Three hydrophilic polysiloxane-polyether block a-hydroxy alkylphenones macromolecular photoinitiators with ionic liquid character (SiE (n) Im-HHMP (n = 1, 3, 5) were designed and synthesized as a novel green photoinitiator based on polysiloxane, traditional photoinitiator 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl propan-1-one (HHMP) and imidazolium. The photochemical properties, and photodegradation and photoinitiation mechanism of SiE (n) Im-HHMP (n = 1, 3, 5) were investigated by ultraviolet absorption spectroscopy, real-time infrared (RTIR) spectroscopy, electron spin resonance (ESR) and H-1-NMR. The SiE (n) Im-HHMP (n = 1, 3, 5) had good solubility in water and an absorption centered at 267 nm. The SiE (n) Im-HHMP (n = 1, 3, 5) not only can effectively initiate photopolymerization, but also have good thermal properties and low saturated vapor pressure. In addition, HPLC-MS chromatograms demonstrate that the migration of photolysis fragments of SiE (n) Im-HHMP (n = 1, 3, 5) from the cured material was alleviated significantly due to their high molecular weight. The cured films initiated by SiE (n) Im-HHMP (n = 1, 3, 5) have good thermostability compared with that by HHMP. More importantly, antibacterial tests of the films prepared using SiE(1)Im-HHMP against Escherichia coli and Staphylococcus aureus bacteria strains proved that SiE(1)Im-HHMP possesses effective antibacterial activity. The SiE (n) Im-HHMP (n = 1, 3, 5) exhibits promise in preparing green materials and antibacterial materials.