**2. Synthesis and functionalization**

Well-defined polymers with narrow polydispersity and controlled molecular weight are essential to delineate the structure–property relationship of polymeric materials [6]. Using N,N-diethyl hafnium derivative as active transition metal propagation center and ZnEt2 as metal alkyl chain transfer agent, Sita first demonstrated the living coordinative chain transfer polymerization of propene to produce amorphous atactic polypropylene (a-PP) with narrow polydispersity and various molecular weights from 12.6 kDa to 111 kDa [7]. Compared with a-PP, isotactic polypropylene (iPP) is more practical for applications in packaging and automotive parts. Coates designed a pyridylamidohafnium catalyst that produced PP with high iso-selectivity (91%) and living polymerization behavior (**Figure 3**) [8]. The study also confirmed a ligand-monomer interaction as the mechanism of stereo-control. The progress of using coordinative chain transfer polymerization has been thoroughly reviewed elsewhere [9, 10].

Block copolymers have contributed significantly to thermoplastic elastomers, soft lithography, and drug delivery [11]. Block copolymers containing polypropylene can serve as a compatibilizer to improve the interface interaction between polyolefin and other polar materials. Chen demonstrated an early example of polypropylene-block-poly(methyl methacrylate) (PP-b-PMMA) diblock copolymer using Group IV metal catalyst [12]. By taking advantage of the solubility, the
