Study of Glass Transition and Partial Melting in Melt-crystallized Poly(oxymethylene) by X-Ray Small-angle Scattering

1977

ABSTRACT:The temperature dependence of two Bragg reflections was measured for solid poly(r-methyl o-glutamate) in the p-form in the temperature range from -80 to 120°C. The spacing-temperature curve has a break point in the vicinity of 20°C. From the temperature dependence of integrated intensity, the break point observed is considered to be related to the onset of side-chain motions and to be a transition analogous to the glass transition.KEY WORDS X-Ray / Poly(r-methyl o-glutamate) / p-Form / Transition / Structures and properties of poly(a-amino acid)s in the solid state have been studied extensively. While most previous efforts have been focussed on the a-helical form, little work has been done with the p-form.Molecular motions of a-helical poly(a-amino acid)s in the solid state have been accounted for wholly in terms of side-chain motions. It was suggested that poly(r-benzyl L-glutamate) (PBLG) and poly(r-methyl L-glutamate) (PMLG), whose side chains are rather flexible, manifest a glass transition at room temperature, due to the onset of the side-chain motions. 1 -5 We also obtained the same conclusion from X-ray studies. 6 The molecular motions of ,8-forming poly(aamino acid)s in the solid state have been investigated on poly(S-benzyloxycarbonyl-L-cysteine), poly(S-benzyloxycarbonylethyl-L-cysteine), and poly(S-methoxycarbonylethyl-L-cysteine) using NMR and dielectric methods. 7 All results obtained were interpreted in terms of the rotation of the side chains.It is, of interest therefore to examine whether a transition related to the onset of the side-chain motions occurs even in the p-form, and what that transition is, if it occurs. The purpose of * Address of person to whom correspondence should be directed. this work is to obtain a more detailed understanding about the relation between the structure and the thermal motion of solid poly(a-amino acid) in the ,8-form. EXPERIMENT ALPoly(r-methyl o-glutamate) (PBDG) used in this work was kindly supplied Ajinomoto Co., Ltd. The film was obtained by casting trifluoroacetic acid solution of the polymer on a glass plate. The film in the p-form was prepared by allowing it to swell in formic acid at room temperature for two weeks and then annealing it in vacuo at a temperature of 160°C for an hour. 8 X-ray diffractometric measurements were performed using a Rigaku Denki diffractometer equipped with a scintillation counter and a pulse height analyzer. Cu-Ka radiation at 40 kV and 20 mA was used. A symmetrical reflection (SR) technique and a symmetrical transmission (ST) technique were employed to measure two strong Bragg reflections of ( 100) and (020). 9 Intensities were counted in the step-scan mode for 40 sec. at intervals of 0.05° in Bragg angle. The peak position was defined as the center of the halfwidth. Only the relative change in the peak position with temperature was measured. The 391

Section: Resultsmentioning

confidence: 91%

Section: Resultsmentioning

confidence: 99%

X-Ray Scattering of Synthetic Poly(α-amino acid)s in the Solid State. IV. Transition of Poly(γ-methyl D-glutamate) in the β-Form

Matsushima

1977

“…According to the SAXS theory for crystalline polymers, 19 the intensity is proportional to the product of the lattice factor and the square of the structure factor, the latter being related to the electron density difference between the two phases and their volume fractions. Since the lattice factor and the volume fraction are insensitive to temperature, and the electron density is proportional to the mass density, the temperature dependence of the intensity is written as…”

Section: Resultsmentioning

confidence: 99%

X-Ray Scattering of Synthetic Poly(α-amino acid)s in the Solid State. I. Transition of Poly(γ-benzyl L-glutamate) and Poly(γ-methyl L-glutamate)

Matsushima

Tsutsumi

et al. 1975

Self Cite

ABSTRACT:Lateral spacings between helices and corresponding X-ray diffraction intensities for poly(r-benzyl L-glutamate) and poly(r-methyl L-glutamate) in the solid state have been measured as a function of temperature from -100 to 100°C. The integrated intensity increased with increasing temperature and moreover showed breaks in the vicinity of room temperature, where breaks were also observed in the spacingtemperature relation. The temperature dependence of the intensity is approximately interpreted in terms of the same concept encountered in the small-angle X-ray scattering for crystalline polymers. The breaks observed are considered to be a transition analogous to the glass transition which occurs in a paracrystalline region and is related to sidechain motion. The results seem to suggest that the side chain does not assume any definite structure above the transition temperature.KEY WORDS X-Ray I Spacing I Intensity I Poly(r-benzyl L-glu-It has been well established that several synthetic poly(a-amino acid)s, such as poly(r-benzyl L-glutamate) (PBLG) and poly(r-methyl L-glutamate) (PMLG), have the a-helical molecular conformation in solutions and in the solid state. 1 • 2 Structural investigations of oriented fibers of PBLG show that the polymer is paracrystalline, composed of approximately hexagonally packed a-helices with random displacement along the fiber axis, screw dislocations, and probably a random chain sense. 3 ' 4 PMLG molecules are reported to be packed into a hexagonal unit cell with the a-helical conformation. 1 No atomic positions of side chains of PBLG and PMLG have been reported.Recently, interest has grown in the study of the conformations which the side chain adopts. Squire and Elliott 5 ' 6 have suggested that an ordered arrangement of the side chains is likely to occur in the liquid-crystalline phase of PBLG, and in the solid mixture of equal parts by weight of this polymer and its D isomer.At the same time, molecular motions occurring in these synthetic poly(a-amino acid)s in the solid 44 state have been widely studied. 7 -14 Experimental results for PBLG and PMLG have shown that considerable side-chain motions are liberated near room temperature for these polymers.McKinnon and Tobolsk/ 0 • 11 studied creep modulus and specific volume as a function of temperature for PBLG. They showed that the solid film of PBLG contains both paracrystalline and mesomorphic regions. Further, the mesomorphic regions are noncrystalline region whose density is lower than that of the paracrystalline regions. They also stated that a glass transition occurs at l2°C, due to the onset of side-chain motion in the mesomorphic region. These results of studies on side-chain motion seem to indicate that the structures of the side chain is not definitely determined, in contrast with the results of the structural study by Squire and Elliott.The purpose of the present work is to be obtain a more detailed understanding of such studies. X-ray diffraction measurements for PBLG and PMLG in the solid state were performed to ...

“…s-io It is reasonable to assume that the narrow component is contributed from the amorphous layer on the fold-containing surfaces. Aoki, et al, 4 reported from their small-angle X-ray scattering (SAXS) study of POM that the glass transition occurs at a temperature of -60°C. Miki, et al, 11 suggested that the glass transition of POM is -65°C on the basis of their dynamic mechanical and dielectric measurements.…”

Section: Resultsmentioning

confidence: 99%

Nuclear Magnetic Resonance Study of Poly(oxymethylene)

Tsutsumi

Oda

et al. 1974

Self Cite

NMR measurements were carried out for poly(oxymethylene) samples which were subjected to various kinds of treatment such as annealing, rolling, and rirradiation. It was found that the-narrow component narrows in two steps and that the line narrowing which appeared at higher temperatures is markedly influenced by sample treatment. The second moment of amorphous regions at liquid-nitrogen temperature, <'1H 2 >a, was estimated. The result indicates that the amorphous region of the quenched sample is heterogeneous. Annealing was found to transform the morphology to the more nearly ideal two-phase structure. The decrease of the second moment between-197 and 20°C is due to molecular motion in the crystalline region as well as the lattice expansion.