Styrene/maleic anhydride polymers can be made more resistant to combustion by incorporation therein of minor amounts of polyvinyl chloride. The compositions can also comprise MBS, ABS and other flame retardant additives.

BACKGROUND OF THE INVENTION 
This invention relates to flame retardant polymers and particularly to fire 
retardant terpolymers of styrene and maleic anhydride. 
Polymers of styrene and maleic anhydride are well known for their high heat 
distortion temperature but they have the limitation that they burn when 
ignited. For many end uses a polymeric molding composition is required to 
be flame-retardant to meet the applicable safety codes. 
The present invention provides a route towards flame retardant compositions 
based on styrene/maleic anhydride polymers that also retain good strength 
and molding characteristics. 
While it is known that polyvinyl chloride is resistant to burning, its use 
as a flame retardant additive may be impeded if this requires significant 
sacrifice of other desirable properties such as impact strength. 
DESCRIPTION OF PRIOR ART 
Both styrene/maleic anhydride copolymers and polyvinyl chloride are known 
in the art and U.S. Pat. No. 3,626,033 teaches high heat deformation and 
high impact vinyl chloride molding resins by incorporating therein minor 
amounts of ABS and a styrene/maleic anhydride copolymer. 
DESCRIPTION OF THE INVENTION 
The present invention provides a molding composition comprising: 
A. from 20 to 85% by weight of a uniform polymer comprising 50 to 85% by 
weight of a vinylaromatic monomer, from 15 to 30% by weight of an 
unsaturated dicarboxylic acid anhydride and from 0 to 20% of a 
copolymerizable monomer; 
B. from 15 to 40% by weight of polyvinyl chloride; and 
C. from 0 to 40% by weight of a composition comprising a graft copolymer of 
from 20 to 40% by weight of a monomer selected from the group consisting 
of methyl methacrylate and acrylonitrile and 80 to 60% by weight of a 
vinyl aromatic monomer, said copolymer being grafted on to from 10 to 60% 
of the weight of the composition of a substrate rubber having a glass 
transition temperature below 0.degree. C. 
The presence of Component C is a desirable expedient if the product needs 
to have good strength properties. However its inclusion renders the 
effectiveness of the PVC (Component B) less and in such event to obtain 
very good flame retardant characteristics, an added flame retardant may be 
employed. In such compositions the preferred flame retardants include 
decabromodiphenylether, halogenated (di)methanodibenzocyclooctene adducts, 
halogenated paraffin hydrocarbons, halogenated octadiene-cyclopentadiene 
adducts, tetrabromobisphenol A, tetrabromoxylene, pentabromoethylbenzene, 
tetrabromobisphenol A diacetate, and bis(tribromophenoxy)ethane. In 
general the amount of such additive present can be from 1 to 10% by weight 
of the total composition. 
Component A of the polyblend is conventionally a styrene/maleic anhydride 
copolymer or preferably a terpolymer comprising in addition methyl 
methacrylate. However the styrene component can be replaced in whole or in 
part by other vinylaromatic monomers such as .alpha.-methyl styrene, 
bromostyrene, chlorostyrene, p-methylstyrene and vinyl toluene. Likewise 
the anhydride component can be supplied in whole or in part by itaconic, 
citraconic or aconitic anhydride. The copolymerizable monomer is 
conventionally selected from C.sub.1 to C.sub.3 acrylates and 
methacrylates and unsaturated nitriles. Typically comonomers are methyl 
methacrylate, ethyl acrylate and acrylonitrile. In a preferred terpolymer 
the anhydride provides from 20 to 30% and methyl methacrylate provides 
from 5 to 15% of the Component A polymer weight. 
The polymer has a uniform composition and in practice this implies 
controlled late addition of the anhydride in the manner taught for example 
in U.S. Pat. No. 2,971,939 and 3,336,267. 
Component B of the polyblend is polyvinyl chloride and it is understood 
that this term also is intended to embrace various degrees of halogenation 
of a basic hydrocarbon chain. Thus the term includes halogenated polyvinyl 
chloride and halogenated polyethylene as well as simple polyvinyl chloride 
which is the most common exemplar of such compounds. The preferred 
Component B is a conventional polyvinyl chloride of the kind typically 
sold for molding applications. The proportion of component B actually used 
depends largely on the desired properties of the product. It is however 
found that when Component C is present it is desirable to use from 30 to 
40% by weight of Component B, not only for good flame retardance but also 
because a beneficial effect on the impact properties is revealed. 
Component C is conventionally an ABS or an MBS; that is, a terpolymer of 
acrylonitrile or methyl methacrylate, butadiene and styrene formed by 
polymerizing the other monomers in the presence of a butadiene-based 
rubber. Both these compositions are known to be compatible with both PVC 
and styrene/maleic anhydride copolymers and to function as impact 
improvers to both. 
