**2.2 Modification of natural pre-polymers**

Water swellable hydrophilic hydrogel polymer can also be synthesized by performing appropriate chemical modification of natural polymers such as gelatin, *Smart Polymer Hydrogels as Matrices for the Controlled Release Applications… DOI: http://dx.doi.org/10.5772/intechopen.102904*

**Table 1.**

*Typical monomers used for hydrogel synthesis.*

starch, alginate, cellulose, chitosan, pectin, etc. via grafting using acrylic monomers. Insitu incorporation of micronutrient (boron) on acrylic acid grafted guar gum-based hydrogel [19], acrylic monomers grafted chitosan hydrogel [20], urea loaded cellulose [21], carboxymethylcellulose-hydroxyethylcellulose cross-linked with citric acid [22], etc. can also be used as matrices for the controlled release of fertilizers and water in agricultural field.
