Alcoxysilane vs. Phosphonic Acid Linking Groups

DATE

July 2021

SPECIFIC POLYMERS research activity mainly focus on organic polymers based materials. Nevertheless, the problematic of interactions between organic and inorganic matters has been the subject of numerous studies. Indeed, in most of the cases, the chemical nature of interaction between the inorganic particles and the polymer drives the performance of the resulting system. In this field, SPECIFIC POLYMERS research are mainly oriented toward (macro)molecules bearing either alcoxysilane or phosphonic acid groups. Both functional groups are often used as linkers in between inorganic and organic phases within hybrid or composite materials or for surfaces/particles functionalization.

For instance, in recent work published in Microporous and Mesoporous Materials Journal (Nov. 2020), N. Kyriakou and co-workers highlighted the fact that, working on PEG based hydrophilic coatings on Mesoporous γ-alumina membranes surfaces, phosphonic acid linking agents provided enhanced stability compared to alkoxysilane moieties. Indeed, phosphonic acid as linking agent shows a stable PEG graft in pure water for more than 200 h whereas alkoxysilane linker was unstable in pure water.

Note: This study was achieved with SPECIFIC POLYMERS products: ‘MethoxyPEG10-phosphonic acid ethyl ester (MePEG10PE, 650 g/mol – SP-1P-1-001), PEG10-phosphonic acid ethyl ester (PEG10PE, 588.1 g/mol – SP-1P-1-006), MethoxyPEG11-triethoxysilane (MePEG11Si, 720.96 g/mol – SP-1P-2-009), MethoxyPEG7-triethoxysilane (MePEG7Si, 544.75 g/mol – SP-1P-2-009) starting materials were purchased from Specific Polymers and used as received’.

Thus, what are the pors and the cons related to each anchoring groups? In which case you should rather use one over the other? We try to provide the elements of answers in this article.

Alcoxysilane anchoring moiety

If you are looking for grafting specific molecules on inorganic substrate or particles, developing coating for glass substrates with a particular polymer or if you are working on hybrid sol-gel materials with innovative properties, then  polymer functionalized with alkoxysilanes can be the best answer to your technical challenges. Indeed, alkoxysilanes present the ability to create strong bonds with hydroxylated particles and surfaces and can also be used as precursors in sol-gel formulation.

Thus, Alkoxysilane are of great interest to link silica or glass surfaces or to developed hybrid sol-gel coatings for such substrates. SP has developed a wide range of Si-Polymers for such purposes.

Thanks to their specific structure, Si-Polymers can be used to bond organic and inorganic phases, avoiding phase segregation and limited performances. They are thus a real step forward compared to non-functionalized compatibilizing agents and are a key topic in the development of tomorrow’s materials. In this field, main industrial actors are KANEKA with MS Polymers* and EVONIK with Polymer ST and TEGOPAC®**. Si-Polymers® are of great interest for their adhesive and sealant properties and are used in many aeras such as construction industry, coating industry, automotive or aeronautics.

SPECIFIC POLYMERS masters both isocyanate alcoholysis (Si-U Polymers) and hydrosilylation reaction (Si-C Polymers) and can apply these reaction processes to a wide range of polymeric precursors like Polyethylene glycol (PEG), Polytetrahydrofuran (PolyTHF), PDMS, Polybutadiene, Polyester Polyols, etc. Depending on customer’s needs, the Si-functionalization can be oriented on the chain ends or on the lateral chains. Some example of Si-Polymers from our R&D product portfolio are presented here. Besides, these chemistries can be extended to a large range of polymers and we can offer custom synthesis to specifically answer the requirements of your application.

*KANEKA MS Polymers are mainly PPG and Poly(meth)acrylic polymers functionalized with alkoxysilane functions. The covalent linkage between the polymer chain and the alkoxysilane is an Alkyl chain. Alkyl spacer offer good processability, superior stability in hot and cold water as well as heat resistance.

**EVONIK Polymers ST and TEGPAC® are PPG polymers functionalized with alkoxysilanes functions. TEGOPAC® exhibit lateral functionality and Alkyl spacer. Polymer ST are functionalized on chains ends with urethane linkages. The latters bring higher viscosity and enhanced mechanical properties.

CASE STUDY

Hydrophobic sol-gel coatings

Research efforts were conducted in the scope of a PhD study in order to develop and implement highly stable and efficient water and oil-repellent optical coatings. It was demonstrated that with a minimal proportion of fluoroalkylsilanes (SP-02-004) introduced into a sol-gel formulation similar properties than with a classic silanization could be obtained according to a more industrial compliant and straightforward process. Further details on the influence of the fluoroalkylsilane’s distribution on resulting coating properties are reported in this paper. This work opens interesting perspectives in the development of hydrophobic coatings as this technique can be extended to silicones, alkyls or perfluoropolyalkylethers bearing alkoxysilanes moieties.

