320) 32.1 (4,660) +8

Izod Impact Value in Joules per meter 214 (4.0) 80 (1.5) -63 (ft-lb/in) of notch

Gardner Dart in 36 (320) 2.8 (25) •92 Joules (in-lb)

Vicat Softening Point in °C (°F) 104 (220) 106 (222) +1

TABLE III continued

% Change in Properties Due to the Effect of the

GRC 1 GRC 2 Rubber Particle Size

50/50 Copolymer

Tensile Yield in MPa (psi) 31.9 (4,620) 34.1 (4,940) +7

Izod notch) Impact Value in 150 (2.8) 192 (3.6) +29 Joules per Meter (ft-lb per inch) of notch

Gardner Dart in 10.2 (90) 17 (150) +67 Joules (in-lb)

Viscat in Softening Point 127 (260) 127 (260) 0 °C (°F)

The use of the graft rubber concentrate 2 in place of graft rubber concentrate 1, (substituting the smaller rubber particles) causes a loss of impact resistance in blends with general purpose polystyrene while similar substitutions in styrene alpha-methylstyrene blends result in substantial gain in impact resistance.

The polyblends made from the controlled particle size grafted rubber concentrates having only the smaller particles that were prepared with homopoly- styrene base resin in the admixture had poor toughness as shown by Izod and Gardener Dart tests as compared to those made in accordance with practice of the present invention utilizing the α-methylstyrene/styrene copolymer.

Experiment 6 Identical cups were fabricated from a conven¬ tional polybutadiene-rubber-modified high-impact poly¬ styrene (equivalent to that described as Test Product (a) in the foregoing Table I) and from a polyblend in accordance with the present invention analogous to that described in the Experiment 3 above. Both were subjected to immersion in boiling water for fifteen (15) minutes. The high-impact polystyrene cup failed the heat treat¬ ment test completely, becoming badly distorted. The polyblend cup was completely unaffected and retained its original shape despite the same boiling water test treatment.

Also of great practical importance for syn¬ thetic resinous materials is their resistance to food oils. In a test of resins resistant to food oils, samples of the polymers in accordance with the present invention, were placed under a tensile load of about 5.5 MPa (800 pounds per square inch), while subjected to an environment of simulated food oil using a one-to-one mixture of lactic acid and cottonseed oil. Samples of resins in accordance with the present invention were exposed for a period of 100,000 minutes or more, and did not show signs of failure. When similar samples were prepared utilizing polystyrene rather than α-methylstyrene copolymers, the samples prepared with the general purpose polystyrene failed between about 2,000 and 4,000 minutes.

While it is known that copolymers of α- methylstyrene and styrene typically have good heat distortion resistance, the polyblends of the present invention have heat distortion characteristics that are higher than predictable. The grafted rubber con¬ centrate materials would tend to reduce heat distortion resistance upon polyblending thereof with even an α-methylstyrene/styrene copolymer component.

The heat distortion values of polyblends prepared in accordance with the present invention are at least equal to and often greater than those pre¬ dictable from the components of homopolystyrene and/or α-methylstyrene/styrene copolymers when the latter are individually subjected to the same heat distortion testing.

Claims

WHAT IS CLAIMED IS:

1. An impact resistant and heat distortion resistant and tough polyblend composition that is comprised of an admixture of:

(a' ) at least one isopropenyl aromatic monomer of the Formula:

CH-

CH₂=C-Ar (I)

wherein Ar is an aromatic radical, and

(a") at least one vinyl aromatic monomer of the Formula:

CH-CH-AR ( I I )

wherein Ar is an aromatic radical said copolymer containing 10 to 70 mole percent based on total copolymer weight of at least one copolymerized monomer of said Formula (I); and

(B) 5 to 60 percent by weight based on total weight of the polyblend of a graft-copolymer, grafted rubber concentrate material dispersed in Component (A) in the form of particles having a core/shell structure comprised of:

(b¹) 10 to 75 weight percent based on total weight of Component (B), grafted in an exterior shell portion of its structure, of an interpolymer of at least one monomer of the Formula:

G CH₂=C-Ar (III)

wherein G is hydrogen or methyl and Ar is an aromatic radical; said interpolymer (b' ) being formed upon a substrate or backbone core portion of said graft-copolymer of:

(b") 90 to 25 weight percent based on total weight of Component (B) of an elastomeric, graft- able rubber which provides the core in said grafted rubber concentrate material of said Component (B).

2. A polyblend composition according to Claim 1, wherein the content of said Component (A) therein is from 60 to 90 percent by weight.

3. A polyblend composition according to Claim 1 wherein said copolymer (A) contains between 20 and 70 weight percent of monomer (a').

4. A polyblend composition according to Claim 1, wherein (B) contains 20 to 30 weight percent (b').

5. A polyblend composition according to Claims 1-4 wherein the Formula (I) monomer is α-methyl- sytrene; both said Formulae (II) and (III) monomers are styrene; and said core (b") graftable rubber is polybuta¬ diene.

6. A polyblend composition according to Claim 1 wherein the copolymer of which (A) is comprised has a weight average molecular weight (M W) of 50,000 to

500,000 and a molecular weight distribution value between 1 and 3.

7. A polyblend composition according to Claim 1 wherein the copolymer of which (A) is com¬ prised has a M W of from 100,000 to 200,000 and a molecular weight distribution value between 1 and 2.5.

8. The use of a polyblend composition accor¬ ding to Claim 1 in a fabricated article.