New effort to synthesize star isotactic polypropylene

This study demonstrates an efficient arm-first approach for the synthesis of star isotactic polypropylene (iPP) via two steps. In the first step iPP “arm” containing a methoxysilane-terminal end was prepared via a designed chain-capping reaction in propylene polymerization, and in the second step an acid-catalyzed intermolecular elimination reaction was carried out between methoxysilane groups at these “arm-ends”, finally giving star polymers with iPP as the arm and Si–O–Si cross-linking structure as the core. Moreover, the arm number could be tailored from 3 to 8 by adjusting the star-forming (cross-linking) reaction time. The chemical structures of “arm” and star polymers were monitored by ¹H-NMR, and the star-topological structure evolution was investigated via gel permeation chromatography incorporating a light scattering detector (GPC-LS). The star polymers’ absolute molecular weights as well as their dilute solution properties including the intrinsic viscosity ([η]) and the Mark–Houwink exponent (α) were determined by GPC-LS, confirming the successful synthesis of star iPPs.