Shape-memory polymers (SMPs) have attracted significant attention from both industrial and academic researchers due to their useful and fascinating functionality. This review thoroughly examines progress in shape-memory polymers, including the very recent past, achieved by numerous groups around the world and our own research group. Considering all of the shape-memory polymers reviewed, we identify a classification scheme wherein nearly all SMPs may be associated with one of four classes in accordance with their shape fixing and recovering mechanisms and as dictated by macromolecular details. We discuss how the described shape-memory polymers show great potential for diverse applications, including in the medical arena, sensors, and actuators.

http://research.vuse.vanderbilt.edu/srdesign/2009/group8/Papers/shape%20memory%20polymers%20review%20article.pdf

Review of progress in shape-memory polymers

Shape-memory polymers and their composites: Stimulus methods and applications

Because of the tremendous effort of a great number of researchers, the catalytic asymmetric dialkylzinc addition to aldehydes has become a mature method. Ligands of diverse structures have been obtained, and high enantioselectivity for all different types of aldehydes have been achieved. Among the representative excellent catalysts are compounds 1, 8, 120, 325, 352, and 360 discussed above. However, compared to the well-developed dialkylzinc addition, the catalytic asymmetric reactions of aryl-, vinyl-, and alkynylzinc reagents with aldehydes are still very much under developed. Although catalysts such as (S)-402 and 210 prepared by Pu and Bolm have shown good enantioselectivity for the reaction of diphenylzinc with certain aromatic and aliphatic aldehydes, the generality of these catalysts for other [formula: see text] arylzinc reagents have not been studied. The vinylzinc additions using ligands 1 and 412 reported by Oppolzer and Wipf were highly enantioselective for certain aromatic aldehydes but not as good for aliphatic aldehydes. Carreira discovered highly enantioselective alkynylzinc additions to aldehydes promoted by the chiral amino alcohol 415, but this process was not catalytic yet. Ishizaki achieved good enantioselectivity for the catalytic alkynylzinc addition to certain aldehydes by using compounds 160, but the enantioselectivity for simple linear aliphatic aldehydes was low. Another much less explored area is the organozinc addition to ketones. Yus and Fu showed very promising results by using ligands 381 and 406 for both dialkylzinc and diphenylzinc additions to ketones, but the scope of these reactions were still very limited. Therefore, more work is needed for the aryl-, vinyl-, and alkynylzinc additions and for the organozinc addition to ketones, although many good catalysts have been obtained for the dialkylzinc addition to aldehydes. Development of these reactions will allow the catalytic asymmetric synthesis of a great variety of functional chiral alcohols that are either the structural units or synthons of many important organic molecules as well as molecules of biological functions. Macromolecular chiral catalysts have become a very attractive research subject in recent years because these materials offer the advantages of simplified product isolation, easy recovery of the generally quite expensive chiral catalysts, and potential use for continuous production. Three types of macromolecules including flexible achiral polymers anchored with chiral catalysts, rigid and sterically regular main chain chiral polymers, and chiral dendrimers have been used for the asymmetric organozinc addition to aldehydes. Among these materials, the binaphthyl-based polymers such as (R)-451 developed by Pu have shown very high and general enantioselectivity. Study of the binaphthyl polymers in the asymmetric organozinc addition has demonstrated that it is possible to systematically modify the structure and function of the rigid and sterically regular polymer for the development of highly enantioselective polymer catalysts. The catalytic properties of highly enantioselective monomer catalysts can also be preserved in the rigid and sterically regular polymer provided the catalytically active species of the monomer catalyst is not its aggregate. The TADDOL-based polymers and dendrimers prepared by Seebach showed very high and stable enantioselectivity for the diethylzinc addition to benzaldehyde even after many cycles. These studies on macromolecular chiral catalysts demonstrate that these materials are potentially very useful for practical applications.

