Multifunctional coupling agents for living cationic polymerization. I. Sodiomalonate anions for vinyl ethers

A series of multifunctional malonate anions, [Na⊕⊖C(COOEt)2CH2]mC6H6−m(I; m = 2–4), were examined as polymer coupling agents for the living cationic polymerization of vinyl ethers initiated with the hydrogen iodide/zinc iodide (HI/ZnI2) initiating system. The bifunctional anion (2;I, m = 2), 1,4‐[Na⊕⊖C(COOEt)2CH2]2C6H4, terminated living polymers of isobutyl vinyl ether (IBVE) (DPn = 10) almost quantitatively in toluene at −15°C to give coupled living polymers with doubled molecular weights in 96% yield; the dianion 2 was dissolved in tetrahydrofuran containing 18‐crown‐6 for maintaining the solution homogeneous. The yield of the coupled polymers was increased with shorter living chains or in less polar solvents. Also by coupling via 2, ABA block copolymers were obtained from living AB block polymers of IBVE and an ester‐functionalized vinyl ether (CH2CHOCH2CH2OCOCH3). Coupling of living poly(IBVE) with the trifunctional anion (3; I, m = 3) led to tri‐armed polymers in 56% yield, whereas with the tetrafunctional version (4; I, m = 4), only three out of the four anions reacted to give another tri‐armed polymer in 85% yield.