Tuning polymerization performance in ethylene–propylene copolymerization using a constrained geometry titanium catalyst [t-BuNSiMe2(Me4Cp)]TiMe2: Insights from random and block copolymerization studies

In this study, a titanium-based constrained geometry catalyst, [t-BuNSiMe2(Me4Cp)]TiMe2, was synthesized and activated with methylaluminoxane for ethylene-propylene random and block copolymerization. The catalyst exhibited optimal activity at 70°C, yielding random copolymer chains with trace amounts of long polyethylene crystalline segments. When the ethylene content fell below 35%, random copolymers failed to crystallize. The block copolymerization system achieved maximum catalytic activity at a reaction temperature of 50°C and an ethylene block duration of 10 minutes. Shorter ethylene block durations correlated inversely with enhanced catalytic activity, increased molecular weight (peaking at 2.88 × 105 g/mol), and a narrower molecular weight distribution. The predominant component comprised extended PPP segments, constituting over 50% of the total copolymer composition. Within the polymer chains, propylene monomers were primarily incorporated as PPP and PPE structural motifs. Moreover, a progressive decrease in [PPP] content was observed with increasing ethylene block duration, whereas [PPE] content exhibited the opposite trend. This inverse relationship suggested that PPP segments gradually transform into PPE configurations via ethylene monomer insertion. These findings demonstrated that product structure and properties can be effectively tuned by adjusting initial monomer feed ratios or the timing of monomer block introduction.