Hydrogels
are soft water-rich materials with physical properties
that can be easily tuned by modifying their network structure. For
instance, increasing or decreasing the cross-linking density has a
profound effect on their water absorption capabilities and mechanical
strength. These physical changes are showcased in a new experiment
for organic chemistry and polymer science teaching laboratories based
on the practical green synthesis and characterization of lactose methacrylate
derived hydrogels. Lactose, a disaccharide derived from dairy waste
byproducts, is functionalized with photoreactive methacrylate groups
using methacrylic anhydride. The resulting mixture is subsequently
photoirradiated to generate a cross-linked hydrogel. Structure–property
relationships are assessed through comparative studies of three hydrogels
of varying compositions. Compression tests and swelling studies in
different aqueous environments offer a guided-inquiry experience.
Students determine a relationship between cross-linking density and
the physical properties of the hydrogels. This experiment highlights
the valorization of biomass and multiple green chemistry principles
including use of renewable feedstocks, atom economy, energy efficiency,
waste prevention, and water as a benign solvent. Learning outcomes
for an organic chemistry laboratory course include introduction to
disaccharide and cross-linked polymer structures, observable physical
change dependency with cross-linking density, and laboratory methods
for evaluating water absorption capacities. Objectives aligned with
a polymer course are incorporating mechanical compression instrumentation,
mechanistic understanding of light-induced free radical polymerizations,
and an appreciation for the application of hydrogels to commercial
products. Overall, the translation of a current literature publication
to an inexpensive and versatile experiment engages students in a modern
example of sustainable polymer chemistry.