Catalytic Asymmetric Organozinc Additions to Carbonyl Compounds

Transition metal-catalyzed enantioselective hydrogenation of enamides and enamines is one of the most important methods for the preparation of optically active amines. This review describes the recent developments of highly efficient catalytic asymmetric hydrogenation of enamides, and enamines. It specifically focuses on the substrates because hydrogenation of enamides and enamines is highly dependent on the substrates although the chiral metal catalysts play a significant role.

Transition Metal-Catalyzed Enantioselective Hydrogenation of Enamines and Imines

Departament of Organic Chemistry, University of Geneva, 30 Quai Ernest Ansermet, 1211 Geneve 4, Switzerland, Department of Organic Chemistry, Stockholm University, Arrhenius Laboratoriet, 106 91 Stockholm, Sweden, Organic Chemistry II, Dormund University of Technology, Otto-Hahn-Strasse 6, D-44227 Dortmund, Germany, and Departament de Quimica Fisica i Inorganica, Universitat Rovira i Virgili, C/ Marcel · li Domingo s/n, 43007 Tarragona, Spain

Enantioselective Copper-Catalyzed Conjugate Addition and Allylic Substitution Reactions

The enantioselective addition of diethylzinc to aldehydes was conveniently achieved by using a catalyst prepared in situ by mixing titanium tetraisopropoxide with S - or R -binaphthol. Optical yields as high as 95.6% were obtained.

Enantioselective addition of diethylzinc to aromatic aldehydes catalyzed by Ti(BINOL) complex

Novel Asymmetric Alkylation of Aromatic Aldehydes with Triethylaluminum Catalyzed by Titanium·(1,1‘-bi-2-naphthol) and Titanium·(5,5‘,6,6‘,7,7‘,8,8‘-octahydro-1,1‘- bi-2-naphthol) Complexes

A new chiral tertiary aminonaphthol ligand 3b served as a highly efficient ligand for the asymmetric catalytic phenyl transfer to aromatic aldehydes and a variety of chiral diarylmethanols was prepared in high ee values (ee up to 99%) and chemical yields. The straightforward syntheses of both 3b and its enantiomer provide an excellent opportunity for large-scale applications.

Highly enantioselective phenyl transfer to aryl aldehydes catalyzed by easily accessible chiral tertiary aminonaphthol.

Complexes of a poly(methacrylic acid-co-methyl methacrylate) network with poly(ethylene glycol) stabilized by hydrogen bonds were prepared. By introducing poly(ethylene glycol), the complexes possessed shape memory effect, due to which a large difference in storage modulus below and above the glass transition temperature occurred. The morphology of the complexes was investigated and the mechanism of the shape memory behavior was discussed. This kind of complexes can be regarded as a novel shape memory network.

Hydrogen-bonded polymer network—poly(ethylene glycol) complexes with shape memory effect

A one-pot, titanium-catalyzed tandem sulfoxidation-kinetic resolution process, which combines asymmetric oxidation (at lower temperature) and kinetic resolution (at room temperature), has been developed. Excellent ees (up to>99.9%) and higher chemical yields of sulfoxides were obtained and the results compared favorable with those from either oxidation or kinetic resolution.

C. W. Yip

Papers

Enantioselective addition of diethylzinc to aromatic aldehydes catalyzed by Ti(BINOL) complex

Novel Asymmetric Alkylation of Aromatic Aldehydes with Triethylaluminum Catalyzed by Titanium·(1,1‘-bi-2-naphthol) and Titanium·(5,5‘,6,6‘,7,7‘,8,8‘-octahydro-1,1‘- bi-2-naphthol) Complexes

Highly enantioselective phenyl transfer to aryl aldehydes catalyzed by easily accessible chiral tertiary aminonaphthol.

Hydrogen-bonded polymer network—poly(ethylene glycol) complexes with shape memory effect

Titanium-Catalyzed Tandem Sulfoxidation-Kinetic Resolution Process: A Convenient Method for Higher Enantioselectivities and Yields of Chiral Sulfoxide