CA1039439A - Polyblend comprising a styrene/acrylonitrile copolymer, and a mixture of two graft copolymers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A polyblend of the ABS-type having a matrix phase of a styrene/acrylonitrile type resin and two dispersed phases therein. One dispersed phase is a highly grafted alkadiene rubber, the other dispersed phase is a lowly grafted homo-polybutadiene rubber which is agglomerated to particle sizes in the range from about 0.6 to 3.0 micron. The graft super-strate on both dispersed phases is formed by styrene and acrylonitrile type monomers. These polyblends display a combination of low temperature impact strength and room tem-perature tensile strength suitable for the manufacture of DWV
pipe.

Description

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The present invention relates to a polyblend of ABS-type resins which may be made by the emul~ion route and which 5 demonstrates good low-temperature tensile strength properties toget}ler with a good balance of other properties. In a heat-fused form, this polyblend compri es a matrix phase of a styrene~acr~lonitrile type copolymer in which are distributed particles of t~o different types of grafted alkadiene rubber.
One such type o~ graft rubber particle comprises relatively medium si2ed diene rubber particles rather highly grafted with styrene and acrvlonitrile type monomers; the other such type comprises relatively large sîzçd diene rubber type particles ~rafted rather lowly with styrene and acrylonitrile type mono-mers. The rubher particles in this :Last type are in fact com-posed of stable agglomerates cf relatively small rubber particles. Both such types of grafted diene rubber particles are readily produced by emulsion polymerization technology.
'rhe matrix phase can be produced by emulsion, suspension or mass route~, or combinations therao~.
~ he polyblends of the present invention di~play a combination of low temperature impact strength and room tempera-ture tensile strength which i~ far better than the corrésponding combination of strength displayed by a styrene/acrylonitrile matrix containing only one of the two ~uch grafted rubber components individually and in equivalent amounts. Furthermore, the polyblends of the present invention display such a combina-tion of strength propertie~ and are considered to be a synergi~tically effective combination of a particular lowly and a particular highly grafted ABS-type rubber component in a ~tyrene/acr~lonitrlle type matrix. Nothing in the prior art teaches or ~ugge~ts such a synergi~tic combination. ~ ' ~L~39~;~9 SUMMARY

rrhe present invention relates to polyblends adapted to display a combination of low temperature impact strength and room temperature tensi}e strengthO The polyblends also display, when heat-fused, relatively high surface gloss. These polyblends comprise from about 70 to 89 weight per cent styrene/acrylonitrile with the balance up to 100 weight per cent thereof being a mix-ture of two clas~es of graft copolymer particles, each class being dispersed throughout the styrene/acrylonitrile which, when the polyblends are in a heat-fused form serves as the matrix phase. The styrene/acrylonitrile has a weight average molecular weight of from about 75,000 to 300,000, and the weight ratio of styrene to acrylonitrile in such copolymer ranges from about 95:5 to 30:70, The weight ratio of the first graft copolymer to th~ second graft copolymer in a polyblend ranges from a~out 85:15 to 5:95.
'~he first class of graft copolymer particles is cha-racterized by having:

(1~ a number average particle size of frnm about 0~03 to 0.6 micron, ~ 2) a substrate elastomer comprising a copolymer of fro~ about 70 to 98 weight per cent of a conjugatèd alkadiene with correspondingly ~rom about 30 to ~ weight per cent based on total substrate elastomer weight of at least one compound selected from the group consisting of styrene and acrylonitrile, preferably acrylonitrile.
(3) a superstrate grafted to said substrate elastomer and comprising polymerized styrene and acrylonitrile in the weight ratio of from about 95:5 to 30:70, and C-08-12-0242 ~ 3~

(4) there being from about 30 to 100 partq by weight of grafted superstrate for each 100 parts by weight of said substrate elastomer.
The second class of graft copolymer particles is cha-racterized by having:
~1) a number average particle size of from about 0.6 to 3.0 micron, and at least half of such particles have a parti-cle size a~ove about 0.8 micron,

