The kinetics of aminolysis between two different active ester polymer brush platforms, poly(4-pentafluorophenyl acrylate) (poly(PFPA)) and poly(N-hydroxysuccinimide-4-vinyl benzoate) (poly(NHS4VB)), are compared using primary and aromatic amines with varying reactivity toward postpolymerization modification. UV-vis was used to monitor the aminolysis of both brush platforms with 1-amino-methylpyrene (AMP), 1-aminopyrene (AP), and Ru(bpy)(2)(phen-5-NH2)(PF6) (Ru(2+)A). Using a pseudo-first-order kinetics model, the pseudo-first-order rate constant (k') was calculated for each system. The k' of poly(PFPA) modified with AMP, AP, and Ru(2+)A were 2.46 x 10(-1), 5.11 x 10(-3), and 2.59 X 10(-3) s(-1), respectively, while poly(NHS4VB) can only be functionalized with the alkyl amine, albeit at a slower rate constant, k' of 3.49 X 10(-3) s(-1), compared to that of poly(PFPA) with AMP. The kinetics of surface-initiated photopolymerization of PFPA from oxide surfaces was also investigated as an effective method to control grafting density and film thickness.