Scope of the Copper Halide/Bipyridyl System Associated with Calixarene-Based Multihalides for the Synthesis of Well-Defined Polystyrene and Poly(meth)acrylate Stars

Abstract

Novel multihalide compounds which were readily obtained by derivatization of 4-tert-butylcalix[4,6,8]arenes were used to initiate the atom transfer radical polymerization (ATRP) of styrene, tert-butyl acrylate (t-BuA), and methyl methacrylate (MMA), in the presence of CuX (X = Br or Cl) and 2,2‘-bipyridyl. Well-defined polystyrene (PS) stars constituted of precisely four, six, and eight arms could be synthesized with a narrow polydispersity in this way. For instance, octafunctional polystyrene stars exhibiting molar masses as high as 600 000 g mol-1 could be prepared. However, the polymerization had to be restricted to low conversion, typically below 15−20% to prevent stars from mutually coupling and avoid their contamination with species of higher functionality. Besides the concentration of polymeric radicals [P•], the factor that was found to play a significant role in the occurrence of star−star coupling is their overlapping concentration (C*): intermolecular coupling indeed appeared to be enhanced whenever stars crossed their C*, but ways to alleviate this phenomenon of star−star coupling were also reported. In the case of hexa- and tetrafunctional PS stars, well-defined samples could be obtained within a large range of conversion because of the lower probability of such hexa- and tetraarmed species to get coupled. With octaarmed poly(methyl methacrylate) stars as well, the polymerization had to be discontinued at relatively low conversion in order to isolate samples with the expected functionality of 8, although this class of polymeric radicals tend to disproportionate rather than to recombine upon reaction. In contrast, no such side reactions could be detected while synthesizing poly(tert-butyl acrylate) stars, because the ATRP of t-BuA is associated with a much lower equilibrium constant (K eq) between dormant and active speciesand therefore to a lower concentration of growing radicals for a same initial concentration of initiatorthan in the case of styrene or MMA. The functionality of the stars obtained was checked by comparing their molar mass with that of their individual arms isolated after hydrolysis of the ester functions of the central core. The viscometric characterization also attested to the well-defined character of the star polymers generated from the calixarene derivatized initiators, as confirmed by the comparison of their intrinsic viscosity with that of linear homologues of same molar mass.

Polycationic star polymers with hyperbranched cores for gene delivery

“…The hydrolysis conditions were chosen to cleave only the ester linkages between the core and the arms and to preserve the polymethacrylic backbone. This type of reaction has been successfully used previously for different types of star polymers [37][38][39][40][41][42].…”

Applications of Calixarenes in Polymer Synthesis

“…Another kind of rare earth calixarene complexes, rare earth 5,11,17,23-tetra-tertbutyl-25,27-chlorolanthanide dioxyl-26,28-dimethoxyl-calix [4]arene (C4LnCl), were synthesized as shown in Scheme 3. These complexes have also been employed as a catalyst for styrene polymerization with Mg(nBu) 2 and HMPA to show a very high catalytic activity (7 Â 10 3 kg PSt/mol Nd Á h) and giving polystrene with a very high molecular weight (>5 Â 10 5 ).…”

“…A novel neodymium calix [4]arene derivative has been synthesized (Scheme 4) and used as catalyst for propylene oxide polymerization in the presence of Al(iBu) 3 and H 2 O. [16] Poly(propylene oxide) that is 58-70% isotactic and has a viscosity average molecular weight of 1.…”

“…The groups of Gnanou and Sawomoto [3][4][5] have reported the atom transfer radical polymerization (ATRP) of St and methyl methacrylate (MMA) initiated by calixarene halide derivatives as multifunctional initiators to prepare star-shaped polymers. Here we describe the anionic polymerization of optically active N-phenylmaleimide derivatives and the ring-opening polymerization of lactones, cyclic carbonates, using calixarenes as multifunctional initiators to prepare star-shaped polymers.…”

Fluorescently tagged star polymers by living radical polymerisation for mucoadhesion and bioadhesion

“…These properties often derive from the differences in hydrodynamic volumes and higher degrees of chain end functionality compared to linear polymers of similar composition due to increased intermolecular constraints [2,3]. A variety of approaches has been reported for the synthesis of star polymers [4,5]. The first approach is the arms first method which uses living polymerisation to prepare the arms followed by quenching with a multi-functional coupling agent which serves as the core [6][7][8][9].…”