An immediate need in polymer chemistry is to control the chain length of a polymer. Hence it is necessary to develop a strategy that controls the chain length of a polymer. In our present work we have tried to control the chain length of acrylic acid polymer by polymerizing it using a soft-oxometalate (SOM) based catalyst. This soft-oxometalate has a porous material hydrocalumite core and on its pores, a polyoxometalate [BMIm]₂[DMMm][α-PW₁₂O₄₀] (1) (where BMIm = 1-butyl 3-methylimidazole; DMIm = 1,3-dimethylimidazole). The soft-oxometalate, [BMIm]₂[DMIm][α-PW₁₂O₄₀]@hydrocalumite (SOM 2) was synthesized by sonication within an hour. Using this SOM 2 as an initiator catalyst we obtained poly-acrylic acid of MW 1.2 kDa. While using AIBN@hydrocalumite 3 as an initiator catalyst, the M_W of PAA is obtained at around 150 kDa. This difference is attributed to the more favourable interaction of ionic POM with inorganic hydrocalumite, as compared to the less favourable interaction of organic AIBN with inorganic hydrocalumite. More favourable interaction of POM 1 with hydrocalumite leads to higher radical generation and hence shorter polymer chains as compared to that in the case of AIBN in 3, where longer chains are generated due to the low abundance of radicals at the pores of hydrocalumites. SOM 2 was characterized by X-ray diffraction (XRD), horizontally attenuated total reflection infrared spectroscopy (HATR-IR), scanning electron microscopy (SEM), electron dispersive scattering technique (EDS) and dynamic light scattering (DLS).