Abstract
The aqueous photo-living radical polymerization of sodium methacrylate (NaMA) was attained using 2,2′-azobis2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]-propionamide (V-80) as the initiator and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HTEMPO) as the mediator in the presence of (4-fluorophenyl)diphenylsulfonium triflate (FS). The polymerization was carried out in water at room temperature by irradiation using a high-pressure mercury lamp. Whereas the polymerization by V-80 and/or FS in the absence of HTEMPO produced polymers with very high molecular weights and broad molecular weight distributions, the HTEMPO-mediated polymerization provided still lower-molecular-weight distributions using both V-80 and FS. The first-order time-conversion plots had an induction period up to 2.5 h; however, they thereafter showed a linear increase. The conversion-molecular weight plots also exhibited a linear correlation. A linear correlation was also obtained for the plots of the molecular weights versus the reciprocal of the initiator concentration. Based on these three correlations, it was found that the HTEMPO-mediated photopolymerization proceeded by a living mechanism.
Highlights
Poly(sodium methacrylate) (PNaMA), a water-soluble polyelectrolyte, has been used for many objectives, such as surface modification of the wettability and friction [1], suppression of cell adhesion and protein adsorption [1, 2], and self-assembly studies on amphiphilic block copolymers in aqueous media [3,4,5,6,7]
This paper describes the photoliving radical polymerization of NaMA in an aqueous medium using 4-hydroxy-TEMPO (HTEMPO) as the mediator, (4-fluorophenyl)diphenylsulfonium triflate (FS) as the water-soluble photo-acid generator (PAG), and 2,2 -azobis{2-methyl-N-[1,1bis(hydroxymethyl)-2-hydroxyethyl]propionamide} (V-80) as the initiator
The photoradical polymerization of NaMA was performed in water using HTEMPO as the mediator, V-80 as the initiator, and a water-soluble photo-acid generator, FS, as the accelerator at room temperature by irradiation (Scheme 1)
Summary
Poly(sodium methacrylate) (PNaMA), a water-soluble polyelectrolyte, has been used for many objectives, such as surface modification of the wettability and friction [1], suppression of cell adhesion and protein adsorption [1, 2], and self-assembly studies on amphiphilic block copolymers in aqueous media [3,4,5,6,7]. The nitroxide-mediated photo-controlled/living radical polymerization has been established for methyl methacrylate (MMA) using the derivatives of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in the presence of the photo-acid generator (PAG) of diaryliodonium hexafluorophosphate [13,14,15,16,17], triarylsulfonium triflate [18,19,20,21,22], and an iron-arene complex [23] This polymerization was used for the photodispersion polymerization of MMA in an alcoholic medium that produced monodispersed microspheres [24]. Scheme 2: The mechanism of the HTEMPO-mediated photopolymerization of NaMA in the presence of V-80 and FS
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