Dissertation
Hyperbranched prepolymer additives and in situ NMR to improve material properties and methods for monitoring reaction kinetics in photopolymer systems
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2025
DOI: 10.25820/etd.008232
Abstract
The unique properties of light, including high energy efficiency and precise spatial and temporal control, endow photopolymerization with the ability to produce materials that pose significant challenges to conventional manufacturing methods such as intricate 3-dimensional structures, rapidly cured thin film coatings, or nanometer-sized data storage structures. However, the network morphology inherent to photopolymer materials generally results in poor mechanical properties, detrimental polymerization-induced volumetric shrinkage, and unreacted species in the cured material. While linear prepolymers are commonly included in photocurable resins to counteract these effects, such additives can have a significant impact on resin rheology and as a result cause processing difficulties in systems requiring narrow viscosity ranges (e.g., inkjet printing). Conversely, hyperbranched prepolymers (HBPs) have shown promise as potential alternatives to linear polymer additives as a result of their unique structural and rheological properties.
In this work, HBPs were synthesized using PI-RAFT polymerization and used as additives to photocurable networks. A comprehensive study of the effect of branching density and size on mechanical properties revealed superior material toughness in HBP-modified networks compared to those containing linear analogues. Moreover, it was shown that the inherently branched architecture of HBPs permits for their higher loading levels in photopolymer systems without detrimentally affecting material or resin properties. Acrylic functionality was controllably placed on HBPs via block addition by reinitiating residual PI-RAFT endgroups in the presence of multifunctional crosslinker. Functionalized HBPs were then used to cure photopolymer networks by serving both as the sole crosslinking and photoinitiating species.
As conventional methods for photopolymer reaction monitoring are limited in their ability to study complex photopolymer systems, we herein developed a technique to monitor and initiate photopolymerizations using a fiber optic guiding light directly into an NMR magnet. By using a concentric inner capillary to contain both the fiber optic tip and lock solvent, the photopolymer resin remained isolated and could thus be cured in a truly solvent-free environment. In situ photopolymerization of a basic monomer system revealed exceptional reproducibility and agreement to conventional techniques in addition to high sensitivity to subtle changes to reaction conditions. To illustrate the potential of this technique to serves as a powerful analytical tool, photopolymer systems posing significant challenges to conventional techniques including the independent monitoring of acrylate/methacrylate copolymerizations were successfully performed in situ. Lastly, by optimizing instrumental acquisition parameters and automating data processing, collection speed was expedited substantially to enable real-time measurements of rapidly curing photopolymer networks such as those commonly seen in industrial settings.
As a whole, this work serves to: (1) demonstrate the controllable synthesis and functionalization of HBP additives enabling significant enhancements to photopolymer material and kinetic properties and (2) develop, test, and optimize an analytical real time monitoring technique complementary to conventional methods to advance insight and understanding of photopolymer reaction kinetics.
Details
- Title: Subtitle
- Hyperbranched prepolymer additives and in situ NMR to improve material properties and methods for monitoring reaction kinetics in photopolymer systems
- Creators
- Luis L. Jessen
- Contributors
- C. Allan Guymon (Advisor)Alec B. Scranton (Committee Member)Kristan Worthington (Committee Member)David G. Rethwisch (Committee Member)Eric Nuxoll (Committee Member)Beth Rundlett (Committee Member)Robin Willemse (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemical and Biochemical Engineering
- Date degree season
- Autumn 2025
- DOI
- 10.25820/etd.008232
- Publisher
- University of Iowa
- Number of pages
- xviii, 234 pages
- Copyright
- Copyright 2025 Luis L. Jessen
- Language
- English
- Date submitted
- 11/03/2025
- Description illustrations
- Illustrations, graphs, charts, tables
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Over the past 70 years, photopolymerization (a method using light to cure thin layers such as coatings) has significantly grown in its role in manufacturing due to high energy efficiency, spatially controllable curing, and the unique ability to abruptly terminate the curing process. While industries ranging from restorative dentistry to 3D-printing have adopted this technique, persistent challenges including the need for linear polymer additives continue to limit expansion into further sectors. In this work, the synthesis and use of highly-branched polymer additives (HBPs) with minimal impact on resin viscosity is studied in detail. By exercising control over HBP structure and size, we demonstrate the ability to engineer photopolymer materials with improved material toughness and curing behavior compared to linear additives. We further explore the controllable placement of chemical side groups on 3D-printable HBPs, while avoiding toxic reagents typically used in such a step. Furthermore, as current instrumental techniques are limited in their ability to analyze complex photopolymerizations, the latter part of this work describes the development of a technique capable of monitoring photopolymer reactions inside a Nuclear Magnetic Resonance spectrometer, a powerful instrument similar to an MRI used to study chemical structure and composition. This innovative approach enables the meticulous analysis of complex photopolymer systems that are otherwise difficult to monitor using conventional methods and without the need for sample dilution, typically required in NMR. This work served to (1) explore the controllable synthesis of HBP additives to manipulate material properties and (2) develop an instrumental technique for the monitoring of complex photopolymer reactions.
- Academic Unit
- Chemical and Biochemical Engineering
- Record Identifier
- 9985135048502771
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