Ultraviolet (UV)-induced cationic frontal polymerization has emerged as a novel technique that allows rapid curing of various epoxy monomers upon UV irradiation within a few seconds. In the presence of a diaryliodonium salt photoinitiator together with a thermal radical initiator, the cationic ring opening polymerization of an epoxide monomer is auto-accelerated in the form of a self-propagating front upon UV irradiation. This hot propagating front generates the required enthalpy to sustain curing reaction throughout the resin formulation without further need for UV irradiation. This unique reaction pathway makes the cationic frontal polymerization a promising route towards the efficient curing of epoxy-based thermosetting resins and related composite structures. This review represents a comprehensive overview of the mechanism and progress of UV-induced cationic frontal polymerization of epoxy monomers that have been reported so far in literature. At the same time, this review covers important aspects on the frontal polymerization of various epoxide monomers involving the chemistry of the initiators, the effect of appropriate sensitizers, diluents and fillers.

The idea to modify polystyrene sulfonated divinyl benzene (PSS/DVB) resin particles with electroactive polyaniline (PANI) prior to incorporating these into a polymer matrix (PVC in the present case) has been trialed in this study. The extent of PANI layering on resin particles was controlled by changing polymerization time during aniline polymerization reaction. The PANI modified PVC–PSS/DVB heterogeneous cation exchange membranes were characterized for their morphological, physical and structural properties using scanning electron microscopy (SEM), measurements of water uptake and ion exchange capacity, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). SEM micrographs showed PANI layering around PSS/DVB particles and shape change depending on aniline polymerization time that has been also confirmed by FTIR spectra through growing PANI peaks. PANI layering around resin particles resulted in lower water uptake of PANI modified resin membranes as compared to unmodified PVC–PSS/DVB membranes. The ion exchange capacity decreased initially at shorter PANI deposition times and increased slightly on prolonged deposition because of the cation character of doped PANI that was originated by excessive layering around the particles. TGA curves showed PANI degradation in addition to PVC and PSS/DVB resin degradations thus decreasing the overall thermal stability of PANI modified membranes. Ion transport studies in a two-compartment cell showed significantly different transport numbers for monovalent (Na⁺) and divalent (Ca²⁺) cations that decreased by increasing PANI layering around resin particles. The difference between transport numbers, a measure of membrane permselectivity, increased by increasing PANI deposition showing the strong screening effects of PANI layering.

Frontal polymerization of epoxy-based thermosets is a promising curing technique for the production of carbon fiber reinforced composites (CFRCs). It exploits the exothermicity of polymerization reactions to convert liquid monomers to a solid 3D network. A self-sustaining curing reaction is triggered by heat or UV-radiation, resulting in a localized thermal reaction zone that propagates through the resin formulation. To date, frontal polymerization is limited to CFRCs with a low fiber volume percent as heat losses compromise on the propagation of the heat front, which is crucial for this autocatalytic curing mechanism. In addition, the choice of suitable epoxy monomers and thermal radical initiators is limited, as highly reactive cycloaliphatic epoxies as well as peroxides decarboxylate during radical induced cationic frontal polymerization. The resulting networks suffer from high defect rates and inferior mechanical properties. Herein, we overcome these shortcomings by introducing redox cationic frontal polymerization (RCFP) as a new frontal curing concept. In the first part of this study, the influence of stannous octoate (reducing agent) was studied on a frontally cured bisphenol A diglycidyl ether resin and mechanical and thermal properties were compared to a conventional anhydride cured counterpart. In a subsequent step, a quasi-isotropic CFRC with a fiber volume of >50 vol%, was successfully cured via RCFP. The composite exhibited a glass transition temperature > 100 °C and a low number of defects. Finally, it was demonstrated that the redox agent effectively prevents decarboxylation during frontal polymerization of a cycloaliphatic epoxy, demonstrating the versatility of RCFP in future applications.

Radical induced cationic frontal polymerization (RICFP) is a promising route to achieve rapid curing of epoxy‐based thermosets, requiring only a localized exposure with UV light. In the presence of a diaryliodonium‐based photoinitiator and a thermal radical initiator, a self‐sustaining hot front cures epoxide monomer via a cationic mechanism. However, the cationic polymerization of diglycidyl ether derivatives is slow (in comparison with other epoxides with higher reactivity) and, as a consequence, frontal polymerization is sluggish because the heat loss is not compensated by the rate of heat release. Cycloaliphatic epoxies possess a higher ring strain than diglycidyl ether derivatives and can be blended with the latter to increase its rate of frontal polymerization. In the current work, a comprehensive study on the influence of 3,4 epoxycyclohexylmethyl 3,4‐epoxycyclohexane carboxylate (CE) on cure kinetics, viscosity, front velocity, mechanical, and thermo‐mechanical properties of frontally cured bisphenol A diglycidyl ether derivatives is presented. The results show a direct relationship between frontal velocity and amount of reactive diluent while an inverse relationship with the storage viscosity is observed. It is found that increasing the content of cycloaliphatic epoxide reduces the glass transition but increases mechanical properties of frontally cured bisphenol A diglycidyl ether derivatives.

In today's IaaS clouds users only get a logical view of the underlying network and have limited control. Delegating more control to end users would be beneficial but would also raise security concerns for the provider. Emerging Software Defined Networking (SDN) technologies have the capabilities to facilitate delegation of network controls and provide some level of network abstractions to end users. However, any delegation solution should try to balance the level of controls delegated to end users with the security constraints of the provider. In this paper, we propose a SDN-based framework to facilitate delegation of some network controls to end users, providing the means to monitor and configure their own slices of the underlying networks. Using two instantiations of this framework, we illustrate the tradeoffs between security and the level of network abstractions provided to end users.