Cyclopolymerization of dipropargylgermaniums by transition metal catalysts

Abstract

Dipropargylgermaniums $[RR``Ge(CH_2C\equiv{CH})_2; R,R``=CH_3\;\mbox{or}\;ph]$ were prepared by a Grignard reagent of propargylbromide with dimethyl(or diphenyl) dichloro germanium. Polymerization was atempted by $WCl_6$ and $MoCl_5$ associated with cocatalyst such as organotin and organoaluminium compounds. A molybdenum catalyst was found to be a particularly effective catalyst for the cyclopolymerization of dipropargylgermaniums and $EtAlCl_2$ was very effective cocatalyst. Polymerization of diphenyldipropargylgermanium (DPPGe) by various catalysts leads to a dark red solid ($\overline{Mn}=12000$), soluble in common organic solvents. Thus, film could be obtained by solution casting. Polymerization of dimethyldipropargyl germanium (DMPGe) under the same conditions, however, gives only a partially soluble polymer. The structure of ploymer was identified by $^1$H-NMR, $^{13}$C-NMR, IR, UV-VIS and Raman spectroscopies. From these spectroscopic results, Poly(dipropargylgermanium) s possess polyene structures having cyclic recurring units in the polymer backbone. Poly(dipropargylgermanium)s have been investigated in terms of physical properties, thermal, oxidative stability and electrical conductivity. TGA exhibits that Poly(DMPGe) retained 95\% of its original weight at $180\,^\circ\!C$ and Poly(DPPGe) retained 95\% of its original weight at $350\,^\circ\!C$. Poly(DPPGe) was more stable to air oxidation than Poly(DMPGe). Consequently, cyclopolymers having bulkier substituents have better properties such as solubility, air stability and thermal stability than those having smaller substituents. $[PDMPGe < PDPPGe]$ The electrical conductivity, $\sigma$, rises from the undoped level of $10^{-11} S/cm$ to a maximum value $10^{-4} S/cm$ for $I_2$ doping.