Polymethacrylates living polymerization

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. 

Block copolymers comprised of PS and polymethacrylate blocks with aliphatic stearyl or decyl side groups were prepared by the sequential addition of monomers, as shown in Scheme 1. Styrene was polymerized in THF at - 78 °C using s-BuLi as the initiator [11,12]. The nucleophilicity of the living polystyryllithium was reduced by reaction with DPE (in order to avoid reactions with the carbonyl groups), followed by the polymerization of the methacrylate monomer. Stearyl methacrylate, SMA is associated with... 

Various methacrylic-styrene copolymers were prepared in which the reactivity of methacrylate monomers used in the first step decreases in the order MM A > BuMA > benzyl methacrylate. For instance, the bulk polymerization of MMA with such an aromatic azo compound proceeds via a living radical mechanism and the sterically crowded C-C(C6H5)3 terminal bond of polymethacrylate 37 can be cleaved thermally to produce a,co-diaromatic PMMA-h-PS block copolymers in 48-72% yield. 

Because LiCl-mediated anionic polymerization of methacrylates is living, the addition of a second monomer to living polymethacrylate chains expectedly results in diblock copolymers, such as PtBuA-fc/ock-PMMA , PtBAEMA-/)Zock-PMMA , PtBMA-block-VGMA , PtBAEMA-fc/ock-PtBuMA and PtBMA-/)Zock-PDMAEMA 4. 

Polymerization or copolymerization of properly snbstitnted methacrylates is a direct and very effective strategy for the preparation of polymers grafted by a series of substituents. For instance, polymethacrylate containing amino groups was prepared by living LiCl-mediated anionic polymerization of 2-(dunethylamino)ethyl methacrylate (DMAEMA) °° and 2-(f-butylamino)ethyl methacrylate in THF at —78 °C. Mixtures of DMAEMA and tBuMA were also copolymerized . 

Figure 5.S Water-soluble thermoresponsive polymethacrylates obtained by living anionic polymerization.

Therefore, the anionic ends of these living polymers can be used to produce block copolymers of specific construction. An electronegative macroanion can initiate the polymerization of a monomer whose e value is higher than that of the monomer forming the anion (see Section 22.4.5). The polymethacrylic anion (monomer e = 0.40), for example, initiates the polymerization of acrylonitrile e =. 20) but not that of styrene e = — 0.80). 

Controlled structure PMAA can be prepared by the deprotection of an appropriate precursor polymethacrylate which has itself been polymerized under living conditions. Both anionic polymerization and GTP have been used to prepare PMAA employing a variety of PMAA precursor monomers such as benzyl methacrylate (125), ter -butyl methacrylate (126), trimethylsilyl methacrylate (127) and 2-tetrahydropyranyl methacrylate (128,129). Removal of the protecting group yields the desired PMMA. 

PMMA is mostly homo- or copolymerized in aliphatic hydrocarbon dispersions, using different rubbers, polysiloxanes, long-chain polymethacrylates, or different block and graft copolymers as stabilizers. An interesting variant of the dispersion polymerization of acrylates is carried out in supercritical carbon dioxide [45,46]. Transition-metal-mediated living radical suspension polymerization is discussed in Ref. [47]. Common radical initiators are described in Refs. [48] and [49]. The entire field is reviewed extensively in Ref. [50]. 

Han, S., Hagiwara, M. and Ishizone,T. (2003) Synthesis of thermally sensitive water-soluble polymethacrylates by living anionic polymerizations of oligo(ethylene glycol) methyl ether methacrylates, Macromolecules, 36, 8312-8319, doi 10.1021/ma0347971. 

As mentioned in the macromonomer section, a,co-dihydroxy polyacrylates and polymethacrylates were obtained by coupling two living chains that were initiated by an initiator containing a protected hydroxy group. Scheme 38 shows how coupling was obtained with l,4-bis(bromomethyl) benzene. " Similarly, a,o)-dicarboxy(PMMA) was prepared by initiating the polymerization with l,T-bis(trimethylsiloxy)-2-methylpropene-l (55). " ... 

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