A Compatibilizing Strategy for Upcycling Polyethylene and Polystyrene with Ethylene/(Phenyl Functionalized α-Olefin) Copolymers Containing Continuous Comonomer Segments

Polyethylene (PE) and polystyrene (PS) are commercial plastics with large amounts of output, and their wastes have brought serious burden to our living environment. These usually exist as PE/PS mixtures and are hard or expensive to sort in some cases. PE/PS blends have poor mechanical properties due to thermodynamic incompatibilization. In principle, ethylene/(phenyl functionalized alpha-olefin) copolymers (containing PE and continuous phenyl alpha-olefin segments on one polymeric chain) would be good compatibilizers for PE/PS, but the synthesis of corresponding copolymers is much more difficult. Herein, we report the synthesis of ethylene-styrene (E-St), ethylene-allylbenzene (E-AP), and ethylene-(4-phenyl-1-butene) (E-BP) copolymers containing continuous comonomer segments via the copolymerization of E with various phenyl functionalized alpha-olefin monomers (St, AP, and BP) catalyzed by thiophene-fused cyclopentadienyl scandium complexes and study the compatibilization of resultant copolymers for HDPE/PS blends by using tensile test experiment and SEM and TEM analyses. E-BP copolymers behaved like adhesive materials with high BP incorporation ranged from 13.5 to 24.1 mol % and showed better compatibilization effect for HDPE/PS blends compared with E-St and E-AP, probably because of the longer distance between the polymeric main chain and phenyl group on its molecular structure, which favors the intermolecular pi-pi interaction between E-BP and PS during melting mixing. HDPE/PS/P4 (weight ratio: 80/20/2) blend (P4: E-BP copolymer with 24.1 mol % BP content) exhibited the greatest improvement in elongation at break (1397%), which showed a 26.3% increase, compared with the uncompatibilized HDPE/PS (80/20) blend and reached 91.5% of ultimate elongation of pure HDPE, and its tensile stress was also close to that of HDPE, indicating that P4 could be used as an effective compatibilizer for HDPE/PS mixtures that are difficult or expensive to sort.