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Monomer sequence control in Polymers : Toward next-generation precision materials

Periodic Reporting for period 2 - EURO-SEQUENCES (Monomer sequence control in Polymers : Toward next-generation precision materials)

Reporting period: 2017-01-01 to 2018-12-31

The aim of the project EURO-SEQUENCES is to establish a multidisciplinary training network on the emerging topic of sequence controlled polymers (i.e. macromolecules containing ordered sequences of monomers). It has been shown during the last five years that such polymers open up unprecedented options for the future of manmade materials. Indeed, similarly to biopolymers such as nucleic acids and proteins, synthetic sequence-controlled polymers contain precisely engineered chain-microstructures that allow a fine control over their molecular, nanoscopic and macroscopic properties. For instance, these new types of polymers are relevant for applications in molecular data storage, catalysis, photovoltaics and nanomedicine.
The scientific objectives of the project are listed below:

Objective 1 (Polymer Chemistry): an important goal of the project will be the development of new synthetic routes for preparing sequence-controlled copolymers. In particular, an emphasis will be put on non-biological methods such as iterative chemistry, template chemistry, and chain-growth polymerization. One important target is the development of high-molecular weight sequence-defined polymers using fast and easy chemical protocols. In order to reach that goal, automatized chemical protocols will be used in several individual sub-projects.

Objective 2 (Characterization and sequencing): The analytical methods that are currently used to analyze sequence-controlled macromolecules (e.g. NMR or mass spectrometry) do not allow, in general, a full molecular description of the chain microstructures. Inspired by methods used for the sequencing of proteins and nucleic acids, new approaches will be studied in this project for the analysis of synthetic macromolecules. In particular supramolecular read-outs and nanopore analysis will be developed.

Objective 3 (Self-assembly and folding): As learned from biopolymers such as proteins, the primary structure of synthetic macromolecules has a direct influence on their folding and supramolecular self-organization. Hence, an important objective of the project will be to use controlled comonomer sequences for preparing folded macromolecular origami. In particular, an emphasis will be put on the folding of individual polymer chains into discrete functional nanoparticles (i.e. single-chain technology).

Objective 4 (Materials and properties): The correlation between primary structure and materials properties will be studied in this project. In particular, the influence of ordered monomer sequences on thermal and mechanical properties (e.g. tensile strength, rupture) of synthetic polymer materials will be examined in detail. The ultimate objective will be the development of precision polymer materials for the plastics industry.
The first main objective of the project is the development of new routes for the synthesis of sequence-defined and sequence-controlled polymers. In that regard, interesting new approaches have been discovered during the period covered by this report. For example, an orthogonal iterative method was found and published for the synthesis of sequence-coded poly(alkoxyamine phosphodiester)s. Perfectly sequenced-defined polymers were also prepared using a thiolactone-based strategy. In more-challenging sequence-controlled chain-growth polymerizations, interesting step forwards have been also made through the use of thio-acrylate monomers.

Significant advances have been also made in this project for the sequencing of unnatural macromolecules. For instance, high molecular weight ester-imide homopolymers and copolymers have been synthetized and their sequences have been analyzed by NMR. In addition, significant research has been devoted to the nanopore sequencing of sequence-coded non-natural polymers. For instance, tailor-made poly(phosphodiester)s were specifically synthesized for nanopore sequencing. This topic is highly challenging and sequencing conditions haven’t been discovered yet. However, the threading of these macromolecules through the pore has been already evidenced, thus paving the way for sequencing.

The folding and self-assembly of sequence-controlled polymers was also examined in order to understand the correlation between controlled primary structure and higher levels of organization. For example, the self-assembly of new types of siloxane-BTA derivatives was studied. Moreover, an artificial molecular machine based on a [2]rotaxane (a track mechanically locked with a macrocycle) architecture and building blocks containing side reactive functions (selenol and thiol moieties) was synthetized. The synthesis and the supramolecular properties of these complex molecules have been studied.

The impact of monomer sequence control on materials properties has also been investigated during the period covered by this report. For example, sequence-defined oligomers have been tested as precision compatibilizers for high-performance composites used in automotive industries. Interesting properties have been already observed for the reinforcement of Kevlar-based composites. Other types of sequence-defined polymers were also synthesized and tested as molecular barcodes for the labelling of different kind of commodity plastics. Regarding the potential biomedical application of sequence-controlled polymers, new types of star initiators and three different glycol-monomers has been synthesized.
The general scientific context of this project is the development of a new generation of synthetic polymer materials. This topic is of prime importance for future European Science. Indeed, plastic and polymer industry remains today one of the largest manufacturing industry in Europe. Besides commodity polymers (i.e. polymers produced in large scale such as PE, PS or PVC) that have been primarily developed during the 20th century, new types of complex polymer materials have recently emerged in academia and industry. In particular, the next step in the field of polymer science seems to be the elaboration of polymer structures that are as complex and functional as those found in nature (e.g. nucleic acids; structural and globular proteins). Indeed, some fascinating properties of biopolymers such as information storage, self-replication, biocatalysis, photosynthesis and selective molecular transport cannot be attained - or are poorly mimicked - with current synthetic polymer materials. In this context, the present project has a high relevance since it federates the European scientific community on the topic of sequence-controlled polymers. As a consequence of this active research network, important discoveries have been already made during the period covered in this report. The progress beyond the state of the art include: (i) the discovery of new facile pathways for the synthesis of sequence-controlled polymers, (ii) the screening of new original analytical methods that permit to “read” the sequences of sequence-controlled polymers, (iii) the assembly of sequence-controlled polymers into unprecedented nanoscale morphologies and (iv) the use of sequence-controlled polymers as advanced materials for various applications. These advances are important for fundamental polymer knowledge but have also an economic and societal potential. For example, the development of sequence-coded polymers that permit to store digital information could be a discovery with significant technological implications in a near future.
Toward new generations of man-made functional polymers