(2) a substrate elastomer comprising homopolyalkadiene, pre~erably homopolybutadiene, (3~ a superstrate grafted to said sub~trate elastomer and comprising polymerized styrene and acrylonitrile in the weight ratio of from about 95:5 to 30:70, (4) there being from about 3 to 30 parts by weight of grafted superstrate for each 100 parts by weight of said substrate elastomer, and, (5) said second grat copolym~r particles heing com-prised of agglomerated grafted subparticles at least 90 weight per cent of which have particle sizes in the range of from about 0.05 to 0.15 micron, This pol~blend has a total elastomer content (ungrafted basis) ranging from about 10 to 30 weight per cent (based on total polyblend).
FIGURE DESCRIPTION
. .-- . . .
The invention is better illustrated by reference to the appended drawings wherein:
Figure 1 is a simplified flow sheet illustrating preparation of the polyblends of this invention.
Figure 2 is a flow sheet i~lustrating in greater detail one preferred procedure for preparing the polyblends of the pres~nt invention.

C-08-12-0242 ~39~9 Figure 3 is an artist's drawing of amicrograph of a heat-fused polyblend of the present invention.
~ igure 1 is believed to be self-explanatory. In general~ one prepares the fir~t and the second graft copolymers separately and then blends same with added styrene/acrylonitrile copolymer as necessary or desirable to make a polyblend of this invention. Conventional procedures are used.
Methods for the preparation of first and second graft copolvmer are well known to the art generally; see, for example, U.S.P. 3,509,238.
In figure 2 is present a flow sheet illustrating one procedure suitable for the preparation on a commercial scale of polyblends of the pre~ent invention. Micron size ranges shown are weight averages. The designation "A.O." indicates antioxi-lS dant. The dotted line arrows indicate an optional procedure.Briefly, butadiene (Bd.) is first homopol~merized in emulsion and then graft polymerized in emulsion with styrene and acrylonitrile monomexs. Independently, styrene and acrylonitrile are emulsion copolymerized. This copolymer emulsion and the graft copolymer emulsion are then blended with an antioxidant and the solids of the resulting mixed latex recovered by spray drying or coagulation ~ollowed by a drying operation.
Independently, a butadiene copolymer elastomer with s~-yrene or acrylonitrile is emulsion polymerized and then grafted in emulsion with styrene and acrylonitrile monomers. Recovery with antioxidant by spray drying, or by coagulation followed by a drying operation, then occurs. A product polyblend is finally made by blending this last grafted product with the blend earlier prepared. Added styrene/acrylonitrile copolymer in bead or pellet form may be added in the product blend, ~o~

InFigure3is illustrated the usual appearance of a heat-fused section of a polyblend of this invention. The smaller particles are those of the highly grafted diene copolymer;
the larger particles develop when an emulsion of the graf~ed homopolybutadiene particles is coagulated and dried, or simply spray dried directly.
Other conjugated alkadiene besides butadiene may be employed, such as isoprene, and the like.
~ composition of a matrix phase preferably approxi-mates the chemical composition of the superstrate of the graftcopolymers so as to obtain matching oE chemical properties.
THE ~TRIX PHASE
Those skilled in the art will appreciate that a matrix composition may be prepared by any conventional means known to those skilled in the art, including, for example, emulsion, sus-pension, and/or mass polymerization. Those skilled in the art will appreciate that in a polyblend product of this invention, the matrix phase tyoically may comprise a mixture of different S/AN type copolymers derived from several source~, including ungrafted superstrate material from each of the graft components as well as added matrix copolymer.
THE DI5PERSED P~SE
The dispersed phase graft copolymers may be prepared by any conventional means known to those skilled in the art.
However, for purposes of the practi~e of the present invention, it is greatly preferred to produce a dispersed phase by polymer-izing the superstrate monomers in the presence of a preformed rubber substrate. In such a prepared graft polymer system, it is genexally not possible to extract the rubber from the poly-merized mass with the usual rubber solvents, but some of the ~ 3~3~

