Synthesis and characterization of propargylphosphonamide helical polymers

Phosphorus has a structure with five coordination, this compound is easy to form enantiomers and can hardly be separated. In this paper, four propargylphosphonamide monomers [HC≡CCH₂NH(P=O)-R ₁R₂. Monomer 1;R₁ = OPh, R₂ = NC₄H₇COOCH₃; monomer 2:R₁ = OPh, R₂ = NC₄H₇COOCH₂CH₃; monomer 3:R₁ = OPh, R₂ = NC₄H ₇COOC(CH₃)₃ and monomer 4; R₁ = Ph, R₂ = NC₄H₇COOC(CH₃)₃] were designed and synthesized. ¹ H-NMR and ³¹P-NMR show that monomer 1 can only form enantiomer and cannot be separated. But monomer 2, monomer 3 and monomer 4 can be separated by resolving agent to form P-chiral diastereomeric monomers. Polymerization was carried out with (nbd)Rh⁺ [η⁶-C₆H₅ B^--(C ₆H₅)₃] as catalyst in CHCl₃ giving four polymers with moderate molecular weights (M_n) (0. 4 × 10⁴ ∼ 0. 7 × 10⁴) and M_w/M _n (1. 26 ∼ 1. 98) by GPC, two factors (the pendent group and temperature) were observed to affect the helix structure of polymers. The optical activity and secondary structure of the polymers were characterized by specific rotations ([α]_D).circular dichroism (CD) spectra and UV-Vis. It shows that the polymers have good optical activity and can form a single direction of the helical conformation. It was found that the secondary structure stability of the copolymer is better than homopolymer's in different mixed solvents, when the methanol quantity was up to 50%, CD spectra of poly3 and poly4 change largely, which shows methanol broke the hydrogen bond between phosphorus-oxygen bond and nitrogen-hydrogen bond.