PVA was purchased from Dong Yang Chemical Indus-
tries Co. Ltd. The number-average degree of polymeriza-
tion (P n ) and degree of saponification (DS) were 1700
and 99.9%, respectively. Glyoxal (40% aqueous solution)
and PAA were obtained from Aldrich. Polyethylene gly-
col (PEG 400), phosphoric acid, and sulfuric acid