Growing polymers of different lengths

Date:
June 26, 2020
Source:
ETH Zurich
Summary:
Researchers have developed a new method for producing polymers with
different lengths. This paves the way for new classes of polymer
materials to be used in previously inconceivable applications.



FULL STORY ==========================================================================
It is hard to imagine everyday life without materials made of synthetic polymers. Clothes, car parts, computers or packaging -- they all consist
of polymer materials. Lots of polymers are present in nature, too,
such as DNA or proteins.


========================================================================== Polymers are built on a universal architecture: they are composed
of basic building blocks called monomers. Polymer synthesis involves
linking monomers together to form long chains. Imagine threading glass
beads onto a string and creating chains of different length (and weight).

Polymerization processes with limits An important industrial process for producing polymers is free radical polymerisation (FRP). Each year the
chemical industry uses FRP to produce 200 million tonnes of polymers
of various types, such as polyacrylic, polyvinyl chloride (PVC) and polystyrene.

Although this production method has many advantages, it also has its limitations. FRP produces an uncontrollable mixture of countless polymers
of different lengths; in other words, its dispersity is high. Dispersity
is a measure of how uniform or non-uniform the length of the polymer
chains in a material is. Material's properties are determined to a large
extent by this dispersity.

In the case of everyday polymers, polymers with both low and high
dispersity are required. In fact, for many high-tech applications
including pharmaceuticals or 3D printing, high dispersity can even be
an advantage.



========================================================================== Polymers with new properties However, if chemists want to produce polymer materials with very specific properties, they must first and foremost be
able to adjust the dispersity as desired. This lets them produce a wide
range of polymer materials that either contain uniform polymer species,
i.e. have a low dispersity, or are highly dispersed with a great number of polymers of different lengths. Until now, this has hardly been possible.

A group of researchers led by Athina Anastasaki, Professor of Polymer
Materials at the Department of Materials Science, has now developed a
method of controlling radical polymerisation, thus enabling researchers
to systematically and completely control the dispersity of polymer
materials. The results of their research were recently published in the
journal Chem.

In the past, in order to be able to control the radical polymerisation
process at least to some extent, chemists would use a single
catalyst. While this ensures that the resulting polymer chains become
uniformly long, it doesn't allow the overall dispersity to be controlled
as desired.

Two catalysts do the trick Now the ETH researchers simultaneously employ
two catalysts with different effects -- one is highly active, the other
only slightly active. This enabled them to adjust the dispersity precisely
as a function of the ratio in which they mixed the two catalysts. If
the more active catalyst was more abundant, more uniform polymers were produced, which meant the resulting material had low dispersity. If,
however, the less active catalyst was more abundant, a large number of different polymer molecules were formed.

This work means Anastasaki and her team have created a basis for the development of new polymer materials. In addition, their process is also scalable; it works not only in the laboratory, but also when applied
to larger quantities of substances. Another advantage of this method
is that even polymers with high dispersity can continue growing once
the polymerisation process itself is complete -- something that was
previously considered impossible.

The high efficiency and scalability of the approach have already attracted interest from industry. Polymers produced with the new process could be
put to use in medicine, vaccines, cosmetics or 3D printing.


========================================================================== Story Source: Materials provided by ETH_Zurich. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Richard Whitfield, Kostas Parkatzidis, Nghia P. Truong, Tanja
Junkers,
Athina Anastasaki. Tailoring Polymer Dispersity by RAFT
Polymerization: A Versatile Approach. Chem, 2020; 6 (6): 1340 DOI:
10.1016/ j.chempr.2020.04.020 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200626161203.htm

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