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Crosslinked Polyethylene

U.S. Patent 8,680,173 (March 25, 2014), “Sequentially Cross-Linked Polyethylene,” Aiguo Wang, John H. Dumbleton, Aaron Essner, and Shi-Shen Yau (Howmedica Osteonics Corporation, Mahwah, New Jersey, USA).

Radiation-induced crosslinking improves the properties of ultra-high molecular-weight polyethylene (UHMWPE) prostheses. However, after this process, some free radicals persist, reacting with oxygen and other reactive chemicals, degrading properties such as wear and oxidation resistance.

Wang et al. produced an improved polyethylene, especially UHMWPE materials, by a sequence of irradiation steps with low doses and annealing, resulting in minimal free-radical residue. The process may be applied either to a pre-formed material, such as a rod, bar, or sheet, or to a finished part. This process does not use stabilizers, antioxidants, or any other chemical which may have adverse effects in their orthopedic applications. For each stage, doses range from 5 to 10 Mrads, with 110-135°C annealing for four hours.

Functionalized Polymers

U.S. Patent 8,680,210 (March 25, 2014), “Method for Making Functionalized Polymer,” Yuan-Yong Yan (Bridgestone Corporation, Tokyo, Japan).

In crosslinked rubber such as a tire rubber, the loose polymer chain ends from the crosslinked network are major sources of hysteretic losses, shortening the elastomer’s lifetime. Yan developed a crosslinked elastomer with terminal groups that can attach to filler particles, thus eliminating hysteric losses. These groups include ring-opened cyclosilazanes and cyclic hydrosiloxanes. The loose chains have unsaturated mer units which react with these groups by anionic polymerization. The attached groups interact with filler particles such as carbon black and silica, immobilizing the loose chains.

Silicone Cosmetics

U.S. Patent 8,680,304 (March 25, 2014), “Polyglycerol Silicone Polyesters,” Thomas George O’Lenick (Surfatech Corporation, Lawrenceville, Georgia, USA).

Polyglycerol polyesters are “high-definition polymers” in that their properties can be varied by changing the ratio of fatty groups and crosslinking agent. O’Lenick developed a series of polyglycerol silicone polyesters with tunable cosmetic properties. These silicone polyesters are prepared by the reaction of a mixture of fatty acids, polyglycerol, and a silicone succinate. One particular structure enables efficient deposition on skin, hair, and fibers. In a sunscreen, such a structure provides excellent water-proofing and a “dry skin” feel.

Synthetic Delivery Agents

U.S. Patent 8,685,368 (April 1, 2014), “Polyamides for Nucleic Acid Delivery,” Theresa M. Reineke (Blacksburg, Virginia, USA). 

Nucleic acids show great promise to treat both acquired and inherited diseases. However, effective delivery with viral particles, without inducing immune and inflammatory responses, remains a problem.

Synthetic polymer-mediated gene delivery shows promise by not inducing these responses. They also are cheaper, with a large nucleic acid-loading capacity. Reineke developed a gene transfer vector based on synthetic polymers with an efficiency comparable to a viral vector, without the potential for life-threatening immune responses. These molecules form complexes with nucleic acid, enabling delivery into cells. These carriers include polyamides, dendritic macromolecules, and carbohydrate-
containing degradable polyesters.

Sensitive Surfaces

U.S. Patent 8,691,362 (April 8, 2014), “Surfaces Physically Transformable by Environmental Changes,” Joanna Aizenberg, Thomas N. Krupenkin, Oleksandr Sydorenko, and Joseph Ashley Taylor (Alcatel Lucent, Paris, France).

Protruding nanostructures on a surface can make it superhydrophobic. Aizenberg et al. developed a material with a regular array of raised structures on an environmentally sensitive layer on the surface. These structures rise or fall depending on the environment because of swelling or contraction of the supporting layer. The supporting layer is a hydrogel sensitive to humidity, temperature, light, or liquids. In addition, these hydrogels can be sensitive to organic solvents, hydronium, and hydroxide ions or selected metal ions such as copper, nickel, cobalt, or palladium ions.

Foam Implants

U.S. Patent 8,691,259 (April 8, 2014), “Reinforced Foam Implants with Enhanced Integrity for Soft Tissue Repair and Regeneration,” Steven M. Bowman, Izi Bruker, Alireza Rezania, Mora Carolynne Melican, Francois Binette, and Julia Hwang (DePuy Mitek, LLC, Raynham, Massachusetts, USA).

Injuries to tissues such as cartilage, muscle, bone, and tendons often require surgery. These repairs can be aided with biocompatible tissue implants. However, biologically derived materials can transmit disease, while synthetic materials are difficult to manufacture.

Bowman et al. developed a biocompatible tissue repair implant (or “scaffold”) for ligaments, tendons, and nerves. Such implants are especially useful in surgical repair of injuries to ligament, tendon, and nerve tissue in the hand and foot. These implants consist of a bio-absorbable polymeric foam with an open-cell pore structure reinforced with a biodegradable mesh. A suitable pore size is 150 to 500 microns. The polymers include aliphatic polyesters reinforced with bio-absorbable, biocompatible elastomers such as ε-caprolactone and glycolide copolymers reinforced with a polydioxanone mesh.