A. Bouvet-Marchand, A. Graillot, M. Abel, M. Koudia, G. Boutevin, C. Loubat and D. Grosso, Journal of Materials Chemistry A, (2018), 6, 24899-24910 >

Alkoxysilane Polymers to graft silica particles

SPECIFIC POLYMERS has worked for several years with CEA-Le Ripault (ADEME – PREMHYOME) in order to develop composite fuel cells membrane (PEMFC). Targeted membranes are prepared by inserting poly(sodium 4-styrenesulfonate) grafted silica particles (Si-PSSNa – SP-59P-9-001) dispersed in PVDF-HFP polymer matrix. Si-PSSNa particles are synthesized thanks to the grafting of alcoxysilane functional ATRP precusor on the surface of Silica Particles. It then possible to build-up well-defined polymeric coating of any kinds. Such strategy would enable preparing coating a various chemical nature on silica or other inorganic particles.


Related Patent :
• Proton conductive inorganic particles, method for the preparation thereof, and use thereof to form a fuel cell membrane. By: Buvat, Pierrick; Bigarre, Janick; Cellier, Julien; Loubat, Cedric; Crouzet, Quentin. Assignee: Commissariat à l’Énergie Atomique et aux Energies Alternatives et Specific Polymers. Patent n° : WO 2018138433, FR 3062075

• Fluorinated proton-conducting inorganic particles and use of said particles in proton-conducting membranes. By: Buvat, Pierrick; Bigarre, Janick; Cellier, Julien; Dru, Delphine. Assignee: Commissariat à l’Énergie Atomique et aux Energies Alternatives, Fr. WO2018138434

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Phosphonic acid linking group

On the other hand, phosphonic acid have the ability to bind metal or metal oxides (iron, aluminum, cerium, titanium, uranium, ITO, gadolinium, nickel, copper, zinc, calcium, quantum dots, nano-metals, etc.) and thus can also be used for functionalization of surfaces or particles. As for example, phosphonic acid functionality was often found to be superior to alkoxysilanes moieties for binding inorganic substrates other than silica, because of the higher robustness and stability of metal-OP over metal-OSi bonds. This is consistent with above mentioned results obtained by N. Kyriakou and co-workers.

Over the last 15 years, SPECIFIC POLYMERS has develop the synthesis of a number of phosphorus-containing monomers, polymers and building-blocks. Thanks to the organophosphorus functionality and corresponding chelating abilities, interesting studies were performed, notably in the field of nanomedicine, water treatment or surfaces coating (metal adhesion, anticorrosive).

Discover some of our R&D products bearing phosphonic acid moieties

MAPC1 (SP-41-003) is one of the most sell and used phophonate monomer from SPECIFIC POLYMERS R&D products portfolio. Batches up 100 grams are produced. Whatever the application, MAPC1 can be copolymerized with other monomers to reach the targeted properties. Controlled polymerization (RAFT, ATRP) of this monomer allow reaching many different architectures (statistical, diblock, triblocks, grafted, stars, etc.). This monomer is widely used in the design of polymers bearing phosphonic acid moieties of interest for several applications.

Other phosphonated monomers:

AAmEPA

MAPC1 Acid

Allyl phosphonic acid

MAPC2 Et

CASE STUDY

Polymer coating for MeOx Particles

SPECIFIC POLYMERS is working for almost 10 years with Paris Diderot and Paris Descartes University on polymer coated iron oxide particles for MRI Medical Imaging and other theragnostic applications in the biomedical field. In the scope of these projects, SPECIFIC POLYMERS developed, for instant, statistical copolymers bearing Pegylated laterals chains for biodistribution and stealthiness and phosphonic acid moieties as polymer coating anchoring groups on the FeO2 particles surfaces. It was proved that developed coating significantly enhanced the stability of FeO2 particles and allow performing MRI medical imaging. More recently, similar copolymers were used for the coating of other particles such as Cerium Oxide, Titanium Oxide or Aluminum Oxide.

V. Baldim, Y. Nisha, N. Bia, A. Graillot, C. Loubat, S. Singh, A. S. Karakoti, J.-F. Berret, ACS Applied Materials & Interfaces, 12, 37, 42056–42066, (2020) >

N. Baldim, A. Graillot, C. Loubat, J-F. Berret, Advanced Materials Interfaces, 6, (2019) >

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Thermosensitive Polymers for water treatment

Still based on the chelating properties of phosphonic acid moieties, thermosensitive polymers were developed in close collaboration with Montpellier II University (ICGM – IAM) and Veolia in the frame of COPOTERM project in order to implement an innovative water treatment process aiming at the removal of metal cations from wastewater. Phosphonic acid groups allow the sorption of aluminum, nickel, calcium, cadmium cations in water solution at room temperature and were proved to be selective toward trivalent aluminium. Thanks to the thermosensitive behavior of developed copolymers, a slight increase of the temperature above LCST lead to precipitation of polymer-metal complexe and ease the final separation step (microfiltration).

A. Graillot, C. Cojocariu, D. Bouyer, S. Monge, S. Mauchauffe, J-J. Robin, C. Faur, Separation and Purification Technology, 141, 17-24, (2014) >

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