Polyurethanes with synergistically enhanced thermal, mechanical, and surface properties via bulky TMS side chains

Two novel types of amine-terminated siloxane chain extenders bearing bulky trimethylsiloxy (TMS) side groups (EAA-trisTMS and EAA-diTMS) were successfully synthesized via the addition reaction of 1,3-bis(3-glycidyloxypropyl)-1,1,3,3-tetramethyldisiloxane with 3-aminopropyltris(trimethylsiloxy)silane or 3-aminopropyldi(trimethylsiloxy)methylsilane. Subsequently, these chain extenders were incorporated into polyurethane (PU) backbones to prepare a series of TMS-modified polyurethane films. The chemical structure, thermal stability, mechanical properties, surface morphology, and dielectric properties of the resulting copolymers were systematically investigated. The results demonstrate that the introduction of bulky TMS side chains significantly enhances the thermal stability of the PU matrix. The modified polyurethanes exhibit a distinct microphase-separated morphology. The flexible, bulky organosilicon side chains act as internal plasticizers, resulting in a remarkable increase in elongation at break. Surface analysis reveals that the umbrella-like TMS groups preferentially migrate to the air/polymer interface, forming a dense hydrophobic layer. The water contact angle increases significantly to above 100 °, and surface saturation is achieved at approximately 10 wt% loading. Moreover, the incorporation of non-polar organosilicon segments effectively reduces the dielectric constant of the material. This work presents a new strategy for designing high-performance polyurethane materials with excellent hydrophobicity, thermal stability, and low dielectric properties. • Novel amine-terminated siloxane chain extenders with bulky TMS side groups synthesized. • TMS-modified PU shows ∼27 °C higher thermal stability and improved flexibility. • Hydrophobicity enhanced: water contact angle >100 °, surface saturated at ∼10 wt%. • Bulky TMS side chains promote microphase separation and act as internal plasticizers. • Low dielectric constant achieved via non-polar TMS incorporation and free volume increase.