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
1999-10-28
2002-08-27
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...
C525S089000, C525S098000, C525S099000
Reexamination Certificate
active
06441090
ABSTRACT:
The present invention relates to rubber modified monovinylidene aromatic polymers, particularly polymers containing two distinct rubber volume average particle sizes, herein referred to as bimodal compositions, and a process for preparing.
Rubber modified monovinylidene aromatic polymers have typically been prepared from vinyl aromatic monomers by polymerizing the vinyl aromatic monomer in the presence of a dissolved rubber. The vinyl aromatic monomer polymerizes, forming a discontinuous phase dispersed throughout a continuous phase of dissolved rubber in monomer. As the vinyl aromatic monomer continues to polymerize, the discontinuous polymer phase becomes larger in volume, thus forming a continuous phase, while the rubber forms a discontinuous phase dispersed throughout. This phenomenon, referred to as “phase inversion”, is, therefore, the conversion of the polymer from a discontinuous phase dispersed in the continuous phase of the rubber/monomer solution, through the point where there is no distinct continuous or discontinuous phase in the polymerization mixture, to a continuous polymer phase having the rubber dispersed throughout.
Various bimodal compositions containing two distinct rubber particle sizes have been produced to attempt to effectively balance and achieve high gloss, while maintaining high impact properties using several types of rubbers. U.S. Pat. No. 4,334,039 issued to Dupree et al. and U.S. Pat. No. 4,153,645 issued to Lanza et al. disclose the use of butadiene rubbers to obtain polymers having a bimodal rubber particle size distribution. Such polymers, while having good toughness, do not have the desired level of gloss. EP-048,389 by Echte discloses the use of styrene/butadiene block copolymer rubbers wherein small particles are made from a 40/60 styrene/butadiene block copolymer and are of core-shell type morphology. While such products have the desired balance of gloss and impact, they are economically disadvantageous because of higher cost due to the use of the block copolymer rubbers. Additionally, higher amounts of block copolymer must be used in order to obtain a given polybutadiene level, additionally increasing cost.
It is well known in the art that the balance of gloss and impact strength of high impact monovinylidene aromatic polymers is dependent on rubber particle size, rubber level and flow properties of the product. Typically, smaller rubber particle containing resins have higher gloss and lower impact, while larger rubber particle containing resins have lower gloss and higher impact. Standard rubbers, usually known as butadiene homopolymer type, cannot be sized small enough to make the desired high gloss products. Block copolymers usually lead to small rubber particles but are more expensive. Other approaches have been used to solve the problem of obtaining small particles using polybutadiene rubbers. EP-277,687 discloses a rubber modified polymer containing radial or branched polybutadiene rubber having volume average diameter of 0.1 to 1.2 microns (&mgr;) and rubber particles containing either radial, branched or linear rubber having a volume average particle diameter of from 1 to 5&mgr;. However, while these compositions have high gloss, they do not have sufficient toughness.
Therefore, there remains a need to produce rubber modified monovinylidene aromatic polymers having gloss and impact properties similar to those products which use block copolymer rubbers, but without the high cost of block copolymer rubbers.
The present invention is a rubber modified monovinylidene aromatic polymer having a bimodal particle size distribution comprising:
a) rubber particles of a star or branched low viscosity rubber having a volume average particle size of from 0.1 to 2&mgr;, and a cellular or core shell morphology or mixture thereof, and
b) rubber particles of a star or branched low viscosity rubber, linear diene rubber or block copolymer rubber having a volume average particle size of from 0.5 to 10&mgr;, characterized in that the rubber particles of b) are more dense than the rubber particles of a), having a smaller occluded monovinylidene aromatic polymer content than the particles of a),
wherein the particles of a) are from 50 to 99 weight percent of the total diene rubber content.
This product has excellent gloss and impact properties. It has the balance of gloss and impact properties of a resin containing block copolymer without the high cost. Such products are highly desirable in replacing higher cost products in injection molding and extrusion applications.
The present invention is related to rubber modified monovinylidene aromatic polymers. The monovinylidene rubber modified polymers are derived from one or more vinyl aromatic monomers. Representative vinyl aromatic monomers include styrene, alkyl substituted styrenes such as alpha-alkyl-styrenes, for example alpha-methylstyrene, alpha-ethylstyrene; ring substituted styrenes, for example vinyltoluene, particularly p-vinyitoluene, o-ethylstyrene and 2,4-dimethylstyrene; ring substituted halostyrenes such as chlorostyrene, and 2,4-dichloro-styrene; styrene substituted with both halo and alkyl groups, such as 2-chloro-4methylstyrene, vinyl anthracene; and mixtures thereof. Preferably styrene and/or alpha-methyl-styrene is used as the vinyl aromatic monomer, with styrene being most preferred.
Comonomers may also be used in combination with the vinyl aromatic monomer, preferably in an amount of up to 40 percent by weight of the polymerizable monomer mixture. Representative comonomers include unsaturated nitriles, such as acrylonitrile; alkyl acrylates and alkyl methacrylates such as methyl methacrylate or n-butylacrylate; ethylenically unsaturated carboxylic acids; and ethylenically unsaturated carboxylic acid derivatives including anhydrides and imides, such as maleic anhydride and N-phenyl maleimide.
The rubber suitable for use to produce rubber particles having a volume average particles size of from 0.1 to 2&mgr; as recited in a), is a low viscosity rubber having a solution viscosity (5 percent in styrene at 20° C.) in the range 20 to 120 centipoise (cps) and a Mooney viscosity (ML+1, 100° C.) of 30 to 80. Suitable rubbers include both so-called radial or star rubbers having three or more polymer segments bonded to a single polyfunctional element or compound, or a branched rubber having a cis content of less than 75 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. Such rubbers useful in a), 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 cps.
The radial or branched rubber preferably employed in a) of the present invention typically exhibits a second order transition temperature not higher than 0° C., and preferably not higher than −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.
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. Felters.
Radial or star polymers, commonly referred to as polymers having designed branching, are conventionally prepared using a polyfun
Black Steven M.
Demirors Mehmet
Schrader David
Mullis Jeffrey
The Dow Chemical Company
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