Chain-transfer-catalyst: strategy for construction of site-specific functional CO2-based polycarbonates

Site-specific functional polymers are generally synthesized from functionalized chain transfer agents (CTA) in the presence of catalysts. However, the poor solubility or chemical inertness of CTAs may lead to polymerizations uncontrollable. Now, this issue is addressed by proposing a strategy of designing chain-transfer-catalyst (CTC) that combines catalyst and CTA into one. The occurrence of catalytic effect naturally triggers the chain transfer process to give catalyst-labeled polymers with well-defined structures. As a proof-of-concept, cobalt(III) porphyrin catalysts with one, two and four hydroxyl groups act as efficient CTCs, giving the corresponding site-specific functional poly(propylene carbonate)s (PPC), diversifying the topology of polymers. Furthermore, porphyrin-capped PPCs with controllable Mn in the range of 1,000–16,800 g mol−1 were obtained by using monofunctional CTC (CTCOH). Moreover, different from traditional “catalyst+CTA” systems, a novel dynamic network transfer mechanism of CTCOH was proposed. This study provides a CTC strategy for the synthesis of site-specific functional polymers.