Stress-induced crystalline phase transition in block copolymers of poly(tetramethylene terephthalate) and poly(tetramethylene oxide). I Dependence of transitional behavior on hard/soft segmental ratio.
Abstract:Stress-induced solid-state transition has been found to occur in the multi block copolymers of poly(tetramethylene terephthalate)[PTMT] and poly(tetramethylene oxide) [PTMO]. In the crystalline regions of PTMT hard segments, the reversible structural change has been observed when the uniaxially-oriented sample is stretched along the draw direction. This is essentially the same phenomenon as that observed in PTMT homopolymer, although the transition in the block-copolymer requires appreciably larger tensile str… Show more
“…Therefore, we ascribe this new resonance at 72.5 ppm appearing in the stretched and also in in-situ stretched A2000/60 samples to straininduced crystallization of PTMO segments. The ability of PTMO to crystallize under strain was also found by Tashiro et al 15 using IR spectroscopy.…”
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.
“…Therefore, we ascribe this new resonance at 72.5 ppm appearing in the stretched and also in in-situ stretched A2000/60 samples to straininduced crystallization of PTMO segments. The ability of PTMO to crystallize under strain was also found by Tashiro et al 15 using IR spectroscopy.…”
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.
“…Similar transitions were reported for poly(pivalolactone), polypeptide (α-helix to β-pleated sheet), α-to-β keratin, and so forth. As already mentioned, the reversible transition is observed for PTMT − and poly(tetramethylene succinate), − in which the α-form of the contracted chain conformation transforms reversibly to the β-form of the fully extended conformation at a critical stress. The phase transition occurring in the crystallite affects the lamellar stacking structure, but the change is not very remarkable in the strain region of the transition, as known from the simultaneous measurement of WAXD, SAXS, and FTIR spectral data .…”
Section: Resultsmentioning
confidence: 67%
“…These observations suggest that the α-to-β phase transition occurs following the concept of the stress -induced transition mechanism. Such a stress-induced transition was reported for the α-to-β phase transition of poly(tetramethylene terephthalate) (PTMT), − poly(tetramethylene nathalate), and poly(tetramethylene succinate), − which occurs at a critical stress value; but, one different point is observed between the cases of PTMT and PHB. In the former case, the transition is completed at an almost constant stress (σ*), during which the sample strain increases remarkably.…”
The
crystal structure of poly(3-hydroxybutyrare) β crystal
form has been analyzed on the basis of two-dimensional X-ray diffraction
data. The all-trans zigzag chains are packed in the hexagonal unit
cell of a = b = 9.22 Å, c (chain axis) = 4.66 Å, and γ = 120° with
the space group P3221. The upward and
downward chains are statistically located at one lattice site at 50%
probability. By combining the thus-analyzed structure information
of the β-form with the previously reported structure information
of the α-form, the geometrical relation between these two crystalline
phases has been clarified in detail. The tension-induced α-to-β
phase transition affects the higher-order structural change, as known
from the small-angle X-ray scattering (SAXS) data collected in the
tensile deformation process. By analyzing all experimentally obtained
wide-angle X-ray diffraction and SAXS data, the following transition
model has been proposed: the high tension to the oriented sample causes
the increase of the long period of the α-form lamellae. As the
tensile force is increased, the local stress concentration starts
to occur at the short tie chain segmental parts in the amorphous region
sandwiched between the stacked lamellae. These highly tensioned tie
chains induce the α-to-β structural change in both amorphous
and directly connected crystalline regions and generate the 40 Å-wide
bundles of zigzag chain segments passing through several neighboring
lamellae along the draw direction. These bundles are repeated with
the averaged period of about 90 Å in the lateral direction perpendicular
to the draw axis. Further stretching causes the cut of the highly
tensioned extended chain parts, resulting in the formation of voids
and finally the breakage of the whole sample before the completion
of the phase transition from the α- to β-form.
“…All these phenomena could be interpreted reasonably in terms of the thermodynamic first-order phase transition. ,,, Another characteristic point typically observed for the uniaxially oriented PTMT sample is that the plateau length is longer for the sample annealed at higher temperature or for the sample with a higher degree of crystallinity . These observations could be interpreted quantitatively on the basis of a mechanical model constructed by a serial connection of crystalline α phase and amorphous region. , As the stress is increased, the α phase region experiences the transition to the β phase and the strain of the sample increases remarkably due to the increment of the crystallite size along the chain axis, giving a plateau in the stress−strain curve. Therefore it may be easily understood that the plateau length is proportional to the degree of crystallinity.…”
Section: Introductionmentioning
confidence: 69%
“…Most of these transitions are irreversible and the crystal form obtained after transition does not return to the original crystal form even when the stress is relaxed. In such a sense, the phase transition observed for uniaxially oriented poly(tetramethylene terephthalate) [PTMT] is somewhat special because it occurs reversibly between α and β forms by increasing or decreasing stress. − The α form takes the molecular conformation including gauche-type C−C bonds (G) and the chain is slightly contracted, while the β form takes the fully extended conformation of the trans type (see Figure ), where G and T are not exactly 60° and 180°, respectively. 1 Molecular conformations of the α and β forms of poly(tetramethylene terephthalate) 5-8 and poly(tetramethylene naphthalate) …”
Crystalline modifications R and β of uniaxially oriented poly(tetramethylene naphthalate) [PTMN] sample have been found to show a reversible phase transition, which is induced by an application of a tensile force along the draw axis, as clarified by the measurement of polarized infrared spectra under tension. The transition behavior was found to be essentially the same with that observed for uniaxially oriented poly(tetramethylene terephthalte) [PTMT] sample. The β phase fraction, evaluated by quantitative analysis of the infrared spectra, was found to be linearly proportional to the strain and increase dramatically beyond a critical stress. The stress-strain curve measured for the bulk PTMN sample showed a plateau region, in which the R-β transition occurred. The plateau length became longer by raising the temperature of heat treatment of the samples or with increasing the degree of crystallinity. All these characteristic features are similar to those observed for PTMT. But, in the PTMT case, the plateau stress was almost constant irrespective of the annealing temperature. The stress-strain curve of the PTMT sample could be interpreted reasonably on the basis of a mechanical model in which R crystal and amorphous region are connected in a series mode. On the other hand, the plateau region in the stressstrain curve of the PTMN sample was found to shift apparently toward higher stress side and became more difficult to detect for the sample annealed at lower temperature. This was due to higher residual strain or β fraction remained in the sample. High-temperature annealing accelerated a stress relaxation, causing a recovery of the original R form and making the plateau part clearer. All these behaviors could be interpreted reasonably by employing a mechanical model in which a serially connected part of R crystal and amorphous region is combined in a parallel mode with a serial part of β crystal and amorphous region. The contribution of the β crystal is higher for the sample prepared at a lower temperature.
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