Hydrophobicity of Polysaccharides

Question

Are polysaccharides generally considered to be hydrophobic and/or hydrophilic? My reasoning is that although they have polar groups/electronegative atoms, the polymeric nature of polysaccharides excludes water so I'm leaning towards them being hydrophobic.

Answer 1

Are polysaccharides generally considered to be hydrophobic and/or hydrophilic?

They are generally considered to be hydrophilic unless they are highly modified (e.g. to siloxanes).

My reasoning is that although they have polar groups/electronegative atoms, the polymeric nature of polysaccharides excludes water so I'm leaning towards them being hydrophobic.

There is no rule that polymers exclude water. Linear polymers can either stretch out in water (when the interactions with water are favorable) or clump up (if the interactions with itself or another polymer is favorable.

One notable exception is cellulose. The straight chains of cellulose make perfect interactions (involving both hydrogen bonding and dispersion forces), yielding a non-water soluble fiber. Cotton is made of cellulose fibers. The cotton fibers are highly hydrophilic (they are not water repellent) because the surface of the fiber is studded with hydroxyl groups.

Perhaps surprisingly, methyl cellulose (where all hydroxyl group are modified into methyl ether groups) is moderately soluble in cold water. The methyl groups prevent the packing of straight chains to cellulose fibers, and the polymer contains sufficiently hydrophilic groups to be water soluble (similar to polyethylene glycol, which also is an ether-containing polymer).