Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sorted Building Blocks

18.03.2011
Poly(propylene carbonate) stereogradient

The properties of polymers—long chain molecules from which plastics are made—depend on the type of individual building blocks in them, as well as the order they are in and how they are arranged in space.

Although the order of the components can easily be controlled, control of their spatial arrangement, called stereochemistry, remains one of the biggest challenges in polymer chemistry. Kyoko Nozaki and a team from the University of Tokyo report in the journal Angewandte Chemie that they have made the first poly(propylene carbonate) with polymer chains built up in the form of a gradient of two stereochemically different propylene building blocks.

Poly(propylene carbonate) is used as a binding agent and as a component of biodegradable plastics. It is made from propylene oxide and carbon dioxide in a catalytic process. Propylene oxide contains three carbon atoms, two of which form a ring together with an oxygen atom. This ring opens during polymerization. Propylene oxide exists in two forms that are mirror images of each other; these are designated as the S and R stereoisomers.

Poly(propylene carbonate)s that are made primarily of one of the two forms or have both forms in an alternating pattern have been made before. Nozaki’s group has now been the first to synthesize both a stereoblock and a stereogradient. A stereoblock copolymer is a chain, half of which is made of the S form and the other half of the R form. In a stereogradient copolymer, the composition changes gradually from the S form to the R form.

Making a block copolymer is theoretically relatively easy because use of an asymmetric catalyst causes one of the two forms of building block to be used preferentially, so it is built into the polymer chains first; the less favorable form is incorporated afterward. In the case of poly(propylene carbonate), however, this process isn’t so trivial because once the favored form of the propylene oxide is converted to a polymer, the other form decomposes instead of polymerizing. The Japanese scientists found a special asymmetrical cobalt complex that allows nearly complete conversion to the polymer. Although the catalyst prefers the S form, it also ensures that it is more favorable for the R form to polymerize than to decompose.

The researchers experimented further with variations on the cobalt complex. A special ammonium side branch on a ligand brought success: It balances the degree of preference of the catalyst for the S form over the R form so that the R form begins to be incorporated into the polymer chain as the amount of the S form decreases. This allows the formation of the stereogradient copolymer. Interestingly, both of the new types of poly(propylene carbonate), stereoblock and stereogradient, are significantly more heat-tolerant than pure S or R polymers or mixtures of the two.

Author: Kyoko Nozaki, University of Tokyo (Japan), http://park.itc.u-tokyo.ac.jp/nozakilab/indexE.html

Title: Synthesis of Stereogradient Poly(propylene carbonate) by Stereo- and Enantioselective Copolymerization of Propylene Oxide with Carbon Dioxide

Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201007958

Kyoko Nozaki | Angewandte Chemie
Further information:
http://park.itc.u-tokyo.ac.jp/nozakilab/indexE.html
http://pressroom.angewandte.org

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>