Toward an enhanced understanding and implementation of photopolymerization reactions

Abstract

in Wiley InterScience (www.interscience.wiley.com).Photopolymerization reactions proceed rapidly at ambient conditions and are able to exhibit both temporal and spatial control, nevertheless their full potential has been limited by a lack of understanding of the polymerization kinetics and polymer network evolution as well as a lack of custom, functional monomers, and polymerization mechanisms. For the last 15 years, our group has sought to address these limitations by reaction engineering at both the fundamental and applied levels with a focus on increasing the understanding, potential, and implementation of photopolymerization reactions. In particular, we have modeled and experimentally validated the complex spatially dependent polymerization kinetics and network heterogeneity, and we have implemented these systems for applications improvement or development in lithography, microdevice fabrication, biomaterials, biodetection, dental materials, and surface coatings.An illustration of typical photopolymerization kinetic behavior is presented in Figure 2a, where the polymerization rate is plotted as a function of the double bond conversion for two different photoinitiation rates. Two polymerization regimes are clearly identifiable in each curve and are typical Here, the chain length dependence is most prominent at the early stages of the reaction, during autoacceleration and is largely absent at the higher conversions where reaction diffusion controlled termination dominates the termination reaction process. Figure adapted from ref. 80.

Modeling and simulation of electrostatically gated nanochannels

“…A slight positive tapering of the channel wall was a consequence of a slight overexposure. However, the presence of this tapering indicates that very little broadening of the features occurred, which is in stark contrast with the broadening in stoichiometric thiol-ene reported by Bowman et al [31] Our group has recently reported an aspect ratio of 1:8 for photopatterned micropillars [29]. For the OSTE formulation used in this work, aspect ratio tests have been performed and revealed that an aspect ratio 1:4 were achievable without difficulties for both pillar and hole structures.…”

Photopolymerization of coordinated ionic liquid monomers: Realizing the benefits of structured media using only common reagents

“…Although the reaction profiles conform to classical kinetics in the early stages of the process, increases in the degree of polymerization result in increased viscosity, decreasing the mobility of growing polymer chains to a greater extent than monomers. 1,[7][8][9][10][11][12][13] This effect causes a decrease in the rate of termination for the reaction mixture while the rate of propagation is relatively unchanged, resulting in an increase in the rate of polymerization known as autoacceleration. 1,[9][10][11][12][13] Eventually, increases in the viscosity of the reaction medium also slow monomer diffusion toward the active radical, resulting in a decrease in the rate of propagation and rate of polymerization that is not the result of the decrease in monomer concentration.…”

“…1,7,12,[14][15][16] This phenomenon, known as autodeceleration, poses a substantial challenge to chain addition radical polymerization reactions as it can occur at conversions as low as 40% in cross-linked systems and results in significant amounts of residual, unreacted monomer in the product. 1 As the presence of these impurities can detrimentally affect product properties, mass transfer limitations pose a significant challenge for photopolymerization processes.…”

“…[1][2][3] Photopolymerization reactions can be performed in bulk (i.e., no cosolvent) wherein reaction mixtures contain only polymerizable species (e.g., monomers, cross-linking agents) and initiator, although the presence of a cosolvent such as water is used in tissue engineering and other applications. [3][4][5] Bulk processes offer multiple advantages including the ability to produce a relatively pure product and control over polymer shape and thickness.…”

A Single-Step Monomeric Photo-Polymerization and Crosslinking via Thiol-Ene Reaction for Hydroxide Exchange Membrane Fabrication

“…In contrast, chain-growth polymerization reactions typically form more heterogeneous networks since the evolution of molecular weight is spatially heterogeneous (evolving from microgel formation to reduced radical mobility). 26 Chain-growth reactions often fall short of reaching full conversion of the vinyl functional groups owing to transport limitations (e.g., vitrification). 16 This fundamental difference between these reaction mechanisms is expected to lead to drastically different HEM microstructures, resulting in the HEM property differences shown in Table II.…”