GB2056465A

GB2056465A - Compatible Polymer Blends

Info

Publication number: GB2056465A
Application number: GB8026408A
Authority: GB
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1979-08-15
Filing date: 1980-08-13
Publication date: 1981-03-18
Also published as: DE3030804A1; CA1141065A; GB2056465B; BE884819A

Abstract

A compatible blend of polymers comprises a block copolymer of styrene and a conjugated diolefin of 4-6 carbon atoms, and certain graft copolymers of styrene with up to 40% of acrylonitrile and/or methyl methacrylate, and a rubbery substrate which is polybutadiene or a copolymer of butadiene, styrene and up to 10% of acrylonitrile, optionally with polystyrene or a thermoplastic elastomeric polyurethane containing a relatively high molecular weight segment of a polyester.

Description

SPECIFICATION Compatible Polymer Blends The invention of this application is a blend of polymers which has good impact strength, is flexible and yet hard, and has good resistance to scuffing. Moreover, the blended polymers are compatible with each other.

The above physical properties are all important in many applications. Automobile bumpers require these properties to a high degree. So does the material that is used in the manufacture of footwear, especially sport boots. Many other uses suggest themselves for 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 manufacture of ski boots, for example, but these polyurethanes are relatively expensive. Nevertheless, they have the ridigity of plastics and the resiliency of rubber and are thus well suited to this type of application.

The recent development of block copolymers from such monomers as styrene and conjugated dienes has made available a valuable raw material for many applications. In many cases such copolymers exhibit elastomeric properties at ambient temperatures and are thermoplastic at elevated temperatures. They exhibit the general chracteristics of vulcanized rubbers but do not require vulcanization to attain these properties. Depending on the monomer composition, i.e., the proportion of styrene in the block copolymer, the properties of the polymer will resemble those of vulcanized rubber, as with a high conjugated diene content, or with a high styrene content the polymer will more nearly resemble a thermoplastic material such as a high impact polystyrene. The range of desirable possibilities is apparent and these block copolymers have found wide usage.

Nevertheless, for some uses, such block copolymers are not entirely satisfactory. Some of the required properties for sport boot material, for example, are hardness and scuff resistance and presently available block copolymers 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 in U.S. 3,833,687. A similar combination wherein the graft interpolymer is a graft copolymer of a diene rubber with a styrene monomer is shown in U.S. 3,835,200. A process for polymerizing 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 of styrene/butadiene/styrene block copolymers with polystyrene, with polyethylene and with polypropylene.

The combination of a graft copolymer of polybutadiene, styrene and acrylonitrile, and a polyurethane is shown in U.S. 3,049,505. The combination of a block copolymer of styrene and butadiene and a polyester polyurethane is shown in U.S. 3,562,355.

The polymerization of styrene in the presence of a styrene-butadiene copolymer is shown in U.S.

3,062,777.

The present invention is 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% (based on substrate) of acrylonitrile.

The blend may also contain polystyrene or a thermoplastic elastomeric polyurethane containing a relatively high molecular weight segment of a polyester.

The above blend is characterized by good flexibility, hardness, resistance to impact, gloss, abrasion resistance and scuff 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 formulation of a wide range of compositions having a corresponding range of the above desirable properties.

Block Copolymer The conjugated diolefin generally is butadiene or isoprene, preferably butadiene; 2,3dimethylbutadiene is also contemplated. The block copolymer is characterized by styrene end blocks with elastomeric diolefin center blocks, i.e., it has an ABA structure where B is an elastomeric diolefin polymer unit. A preferred embodiment is a styrene-butadiene-styrene block copolymer.

The block copolymers herein are linear and may be prepared by sequential anionic polymerization of styrene, the conjugated diolefin and, finally, styrene. Thus, for example, styrene is polymerized in the presence of an alkyl lithium catalyst to form a so-called "living polymer," 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 form a polystyrene block, and finally 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 35,000 and 1 50,000. The details of processes by which these block 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.81-87), Applied Science Publishers, London (1974).

Graft Copolymer The graft copolymers of this invention may be prepared by known methods such as (1) preparing a polymer latex (substrate) by polymerizing (in an aqueous emulsion) butadiene or a mixture of 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% of 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 polybutadiene, a copolymer of butadiene and styrene or a copolymer of butadiene, styrene and acrylonitrile.As little as 15% and up to 70% of styrene, based on the overall monomer content may be present in the graft copolymer; and the mixture-of (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 from about 10% to about 60%.

