Toughened carbon fibre fabric-reinforced composites were obtained by compression moulding of powder prepregs, using a modified cyclic butylene terephthalate (pCBT) matrix and a bi-directional [0°/90°] carbon fibre fabric. Modification of the pCBT matrix was done by adding small amounts of epoxy resin or isocyanates, acting as toughening agents. Homogeneous CBT/epoxy and CBT/isocyanate blends were obtained by melt blending in a lab-scale batch mixer by applying low temperatures and short processing times. Melt blending was stopped before the ring-opening polymerization of CBT could start. This was assured by monitoring the torque of the batch mixer. Modified CBT was then used as matrix for carbon fibre reinforced pCBT composites prepared by a simple powder prepreg method with subsequent in situ polymerization during compression moulding. Physical properties such as composite density, fibre- and void content were not significantly altered by the presence of the toughening agents. Mechanical properties were assessed by short beam interlaminar shear strength and flexural tests. ILSS, flexural strength and failure strain of the chemically modified composites increased up to 50-60% with respect to unmodified pCBT composites. Nevertheless, the flexural moduli slightly decreased due to the toughening effect of the chain extender on the pCBT matrix. Moreover, it was found that thermal properties and stability were not affected by the presence of modifiers.

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