starting rubber polymer may not be in actual chemical comhination with ~he superstrate. Also, since 100 per cent grafting effi-ciency of superstrate monomers to such rubber substrate normally is approached on1y at weight ratios of monomers to substrate of below about 0.3sl, at least a portion of the monomers poly-merized in the presence of the preformed rubber will not chemic-ally combine therewith so as to provide the graPt copolymer product. This portion may be increa~ed or decreased depending upon the ratio of monomers to rubber, the particular monomer starting formulation, the nature of the rubber, and the conditions of pol~merization. ~ience, a dispersed phase typically contains some amount of (relative to the amount of the first composition described above) a second copolymer of monovinylidene aromatic ; monomer and alkene nitrile monomer~ ~ny of the usual graft lS polymerization processes may be used to accomplish polymerization of the ungrafted ~u~erstrate monomers to the substrate, including ma~s, suspension, and emul~ion, or combination thereof, Such techniques are ~enerally well known to those skilled in the art.
Although the rubber may contain up to about 2 per cent of a cross-linking agent, based on the weight of the rubber--forming monomer or monomers, cross-linking may present problems in dissolving the rubber in the monomers for the subsequen~
graft polymerization reaction. In addition, excessive cros~-linking can result in loss of the rubbery characteristics. The cross-linking agent can be any of the agents con~entionally amployed for cross-linking diene rubbers, e.g., divinyl benzene, diallyl maleate, diallyl fumarate, diallyl adipate, allyl acrylate, allyl methacrylate, dlacrylates, and dimethacrylates oP polyhydric alcohols, e.g., ethylene glycol dimethacrylate, etc.

C-08-12-0242 ~3~39 Of the various techniques customarily employed for the pol~Imerizing of rubber monomers; including mass/ suspension, and emulsion polymerization, emuision polymerization is preferred since such will provide the particle size distxibution most preferred for use in the present invention. Furthermore, emul-sion polymerization of rubber monomers produces a latex which is useful as a base for subsequent emulsion polymerization of the graft copolymer in the preparation of a dispersed phaseO

The graft copol~mers of a dispersed phase may be pre-pared by polymerizing superstrate monomers in the presence of the preformed rubber substrate, generally in accordance with conventional graft polymerization techniques. Although suspen-sion and mass polymerization techniques may be employed, the preferred processes use an emulsion technique to obtain the particle size of not more than about 0.6 microns for the graft copolymer which is preferred for use in the practice of the present invention. In such graft polymerization a preformed rubber substrate generally is dissolved or dispersed in the monomers and this admixture is polymerized to combine chemically or graft a portion of the uperstrate monomers upon the rubber substrate. Depending upon the ratio of monomers to rubber sub-strate and polymerization conditions, it is possible to produce both the desired degree of grafting of the superstrate monomers onto the rubber substrate and the polymerization of ungrafted matrix copolymer to provide a portion of the matrix at the same time. The ratio of monomers to rubber charged to the graft polymerization reaction zone is the primary determinant of the superstrate: substrate ratio of the resultant graft copolymer, although conditions of polymerization, rubber chemistry and particle size, rates of monomer addition, chai~ transfer agents, etc,, may also exert an effect.

