DS0303 - Matériaux et procédés

Asymmetric copolymers: neither block nor random – ASYMCOPO

Asymmetric copolymers: neither block nor random

The ASYMCOPO project aims to classify asymmetric copolymers - polymers that are neither pure block copolymers nor random copolymers, but fall somewhere between the two. To do so, we are generating a libraries of asymmetric copolymers and linear gradient copolymers. These copolymers will be characterized in terms of their ability to self assemble in solution or stabilize interfaces. Their properties will be compared in order to determine what are the essential features of an asymmetric copolymer.

An easier way to make gradient copolymers

Gradient copolymers, whose composition varies continuously as a function of chain length, are an intriguing class of materials with many potential applications, including as shock- and noise-absorbers and as interfacial stabilizers. However, the preparation of a polymer with a pre-defined gradient of composition requires a semi-continuous process with careful control over monomer addition and constant feedback in order to regulate the composition at each stage of the polymerization. In the ASYMCOPO project we ask: what is the defining structural feature of a gradient copolymer? And can these properties be mimicked using structures that are easier to prepare, using well-understood batch polymerization processes? <br /> <br />The global objectives of the ASYMCOPO project are <br />1) to develop a classificatory framework for asymmetric copolymers based on a ‘moment of asymmetry’ – an index that we have developed that varies from 0 for a random copolymer to 1 for a random copolymer. Our hypothesis is that polymers with a similar composition and index of asymmetry will display similar properties. <br />2) to prepare a library of copolymers of different structures to test this hypothesis. The library will be composed of sets of copolymers of identical composition and moment of asymmetry, but different structure. Included in the structures to be tested are copolymers with a linear gradient of composition, and block copolymers containing 2, 3 or 4 blocks of constant average composition. <br />3) to explore the structure-property relationships of the resulting copolymers, in terms of their thermal properties and their self-assembly behavior in bulk and in solution. This will give an indication of their ability to act as shock- and noise-absorbing materials, as well as their ability to provide interfacial stabilization

We are using two techniques for polymer synthesis: semicontinuous polymerization with carefully controlled addition of monomers to prepare polymers with a linear gradient, and high throughput automated synthesis to prepare a library of asymmetric block and multiblock copolymers.

These polymers are then characterized using a variety of techniques. We are primarily interested in their ability to self-organize, either in the solid phase or in solution. We investigate their microphase separation in bulk using differential scanning calorimetry, and their self-assembly behavior in solution using a range of scattering-based techniques: dynamic light scattering and small angle neutron or X-ray scattering. We have also investigated the relationship between composition and molecular weight using two-dimensional chromatography (SEC-LCCC).

To date, we have prepared a library of gradient copolymers based on several different acrylate monomers, with composition profiles that are very close to linear. In parallel, we have developed techniques to allow the preparation of block copolymers in high throughput conditions. We have also measured the reactivity ratios of a wide range of monomers, which determine how they copolymerize.

With a library of polymers in place, we are now at the stage of characterizing their behavior. We hope that our results will lay the groundwork for a new way of classifying polymers based on their degree of asymmetry. These polymers are expected to show applications ranging from shock- and noise-absorption to improved interfacial stabilizers.

Our preliminary results on reactivity ratio measurement have appeared in two peer-reviewed articles to date:
1. Sykes, K. J., Harrisson, S. and Keddie, D. J., Phosphorus-Containing Gradient (Block) Copolymers via RAFT Polymerization and Postpolymeri

The goal of the ASYMCOPO project is to develop new materials that mimic the useful shock- and noise-absorbing and interfacial stabilizer properties of gradient copolymers, but which do not reauire complex synthetic procedures for their preparation.
Gradient copolymers, whose composition varies continuously as a function of chain length, are an intriguing class of materials with many potential applications, including as shock- and noise-absorbers and as interfacial stabilizers. However, the preparation of a polymer with a pre-defined gradient of composition requires a semi-continuous process with careful control over monomer addition and constant feedback in order to regulate the composition at each stage of the polymerization.
It has recently been noted that the very idea of a gradient copolymer is something of a contradiction in terms: while the average composition of all the chains of a polymer may vary smoothly from one end of the chain to the other, each individual chain is composed of discrete monomer units, and at any point in the chain the composition must take one of only two possible values. Thus polymers which, on average, exhibit a gradient composition contain a broad distribution of structures. Furthermore, it is impossible to reconstruct the composition gradient of the entire polymer from a single polymer chain.
It is thus natural to ask, what is the defining structural feature of a gradient copolymer? And can these properties be mimicked using structures that are easier to prepare, using well-understood batch polymerization processes?
In the ASYMCOPO project we aim to answer this question by introducing the concept of asymmetric copolymers: polymers that are intermediate in structure between block and random copolymers. We have developed a framework for the classification of this class of polymers, centered on the concept of an ‘moment of asymmetry,’ which we will use to guide our research in first synthesizing, then exploring the properties of this new class of materials. In particular, we seek to define structures consisting of 2, 3, or 4 random copolymer segments which mimic the useful properties of gradient copolymers, but are substantially easier to synthesize.
This project requires the preparation of an extensive library of copolymers of different structures, and hence necessitates the involvement of a laboratory with expertise in high-throughput polymer synthesis and characterization. The Institute for Organic and Macromolecular Chemistry, in Jena, Germany, is the Europe’s leading research group in this domain. In parallel, synthesis of well-defined gradient copolymers requires careful control of polymerization conditions, employing the expertise of the IMRCP laboratory of Toulouse, France, in polymerization kinetics, polymer synthesis and characterization.
This Franco-German International Collaborative Research Project is submitted to the ANR generic program within the societal challenge “Stimulate Industrial Renewal” and the “Materials and Processes” axis. The thematic priority of the project is ‘Multifunctional Multiscale Materials.’ The proposed research is fundamental (Technology Readiness Level 1) and knowledge-based.

Project coordinator

Monsieur Simon Harrisson (LABORATOIRE DES IMRCP)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IOMC Institut für Organische Chemie und Makro-molekulare Chemie
IMRCP LABORATOIRE DES IMRCP

Help of the ANR 145,496 euros
Beginning and duration of the scientific project: November 2015 - 24 Months

Useful links