Photopolymerization kinetics in and of self‐assembling lyotropic liquid crystal templates

Abstract

Photopolymerization in and of lyotropic liquid crystal (LLC) template phases shows great promise for generating nanostructure in organic polymers. Interestingly, the order imposed on the polymerization system in LLCs significantly alters polymerization kinetics. The rate of polymerization of hydrophilic monomers increases with increasing LLC order, primarily due to monomer/polymer association with surfactant and the resulting decrease of growing polymer chain diffusion. Conversely, as LLC order increases, hydrophobic monomers become less segregated as nonpolar volume increases, which decreases polymerization rate. The efficiency of initiators is also dependent on LLC template order, further contributing to polymerization rate changes. When reactive surfactants are used, LLC mesophase, location of reactive group, and aliphatic tail length also affect polymerization kinetics. Overall, these photopolymerization kinetics directly relate to the segregation behavior and local order of reactive groups and thus can be used to probe nanostructure evolution, facilitating understanding and control of ultimate polymer nanostructure.

A Semiempirical Scaling Model for the Solid- and Liquid-State Photopolymerization Kinetics of Semicrystalline Acrylated Oligomers

“…The equation is equally relevant for any other structure for which the center-of-mass mobility of the radical bearing moieties is strongly inhibited such as amorphous solids or soft gel networks. 51,53 The conversion-dependent factors under the square root describe from left to right the radical buildup toward steady state, the first-order kinetic behavior, and the deviation of first-order kinetics due to gradual structural arrest of the polymerization (i.e., k p M a • → 0). Figure 1 provides an illustrative example of eq 18 along with the corresponding k p and k t profiles for the following set of parameters: p f = 0.9, R i k p 0 = 0.01 s −2 , AM 0 = 5, μ = 20, ν = 0.5, and ξ = 2 and where k t,d 0 /k p 0 is varied from 0.01 to 1000 in logarithmic spacing.…”

“…This expression predicts in a concise way the phenomenology behind the FRP kinetics of semicrystalline acrylated oligomers in solid conditions where the double bonds, packed in the periphery of the crystalline domains, form a functional network. The equation is equally relevant for any other structure for which the center-of-mass mobility of the radical bearing moieties is strongly inhibited such as amorphous solids or soft gel networks. , The conversion-dependent factors under the square root describe from left to right the radical buildup toward steady state, the first-order kinetic behavior, and the deviation of first-order kinetics due to gradual structural arrest of the polymerization (i.e., k p M a • → 0).…”

Impact of Comonomer Chemistry on Phase Behavior of Polymerizable Lyotropic Ionic Liquid Crystals: A Pre‐ and Post‐Polymerization Study

“…A promising alternative, which could address both thermal stability and mechanical integrity simultaneously, lies in the development of photopolymerized LLC systems, whereby long‐range order is retained after UV‐polymerization . Photopolymerized LLC systems reported so far can be categorized into two subclasses where: i) an LLC system is used as a pore former and is subsequently removed post‐polymerization, resulting in the formation of nanoscale porosity or where ii) a polymerizable LLC is used and covalently bonded to the polymer backbone. The latter case allows the amphiphile to be used as a permanent scaffold for the incorporation of host molecules, particles, and peptide‐based channels …”

Nanoporous Polymer Networks Templated by Gemini Surfactant Lyotropic Liquid Crystals

“…23,25 LLC-templated polymerizations have emerged as a versatile and attractive alternative strategy for producing nanoporous polymeric materials from relatively inexpensive starting materials. 26,27 This methodology relies on spatially localizing monomers within either the hydrophilic or the hydrophobic domains of a small molecule surfactant LLC and inducing their polymerization. 28 Various successful syntheses of nanoporous hydrophilic polymers have been achieved by this strategy through the careful selection of Type I LLC templates that allowed for their loading with cross-linkable monomers and their subsequent photopolymerization to yield anisotropic structures.…”