In this study, poly (dimethylsiloxane)urethane-graft-poly(methyl methacrylate) (PDMS urethane-g-PMMA) copolymers with low crosslinking density were synthesized. Glass transition temperatures of the copolymers were investigated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Results confirm that PDMS urethane-g-PMMA is miscible in the 2,4-TDI (2,4- toluene diisocyanate) system, whereas it is partially miscible in the m-XDI (m-xylene diisocyanate) system. Free, intra- (urethane-urethane), and inter-(urethane-ester) association hydrogen bonding exist in the urethane group of copolymers. The inter-association hydrogen bonding can improve the compatibility of the copolymer components. The relationship between the frequency shift and enthalpy confirm the distribution of hydrogen bonding in the macromonomer and copolymer. Ninety percent of the hydrogen bonding is by interassociation in the 2,4-TDI system. The intra-association hydrogen bonding in the m-XDI system is higher than that in the 2,4-TDI system. Consequently, aggregation may occur easily in the siloxanegrafted chain in the m-XDI system.