Silyl ether-modified polyalkylene glycols with high viscosity index

Abstract To improve the viscosity index (VI) of polyalkylene glycol (PAG), the hydroxyl group was modified into a silyl ether. The hydrogen bond of the unmodified PAG was broken and its kinematic viscosity at 40 oC (KV40) was substantially reduced. The kinematic viscosity of the modified PAG at 100 oC (KV100) showed a slight reduction, compared with the unmodified one, demonstrating that the VI could be greatly improved. The VIs of polypropylene glycol (PPG), which contains two hydroxy groups, (Mn = 1,120) and its trimethylsilyl ether (PPG-TMS), were 146 and 299, respectively. A similar improvement in VI was observed in PAG with different molecular weights and with different types of silyl ethers.