Search

 

PressCNRS international magazine

Table of contents

Chemistry

Making the Best of Polymers

In Pessac, near Bordeaux, chemists are using both their imagination and inspiration from nature to produce new polymers with original new functions. From synthesis to analysis, a visit to the Organic Polymer Chemistry Laboratory (LCPO).(1)

 

polymers

© F. Jannin/CNRS Photothèque

The polymerization reaction is followed by using a UV spectrometer and an IR spectrometer simultaneously in situ.


 

You can see quite a bit walking through the corridors of the LCPO, located on the Bordeaux University campus. Behind glass walls, researchers are synthesizing long chains of macromolecules in reactors. Turn a corner and others are working on the shape, size, and above all, the function of these macromolecules using spectrometry, calorimetry, or imaging tools. In fact, a total of 80 chemists are working toward the same goal: linking monomer2 molecules in chains to make polymers.

“Polymers are everywhere,” says Yves Gnanou, director of the LCPO. “Think of polystyrenes, polyurethanes, polyesters. And they have very different architectures, formulations, and functions. These materials, which are relatively recent, account today for 40% of the volume and turnover of the chemical industry.” And there are still many aspects that remain to be explored, both in terms of synthesis and applications... This is exactly why these researchers, and about 50 PhD students and postdoctoral researchers–the lifeblood of the Bordeaux lab–are working so tirelessly. They've already come up with several ideas for producing polymers in more ecologically sound and economically efficient conditions in addition to identifying new uses for them. To make a polymer macromolecule, formed by thousands of monomers linked together in a chain, we need to add a monomer to each end of the original one, and repeat this same reaction thousands of times. This chain reaction, known as “polymerization,” is what many LCPO researchers are studying. They try to optimize the act of adding a monomer unit, in other words, to increase the probability that the reaction will happen with a minimum of errors to produce the right polymer. “We're studying the three types of chain reactions currently used for producing polymers: ionic, radical, and Ziegler-Natta polymerization reactions.3 This last type of reaction is used for polymerizing particular molecules,” explains Gnanou.

 

Green inspiration

But in this lab, they don't just study “classic” reactions. Alain Deffieux and Frédéric Peruch, for example, have chosen to observe nature and get their inspiration from it. As Deffieux explains: “In today's context, with oil resources becoming scarce, it is urgent to find new ways of producing polymers that are not based on oil, but on renewable raw materials.” They have been looking at natural rubber, produced by Hevea brasiliensis from isopentyl pyrophosphate. Industrially, this polymer is produced from isoprene, which is an oil derivative. The reactions used by nature and industry are really completely different. “But we are taking up the challenge of synthesizing rubber by replicating nature,” says the chemist. “We are trying to faithfully replicate the active site of the enzyme produced by rubber trees (heveas), which polymerizes isopentyl pyrophosphate into rubber. With this research we're now starting to understand the mechanism, and have been able to produce small quantities of polymers from pyrophosphate analogs.” Although the structure of the polymer obtained is not quite the same as natural rubber, the approach is very promising, and according to the researchers, could be applied to many other polymers.

A few doors down, Henri Cramail and his colleagues are on a different track. They are thinking up ways of carrying out polymerization reactions in water or carbon dioxide, rather than in the usually toxic organic solvents used until now. “CO2 has several advantages. First of all, it's a good replacement for the solvents used to carry out the reaction. What's more, once the polymerization is done, we just have to release the pressure to recover the polymer directly,” explains the researcher. This avoids using yet another solvent to extract the polymer. “We are also studying the possibility of using CO2 as a reaction intermediate. We're working on the synthesis of polyurethanes obtained from alcohol and isocyanate for this aspect. When present, the CO2 even acts as an activator in the reaction.” If confirmed, this result could be very useful for manufacturing polyurethanes for the biomedical industry. The process could do away with using the usual catalyst, an extremely toxic tin compound.

 

Industrial design

While some LCPO researchers are working at improving polymerization mechanisms through the principles of green chemistry, others are more interested in what these new polymers can actually do. “A polymer chain is like a piece of spaghetti,” Gnanou points out. “If we want it to do a particular job, we have to give it the accurate shape. So we customize the polymer chains either by introducing branching, or by introducing 'information' that generates self-assembly. 

polymere microscope

© M.Schappacher et A. Deffieux

Researchers give specific shapes to polymers by introducing branching into the chain. This is an atomic microscope view of two comb-shaped macromolecules, each made up of polystyrene molecules (white) and polyisoprene molecules (light brown).


In other words, we 'tell' the molecule to reorganize itself.”  Valérie Heroguez-Sabaut is one of the “architects” or “designers” who create polymers with very specific functions. She works on particles that can liberate drugs, either by vectorization–where the active principle is carried to the target–or by grafting the particle onto biomaterial. “We have designed particles with pH-sensitive bonds to the active ingredient,” explains the researcher. “Then we were able to introduce anchor points, so that we could graft them onto biocompatible material.” This new successful technique has enabled her to work with an orthopedics manufacturer on a bone-implant application. The results are amazing: “An implant placed in the body creates an inflammation,” explains the scientist. “And inflammation brings about a local decrease in pH. Due to this pH drop, the particles that we have grafted onto the implant liberate the anti-inflammatory drug that they contain.” The end result is that the drug is liberated only at the appropriate location, which means that a smaller quantity can be used, with fewer secondary effects.

 

Controlled structures

 

chimiste

© F. Jannin/CNRS Photothèque

Physical chemists study the properties of polymers by measuring their elasticity and mechanical properties using a dynamometer.


 

Once any new types of molecules have been created, their characteristics have to be determined. That's where the LCPO physical chemists come in. Their labs are equipped with hi-tech apparatus for X-ray diffusion, rheology, and imaging. “We use all available physical chemistry techniques to understand the properties, structure, and dynamics of the controlled-structure polymers that the chemists produce,” explains Redouane Borsali, leader of this team. But they don't stop there. Recently, they have developed a new engineering technique which consists in controlling the morphology–and thus the function–of natural polymers such as polysaccharides, by coupling them to blocks of synthetic polymers. Yet another indication that the LCPO researchers are well aware of green chemistry issues, since this research aims at reducing the use of oil-based polymers and replace them with natural ones.

With the wealth of ideas springing from this French lab, manufacturers across the board, from pharmaceuticals to cosmetics, are starting to take notice... Between 2002 and 2005, no less than 36 patents were filed, 160 articles were published, and three promising start-ups were created. The most recent, appropriately named Polyrise, specializes in UV activated polymerization.

 

Stéphanie Belaud

Notes :

1. Laboratoire de chimie des polymères organiques (CNRS / ENSCP Bordeaux / Université Bordeaux-I joint lab).
2. A monomer is a simple molecule that can react with others to form a polymer chain.
3. In ionic polymerization, an ion attacks the monomer to make it bind to the macromolecule under construction. In radical polymerization, it's a free radical that attacks. Ziegler-Natta catalysts are based on titanium tetrachloride and the organometallic compound triethylaluminium.

Contacts :

Laboratoire de chimie des polymères
organiques (LCPO), Bordeaux.
> Yves Gnanou, gnanou@enscpb.fr
> Alain Deffieux, deffieux@enscpb.fr
> Valérie Heroguez-Sabaut, heroguez@enscpb.fr
> Redouane Borsali, borsali@enscpb.fr
> Henri Cramail, cramail@enscpb.fr


Top

Back to homepageContactcredits