Thermal Degradation of Aminosilicone Carbamates

The major thermal degradation pathway seen with 1,5-bis­(3-aminopropyl)-1,1,3,3,5,5-hexamethyltrisiloxane/triethylene glycol (GAP-1/TEG) is the formation of a urea-containing compound. Degradation is increased at higher temperatures, longer reaction times, higher CO2 concentrations (in the form of carbamate loading), and low water levels. A judicious choice of operating conditions can significantly decrease urea byproduct formation. Reducing the desorption temperature from 140 to 100 °C and adding 5 wt % water to the 60:40 mixture of GAP-1/TEG resulted in a 500-fold reduction in amine loss after 4 days in a CO2-rich environment. After 56 days of continuous heating under the same conditions, ∼87% original GAP-1 was retained at 100 °C compared to only ∼20% at 140 °C. The urea byproduct appears to be the only major degradation pathway under these conditions, with 100% of the mass balance accounted for by the urea and amine components.