Component C can however be varied in composition beyond the above 
conventional formulations. Thus the styrene can be replaced in whole or in 
part by monomers such as .alpha.-methylstyrene, chlorostyrene, 
bromostyrene, p-methylstyrene or vinyl toluene and the like. The rubber 
need not be based on butadiene but can be provided by polyisoprene, 
polychloroprene, polypentenamer, EPDM rubbers and acrylate rubbers. The 
rubber can also be a diene-based block or radial block-type rubber. 
The proportion of Component C is determined by the properties of the 
desired product. However where it is used, best results are obtained with 
a proportion no greater than that of Component A. Particular preferred 
polyblends of the invention comprise from 30 to 40% of each of Components 
A and C. 
In addition to the three components A, B and C described above and the 
optional flame retardant additive the compositions of the invention can 
further comprise flame retardant adjuvants such as antimony oxide, 
stabilizers, plasticizers, antioxidants, fillers, mineral fibers, pigments 
and the like in appropriate amounts. 
The components of the polyblend can be blended in any convenient manner but 
the most suitable technique involves the use of a compounder-extruder or a 
banbury mixer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention is now described with reference to the following example 
which is for the purposes of illustration only and is not intended to 
imply any limitation on the essential scope of the invention. 
The components described below were blended in a number of different ratios 
and tested for various properties. 
ABS 1--prepared by the graft emulsion polymerization of acrylonitrile and 
styrene in a weight ratio of 30:70 in the presence of polybutadiene. ABS-1 
contains 40% by weight of polybutadiene. 
ABS 2--prepared by the graft suspension polymerization of acrylonitrile and 
styrene in a weight ratio of 28:72 in the presence of polybutadiene. ABS-2 
contains 14% by weight of polybutadiene. 
S/MA/MM--prepared by polymerizing a monomer mixture of styrene, maleic 
anhydride and methyl methacrylate to produce uniform polymer composition 
in which the above monomers are the weight proportions 68:26:6 
respectively. 
PVC--Rucon B-221 (Hooker Chemical Co.) 
MBS--Acryloid-K 653 (Rohm and Haas Co.) a methylmethacrylate 
butadiene/styrene terpolymer. 
Plasticizers/Flow Aids--Butyl Stearate Acryloid K-175--(Rohm and Haas), an 
acrylic polymer 
Antioxidants/Stabilizer 
Ethanox 330--an alkylated phenol available from Ethyl Corp. 
Mark 1900--a methyl tin mercapto-ester complex available from Argus 
Chemical Co. EXAMPLE 
The components indicated in Table 1 below were formulated and tested for 
their DTUL, (using ASTM D 648.56 on a 12.7 mm.times.12.7 mm cross-section 
sample), and Izod impact (using ASTM method D-256.56) Gardner impact was 
assessed on a 2.54 mm thick sample using a 1.27 cm diameter dart. 
The samples were also tested for flammability using the UL-94 "V" test and 
"HB" test. (1) 
(1) "Materials designated `fire or flame-retardant` generally are more 
difficult to ignite or once ignited, burn at a slower rate than 
corresponding conventional materials. These terms do not mean that 
fire-retardant materials will not burn. However, when properly used, 
Monsanto fire-retardant additives and materials are useful in helping 
customers formulate or construct finished products meeting specified fire 
codes and regulations." 
TABLE 1 
______________________________________ 
FORMULATIONS & PROPERTIES 
Comparative Invention 
______________________________________ 
Polymer 
Components 
C1 C2 C3 1 2 3 4 
(phr) 
ABS-1 38 30.4 22.8 
ABS-2 12 9.6 7.2 
S/MA/MM 100 50 40 30 70 50 
PVC 100 20 40 30 25 
MBS 25 
Stabilizers/ 
Antioxidants 
Ethanox 330 0.3 0.3 0.3 0.3 
Mark 1900 0.8 1.6 1.2 1.2 
Plasticizers 
Butyl 1.0 1.0 
Stearate 
K-175 0.3 1.0 
Properties 
DTUL (.degree.C.) 
69 135 112 105 100 125 105 
Izod 
(J/M notch) 
32 11 150 32 49 39 27 
Gardner (J) 
1.7 .1 8.6 2.3 &gt;24 &lt;.1 .3 
UL Tests 
"HB" ratings 
Pass Fail Pass Marg. Pass Marg. 
Fail Fail 
Dripping No Yes No No No No 
"V" rating 
V-O+ Fail V-2 
Dripping No Yes No 
______________________________________ 
From the data on Table 1 it can be seen that, at the levels of 
reinforcement contemplated, ABS performs somewhat better than MBS. It can 
also be seen that certain formulations are substantially superior to 
others in their strength properties particularly Gardner impact. It is 
considered probable that these represent compositions of significantly 
greater compatibility than other marginally different systems. An example 
of this effect is provided by a comparison of formulations 1 and 2 where 
an enormous increase in Gardner impact is obtained for a relatively minor 
adjustment in the formulation. Moreover although the blend contains 40% 
PVC the DTUL is still 31.degree. C. higher than for PVC alone.