CA1141065A

CA1141065A - Compatible polymer blends

Info

Publication number: CA1141065A
Application number: CA000357066A
Authority: CA
Inventors: King-Han Tan; Jan L. De Greef
Original assignee: Borg Warner Chemicals Inc
Current assignee: GE Chemicals Inc
Priority date: 1979-08-15
Filing date: 1980-07-25
Publication date: 1983-02-08
Also published as: GB2056465A; DE3030804A1; BE884819A; GB2056465B

Abstract

ABSTRACT
A blend of polymers comprising a block copolymer of styrene and a conjugated diolefin of 4-6 carbon atoms, and a graft copolymer wherein a polymer of styrene and up to 40 parts, based on the weight of graft copolymer, of acrylonitrile and/or methyl methacrylate is grafted onto a rubbery substrate which is polybutadiene or a copolymer of butadiene, styrene and up to 10% of acrylonitrile. The blend may also contain polystyrene or a thermoplastic elastomeric polyurethane containing a relatively high molecular weight segment of a polyester. The polymer blends are flexible yet hard and have good impact and scuff resistance. The blended polymers are also compatible with each other.

Description

;5 CO~PATIBLE P01~.,qER BLEND~
Description The invention of this application is a blend o~
polymers which has good impact strength, is flexible and yet hard, and has good resistance to scuffing. Moreoever, the blended polymers are compatible with each other.
The above physical properties are all important in many appllcations. Automobile bumpers require these pro-perties to a high degree. So does the material that is used in the manu~acture of ~ootwear, especially sport boots.
Many other uses suggest themselves ~or a material having this combination of properties.
" In almost all instances, the materials presently used for these applications are'expensive, so that there is a strong incentive to develop a substitute. Polyurethanes are a typical raw material for the manu~acture of ski boots, ior example, but these polyurethanes are relatively expensive.
Nevertheless, they have the rigidity o~ plastics and the resiliency o~ rubber and are thus well suited to this type of application.
The recent devel'opment o~ block copolymers ~rom such monomers as styrene and conj~gated dienes has made available a valuable raw material ~or many applications. In many cases such copolymers exhibit elastomeric properties at ambient temperatures and are thermoplastic at elevated t~mperatures.
They exhibi-t the general characteristics o~ vulcanized rubbers but do not require ~ulcanization to attain thes~ properties.
~epending on the monomer composition, i.e., the proportion o~
styrene i.n the block copolymer, the properties o~ the polymer will r~semble those o~ vulcani~ed rubber, a~ with a high conjugated diene content, or with a high styrene content the polymer will more nearly resemble a thermoplastic 078161~ 2-material such as a high impact polystyrene. The range of desirable possibilities is apparent and these block copolymers have ~ound wide usage.
Nevertheless~ for some uses, such block copolymers are not entirely satis~actory. Some o~ the required pro-perties ~or sport boot material, for example, are hardness and scu~ resistance and pr~sently available block copoly-mers do not provide these properties to the extent desired.
The combination of a polyphenylene oxide, a block copolymer of a vinyl aromatic compound with a conjugated diene and a graft interpolymer of an acrylic monomer with a diene rubber, is shown i~ U.:S. 3,833,687. A similar combination wherein the gra~t interpolymer is a graft copolymer of a die~e rubber with a styrene monomer is shown in U. S. 3,835:,200. A process for poly~erizing a mixture of styrene and acrylonitrile in the presence of a block copolymer of an ethylene-propylene copolymer and a diene rubber, is shown in U. S. 3,719,731. Shell Chemicals Technical Bulletin . RBX/76/3 shows the combination o~ styrene/butadiene/styrene block copolymers with polystyrene, wi.th polyethylene and with polypropyl.ene.
The combination of a gra~t copolymer o~ polybutadiene, styrene and acrylonitrile, and a polyurethane is shown in U. ~. 3,049,505. The combination o~ a block copolymer of styrene and butadiene and a polyester polyurathane is sho~n in U. S. 3,562,355.
The polymerization o~ styrene in the presence o~ a styrene-butadiene copolymer is show~ i~ U. S. 3,062,777.
The present invention is a blend o~ polymers com-prising a block copolymer o~ styrene and a conjugateddiole~in o~ 4-6 carbon atoms, and a gra~t copolymer wherein a polymer o~ styrene and up to 40 parts, based on the weight o~ gra~t copolymer, o~ acrylonitrile and/or methyl 078161-M ~3-methacrylate is gra~ted onto a rubbery substrate which is polybutadiene or a copolymer of butadiene, styrene, and up to 10% (based on substrate) o~ acrylonitrile.
The blend may also contain polystyrene or a thermo-plastic elastomeric polyurethane containing'a relativelyhigh molecular weight segment of a polyester.
The above blend is characterized by good ~lexibility, hardness, resistance to impact, gloss, abrasion'resistance and scu~f resistance~ Moreover, its cost is much less than that of presently used materials which it would replace in the market. The unexpected compatibility of these polymers permits the iormulation o~ a wide range of compositions having a corresponding range'oi the above desirable properties. ' ' ' ' Block' _ pol'ym'er The conjugated dioleiin generally is butadiene'or isoprene, preferably butadien'e; 2,3-dimethylbutadiene is also côntemplated. The block copolymer is characterized by styrene end blocks with elastomeric diolefin c~nter blocks, i.e., it has an ABA structure'where B is an elastomeric diolefin polymer unit. A preferred embodiment is a styrene-butadiene-styrene bloc~ copolymer.
The block copolymers herein are linear and may be prepared by sequential anionic polymerization of styrene, the conjugated diole~in andJ finally, styrene. ThusJ for example J styrene ls polymerized in the presence of an alkyl lithium catalyst to form a so-called 'iliving polymex,"
butadiene is added to this living polymer to continue the polymerization with the formation of an intermediate block A-B-Li (still a living polymer), then more styrene is added to ~orm a polystyrene block, and ~inally a terminating agent is added. Alternatively, the A-B-Li living polymer may be coupled with itself. The result in either case is an ABA

