Anionic Polymerization of Styrenic Macromonomers

Abstract

Introduction. Polymacromonomers 1-3 are comblike polymers with an extremely high-density branching, since each monomeric unit bears a polymeric chain. Depending on the degree of polymerization of the side and the main chain, they can form either starlike or brushlike (molecular brushes) structures. The most popular polymerization of macromonomers 4-6 is by using radical initiators. [7][8][9][10] Ring-opening (ROMP), 11,12 atom transfer radical (ATRP), [13][14][15][16][17] and Ziegler-Natta 18 polymerization of macromonomers 19 have also been reported in the literature. A few attempts have been undertaken for the anionic polymerization of macromonomers without complete success. 20 It seems that during the polymerization the growing macroanions are terminated by impurities accompanying the macromonomers. These impurities are introduced during the isolation step of macromonomer by pouring the macromonomer solution into the nonsolvent. Since macromonomers are solid materials, their purification to the standards required for anionic polymerization is extremely difficult.In this communication, we are proposing a new methodology to overcome this problem by synthesizing and polymerizing the macromonomer in the same reactor and by using high-vacuum techniques.Experimental Section. Purification of all monomers (isoprene, butadiene, styrene), solvents (benzene and tetrahydrofuran), and terminating agent (methanol) were performed using standard high-vacuum techniques, described in detail elsewhere. 21 sec-Butyllithium (sec-BuLi), prepared from sec-butyl chloride and lithium dispersion, was the initiator for all polymerizations. Magnesium turnings (Aldrich) were washed with THF and dried in the vacuum line. p-Chlorostyrene was distilled under vacuum, over calcium hydride, to ampules equipped with break-seals. 4-(Chlorodimethylsilyl)styrene (CDMSS) was prepared from the Grignard reagent of p-chlorostyrene and dichlorodimethylsilane, using high-vacuum techniques, as reported in detail recently. 22 Polymerizations and linking reactions were carried out in evacuated, n-BuLi-washed, and solvent-rinsed glass reactors. Reagents were introduced via breakseals, and aliquots for characterization were removed by heat-sealing of constrictions. Full details of the highvacuum techniques are given elsewhere. 21 The apparatus of Figure 1 was used for the synthesis and polymerization of macromonomers.

The Strength of the Macromonomer Strategy for Complex Macromolecular Architecture: Molecular Characterization, Properties and Applications of Polymacromonomers

“…[62] The macromonomers were not isolated but were polymerized in the same reactor using sec-BuLi as initiator, as revealed in Scheme 11. Under these conditions the introduction of impurities in the system, which are able to terminate the polymerization, is avoided.…”

Micelle Formation from Amphiphilic “Cylindrical Brush”—Coil Block Copolymers Prepared by Metallocene Catalysis

“…[3] All other attempts to achieve this goal by other methods, particularly by living or controlled polymerizations such as anionic, [8] radical, [9] ring opening, [10] or metallocene-catalyzed [11] polymerization failed in so far that the degree of polymerization of the main chain hardly exceeded that of the side chain. The resulting structures could be described as spherical or star like.…”

Architecture of brush-on-brush copolymers by photoinduced ATRP approach

“…Comb-shaped polymers are special graft copolymers in which many branches are connected to a polymer backbone, and they can be prepared either by copolymerization of macromonomers with another monomer (grafting through) or by reacting an excess of active chains with a multifunctional backbone (grafting onto). Recently, it was found [5][6][7] that the anionic homo-or copolymerization of macromonomers leads to living species, if the polymerization is performed without isolation of macromonomer (in situ). By using this in situ strategy, Hadjichristidis et al [8] have synthesized well-defined comb, star-comb, and comb-on-comb (brush-on-brush) polybutadienes.…”