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

More articles from Life Sciences:

nachricht Bacteria as pacemaker for the intestine
22.11.2017 | Christian-Albrechts-Universität zu Kiel

nachricht Researchers identify how bacterium survives in oxygen-poor environments
22.11.2017 | Columbia University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Corporate coworking as a driver of innovation

22.11.2017 | Business and Finance

PPPL scientists deliver new high-resolution diagnostic to national laser facility

22.11.2017 | Physics and Astronomy

Quantum optics allows us to abandon expensive lasers in spectroscopy

22.11.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>