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Authors: Kirschbaum, Stefan
Title: Vinyl ether functional polyurethanes as novel photopolymers
Online publication date: 7-Feb-2017
Year of first publication: 2017
Language: english
Abstract: Photopolymers with unique curing capabilities are introduced by combining living cationic polymerization with network formation and restricted polymer motion. A vinyl ether diol (VEOH) was synthesized as functional building block and incorporated into a polyurethane prepolymer (VEPU) with high vinyl ether functionality. In combination with cationic photoinitiators fast polymerization is observed upon short UV-irradiation. Curing proceeds in the absence of light and under ambient conditions without oxygen inhibition. Cationic active sites become trapped, dormant species upon network-induced vitrification and surprisingly remain living for several days. The polymerization can be reactivated, triggered by additional UV-irradiation and/or temperature. The curing behavior was studied in detail using UV and FT-NIR coupled rheology and photo-DSC to simultaneously observe spectroscopic and mechanical information as well as thermal effects. Besides vinyl ether terminated VEPUs also isocyanate terminated VEPUs are introduced as highly synergistic dual cure materials. The presence of isocyanate groups ensures low levels of free nucleophiles (“self-drying”) and hence provides extraordinary robust conditions for cationic chain growth of vinyl ethers. Thickening or setting of the material can be adjusted upon a short, initial irradiation period, while the subsequent moisture-induced curing of isocyanate groups via urea formation proceeds over several hours or days. Furthermore, the isocyanate functionality can contribute to increased adhesion with various substrates. Moreover, VEPUs were combined with mono- or difunctional alcohols as transfer agents and subjected to photoinduced, cationic polymerization. The hydroxyl compounds become covalently incorporated into the resulting polymer network via formation of acetal linkages in a nucleophilic addition reaction followed by proton transfer. The resulting curing mechanism is an interplay between cationic polymerization and polyaddition, and is hence introduced and discussed as cationic phototransfer polymerization. Highly adjustable acetal-containing polymer networks are obtained, which enable pH-responsive degradation and controlled release of the hydroxyl components from crosslinked, insoluble carriers. 13C MAS NMR spectroscopy and extractive GC analysis were applied to verify the formation of acetal groups and investigate the release efficiency and kinetics under different pH conditions. This concept was transferred to a vinyl ether functionalized polyhydroxyurethane (VEPHU) prepared via aminolysis of a vinyl ether functional dicarbonate. The VEPHU can be cured via a cationic phototransfer polymerization, under consumption of hydroxyl groups. This procedure allows the preparation of crosslinked polyhydroxyurethenes (PHUs) with reduced hydroxyl content and provides an efficient method to overcome low molecular weight and high water absorption, which are the main limitations of classical PHUs. In addition, simplified and scalable synthetic pathways towards VEOHs are described, which are as well based on the ring-opening reaction of cyclic carbonates with amines, whereas one component contains vinyl ether functional groups. The resulting urethane containing VEOHs significantly contribute to the polymer properties and are besides utilized to prepare polyhydroxyurethanes via photoinduced radical mediated thiol-ene polyaddition.
DDC: 540 Chemie
540 Chemistry and allied sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: MaxPlanck GraduateCenter
Place: Mainz
URN: urn:nbn:de:hebis:77-diss-1000009951
Version: Original work
Publication type: Dissertation
License: In Copyright
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Extent: XVI, 183 Seiten
Appears in collections:JGU-Publikationen

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