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Copolymerization of ethylene (E) and halogenated styrenes is screened by half-sandwich scandium catalyst 1 and constrained geometry scandium catalysts 2 – 4. The methyl-substituted N -heterocyclic carbene fluorenyl catalyst 3 initiates the E copolymerization with para -fluorostyrene (p FSt), para -chlorostyrene (p ClSt) and para -bromostyrene (p BrSt) to pseudo -random copolymers with an incorporation level of up to 46.3 mol%, 45.1 mol% and 37.5 mol%, respectively. Increasing reaction temperatures from 20 to 60 °C results in an increment of E/ p FSt copolymerization activity from 5.64 × 105 to 8.10 × 105 g mol Sc −1h−1. In contrast, a higher temperature dramatically depresses the E/ p ClSt copolymerization (4.86 × 105 g mol Sc −1h−1 at 20 °C vs 0.90 × 105 g mol Sc −1h−1 at 60 °C). At 20 °C, the E/ p BrSt copolymerization only affords a little pure polyethylene, and the E- p BrSt copolymer with 37.5 mol% p BrSt is obtained at 0 °C. The pseudo -random copolymers of E and halogenated styrenes give one glass transition temperature and decomposition temperature on DSC and TGA curves. Image 1 • Pseudo-random ethylene-halogenated styrene copolymers are synthesized using constrained geometry scandium catalysts. • A positive comonomer effect is found in ethylene copolymerization with halogenated styrenes. • The copolymerization activity is very sensitive to the reaction temperature. [ABSTRACT FROM AUTHOR]