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The frontal polymerization technique has been successfully applied, for the first time, to obtain an unsaturated polyester/styrene resin. The effect of the ratio of the two aforementioned components, as well as of the type and amount of free-radical initiator on both front velocity and maximum temperature reached by the front, has been thoroughly studied. The resulting products have been characterized in terms of their thermal and dynamic-mechanical behaviour. A comparison of such products with the corresponding materials obtained by the classical batch polymerization technique has evidenced that frontal polymerization allows to reach a higher degree of crosslinking with respect to batch copolymerization and hence a better thermal and mechanical behaviour.

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It has been found that anionic poly(ε-caprolactam) exhibits the peculiarity of a secondary SEC peak at intermediate elution times between the traces pertaining to the high polymer and those of the extracted oligomer fraction, irrespective of the conditions of synthesis, either nonisothermal (quasi-adiabatic) or isothermal. As yet, such a peak has never been evidenced in the literature. Synthesis in isothermal conditions at relatively low T allows to get rid af all structural irregularities, linked to nonisothermal anionic conditions, and analyze in depth the nature and extent of the above peak. Together with other characterization techniques, MALDI-TOF analysis has revealed that the peak is entirely composed of macrorings made of multiples of ε-caprolactam repetition unit, typically from M9 to M19, in amounts linked to the experimental conditions of the synthesis, but usually of ca. 2.5 wt %, as referred to the high polymer content. This amount is exceedly larger than the value extrapolated from the lower oligomer (x ≤ 8) content and cannot be justified by any ring−chain thermodynamic equilibrium approach. On the other side, also for lower oligomers striking discrepancies exist between theory and experimental results. A general overview, including also cyclic oligomer content in hydrolytic poly(ε-caprolactam) samples, is provided, and a critical analysis of the extraction methods described so far in the literature is given.