Block copolymers, aluminum porphyrin

Pyridine in place of methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (3e) was also effective for the polymerization of MAN from the living PMMA (2). An example is shown by the polymerization of MAN under irradiation with the 2 (Mn=4000,Mw/Mn=1.09 prepared with [MMA]o/[l]o=40,100% conversion)-pyridine system at the initial mole ratio [MAN]q/[2] q/[pyridine]q of 100/1.0/0.6. MAN was polymerized up to 63% conversion in 65 h [Fig. 25 ( )], where the GPC peak of the polymer formed was observed to shift clearly towards the higher molecular-weight region (Mn=7600), retaining the narrow MWD (Mw/Mn=1.26), and the peak corresponding to the prepolymer of MMA was not observed. These facts clearly demonstrate the successful polymerization of MAN from 2, affording a PMMA-PMAN block copolymer. In sharp contrast to the polymerization of MAN, polymerization of MMA with aluminum porphyrin 2 was retarded by pyridine. For example, in the presence of 2 equiv of pyridine with respect to 2, the polymerization of 100 equiv of MMA proceeded very slowly to attain 25% conversion in 18 h under irradiation, while in the absence of pyridine, the polymerization of MMA with 2 was complete within 12 h under otherwise identical conditions. 

By using the aluminum porphyrin-Lewis acid system, we attempted the synthesis of a narrow MWD block copolymer from oxetane and methyl methacrylate (MMA). Methacrylic monomers can be polymerized radically and anioni-cally but not cationically, so a block copolymer of oxetane and methyl methacrylate has never been synthesized. As already reported, methacrylic monomers undergo accelerated living anionic polymerization with the (TPP)AlMe (1, X= Me)-3e system via a (porphinato)aluminum enolate as the growing species. 

Aluminum porphyrins have been used to prepare block copolymers by sequential monomer addition of two oxiranes [68, 318], of two )8-lactones [319], of a j5-lactone and an oxirane [319], of ethylene oxide and e-caprolactone [74] of propylene oxide and D-lactide [75], and of two methacrylates [76]. In the one example involving monomer pairs (j3-lactone and oxirane) which generate two different types of propagating species, the )8-lactone had to be polymerized... 

The wide applicability of aluminum porphyrin initiators (1) leads to a variety of tailored block copolymers such as polymethacrylate-polyether and polymethacrylate-polye-ster, as well as polymethacrylate-polymethacrylate and polymethacrylate-polyacrylate, that can be synthesized by sequential living polymerization of the corresponding monomers.- For example, when 1,2-epoxypropane (11, R = Me) is added to a polymerization mixture of methyl methacrylate (21, R = Me) with la at 100% conversion of 21, the polymerization of 11 takes place from the enolate growing end (32 ) to give a narrow MWD polymethacrylate-polyether block copolymer having an alcoholate growing terminal (Table 4). Likewise, the aluminum enolate species (32 ) can also react with lactones (14,15), thereby allowing the formation of a poly(methyl methacrylate)-polyester block copolymer with narrow MWD. 

Kuroki, M. Nashimoto, S. Aida, T. Inoue, S. Sequential addition-ring-opening living polymerizations by aluminum porphyrin. Synthesis of alkyl methacrylate-epoxide and -lactone block copolymers of controlled molecular weight. Macromo/ec Ze 1988, 21, 3114—3115. 

Addition polymerization of methaciylic esters (5), followed by ring-opening polymerization of heterocyclic monomers such as epoxides and lactones, is successful by aluminum porphyrin initiators to give novel polyvinyl - polyether and - polyester block copolymers of tailored block lengths. ... 

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