Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-11-24
2002-02-26
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S098000, C525S099000
Reexamination Certificate
active
06350813
ABSTRACT:
BACKGROUND OF THE INVENTION
The process of the present invention relates to high impact rubber modified monovinylidene aromatic polymers.
Past research has focused on the production of high impact modified monovinylidene aromatic polymers, having a good balance of gloss and impact properties. Various rubbers have been used, such as block copolymer rubbers, in order to increase the impact strength without sacrificing the gloss of the final molded product. However, the use of block rubbers significantly increases the cost of production. Additionally, star branched rubbers have also been used, however the desired balance of gloss and impact strength is not obtained. U.S. Pat. No. 5,708,081 discloses a high impact vinyl aromatic polymer obtained by virtue of two polybutadienes, wherein one has a high viscosity and cis 1,4 structure of greater than 80 percent, while the other has a low viscosity and cis 1,4 structure of less than 80 percent. However, this composition also does not obtain the desired balance of gloss and impact properties.
Therefore, there still remains a need for a cost effective solution to the problem of obtaining increased gloss of an impact modified monovinylidene aromatic polymer, while maintaining high impact properties.
SUMMARY OF THE INVENTION
The present invention is a rubber modified monovinylidene aromatic polymer composition comprising:
I) a matrix comprising a monovinylidene aromatic polymer, and
II) a rubber, in the form of discrete dispersed rubber particles, dispersed within the matrix, wherein the rubber comprises:
a) from 75 to 25 weight percent of a star branched diene rubber, having a cis 1,4 structure content of less than 75 weight percent; and
b) from 25 to 75 weight percent of a linear diene rubber, having a cis 1,4 structure content of less than 50 weight percent.
This composition has been found to have increased gloss, while maintaining excellent impact properties, in comparison to other compositions containing a low cis star branched diene rubber.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Monovinylidene aromatic polymers suitable for use as the matrix in the composition of the present invention are those produced by polymerizing a vinyl aromatic monomer. Vinyl aromatic monomers include, but are not limited to those described in U.S. Pat. Nos. 4,666,987, 4,572,819 and 4,585,825, which are herein incorporated by reference. Preferably, the monomer is of the formula:
wherein R is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl substituted phenyl group, with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include: styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene and the like, and mixtures thereof. The vinyl aromatic monomers may also be combined with other copolymerizable monomers. Examples of such monomers include, but are not limited to acrylic monomers such as acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, acrylic acid, and methyl acrylate; maleimide, phenylmaleimide, and maleic anhydride. The polymerization of the vinyl aromatic monomer is conducted in the presence of predissolved elastomer to prepare impact modified, or grafted rubber containing products, examples of which are described in U.S. Pat. Nos. 3,123,655, 3,346,520, 3,639,522, and 4,409,369, which are incorporated by reference herein.
The rubber present in the composition of the present invention is in the form of discrete, dispersed rubber particles comprised of a) a star branched diene rubber having a cis 1,4 structure content of less than 75 weight percent, and b) a linear diene rubber, having a cis 1,4 structure content of less than 50 weight percent. It has been surprisingly discovered that a blend of such rubbers will perform as well or better than compositions wherein the star branched rubber is used alone. The star branched rubber of a) is a low viscosity rubber having a solution viscosity (5% in styrene at 20 C.) in the range of 20 to 120 centipoise (cps), preferably 25 to 100, more preferably 25 to 60 and most preferably 30 to 50, and a Mooney viscosity (ML4, 100 C.) of 30 to 80, preferably 35 to 75, more preferably 35 to 60 and most preferably 50 to 60. Suitable rubbers include radial or star branched rubbers having three or more polymer segments bonded to a single polyfunctional element or compound, and branched rubbers having a cis 1,4 structure content of less than 75 weight percent and at least one, or a significant number of subordinate chains of sufficient length such that the viscosity of the rubber is less than the viscosity of a linear polymer of the same monomeric components and same molecular weight. These rubbers typically have a relatively high average molecular weight, a relatively low solution viscosity and a medium to high Mooney viscosity. In general, the solution viscosity for the rubber will be below 120 cps, while the Mooney viscosity will be less than 80.
The radial or star branched rubber preferably employed in the present invention, typically exhibits a second order transition temperature not higher than about 0 C., and preferably not higher than about −20 C. Suitable rubbers include alkadienes which include 1,3-conjugated dienes such as butadiene, isoprene, chloroprene or piperylene. Most preferred are homopolymers prepared from 1,3-conjugated dienes, with homopolymers of 1,3-butadiene being especially preferred. Alkadiene copolymer rubbers containing small amounts, for example up to 10 or 15 weight percent, of other monomers such as vinyl aromatics can also be employed if the rubbers meet the other qualifications described herein.
Rubbery polymers having random branching, as well as methods for their preparation, are known in the art and reference is made thereto for the purpose of this invention. Representative branched rubbers and methods for their preparation are described in Great Britain Patent No. 1,130,485 and in
Macromolecules,
Vol. II, No. 5, pg. 8, by R. N. Young and C. J. Fetters.
Radial or star branched polymers, commonly referred to as polymers having designed branching, are conventionally prepared using a polyfunctional coupling agent or a polyfunctional initiator. Methods for preparing star branched or radial polymers having designed branching are well-known in the art. Methods for preparing a polymer of butadiene using a coupling agent are illustrated in U.S. Pat. Nos. 4,183,877; 4,340,690; 4,340,691 and 3,668,162, whereas methods for preparing a polymer of butadiene using a polyfunctional initiator are described in U.S. Pat. Nos. 4,182,818; 4,264,749; 3,668,263 and 3,787,510, all of which are herein incorporated by reference.
As known by those skilled in the art, various techniques such as control of the branching and molecular weight control can be used to adjust and tailor these polymers to achieve the necessary solution and Mooney viscosities, as well as the ratio of these two.
The linear diene rubber of b) can be any linear diene rubbery polymer having a cis 1,4 structure content of less than 50, preferably less than 45, and more preferably less than 40 weight percent. Preferred rubbery polymers include a homopolymer or copolymer of an alkadiene or a ethylene-propylene copolymer optionally containing a non-conjugated diene. More preferably, the rubber is a homopolymer of a 1,3-conjugated diene such as butadiene, isoprene, piperylene, chloroprene and the like, or a copolymer of a conjugated diene with one or more vinyl aromatic monomers such as styrene; alpha, beta-ethylenically unsaturated nitrites such as acrylonitrile; alpha-olefins such as ethylene or propylene, and the like. Most preferred rubbers are homopolymers of 1,3-butadiene and block
Black Steven M.
Schrader David
Mullis Jeffrey
The Dow Chemical Company
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