Study On The Reactive Blending Of PET/PEN By Chain-Extension

Reactive blending of incompatible polyester blend systems is an important subject which has gained increasing attention in the recent years because the block or random copolyester can be in-situ formed via transesterification of the components under melt state, which may act as a compatibilizer to improve their compatibility and in turn, enhance their properties. Therefore, to obtain better understanding of the factors which affect the transesterification between them has profound significance in both academic and application aspects since it will further determine the chain structures and morphology of the blends, as a consequence, predominate the final physical and mechanical properties of the produced materials.In this paper, for the first time we systematically studied the reactive blending of PET/PEN, which has a good outlook of application, by chain extension in the presence of 2,2-bis (l,3-oxazoline)(BOZ). The main results obtained are as follows: 1. Two kinds of chain extenders, BOZ and EMDI (4,4-diphene methane diisocyanate capped by ethanol), were synthesized. The effect of BOZ, EMDI, Bisphenol-A epoxy resin E-20 and E-12 on enhancing the intrinsic viscosity [η] of PET was compared. The results indicate that BOZ has better activity in chain extension which can to some extent increase the [η] values within a short time. Furthermore, the effect of BOZ on enhancing the intrinsic viscosity of PET/PEN blend system was studied for the first time. It is found that BOZ has a significant effect of increasing the [η] values within initial 10 minutes; with further prolonging the blending time the [η] values is in a decreasing tendency because of the degradation of the polyesters at elevated temperatures. However, they are still higher than those of PET/PEN blends without addition of BOZ.2. A series of PET/PEN reactive blends were prepared at different conditions. The factors which affect the transesterification of the blends, including blending time, temperature, BOZ and composition, were quantitatively investigated by using 1HNMR for the first time. The results show that with prolonging the blending time and elevating the temperature the transesterification level is monotonically increased; BOZ can markedly promote the transesterification reaction at 275 ℃, and the effect is reduced under further elevated temperatures due to the degradation of BOZ in part; The transesterification level is also to some extent affected by composition so that the PET/PEN 50/50 has the highest value. With the transesterification level increasing the number-average sequence length of LnPET and LnPEN tends to be reduced; At the same time the randomness increases to about 0.76, indicating that the reactive blends have the multi-block structure in character.3. Three kinetic approaches were compared to deal with the data of transesterification measured by 1H NMR for the first time. The results indicate that the second-order reversible kinetics can be used well to describe the mechanism of transesterification of the PET/PEN reactive blends. At 275 ℃ the reaction rate of PET/PEN blends with BOZ is higher than that of the blends without BOZ and the activation energy reduces from 167.8KJ/mol to 94.0 KJ/mol.4. Monte Carlo simulation was used to study the transesterification of PET/PEN blends for the first time. The results show that the data obtained based on second-order reversible kinetics can predict the change of transesterfication level and number-average sequence length in the PET/PEN reactive blends which match well with the experimental results and further prove the transesterfication mechanism mentioned above.5. The effect of mixing conditions, BOZ, and composition on the glass transition Tg, the cold crystallization temperature Tcc and the melting point Tm was investigated by using DSC, which was explained from the change of the sequence structure of the reactive blends for the first time. The results indicate that the cold crystallization peak disappeared as the number-...