Cross-linking agents can be used as desired, in the above process. They may be used in the step of preparing the latex and in step (3) involving preparation of the superstrate. Illustrative cross-linking agents include divinylbenzene, dimethacrylates such as mono-, di-, tri- and tetraethylene glycol dimethacrylate and 1,3-butylene glycol.di-methacrylate, triallyi phosphate, triallyl cyanurate, tetrallyl silane, diallylitaconate, diethylene glycol diacrylate, etc.

Methods of making the graft copolymers herein are well known. U.S. 2,082,808 (Hayes), for example, shows methods for preparing ABS resins, as does also U.S; 2,994,683 (Calvert). The MBS resins and other graft copolymers herein are prepared similarly.

Particularly preferred graft copolymers are those wherein the superstrate, i.e., the grafted polymer, is a copolymer of styrene and acrylonitrile and the substrate is polybutadiene. Another preferred species is an MABS resin, i.e., one where the superstrate is a grafted copolymer of acrylonitrile, methyl methacrylate and styrene. Still another preferred species (MBS) is prepared by copolymerizing 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 of two different MBS resins, or a mixture of an ABS resin and two different MABS resins.

A particularly preferred graft copolymer is one wherein a copolymer of from about 70 parts to about 90 parts of styrene and from about 10 parts to about 30 parts of methyl methacrylate is grafted onto a polybutadiene substrate.

Polystyrene The polystyrene component is that known in the trade as general purpose polystyrene, i.e. the homo-polymer. It is semi-linearin structure and is non-crystalline. Although it is one of the most widely used thermoplastics, by itself it is characterized by limited resistance to weather and by relatively poor impact strength.

Polyurethane The polyurethane component of the polymer blends herein are derived from polyesters. More particularly, they are derived from polyesters containing hydroxyl end groups. These polyesters may in turn be prepared either by condensation of approximately equivalent proportions of a glycol and a dicarboxylic acid (or anhydride thereof), or by reacting a lactone having at least six carbon atoms in the lactone ring with a small proportion of a bi-functional initiator such as a glycol, an amino alcohol or a diamine. In either case, the molecular weight of the polyester is relatively high, i.e., within the range of from about 1000 to about 3000.

Where the polyester is prepared by condensation of a glycol and a dicarboxylic acid, the glycol is one containing 2-6 carbon atoms, e.g., ethylene, trimethylene, tetramethylene, hexylene and propylene glycols. The dicarboxylic acid is aliphatic and contains 2-8 carbon atoms, e.g., succinic, glutaric, adipic, pimelic and suberic acids. The condensation polymerization is carried out by known methods.

Alternatively, the polyester may as indicated be derived by polymerization of a lactone such as caprolactone. The polymerization is accomplished merely by mixing the lactone and bifunctional initiator at an elevated temperature, e.g., between about 1 200C and 2000C. Preferably, a catalyst is used, at a concentration of from about 0.001% to about 0.5%. A wide variety of catalysts are effective, and basic and neutral ester interchange catalysts are preferred. More specific information regarding the process for preparing lactone polyesters of the type contemplated herein may be found in 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 80-1 200C, 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 having 2-10 carbon atoms, e.g., ethylene glycol, 1 4-butanediol, 1,ibis (2-hydroxyethoxy) benzene and 1,6-hexamethylene glycol.A typical polyurethane contemplated herein may be prepared from 1 molar equivalent of a dihydroxy polyester, 6 molar equivalents of a diisocyanate and 5 molar equivalents of a chain extender. Generally, it is desirable to use 2-6 mols of diisocyanate per mol of dihydroxy polyester.

The polyurethanes herein are preferably 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 polyurethane product may be combined and carried out as a single step.

Additional process information may be had by referring to Allport and Jones, "Block Copolymers". pp.227-234, Applied Science Publishers, London (1973).

Polymer Blends The relative proportions of the polymers present in the blend of the invention are from about 20 to about 90 parts of block copolymer and from about 10 to about 80 parts of graft copolymer.

