In this work, the problem of controlling (possibly open-loop unstable) continuous free-radical solution polymer reactors with continuous measurements of temperature, level and flows and discrete-delayed (DD) measurements of molecular weight (MW) is addressed. On the basis of physical insight and the relative degrees and detectability structure of the reactor system, a muti-input-multi-output (MIMO) interlaced observer-control design is performed within a constructive framework yielding a linear-decentralized control scheme with volume, temperature, and monomer components driven by continuous-instantaneous measurements, and a MW component driven by DD measurements. The scheme has reduced modeling requirements and conventional-like tuning guidelines drawn from stability considerations. The proposed approach is illustrated and tested with a representative example through simulations.