Methacrylates, alkyl group transfer polymerization

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... 

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). 

The influence of the reaction conditions upon the stereochemistry of polymerization has been examined for a number of systems. The presence of a small amount of water increased the isotacticity of the polymerization of ethyl methacrylate in toluene at -78 °C. A new type of cyclic structure for polybutadiene-a substituted cyclopentane - was identified in polymer prepared using an organo-lithium initiator in the presence of tetramethylethylene diamine. The polymerization of 1-phenylbutadiene initiated by alkyl-lithium in hydrocarbon solvents results in 50—60% trans-, A, some 25% c/r-1,4, and 10— 25% 3,4 enchainment. When THF is employed as solvent, the corresponding values are about 80, 10, and 10%, respectively. The anionically-prepared polymers have structures very different from those formed cationically, which comprise lately 3,4 addition accompanied by extensive cyclization. The distribution of cis-and trans-1,4 structures in polyisoprene prepared using Bu Li in non-polar media has been shown by C n.ra.r. spectroscopy to be nearly random. The polymerization of fumaronitrile is initiated in benzene solution by the addition of butyl-lithium across one C N group in THF solution initiation is by transfer of an electron from BuLi. ... 

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]. 

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