3~

The catalyst is generally included within the range of from about 0.001 to 2 0 weight per cent, and preferably from about 0.005 to 1 D 0 weight per cent of the polymerizable material, the exact amount depending upon the monomers and the desired polvmerization cycle.
~ s is well known, it is often desirable to incorporate molecular weight regulators such as mercaptans, halides and terpenes in relatively small percentages by weight,on the order of from about 0.001 to 2.5 per cent by weight of the polymeriza-ble material. In addition, it may be desirable to includerelatively small amounts of antioxidants or stabilizers, such as the conventional alkylated phenols, although these may be added during or after polymerization.
In the emulsion polymerization grafting process, the monomers and the rubber substrate are emulsified in water by ; use of suitabla emulsifying agents, such as fatty acid soaps, alkali metal or ammonium soaps of high molecular weight, alkyl or alkaryl sulfates and sulfonates, mineral acid salts of long chain aliphatic amines, etcO Emulsifying agents which have proven particularly advantageous are ammonium oleate, sodium palmitate, sodium stearate, and other sodium soaps. Generally, the emulsiyinga~ent is pxovided in amounts of from about 0.1 to 15 parts by weight per 100 parts~y weight of the monomers, and water is provided in an amount of from about 1 to 4 parts per part of monomers, and even in larger ratios where greater dilution is desirable.
If desired, an aqueous latex formed in the emulsion polymerization of the rubber sub~trate may provide the aqueous medium onto which the monomers are grafted, with or without the addition of further emulsiying agents, water, and the like.
However, the rubber may be dis~olved in the monomer8, and the mixture reemulsified, or a latex thereof may be separately C-08-12-0242 ~39~39 prepared r Various water soluble free radical polymerization initiators are conventionally used for emulsion polymerization of the rubber monomer, including conventional peroxi/ and azo-cataly~ts, and the resulting latex may be used as the aqueous medium in which the graft copolymer monomers are admixed. In this manner the catalyst for the rubber polymerization may function in whole or part as the catalyst for the graft polymeri-zation. However, additional catalysts may be added at the time of graft polymerization.
Typical emulsion polymerization conditions involve temperatures in the range of from about 20 to 100 C. with agitation, and preferably an inert atmosphereO Pressures of from about 0O07 to 7,03 ~g/cm2 may be employed, and monomers and/or additional catalysts may be added incrementally or con-tinuously over a portion of the reaction cycle. Polymerization is preferabl~ continued until substantially all, that is, more than 90 per cent, of the monomers have polymerized. The remain-ing monomers and other volatile components are then distilled away from the latex, preferably~ which is then de-watered, washed and dried.
Particle size of the emul~ion latex graft particles may be varied by seeding, Pmulsiying agent concentration, agitation, rubber size variation through agglomeration prior to grafting, coagulation techniques, etc.
The particles 3ize of the ru~ber has an effect upon the optimum grafting level for a graft copolymer. For example, a given weight percentage of smaller size rubber particles will provide considexably higher surface area for grafting than the equivalent weight or a larger size rubber particle. Accordingly, the density of grating can be varied depending upon the size C-08-12-0242 ~39439 of the rubber particle. Generally the smaller particles will tolerate a hi~her superstrate/substrate ratîo than the larger size particles.
The particle size of the rubber graft copolymer has a significant ~ffect upon the gloss and tensile properties of the product produced hy the processes of this invention. Typically, the particle size of the graft copolymers used in the practice of the presen~ invention may be varied in an emulsion before ag-glomeration from as little as about 0.03 microns to as much as about 0.6 microns, depending upon the ultimate properties desired for a given product.
For purposes of determining weight average particle size, one can prepar~ a dispersion of the graft copolymer par-ticles and make a photo-micrograph thereof. The size of approxi-mately 200 to 1,000 particles is then measured and an average taken thereo, so as to obtain the average particle size based upon a number average or a weight average. Alternatively, other techniqu2s of measurement mav be employed, including light scattering techni~ues, so long as a reasonably close relationship is established between actual size and the techniques employed.
Although a starting rubber may be cross-linked, this may present problems from the standpoint of dissolving or dis-persing the rubber for a suspension polymerization process. How-ever, for emulsion polymerization processes the rubber desirably ha~ a significant degree of cross-linking. With respect to the graft copolymers, however, at least some degree of cross-linking is inherent during the graft polymerization processes, and this desirably may be augmented through the addition of cross-linking agents or control of the polymerization conditions.

