Crystal Transition Mechanisms in Poly(tetramethylene succinate)

Abstract

ABSTRACT:Poly(tetramethylene succinate) (PTMS) showed a crystal transition between the r:J. (T7 GTG) and /J (T10) form under the strain and relaxation conditions, where T, G, and G denoted trans, gauche, and minus gauche, respectively. We have investigated the mechanisms of this crystal transition by FT-IR and X-ray diffraction. In the FT-IR, the absorbance peaks at 920 cm -1 and 955 cm -1 , corresponding to the fl. form, started decreasing at strain of s 8%, while the absorbance at 977cm-1 , corresponding to the /J form, appeared at e~8%, then increased with strain. In addition, the isobestic point was observed at 965 cm -1 , indicating that the crystal transition occurred only between the fl. and /J form, where no amorphous part contributed. In the X-ray diffraction, the meridional reflection of fl. (at 20=25.1°) started decreasing at e~8%. In addition, the reflection of /i (at 20=22.5°) appeared at s~8%, then increased withe. These FT-IR and X-ray results were thus consistent with each other. The molar fraction of the /J form, Xp, was determined as a function of stress, rr, by X-ray. The Xp showed a drastic increase at a critical value of rr= 140MPa. It was hence concluded that the thermodynamic first-order phase transition was the operative mechanism of the transition. Such a crystal transition mechanism had been also reported in poly(butylene terephthalate) (PBT). The free energy difference between the fl.and /J form, .JG, was determined to be .JG~ 1.6 (kJ mol-1 of monomer unit), being close to the reported value of LlG-1.4 (kJmol-1 of monomer unit) for the crystal transition in PBT. The stress-strain curve was measured. The rr increased withe when r,<8%, then remained approximately constant up to s~ 16%, followed by the second increase fore> 16%. Such a stress-strain characteristics could be explained in terms of the crystal transition. KEY WORDS Poly(tetramethylene succinate) / Crystal Transition Mechanism/ Crystal Structure/ X-Ray Diffraction/ FT-IR/ Stress-Strain Curve/ As represented by poly(tetramethylene succinate) (PTMS), which is crystalline polymer, biodegradable aliphatic polyesters have received a great attention from industry, particularly from the ecological viewpoint. 1 • 2 Mechanical properties of such crystalline polymers, in general, depend strongly on their crystal structure as well as on the crystallinity of the polymers. 3 Crystal structures can be controlled by pressure, temperature and strain.Recently, we have discovered such crystal modifications in PTMS (a and /3 form): the trans1t10n occurred under application or removal of strain, and the /3 form appeared under strain. 4 The conformations of the two forms were (T 7 GTG) 5 and (T 10 )4 for the a and f3 form, respectively: the conformational modification occurred in the tetramethylene units.Strain induced crystal modifications have t Part of this work was presented at

Synthesis and characterization of novel poly(butylene succinate-co-2-methyl-1,3-propylene succinate)s

“…Figure 6 displays WAXD patterns of PBSu, PMPSu, and PBSu-rich PBMPSu copolyesters that were isothermally crystallized at 10-12°C below their respective T m values. The unit cell of the crystalline PBSu # form is monoclinic [5][6][7][8][9], and the diffraction peaks from the (020) and (110) planes are detected at 2% ! 19.6 and 22.7°, respectively.…”

“…The crystalline structure [5][6][7][8][9], and crystallization and melting behavior [10][11][12][13][14][15][16][17][18] of PBSu have been investigated extensively. PBSu has a relatively low biodegradation rate because of its high crystallization rate and high crystallinity.…”

Crystallization Kinetics of Biodegradable Poly(butylene succinate) under Isothermal and Non‐Isothermal Conditions

“…[6][7][8][9] The crystalline structure of PBSu has been described by several authors. [10][11][12] Chatani et al [10] reported that the crystal structure of the PBSu a-form is monoclinic with unit cell dimensions a ¼ 0.521 nm, b ¼ 0.914 nm, c ¼ 1.094 nm: b ¼ 1248, P2 1 /n-C 2h . The multiple melting behavior of PBSu, mainly for samples crystallized under isothermal conditions, was also studied recently.…”

Crystal structure and biodegradation of aliphatic polyester crystals

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