Cross-linking agent for elastomeric composites and relative process for cross-linking elastomeric blends by means of said cross-linking agent

The object of the present invention is a copolymer comprising at least one repeating unit of a dipyrrolic monomeric compound, having a structure of formula (I1), wherein n is a number comprised between 2 and 11, the copolymer having a structure of formula (I3), wherein n is an integer comprised between 2 and 11, k is equal to 1, and m is an integer comprised between 1 and 5. The copolymer containing the repeating units having a structure of formula (I3) is prepared with a method comprising the following steps: i) arranging sulphur (S₈) and a monomeric compound, having a structure of formula (I1), in a molar ratio comprised between 0.74:1 and 9.58:1, respectively; ii) conducting a cross-linking reaction by reacting the sulphur with the monomeric compound, having a structure of formula (I1), arranged in step i), at a temperature comprised between 160 and 190 °C, preferably 185 °C, to obtain the polymeric compound having a structure of formula (I3); iii) optionally, isolating the polymeric compound from step ii). It should be noted that, advantageously, the dipyrrolic compounds having a structure of formula (I1) are easily obtainable from end-of-life polymers, such as a polyamide (6,6), which, alone or in combination with crystalline sulphur S₈, can advantageously cross-link elastomeric composites. The present invention further concerns a cross-linking agent for elastomeric composites, comprising: a) at least one polymeric compound having a structure of formula (I3), wherein n is an integer comprised between 2 and 11, k is equal to 1, and m is an integer comprised between 1 and 5; or b) at least one dipyrrolic monomeric compound having a structure of formula (I1), wherein n is an integer comprised between 2 and 11, in the presence of sulphur (S₈); or c) at least one polymeric compound having a structure of formula (I3), wherein n is an integer comprised between 2 and 11, k is equal to 1, and m is an integer comprised between 1 and 5, in the presence of sulphur (S₈). A further object of the present invention is a process for cross-linking elastomeric blends, comprising the following steps: Preparing, at a temperature comprised between 25 and 120 °C, preferably between 30 and 100 °C, more preferably between 60 and 90 °C, and most preferably at 80 °C, a masterbatch comprising a cross-linkable elastomeric composite comprising: at least one polymer belonging to the group R, according to standard DIN/ISO 1629, preferably a styrene-butadiene copolymer, and an organic and/or inorganic filler, preferably carbon black; Adding the cross-linking agent to the masterbatch in accordance with the present invention, keeping the system under stirring, at a temperature comprised between 25 and 120 °C, preferably between 30 and 100 °C, more preferably between 60 and 90 °C, most preferably equal to 80 °C and ideally the same as in step 1, to obtain a cross-linkable elastomeric blend; Cross-linking the cross-linkable elastomeric blend from step 2 by heating it at a temperature comprised between 150 and 220 °C, preferably between 170 and 200 °C, and preferably for a time of 30 minutes, to obtain a cross-linked elastomeric blend.