Polymeric aluminum porphyrin:Controllable synthesis of ultra-low molecular weight CO_(2)-based polyols

Carbon dioxide-based polyols with ultra-low molecular weight(ULMW,Mn<1000 g/mol)are emergent polyurethane precursors with economic and environmental benefits.However,the lack of effective proton-tolerant catalytic systems limits the development of this field.In this work,the polymeric aluminum porphyrin catalyst(PAPC)system was applied to the copolymerization of CO_(2)and propylene oxide,where sebacic acid,bisphenol A,poly(ethylene glycol),and water were used as chain transfer agents to achieve the controlled synthesis of CO_(2)-polyols.The molecular weight of the resulting CO_(2)-polyols could be facilely regulated in the range of 400–930 g/mol at low catalyst loadings,fully demonstrating its catalytic advantages of high activity,high product selectivity,and excellent proton tolerance of PAPC.Meanwhile,the catalytic efficiency of PAPC could reach up to 2.1–5.2 kg/g under organic CTA conditions,even reaching 1.9 kg/g using water as the CTA.The cPC content could be controlled within 1.0 wt%under the optimized conditions,indicating the excellent controllability of the PAPC system.ULMW CO_(2)-polyols combines the advantages of low viscosity(∼3000 mPa s at 25°C),low glass transition temperature(∼−73°C),and high carbonate unit content(∼40%),which is important for the development of high-performance polyurethanes.

Polymeric catalyst with polymerization-enhanced Lewis acidity for CO_(2)-based copolymers

Ring-opening copolymerization of CO_(2) and epoxides is a promising way to manufacture high value-added materials.Despite a variety of catalyst systems have been reported,the reaction is still limited by low activity and polymer selectivity.Herein,a strategy of polymerization-enhanced Lewis acidity is reported to construct a series of highly efficient polymeric aluminum porphyrin catalysts(PAPCs).The characterization of the coordination equilibrium constant(K_(eq))showed significantly enhanced Lewis acidity of PAPC(K_(eg)=18.2 L/mol)compared to the monomeric counterpart(K_(eq)=6.4 L/mol),accompanied with increased turnover frequency(TOF)from 136 h^(-1) to 5500 h^(-1).Through detailed regulation of Lewis acidity,the highly Lewis acidic PAPC-OTs displayed a record high TOF of 30,200 h^(-1) with polymer selectivity of up to 99%.

Chain-transfer-catalyst: strategy for construction of site-specific functional CO_(2)-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 make 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.