Aggregation behavior of polypropylene oxide end-capped by positive charges

Area of Science:

• Polymer Science
• Physical Chemistry
• Materials Science

Background:

• Poly(propylene oxide) (PPO) is a versatile polymer with applications in various fields.
• Understanding the aggregation behavior of charged polymers in aqueous solutions is crucial for designing advanced materials.
• The presence of positive charges at the polymer chain ends significantly influences its self-assembly in water.

Purpose of the Study:

• To investigate the temperature- and concentration-dependent aggregation behavior of poly(propylene oxide) with positive charges in aqueous solution.
• To identify the different aggregation states formed by the polymer.
• To elucidate the role of polymer chain end-charges and potential impurities in aggregation.

Main Methods:

• Solution turbidity measurements
• Dynamic light scattering (DLS) for particle size analysis
• Solubilization of a fluorescence probe to assess micelle formation
• Optical microscopic observation for direct visualization of aggregates

Main Results:

• The polymer exists as unimers at low temperatures and transitions to micelles at high temperatures.
• At intermediate temperatures, distinct aggregation states emerge: 100-nm aggregates (potentially vesicles), 1-micrometer oil droplets, and a turbid phase.
• Filtration experiments identified insoluble, less hydrophilic impurities as the cause of oil droplet formation, suggesting the 100-nm aggregates and other phases are intrinsic to the charged PPO.

Conclusions:

• The aggregation behavior of charged poly(propylene oxide) in water is complex and highly dependent on temperature and concentration.
• The formation of 100-nm aggregates and other intermediate phases is an intrinsic property of the charged polymer chain ends.
• Impurities can significantly influence the observed aggregation, leading to the formation of larger particles like oil droplets.