Poly(L-lactide) macromonomers have been copolymerized with methyl methacrylate, methyl acrylate N, N’-dimethyl acrylamide (DMA) and N-vinyl pyrrolidone (VP) in order to obtain biodegradable-biocompatible comb-like copolymers with different hydrophilic characteristics. Comonomer reactivity ratios have been determined and compared with those obtained when the same comonomers are copolymerized with a model compound of the macromonomer. All results are in the range of values reported in the literature for the same comonomers in similar copolymerization processes. However, macromonomer reactivity differs from that of the model compound, depending on the comonomer considered. Thus, striking deviations are found when VP or DMA are concerned. It seems that compatibility between the growing chain and the macromonomer plays the main role in the copolymerization behaviour of the macromonomer. Miscibility studies of blends of poly(DL-lactate) (PDLA) with poly(methyl methacrylate), poly(N, N’-dimethyl acrylamide) (PDMA) and poly(N-vinyl pyrrolidone) (PVP) confirmed the repulsive interactions between PDLA and PVP and PDMA chains, which account for the deviations in the reactivity of the macromonomer when compared with that of the model compound.