Methacrylates living polymerization

Group-Transfer Polymerization. Living polymerization of acrylic monomers has been carried out using ketene silyl acetals as initiators. This chemistry can be used to make random, block, or graft copolymers of polar monomers. The following scheme demonstrates the synthesis of a methyl methacrylate—lauryl methacrylate (MMA—LMA) AB block copolymer (38). LMA is CH2=C(CH2)COO(CH2) CH2. 

The most important side reactions are disproportionation between the cobalt(ll) complex and the propagating species and/or -elimination of an alkcnc from the cobalt(III) intermediate. Both pathways appear unimportant in the case of acrylate ester polymerizations mediated by ConTMP but are of major importance with methacrylate esters and S. This chemistry, while precluding living polymerization, has led to the development of cobalt complexes for use in catalytic chain transfer (Section 6.2.5). 

Polymerizations of methacrylic monomers in the presence of methacrylic macromonomers under monomer-starved conditions display many of the characteristics of living polymerization (Scheme 9.36). These systems involve RAFT (Section 9.5.2). However, RAFT with appropriate thiocarbonylthio compounds is the most well known process of this class (Section 9.5.3). It is also the most versatile having been shown to be compatible with most monomer types and a very wide range of reaction conditions.382... 

Chain transfer to methacrylate and similar maeromonomers has been discussed in Section 6.2.3.4. The first papers on the use of this process to achieve some of the characteristics of living polymerization appeared in 1995.380 The structure of macromonomer RAFT agents (163) is shown in Figure 9.3. An idealized reaction scheme for the case of a MMA terminated macromonomer is shown in Scheme 9.36. 

The highly syndiospecific-living polymerization of methyl methacrylate has been initiated by the neutral bis(pentamethylcyclopentadienyl)lanthanide-alkyl or -hydride complexes [215,216]. The plausible reaction mechanism is shown in Scheme XI. 

Highly Stereospecific Living Polymerization of Alkyl Methacrylates... 

Living organisms, fermentation by, 11 1-2 Living polymerization, 23 728 of acrylic ester monomers, 1 386 of methacrylic ester polymers, 16 291 Living polymers, 24 705 Living ring-opening metathesis... 

Another very important visible light-initiated reaction of alkyl aluminum porphyrins is their 1,4-addition to alkyl methacrylates to produce ester enolate species [Eq. (4)]. This enolate then acts as the active species in the subsequent polymerization of the acrylate monomer. For example, Al(TPP)Me acts as a photocatalyst to produce polymethylmethacrylate with a narrow molecular weight distribution in a living polymerization process [Eq. (4)]. Visible light is essential for both the initiation step (addition of methylmethacrylate to Al(TPP)Me) and the propagation... 

Fig, 4, Schematic illustration of high-speed living polymerization of methacrylate esters accelerated by steric separation of the aluminum porphyrin nucleophile and bulky Lewis acid. ... 

Aluminum porphyrins (Z = Cl, OR, SR) also initiate living polymerizations of methacrylates and acrylates without the need for low temperatures [Aida and Inoue, 1996 Inoue, 2000 ... 

Living Polymerization of Methacrylic Ester with Aluminum... 

Living Polymerization of Methacrylic Ester with Aluminum Porphyrin-Organoboron Compound Systems [19]... 

One-Shot" Lewis Acid Promoted Living Polymerization of Methyl Methacrylate [31]... 

For Lewis acid promoted living polymerization of MMA with (TPP)AlMe (1,X= Me) as initiator, a photoinitiation prior to the addition of the Lewis acid is required. This is because (1) 1 (X=Me) without irradiation does not have the ability to initiate the polymerization even in the presence of Lewis acid, and (2) all-at-once polymerization by direct irradiation of a mixture of MMA, 1 (X=Me), and the Lewis acid results in the formation of a relatively broad MWD PMMA with Mn much higher than expected. In this sense, the procedure using 1 (X= Me) as initiator is not convenient for practical application. In this section, we report on aluminum porphyrins with various axial ligands which were tested as initiators in order to realize a more convenient, one-shot high-speed living polymerization of methyl methacrylate with no need for irradiation with visible light. 

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-... 

Fig. 19. The polymerization flask designed for the synthesis of high-molecular-weighi (Mn>500,000) poly(methyl methacrylates) by the high-speed living polymerization with the (porphyrinato)aluminium enolate (2)-Lewis acid (3e) systems...

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. 

A new type of diblock copolymer of propylene and methyl methacrylate (MMA) was prepared by adding MMA monomer during the living polymerization of propylene with the soluble V(acac)3/A1(C2H5)2C1 catalyst at —78 °C and by subsequently raising the polymerization temperature to 25 °C U2 ... 

Another real active species was isolated form the reaction of [Cp 2SmH]2 with two equivalents of MMA monomer (methyl methacrylate) [289]. Or-ganolanthanide complexes of type Cp2LnR (R = H, alkyl) are not only effective precatalysts in the polymerization of nonpolar monomers such as ethylene, but also initiate the ideal living polymerization of MMA [289-291]. 

Triflic anhydride is an efficient initiator used in thfe living polymerization of oxolane 60), and bifunctional poly-THF oligomers can be further employed to initiate the polymerization of t-butylaziridine yielding polymers with aziridinium sites at both ends of their chain61 which can be reacted with methacrylic acid. 

As mentioned above, the ability to have living polymerizations offered the potential to make block copolymers. In the preparation of a block copolymer the sequence of addition can be important to ensure that the second monomer is capable of adding to the living end. An example is the formation of a polystyrene—polymethyl methacrylate block copolymer.38 In this case polystyrene is polymerized first, followed by addition of the methyl methacrylate. The block copolymer could not be formed if methyl methacrylate were polymerized first, as styrene will not add... 

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