Associative behaviour of hydrophobically modified carboxymethylpullulan derivatives

Area of Science:

• Polymer Chemistry
• Materials Science
• Biochemistry

Background:

• Carboxymethylpullulan is a polysaccharide modified with hydrophobic alkyl chains.
• Hydrophobically modified polymers self-assemble in aqueous solutions.
• Understanding solution properties is crucial for material applications.

Purpose of the Study:

• To synthesize and characterize hydrophobically modified carboxymethylpullulan (HMCMP).
• To investigate the solution properties of HMCMP, focusing on viscosity and aggregation behavior.
• To determine the impact of hydrophobic modification and environmental factors on polymer structure.

Main Methods:

• Synthesis of HMCMP via reaction of carboxymethylpullulan with C16 alkylamine.
• Viscometric analysis to measure solution viscosity.
• Size-exclusion chromatography coupled with light-scattering to determine molecular weight and aggregation.

Main Results:

• HMCMP viscosity significantly increases with hydrophobic content and polymer concentration.
• Pseudoplastic behavior observed in highly modified samples (6.8% hydrophobic content).
• Polymers form intermolecular aggregates with a compact globular structure in dilute solutions.
• Addition of NaCl or ethanol leads to viscosity decrease, indicating aggregate collapse.

Conclusions:

• Hydrophobic modification of pullulan induces intermolecular aggregation and globular structures.
• Viscosity is highly dependent on hydrophobic content, polymer concentration, and solution conditions.
• The observed viscosity changes are consistent with the collapse of polysaccharide aggregates upon addition of salt or ethanol.