Preferably, the blend will contain from about 30 to about 80 parts of block copolymer and from about 20 to about 70 parts of graft copolymer. When the polymer blends contain polystyrene the relative proportions of the polymers are from about 30 to about 80 parts of block copolymer, from 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, from about 10 to about 50 parts of graft copolymer and from 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 of the indicated polymers usually with intensive mixers, e.g., a Banbury mixer, or a two-roll mill, or with any of variously available 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 Table I.

The tests include mixing in a Banbury at 1 600C, injection molding, and milling on a 2-roll mill.

The test samples are rated on a scale of 1-10 (based on the ease and rapidity with which the mixture forms a smooth, homogenous mass) where 1 is very good and 10 is very bad. These test results are shown in Table II which contains also compatibility ratings on a scale of 1-10 where 1 is bad (incompatible) and 10 is good (compatible). The compatibility ratings are based on considerations of whether or not the sample delaminates or cracks when bent, and the general homogeneity of appearance of the sample. Also shown in Table II are Taber abrasion test data (ASTM D 1044-73).

ABS-1, ABS-2, ABS-3 and ABS-4 denote ABS resins in which the substrate is polybutadiene and the monomer proportions are as follows: Butadiene Styrene Acrylonitrile ABS-1 50 32 18 ABS-2 20 51 29 ABS-3 29 46 25 ABS-4 45 40 15 MABS-1, MABS-2, and MBS denote graft copolymers in which the substrate is a 25-75 copolymer of styrene and butadiene, the monomer proportions being as follows: Methyl Bu tadiene Styrene A crylonitrile Methacrylate MABS-1 57 19 4 20 MABS-2 49 31 2 18 MBS 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 has a Shore A hardness rating of 62, a tensile strength of 4600 psi, a molecular weight (GPC) of 150,000-200,000, a styrene content of 28%, and a solution viscosity (25% in toluene) of 1220 cps.

Table I Sample ABS-1 ABS-2 ABS-3 ABS-4 MABS- 1 MABS-2 MBS SBS 1 100 2 20 80 3 50 50 4 50 50 5 20 80 6 20 80 7 50 50 8 30 70 9 30 70 10 30 70* 11 20 10 70* 12 30 70* 13 10 20 70 14 20 20 60 15 30 10 60 16 20 10 17 20 30 50 18 30 20 50 19 40 60 20 70 30 21 15 15 70 22 10 20 70 23 40 10 50 24 10 40 50 25 70 30 26 50 50 27 50 50 28 70 30** 29 50 50** 30 40 50** 31 40 60 32 50 50** 33 40 60 34 25 25 50** 35 50 50** 36 70 30** 37 50 50 38 50 50 * Contains about 30% of a low aromatic naphthenic oil plasticizer; Shore A rating of 46.

** Higher molecular weight, contains about 30% of a low aromatic naphthenic oil plasticizer.

Table II Processabllity Compatability 2-Roll Injection Sample Banbury Mill Mold Visual Taber 1 2 10 2 2 1 2 9 3 1 1 2 9 200 4 1 t 2 9 80 5 1 1 9 6 1 1 8 7 1 1 8 8 1 1 9 Table II (cont).

9 1 1 8 10 1 2 10 11 1 2 8 12 1 2 8 13 1 1 8 14 1 1 8 15 1 1 8 16 1 1 8 17 1 1 8 18 1 1 8 131 19 2 2 6 20 2 2 9 21 1 1 8 22 1 1 8 23 1 1 7 117 24 1 1 8 25 1 1 9 26 1 1 9 27 2-3 2-3 9 145 28 1 1 9 29 1 1 9 30 1 1 8 200 31 1 1 4 32 1 1 4 33 1 1 4 34 2 2 7 35 1 1 8 36 1 1 8-9 37 1 1 8-9 38 1 1 9 The compatibility (1) of the polymeric components of the polystyrene blends herein is shown in Table Ill. The rating is based on considerations of whether or not a sample (a pressed placque or injection molded placque) delaminates or cracks when bent, and the general homogeneity of appearance of the sample. The samples are rated on a scale of 1-10 where 1 is bad (incompatible) and 10 is good (compatible). Processability (2) (mixing in a Banbury at 1 600C followed by milling on a 2-roll mill) and scuff resistance ratings are also shown, the ratings in these instances being based on scales of 1-10 where 1 is good and 10 is bad.

