The ratio of ethylene oxide (EO) and propylene oxide (PO) units in allyl polyethers, as well as their arrangement, significantly affects the properties of polyether-modified polydimethylsiloxane (PDMS). This influence is reflected in the following aspects:
1.Hydrophilic-Lipophilic Balance (HLB Value)
Effect of EO Units:
EO is a strongly hydrophilic group. Increasing the proportion of EO enhances the water solubility and hydrophilicity of polyether trisiloxane, making it suitable for applications requiring high wettability or water-based systems (e.g., pesticide spray adjuvants).
Effect of PO Units:
PO contains a methyl group, imparting hydrophobicity. A higher PO ratio improves oil solubility and reduces dynamic surface tension, making it suitable for oil-based environments or applications requiring spreading performance (e.g., coating leveling agents).
2.Surface Activity and Wettability
Surface Tension: A higher proportion of PO increases hydrophobicity, further reducing surface tension (especially at low concentrations), but excessive PO may decrease solubility.
Dynamic Wetting Speed: Short EO chains (e.g., EO=5~8) combined with PO optimize dynamic wettability, making them suitable for rapid-spreading scenarios (e.g., foliar fertilizer adjuvants).
Electrolyte Resistance: A higher PO ratio improves salt tolerance (e.g., in hard water environments).
3.Molecular Structure Arrangement and Thermal Stability
Block vs. Random Structure:
EO-PO Block Copolymers: EO segments on the outside enhance hydrophilicity, while PO segments inside strengthen hydrophobicity, forming micellar structures and improving emulsification.
EO-PO Random Copolymers: Uniform distribution of hydrophilic and hydrophobic segments ensures stable interfacial adsorption.
Thermal Stability: The methyl group in PO provides steric hindrance, making it more resistant to thermal decomposition than EO segments.
4.Biodegradability and Environmental Adaptability
EO Units: Poly-EO chains are easily degraded by microorganisms, offering better environmental friendliness.
PO Units: Hydrophobic methyl groups slow degradation but enhance persistence in soil or oily media.
5.Viscosity and Molecular Weight
Higher EO Ratio: Increases chain flexibility, lowers viscosity, and improves fluidity (suitable for spray applications).
Higher PO Ratio: Increases chain rigidity, raising viscosity and potentially affecting permeability.
6.Optimization Strategies in Practical Applications
Pesticide Adjuvants: Introducing a certain proportion of PO reduces the surface tension of spray solutions to 20-25 mN/m, promoting leaf spreading.
Defoamers: A higher PO content enhances hydrophobicity, improving foam-breaking efficiency.
Cosmetic Emulsifiers: EO/PO block structures (e.g., Allyl-PPO-PEO) balance water-oil compatibility.
Conclusion
By adjusting the EO/PO ratio and segment arrangement, the HLB value, surface activity, thermal stability, and other properties of polyether-modified PDMS can be precisely tailored. For example:
High-EO Systems: Suitable for water-based, high-wettability, and eco-friendly applications.
High-PO Systems: Suitable for oil-based, high-temperature, and fast-spreading requirements.
In practical applications, molecular design should consider specific performance needs (e.g., dynamic wetting, salt resistance, degradability).
Hangzhou Danwei Technology Co., Ltd. has specialized in the development of specialty polyethers for over 20 years. For more product information and technical insights, visit our website: https://www.danweichem.com/
