The microstructure of segmented block copoly(ether esters) composed of poly(tetramethylene oxide) (PTMO) “soft” blocks and poly(butylene terephthalate) (PBT) “hard” blocks was investigated. A variety of analytical techniques, including 13C solid-state NMR, infrared spectroscopy, dynamical mechanical analysis, dielectric spectroscopy, differential scanning calorimetry, and transmission electron microscopy, were applied. The samples vary in the amount (35−60 wt %) and block length (1000−2000 g/mol) of the soft component. It is generally assumed in the literature that copoly(ether esters) have a two-phase structure consisting of a crystalline PBT phase surrounded by an amorphous phase which is a homogeneous mixture of PTMO soft segments and amorphous PBT segments. Our experimental results reveal that the amorphous phase is not a homogeneous mixture of “hard” and “soft” segments but consists of a highly mobile “PTMO-rich phase” and a less mobile “PBT/PTMO mixed phase”. The extent of microphase separation in the amorphous phase appeared to be strongly dependent on the block length and composition. Those samples that revealed a strong microphase separation showed strain-induced crystallization of the soft segments upon mechanical deformation.

A series of fibers of polyethylene terephthalate) with different physical structures, varying from amorphous to 36 % crystalline, has been investigated by 13C solid-state NMR measurements. Several relaxation times, i.e., relaxation times in the rotating frame ( / ), Tip(13C)) and -130 cross-polarization transfer times (7ch), have been studied. 13C CP/MAS spectra show that, especially with respect to the ethylene and carbonyl carbons, the chemical shift for carbons in ordered structural surroundings ("NMR crystalline") is higher than that for carbons in unordered surroundings ("NMR amorphous"). Also the width of the distribution of chemical shifts in an ordered structure is smaller than that in a less ordered structure (narrow vs broad resonance line). Analysis of the line-shape changes during the Tip(13C) relaxation process of semicrystalline yarns showed that the NMR amorphous phase relaxes with two time constants. A threeregion model composed of NMR crystalline, rigid NMR amorphous, and mobile NMR amorphous regions is proposed. The sizes of the rigid domains in semicrystalline PET yarns estimated from / ) measurements correspond well with the crystal sizes as determined with X-ray diffraction. In a yarn, which is almost completely amorphous according to X-ray measurements, fast and slow ethylene and aromatic group motions, relative to a correlation time of 5 X 10-6 s, occur. From 1 ) experiments it can be concluded that both mobile and rigid regions in the amorphous yarn have dimensions smaller than 50 A. Tch measurements reveal that ethylene and aromatic groups in the mobile amorphous domains of all yarns undergo large-amplitude motions. The principal elements of the chemical shift tensor of aromatic carbons remain independent of temperature up to at least 327 K, indicating that, in crystalline regions in semicrystalline yarns and in rigid parts of the amorphous yarn, phenyl reorientations have a very small amplitude (not exceeding ~5°).

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The changes in phase structure under mechanical deformation of poly(butylene terephthalate) (PBT)/poly(tetramethylene oxide) (PTMO) multiblock copolymers differing in the amount and block length of PTMO have been investigated by 13C magic-angle-spinning NMR. Measurements have been performed on unstretched samples, on stretched samples allowed to relax before the NMR experiment, and on samples that are kept under tension in the spinning rotor (in-situ stretched). For unstretched samples a heterogeneity in NMR relaxation behavior of the OCH2 carbons of PTMO was observed (TCH, 13C−T1 ρ, 1H−T1 ρ), which is attributed to a microphase separation in the amorphous phase into a PTMO-rich phase (mobile) and a mixed PBT/PTMO phase (restricted mobility). Long PTMO block lengths and high PTMO contents favor the formation of the PTMO-rich phase. For stretched and in-situ stretched samples with relatively long PTMO block lengths, an additional resonance with different chemical shifts for the OCH2 carbons of PTMO and with a restricted mobility was observed. This new resonance, which is also found in unstretched samples at temperatures of −30 °C, is assigned to strain-induced crystalline PTMO. The amount of crystalline PTMO increases linearly with the sample strain. It appears that, in stretched samples, heating to 50 °C leads to irreversible melting of the PTMO crystals, in contrary to the in-situ stretched samples, which show recrystallization upon cooling to room temperature. 2D rotor-synchronized 13C−CPMAS experiments revealed a high orientation of the hard and soft phases upon stretching.

The effect of drawing on the structure and molecular orientation of polyamide-6 fibers has been investigated by 13C solid-state NMR. The molecular orientation in the fibers is determined using a two-dimensional rotor synchronized magic-angle spinning (MAS) experiment. For the highly oriented fibers order parameters up to 〈P 6〉 are determined. By using a 13C T1 ρ filter, the orientation in the rigid (crystalline + rigid amorphous) and mobile (amorphous) regions are separately determined. The orientation in the rigid phase increases rapidly at low draw ratios up to λ = 3.5 and levels off at higher draw ratios (〈P 2〉 ≈ 0.75). The mobile amorphous phase remains disordered for low draw ratios but orients rapidly for draw ratios above λ = 3.5. By using a 13C T1 filter, 13C MAS spectra of the crystalline phase are obtained, from which the relative amounts of the α- and γ-phase can be quantitatively determined using spectral deconvolution. It appears that upon drawing the α/γ ratio changes from 60/40 for an undrawn fiber to almost completely α for a fully drawn fiber. The NMR results are qualitatively supported by wide-angle X-ray spectroscopy (WAXS) photos.