Table Ill MABS ABS PS SBS-1 SBS-2 SBS-3 { 2) (3) 1. 20 20 60 8 1 2 2. 15 25 60 8 1 3 3. 25 25 50 5.5 3 2.5 4. 25 25 50 8 1 4 5. 20 30 50 9.5 1 4.5 6. 10 20 70 8 1 4 7. 20 10 70 8 1 3.5 8. 25 25 50 - 9 - 9. 15 25 60 8 1 3.5 10. 19 19 62 8 1 4 11. 25 25 50 8 1 4 12. 15 25 60 8 1 4 13. 19 19 62 8 3 4 14. 19 19 62 9 1 15. 25 25 50 8 1 6 In the above table PS represents polystyrene.

The compatibility of the polymeric components of the polyurethane blends herein is shown in Table IV. The rating is based on considerations of whether or not a sample (a pressed placque or injection molded placque) delaminates or cracks when bent, and the general homogeneity of appearance of the sample. The samples are rated on a scale of 1-10 where 1 is bad (incompatible) and 10 is good (compatible).

Table IV MABS ABS PU- 1 PU-2 SBS- 1 SBS-2 Rating 1. 20 10 70 6.5 2. 27 18 55 6.5 3. 22 11 67 6.5 4. 14 43 43 43 6.5 5. 20 40 40 9.5 6. 30 35 35 9.0 7. 30 35 35 9.0 8. 30 35 35 9.0 In the above table PU-1 and PU-2 have the following meanings: PU-1: A slightly cross-linked polyurethane derived from polycaprolactone having a Shore D hardness of 53.

PU-2: A slightly cross-linked polyurethane derived from a lower alkylene adipate having a Shore D hardness of 53.

It will be seen that the blends all are compatible and that some are especially so. These blends, as mentioned earlier, are characterized by good scuff-resistance, gloss, hardness, abrasion resistance, flexibility and impact-resistance. Moreover, they are relatively inexpensive, as compared to polyurethane itself.

All parts and percentages herein, unless otherwise expressly stated, are by weight.

Claims

1. A blend of polymers comprising a block copolymer of styrene and a conjugated diolefin of 46 carbon atoms, and a graft copolymer wherein a polymer of styrene and up to 40 parts by weight, 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% by weight of acrylonitrile.

2. A blend according to claim 1 wherein the block copolymer is a copolymer of styrene and butadiene.

3. A blend according to claim 1 wherein the block copolymer is a styrene-butadiene-styrene block copolymer.

4. A blend according to claim 1, 2 or 3 wherein the graft copolymer has been prepared by grafting a copolymer of styrene and acrylonitrile onto the rubbery substrate.

5. A blend according to claim 1,2 or 3 wherein the graft copolymer has been prepared by grafting a copolymer of styrene and methyl methacrylate onto the rubbery substrate.

6. A blend according to claim 1,2 or 3 wherein the graft copolymer has been prepared by grafting a copolymer of styrene and from 10 parts to 30 parts by weight of methyl methacrylate onto the rubbery substrate.

7. A blend according to any one of the preceding claims wherein the rubbery substrate is polybutadiene or a copolymer of butadiene and styrene, and the blend also comprises polystyrene.

8. A blend according to claim 7 wherein the graft copolymer has been prepared by grafting a copolymer comprising from 70 to 90 parts by weight of styrene and from 10 to 30 parts by weight of methyl methacrylate onto the rubbery substrate.

9. A blend according to any one of claims 1 to 6 which also comprises a thermoplastic elastomeric polyurethane containing a relatively high molecular weight segment of a polyester.

10. A blend according to claim 9 wherein the graft copolymer has been prepared by grafting a copolymer comprising from 70 to 90 parts by weight of styrene and from 10 to 30 parts by weight of methyl methacrylate onto a rubbery substrate.

11. A blend according to claim 9 or 10, wherein the polyester segment of the polyurethane is a polycaprolactone.

12. A blend according to claim 9 or 10, wherein the polyester segment of the polymethane is a lower alkylene adipate.

13. A blend according to any one of claims 9 to 1 2 wherein the polyurethane is cross-linked.

14. Shaped articles of a blend as claimed in any one of the preceding claims.