block copolymer The polystyrene blocks each have a molecular weight between about 10,000 and 45,000 and the polystyrene block has a molecular weight between about 35,00 and 150,000. The details oi processes by which these blocX
S copolymers can be prepared may be found in U. S. 3,231,635;
U. S. 3,239,478; U. S. 3,265,765, and "Block Copolymers"
by Allport and Jones, Ch. 3(pp. 81-8~), Applied Science Publishers, London (1974).
' Gra~'t Copolymer . The graft copolymers o~ this invention may be preparéd by known methods such as (I) preparing a polymer latex (substrate) by pol~merizing (in an aqueous emulsion) butadiene or a mixture o~ butadiene, styrene and up to 10%
(based on monomer content of the latex) of acrylonitrile,

(2) adding to said latex a mixture of styrene and up to 40~0 oi acrylonitrile and/or methyl methacrylate (based on monomer content of the added mixture), and (3) polymerizing the mixture of (2). Thus, the polymer latex of (1) may be poly-butadiene, a copolymer of butadiene and styrene or a co-polymerof.butadiene, styrene and acrylonitrile. As littleas 15% and up to 70% of styrene, based on the overall monomer content may be present in the gra~t copolymer; and the mixture o~ (2) may be styrene and acrylonitrile,' styrene and methyl methacrylate, or styrene, acrylonitrile'and methyl methacrylate.
The butadiene content of the graft copolymer will range ~rom about 10% to about 60%.
Cross-linking agents can be used as desired, in the above process. They may be used in the step o~ preparing the latex and in step (3) involving preparation o~ thè super-strate. Illustra~i.ve cross-linking agents include diviny7-benzene, dimethacrylates such as mono-, di-, tri- and tetra-ethylene glycol dimethacrylate and 1,3-butylene glycol di-methacrylate, triallyl phosphate, tr.iallyl cyanurate, tetrallyl silane, diallylitaconate, diethylene glycol diacrylate, etc..

