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).