A study on temperature control of a free-radical polymerization continuous stirred tank reactor (PCSTR) system was carried out subject to physical input constraint and output multiplicity. Strong thermal effects tend towards operation with stability margins, and process states are unavailable in the real-time evaluation. First, nonlinear control algorithms derived from the state-space formulation of model-based controller design for nonlinear relative-degree-one and relative-degree-two systems are addressed. Second, modified PI- and PID-types control frameworks with the aid of the equilibriumbased design are developed. In addition, the tuning procedures of controllers are relatively simple and straightforward, and the low-and-high gain technique connected to anti-reset windup design is used to enhance the process control performance.