The double bond of allyl polyether can indeed participate in UV-induced free radical polymerization, but its reactivity and efficiency are significantly influenced by molecular structure and reaction conditions. Here is a detailed analysis:
1.Feasibility of Allyl Double Bond Polymerization
Basic Characteristics:
The end group of allyl polyether is the allyl group (—CH₂—CH=CH₂), which contains an isolated double bond with relatively low steric hindrance, making it theoretically capable of free radical polymerization.
Reactivity:
Compared to highly reactive monomers like acrylates or styrene, the polymerization activity of the allyl double bond is lower due to:
Autoinhibition Effect: The allyl radical tends to undergo intramolecular hydrogen transfer during chain propagation (e.g., forming a more stable allylic radical), leading to chain termination and reduced polymerization efficiency.
Electronic Effects: The adjacent ether group (—O—) may weaken the double bond's reactivity through electron donation.
2.Optimization of UV-Induced Free Radical Polymerization Conditions
Despite these challenges, the following strategies can enhance the UV polymerization of the allyl double bond:
(1) Selection of Photoinitiators
Highly Efficient Photoinitiators: Use UV-sensitive photoinitiators (e.g., Irgacure 1173, TPO-L) that generate sufficiently reactive radicals to attack the allyl double bond.
Synergistic Initiation Systems: Combine redox initiators (e.g., ammonium persulfate/TMEDA) or co-initiators (e.g., amine compounds) to improve radical generation efficiency.
(2) Introduction of Comonomers
Highly Reactive Comonomers: Incorporate monomers with higher reactivity, such as acrylates (e.g., methyl methacrylate, hydroxyethyl acrylate) or vinyl ethers, to indirectly activate the allyl double bond via copolymerization.
Mechanism: The highly reactive monomers initiate chain propagation first, forming active chain ends that subsequently react with the allyl double bond, creating a crosslinked network.
Example Formulation:
In a waterborne polyurethane system, blending allyl polyether with hydroxyethyl acrylate and UV curing can form an interpenetrating network (IPN), improving coating water resistance and hardness.
(3) Optimization of Reaction Conditions
UV Intensity and Wavelength: Use high-intensity UV sources (e.g., mercury lamp, 365 nm) to ensure complete photoinitiator decomposition.
Oxygen Inhibition Control: Employ inert gas (e.g., nitrogen) purging or add oxygen scavengers (e.g., thiol compounds) to minimize oxygen-induced radical quenching.
Temperature Control: Moderate heating (e.g., 40–60°C) can accelerate radical migration and reaction rates.
3.Experimental Validation and Data Support
Case Study:
Literature reports that in a waterborne polyurethane system modified with allyl polyether, adding 2% Irgacure 184 photoinitiator and 10% tripropylene glycol diacrylate (TPGDA) under UV curing resulted in:
Crosslink density increasing by 1.5 times compared to unmodified systems;
Water absorption decreasing from 12% to below 5%;
Tensile strength improving from 15 MPa to 25 MPa.
Conclusion: Through copolymerization and process optimization, the allyl double bond can achieve effective UV curing, significantly enhancing material properties.
4.Summary
The double bond of allyl polyether can participate in UV-induced free radical polymerization, but its inherent low reactivity requires optimization of comonomers, photoinitiators, and reaction conditions.
Practical Applications: In waterborne polyurethanes, UV curing of allyl polyether's double bond has been successfully used to prepare high-performance coatings, adhesives, and functional films, particularly in fields requiring rapid curing and environmental friendliness (e.g., electronic encapsulation, automotive interiors).
Future Directions: Develop novel photoinitiation systems (e.g., visible-light initiators) or click chemistry (e.g., thiol-ene reactions) to further improve reaction efficiency.
Hangzhou Danwei Technology Co., Ltd. has specialized in the development of specialty polyethers for over two decades. For more product information and technical insights, visit our website: https://www.danweichem.com/.
