## 1 Introduction  
The cross-linking polymerization of multifunctional aromatic monomers initiated by exposure to high-energy radiation continues to be explored as a promising alternative to thermal curing for the production of high-performance composite materials [1; 2; 3; 4]. High-energy radiation processing offers technical and economic advantages over thermosetting technology by allowing for fast and out-of-autoclave curing operation applicable to large and complex structures. It induces lower energy consumption and reduces development costs. Curing times are shorter, and resin formulations have longer shelf lives. The absence of highly volatile monomers reduces industrial and sanitary risks in the process. Radiation-induced curing is based on free radical and cationic chemistries commonly used for coating applications but not for the fabrication of massive composite parts, aside from some specific applications such as dental restorative materials [5]. As the typical thickness for structural composites ranges from few millimeters to centimeters and requires the use of shaping tools such as metal modids, the penetration of radiation, energy deposition and thermal effects are completely different from the standard conditions for 5 to 100 \(\upmu\)m thick strongly pigmented ink and paints cured by exposure to ultraviolet (UV) or electron beam (EB) radiation [6]. Moreover, the requirements in terms of thermophysical and mechanical properties as well as resistance to ageing under normal operation conditions are extremely different. Thisresults in the need for deep knowledge on the relationships between resin composition, processing conditions and resulting properties for the cured matrix and at the interfaces between the matrix and fillers or fibers [7]. Epoxy resins form a large class of multifunctional monomers and prepolymers possessing reactive 1,2-epoxide functions (oxiranes). They are most commonly produced by the reaction under basic conditions of epichlorohydrin with various types of phenols, such as bis-phenol-A, leading to diglycidyl ether of bis-phenol A, DGEBA [8; 9]. Another approach consists of the epoxidation of unsaturated hydrocarbon segments yielding various types of aliphatic and alicyclic epoxy monomers, such as epoxidized soya or linseed oils and cyclohexene-based esters [10]. These two sub-classes of epoxy resins are converted into solid networks by a variety of chemical mechanisms, yet with their specific reactivity and time-temperature conversion dependence due to blend composition and vitrification behavior. Monomers and prepolymers fitted with two or more epoxy functions indeed form covalent networks either by step-growth polymerization or by chain-growth ring opening polymerization through cationic or anionic ring-opening reactions, the latter being essentially used for the linear polymerization of epoxy monomers having a simple structure (Scheme 1). The two modes of polymerization by chain and by stepwise growth proceed through drastically different mechanisms. In ionic chain polymerization, there is no spontaneous chain termination such as the recombination of free radical species. Additionally, cationic polymerization is a pseudo-living process, with active centers which are accumulated in the medium as the initiation takes place (no steady state concentration). Those active centers survive and can continue propagation as long as monomer functions are still present, provided that mobility of the reactive species (cationic centers and monomers) is not restricted [11; 12]. Once the production of new initiating centers has ceased, cationic polymerization continues by the so-called dark cure phenomenon [13], until the active centers are trapped in the glassy network or quenched by some inhibitor entering the material. This pseudo-living behavior enables further thermal activation giving rise to some beneficial post-cure effect [14; 15].