A uniform dispersion of reactants is necessary to achieve a complete reaction involving multiple components. Utilizing a combination of infrared spectroscopy, thermal analysis and low field NMR, we have elucidated the role of three types of reactive plasticizers on the crosslinking reaction between hexamethylenetetramine and phenol formaldehyde resin. These two seemingly dissimilar reactants are responsible for the exceptionally high mechanical strength in a number of organic-inorganic composites. The efficiencies of the curing reaction and the achieved crosslinked structures are strongly dependent on the type of plasticizer employed. Infrared active vibrations are used to characterize the changing molecular structures of the individual reactants as a function of temperature. The T-1 spin-lattice relaxation time measured using low field NMR is especially useful for the characterization of segmental dynamics of the chains in the formation of the extremely rigid crosslinked product. This study shows that the amount of crosslinking and the crosslinked structure can be very different for the three types of reactive plasticizers and also different in comparison to non-reactive plasticizers. We are also able to correlate the reactivity and functionality of the plasticizer to the crosslink density in the reacted product. (C) 2016 Published by Elsevier Ltd.