Graft copolymerization of acrylic acid on methylcellulose by ceric ion/p‐xylene redox pair

Abstract

ABSTRACT:The graft copolymerization of acrylic acid onto methylcellulose by ceric ion/p-xylene redox pair was investigated in aqueous media under homogeneous conditions. The graft yield dependency on p-xylene concentration in the range 1.8 -45.0 ϫ 10 Ϫ5 M showed a minimum and an enhanced yield when the methylcellulose interacted with ceric ion and p-xylene for an initial period of 10 min (preoxidation time) prior to addition of monomer to the reaction medium. This was attributed to the presence of two kinetically controlled reactions initiated by p-xylyl radical and diradical species. At prolonged preoxidation times of 30 and 60 min, the graft yield dependency on p-xylene concentration was normal and suggested the presence of only one initiating species. The effect of ceric ion on the graft reaction in the concentration range of 8.33-83.3 ϫ 10 Ϫ3 M was optimal at 131% graft yield for ceric ion concentration of 16.7 ϫ 10 Ϫ3 M and was reduced significantly by as much as 75% at the highest concentration of the latter. The temperature dependency of graft yield was negative in the region 30 -50°C. At 50°C the initial rate of graft was only 37% of the value at 30°C.

Polyacrylamide‐g‐alginate‐based electrically responsive hydrogel for drug delivery application: Synthesis, characterization, and formulation development

“…After 60 min, the resulting copolymer was allowed to cool to ambient temperature and the product was poured into excess methanol and kept for 24 h to dewater. The copolymer was then filtered, washed repeatedly with methanol, and dried at 50 C. Mass of the graft copolymer was taken and the percent grafting efficiency was calculated using the following relation 21 :…”

Graft copolymerization of acrylic acid onto methylcellulose by potassium permanganate‐p‐xylene redox pair

“…These features were associated with two kinetically controlled reactions, arising from two distinct initiating species, namely, a p-xylyl radical and a diradical. [11][12] Similar features have been observed for the potassium permanganate-p-xylene redox pair as an initiator of the graft copolymerization of acrylonitrile onto kenaf fiber, 11 although no detailed studies were conducted on the overall grafting characteristics.…”

“…The minimum and maximum graft yields of 61 and 128% correspond to XY concentrations of 3.73 ϫ 10 Ϫ3 and 5.60 ϫ 10 Ϫ3 M respectively. The profile of the post minimal graft yield may be associated with initiation of the graft reaction by a diradical species (II) derived from the mutual interactions of two p-xylyl radicals (I): [11][12] Ceric ion in combination with XY appears to be more effective for the graft copolymerization of vinyl monomers onto cellulosic substrates than the analogous permanganate-XY redox pair under identical reaction conditions.…”

“…The observance of negative temperature dependence for the permanganate-XY redox initiated system is consistent with a previous report on ceric-ion-XY initiated graft copolymerization of acrylic acid onto methylcellulose. 12 It would seem that the negative temperature dependency of the graft reactions is trace- able to the reactivities of XY and its diradical derivative, both of which are expected to participate in transfer reactions. The negative dependence of graft yield on temperature suggests that the composite activation energy for the process is positive and that transfer reactions of high activation energy are favored as temperature increases.…”