2,4,4-Trimethyl-2-oxazoline was polymerized, using an acid exchanged montmorillonite clay as catalyst, with the aim to study the influence of the methyl group size in the initiation and propagation processes. The effect of amount of catalyst temperature, time, and solvent on the polymerization yield and viscosity of the polymers were studied. The polymers obtained were characterized by spectrometric methods and their average molecular weights were determined by viscosimetrie and GPC data. The polymers presented similar spectrometric results and narrow molecular weight distributions. The kinetics indicated that the polymerization rate is first order with respect to monomer concentration. The polymerization results showed that the methyl groups present in the monomer affected the initiation process. Mechanism studies showed that polymerization of TMOX involves nucleophilic ring opening by attack of nitrogen to cleave the CH2-O bond of the oxazoline ring. (c) 2007 Wiley Periodicals, Inc.