Towards highly functionalized and semi-rigid polyzwitterions, 1. Poly(dizwitterionic methacrylates): synthesis and specific properties

Abstract

Monoamino-monozwitterionic (AZ) and dizwitterionic (Z2) methacrylates (CH2=C(CH3)— CO[O—(CH2)2] p—(NH—CO)q—O—CH[CH2—N+(CH3)2—O—CO—C–(CN)2]2 as Z2 species) were synthesized by controlled quaternization of their diamino (A2) precursors with 2,2-dicyanoketene ethylene acetal (DCKEA). In absence of a spacer group (p = q = 0), free radical polymerization in homogeneous dimethyl sulfoxide (DMSO) solution is possible only for the AZ monomer but not for the Z2 one, as a result of steric hindrance in the latter case. In presence of a spacer group (p = 0, q = 1 and p = q = 1), polymerization of the Z2 monomers readily leads to high molecular weight polymers (degree of polymerization DPw > 103). The poly(dizwitterionic methacrylate) bearing the longer spacer group (p = q = 1) displays specific solution and bulk properties: a) solubility either in highly dipolar aprotic solvents with lower critical solution temperatures (N,N-dimethylacetamide (DMAC): 54°C) and a “salting-in” effect of LiCl or in concentrated aqueous NaSCN solutions (≈ 3 mol·L–1) with upper critical solution temperatures (dT/d[NaSCN] ≈ –71°C·L·mol–1); b) slightly reduced chain flexibility characterized by a persistence length of about 30 Å; c) lyotropic behavior in concentrated N,N-dimethylformamide (DMF) solution (local nematic order for a polymer volume fraction φP > 0.4); d) ability to dissolve LiClO4 up to stoichiometric amounts ([LiClO4]/[zwitterion] = 1) to yield amorphous blends showing glass transition temperatures much lower than that of the pure polymer (Tg = 160°C) and local order likely corresponding to a double-layer lamellar structure.