Polymers having a zwitterionic pendant group have found a wide range of applications such as fungicides, fire-retardants, lubricating oil additives, emulsifiers, cryoprotectants, and electronic materials. Their properties depend not only on the polymer main chains but also on the zwitterionic structures. In this article, the synthesis of novel polymers having zwitterionic structures is described. A zwitterionic monomer (4-vinylphenyl isothiocyanate [VPI]-1,2-dimetyl-1,4,5,6,-tetrahydropirimidine [DMTHP]) was synthesized by the reaction of VPI and a cyclic amidine DMTHP. A radical polymerization of VPI-DMTHP was carried out using 2,2-azobis(2,4-dimethyl-4-methoxy)valeronitrile (V-70) as an initiator to give poly(VPI-DMTHP). The obtained poly(VPI-DMTHP) was not soluble in any of the investigated organic solvents, probably because it had a networked structure resulting from the ionic interactions. Copolymers of VPI-DMTHP and other vinyl monomers such as styrene, methyl methacrylate, t-butyl methacrylate, and N-vinylpyrrolidone were synthesized. The obtained copolymers were also insoluble in all of the examined common organic solvents even when the VPI-DMTHP content was low (5 mol %), indicating the existence of strong ionic interactions in the zwitterionic moieties. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2303-2309