Blanc SIMI 8 - Blanc - SIMI 8 - Chimie du solide, colloïdes, physicochimie

Supramolecular chemistry of well-defined end functional polyethylenes – SUPRA PE

Supramolecular polyethylenes

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A two-fold objective

Polyolefins are commodity polymers that represent more than half of the worldwide production of thermoplastics. The desirable chemical and physical properties of polyolefins along with their low production cost makes this class of polymer highly attractive commercially. The introduction of functional groups into polyolefin chains facilitates their use in polymer blends or in composite and the design of new macromolecular architectures based on polyolefins. However, this still consists in a real challenge in the field.<br />SUPRA PE aims at developing strategies for the introduction of functionalities on PE chain ends that are able to interact via hydrogen bonds for the use of the resulting building blocks for the elaboration of macromolecular self-assemblies. This research is meant to provide the scientific community with new tools for the elaboration of macromolecular architectures constructed from polyolefin building blocks and to take advantage of the unique properties of polyolefins to turn a commodity polymer into a high value-added material.

To achieve the above-mentioned goals, one of the main challenges was the identification of efficient strategies to end functionalize PE chains. The concept of catalyzed chain growth was indeed exploited to produce original synthetic protocols for the production of monofunctional PE but also telechelic PE (functional group on both chain ends) for the first time starting from ethylene as monomer and using catalytic polymerization. Then, monofunctional, homo- or hetero-bifunctional supramolecular PE grafted with Thymine (Thy) ou Diaminotrazine (DAT) moieties - able to self assemble via hydrogen bonds - were produced from these PE building blocks (PE-Thy, PE-DAT, DAT-PE-DAT, Thy-PE-Thy, DAT-PE-Thy).
Besides, polymers of very different chemical nature (polarity, flexibility, hydrophilicity) from PE such as poly(ethylene oxide) (PEO), poly(propylene oxide (PPO) or polydimethylsiloxane (PDMS) grafted with Thy and DAT moieties at one or both chain ends were also synthesized.
The structuration of PEs equipped with Thy or DAT end groups on one hand, and PEs with these other polymers on the other hand were finally studied, relying on the association through hydrogen bonds between Thy or DAT moieties alone (Thy-Thy giving crystalline assembly), or Thy and DAT.

Concerning the self-assembly of PE, the segregation that is taking place between apolar PE chains and the polar supramolecular units results in a lamellar organization in which there is no binding chain between lamella. The original idea based on the potential of forming high molar mass PE analogues by assembling low molar mass PE building blocks was thus disproved.
The formation of supramolecular block copolymers by assembling Thy-based PE with DAT-based PDMS (PE-b-PDMS and PE-b-PDMS-b-PE) allowed identifying a unique system. At high temperature, H-bond associations are broken and the very different chemical nature between PE and PDMS led to a macrophase separation. At low temperature, the re-formation of block copolymers through terminal H-bonds allows micro phase separation to take place. This phenomenon is observed for the first time to our knowledge.

In conclusion, the impact of SUPRA PE is not appreciated from the nature of the products obtained though some of them (telechelic PE, new functional chain transfer agents) are really resulting from breakthroughs in the field. SUPRA PE remains however a very useful tool for the understanding of the structuration of PE chains carrying supramolecular linkers or of supramolecular block copolymers based on PE segments. SUPRA PE has(is) fed(feeding) discussions between the two teams involved that resulted in strategies which can alleviate the limitations shown by SUPRA PE. These discussions involved other polyolefins of interest and will be the subject of future grant proposals that will be submitted to the ANR.

