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(12) United States Patent
Zheng et al.
(io) Patent No.: (45) Date of Patent:
US 7,812,092 B2 Oct. 12, 2010
HAIRY POLYMERIC NANOPARTICLES
Inventors: Lei Zheng, Apex, NC (US); Eric Sean
Castner, Uniontown, OH (US); Thierry
Florent Edme Materne, Lasne (BE)
Assignee: The Goodyear Tire & Rubber
Company, Akron, OH (US)
Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 351 days.
Filed: Jun. 10, 2008
Prior Publication Data
US 2008/0242813 Al Oct. 2, 2008
Related U.S. Application Data
Division of application No. 11/072,986, filed on Mar. 5, 2005, now Pat. No. 7,408,005.
C08F 279/02 (2006.01)
U.S. CI 525/70; 525/86; 525/87;
525/243; 525/271; 525/326.1; 525/331.9;
Field of Classification Search 525/70,
525/86, 87, 243, 271, 326.1, 331.9, 332.2,
See application file for complete search history.
U.S. PATENT DOCUMENTS
4,695,607 A 9/1987 Spinelli 525/272
5,395,891 A 3/1995 Obrecht et al 525/194
5,585,441 A 12/1996 Brandes et al 525/193
6,127,488 A 10/2000 Obrecht et al 525/333.3
6,133,364 A 10/2000 Obrecht et al 524/495
6,207,757 Bl 3/2001 Obrecht et al 525/194
6,242,534 Bl 6/2001 Obrecht et al 525/194
6,437,050 Bl 8/2002 Konno et al 525/313
6,653,404 B2 11/2003 Konno et al 525/84
6,747,095 B2 6/2004 Konno et al 525/89
6,777,500 B2 8/2004 Leanetal 525/316
6,956,084 B2 10/2005 Wangetal 428/401
7,344,752 B2 3/2008 Zheng et al 427/213.3
2003/0198810 Al 10/2003 Wangetal 428/401
2006/0114150 Al 6/2006 Van Diggelen 342/357.02
Bi and Fetters, "Synthesis and Properties of Block Copolymers 3.
Polystyrene Polythene Star Block Copolymers" Macromolecules,
vol. 9, Issue 5, pp. 732-742 (1976).
Szakacs et al., STN AN 1978: 191563 (1984).
File Registry of STN, entry for RN501-60-0 (1984), no author.
Primary Examiner—Jeffrey C Mullis
(74) Attorney, Agent, or Firm—Alvin T. Rockhill
This invention discloses a process for synthesizing a hairy polymer particle which comprises the steps of (1) polymerizing a vinyl aromatic monomer by emulsion polymerization in an aqueous medium to produce core particles, (2) recovering the core particles from the aqueous medium, (3) dispersing the core particles in an organic solvent, (4) adding an organo-lifhium compound to the dried core particles in the organic solvent to produce the hairless core initiator, and (5) utilizing the hairless core initiator to initiate the anionic polymerization of a conjugated diolefin monomer in an organic solvent to produce a solution of the hairy polymer particles. The hairy polymer nanoparticles can then be recovered from the organic solvent. These hairy polymer particles are comprised of (1) a core which is comprised of a polymer of a vinyl aromatic monomer and (2) hairs which are polymer chains of a conjugated diolefin monomer, wherein the hairs are covalently bonded to the core. The core is typically spherical in shape, has a diameter of less than 1000 nm, and is comprised of a crosslinked polymer of a vinyl aromatic monomer. The hairy polymer particles of this invention are useful as fillers in rubber compositions used in making articles of manufacture, such as tires, hoses, power transmission belts, windshield wiper blades, and the like.
20 Claims, 2 Drawing Sheets
HAIRY POLYMERIC NANOPARTICLES
This application is a divisional of U.S. patent application Ser. No. 11/072,986, filed on Mar. 5, 2005, which claims the benefit of U.S. Provisional Patent Application Ser. No. 5 60/552,617, filed on Mar. 12, 2004. The teachings of U.S. patent application Ser. No. 11/072,986 and U.S. Provisional Patent Application Ser. No. 60/552,617 are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
Particles of various types are commonly incorporated into rubber compositions as fillers. For instance fillers are typically included in the rubber compositions utilized in manu- 15 factoring tires, hoses, belts, windshield wiper blades, floor mats, and other rubber products. The fillers are chosen to enhance certain physical characteristics of the rubber composition. The use of carbon black, silica, and crosslinked polymers as fillers, is well known in the art of rubber com- 20 pounding. The addition of fillers tends to improve the physical properties of the polymer matrices to which they are added. Some specific physical properties that are improved by the addition of fillers are tensile strength and abrasion resistance. For instance, the inclusion of fillers in tire tread 25 rubber compounds is critical to attain required strength and tread wear characteristics.
