The molecular weight of this product is not determined. It is described as a soluble starch, meaning that it is soluble in hot water. Note that the description of being a soluble starch is based on the method of preparation for the product; there is no specification for solubility:
https://www.sigmaaldrich.com/specification-sheet/SPEC/MDA/CHEM/1.01252/1012520100
The recommendation is to follow the method of preparing a 2 percent solution as found in the book Reagent Chemicals, published by the American Chemical Society:
Prepare a paste of 2.0 g of the sample with a little cold water and add to it with stirring 100 mL of boiling water. The solution should be no more than opalescent, and on cooling it should remain liquid and not increase in opalescence.