This product is not tested for solubility.
A literature search yielded the following: "Cross-linking agent for polyacrylamide gel electrophoresis that produces a gel which is soluble in dilute periodic acid or dilute aqueous solutions of bases". This information is from 'Polyacrylamide gels with modified cross-linkages' (P B O'Connell and C J Brady, Analytical biochemistry, 76(l), undefined (1976-11-1))
There is also a recommendation to incubate at 50 °C for 16 hours until solubilized (in Periodic acid).