From Paris-Montparnasse to Rennes, many high-speed trains (TGV, "Train à Grande Vitesse") are scheduled. The trip takes about 2h00/2h15.
15 to 20 minutes are required by taxi to join the campus from Rennes station.
If you prefer public transportation, take the subway (line A) to "République", and then the bus 4 to "École de Chimie".
This services are provided from 5h20 am to 0h35 (a bus every 8 minutes).