Hydrosoluble hybrid and multifunctional polysiloxane-based photoinitiators for initiating gradient photopolymerization of acrylamide aqueous solution

Abstract

A novel hydrosoluble hybrid polysiloxane photoinitiator (W–Si–HBP₂–HHMP₂) and a hydrosoluble four-functional polysiloxane benzophenone photoinitiator (W–Si–HBP₄) were synthesized based on 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl propan-1-one (HHMP), 4-hydroxybenzophenone (HBP) and aminopolysiloxane, and their structures were confirmed by ¹H NMR, ¹³C NMR, ²⁹Si NMR and FTIR. The solubility in water, the photochemical properties, and the self-floating ability of the photoinitiators were evaluated. Both the photoinitiators exhibited great water solubility, high hydrogen abstraction rate constant (more than 7.0 × 10⁹ M⁻¹ s⁻¹), excellent photoinitiating efficiency and relatively good self-floating ability. The initiating efficiency of the polysiloxane photoinitiators was improved by appropriate increase of photosensitive groups in the molecules, but without compromise to the self-floating ability. Remarkably, the hybrid photoinitiator W–Si–HBP₂–HHMP₂ efficiently initiated photopolymerization without an amine coinitiator due to the interaction between the HBP and HHMP groups. This led to the reduction of the dosage of the amine coinitiator, and even no amine coinitiator, thereby mitigating the harm to materials and the environment derived from the amine coinitiator. Therefore, W–Si–HBP₂–HHMP₂ has great potential for application in green chemical industry. Moreover, gradient properties, involving molecular weight, glass transition temperature (T_g), and thermostability, of the polyacrylamide (PAM) rods prepared by using W–Si–HBP₂–HHMP₂ and W–Si–HBP₄ were explored by GPC, differential scanning calorimetry (DSC) and thermogravimetry (TG).