Tuning thermal and chemical stability of silicone rubbers via incorporation of diphenylsiloxane and methyltrifluoropropylsiloxane units

초록

Fluoro-phenyl silicone (FPS) copolymers were synthesized via anionic ring-opening polymerization of cyclic siloxane monomers containing methyltrifluoropropylsiloxane (MFS) and diphenylsiloxane (DPS) units. 1H and 29Si NMR, and ATR-FTIR confirmed random incorporation of the functional units, while GPC and viscometry related changes in molecular weight and viscosity to steric hindrance and pi-pi or dipole-pi interactions. varying the MFS/DPS contents, the glass-transition temperature (Tg) of the copolymers was tuned. FPS rubbers (FPSRs) were evaluated by thermogravimetric analysis under nitrogen and air. DPS units enhanced thermal resistance by suppressing back-biting and promoting thermally induced crosslinking through phenyl-radical formation, whereas MFS units, although increasing polarity, facilitated back-biting and lowered thermal stability in both atmospheres. Morphological characterization by SEM with F EDS mapping and elemental analysis showed that FPSRs form single-phase random copolymer networks with finely dispersed silica; only the fluorine-rich, phenyl-free FPSR-F50-P0 displayed slight local clustering, which was mitigated adding a small amount of DPS. Chemical-resistance tests revealed that MFS markedly improves resistance owing to its low surface energy and high polarity, while excessive DPS promotes swelling in nonpolar liquids. Increasing MFS contents lower surface free energy and suppresses oil permeation, whereas higher DPS contents slightly raise surface free energy and correlate with enhanced oil uptake. The cooperative effects of MFS and DPS therefore allow tuning morphology and structure-property relationships in FPSRs, providing guidelines for designing silicone materials with improved thermal and chemical durability for demanding applications.

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