078161~ 5-Methods of making the graft copolymers herein are well known. U. S. 2JO827808~(Hayes), for example, shows methods for -preparing ABS resins, as does also U. S.
2,994,683 (Calvert). The ~BS resins and other graft copolymers herein are prepared similarly.
Particularly preferred graft copolymers are those wherein the superstrate, i.e., the grafted polymar, is a copolymer of styrene and acrylonitrile and the substrate ls polybutadiene. Another preferred sp~cies is an .MABS
resin, i.e., one where the sùperstrate is a gra~ted co-polymer of acrylonitrile, methyl methacrylate and styrené.
Still another preferred species (MBS) is prepared by co-polymerizing styrene and methyl methacrylate in the presence of polybutadiene (as the substrate).
Mixtures of graft copolymers may be used. Thus, two different ABS resins may be used, or a mixture of an ABS
resin and an MABS resin, or a mixture of an MBS resin and an MABS resin, or a mixture o~ two different lUBS resins, or a mixture of an ABS resin and two different MABS resins.
A particularly pre~erred graft copolymer is one wherein a copolymer of ~rom about 70 parts to about 90 parts o~ styrene and from about 10 parts to about 30 parts o~
methyl methacrylate is grafted onto a polybutadiene substrate.
~
The polystyrene compone~t is that known in the trade as general purpose polystyrene, i.e., the homo-polymer. It is semi-linear in structure and is non-crystalline.
Although it is one of the most widely used thermoplastics, by itsel~ it is characterized by limited resistance to weather and by relatively poor impact strength.

'Polyu~ th'ane The polyurethane component o~ the polymer bl'ends herein ar-e'derived from polyesters. l~ore particularly, they are derived ~rom polyesters containing hydroxyl end groups. These polyesters may in turn be prep~rPd either by condensation o~ approximatel'y equivalent proportions o~ a glycol and a dicarboxylic acid (or anhydride thereo~), or by reacting a lactone having at least six carbon atoms in the lactone ring with a small proportion of a bi- -~unctional initiator such as a glycol, an amino alcohol or a diamiDe. In either case, the molecular weight o~ the polyester is relatively hi'gh,' i.e.', within the range o~
from about 1000 to about 3000.
Where the polyester is prepared by co~densation o~ a glycol and a dicarbox~lic acid, the glycol is one containing 2-6 carbon atoms, e.g.~ ethylene, trimethylene, tetra-methylene, hexylene and propylenê glycols. The dicarbbxylic acid is aliphatic and~contains 2-8 carbon atoms, e.g., suc~inic, glutaric, adipic, pimelic and suberic acids. The ! condensation polymerization is carried out by kno~vn me*hods.
Alternatively, the polyester may as indicated be derived by polymerization o~ a lactone such as caprolactone.
Th~ polymerization is accomplished merely by mixing the lactone and bi~unc~ional initiator at an elevated temperature, e.g., between about 120~ and 200. Pre~erably, a catalyst is used, at a concentration o~ ~rom about 0.001% to about 0.5%. A wide variety o~ catalysts are ef~ective, and basic and neutral ester intercha'nge catalysts are pre~erred.
More speci~ic in~ormation regarding the process ~or pre-paring lactone polyesters of the type contemplatèd herein may be ~ound i~ U. S. 2,933,477 and 2,933,478.

