Acrylates, controlled polymerization

As an initial (demonstration) application of the Icon/1000 control system, we automated two simultaneous acrylic lab polymerizations. In this application, heaters, agitators, and metering pumps are controlled. A batch proceeds automatically from state to state unless the operator intervenes through one of a series of color CRT touch screens allowing him to take complete manual control of the batch for as long as he desires. All important process variables are continually monitored and recorded. The entire control scheme was created, tested, and modified several times in the space of two months, without formal instruction, by a chemical engineer with little previous programming experience and no previous experience at all with this system. 

Webster OW (2004) Group transfer polymerization mechanism and comparison with other methods for controlled polymerization of acrylic monomers. In New synthetic methods. Advances in polymer science, vol 167. Springer, Berlin, pp 1-34... 

The controlled polymerization of (meth)acrylates was achieved by anionic polymerization. However, special bulky initiators and very low temperatures (- 78 °C) must be employed in order to avoid side reactions. An alternative procedure for achieving the same results by conducting the polymerization at room temperature was proposed by Webster and Sogah [84], The technique, called group transfer polymerization, involves a catalyzed silicon-mediated sequential Michael addition of a, /f-unsaluralcd esters using silyl ketene acetals as initiators. Nucleophilic (anionic) or Lewis acid catalysts are necessary for the polymerization. Nucleophilic catalysts activate the initiator and are usually employed for the polymerization of methacrylates, whereas Lewis acids activate the monomer and are more suitable for the polymerization of acrylates [85,86]. 

Webster, O. IV Group Transfer Polymerization Mechanism and Comparison with Other Methods of Controlled Polymerization of Acrylic Monomers. Vol. 167, pp. 1-34. 

Significant improvement in controlled polymerizations of a variety monomers, including styrene, acrylates, acrylamide, acrylonitrile, 1,3-dienes, and maleic anhydride has been achieved when alkoxyamines have been used as initiators for living, free radical polymerization.(696c, 697) Alkoxyamines can be easily synthesized in situ by the double addition of free radicals, generated by thermal decomposition of an azo-initiator, such as 2,2 -azo-h/.s-/.so-butyronitrile (AIBN), to nitrones (Scheme 2.206). 

The first diblock copolymer brushes synthesized in our group were made by a combination of carbocationic polymerization and ATRP (Scheme 1) [46]. Zhao and co-workers [47] synthesized diblock copolymer brushes consisting of a tethered chlorine-terminated PS block, produced using carbocationic polymerization, on top of which was added a block of either PMMA, poly(methyl acrylate) (PMA) or poly((Ar,M -dimethylamino)ethyl methacrylate) (PDMAEMA), synthesized using ATRP. The thickness of the outer poly(meth)acrylate block was controlled by adding varying amounts of free initiator to the ATRP media. It has been reported that the addition of free initiator is required to provide a sufficiently high concentration of deactivator, which is necessary for controlled polymerizations from the sur-... 

Desirable Attributes for Commercial Controlled Polymerization of (Meth)acrylates... 

Controlled Polymerization of Styrene Using n-Butyl Acrylate and 1-Hexene [Atom Transfer Radical Polymerization ATRP]... 

A Cu(II) complex with a bipyridine-type ligand (Cu-4) is effective in the controlled polymerization of styrene and acrylates in the presence of Al(0-i-Pr)3, which most probably serves as a reducing agent of Cu(II) into Cu(I).93-94 A fluoroalkyl-substituted bipyridine ligand (L-7) was also employed in supercritical carbon dioxide for the polymerization of fluorinated acrylates and methacrylates.95 Similar pyridine-based bidentate ligands, 1,10-phenanthroline and its... 

A series of a-halopropionates (1-21 and 1-22, X = Cl, Br), model compounds of the dormant polymer terminal of acrylates, are suitable for not only acrylates but also styrenes and acrylamides. Ethyl 2-chlo-ropropionate (1-21, X = Cl) was employed for the controlled radical polymerizations of MA and styrene catalyzed by CuCl/L-1 to afford relatively narrow MWDs (MwIMn 1.5).84 A better controlled polymerization of MA is achieved with the bromides 1-21 and 1-22 (X = Br) in conjunction with CuBr/L-1 to give narrower MWDs (MJMn 1.2).84 A similar result was obtained with the combination of 1-23 and CuBr/L-1 for the polymerization of styrene.166 A nickel-based system with Ni-2 and 1-21 (X = Br) gave another controlled polymerization of nBA.134 The iodide compound 1-21 (X = I) is specifically effective in conjunction with an iodide complex such as Re-1 to induce controlled polymerization of styrene.141... 

Living anionic polymerization can also be used to produce well-controlled block copolymers. For PMMA, the best procedures need temperatures below O C and are therefore unlikely to be commercially attractive. Hiey are, furthermore, largely unsuccessful for the controlled polymerization of acrylates, which are far too reactive. The use of tetraalkyl ammonium ate complexes, in conjunction with an appropriate aluminum catalyst, solved fhis problem [225]. The function of the ammonium counterion is to promote dissociation of the complex ion to form the reactive ate complex of the aluminum enolate of the ester (Scheme 6.176). Thus, polymerization was initiated by the lithium enolate of isobutylate in the presence of the ate complex of Me3Al-R3NCl. A controlled block copolymer (PMMA-block-... 

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