Raman spectroscopy studies on structural modifications in poly(3,3-dimethyl oxetane)

Monoclinic(II) and orthorhombic(III) modifications of poly(3,3-dimethyl oxetane) can be obtained from the relaxed melt state depending on crystallization temperature. However, if the crystallization of a given modification is not completed, the other modification can be obtained from the amorphous phase. Raman spectroscopy has been used to study the influence of the temperatures and times of crystallization on the structural modifications of this polymer. The influence of the annealing process on the crystalline amount is also examined.     

Crystallization behavior of poly(3,3-bisethoxymethyl oxetane) and poly(3,3-bisazidomethyl oxetane)

Two crystal modifications have been found for poly(3,3-bisethoxymethyl oxetane) [poly- (BEMO)] by wide-angle x-ray powder diffraction and differential scanning calorimetry, while only one modification has been found for poly(3,3-bisazidomethyl oxetane) [poly(BAMO)]. Melting temperatures for the two polymers were nearly the same, varying from about 70 to about 90°C depending on the thermal treatment; higher crystallization temperatures resulted in higher melting temperatures. The equilibrium melting temperature T was found to be 125 and 128°C for poly(BEMO) and poly(BAMO), respectively, by using the Hoffman-Weeks extrapolation procedure. Measurement of the melting-point depression of Poly(BEMO) and poly(BAMO) in dibutyl phthalate yielded enthalpy of fusion values of 2.25 and 12.8 kcal/mol, respectively. The percent crystallinity for poly(BEMO) and poly(BAMO), respectively, was calculated to be 55-60 and 13-30% based on DSC and x-ray analysis.     

Crystallization behaviour of polyoxetanes: poly(oxetane), poly (3,3-dimethyloxetane) and poly(3,3-diethyloxetane)

The influence of the crystallization temperature on the melting behaviour and crystalline structure of polyoxetane (PTO), poly(3,3-dimethyloxetane) (PDMO) and poly(3,3-diethyloxetane) (PDEO) has been studied using differential scanning calorimetry (DSC) and X-ray techniques. When PTO is crystallized by cooling from the relaxed melt state, only the orthorhombic modification is obtained. However, PDMO and PDEO can be crystallized in two different modifications depending on crystallization temperature. The effect of the substituents in the stability of main chain conformations in crystalline state is discussed.     

Crystallization kinetics of poly(3,3-diethyl oxetane)

Poly(3,3-diethyl oxetane) fractions (number-average molecular weights from 10,000 to 800,000) have been isothermally crystallized from the relaxed melt state in the temperature range 10–65°C; two crystalline modifications are formed, orthorhombic in the range 10–25°C and monoclonic in the range 45–65°C. The influences of molecular weight and undercooling on the crystallization kinetics have been analyzed. The crystallization temperature-coefficient was determined; a variation of the product of the interfacial energies was found in the range of molecular weights which has been examined. Comparison of the experimental results for this polymer with those reported for other polyoxetanes shows that the crystallization rate for a given undercooling is lower for PDEO than for PDMO and PTO and that the interfacial basal free energies decrease from polyoxetane to the 3,3-dialkyl oxetanes.     

Structural differences between two crystal modifications of poly(γ-benzyl L-glutamate)

X-ray diffraction patterns were obtained for as-cast and oriented films of poly(γ-benzyl L -glutamate) and a comparison was made of the molecular packing of the α-helices in forms B and C. Form B snowed Bragg reflections on the layer lines as well as on the equator. The spacings were explained by a monoclinic unit cell comprising two chains, with a = 29.0₆ Å, b = 13 2₀ Å, c = 27.2₇ Å α = γ = 90°. and β = 96°. The chains contained in this unit cell and consequently alternating in the crystal have opposite chain directions. Form C showed continuous scattering on the layer lines and reflections on the equator. This form, therefore, is a nematiclike paracrystal in which the packing of α-helices is periodic in the direction lateral to the chain axis (a = 14.8–115.2 Å, b = 14.3–14.8 Å, c = 27 Å, and γ = 118°–120°), but the relative levels of the chains along the chain axes are displaced. The formation of form C may be attributed to random placement of two chains with mutually opposite chain directions.     

Structures of two modifications of 6,9-bis-pyridine-nidodecaborane(12)

An x-ray diffraction structural analysis showed the molecular and crystal structures of two modifications of 6,9-bis-pyridine-nido-decaborane(12). The orientation of the pyridine rings relative to the ¦B₁₀H₁₂¦ unit proposed by Graybill and Hawthorne [1] was not confirmed for the crystalline states of B₁₀H₁₂(C₅H₅N)₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1905–1909, August, 1989.The authors express their gratitude to S. T. Dunaev for synthesizing these compounds, to V. A. Shipachev for taking the UV spectra, and to N. V. Podberezskaya and L. A. Glinskaya for assistance in obtaining the diffractometric data.     

Effect of Solvent Annealing Temperature on Crystal Modifications and Phase Transition Behavior of Regioregular Poly（3-octylthiophene）

In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the subsequently dried poly（3-octylthiophene） （P3OT） film has been investigated by the combination of DSC, WAXD and FTIR techniques. When chloroform is employed as the solvent, it is unexpectedly found that form I and form II crystal modifications of P3OT could be respectively obtained by room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form II, i.e. carbon disulfide （CS2） which is toxic and corrosive, chloroform is less toxic and corrosive and more suitable for solution processing of P3OT. Therefore, this finding provides an alternative way to obtain form II. By temperature dependent IR spectroscopy, the structural evolution of P3OT during the form II to form I phase transition process has also been studied in detail.     

