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Poly(methylenephosphine)s : homo- and copolymers bearing conjugated substituents Chun, Cindy Patricia

Abstract

New P-Mes (Mes = 2,4,6-trimethyiphenyl) phosphaalkenes bearing conjugated C substituents have been prepared: MesP=C(Naph)(Ph) (Naph = 1-naphthyl) (la), MesP=C(Phen)(Ph) (Phen = 9-phenanthrenyl) (ib), and MesP=C(C₄H₃S)(Ph)(C₄H₃S= 2- thienyl) (lc). Compounds la and ic were prepared by the base-catalyzed phospha-Peterson reaction, whereas lb was prepared via the standard phospha-Peterson route. Anionic polymerization of la and lb afforded [MesP—C(Naph)(Ph)] (2a) and [MesP—C(Phen)(Ph)] (2b), respectively. The anionic polymerization of ic was attempted, but there was no polymer formation. Poly(methylenephosphine)s 2a and 2b were chemically functionalized at the phosphorus centres by oxidation and coordination to B3H moeities. The electronic properties of la, ib, 2a, 2b, and the functionalized polymers were investigated by UV/Vis and fluorescence spectroscopy. The results showed that naphthyl-derivatized phosphaalkene la and poly(methylenephosphine) 2a were non-emissive, whereas the functionalized naphthyl derivatized polymers emitted in the UV region when excited at 288 nm. Similarly, for the phenanthrenyl-derivatized species, phosphaalkene lb and phosphine polymer 2b were observed to be weakly fluorescent in comparison to the more emissive functionalized polymers. These results are consistent with the sensory behavior exhibited by “turn-on” chemical sensors. The phosphaalkene monomer, MesP=CPh₂ (3) was copolymerized with styrene (Sty) using radical initiator 1,1 ‘-azobis(cyclohexanecarbonitrile) over a range of monomer feed ratios to afford poly(methylenephosphine)-co-polystyrene (PMP-co-PS) copolymers. The compositions of these copolymers were evaluated using inverse gated proton decoupled ¹³C NMR spectroscopy. An adaptation of the Tidwell-Mortimer experimental approach was employed to calculate reactivity ratios for the PMP-co-PS system. The first step of the approach involved a preliminary estimation of the reactivity ratios by the Fineman-Ross linearization and the Mayo-Lewis intersection method. Using the preliminary estimates, the Tidwell-Mortimer heuristic rules were applied to determine optimal feed compositions for further experimentation. Lastly, a nonlinear least squares regression was performed to provide the best estimates of the reactivity ratios (rpA = 0.11 and rs = 0.24). Based on these r values, Q-e reactivity parameters of phosphaalkene 3 were computed and the microstructure of PMP-co-PS was examined which revealed an alternating pattern of phosphaalkene and styrene units in the copolymer backbone.

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