Photopolymer Systems for Holography and Additive Manufacturing
This thesis is focused on the advancement of enabling photopolymer materials for holography and additive manufacturing. The first part of this thesis covers the design, synthesis and implementation of novel chemistries in two-stage holographic photopolymers. First, photopolymerizable high refractive index monomers (nD/20ºC: 1.60 – 1.67) with enhanced solubilities were developed and employed in two-stage photopolymers, achieving high refractive index modulations (peak-to-mean Δn) of up to 0.03 in transmission holograms (pitch spacing ~ 1 μm); competitive with state-of-the-art commercial materials. These materials were also investigated towards alternative recording methods such as the facile optical fabrication of millimeter-scale flexible gradient refractive index (GRIN) lenses. In general, using efficient thiol-X chemistries, a diverse set of liquid acrylate writing monomers with a balanced set of properties (viscosity, color, dispersion, solubility etc.) were obtained. Correspondingly, a general and scalable synthetic strategy was devised that significantly expanded the thiol-X monomer toolbox for realizing high refractive index step-growth (photo)polymers. This highly modular approach enabled precise control over the monomer structure. Using only commercially available starting materials, synthesized thiol and diallyl ether monomers (nD/20ºC > 1.64) formed low viscosity thiol-ene resins (< 200 cP) that exhibited rapid and high conversions, achieving high refractive index values (nD/20ºC) up to 1.665. Separately, aspects of configuring the network in two-stage systems with dynamic covalent chemistries were developed to enable stress relaxation during and after holographic exposure.
The second part of this thesis comprises the foundational study of photopolymerizable thermoplastics, a unique class of high molecular weight polymers (> 104 g/mol) rapidly fabricated with light in seconds. This includes the investigation of photopolymerized linear thiol-ene polymers that subsequently crystallize within minutes at ambient to form mechanically strong and tough semicrystalline materials. Fundamental structure-property studies revealed a unique sub-class of polymers characterized by elastomeric-like elongations (~800%) with thermoplastic-like tensile strength and toughness values of 25 MPa and 100 MJ/m3 respectively. The potential of these materials for vat photopolymerization additive manufacturing was conclusively demonstrated using commercial 3D printers achieving good patterning resolutions at standard print times. The salient feature of being able to dissolve or melt otherwise mechanically robust 3D printed objects opens the door to a new class of intrinsically recyclable and reprocessable 3D printable photopolymers.
Full pdf - https://www.colorado.edu/mse/node/505/attachment