Modification of PBT with 1,2-Epoxybutane

In our investigation into the chemical modification of swollen polymer particles in supercritical fluids, PBT with 44 mmol kg carboxyHc acid end groups was modified with 1,2-epoxybutane in supercritical CO2 or in a supercritical or sub-critical mixture of CO2 with 10 mol% 1,4-dioxane. The critical pressures (Pc) and temperatures (TJ of CO2, and the Pc and Tc values for mixtures of CO2 with 10 mol% 1,4-dioxane, calculated using Ka/s rule [79], have been given in Section 13.3.1. 

Temperatures of 120 and 180 °C and pressures of 6, 15 and 30 MPa were ap-pHed. The reactions were performed for periods of 1, 2, 4 and 24 h. Modification at a pressure of 6 MPa (subcritical conditions, i.e., both CO2 and 1,4-dioxane are in the gas phase) was chosen in order to be able to trace possible differences between supercritical and subcritical end-group modification. The reaction temperature needs to be above the Tg of the PBT granules to ensure sufficient chain mobility, but below the T to avoid deformation or melting of the granules and, after depressurization, to regain their original form and their free- 

In Fig. 13.11, the carboxylic acid end-group concentrations of PBT samples, which were modified with 1,2-epoxybutane under several different conditions, are given versus modification time (experimental error is 2 mmol kg ). 

Comparing the results of the modification of the carboxyhc acid end groups with 1,2-epoxybutane in SCCO2 at 120°C (- -) and at 180°C (- -), it is found that at 

Error bars are 2. (Reproduced with permission from Elsevier). 

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