Photo-stable cross-linked micron bead with functionalized quantum via suspension polymerization for color conversion

• Published in: Polymer (Guilford) Vol. 177; pp. 19 - 24
• Main Authors: Lee, Changmin, Nam, Eunhee, Chae, Heeyeop
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 26.08.2019; Elsevier BV
• Subjects: Beads; Color; Conversion; Crosslinking; Functional groups; Ligand exchange; Ligands; Light emitting diodes; Monomers; NMR; Nuclear magnetic resonance; Organic solvents; Photo-stability; Polymerization; Polymers; Polymethyl methacrylate; Polymethylmethacrylate; QD-Polymer bead; Quantum dot; Quantum dots; Suspension polymerization; Trimethylolpropane triacrylate; Ligand exchange; Quantum dot; Photo-stability; Suspension polymerization; QD-Polymer bead
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2019.05.059

Acrylate groups were introduced on quantum dots (QD) via ligand exchange followed by nucleophilic reaction. The QDs were then polymerized with other multi-functional acrylic monomers in this study. Two acrylate groups were introduced at the end of an elongated ligand and the ligands with two acrylate groups were fully coordinated on the entire surface of the QD. This ligand modification scheme made the QDs highly reactive and also compatible with common organic solvents. No decrease in the quantum yield of the QDs was observed after ligand modification and the adduction reaction. The acrylate functional groups in the QDs were verified by 1H NMR and FT-IR. The prepared QDs with a terminal acrylate group were reacted with trimethylolpropane triacrylate and 1,6-hexanediol diacrylate to form micrometer scale beads via suspension polymerization. The diameter of the spherical beads was in the range of 80–150 μm and QDs 13 nm in diameter were found to be evenly dispersed in the polymer beads. The QD-polymer beads were applied to color conversion layers (CCL) on a blue light emitting diode (LED). The QD-polymer beads showed a 50% reduction over 72 h from the initial optical efficiency, while the QD embedded in the PMMA matrix (QD-PMMA) was reduced by 50% for 14 h. [Display omitted] 1.The effective functionalization method of QD surface for introduction of highly reactive and compatible ligand with a novel structure, which can be radical polymerized, without any degradation.2.Preparation of the QD-polymer bead, which was composed by covalent bonds between the designed QD and the other multi-functional acrylic monomers via suspension polymerization.3.The method for investigation of photo stability, which was designed with tailor-made LED kit for reproducibility of the test by 3D printing.4.The meaningful gap of photo stability between the QD-polymer bead and conventional QD matrix.