Synthesis And Properties Of Novel Trisiloxane Surfactants

Trisiloxane surfactant is a kind of efficient organic silicone surfactant with hydrophobic groups based on1,1,1,3,5,5,5-heptamethyl trisiloxane and hydrophilic group based on the hydrophilic chain segment. Trisiloxane surfactant distributes in the interface with the "umbrella" structure, makes the surface tension of water fall to about20mN/m and possesses the ability of "super wettability" or "super spreadability". So it could be widely used in wetting agent, foam stabilizer, lubricant, emulsifier, coating, agriculture and cosmetic etc.At present, the most studied polyether modified trisiloxanes are allyl polyether modified trisiloxane3, but the conversion rate is not high. The synthetic procedure of allyl polyether modifyed trisiloxane3was studied and optimized in this paper. The results showed that the reaction temperature was100℃, the molar ratio between polyether and trisiloxane was1.2:1, the activated temperature was60℃, the activated time was30min, the amount of catalyst was0.0015wt%of trisiloxane, the reaction time was2h. The conversion rate reached99.3%.Trisiloxane surfactant has some prominent advantages, but it is easy to hydrolyze. So the increase of surface tension and the reduction of the surface activity derived from hydrolysis affect the applications.In this paper, monomethy/ether of polyethylene glycol olefinic acid esters6,9,13and15were obtained from methoxy polyethylene glycol and unsaturated acid chloride4,8and12. And then platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Karstedt catalyst) was selected from different catalytic systems and different reaction conditions, to be used to synthesize the modified trisiloxane7,14and16in the microwave reactor, and their structures were confirmed by IR,1HNMR,13CNMR and Mass spectroscopy.The properties of the modified trisiloxanes were tested, such as the surface tension, the stabilities under acidic and basic conditions, contact angle, emulsification and foaming performance. The results showed that compounds3,7,14,16had strong abilities to reduce the surface tension of solution. The surface tensions were20.2,19.3,19.2and19.6mN/m respectively, the value of CMCs were1.7×10-4,9.5×10-4,5.1×10-4and8.1×10-4mol/L respectively. Trisiloxane3could be stable for a month when the value of pH was5-9; trisiloxane7could be stable for a month when the value of pH was4～9; crotonic acid ester modified trisiloxane14could be stable for a month when the value of pH was3～9; butanol acid ester modified trisiloxane16was unstable under acidic and basic conditions. This indicated that trisiloxane14had good stability under acidic and basic conditions due to the ethyl protective effect. It also showed that the trisiloxane surfactant had the super spread ability and excellent emulsifying properties, and it belongs to the low foaming type surfactant.Therefore, introduction of hydrophobic substituents (such as methyl, ethyl or isopropyl) neighboring to Si-O bond is feasible for preventing the contact between silicon oxygen bond and water molecules. This method can slow the hydrolysis rate, so as to enhance the stability under acidic and basic conditions.