Frontal Polymerization: a valuable method for obtaining functionally gradient materials

Functionally gradient materials (FGMs) show gradual and continuous changes of their properties in one or more dimensions: this peculiarity justifies the growing interest they are obtaining, both from academics and industries. The manufacturing of these materials with an accurate control of the gradient, especially when the gradient is non-linear, is not easy. In this work, frontal polymerization (FP) was utilized for synthesizing polymeric FGMs. An ascending FP with continuous feeding of monomers with computer-controlled peristaltic pumps was exploited for obtaining FGMs with programmed gradients. In particular, copolymers made from triethyleneglycol dimethacrylate/hexyl methacrylate with linear and hyperbolic gradient in composition were synthesized and thoroughly characterized. A linear dependence of the Tg values on the FGM composition was observed, in agreement with the theoretical trends calculated by the Fox equation. Conversely, the other properties (Shore A hardness measurements, compression tests and swelling studies) exhibited different and peculiar behaviors as a function of the compositional gradient.