Kinetics and crystallization in pH‐sensitive free‐radical crosslinking polymerization of acrylic acid

Abstract

Free-radical crosslinking polymerization and crystallization of acrylic acid (AAc) were investigated by shear storage modulus (G 0 ) measurements in pH 2, as well as in pH 6 and pH 10, by varying the molar ratio of crosslinking agent (N,N 0 -methylene bisacrylamide; MBAAm) to AAc (0.583 3 10 23 , 1.169 3 10 23 , 1.753 3 10 23 , and 2.338 3 10 23 ). Our results showed that the pregelation time was the same at pH 2, regardless of the concentration of MBAAm. The propagation time was determined by the initial feed concentration of AAc, and the length of the linear curve in the propagation was proportional to the concentration of MBAAm. The Avrami exponent (n), as an indicative of growing pattern of an infinite molecule, in the crystallization was increased in proportional to the concentration of MBAAm, and generally low at pH 2. In the deceleration phase, n was observed near 1.0 throughout the all specimens. These results indicated that (1) the length of the pre-gelation period was determined by the ionization of AAc (or pH), (2) the polymerization rate of AAc was not affected by the concentration of MBAAm, and (3) the inhomogeneity of hydrogel was determined by the growing pattern of infinite molecule in propagation phase. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42195.

Particle number and size of polystyrene‐dependent micellar crosslinking polymerization of acrylic acid

“…In the process of forming the network, trifunctional molecules composed of PAAc radicals and more than two pendant (MBAAm) molecules are generated; the infinite molecule is formed by bridging of these molecules with each other . When the infinite molecule is formed, G ′ increases significantly and gelation is observed (water soluble molecules are precipitated).…”

“…This could be attributed to the large size of the branched molecules. The size of the branched molecule may be reduced as the concentration of the crosslinking agent is increased . More compact branched molecules may result in a faster crosslinking rate .…”

“…The size of the branched molecule may be reduced as the concentration of the crosslinking agent is increased . More compact branched molecules may result in a faster crosslinking rate . If polystyrene particles are incorporated into these branched molecules, the size of branched molecules will increase significantly and the crosslinking rate will decrease.…”

“…In the free‐radical crosslinking polymerization, the molar ratio of the monomer to the crosslinking agent is important for determining the mesh size of the hydrogel. The MBAAm molecules contribute to imparting functionality to the molecules, especially trifunctional molecules . The main role of MBAAm in crosslinking is to induce the formation of junctions in the linear PAAc chain.…”

Protein and Polysaccharide-Based Electroactive and Conductive Materials for Biomedical Applications

“…These spinning methods can be implemented to improve many different biomedical applications, such as drug delivery, tissue engineering scaffolds, assistance in wound healing, and creating biosensors [10][11][12][69][70][71]. There are also other miscellaneous applications like cosmetics, producing protective clothing, and generating energy [15,18,24,25,72]. Several variants of the basic spinning method exist in addition to the basic solution electrospinning previously described, and a few related to biopolymer materials fabrication are highlighted here.…”