Light-Emitting Polymers

U.S. Patent 8,697,982 (April 15, 2014), “Light-Emitting Polymer,” James W. Smith, and Bruce McKague (LEP America, Incorporated, Bloomfield Hills, Michigan, USA).

Light-emitting materials are used for self-illuminated signs and nuclear batteries. One example consists of polystyrene labeled with tritium that emits beta particles. The polymer is doped with a phosphor, emitting visible light when irradiated by the beta particles from the tritium. Instability because of phosphor diffusion is a problem for these systems.

Smith and McKague developed a stable radiation-emitting material based on a silicone with tritium and a wavelength-shifter side chain (phosphor) bonded to the silicone. The wavelength-shifter contains a cyclic, aromatic group emitting light in response to the tritium beta particles. The wave shifter content is 0.015 g per gram of silicone.

High-Temperature Crosslinking

U.S. Patent 8,697,823 (April 15, 2014), “Catalysis of Cross-Linking,” Jan-Erik Rosenberg, Erik Lager, Daniel Rome, and David Persson (Nexam Chemical AB, Lund, Sweden).

Polymers are replacing metals in many applications because of reduced weight and processability. However, polymers have lower mechanical strength and are less heat-resistant than metals.

Polyimides are heat-resistant, but they are difficult to process. Crosslinking improves both mechanical properties and heat resistance. Polyimide oligomers and low molecular-weight polyimides are easy to process, and the final crosslinking develops adequate stiffness and strength. However, such thermoset polyimides will not withstand oxidative degradation over long-term exposure at temperatures above 200°C because of inferior stability of the crosslinking groups.

Rosenberg et al. developed catalysts for chain extension and/or crosslinking of oligomers or polymers based on carbon-carbon triple bonds, such as phenylethynyl-terminated imide oligomers. However, these agents require 350°C for reaction. This curing temperature is lowered with crosslinking catalysts such as cyclic aliphatic tertiary amine and a heteroaryl or a tertiary nucleophilic organophosphorus compound.

Slippery Polycarbonates

U.S. Patent 8,697,796 (April 15, 2014), “Slidable Resin Composition and Molded Article thereof,” Ryusuke Ikematsu (Teijin Chemicals, Ltd., Tokyo, Japan).

Since aromatic polycarbonate resins have many excellent characteristics, they are processed into various products by injection molding for a wide variety of applications. Aromatic PC resins have excellent dimensional accuracy, mechanical strength, and heat resistance, so they are increasingly used in sliding members such as gears. However, when the PC resins are used alone, their slidability is unsatisfactory.

Ikematsu improved slidability by adding to PC, at three to seven parts per hundred by weight, a silicone with grafted methacrylic ester and another unsaturated monomer.

Renewable Plasticizers

U.S. Patent 8,697,787 (April 15, 2014), “Flexible PVC Compositions Made with Plasticizers derived from Renewable Sources,” Bharat I. Chaudhary (Dow Global Technologies LLC, Midland, Michigan, USA).

Flexible polyvinyl chloride (PVC) materials require substantial amounts of plasticizers, such as phthalic acid diesters. Phthalate plasticizers have some negative environmental and potential adverse health effects.

Chaudhary developed effective biochemical plasticizers for PVC materials composed of PVC resins, compatibilizers, biochemical plasticizers, and, optionally, a thermoplastic elastomer impact modifier. Epoxidized vegetable oils, such as epoxidized soybean oil and epoxidized linseed oil, are candidate biochemical plasticizers. 

Microcellular Injection Molding

U.S. Patent 8,696,957 (April 15, 2014), “Methods for Microcellular Injection Molding,” Eugene P. Dougherty, Jr., Keith Edgett, Lih-Sheng Turng, Chris Lacey, Jungjoo Lee, Patrick J. Gorton, and Xiaofei Sun (Eveready Battery Company, Inc., St. Louis, Missouri, USA).

It’s difficult to injection mold microcellular foams with good surface quality. Undesirable surface features include swirling patterns or gritty textures.

Dougherty, Jr., et al. developed a method of microcellular injection molding a polymer with a supercritical fluid such as nitrogen or carbon dioxide. The resulting mix is a single-phase polymer/supercritical fluid which is injected into a mold. After injection, a pressure drop causes the supercritical fluid to nucleate in the melted polymer, forming micro-bubbles. The surface appearance for the produced parts, exhibiting a weight reduction of about 7% with low supercritical fluid concentrations, is more desirable than that observed for solid (i.e., unfoamed) parts. The surface irregularities are minimal and there are no observable swirling patterns.

Microspheres with Holes

U.S. Patent 8,696,955 (April 15, 2014), “Method of Making Polymer Hollow Particles with Controllable Holes in their Surfaces,” Younan Xia, Sang Hyuk Im, and Unyong Jeong (University of Washington, Seattle, Washington, USA).

Colloidal particles with hollow interiors can be used for micro- encapsulation. This has found widespread use in applications such as controlled release of drugs, cosmetics, inks, pigments, or chemical reagents; protection of biologically active species; and removal of pollutants. However, diffusion through these closed shells with pores less than 10 nm in diameter is very slow.

Xia, Im, and Jeong produced hollow 400-1000 nm colloidal particles with circular holes by suspending polymer particles in a solvent, swelling the particles with a second immiscible solvent, freezing the second solvent, and warming the particles to allow the incased solvent to liquefy and escape, thus forming the hole in the colloidal particle.