Synthesis of poly(NIPAAm-g-PDMS) polymers using monomethacrylate-functional PDMS macromonomers was carried out over a range of compositions and graft lengths using a facile ambient initiation scheme based on the decomplexation of stabilized alkylborane-amine complexes that is triggered by simple mixing. The copolymerization of NIPAAm with MA-PDMS by this technique was confirmed by monitoring the reaction kinetics and estimating the reactivity ratios via online H-1 NMR spectroscopy. These copolymers were confirmed to contain immiscible grafts that are dispersed into nanosegregated domains by AFM, with supporting DSC analysis showing separate T(g)s for each polymer phase. DSC studies also show that both the monomer ratio and the PDMS graft length affect the locus of composition-dependent demixing temperature (T-dem) points that delineates the LCST behavior of the copolymer in water. The contrasting impact of low molecular weight (M-n similar to 1000 Da) PDMS grafts and higher molecular weight (similar to 5000 and similar to 120 000 Da) PDMS grafts on copolymer T-dem are consistent with the frequency of incorporation of hydrophobic graft segments into the acrylic main chain. These results demonstrate the feasibility of using room temperature alkylborane chemistry as a simple, convenient route for producing a variety of thermoresponsive siloxane-acrylamide copolymers that span a broad range of physical and hydrothermal properties.