A radical evolution of intellectual property law and practices has followed the rise in importance of new technology industries. Many patents today directly protect knowledge. We endeavour to account for this evolution in a simple R&D-based growth model. To deal with the non-convexity property of technologies in which knowledge is an input and fund research privately, we construct a dynamic general equilibrium with Cournot competition and free entry where knowledge is exchanged on competitive micro-markets that can be subject to imperfect exclusion.