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) (PPA(Nb)-g-PEtOx(47)-sigma(g)) samples with varied grafting densities (sigma(g)) ranging from 0 to 0.68. An azido end-functionalized linear poly(2-ethyl-2-oxazoline) (PEtOx-N-3) 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 PPA(Nb)-g-PEtOx(47)-sigma(g) samples with different sigma(g) were eventually obtained by grafting PEtOx-N-3 onto PPA backbone via the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction under varied [PEtOx-N-3](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 (R-eta), and intrinsic viscosity ([eta]), etc. The comb-like chain showing a scaling-law of R-eta similar to sigma(0.34)(g) 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 starlike 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.

Automated summary

In this study, a library of comb-like polymers with varied grafting densities was prepared and their conformational properties in solution were investigated. PEtOx-N-3 was synthesized as the grafting side chain and grafted onto PPA backbone to obtain comb-like PPA(Nb)-g-PEtOx(47)-sigma(g) samples with different grafting densities. The molecular parameters of these comb-like polymers were extracted using a Quadruple-detection size-exclusion chromatography system. The study revealed a transition in polymer shape from starlike to comb-like, and further to branched comb-like structure as the backbone length increases.