Synthesis, surface properties, and antibacterial activity of polysiloxane quaternary ammonium salts containing epoxy group

Polysiloxane containing tertiary amino group (P(SiO)m(SiOTA)n) with different molecular weight was synthesized through equilibrium polymerization of octamethylcyclotetrasiloxane (D4) and hydrolysis of N,N-diethyl-aminopropyl-methyldimethoxysilane (TAMDESi) in the presence of potassium hydroxide (KOH) as catalyst. After that, polysiloxane quaternary ammonium salt containing epoxy group (P(SiO)m(SiOQAEp)n) with different molecular weight and cationic concentration was obtained from P(SiO)m(SiOTA)n and epichlorohydrin by quaternization. It was shown that P(SiO)m(SiOQAEp)n surfactant exhibited low surface tension (γCMC < 30.00 mN/m) at the critical micellization concentration. The thermodynamic parameters of micellization (ΔG0m, ΔH0m, ΔS0m) indicated that the micellization of P(SiO)m(SiOQAEp)n surfactant was enthalpy-driven. In particular, it was found that the glass transition temperature (Tg) of P(SiO)m(SiOQAEp)n varied in the range of −15 ∼ –70 °C according to the molecular weights, and the thermal decomposition temperature was higher than 220 °C. This type of surfactant had excellent low temperature flexibility as well as good chemical and thermal stability. The antimicrobial activity was evaluated against Gram-negative (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus), respectively. The minimum bactericidal concentration (MBC) values against S. aureus and E. coli were below 1.5–2.8 × 10−5 mol/L, which indicated that P(SiO)m(SiOQAEp)n had strong antibacterial activity.