We have prepared a series of carboxyalkyl methacrylates from the corresponding methoxy protected acids using pig liver esterase. From a set of these methacrylate derivatives with 3, 4, 5 and 7 methylenes as spacers, the enzymatic reaction exhibits a substrate selectivity for the terminal ester group of the molecule containing a short side-chain (3 methylenes); however, selectivity decreases as the length of the side-chain increases, resulting in partial cleavage of both ester groups in the methacrylates containing 4, 5 and 7 methylenes. This was probably due to the poor water solubility of the substrates, since the use of a tensoactive compound improved the selectivity of hydrolysis and yield. Furthermore, for side chains with 7 methylenes, hydrolysis of both esters groups is considerable (even in the presence of a tensoactive compound); therefore, the procedure is not recommended for highly hydrophobic molecules. Using the obtained carboxyalkyl methacrylates, polyelectrolytes were prepared by free radical polymerization. A pH-dependent phase-separation behavior was presented by the materials, making them suitable for applications in areas such as controlled drug release.