NEWS OF THE WEEK
self-assemble into a layered pattern of “hard” semicrystalline and “soft” amorphous phases, Hustad explains. Each phase has a different refractive index, which enables the polymer films to function as photonic crystals and POLYMER SCIENCE: Unique block scatter visible light. copolymers yield colorful, low-cost Block copolymers have been used to form materials for many applications photonic crystals in the past, Hustad says, but achieving structural features large enough to interact with visible light has proven difficult. OW CHEMICAL scientists have used their Such materials have only been prepared by unique “chain-shuttling” polymerization techusing very high molecular weight copolymers, nique to make polyethylene block copolymers typically up to 1 million g/mol, and maintaining that can self-assemble into materials with ordered uniform (monodisperse) polymer chain lengths, phases that give rise to colorful optical properties (Mac- which requires solution processing that adds romolecules, DOI: 10.1021/ma9002819). Compared with complexity and cost. colloidal crystals and other photonic materials, these The Dow Chemical polydisperse polyolefin photonic polyethylenes could become a low-cost staple diblock copolymers achieve the same effects polymer for a new range of applications, including ener- with an order of magnitude lower molecular gy-efficient building materials that reflect sunlight. weight and without solvent processing. In adIn 2006, a Dow Chemical team identified a pair of dition, the semicrystalline nature of the new catalysts that work in combination to build polyethmaterials allows them to be reversibly switched ylene block copolymers from ethylene and 1-octene from reflective to nonreflective states by heating and (C&EN, May 8, 2006, page 9). The process takes advan- cooling. tage of diethylzinc as a transfer reagent to shuttle the Polymer chemist Marc A. Hillmyer of the University growing polymer chains back and forth between the of Minnesota, Twin Cities, says the Dow Chemical apcatalysts in a continuous reaction that adds alternating proach allows the synthesis of polymers that “simply blocks of ethylene and 1-octene with precise control cannot be prepared by conventional methods.” The reover polymer composition. search is “a nice example of how increased polydispersiNow, Phillip D. Hustad, Jeffrey D. Weinhold, Gary ty can actually be beneficial and lead to new phenomena R. Marchand, Eddy I. Garcia-Meitin, and Patricia L. in certain block copolymer systems,” Hillmyer notes. Roberts at the company’s FreeMIT physicist Edwin L. port, Texas, site have modified Thomas, an expert in photonic the technique to make polypolymers, adds that the Dow y x 1–x 1–y disperse polyethylene diblock Chemical approach “presents a copolymers with a distribution real opportunity to implement C6H13 C6H13 of block lengths. When melted photonic polymers for many and compressed into films, the low-cost applications.”—STEVE Polydisperse diblock copolymer distinct polymeric segments RITTER
DOW CHEMICAL (BOTH)
PHOTONIC POLYETHYLENE
D
Dow Chemical’s diblock copolymers self-assemble into two-phase transparent films that scatter visible light, resulting in an iridescent bluegreen hue in the thin-film example shown.
RESTRUCTURING Celanese throws in towel on PVOH, sells business to Japan’s Sekisui Celanese has agreed to sell its polyvinyl alcohol (PVOH) business to Japan’s Sekisui Chemical for about $173 million. With the sale, Celanese is abandoning a move into derivatives of its core products, while Sekisui tries its hand at making the raw materials it needs. The business, which Celanese owned for nine years, had 2008 sales of $296 million. It includes PVOH facilities in Calvert City, Ky.; Pasadena, Texas; and Tarragona, Spain, and resources in Celanese’s Houston technology center. Water soluble and biodegradable, PVOH is used in applications ranging
from textile sizing to seed coating. PVOH is also a raw material for polyvinyl butyrate, and that’s where Sekisui’s interest lies. The Japanese firm produces polyvinyl butyrate as a raw material for auto safety glass films, a business where it calls itself the world leader. Sekisui says the purchase back-integrates its supply chain, enhances local production capabilities, and permits technological synergies. In contrast, Celanese bought the bulk of the PVOH business from Air Products & Chemicals in 2000 as a forward integration into downstream products. It added the Spanish plant through its 2005 acqui-
WWW.CEN-ONLINE.ORG
11
MAY 4, 2009
sition of Acetex. Polyvinyl alcohol is produced by saponifying polyvinyl acetate, which in turn comes from vinyl acetate. Celanese is a major producer of both vinyl acetate and its raw material, acetic acid. According to Celanese, it will supply Sekisui with vinyl acetate under a longterm supply agreement. The price Celanese is getting shows the extent to which the value of some chemical assets has fallen in recent years. In its deal with Air Products, Celanese paid $326 million for a business with annual sales of less than $200 million.—MICHAEL MCCOY
