Nanoscale constraint is known to have a significant impact on the thermal properties of materials. Although thermosetting resins have been cured in the presence of nanoparticles and nanotubes, cure of thermosetting resins under the well-defined nanoscale constraints imposed by controlled pore glass (CPG) or similar matrices has not been previously documented. In this work, we investigate the isothermal curing under nanoscale constraint of a thermosetting resin, bisphenol M dicyanate ester (BMDC), which trimerizes to form a polycyanurate network material. Differential scanning calorimetry is used to monitor the evolution of the glass transition temperature (Tg) and the conversion during cure as a function of the diameter of the silanized control pore glass matrix which is used for confinement. A Tg depression is observed for both the bisphenol M dicyanate ester monomer and the polycyanurate networks; the depression is only a few degrees for the monomer, whereas a 56 K depression is observed for the "fully cured" network in 11.5 nm pores. The nanoscale constraint is also found to strongly increase the rate of cure of bisphenol M dicyanate ester, but it does not affect the normalized Tg vs conversion relationship. The appearance of a secondary Tg above the primary Tg in the smaller pores and the associated length scale are discussed.