Reversible endothermic process observed by DSC in thermoplastic multiblock elastomers at middle temperature range
Reversible endothermic process observed by DSC in thermoplastic multiblock elastomers
at middle temperature range
Polimery 2003, No 11-12, 809
Endothermic process, so called „annealing endotherm”, at temperature range 40—80 °C was investigated in the following polymers: terpolymer [poly(tetramethylene terephthalate)-block-polyoxytetramethylene -block-polylaurolactam]n with a symbol -(PBT-b-PTMO-b-PA12)n-, copolymer [poly(tetramethylene terephthalate)-block-(hexamethylene amide of dimerized fatty acid)]n with a symbol -[PBT-b-(DFA-HMDA-DFA)]n- and copolymer [poly(tetramethylene terephthalate)-block-(piperazine amide of dimerized fatty acid)]n with a symbol -[PBT-b-(DFA-PIP-DFA)]n-. Effect of conditioning time at temperature 20 °C or annealing temperature (up to 60 °C) on this process was analyzed. It was found, on the basis of DSC thermograms (Figs. 1—4), that conditioning or annealing of -(PBT-b-PTMO-b-PA12)n- terpolymer led to stabilization of multiphase structure. It was observed that amorphic phase became homogeneous with simultaneous creation of structural elements of „quasimelting” point much lower than melting point of crystalline phase. It was assumed that these elements, as intermediates between amorphous state and crystalline one, are mesomorphic aggregates. Analysis of thermal properties of -[PBT-b-(DFA-HMDA-DFA)]n- copolymer (Fig. 5) suggests that not only dispersion forces but also hydrogen bonds can be responsible for creation and stabilization of mesomorphic aggregates. If the flexible block of thermoplastic multiblock elastomer (TPE) is able to create hydrogen bonds, the discussed middle-temperature endotherniic process appears immediately after cooling of elastomer. Mesomorphic aggregates are additional points of crystal lattice of a block elastomer and they improve its elastic and high-elastic properties but only in case if the blocks of have chosen compositions and molecular weights.
Keywords: thermoplastic multiblock elastomers, thermal properties, structure stabilization, mesomorphic aggregates