The above linear dihydroxy polyester may be reacted with an excess of an aromatic diisocyanate, such as 4,4'-diphenylmethane diisocyanate (MDI) or tolylene diisocyanate (TDI), at 80-120C, to give a prepolymer which is a mixture of the excess unreacted diisocyanate and a diisocyanate-terminated polymeric diol. This mixture then may be reacted with a chain extender in such stoichiometric proportions as to just react with all the free isocyanate groups. The chain extender may be a low molecular weight glycol havi~g 2-10 carbon atoms, e.g., ethylene glycol, 1,4-butanediol, 1,4-bis (2-hydroxyethbxy) benzene'and 1,6~-hexamethyle~e glycol.
A typical polyurethane contemplated herein may be prepared from 1 molar equivalent o~ a dihydroxy polyester, 6 molar equivalents o~ a diisocyanate and 5 molar equivalents o~ a chain extender. Generally, it is desirable to use 2-6 mols o~ diisocyanate per mol of dihydroxy polyester.
The polyurethanes herein are pref'erably cross-linked. Cross-linking may be accomplished merely by use of a slight excess of diisocyanate.~
The steps of preparing the prepolymer mixture and the final poiyurethane product may be combined and carried out as a single step.
Additional process in~ormation may be had by re~erring to Allport and Janes, "Block Copolymers". pp.227-234, Applied Science Publishers, London (1973).
'P'ol'ym'er'B'lends The relative proportions o~ the polymers present in the blend of ths invention are ~rom about 20 to about 90 parts of block copolymer and ~rom-about 10 to about 80 parts o~ graft copolymer. Pre~erably, the blend will contain from about 30 to about 80 parts of block copolymer a~d ~rom 078161-M -8~

about 20 to about 70 parts of graft copolymer. When the polymer blends contain polystyrene the relative proportions of the polymers are -~rom about 30 to about 80 parts o~ block copolymer, ~rom'about 10 to about 40 parts of graft copolymer, and from about 10 to. about 40 parts of polystyrene. When the polymer blends contain a polyurethane the relative proportions of the polymers are 'from about 25 to about 80 : parts of block copolymer, ~rom'about 10 to about 50 parts :~ o~ gra~t copolymer and ~rom about 5 to about 50 parts of polyurethane. Obviously, the properties of the blend will vary with its composition.
. The polymer blends herein may be prepared'by melt mixing of two or more o~ the'i~dicated polymers usually with intensive mixers, e.g., a Banbury mixer, or a two-roll mill, or with any o~ ~ariously availabIe single and multi-screw extruders.
The processability and compatibility of the polymer blends of .the invention are:shown by actual processing tests : carried out on blends the composition of which`is shown in TabIe I.
The tests include mixing in a Banbury at 160 C, injection molding, and milling on a 2-roll mill. Tpe : test samples are rated on a scale o~ l-lO (based on the ease and rapidity with which the mixture forms a smooth, homogenous m~ss) where l is very good and 10 is very bad.
These test results are shown in Tabl'e II which`contains also compatibility ratings on a scale of l-10 where 1 is bad.
~ (incompatible) and 10 is good (compatibIe). The compatibility ; ratings are based on consideratio~s o~ whether or not the sample delaminates or cracks whe~ be~t, and the general homogeneity o~ appearance.o~ the sample. Also shown in Table II are Taber abrasion test data (ASTM D 1044-73).

AB~-l, ABS-2, AB~-3 and ABS-4 denote ABS resins in which the substrate is polybutadiene and the monomer pro-portions are as ~ollows:

'But'ad'i'ene 'St'yr~ne 'A'crylonitrile ABS-l 50 32 18 AB~-4 45 40 15 MABS-l, MABS-2, and MBS. denote'graft copolymers i.n which the substrate is a 25-75 copolymer of styrene and butadiene 7 the monomer proportions being as follows .. Methyl : Butadien'e' Styrene Acryl'onitrile_ ethacrylate MABS-l 57 19 4 . 20 - MABS-2 49 31. 2 ,18 ~BS 50 30 - 20 : The terms SBS denotes a styrene-butadiene-styrene block copolymer containing (as a stabilizer) 0.5% by weight of 1076 (n-octadecyl 3-(3'5'-ditertiarybutyl-4-hydroxyphenyl) propionate). The block copolymer ~ a Shore A hardness rating o~ 62, a tensile strength o~ 4600 psi, a molecular weight (GPC) o~ 150,000-20G,000, a styrene content of 28%, and a solution viscosity (25% in toluene) of 1220 cps.

