Synthesis of superabsorbent resin (SAR) was achieved by a new method, that of direct UV photopolymerization, and in particular the synthesis of a SAR of acrylic acid-potassium acrylate copolymer by UV photopolymerization was investigated. Influences of ratio (mol) of acrylate monomer to acrylic acid monomer, photoinitiators, crosslinking agents, and exposure time of UV light on the water-absorbent properties were investigated. The results showed that the water absorbency (Q) of SAR based on Irgacure 1700 or Irgacure 1800 was 545-530 mL/g, but under the same conditions Q was 450 mL/g for the SAR based on Irgacure 651. N,NЈ-Methylene bisacrylamide, hydroethyl acrylate, and glycerol were used as crosslinking agents, of which N,NЈ-methylene bisacrylamide was the most effective. It crosslinked the molecular chains through attending the copolymerization with acrylic acid (AA) and potassium acrylate. When the exposure time was 5 min, the value of Q was 1368 mL/g (the content of N,NЈ-methylene bisacrylamide was 100 ppm).

ABSTRACT:A new method of synthesizing a superabsorbent resin (SAR) from an acrylic acid/ammonium acrylate copolymer by direct UV photopolymerization was studied. The effects of the degree of neutralization of acrylic acid, the photoinitiators, the crosslinking agents, and the UV-light exposure time on the water absorbency (Q) were investigated. The results showed that Q of an SAR based on Irgacure 1700 or Irgacure 1800 and Irgacure 651 was high, reaching about 1200 mL/g, but under the same conditions, Q was low for an SAR based on other photoinitiators. The UV absorption spectrum proved that the photoinitiators matched the UV light source. Among the crosslinking agents, N,NЈ-methylene bisacrylamide was more efficient than the others at a small concentration and a high value of Q.13 C-NMR spectrometry was used to identify the mechanism of the crosslinking reaction through the esterification of hydroxyethyl acrylate (HEA) and 2-hydroxypropyl acrylate with carboxylic acid group in acrylic acid/ammonium acrylate copolymerization, but the efficiency of the crosslinking reaction by esterification was lower than that of the copolymerization of vinyl groups in the crosslinking agent. Q of the acrylic acid/ammonium acrylate copolymer for the SAR reached 1255 mL/g under certain conditions (degree of neutralization of acrylic acid ϭ 75%, Irgacure 651 concentration ϭ 0.2 wt %, [HEA] ϭ 0.2 wt %, exposure time ϭ 10 min).

A new synthesis method of pH-response superabsorbent hydrogels (SHG) was achieved by direct ultraviolet (UV) photopolymerization, and in particular, the synthesis of SHGs of acrylic acid (AA), sodium acrylate (AANa), and methacrylcholine chloride (MACC) tricomponent copolymer by UV photopolymerization were investigated. The pH value responsive behavior of SHG with different monomer ratios of MACC and AA was researched, and SHG showed large swelling properties at pH value approximately 7. Influences of monomer ratio (mol) of AANa to AA, photoinitiators, crosslinking agents, and exposure time of UV light on the water absorbent properties were studied. The results showed that the water absorbent capacity of SHG based on photoinitiators:Esacure KTO46 or Irgacure 651 can reach comparatively high, N,N 0 -Methylene bisacrylamide and diethylene glycol diacrylate (DEGDA) were high efficient crosslinking agents for its crosslinking the molecular chains through attending the copolymerization with monomers. When the exposure time was 10 min, the distilled water absorbency of SHG was 1503 mL/g under the condition: content of MACC, 14.3 wt %; monomer ratio (mol) of AANa to AA: 5.67; content of DEGDA and Irgacure 651, 0.0025 and 0.25 wt %.

Synthesis of superabsorbent hydrogel (SAHG) of acrylic acid-potassium acrylate copolymer by direct Ultraviolet (UV) photopolymerization is a new method. The effects of degree of neutralization of acrylic acid (AA), photoinitiators, crosslinking agents, and exposure time of UV light on water absorbent properties were investigated. The results showed that the water absorbency (Q) and the salt solution (NaCl, 0.9%) absorbency (Qs) of SAHG, based on Irgacure 651, are high, reaching about 1400 and 130 mL/g, respectively. UV absorption spectrum proved that peak of UV absorption of Irgacure 651 matched the UV light source we used. Among the crosslinking agents, N,NЈ-methylene bisacrylamide is more efficient than others, because of its very small content and high Q.13 C NMR spectrometry was used to identify the mechanism of crosslinking reaction through esterification of hydroxyethyl acrylate (HEA) and 2-hydroxypropyl acrylate (HPA) with carboxylic acid group in acrylic acid-ammonium acrylate copolymerization, but efficiency of crosslinking reaction by esterification was lower than that of copolymerization of vinyl group in crosslinking agent. The Q of acrylic acidpotassium acrylate copolymer of SAHG reaches 1592 mL/g under the following conditions: degree of neutralization of acrylic acid is 80%, content of Irgacure 651 is 0.25 wt %, content of HEA is 0.2 wt %, and exposure time is 10 min.