Synthesis and Characterization of Functional Photopolymers for Advanced Applications

Elisabeth Rossegger

Research output: ThesisDoctoral Thesis

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Abstract

Aim of the present thesis was the development of new stimuli-responsive photopolymers for advanced applications. By introducing photoreactive moieties or dynamic covalent bonds into the photopolymer network, smart materials with switchable properties were obtained. In a first step, bi-functional alkynes bearing ortho-nitrobenzyl ester linkages were synthesized and crosslinked with multifunctional thiols by visible light exposure. Via asymmetrical irradiation of the polymer surface with UV-light, polar groups were generated, due to photocleavage reactions of the chrompophores and photooxidation upon prolonged UV exposure under air. The wettability increased with increasing exposure dose and a gradient surface with static water contact angles ranging from 97 to 19 ° was obtained. By introducing the wettability gradient in wedge-shaped patterns, an additional Laplace pressure gradient was inscribed and directional motion of water droplets over a reasonable distance (10 mm) was feasible. In another approach, the directional movement of a water droplet was further increased (20 mm) by applying nanoimprint lithography for additional surface texture changes. To generate highly hydrophobic surfaces (static water contact angle approximately 140 °), photo-reactive thiol-acrylate resins consisting of o-nitrobenzyl alcohol moieties with terminal acrylate groups, multi-functional thiols and a fluorinated methacrylate monomer were patterned via visible light assisted nanoimprint lithography. Subsequent irradiation of the microstructures with UV-light under air resulted in the localized formation of polar groups and erosion of the needle-like microstructures until fully wettable surfaces (static water contact angle of 7 °) were obtained. Along with photocleavable chromophores, thermally triggered dynamic covalent bonds were introduced into 3D printable photopolymers. They enable numerous advanced functionalities such as self-healing, recyclability, malleability and shape memory. One of the most attractive dynamic networks are vitrimers that rely on thermoresponsive exchange reactions such as the transesterification of hydroxyl ester species. A mono-functional methacrylate phosphate was introduced as new transesterification catalyst. First, thiol-acrylate vitrimer systems were developed for prototyping of soft-robotic 3D objects via digital light processing 3D printing. After photocuring, the dynamic networks were able to rapidly undergo thermal induced rearrangement reactions. Triple-shape memory and thermal mendability of the 3D printed objects were successfully demonstrated. In a second step, the toolbox of acrylate monomers for 3D printing of vitrimers was further extended. A series of acrylic dynamic networks was prepared and their mechanical performance was conveniently adjusted by the chemical functionality and structure of the monomers. Rheometer studies demonstrated that the stress relaxation rate decreases with increasing crosslink density and glass transition temperature of the photopolymeric networks. Via digital light processing 3D objects with feature sizes around 50 µm were prepared and the dynamic nature of the network enabled thermally triggered shape-memory and mendability, even of highly crosslinked networks. In a subsequent approach, light and temperature were combined as an external stimulus to locally control the dynamic exchange reactions in 3D printed parts by using a photoacid generator as latent transesterification catalyst. Photoacids form strong Brønsted acids upon UV exposure and enable fast transesterification reactions above the Tv. The photoacid was introduced into visible light curable resins. Based on the orthogonality between the curing reaction and the activation of the catalyst, dynamic exchange reactions were selectively triggered in the 3D printed objects by using a dual wavelength 3D printer. Soft active devices with locally controlla
Translated title of the contributionSynthese und Charakterisierung von Funktionellen Photopolymeren für Fortschrittliche Anwendungen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Wiesbrock, Frank, Assessor A (external), External person
  • Kern, Wolfgang, Supervisor (internal)
  • Schlögl, Sandra, Co-Supervisor (internal)
  • Sangermano, Marco, Assessor B (external), External person
Publication statusPublished - 2021

Bibliographical note

embargoed until 25-04-2022

Keywords

  • Polymer Chemistry
  • Photopolymerization
  • Vitrimers
  • Digital Light Processing
  • Nanoimprinting
  • Photopatterning
  • Thiol-ene
  • Thiol-yne
  • Organic Synthesis
  • Self-healing
  • Shape-Memory
  • Wettability gradient
  • Transesterification
  • Dynamic exchange reactions
  • Covalently adaptable network
  • Droplet transport

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