Chloromethylpolystyrene known as merrifield resin, PL-CMS is a copolymer support for solid phase synthesis of peptides using Boc chemistry.

Boc-amino acids are typically attached to the resin as a cesium salt, although other techniques have also been used. A slight excess of acid is neutralized with cesium carbonate and the activated acid isolated by evaporation.

Other useful techniques for cleavage include saponification or hydrolysis to create free acids, trans-esterification to create methyl esters, or aminolysis to form carboxamides. PL-CMS can be used to generate a variety of other supports by the attachment of appropriate linkers, particularly through Williamson ether synthesis.