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(i9) United States
(12) Patent Application Publication oo) Pub. No.: US 2007/0185273 Al
Wang et al. (43) Pub. Date: Aug. 9,2007
(54) POLYMERIC NANO-PARTICLES OF FLOWER-LIKE STRUCTURE AND APPLICATIONS
(76) Inventors: Xiaorong Wang, Hudson, OH (US);
Yoichi Ozawa, Tokyo (JP); James E.
Hall, Mogadore, OH (US)
Chief Intellectual Property Counsel
Bridgestone Americas Holding, Inc.
1200 Firestone Parkway
Akron, OH 44317-0001 (US)
(21) Appl. No.: 11/697,801
(22) Filed: Apr. 9, 2007
Related U.S. Application Data
(63) Continuation of application No. 10/755,648, filed on Jan. 12, 2004, now Pat. No. 7,205,370.
(51) Int. CI.
C08F 297/02 (2006.01)
(52) U.S. CI 525/242
A flower-like nano-particle composition including a poly (alkenylbenzene) core and a poly (conjugated diene) or a poly(alkylene) surface layer is provided. The nano-particles have a mean average diameter less than about 100 nm and are substantially free of chain ends. The nano-particles can be modified via, for example, hydrogenation. The nanoparticles can advantageously be incorporated into rubbers, elastomers, and thermoplastics.
Patent Application Publication Aug. 9, 2007 Sheet 1 of 2 US 2007/0185273 Al
Patent Application Publication Aug. 9, 2007 Sheet 2 of 2
POLYMERIC NANO-PARTICLES OF FLOWER-LIKE STRUCTURE AND APPLICATIONS
BACKGROUND OF THE INVENTION
 The present invention relates to flower-like polymer nano-particles, methods for their preparation, and their use as, for example, additives for rubber, including natural and synthetic elastomers. The invention advantageously provides several mechanisms for surface modifications and general characteristic tailoring to improve performance in rubbers, elastomers, and thermoplastics.
 Polymer nano-particles have attracted increased attention over the past several years in a variety of fields including catalysis, combinatorial chemistry, protein supports, magnets, and photonic crystals. Similarly, vinyl aromatic (e.g. polystyrene) microparticles have been prepared for uses as a reference standard in the calibration of various instruments, in medical research and in medical diagnostic tests. Such polystyrene microparticles have been prepared by anionic dispersion polymerization and emulsion polymerization.
 Nano-particles can be discrete particles uniformly dispersed throughout a host composition. Nano-particles preferably are monodisperse in size and uniform in shape. However, controlling the size of nano-particles during polymerization and/or the surface characteristics of such nanoparticles can be difficult. Traditional spherical nano-particles may have a high number of chain ends in the individual nano-particles. It has been theorized that these chain ends may alter the hysteresis values of rubber compositions modified with nano-particles. Accordingly, achieving better control over the surface composition, i.e., decreasing the number of polymer chain ends in the nano-particle surface layers, of such polymer nano-particles also is desirable.
 Rubbers may be advantageously modified by the addition of various polymer compositions. The physical properties of rubber moldability and tenacity are often improved through such modifications. Of course, however, the simple indiscriminate addition of nano-particles to rubber is likely to cause degradation of the matrix material, i.e., the rubber, characteristics. Moreover, it is expected that primarily the selection of nano-particles having suitable size, material composition, and surface chemistry, etc., will improve the matrix characteristics.
 In this regard, development of nano-particles having a surface layer with fewer chain ends, which would be compatible with a wide variety of matrix materials, is desirable because discrete particles could likely disperse evenly throughout the host to provide a uniform matrix composition. However, the development of a process capable of reliably producing acceptable nano-particles has been a challenging endeavor. For example, the solubility of various monomers in traditional alkane solvents has made solution polymerization a difficult process by which to achieve nano-particles having a variety of surface layers. Moreover, the development of a solution polymerization process producing reliable nano-particles, particularly nanoparticles advantageously employed in rubber compositions, has been elusive.
SUMMARY OF THE INVENTION  A flower-like nano-particle composition including a poly (alkenylbenzene) core and a poly (conjugated diene)
surface layer is provided. The nano-particles have a mean average diameter less than about 100 nm and substantially no free chain ends within the nano-particle, A flower-like nano-particle composition including polyalkylene is provided. The nano-particles include a poly(alkenylbenzene) core, and a polyalkylene surface layer including at least one alkylene monomer unit. The nano-particles have a mean average diameter less than about 100 nm, and are substantially free of chain ends within the nano-particles.
 A process for forming flower-like polymer nanoparticles is also provided. The particles may be formed by first initiating a conjugated diene polymerization in a hydrocarbon solvent with a divalent anionic initiator to form a living anionic polymerization with two living ends. Alkenylbenzene monomer may then be added and reacted with the living chain ends to form triblock polymer chains with living alkenylbenzene chain ends. A polymerization mixture including micelles of the triblock polymer is then formed, with living alkenylbenzene chain ends substantially located in an interior of the micelles. At least one crosslinking agent is then added to the polymerization mixture to form crosslinked, flower-like nano-particles from the micelles. The nano-particles having a flower-like structure therefore include an alkenylbenzene core and a conjugated diene surface. The poly(conjugated diene) layer is optionally hydrogenated to form nano-particles containing a poly(alkenylbenzene) core and a polycrystalline outer layer.
 According to an additional embodiment, a soft gel composition including a thermoplastic elastomer, flowerlike nano-particles, and an extender is provided. The composition is useful in producing molded products having heat resistance, high elasticity, excellent damping and super soft properties. A process for forming the nano-particles containing soft gel composition is also provided.
 According to a further embodiment, a rubber composition including an elastomer, flower-like nano-particles, carbon black filler and a curing agent is provided. Such compositions can be useful in producing tread rubber, side walls, and other similar materials. A process for forming the rubber composition is also provided.
 A silica rubber composition including an elastomer, flower-like nano-particles, silica and a curing agent having low shrinkage properties is provided. A process for preparing the silica rubber compound is similarly provided.
 A rubber compound composition for engine mount usage is provided. Such a compound demonstrates relatively high hysterisis, good tensile strength, strong resistance to creep, and high temperature resistance. A process of making the rubber compound for engine mount applications is similarly provided.
 A soft compound for HDD gaskets having excellent adhesion properties is provided. A process for making a soft compound for HDD gaskets is also provided.
 Herein throughout, unless specifically stated otherwise:
 "vinyl-substituted aromatic hydrocarbon" and "alkenylbenzene" are used interchangeably; and
 "rubber" refers to rubber compounds, including natural rubber, and synthetic elastomers including sty