Poly-vinyl alcohol (PVA) crosslinked by trisodium trimetaphosphate (STMP) and sodium hexametaphosphate (SHMP): Effect of molecular weight, pH and phosphorylating agent on length of spacing arms, crosslinking density and water interaction

Poly-vinyl alcohol (PVA) with different molecular weight (27 kDa, 31 kDa, 61 kDa, 125 kDa and 195 kDa) were phosphorylated with trisodium trimetaphosphate (STMP) or sodium hexa-metaphosphate (SHMP) working at pH 10 or 12. Strong chemical hydrogels (G’>G”) were obtained starting from polymers with higher MW (61 kDa, 125 kDa and 195 kDa). Infrared Spectroscopy, UV Spectrophotometry and Rheological analyses indicated that crosslinking density is a function of a correct balance between deprotonation of polymeric chain, viscosity of the solution and length of the spacing arms. STMP and SHMP, as phosphorylating agent, behave differently changing pH and polymer MW. Crosslinked density was reflected in different capability to interact with water changing the ratio between freezable free water, freezable bound water and not freezable water.