Solvent-free Radical Polymerization Research Articles

Polyhedral Vinyl Polymer Particles Synthesized Via Solvent-Free Radical Polymerization.

Liquid marbles (LMs) with a cubic shape are created by using various vinyl monomers as an inner liquid and polymer plates with mm size as a stabilizer. The relationship between the surface tension of the vinyl monomers and formability of the LMs is investigated. LMs can be fabricated using vinyl monomers with surface tensions of 42.7-40.3 mN m-1. The cubic polymer particles are successively synthesized via free-radical polymerizations by irradiation of the cubic LMs with UV light in a solvent-free manner. In addition, controlling the number of polymer plates per one LM, the shape of the plate or the coalescence of the LMs can lead to production of polymer particles with desired forms (e.g., Platonic and rectangular solids) that correspond to the shapes of the original LMs.

Contribution of polymaleimide, pyromellitidiimide and polydimethylsiloxane units to the thermal stability of polyimide-silicone materials

To determine the comparative thermal resistance of polydimethylsiloxane, polymaleimide, and pyromellitidiimide (PYRO) under different temperature constraints (scan, high isotherms, thermal shocks), four materials varying in their content of these different units and cross-linking density were synthesized and characterized. For this, two bismaleimide precursors, which are liquid at room temperature, were developed and polymerized by solvent-free radical polymerization. Two other polymaleimide-free materials with cross-linking densities comparable to those of the above materials were studied for comparison. Thermomechanical analysis of these materials showed that they were all elastomers (storage moduli between 1 and 10 MPa and Shore A hardness between 30 and 65). Their thermal stability was studied under temperature scan in air and in argon, at the 250 °C isotherm, and under thermal shocks. The nature of the cross-linking node (cyclosiloxane or maleimide), as well as the presence of PYRO, was decisive for the thermal stability of these materials. These conclusions were then confirmed by TGA-FTIR analyses. Finally, p(D4-PY-RSi) material (containing PYRO units and no polymaleimide) was the most stable of the four materials for long ageing times at 250 °C. However, during thermal shocks the stability of p(BMI-RSi) (with polymaleimide and without PYRO) became comparable to that of p(D4-RSi) (without polymaleimide or PYRO) (equivalent to 340 h at 240 °C).