| Summary: | 碩士 === 萬能科技大學 === 工程科技研究所 === 94 === Two series of Polyurethane copolymers, siloxane/ether-urethane copolymer (PDMS/PTMG-PUBD) and siloxane/ether-urethane-imide copolymer (PDMS/PTMG- PUIM), were synthesized in this study. The chain extenders of copolymers are differential, 1,4-butane diol (1,4-BD) and 3,3’,4,4’-diphenylsulfonetetracarboxylic dianhydride (DSDA). The soft segments of both copolymers consist of polytetramethylene glycol (PTMG) and polydimethylsiloxane diol (PDMS). The hard segments of PDMS/PTMG-PUBD copolymer includ urethane B which is consisted of 4,4-diphenylmethane diisocyanate (MDI) and 1,4-BD, urethane G consisted of MDI and PTMG, and urethane S consisted of MDI and PDMS. For the PDMS/PTMG- PUIM copolymer, the hard segments are urethane G, urethane S and imide segment due to the DSDA instead of 1,4-BD.
The various urethane hard segments of copolymers lead to various thermal degradation behaviors by TGA. The TG/DTG curves of PDMS/PTMG-PUBD copolymer show the degradation regions of urethane B, urethane G and urethane S are 200~300 °C, 310~370 °C and 280~350 °C, respectively. The degradation regions of urethane G and urethane S are unable to distinguish for samples with PTMG and PDMS mixed soft segments due to the overlapping degradation regions of urethane G and urethane S. The TG/DTG curves of PDMS/PTMG-PUIM copolymer in the degradation regions of hard segments only show the degradation of urethane G and urethane S due to the degradation temperature of imide segments above 350 °C. The degradation behaviors of soft segments are affected by the contents of PDMS and PTMG. The DTG curves of PDMS/PTMG-PUBD copolymer in the degradation regions of soft segments display the degradated peak from a single peak, a single peak with shoulder to double peak as the PTMG content increases. The degradation regions of soft segments for PDMS/PTMG-PUIM copolymer include the degradation behaviors of PDMS, PTMG and imide segment. The degradation regions of these segments show overlap, resulting in a wide degradated peak in the DTG curves. The samples with high PDMS contents present a minor shoulder above 520 °C. PDMS degrades into high molecular weight macrocyclics through interchange reaction and the macrocyclics initially degrade above 520 °C. TG-IR is used to analyse the degraded gas products of copolymers in various temperatures. Combining TGA and TG-IR analysis, the degradation mechanisms of copolymers can be further set up.
Four degradation kinetic methods, Friedman method, Kissinger method, Ozawa method and Horowitz-Metzger method, are proposed to investigate the thermal degradation kinetics of copolymers. Various kinetic methods result in various activation energies. But, they demonstrate that hard segments of urethane B, urethane G and urethane S present individually degradation step. Therefore, incropating PDMS or imide segment into copolymers can significantly enhance the activation energies and improve the thermal stability.
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