Polyethylene crosslinking using the epoxy‐anhydride reaction II: Development of a chemorheological model

We have developed a kinetic model attempting to describe the rheological changes observed during crosslinking of blends of epoxide- and anhydride-functionalized polyethylene using the activatable imidazolium catalyst EMIC. The model incorporated first-order formation of an active initiator from a latent state followed by initiation of the crosslinking reaction and continued propagation by an active crosslinking end group. Because the formation of a crosslink does not consume an active end group, the post-initiation crosslinking reaction assumes a first-order dependence in crosslinkable functionality. Application of the model to data generated from rheological studies exploring the effects of initiator and anhydride loading was met with moderate success. While curvature in the rheological plots modeled very well, capturing the active initiator formation and early cure, some data sets did not model well at higher degrees of cure. Extraction of modeled parameters Ginf$$ {G}_{inf} $$, ki,$$ {k}_i, $$ and kp$$ {k}_p $$ from fits showed that the initiation rate constant ki$$ {k}_i $$ was linearly dependent on the anhydride loading. We believe that this indicates the presence of an independent initiation pathway that destroys latency in the system. Additionally, it was found that the modeled value for the plateau modulus, Ginf,$$ {G}_{\mathit{\operatorname{inf}},} $$ showed a remarkably linear dependence on initiator loading. This relationship indicates that the ultimate degree of crosslinking in a system is determined by the sequence length of the crosslinking reaction and how many crosslinking cascades initiate based on the initiator loading.