Imparting optical functionality to aromatic thermosetting copolyester by luminescent silicon nanoparticles cross-linked via in situ thermal polymerization reaction

Aromatic thermosetting copolyester (ATSP) enables high- to low-k tunability as well as providing reliable thermomechanical performance from cryogenic to elevated temperatures, so it is a promising polymer system for silicon-based microelectronics and spacecraft applications. Here we reported on imparting strong photoluminescence to otherwise weak luminescent ATSP matrix by incorporating H-terminated Si nanoparticles (Sinps) to obtain luminescent polymer nanocomposites without degenerating the polymer backbone chain configuration. We employed photoluminescence and ultraviolet-visible (UV-Vis) spectroscopies along with electron microscopy analysis to characterize pre- and post-thermal polymerization processes. In the pre-polymerization stage, a size-dependent convection-like motion was observed in a liquid medium under thermal gradient, which caused the nanocomposites to accumulate and be trapped. Scanning electron microscope (SEM) images revealed the formation of 2-D nanosheets, as small as 50-100 nm, decorated with 10-15 nm size complexes of Sinps and oligomers. The post-polymerization analysis showed that the Sinps homogenously incorporated, with insignificant aggregation, into the polymerization process as a secondary cross-linker neither losing their red-luminescence functionality nor deteriorating the physical properties of the ATSP matrix. Chain relaxation characteristics, measured by dynamic mechanical analysis (DMA), in the glass transition regime likewise indicated the effective conjugation of the Sinps with the cross-linked polymer backbone. The ATSP-Sinps composite structure manifested bandgap imprints of both Sinps and ATSP in the ultraviolet-visible spectral region. Via superb thermomechanical properties enriched with luminescence, the ATSP-Sinps nano composite may potentially afford UV shielding to mitigate photo-degradation and enhance operational efficiency for photonics applications.