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Characterization and intermolecular interactions of hydroxypropyl guar solutions
Yu Cheng1, Kirk M Brown, Robert K Prud'homme
1Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544, USA. yucheng@princeton.edu
Biomacromolecules
|May 15, 2002
Summary
Hydroxypropyl guar (HPG) modification reduces intermolecular interactions in aqueous solutions. Increasing molar substitution (MS) in HPG affects these interactions and chain stiffness, with distinct behaviors observed at low, intermediate, and high MS levels.
Area of Science:
- Polymer Science
- Materials Science
- Physical Chemistry
Background:
- Guar galactomannan is a natural polysaccharide with various industrial applications.
- Modification of guar to hydroxypropyl guar (HPG) alters its properties through the addition of hydroxypropyl groups.
- Understanding the impact of molar substitution (MS) on HPG behavior is crucial for optimizing its use.
Purpose of the Study:
- To investigate the effect of molar substitution (MS) on the intermolecular and intramolecular interactions of hydroxypropyl guar (HPG) in aqueous solutions.
- To characterize the conformational changes and chain stiffness of HPG as a function of MS.
- To compare the properties of HPG with native guar galactomannan.
Main Methods:
- Dilute solution viscometry to measure solution viscosity and infer intermolecular interactions.
- Gel permeation chromatography (GPC) to determine molecular weight and molecular volume.
- Acid hydrolysis to prepare HPG samples with varying molecular weights and controlled polydispersity.
Main Results:
- HPG exhibits reduced intermolecular interactions compared to guar, attributed to steric hindrance of hydrogen bonding sites by hydroxypropyl groups.
- Intermolecular interactions show a sharp decrease at low MS (0-0.4), become independent of MS in the intermediate range (0.4-1.0), and display temperature dependence at high MS (>1.0).
- HPG chain stiffness increases with increasing MS, as indicated by evaluated Mark-Houwink-Sakurada parameters and the characteristic ratio C(infinity).
Conclusions:
- Molar substitution significantly influences the solution behavior and conformational properties of HPG.
- The addition of hydroxypropyl groups effectively modulates inter- and intramolecular associations in guar derivatives.
- HPG offers tunable properties, making it a versatile biopolymer for various applications requiring specific solution characteristics and chain rigidity.