Hello dear, I think that you can modify starch with acrylic acid by esterification reaction and then polymerize by free radical. Another method is the solution polymerization of starch with acrylic acid.
Yes. This is known commercially as Super Slurper, and was invented and patented by the USDA many years ago. See, for example: http://www.m2polymer.com/html/history_of_superabsorbents.html