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Dissertation
Improving photopolymerization outcomes through control of cationic ring-opening systems
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2018
DOI: 10.17077/etd.005710
Abstract
Photopolymerization offers many advantages over traditional thermal polymerization such as energy savings, increased ease of processing, and elimination of volatile organic solvents. These advantages have lead photopolymerization to be used in various applications within the coating, film, adhesive, and ink industries. There are two primary mechanisms within the field of photopolymerization: free-radical and cationic. Cationic polymerization is greatly underused in the field of photo curing compared to free-radical polymerization despite many advantages, such as the ability to cure under ambient conditions, the presence of long-lived active centers that allow for the curing of thick and pigmented formulations, and reduced shrinkage compared to free-radical systems. This work focuses on addressing the disadvantages of cationic curing, including slow reaction rates, the lack of understanding and control of post-cure, and low initiation wavelengths, in order to better utilize cationic polymerization in areas where photopolymerization is lacking.
To enhance reaction kinetics and overall conversion in cationic epoxide systems, the most commonly used type of cationic monomer class in industrial settings, oxetanes were added and the copolymerization was characterized to determine the network structure of each epoxide/oxetane pair. The addition of oxetanes to the difunctional cycloaliphatic epoxide EEC was found to increase kinetics and conversion during both illumination and dark cure using real-time Raman spectroscopy. The copolymerization of EEC and oxetanes was verified and the reactivity and network structure was characterized using a combination of Soxhlet extraction, dynamic mechanical analysis, and Raman spectroscopy.
The impact of long-lived active centers on the physical property testing of cationic dark cure was demonstrated and the factors and reaction variables that control the extent of cationic shadow cure were determined. The process of taking DMA measurements and annealing cationic polymer films was shown to result in increases in conversion and differences in the measured properties long after the films have been cured, proving the necessity for multiple DMA cycles for complete characterization of cationic systems. Additionally, long-term diffusion of the cationic active centers gives the epoxide EEC the ability to cure outside the illuminated region (a process known as shadow cure), and this shadow cure is greatly affected by the photoinitiator concentration, temperature of the system, and presence of reactive and non-reactive diluents such as oxetanes and impurities in the EEC.
In order to provide guidelines for improving the prediction of absorbance and reactivity in cationic photopolymerizations based on the molecular structure, the photon absorbance and polymerization ability of various cationic photoinitiating systems was characterized according to their cation and anion structure. This was done by investigating a series of onium salt photoinitiating systems using UV-Vis spectrophotometry and Raman spectroscopy and determining the effect of the cation and anion on various aspects of the polymerization, including both the initiation of the cationic reaction and the rates of propagation.
This work strives to enhance the performance of cationic photopolymerization in order to see cationic polymerization expand the applications of photopolymerization beyond what are currently dominating in industry, leading to processes that are more energy efficient, environmentally friendly, and easily controlled.
Details
- Title: Subtitle
- Improving photopolymerization outcomes through control of cationic ring-opening systems
- Creators
- Sara Marie Kaalberg
- Contributors
- Julie L. P. Jessop (Advisor)Allan Guymon (Committee Member)David Rethwisch (Committee Member)David Cwiertny (Committee Member)Lei Geng (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemical and Biochemical Engineering
- Date degree season
- Spring 2018
- Publisher
- University of Iowa
- DOI
- 10.17077/etd.005710
- Number of pages
- xviii, 217 pages
- Copyright
- Copyright 2018 Sara Marie Kaalberg
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references.
- Academic Unit
- Chemical and Biochemical Engineering
- Record Identifier
- 9984036087302771
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