Tracking solvent-induced conformational collapse of periodically grafted amphiphilic polymers using PFG NMR...

Area of Science:

• Polymer Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Periodically grafted amphiphilic polymers (PGAPs) feature hydrophobic backbones and hydrophilic pendant segments like polyethylene glycol monomethyl ether (MPEG).
• Previous research demonstrated PGAPs exhibit zigzag folding, leading to lamellar morphology in the solid state with tunable domain sizes.

Purpose of the Study:

• To synthesize and investigate the solution behavior of novel periodically clickable polyesters with varying hydrophobic segment lengths (C12 and C20).
• To explore the impact of different molecular weights of MPEG on the hydrophilic-lyophilic balance (hlb) and folding propensity of PGAPs.
• To determine the chain-collapse transition in solution using advanced NMR techniques.

Main Methods:

• Synthesis of clickable polyesters with dodecyl (C12) and eicosyl (C20) segments.
• Grafting of polyethylene glycol monomethyl ether (MPEG) with varying molecular weights (550, 750, 2000) onto the polyesters.
• Pulse field gradient nuclear magnetic resonance (PFG NMR) diffusometry in chloroform-methanol mixtures to study polymer chain collapse.

Main Results:

• A series of PGAPs with tunable hlb and folding propensities were successfully synthesized.
• PFG NMR studies revealed a distinct chain-collapse transition in chloroform-methanol mixtures, indicated by a sudden increase in diffusion constants.
• The collapse occurred at lower methanol content for polymers with shorter MPEG segments, consistent with their hlb.

Conclusions:

• The chain-collapse transition in PGAPs is sensitive to the molecular weight of hydrophilic segments and overall hlb.
• The collapse results in a structured morphology with a dense core and solvated shell, as evidenced by NMR peak intensity changes.
• This study provides insights into the solution self-assembly behavior of PGAPs, relevant for designing advanced functional materials.