Chapter 40
Downloaded by UNIV MASSACHUSETTS AMHERST on August 9, 2012 | http://pubs.acs.org Publication Date: September 7, 2006 | doi: 10.1021/bk-2006-0944.ch040
Germanium- and Tin-Catalyzed Living Radical Polymerizations of Styrene Atsushi Goto, Hirokazu Zushi, Yungwan Kwak, and Takeshi Fukuda Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Ge and Sn (non-transition-metal) catalyzed living radical polymerizations were developed. Low-polydispersity (M /M ) ~1.1-1.2) polystyrenes with predicted molecular weights were obtained with a fairly high conversion in a fairly short time. The significant rate retardation observed for the GeI system with relatively large concentrations of GeI was kinetically proved to be mainly due to the cross-termination between P with GeI3 . Attractive features of the Ge and Sn catalysts include their high reactivity hence small amounts being required under a mild condition (at 60-80 °C) and high solubility in organic media without ligands. Ge catalysts may also be attractive for their low toxicity. w
n
4
4
•
•
© 2006 American Chemical Society
In Controlled/Living Radical Polymerization; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.
595
Downloaded by UNIV MASSACHUSETTS AMHERST on August 9, 2012 | http://pubs.acs.org Publication Date: September 7, 2006 | doi: 10.1021/bk-2006-0944.ch040
596 Living radical polymerization (LRP) has attracted much attention as a robust and versatile synthetic route for well-defined polymers (/). The basic concept of LRP is the reversible activation of the dormant species P-X to the propagating radical P* (Scheme la) (7,2). A number of activation-deactivation cycles are requisite for good control of chain length distribution. Examples of the capping agent X include nitroxides, halogens, dithioesters, telluride, and stibine (7). Halogens have been used mainly in two systems: namely, in iodide-mediated polymerization (5), P-X (X = I) is activated by P* (degenerative chain transfer; Scheme lb), and in atom transfer radical polymerization (ATRP) (4), P-X is activated by a transition metal complex (Scheme lc, where A is an activator, and X A is a deactivator). Percée et al. used Na S 0 and its analogues as non-transition-metal catalysts (J). These catalysts worked as an irreversible activator, which only once activated alkyl halides forming no effective deactivator. We have attempted to use Ge and Sn compounds as non-transition-metal catalysts. Ge (III) or Sn (III) radical is known to abstract halogen from alkyl halide to give an alkyl radical and a Ge (IV) or Sn (IV) halide (
