Acrylates, alkyl group transfer polymerization

Smooth, but one-way, mechanistic crossover from olefin polymerization to group-transfer polymerization is possible with lanthanocene catalysts, since insertion of an acrylate into the propagating metal alkyl to form an enolate is energetically favorable. Block copolymers of ethylene with MMA, methyl acrylate, ethyl acrylate, or lactones have been prepared by sequential monomer addition to lanthanide catalysts and exhibit superior dyeing capabilities. However, the reverse order of monomer addition, i.e., (meth)acrylate followed by ethylene, does not give diblocks since the conversion of an enolate (or alkox-ide) to an alkyl is not favored. Therefore, although... 

Although organometallic catalysts have attracted the most attention lately with regard to the anionic polymerization of alkyl methacrylates, it is important to recognize that alkali metal alkoxides in a variety of media can initiate the polymerization of both alkyl methacrylates and alkyl acrylates. Especially in view of the recent discovery and reporting of controlled, living acrylate and methacrylate polymerizations via group transfer... 

Alkyl Halides. Transfer to alkyl halides depends on structures of both alkyl group and halogen, but also on the polymeric radicals. Thus, nucleophilic radicals (styrene) react faster with alkyl halides than electrophilic radicals (acrylates). Hence, the C values with styrene and vinyl acetate are higher than those with acrylic monomers. 

Some chiral ILs have been designed and synthesized. They have already been applied in different fields snch as asymmetric synthesis, stereoselective polymerization, chiral chromatography, liquid crystals, chiral resolution, and NMR shift reagents [20,106, 107]. Chiral solvents have been reported in asymmetric syntheses. In the BayUs-HUlman reaction of benzaldehyde and methyl acrylate in the presence of bases, chiral ILs demonstrate their ability in the transfer of chirality, even if the enantiomeric excesses (ee) are stiU moderate. The presence of an alcoholic functional group on the Af-alkyl-fV methylephedrinium is primordial and acts as a fixing point of the chiral IL on the reactants. It is assumed that the OH is connected... 

Similarly, atom transfer radical polymerization (ATRP) has been used by Matyjaszewski and others for the synthesis of polystyrene and polyacrylates witii controlled molecular weights. This process is bas on a Cu(I) assisted atom-transfer radical polymerization (ATRP) One of the end groups is de ed by the structure of the initiator, whereas the other one contains an alkyl halide, such as chloride or bromide that can be converted to other functional groups. Additionally, the radical intermediates of ATRP are tolerant to many function groups, which can not be used directly in anionic or cationic processes, such as hydroxyalkyl, epoxy, enabling the direct synthesis of well-defined glycidyl, hydroxyethyl(meth)acrylates and other functional monomers. Percec and Barboiu have prepared polystyrene derivatives with efficient control of chain-end chemistry by the use of functionalized arenesulfonyl chlorides. 

Monomers which have been successfully polymerized using ATRP include styrenes, acrylates, methacrylates, and several other relatively reactive monomers such as acrylamides, vinylpyridine, and acrylonitrile, which contain groups (e.g., phenyl, carbonyl, nitrile) adjacent to the carbon radicals that stabilize the propagating chains and produce a suf cientiy large atom transfer equilibrium constant. The range of monomers polymerizable by ATRP is thus greater than that accessible by nitroxide-mediated polymerization, since it includes the entire family of methacrylates. However, acidic monomers (e.g., methacrylic acid) have not been successfully polymerized by ATRP and so also halogenated alkenes, alkyl-substimted ole ns, and vinyl esters because of then-very low intrinsic reactivity in radical polymerization and radical addition reactions (and hence, presumably, a very low ATRP equilibrium constant). 

Other monomers that copolymerize with alkyl vinyl ethers are vinyl ketones [47], acrolein diacetate [48], acrylamide [49], alkoxy 1,3-butadienes [50], butadiene [51], chloroprene [52], chlorotrifluoroethylene [53], tri-and tetrafluoroethylene [54], cyclopentadiene [55], dimethylaminoethyl acrylate [56], fluoroacrylates [57], fluoroacrylamides [58], A-vinyl car-bazole [59,60], triallyl cyanurate [59,60], vinyl chloroacetate [61,62], N-vinyl lactams [63], A-vinyl succinimide [63], vinylidene cyanide [64, 65], and others. Copolymerization is especially suitable for monomers having electron-withdrawing groups. Solution, emulsion, and suspension techniques can be used. However, in aqueous systems the pH should be buffered at about pH 8 or above to prevent hydrolysis of the vinyl ether to acetaldehyde. Charge-transfer complexes have been suggested to form between vinyl ethers and maleic anhydride, and these participate in the copolymerization [66]. Examples of the free-radical polymerization of selected vinyl ethers are shown in Table IV. 

After the development of catalyst-transfer condensation polymerization of polythiophene, the block copolymer of polythiophene and poly(alkyl acrylate) was prepared more easily. Vinyl-terminated polythiophene was first prepared. The vinyl group was converted to the 2-hydroxyethyl group by hydroboration, followed by esterification with 2-bromopropionyl bromide to give a macroinitiator for ATRP (Scheme 50) [142]. The allyl-terminated polythiophene was also converted to a macroinitiator for ATRP, which led to block copolymers of polythiophene and poly (aUcyl methacrylate) [143] or poly(acrylic acid) [144]. This allyl-terminated polythiophene has a bromine atom at the other end, which has an adverse effect on the purity of block copolymers prepared by ATRP. Hawker, Kim, and coworkers reported that replacement of the bromine with a phenyl group, followed by functionalization of the allyl group for the ATRP initiator unit, allowed access to narrower molecular weight distribution diblock copolymers of polythiophene and ATRP-derived vinyl block [145]. 

Until the late 1980s, the controlled polymerization of alkyl acrylates had not been achieved. Incomplete polymerization and very broad MWD (see Figures 6 and 11(a)) were reported. It was assumed that this might be due to both backbiting termination and a transfer reaction between the anion and a hydrogen in a-position to an in-chain ester group. In 1987, TeyssiS and his co-workers reported for the first time the... 

---