Q~
078161-M -lO-Table I

Sample ABS-1 ABS-2 ABS-3 ABS-4 MABS-1 MABS-2 MBS SBS

3 50 50

4 50 50 g 30 70 70*
11 20 10 70*
12 30 70*

18 30 _ 20 50 22 10 . 20 70 24 10 40 50' 25. 70 30 27 50 5~
28 70 30**
29 50 ~0* ~
50**

32 50 50**
33 40 _ 60 34 25 25 50**
50**
36 70 30**

* Contains about 30% of a low aromatic naphthenic oil plasticizer; Shore A rating of 46.
** Higher molecular weight, contains about 30~0 of a low aromatic naphthenic oil plasticizer.

078161-M -ll-Table II
PROCESSABILITY COMPATIBILITY
Sample~anbur~ Mlll Mold Visual_ Taber : 4 1 1 2 9 28oo 10 6 ~ - 8 1511 1 22 18o 14 ~ 1 1 8 19 2 - -2~ - _8 _ 131 24 --- -1 ~ - - 1- ~ - ~- -- - --7- 117 2~ 2-3 2-3 2~ l 1 9 145 29 1 1 ~ 9 ~O 35 3~ 1 1 8-9 . . . _ . . _ . _ _ . _ -S

The compatibility (1) of the polymeric components of the polystyrene blends herein is shown in Table III. The rating is based on considerations of whether or not a sample (a pressed placque or injection molded placque) dslaminates or cracks when bent, and the general homogeneity of appearance o~ the sample. The samples are rated on a scale of 1-10 where 1 is bad (incompatible) and 10 is good (compatible). Processability (2) (mi~ing in a Ban'oury at - 160 C followed by milling on a 2-roll mill) and scuff resistance ratin~s are also shown, the ratings in these instances being based on scales of 1-10 where 1 is good and 10 is bad.
Table III

MABS ABS PS SBS-1 SBS-2 SBS-3 ( 1; ( 2) (3) ~0 ~i lo ~ ~ S ~ 2 5 25 1~. 2525 50 8 1 3.5 $~
' 078161-M -13-In the above. table PS represents polystyrene.
The compat.ibility o~ the polymeric components o~ the polyurethane blends herein is shown in Table IV.
The rating is based.on consider'ations o~ whether or not a sample ~a pressed placque or injection molded placque) delaminates or cracks when bent, and the general homogeneit7 o~ appearance o~ the sample. The samples are rated on a scale o~ 1-10 where'l is bad (incompatibl~ and 10 is good (compatibl'e).
' Tabl'e 'IV
.. ._ -2A~ Q 7~ 6.5 2.27 18 ~5 6.5 3.22 11 67 6.. 5 4..14. 6.5

5.20 40 40 - 9.5

6. 30 35 35 9.0

7.'-30 35 35 9.0

8.'3~ 35 35- 9.0 In the above table PU-l and PU-2 have the ~ollowing meanings: -PU-l: A slightly cross-linked pol.yure.thane derived from polycaprolactone having a Shore ~ hardness o~ 53.
PU-2: A slightly cross-linked polyurethane derived ~rom a lower alkylene adi~ate having a Shore D hardness o~ 53.
It will be seen that the blends all are compatible and that some ~re especially so. ~hese blends as mentioned earlier, are characterized by good scu~-resistance, gloss, hardness, abrasion resistanae, ~lexibility and impact-resistance. Moreoever, .they are 0~8161-M -14-relatively inexpensive, as compared to polyurethane itself.
All parts and percentages herein, unless otherwise expressly stated, are by weight.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A blend of polymers comprising a block copolymer of styrene and a conjugated diolefin of 4-6 carbon atoms, and a graft copolymer wherein a polymer of styrene and up to 40 parts, based on the weight of graft copolymer, of acrylonitrile, methyl methacrylate and mixtures thereof is grafted onto a rubbery substrate which is polybutadiene or a copolymer of butadiene, styrene and up to 10% of acrylonitrile.

