Traditionally, multilayered composites have been manufactured in multiple steps that involve the fabrication of each layer separately and the bonding them together by using adhesives or secondary bonding. More recently, manufacturing techniques have been developed that enable the manufacture of multilayered hybrid composite parts in a single step. In one such technique known as coinjection resin transfer molding (CIRTM), two or more resins are simultaneously injected into a mold filled with a stationary fiber bed. This method not only cuts down manufacturing costs and time, but also offers the potential of cocure of the adjacent thermosetting resins inside the mold, which could aid in the formation of a tougher interphase between the layers and improve long-term durability. The advantages offered by coinjection are, however, dependent on the successful cocure of the resins involved, and hence, there exists a need to determine compatible resin systems for coinjection. By compatible, it is meant that the resins must cure when in contact with each other, have compatible cure cycles (i.e., cure temperature, cure time, etc.), and result in acceptable physical and mechanical properties. The most commonly used matrix resins are vinyl-ester resins. The cure of vinyl-ester resin was found to be severely limited by contact with phenolic resin. This necessitates an impermeable separation layer between phenolic and vinyl-ester resins in CIRTM manufacture. A possible candidate for this separation layer was epoxy-amine-based prepregs or adhesive layers. Thus, the cocure of mixtures of phenolic with epoxy-amine was studied, and it was found that phenolic resin significantly affects the cure of epoxy-amines. A model to quantify the effect of phenolic resin on the cure of epoxy-amines has been proposed. By using this model, the fraction of primary amine consumed by the phenolic can be estimated. It was found that increasing the initial amine concentration in the cocure reaction mixture leads to an increase in the epoxy conversion as well as the T-g of the material. Therefore, it is recommended that, in cocure of epoxy-amine and phenolic resins, the initial concentration of amine must be greater than the stoichiometric amount to compensate for the loss of amine to the phenolic resin. (C) 2004 Wiley Periodicals, Inc.