Unraveling the conformational properties of comb-like Poly(propargyl acrylate)-graft-poly(2-ethyl-2-oxazoline) chains in dilute solutions

We report the preparation and conformational property in solution of a library of comb-like poly(propargyl acrylate)-graft-poly(2-ethyl-2-oxazoline) (PPANb-g-PEtOx47-σg) samples with varied grafting densities (σg) ranging from 0 to 0.68. An azido end-functionalized linear poly(2-ethyl-2-oxazoline) (PEtOx-N3) as grafting side chain with a molar mass of 4700 g mol−1 was synthesized by the living cationic ring opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx), followed by the sequential post-polymerization azidation modification at the living chain end of PEtOx. Poly(propargyl acrylate) (PPA) as the backbone was prepared by the chemical transformation from the ATRP-made poly(tert-butyl acrylate) (PtBA). Comb-like PPANb-g-PEtOx47-σg samples with different σg were eventually obtained by grafting PEtOx-N3 onto PPA backbone via the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction under varied [PEtOx-N3]0/[alkyne]0 ratios. Quadruple-detection size-exclusion chromatography (QD-SEC) system was used to extract the molecular parameters of the obtained comb-like polymers, including molar mass (M), viscometric radius (Rη), and intrinsic viscosity ([η]), etc. The comb-like chain showing a scaling-law of Rη ∼ σg0.34 was confirmed in the shortest backbone, which is fairly accordant with our previous results in polystyrene system. In addition, a transition of polymer shape from star-like to comb-like, and further to branched comb-like structure was observed as the backbone length increases. The transition from star-like to comb-like could be attributed to the continuous increase of length-diameter ratio, which would lead to that the comb-like chain changes its molecular feature from isotropic to anisotropic. On the other hand, the transition from comb-like to branched comb-like should be due to the presence of the intermolecular Glasser-Hay coupling side reactions in comb-like polymers.