Compounds of formula (I): ##STR1## [wherein: R.sup.1 is a cyclic amino group, or a dialkylamino group; R.sup.2 a group of formula --NHCHR.sup.3 R.sup.4 wherein R.sup.3 and R.sup.4 are each alkyl aryl or aralkyl, or together form a cycloalkyl group, or R.sup.2 is an aromatic heterocyclic group, or a group of formula --B--S(O).sub.m --R.sup.5 wherein R.sup.5 is a substituted alkyl group, or an aromatic heterocyclic group; B is an alkylene or alkylidene group; m is 0, 1 or 2; A is a group of formula --CH.dbd.CH-- or --(CH.sub.2).sub.n --, where n is 1, 2 or 3]; and salts thereof have valuable anti-ulcer activity.

A method for preparing polymer particles having diameters within the range from less than 0.1 micron to about 200 microns is described. The method involves encapsulating at least one water insoluble monomer within a water soluble polymer containing at least one thiol functional group. This is accomplished by combining an organic phase containing the monomers and a free radical source with an aqueous phase containing the polymer to form a two phase mixture, and subjecting the two phase mixture to agitation or ultrasonic irradiation. This invention allows for the preparation of polymer particles with sizes not available by conventional suspension or emulsion polymerization methods. It also provides for polymer particles within the specifed size range having compositions not readily obtained by other polymerization methods. The polymer particles made by this method have an exterior portion of water soluble polymer bound to an interior polymer. The exterior polymer, when it is a condensation polymer such as for example a protein, may be removed by acid hydrolysis.