The use of rigid polymer particles to enhance the properties of rubbery materials has been explored by numerous researchers. Early work by Kraus et al, "Dynamic Properties 30 of a Model Reinforced Elastomer. Styrene-Butadiene Reinforced with Polystyrene" in Macromolecules, Vol. 3, Issue 1, pages 92-96 (1970) studied the properties of 40 nm polystyrene particles reinforced SBR rubber. Morton et al also examined similar systems in the article titled "Mechanism of Rein- 35 forcement of Elastomers by Polymeric Fillers" in Advanced Chemistry Series, No. 99, pages 490-509 (1971). Recently, Cai et al reported in the Journal of Materials Science, 34, pages 4719-4726 (1999) that crosslinked polystyrene particles in polysulfide rubber gave improved modulus, fracture 40 strength and elongation at break. However, in all these studies, the particles had limited interaction at the interface between the particles and matrix which resulted in physical properties that were only marginally improved.
U.S. Pat. No. 5,395,891 and U.S. Pat. No. 6,127,488 to 45 Obrecht disclose the use of crosslinked polybutadiene and crosslinked styrene-butadiene copolymers, respectively, as fillers. The purported benefits of the inclusion of these crosslinked rubber particles in rubber formulations is lower hysteresis while the polybutadiene gels also impart improved 50 abrasion resistance and styrene-butadiene copolymer gels offer improve wet traction characteristics. U.S. Pat. No. 6,133,364, U.S. Pat. No. 6,207,757, and U.S. Pat. No. 6,242, 534 to Obrecht et al disclose a rubber composition comprising a crosslinked elastomer particle and a non-crosslinked 55 elastomer. The crosslinked elastomeric particles are functionalized to impart unique surface reactivity for improved coupling with the non-crosslinked host elastomer as well as the subsequent ability to employ coupling agents other than the conventional sulfur-bridged bis-alkoxy silanes. The benefits 60 of these gels in tire tread compositions are reported to be lower hysteresis, improved abrasionresistance, andimproved wet traction.
U.S. Pat. No. 6,747,095 and U.S. Pat. No. 6,653,404 to Konno et al disclose a rubber composition comprising as 65 essential components a crosslinked polymer particle and a non-crosslinked rubber component. The rubber composition
may be used to obtain a vulcanized rubber. The crosslinked polymer particles are intended for use as filler to provide a rubber composition having good processability and handling performance as well as improved tensile strength and wear resistance when vulcanized. However, it has been found that the particles disclosed in the Konno et al. application tend to soften at higher service temperatures. The effectiveness of the particles as reinforcing fillers is therefore decreased.
U.S. Pat. No. 6,437,050 to Krom et al disclosed a polymer nanoparticle composition wherein the core is a poly(alkenylbenzene) and the surface layer includes a poly(conjugated diene). The particle is a star polymer with all the diblock copolymer chains attached to one crosslinking center. An article from Fetter and Bi titled "Synthesis and Properties of Block Copolymers 3. Polystyrene Poly diene Star Block Copolymers" in Macromolecules, Vol. 9, Issue 5, pages 732742 (1976) also studied and reported on the identical system. These particles do not have well-defined center particles. The polystyrene domains are formed from phase separation of diblock copolymers. It lacks dimension stability at higher service temperature above the glass transition temperature of polystyrene.
Nanoparticles are currently receiving significant interest as fillers in rubber compositions. Such combinations often provide dimensions and physical properties that differ from those of the bulk material. The use of nanoparticles as fillers is thought to be advantageous because the discrete particles may be more easily and better dispersed in the polymer matrix. The higher surface to volume ratio of the nanoparticles provides a better opportunity for chemical and physical interactions with the polymer matrix.
SUMMARY OF THE INVENTION
The present invention is the result of the discovery that polymer brushes(hairs) on a polymer particle can be prepared by an anionic polymerization technique from aromatic vinyl monomers and conjugated diene monomers, and the resulting polymer nanoparticles provide a controlled structure, size, and morphology which are very useful, for example, as fillers to enhance the properties of elastomeric polymers. The brushes on the particles can be used to control interface properties and to make the particles compatible or incompatible with a rubber matrix. For example, if the hairs are miscible with the polymer matrix, or host polymer, the particles can be ultimately dispersed. If the brushes are incompatible with the matrix, the particles can aggregate and form higher ordered structure. The ability to change the structures of a particle dispersion from point fillers to aggregated structures systematically through modification of hairs (brushes) can be advantageous in attaining desired mechanical properties.
The particle centers and the brushes can be varied depending upon the desired properties and use of the hairy polymer particles. The particle centers and brushes can be a soft or hard polymeric composition. The brushes are grafted to the center particles through covalent bonds. The volume fraction and grafting density of the brushes can be varied depending upon the desired final properties of the hairy particles. The brush composition can be chosen to provide compatibility or incompatibility with the matrix composition. The particle centers can comprise a crosslinkedparticle center where it has a predetermined glass transition temperature (T ) such that the crosslinked polymer particle does not soften at service temperatures up to about 150° C.
The particle centers are synthesized by emulsion polymerization which can be a batch, semi-batch, or continuous process, but which provides excellent control of the polymer