C-08-12~0242 3~4~

To prepare a dispersed phase, it i~ preferred as a first step to mix from about 15 to 99 parts by weigh~ (in terms of solid content) of an alkadiene type rubbery polymer latex with, correspondingly, from about 3 to 200 parts by weight of at least one monomer of the monovinylidene aromatic type or the alkene nitrile type, which is graft polymeriza~le on said rubbery polymer, and then the resulting mixture is subjected to an emulsion graft polymerizationO Thereafter the product is separa-ted and dried before blending to make a polyblend of this inven-tion.
~1BODIMENTS
The following specific examples are exemplary of theefficacy of the present invention. All parts are parts by weight unless otherwise indicated~
EX~1PLE 1 PART A
To 100 parts of a latex homopolybutadiene containing 40 per cent rubber solids and approximately 3.0 parts of rubber reserve ~oap as an emulsifier are added 30 parts water and 15 parts of a 2.0 per cent aqueous solution of potassium persulfate.
rrhe emulsion is heated to 70 C. with stirring and then there is added thereto over a period of about 1 hour, 21 parts styrene and ~ parts acrylonitrile. The emulsion is held at temperature for one hour thereafter with stirring, cooled, coagulated, and the recovered polymer is then washed and dried and is lightly grafted.
The recovered polymer contains graft copolymer par-ticles of from about 0.6 to 1.5 micron, and at least half of such particles have a particle size above about 0.8 micron. The superstrate has a weight ratio of styrene to acrylonitrile of about 68:32 to 72:28. There are about 21 parts by weight of ~3~

grafted superstrate for each 100 parts by weight of substrate homopolybutadiene. These graft copolymer particles are com-prised of subparticles at least 90 weight per cent of which have particle sizes in the range of from about 0.06 to 0.1 micron.
The amount of ungrafted styrene/acrylonitrile copolymer admixed with such graft copolymer particles is about 1 to 8 weight per cent (based on total composition weight), and such copolymer has a number average molecular weight of about 40,000 and a weight ratio of styrene to acrylonitrile of about 68:32 to 72:28.
PART ~
Example 1, Part B, lines 35 50, U.S. Patent 3,509,238 is followed to produce highly grafted copolymer p~rticles.
The recovered polymer contains graft copolymer par-ticles of from about 0.12 to 0.16 micron. The superstrate grafted to the substrate elastomer comprises polymerized styrene and acrylonitrile in the weight ratio of about 64:36 to 68:32.
There are about 100 parts by weight of grafted superstrate for each 100 parts by weight of substrate elastomer. The amount of ungrafted styrene/acrylonitrile copol~mer admixed with such graft copolymer particles is about 35 weight per cent (based on total composition weight), and such copolymer has a number a~erage molecular weight o~ about 35,000 and a weight ratio of styrene to acrylonitrile of about 64:36 to 68:32.
PART C
Emulsion polymerized styrene/acrylonitrile copolymer is prepared conventionally. This copolymer has a weight average molecular weight of about 200,000 and a weight ratio of ~tyrene to acrylonitrile of about 68:32 to 72:28.
PART D
A total of 13 parts of Part A product, 38.1 parts of Part B produc~, and 48.9 parts of Part C product are blended together to produce a polyblend of this invention which comprisss ~L~33~
(on a 100 weight per cent total polyblend basis~ about 57.9 weight per cent of a matrix phase comprising copolymer of styrene and acrylonitrile having a molecular weigh~ average of about 172,000 and a weight ratio of styrene to acrylonitrile in the range of from about 64:36 to 72:28, and about 42.1 weight per cent of a mixture of a first graft copolymer (of Part B above) and a second graft copolymer (of 2art A above). The first and second such graft copolymers are dispersed throughout the styrene/acrylonitrile matrix phase when this polyblend is heat-fused. The weight ratio of first graft copolymer to second graft copolymer in this polyblend ranges from about 28:72 to 30:70J This blend has a total rubber con~ent (ungrafted basis) of about 25 (total blend basis).
This polyblend is found to produce when heat-fused and extruded excellent drain, waste and vent pipe. This polyblend displays a low temperature impact strength of about 19.08 Kgcm/cm notch (Izod) at -40~. and a room temperatuxe tensile strength of about 365.6 Kg/cm2~ This polyblend has excellent gloss characteristics.
EX~lPLES 2 - 4 _ The procedure of Example 1 is gensrally repeated to prepare additional polyblends of this invention and such poly-blends are evaluated. Result~ are summarized in the attached Table:

