Rheokinetic study of crosslinking of α,ω-dihydroxy oligo(alkylene maleate)s with a trisisocyanate

The crosslinking reaction of three series of ?,?-dihydroxy oligo(alkylene maleate)s with a trifunctional isocyanate was followed by dynamic mechanical analysis and FTIR spectroscopy. The evaluation of rheological parameters such as storage G? and loss modulus G", was recorded. A typical G?versus time curve has a characteristic "S" shape, indicating autoacceleration of the crosslinking reaction. The whole curing process starting from G?equal G", or the beginning of gelation is described by a second - order phenomenological rheokinetic equation which takes into account the autoacceleration effect, the latter being a consequence of the superposition of both the chemical reaction and phase segregation. It appears that the crosslinking reaction rate depends on the concentration of the functional groups, i.e., on the molecular weight of the polyester prepolymer and on the length of the aliphatic sequence in the repeating unit or the segmental mobility. The crosslinking rate decreases in the order: poly(octamethylene maleate) > poly(hexamethylene maleate) > poly(butylene maleate). Kinetika reakcije umrezavanja je izucavana pomocu dinamicke mehanicke analize i FTIR spektroskopije na tri serije ?,?-dihidroksi-oligo(alkilen-maleata) i trifunkcionalnog izocijanata. Reakcija umrezavanja polimera pracena je preko promene reoloskih parametara kao sto su modul sacuvane energije G? i modul izgubljene energije G". Kriva zavisnosti G? od vremena ima karakteristican "S" oblik, sto ukazuje na samoubrzavanje pri reakciji umrezavanja. Ceo proces umrezavanja od pocetka zeliranja, odnosno, od trenutka kada je G? jednako G", je opisan fenomenoloskom reokinetickom jednacinom drugog reda koja uzima u obzir efekat samoubrzavanja, kao posledicu superpozicije hemijske reakcije i morfoloskih promena. Pokazano je da brzina reakcije umrezavanja zavisi kako od koncentracije funkcionalnih grupa, tj. od molarne mase poliestarskog pretpolimera, tako i od duzine alifaticne sekvence u osnovnom motivu ili segmentalne pokretljivosti. Brzina reakcije umrezavanja opada u nizu poli(oktametilen?maleat) > poli(heksametilen?maleat) > poli(butilen?maleat).