The synthesis methods of silane-modified polyethers primarily involve introducing silane groups into the polyether chain to improve its weather resistance, adhesion, and flexibility. Below are the common synthesis strategies and steps:
1. Synthesis of the Polyether Backbone
Raw materials: Epoxyalkanes such as ethylene oxide and propylene oxide.
Method: Anionic ring-opening polymerization (using catalysts like KOH or double metal cyanides) to prepare polyether diols with hydroxyl end groups.
2. Methods for Introducing Silane Groups
(1) End-Group Silanization
Isocyanate Silane Method:
Reactants: Polyether diol + isocyanate silane (e.g., isocyanatopropyltrimethoxysilane).
Conditions: Under anhydrous conditions, with a catalyst (e.g., dibutyltin dilaurate), heated to 60–80°C.
Mechanism: The hydroxyl group reacts with the isocyanate group to form a urethane bond, grafting the silane group at the terminal.
Chlorosilane Method:
Reactants: Polyether hydroxyl + chlorosilane (e.g., trimethoxychlorosilane).
Conditions: Reaction in an alkaline environment (e.g., triethylamine), eliminating HCl to form an Si-O-C bond.
Epoxy Silane Ring-Opening Method:
Reactants: Polyether hydroxyl + epoxy silane (e.g., γ-glycidoxypropyltrimethoxysilane).
Conditions: Acid- or base-catalyzed ring-opening to form an ether-linked silane terminal group.
(2) Side-Chain Silanization
Hydrosilylation Method:
Steps: First, introduce a double bond into the polyether chain (e.g., via acrylate modification), then react with an Si-H-containing silane (e.g., trimethoxysilane) under a platinum catalyst to form an Si-C bond.
Graft Copolymerization Method:
Monomer: Use a silane-containing monomer (e.g., vinyltrimethoxysilane) for copolymerization with the polyether backbone.
3. Key Considerations
Moisture Control: Silane groups are prone to hydrolysis, so reactions must be conducted under anhydrous conditions, and products must be stored dry.
Catalyst Selection: Tin-based catalysts are commonly used for isocyanate reactions, while platinum catalysts are required for hydrosilylation.
Stoichiometry: Ensure complete hydroxyl group reaction to avoid residues affecting performance.
Side Reaction Suppression: Avoid silane self-condensation by controlling reaction temperature and adding inhibitors.
4. Characterization and Performance
FTIR: Detect characteristic peaks of Si-O-C (~1100 cm⁻¹) and Si-CH3 (~1250 cm⁻¹).
NMR: Observe proton signals of silane groups (e.g., OCH3 peaks of trimethoxy groups).
GPC: Analyze molecular weight distribution and modified chain structure.
5. Application Fields
Sealants/Adhesives: Hydrolysis and crosslinking of silane groups form a 3D network, enhancing weather resistance and strength.
Coatings: Improve adhesion and flexibility.
Elastomers: Enhance temperature resistance and mechanical properties.
Through the above methods, silane-modified polyethers can be flexibly designed to meet various application requirements, with end-group silanization being the most commonly used due to its simplicity and efficiency.
