Davide Sanna

Synthesis and Characterization of Functionally Gradient Materials Obtained by Frontal Polymerization

Functionally gradient materials (FGMs) with gradual and continuous changes of their properties in one or more dimensions are useful in a wide range of applications. However, obtaining such materials with accurate control of the gradient, especially when the gradient is nonlinear, is not easy. In this work, frontal polymerization (FP) was exploited to synthesize polymeric FGMs. We demonstrated that the use of ascending FP with continuous feeding of monomers with computer-controlled peristaltic pumps provided an excellent method for the preparation of functionally gradient materials with programmed gradients. To test the effectiveness of the method, copolymers made from triethylene glycol dimethacrylate/hexyl methacrylate with linear and hyperbolic gradient in composition were synthesized. Differential scanning calorimetry (DSC), Shore A hardness measurements, compression tests, and swelling studies were performed along the length of the materials to assess the relationship between the gradients and the material properties. Glass transition temperatures, determined by DSC, showed a linear dependence on the composition and were in agreement with theoretical values. The other properties showed different and specific behaviors as a function of the compositional gradient.

Synthesis and characterization of poly(2-hydroxyethylacrylate)/β-cyclodextrin hydrogels obtained by frontal polymerization.

For the first time, the synthesis of polymeric hydrogels containing cyclodextrins (CDs) obtained by frontal polymerization (FP) is reported. In particular, the effects of CDs on poly(2-hydroxyethylacrylate) hydrogel properties are investigated. In a first series of materials, β-cyclodextrin is dispersed into the polymer matrix, while in the second one acryloyl-β-cyclodextrin is grafted to poly(2-hydroxyethylacrylate) chains. FP parameters (front velocity and maximum temperature), swelling properties, glass transition temperatures and mechanical properties of the hydrogels are studied. Results show that both types of cyclodextrin influence the above properties, and the major effects are found for concentration higher than 1mol% of acryloyl-β-cyclodextrin. Namely, a significant increase of glass transition temperature and of compression moduli are found. Finally, this study demonstrates that FP is a convenient technique to obtain CD-containing hydrogels, in which the type and amount of cyclodextrin can be suitably modulated to tune polymer properties, in function of the desired hydrogel applications.

β-Cyclodextrin-based supramolecular poly(N-isopropylacrylamide) hydrogels prepared by frontal polymerization

Frontal polymerization (FP) was successfully applied to the synthesis of poly(N-isopropylacrylamide)-grafted-acryloyl-β-cyclodextrin supramolecularly crosslinked hydrogels. It was established that acryloyl-β-cyclodextrin (AβCD) allowed performing successful frontal polymerizations with N-isopropylacrylamide even in the absence of any covalent crosslinker, which is something generally required. It was found that the swelling properties of the resulting hydrogels can be tuned by varying the amount of AβCD. Namely, when little amounts of this non-covalent crosslinker were used, superabsorbent hydrogels were obtained. Hydrogels containing also a covalent crosslinker were also prepared for comparison. These latter exhibited swelling ratios that are much lower than the others.