Synthesis of azide end-functionalized isotactic polypropylene building block and renewed modular synthesis of diblock copolymers of isotactic polypropylene and poly(ε-caprolactone)

This article details a synthesis of azide end-functionalized isotactic polypropylene (i-PP), a unique polymeric building block that can engage in Huisgen's 1,3-dipolar cycloaddition of azide and alkyne (click reaction) to construct well-defined i-PP-based polymer architecture. Controlled, consecutive chain transfer reaction to 1,2-bis(4-vinylphenyl)ethane and hydrogen in metallocene-mediated propylene polymerization catalyzed by rac-Me₂Si(2-Me-4-Ph-Ind)₂ZrCl₂/MAO resulted in styryl-terminated i-PP (i-PP-t-St) of controlled molecular weight. Following a regioselective hydrochlorination reaction, the terminal styryl groups were quantatively transformed to 1-chloroethylbenzene groups, which was further reacted with NaN₃ to give i-PP terminated with an azide group (i-PP-t-N₃). Structural monitoring of the polymers through the whole transformation process using ¹H NMR and FTIR as well as GPC and DSC reveals a clean and clear formation of i-PP-t-N₃ (Mn in between 10,000 and 40,000 g/mol). This clickable i-PP building block was applied to a renewed, modular synthesis of amphiphilic i-PP-b-PCL (poly(ε-caprolactone)) diblock copolymers. Composition-diversified, structure-well defined diblock copolymers were obtained in high yields, confirming both the high end group selectivity as well as high reactivity of azide the clickable moiety in the i-PP building block and the effectiveness of azide-alkyne click reaction in constructing new i-PP architecture.