Preparation and characteristics of polypropylene with long chain branches utilizing the C–H insertion capability of azidoformate

Abstract

In this study, azidoformate (AF) is investigated as a reactive functional group to mediate noncatalytic C–H insertion reactions to interconnect polypropylene (PP) chains to generate long-chain branches (LCBs). 4,4′-Isopropylidenediphenyl azidoformate (DAF) with two terminal AF groups is synthesized, which is first mixed with propylene/α-olefin copolymer at 100 °C. Then, the prepared mixture with a predetermined amount of DAF is reactively melt mixed with PP at 165 °C. This unique two-step preparation strategy affords PP with prominent rheological properties of LCBs, e.g., shear thinning and strain hardening. The rheological characteristics are easily controlled by adjusting the amount of DAF to afford an effective tool to prepare high-melt-strength PPs. The strength of this strategy is distinct, including a simple/typical melt processing procedure, no degradation of PP chains, and no purification/solvent recycling steps. The C–H insertion capability of azidoformate groups suggests an expandability of this methodology as a platform technology to prepare modified polymers.