~39~39 O j ~ O O ~ 3 ~ 5 ~ i . ~ ~ ~ 3 ~ a ~

ID r n ~? o I ~t o N ~ ~ ~ D g ~ g 3 ~ tD
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U~ ~ U~ o Q ~D ~4 3 ~ V~ I t NU~ ~ N ~ ~D
n ~ ~ e P~ c 1 g ~ g~
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n~ ~ ~ o ,~
n ~ P ~ P
o @
_ ,~ 1 ul ~

w ~ ~ W tV a~ U~ o 1' ~ 1~ Ul o W O ~ ~n Ix ~n ~ o o o o W ~ ~I ~ o ~I
~D cr ~ ~ ~ ~I ~n o o ~ o w o ~ X
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W ~V UlW ~ C~ 1 0 O~ 9 0 o ~ ~ Vl o o ~ o ~ o o W o 1~ X
W ~ W O o W

Claims (3)

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

1. A polyblend adapted to display a combination of low temperature impact strength and room temperature tensile strength comprising from about 70 to 89 weight percent of styrene and acrylonitrile having a weight average molecular weight of from about 75,000 to 300,000 and a weight ratio of styrene to acrylo-nitrile of from about 95:5 to 30:70, being a mixture of a first graft copolymer with a second graft copolymer, said graft copoly-mers being dispersed throughout said matrix styrene/acrylonitrile copolymer when said polyblend is in a heat-fused form, the weight ratio of said first graft copolymer to said second graft copoly-mer in said polyblend ranging from about 85:15 to 5:95, (A) said first graft copolymer particles being characterized by having (1) a number average particle size of from about 0.03 to 0.6 micron, (2) a substrate elastomer comprising a copolymer of from about 70 to 98 weight percent of a conjugated alkadiene with, correspondingly, from about 30 to 2 weight percent based on total substrate elastomer weight of at least one compound selected from the group consisting of styrene and acrylonitrile, (3) said superstrate copolymer grafted to said sub-strate elastomer and comprising polymerized styrene and acrylonitrile in the weight ratio of from about 95:5 to 30:70, (4) there being from about 30 to 100 parts by weight of grafted superstrate copolymer for each 100 parts by weight of said substrate elastomer, (B) said second grafted copolymer particles being character-ized by having (1) a number average particle size of from about 0.6 to 3.0 microns and at least half of such particles have a particle size above about 0.8 micron, (2) a substrate elastomer comprising homopoly-alkadiene, (3) said superstrate copolymer grafted to said substrate elastomer and comprising polymerized styrene and acrylonitrile in the weight ratio of from about 95:5 to 30:70, (4) there being from about 3 to 30 parts by weight of grafted superstrate copolymer for each 100 parts by weight of said substrate elastomer, and (5) said second graft copolymer particles being com-prised of grafted subparticles at least 90 weight percent of which have particle sizes in the range of from about 0.05 to 0.15 micron, said polyblend having total elastomer content (ungrafted basis) ranging from about 10 to 30 weight percent (based on total polyblend).

2. A polyblend according to claim 1, characterized wherein said substrate elastomer of said first graft copolymer is butadiene/acrylonitrile copolymer.

3. A polyblend according to claim 1, characterized wherein said homopolyalkadiene is homopolybutadiene.