A major success has been made on organocatalytic ring-opening alternating copolymerization (ROAP) of phthalic anhydride and ethylene oxide (EO) by use of a simple phosphazene base (t-BuP 1 ). Polyesters with perfectly alternating sequence distribution, controlled molar masses, and low dispersities (Đ M < 1.1) are obtained. The ROAP exhibited a distinct living nature so that block, nonlinear, end-functional structures and postpolymerization modification of the alternating polyesters are readily achieved. Solvent, excess EO, and catalyst can be effortlessly recovered and reused. The ideally suitable basicity of t-BuP 1 is considered crucial for the high selectivity and neatness of the ROAP, which engenders a self-buffering mechanism rendering the carboxy and hydroxy terminals appropriately active to allow chain growth in an strictly alternating manner and complete avoidance of side reactions (epoxide self-propagation, transesterification) even at full conversion of the anhydride.

Alcohol-initiated ring-opening alternating copolymerization (ROAP) of phthalic anhydride (PA) and a variety of mono-, di-, and trisubstituted epoxides has been performed with a weak phosphazene base (t-BuP1) as the catalyst. Each product exhibits a perfectly alternating sequence distribution, controlled molar mass (M n up to 124 kg mol–1), and low dispersity (Đ M < 1.15, mostly). Full conversion of PA can be reached in 0.5–24 h depending on the substituent of the epoxide, the targeted degree of polymerization, and the amount of t-BuP1 used (0.2–5 mol % of PA) when the reactions are conducted under solvent-free conditions at 100 °C with a small excess of the epoxide (0.5 equiv of PA). The glass transition temperature of the polyester ranges from −14 to 135 °C. The living nature of the ROAP allows one-pot construction of well-defined block-alternating copolymers through sequential addition of two epoxides. Statistical-alternating copolymers have also been synthesized by copolymerization of PA and two mixed epoxides. Thus, the structural diversity of aromatic alternating polyesters synthesized by this simple organocatalysis has been largely enriched.

Phthalic anhydride and propylene/ethylene oxide are copolymerized at room temperature by a bicomponent metal-free catalyst comprising a mild phosphazene base and triethylborane. Provided with proper loadings of the two catalytic components, block copolymers with strict (AB) n B m type sequence structures and controlled molar mass (up to 60 kg mol −1 ) can be generated in one synthetic step, and the block architecture can be enriched by the use of mono-, di-, or tetrahydroxy initiators. The obtained polyester−polyether block copolymers readily undergo microphase-separation in bulk and nanoaggregation in selective (aqueous and alcoholic) solvents.

One-step synthesis of block copolymer from mixed monomers is of great interest and challenge. Using a simple non-nucleophilic organobase as the catalyst, we have achieved sequence-selective terpolymerization from a mixture of phthalic anhydride (PA), an epoxide, and rac-lactide (LA). Alcohol-initiated alternating copolymerization of PA and epoxide occurs first and exclusively because PA is substantially more active than LA for reacting with base-activated hydroxyl. When PA is fully consumed, LA polymerizes from the termini of the first block while excess epoxide stays intact because of the mild basicity of the catalyst. The two polymerizations thus occur tandemly, both in chemoselective manners, so that an aromatic–aliphatic block copolyester is generated in this one-step synthesis. The effectiveness and versatility of this approach is demonstrated by the use of ethylene oxide and several monosubstituted epoxides as well as mono-, di-, or tetrahydroxy initiators.

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