Propene and 7-methyl-1,6-octadiene (MOD) were copolymerized with the catalyst system rac-Et[Ind](2)ZrCl2/MAO in semibatch reactions and under constant comonomer concentrations using an autoclave setup that is equipped with an ATR-FTIR sensor coupled with a dosage system for the liquid MOD comonomer. The concentration of the monomer propane is regulated precisely in both types of polymerization by a gas flow controller. This setup enables to monitor the MOD concentration on-line and in real-time during the reaction by following characteristic bands arising from the double bonds. Copolymers with poorly defined incorporation data and thermal properties were obtained without control of the MOD concentration in time. This is caused by a nonuniform distribution of the MOD units over the polymer chains due to a relatively large shift of the MOD concentration during the copolymerization reaction. By means of solvent extraction fractionation experiments, these copolymers could be fractionated into three fractions with different amounts of incorporated MOD, varying from 11.5 to 7.2 mol %. Functional copolymers with uniform architectures (up to 30.5 mol % incorporated MOD) were prepared by using the on-line ATR-FTIR data to control the MOD concentration during the copolymerization reactions.