Use of crown ether in the anionic polymerization of propylene oxide—2. Molecular weight and molecular weight distribution

Anionic synthesis of well-defined, poly[(styrene)-block-(propylene oxide)] block copolymers

“…Although it has been stated that the average molecular weight is limited to ca. 6 000 g/mol at operable temperatures (A90 8C) because of the high rate of chain transfer, i. e. k p / k tr f 100, [16,17] studies by Price and coworkers [19] have shown that number average molecular weights as high as Full Paper: Well-defined, narrow molecular weight distribution (M w /M n f 1.1) poly[(styrene)-block-(propylene oxide)] block copolymers with relatively high molecular weight poly(propylene oxide) blocks [e. g. M n (PPO) = 10 000 -12 000 g/mol] have been prepared by anionic polymerization. The polystyrene block (M n = 5 000; M w / M n = 1.1) was prepared by alkyllithium-initiated polymerization of styrene followed by chain-end functionalization with ethylene oxide and protonation with acidic methanol.…”

Aluminium and rare earths alkoxides as initiators for the heterogeneous anionic coordinated polymerisation of propylene oxide. A1H NMR approach of the regioselectivity and transfer ability of the catalytic system

“…Booth et al 20) give C tr values between 2 6 10 -3 and 8 6 10 -2 in anionic bulk PPO polymerisation at temperatures in the range 90 -110 8C. Later on, the authors observed that the [db]/([PO] 0 6 Q) ratio decreased with increasing molecular weight 21) .…”

The influence of initiator and macrocyclic ligand on unsaturation and molar mass of poly(propylene oxide)s prepared with various anionic system

“…in the absence of alcohol is opposite to similar systems, in which potassium alkoxide/alcohol mixture was used for initiation [8,22]. The presence of the ligand should accelerate propagation as well as deprotonation of monomer and alcohol.…”

“…Moreover, in 2007 Penczek et al [20] reported in review paper concerning ring-opening polymerization of heterocyclic monomers that the side transfer reaction in propylene oxide polymerization can be depressed to the same extent by counterion complexation with crown ethers. However, the results presented in several works [8,10,[21][22][23] revealed that this effect was observed in the systems containing compounds with OH groups. Addition of 18-crown-6 (18C6) to the systems containing alcohol causes further depression of chain transfer to the monomer resulting in distinct decreasing of unsaturation and increasing of M n [8,22].…”

“…However, the results presented in several works [8,10,[21][22][23] revealed that this effect was observed in the systems containing compounds with OH groups. Addition of 18-crown-6 (18C6) to the systems containing alcohol causes further depression of chain transfer to the monomer resulting in distinct decreasing of unsaturation and increasing of M n [8,22]. For example, using a mixture of potassium 1-methoxy-2-propoxide/1-methoxy-2-propanol (1/3), M n of polymers increases even to 12,400 at [18C6]/[K ? ]…”