Ilaria Domenichelli

The grafting of (functionalized) polystyrene from bulk or surface-functionalized polyolefins via nitroxide mediated polymerization is described. High density polyethylene and a poly(ethylene-co-α-olefin) copolymer (EOC) modified with different functional 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) derivatives were used as macroinitiators for the “grafting from” polymerization of various styrene-based monomers to yield polyolefin-g-polystyrene graft copolymers. The successful grafting of styrene and styrene derivatives was demonstrated by complementary analyses such as infrared (ATR-FTIR) and NMR spectroscopy, size exclusion chromatography, thermogravimetric analysis, and differential scanning calorimetry. Typically, IR spectroscopy of the grafted copolymers showed the bands attributable to the aromatic moieties and the obtained thermograms evidenced a lower degradation temperature for the grafted copolymers compared to that of polyolefin starting materials. In addition, solid state ¹⁹F-NMR was chosen to confirm the growth of polystyrene (PS) chains when EOC functionalized with a fluoroalkyl TEMPO was used for NMP. The extent of grafting of PS chains onto the polyolefin backbone was found to depend on the nature of the macroinitiator, especially on the structure and cleavage temperature of alkoxyamine derivatives created by TEMPO functionalization, on its content and on the adopted experimental conditions.

Highly deformable materials, such as elastomers and gels, can withstand very large deformation without failure, and this response is usually insensitive to the presence of macroscopic defects. These polymer‐based materials, different from the traditional ones which are usually characterized by an enthalpic elasticity, show a mechanical response which is governed by the state of internal entropy of their molecular network. If fracture energy is large, the noticeable ability of soft materials to rearrange their network at the microscale, to display large deformation and to dissipate energy thanks to their viscoelasticity, allows the minimization of the local detrimental effect of existing flaws. In the present paper, the mechanical behavior of silicone‐based edge cracked plates with different crack sizes and severity of the intrinsic flaws embedded in the material is examined by taking into account the time‐dependent effects. Experimental and theoretical aspects are discussed to explain the defect tolerance of such materials. The detrimental effect of intrinsic voids is quantified, and the beneficial effect due to strain at low rates is analysed. The critical distance is related to the ultimate stretch value, the quality of the material, and the crack size.