Phase Composition of Block Copoly(ether ester) Thermoplastic Elastomers Studied by Solid-State NMR Techniques

Abstract

The microphase composition of poly(butylene terephthalate)-block-poly(tetramethylene oxide) multiblock (PBT-block-PTMO) copolymers with varying content of PTMO soft block and varying block length was studied by 1 H NMR transverse magnetization relaxation (T2 relaxation) and 1 H 2D DQ NMR experiments under fast MAS. The 2D NMR method showed the existence of the molecular scale mixing of PBT and PTMO blocks. The 1 H and previously obtained 13 C NMR relaxation data provided detailed information on the microphase composition. The content of soft domains (i.e., viscoelastic material which is composed of the soft block and mixed PBT) and hard domains (i.e., crystalline PBT and immobilized PBT chain portions at the crystal-amorphous PBT interface) depends largely on temperature. It was shown that about 15-25% of PBT in the samples is soft due to molecular mixing with PTMO. The results suggest that at 40 °C the mixed phase is composed of approximately one PBT chain unit per eight PTMO chain units. The PBT crystallinity in the copolymers slightly increases with increasing length of the soft block, since this causes increase of the average length of PBT blocks. The content of crystalline PBT is nearly constant for samples with hard blocks containing more than five monomer units and decreases for shorter PBT block lengths. An increase in the content of PTMO with the same block length causes a significant increase in chain mobility in the soft domains. Apparently, the content of the mixed phase and the density of physical/topological junctions at the PBT/PTMO interphase largely affect the molecular mobility in the soft domains.

Synthesis of poly(butylene terephthalate)-poly(tetramethylene glycol) copolymers using terephthalic acid as starting material: A comparation between two synthetic strategies

“…This is because the sample from one-step strategy has relatively shorter hard and soft segment length than the one from two-step strategy. Furthermore, shorter hard and soft segment lengths also result in decreasing of crystallinity [12] . On the other hand, PBT-PTMG copolymers with 70% of soft segment showed significantly different thermal properties with respect to PTMG feeding strategy.…”

Investigation of Soft Component Mobility in Thermoplastic Elastomers using Homo‐ and Heteronuclear Dipolar Filtered 1H Double Quantum NMR Experiments

“…[8] Recently, a detailed model of the phase structure in PBT-block-PTMO was suggested, deduced from 1 H and 13 C relaxation measurements and deuterium lineshape analysis as a function of temperature as well as 1 H DQ correlation experiments. [9] Two domains can be separated in transverse relaxation data, a hard domain with a short transverse relaxation time consisting of crystalline PBT units and a rigid crystal-amorphous PBT interface, and a soft domain with a long transverse relaxation time composed of a PBT/PTMO mixed phase and a PTMO-rich phase. The results suggest rather heterogeneous chain mobility in the soft domains.…”

“…Details of the relaxation measurements and the fitting procedure can be found elsewhere. [9] Analysis The sequence used for excitation of DQ coherences consists of excitation, evolution, reconversion and detection periods. In our case, for the static experiments, the simplest case for excitation of DQ coherences employs two 908 pulses separated by a time t, which is varied in subsequent experiments to obtain a buildup curve (cf.…”

“…Furthermore, analysis of 1 H transverse magnetization relaxation measurements assign a PBT/PTMO mixed phase to the soft domain. [9] Hard and soft domains in that paper are simply assigned by fitting the T 2 decay with a long and a short relaxation time. Herein, from the shape of the relaxation component with a long decay time, one can suggest a large heterogeneity in chain mobility in the soft domain, i.e., a composition of a less mobile PBT/PTMO mixed phase and a more mobile PTMO-rich phase (as described above).…”

“…The presence of a mixed phase of PBT/PTMO was also evident in the 1 H 2D DQ BABA experiment as described above. [9] Using this information, in Figure 13 the average order parameter and the fraction of PTMO in the PTMO-rich phase (values taken from ref. [8] ) are correlated, showing a very good linear relationship.…”