Data from previous articles on the initial polymerization rates of a series of monoalkyl substituted phenyl methacrylates were found to depend strongly on the size and position of the monoalkyl substituent in the phenyl ring. In order to investigate the possibility of correlation of all the rate data obtained, all those for phenyl methacrylate and ten other alkylphenyl substituted methacrylate monomers were fitted into empirical linear free energy relationships (LFER). Assuming steady-state kinetics and separating out the initiator decomposition contribution to the initial overall rate R,,, it was demonstrated that k' = k,/k,1'2 can be successfully correlated with LFER equations containing predominantly steric parameters. The steric influence is more pronounced in the 0-than in the p-substitution, due to the proximity of the o-substituent to the reaction propagation site. The results are corroborated by the existence of an isokinetic relationship of AH' vs. AS*, providing the proportionality of electronic effects, however small, and the predominating steric effects. The treatment is based on the assumption that the initiator efficiency f equals 1 and that the termination rate constants k , are equal for monomers of similar structure, what might represent an approximation of the true situation in the system investigated.