2. The blend of polymers of claim 1 wherein the block copolymer is a copolymer of styrene and butadiene.

3. The blend of polymers of claim 1 wherein the block copolymer is a styrene-butadiene-styrene block copolymer.

4. The blend of claim 1 wherein the rubbery substrate of the graft copolymer is polybutadiene.

5. The blend of polymers of claim 1 wherein the graft copolymer is prepared by grafting a copolymer of styrene and acrylonitrile onto a rubbery substrate.

6. The blend of polymers of claim 1 wherein the graft copolymer is prepared by grafting a copolymer of styrene and methyl methacrylate onto a rubbery substrate.

7. The blend of polymers of claim 1 wherein the graft copolymer is prepared by grafting a copolymer of styrene and from about 10 parts to about 30 parts of methyl methacrylate onto a rubbery substrate.

8. A blend of polymers comprising (1) a block copolymer of styrene and a conjugated diolefin of 4-6 carbon atoms, (2) a graft copolymer wherein a polymer of styrene and up to 40 parts, based on the weight of graft copolymer, of acrylonitrile, methyl methacrylate and mixtures thereof is grafted onto a rubbery substrate which is polybutadiene or a copolymer of butadiene and styrene and up to 10% of acrylonitrile, and (3) polystyrene.

9. The blend of claim 8 wherein the block copolymer is a copolymer of butadiene and styrene.

10. The blend of polymers of claim 8 wherein the block copolymer is a styrene-butadiene-styrene block copolymer.

11. The blend of polymers of claim 8 wherein the rubbery substrate of the graft copolymers is polybutadiene.

12. The blend of polymers of claim 8 wherein the graft copolymer is prepared by grafting a copolymer of styrene and acrylonitrile onto a rubbery substrate.

13. The blend of polymers of claim 8 wherein the graft copolymer is prepared by grafting a copolymer of styrene and methyl methacrylate onto a rubbery substrate.

14. The blend of polymers of claim 8 wherein the graft copolymer is prepared by grafting a copolymer from about 70 parts to about 90 parts of styrene and from about 10 parts to about 30 parts of methyl methacrylate onto a rubbery substrate.

15. A blend of polymers comprising (1) a block copolymer of styrene and a conjugated diolefin of 4-6 carbon atoms, (2) a graft copolymer wherein a polymer of styrene and up to 40 parts, based on the weight of graft copolymer, of acrylonitrile, methyl methacrylate and mixtures thereof is grafted onto a rubbery substrate which is polybutadiene or a copolymer of butadiene, styrene, and up to 10% of acrylonitrile, and (3) a thermoplastic elastomeric polyurethane containing a relatively high molecular weight segment of a polyester.

16. The blend of claim 15 wherein the block copolymer is a copolymer of butadiene and styrene.

17. The blend of polymers of claim 15 wherein the block copolymer is a styrene-butadiene-styrene block copolymer.

18. The blend of polymers of claim 15 wherein the rubbery substrate of the graft copolymers is polybutadiene.

19. The blend of polymers of claim 15 wherein the graft copolymer is prepared by grafting a copolymer of styrene and acrylonitrile onto a rubbery substrate.

20. The blend of polymers of claim 15 wherein the graft copolymer is prepared by grafting a copolymer of styrene and methyl methacrylate onto a rubbery substrate.

21. The blend of polymers of claim 15 wherein the graft copolymer is prepared by grafting a copolymer from about 70 parts to about 90 parts of styrene and from about 10 parts to about 30 parts of methyl methacrylate onto a rubbery substrate.

22. The blend of polymers of claim 15 wherein the polyester segment of the polyurethane is a polycaprolactone.

23. The blend of polymers of claim 15 wherein the polyester segment of the polymethane is a lower alkylene adipate.

24. The blend of polymers of claim 15 wherein the polyurethane is cross-linked.