This work studies the effects of changing equilibrium monomer surface concentration on the deposition rates and the number-average molecular weights (M-n) of polymers deposited from glycidyl methacrylate and cyclohexyl methacrylate using initiated chemical vapor deposition (iCVD) with tert-butyl peroxide as the initiator. Both the surface temperature and the monomer partial pressure were varied to effect different equilibrium surface concentrations, measured using a quartz-crystal microbalance. In either case, the deposition rate and Mn were found to be linear in equilibrium monomer surface concentration. This strong dependence concludes that chain propagation occurs predominantly on the surface and suggests that the surface concentration is at equilibrium during iCVD, which in turn infers that the adsorption of monomer is not the rate-limiting step in the polymerization process.