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Polymer materials are indispensable in our daily lives. This makes polymer technology of critical importance in higher education. In particular, hands-on experiment-based practicals/laboratories with a focus on polymer science are of tremendous value in the undergraduate curriculum. Along these lines, hydrogels are highly cross-linked polymer networks which show some unique properties such as water absorbance and large extensibility, making them particularly well-suited in various biomedical applications. The properties of hydrogels can be systematically varied via changes in composition. In this practical laboratory, we use hybrid hydrogel formulations containing alginate and polyacrylamide to explore the consequences of compositional changes on mechanical behavior. Mechanical properties are determined using a simplified tensile test that is amenable to large groups of students using standard laboratory equipment. We used marbles to induce an extensional force and a ruler to measure the elongation of the gel as a function of the attached weight. Hereby, stress-strain curves can be obtained, and students are able to compare the difference between single and double network hydrogels as well as quantify the influence of network composition. This practical combines the use of chemical synthesis (i.e., reactant calculations) with practical skills which makes it interesting to use in a third year chemical/biomedical course. Furthermore, students can learn how to deal with chemicals and gain insight in polymer chemistry and its wide applicability, making it particularly well-suited for students coming from outside the traditional chemical science background.

Block polymers containing polylactide (PLA) are prepared as the sacrificial component and perfectly linear polyethylene (LPE) as the matrix phase by using a combination of ring-opening polymerizations. Tensile testing has confirmed the mechanical robustness of the nanoporous samples and the treatment with concentrated strong acids has shown the outstanding chemical resistance of the nanoporous LPE samples.

A library of Y-shaped poly(dimethylsiloxane) (PDMS)-b-poly(d,l-lactide) (PLA) diblock copolymers and their corresponding linear counterparts were synthesized, and their morphologies and feature sizes in bulk and thin films were compared using small-angle X-ray scattering (SAXS), scanning force microscopy (SFM), and grazing incidence small-angle X-ray scattering (GI-SAXS). For macromolecular isomers with approximately the same molecular weights and volume fractions (PLA fL: 0.20 and 0.35), different thin film morphologies were obtained for the Y-shaped PDMS-b-PLA derivatives when compared to the corresponding linear derivatives. These data also gave us the option to determine some of the key parameters of these block copolymers. A relatively high χ value of 0.24 was found for these PDMS-b-PLA systems and was shown to be influenced by architecture. [ABSTRACT FROM AUTHOR]

Hydrogels were prepared with physical crosslinks comprising 2-ureido-4[1H]-pyrimidinone (UPy) hydrogen bonding units within the backbone of segmented amphiphilic macromolecules having hydrophihc poly(ethylene glycol) (PEG). The bulk materials adopt nanoscopic physical cross-links composed of UPy-UPy dimers embedded in segregated hydrophobic domains dispersed within the PEG matrix as comfirmed by cryo-electron microscopy. The amphiphilic network was swollen with high weight fractions of water (wH2≈0 0.8) owing to the high PEG weight fraction within the pristine polymers (wPEG 0.9). Two different PEG chain lengths were investigated and illustrate the corresponding consequences of cross link density on mechanical properties. The resulting hydrogels exhibited high strength and resilience upon deformation, consistent with a microphase separated network, in which the UPy-UPy interactions were adequately shielded within hydrophobic nanoscale pockets that maintain the network despite extensive water content. The cumulative result is a series of tough hydrogels with tunable mechanical properties and tractable synthetic preparation and processing. Furthermore, the melting transition of PEG in the dry polymer was shown to be an effective stimulus for shape memory behavior. [ABSTRACT FROM AUTHOR]

Polyacrylamide/sodium alginate (PAM/SA) hydrogel was prepared from sodium alginate (SA) and acrylamide (AM) by covalently cross-linking. Temporary shape double network PAM/SA hydrogels were obtained by ionic cross-linking formed by complexation of SA and six metal cations (Fe3+, Cu2+, Ag+, Ca2+, Ni2+, and Co2+), among the PAM/SA—Fe3+ hydrogels has the best shape fixity ratio (83%). When the hydrogel is placed in different recovery liquids (sodium citrate, EDTA, sulfuric acid, and potassium carbonate), the shape recovery ratio (98.9%) is the best in sodium citrate solution, and the recovery time (182 s) of the hydrogel is the shortest. In general, Fe3+, Cu2+, and Ag+ are suitable for the construction of ionic-shape memory hydrogels. The PAM/SA hydrogels also exhibited excellent adjustable mechanical properties by changing metal cations and soaking time. The strategy could broaden the construction of ion-responsive shape-memory hydrogels. [ABSTRACT FROM AUTHOR]