The scientific production deals with the functionalization of building blocks based on PE (1-2). These building blocks allowed the syntheses of the targeted Thy and DAT capped PE and the study of the their structuration (3-5). The publication of the systems based on supramolecular block copolymers is underway.
1. S. Norsic, C. Thomas, F. D'Agosto, C. Boisson Angew. Chem. Int. Engl. Ed. 2015, 54, 4631-4635.
2. W. Nzahou Ottou, S. Norsic, I. Belaid, C. Boisson, F. D'Agosto Macromolecules 2017, 50, 8372-8377.
3. I. German, F. D'Agosto, C. Boisson, S. Tencé-Girault, and C. Soulié-Ziakovic Macromolecules, 2015, 48, 3257-3268.
4. J. Lacombe and C. Soulié-Ziakovic Polym. Chem, 2017, 8, 5954-5961.
5. J. Lacombe, S. Pearson, F. Pirolt, S. Norsic, F. D'Agosto, C. Boisson, C. Soulié-Ziakovic Macromolecules 2018, accepted, DOI 10.1021/acs.macromol.8b00270.

The aim of this project is to design new polyolefin materials (i.e. materials based on non polar polymers prepared by (co)polymerization of ethylene and ?-olefins) incorporating end groups with hydrogen bonding sites and to evaluate their capacity to recognize complementary sites in other polymers (including polyolefins) or materials.

Polyolefins are commodity polymers that represent more than half of the worldwilde production of thermoplastic. The desirable chemical and physical properties of polyolefins along with their low production cost makes this class of polymer highly attractive commercially. For more than fifty years, the modification of polyolefins has been both an academic and an industrial challenge. The introduction of functional groups into polyolefin chains facilitates (i) their use in polymer blends or in composite and (ii) the design of new macromolecular architectures based on polyolefins. Industrially, polyolefins are produced either by free radical polymerization under high pressure and at high temperature, or by catalytic polymerization using coordination chemistry. These processes that do lead to commodity polymers do not allow an easy and selective introduction of chain-body or terminal reactive groups. As a result, the design of macromolecular architectures based on polyolefins through direct polymerization or by post-polymerization modification is difficult. One of the remaining challenges in this field is thus to design polyolefin macromolecular architectures with the help of systems such as Coordinative Chain Transfer Polymerization (CCTP) that allow the design of end functional polyolefins and that yet remain catalytic.
The future design of advanced macromolecular structures will demand a unique combination of noncovalent and covalent bonding in order to provide both excellent mechanical performance and thermoreversibility during melt processing. This particularly holds true for polyolefin-based materials. Based on the molecular recognition that is often encountered in biological systems and which exploits for example H-bonding, supramolecular chemistry has become a powerful strategy for the creation of functional new materials. The incorporation of noncovalent moieties into organic molecules or polymer chains imparts dynamic, potentially tunable properties, such as self-healing, once higher order structures are achieved upon self-assembly. As non-covalent interactions are formed reversibly and sensitive to their environment, materials are stimuli-responsive (“smart materials”), so that they can be easily processed and recycled unlike conventional polymers that often have high melt viscosities and are difficult to process. Tailor-made supramolecular block copolymers with desirable and tunable properties can be achieved whilst avoiding grafting or two-stage polymerization instead relying on efficient end-group transformations of a parent polymer. The development of strategies to incorporate complementary hydrogen bonding sites at the end of polyolefin chains in a controlled fashion and the use of the resulting macromolecules in self assembly processes has not yet been explored. SupraPE aims at developing such strategies. It would constitute a new way of tackling the design of macromolecular architectures based on polyolefins and of taking advantage of the unique properties of polyolefins to turn a commodity polymer into a high value added material.

The ambition of this project is thus to provide the scientific community with new tools for the elaboration of macromolecular architectures constructed from polyolefin units. To achieve this goal, we would like to make the most of the already well established expertise of the two partners (C2P2 and MMC) involved in this project in the fields of the end functionalization of polyethylene chains and the design of supramolecular architectures.

Project coordination

Franck D'Agosto (Chimie, Catalyse, Polymères et Procédés)

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

C2P2 Chimie, Catalyse, Polymères et Procédés
MMC Laboratoire Matière Molle et Chimie

Help of the ANR 308,880 euros
Beginning and duration of the scientific project: February 2014 - 42 Months

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