Methylaluminum porphyrin

Polymerization of Methacrylonitrile with Methylaluminum Porphyrin in the Presence of Methylaluminum Diphenolate... 

Fig. 24. Sequential three-stage polymerization of methyl methacrylate (MMA), methacrylo-nitrile (MAN), and MAN in CH2CI2 at rt with the methylaluminum porphyrin (1, X=Me)-methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (3e) system. GPC profiles of the polymers formed at I The first stage [MMA]o/[l]o=100, 100% conversion Mn= 13,200, Mw/Mn=1.22, II The second stage [MAN]o/[l]o=50, 100% conversion Mn=17,500, Mw/Mn=1.21, and III The third stage [MAN]o/[l]o=50, 100% conversion Mn=20,700, Mw/Mn=1.29...

Inoue [56] has developed a method similar to GTP for polymerization of acrylic monomers. A methylaluminum porphyrin (MeAlTPP) is converted to a ketene acetal by in situ reaction of MMA and used to polymerize MMA (Scheme 24). A hindered Lewis acid catalyst is needed to activate the MMA. 

Recently, it was found that Lewis acid assisted polymerizations of methyl methacrylate with aluminum porphyrin initiators yield living polymers. The polymerizations of methacrylate esters with al laluminum porphyrin initiators occur through formations of enolate aluminum porphyrin intermediate as the growing species. For the sake of illustration, the methylaluminum porphyrin molecules (see Fig. 3.3) can be designated as... 

Polymerization of Methacryhc Esters via Enolatealuminum Porphyrins in the Presence of Methylaluminum Diphenolates... 

Table 1. Polymerization of methyl methacrylate (MMA) via an enolatealuminum porphyrin (2, R=Me) in the presence of methylaluminum diolates (MeAlX2) ...

Fig.1. Two-stage polymerization of methyl methacrylate (MMA) in CH2CI2 at room temperature with the enolatealuminum porphyrin (2, R=Me)-methylaluminum bis(2,4,6-tri-tert-butylphenolate) (3f) (1.0 1.0) system. GPC profiles of the polymers formed at the first stage (I) [MMA]o/[l (X=Me)]o=50, 100% conversion Mn=7,000, Mw/Mn= 1.12 and the second stage (II) [MMA]o/[2]q=200, 100% conversion Mn=47,600,Mw/Mn= 1.05...

Table 3. Polymerization of methacrylic esters via enolatealuminum porphyrins 2 in the presence of methylaluminum bis(2-tert-butyl-4-methoxyphenolate) (3c) ...

As mentioned above, the new method Lewis acid promoted living polymerization of methacrylic esters, by using enolatealuminum porphyrin (2) as nucleophilic initiator in conjunction with organoaluminum compounds, such as methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (3e), as Lewis acids has enabled us to synthesize poly(methacrylic ester) of narrow molecular-weight distribution [51]. On the other hand, some reactions of aluminum por-... 

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. 

Fig. 27. Polymerization of 1,2-epoxypropane (PO) by the alcoholatealuminum porphyrin (16, n=10)-methylaluminum bis(2,4,6-tri-tert-butylphenolate) (3f) system. Relationship between Mn ( ) [Mw/Mn (O)] of the polymer and conversion...

Polymerization of PO initiated with the (TPP)AlCl (l,X=Cl)-2-propanol (2-PrOH) system in the presence of methylaluminum bis(2,6-di-tert-butyl-4-meth-ylphenolate) (3e) was carried out by the addition of a mixture of PO and 2-PrOH to a CH2CI2 solution of a mixture of 1 (X=C1) and 3e at room temperature in a nitrogen atmosphere (Fig. 36). For example, when a mixture of 200 equiv of PO and 9 equiv of 2-PrOH was added to the solution of 1 containing 0.3 equiv of 3e (0.15 mol% with respect to PO), the color of the solution immediately turned from dark reddish purple to bright reddish purple, characteristic of the alcoho-latealuminum porphyrin family. The polymerizations proceeded very rapidly with heat evolution to attain 57% monomer conversion in 3 min (A). In contrast, the polymerization without 3e under similar conditions proceeded rather... 

In the present study, the novel concept of the Lewis acid assisted living polymerization with the aluminum porphyrin-methylaluminum diphenolate (3) system was successfully extended from the accelerated living addition polymerization of alkyl methacrylates to the accelerated living ring-opening polymerizations of lactones. 

Lewis acids such as methylaluminum diphenolates and trialkyl- and triarylaluminum compounds also accelerate the polymerization of methacrylic esters via aluminum porphyrin enolate (Figure 22). The acceleration effects of trialkylalumi-num in the polymerization of tert-butyl methacrylate (tBMA) and MMA were attributed to monomer activation and suppression of aluminum porphyrin degradation presumably through steric repulsion between the bulky porphyrin ligands and the Lewis acid. - 3 More details can be found in reviews by Aida " and Sugimoto and Inoue. ... 

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