Dielectric properties of poly [3,3-bis(chloromethyl)oxacyclobutane] (Penton)

Ohne Zusammenfassung     

Analysis of crystallization behavior and crystal modifications of poly(butylene‐2,6‐naphthalene dicarboxylate)

Information on the crystalline structure and the properties of poly(butylene‐2,6‐naphthalene dicarboxylate) (PBN) has not been well reported until now, but it is known that there are two different crystal modifications in PBN, as follows: one is formed in isotropic samples by annealing (α form); another appears by annealing with tension (β form). The relation between the crystal modifications and the kinetics of isothermal crystallization for PBN was investigated using in‐situ Fourier transform infrared spectroscopy (FTIR) and wide‐angle X‐ray diffraction (WAXD). The melting behavior of each crystalline form was also studied by means of FTIR and differential scanning calorimetry (DSC) measurements. From the analysis of the melt‐crystallized PBN specimens, the two crystalline forms coexisted in the isotropic samples melt‐crystallized at 230°C, but only the α crystal modification was observed in the films annealed at lower temperatures. In addition, it was revealed that, at 230°C, the β modification was formed only in the primary crystallization process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 561–574, 1999     

Isomorphism in the poly(3,3-bis-hydroxymethyloxetane) family and copolymers: Poly (3,3-bis-hydroxymethyloxetane-co-3-methyl-3-hydroxymethyloxetane)

Copolymers of 3,3-bis-hydroxymethyloxetane, BHMO, 3-metyl-3-hydroxymethyloxetane, MHMO, or with 3-ethyl-3-hydroxymethyloxetane, EHMO, monomer units were characterized by x-ray fiber diffraction, differential scanning calorimetry and ¹³C solid-state nuclear magnetic resonance (NMR). The copolymers are statistically random and crystalline throughout the range of compositions. Both P(BHMO) and P(MHMO) appear to crystallize in the same crystal form. The fiber repeat indicates a planar zigzag backbone conformation, c(fiber axis) = 4.77 ± 0.03 Å. Similarities in the x-ray fiber diagrams as well as a linear dependence of T_m with composition of copolymer with no change in fiber diagrams indicates isomorphism, a phenomenon in which the random substitution of MHMO monomeric units into the crystalline lattice of P(BHMO) occurs without hindering crystallization of the resulting copolymer. © 1994 John Wiley & Sons, Inc.     

Thermoelastic and dielectric studies of poly(3,3-dimethyl oxetane) chains

Poly(3,3-dimethyl oxetane) was synthesized by ring opening polymerization of 3,3-dimethyl oxetane. Elongation experiments were performed on unswollen elastomeric networks prepared from this polymer over the temperature range 30–90°C. The changes in the tensile stress while the networks crystallized were examined at various elongations. From thermoelastic data which were free from the effects of network crystallization, the temperature coefficient of the chain dimensions was found to be 1.1 × 10^?3 K^?1 in the vicinity of 60°C. The dipole moment ratio and its temperature coefficient were also measured; the average values of these parameters at 30°C were 0.20₆ and 2.5 × 10^?3 K^?1, respectively. All of these experimental-configuration-dependent properties were critically interpreted in terms of the rotational isomeric-state model. In comparing theory and experiment, conclusions were obtained which confirm earlier results according to which gauche states about C—C skeletal bonds in poly(3,3-dimethyl oxetane) are strongly favored over the alternative trans states.     

Solution annealing of poly(TMPS) crystal mats

Poly(tetramethyl-p-silphenylene siloxane) crystal mats initially prepared from benzene/methanol (2:1 v/v), when annealed in small amounts of solvent undergo considerable thickening in the chain direction. When the crystals are annealed above their formation temperature, their physical properties change rapidly at first before reaching an asymptotic limit commensurate with annealing time and type of solvent. Changes in melting temperature, heat of fusion, small-angle x-ray spacing, and wide-angle x-ray scattering patterns have been monitored for three solvents of varying solvent power, ranging from very good to extremely poor. Upon solution annealing, the original crystals mats equilibrate to more stable dimensions compatible with their environment. The activation energy of crystal thickening in contact with a liquid is estimated to be about an order of magnitude lower than that deduced from dry annealing data. It appears that the crystal surface and the crystalline core of the crystals comprising the mats must participate in the measured severalfold increase in long period noted after annealing. The lower surface (or interfacial) energy of the liquid annealed mats compared to isothermally melt-crystallized polymer of similar molecular weight has a direct bearing on the polymer morphology and crystallinity.     

The crystal structure of poly(tetramethylene terephthalate)

The unit cell of poly(tetramethylene terephthalate) is triclinic with parameters a = 5.96 Å, b = 4.83 Å, c (fiber axis) = 11.62 Å, α = 115.2. β = 99.9, and γ = 111.3°; space group P1 , calculated crystalline density 1.41 g/cc. The plane of the benzene ring is found to be inclined by about 15° from the fiber axis, contributing to a shortening of the fiber period as compared to the period expected on the basis of analogy with other members of the terephthalate ester series. The remaining shortening of the fiber period occurs in the ? O? °CH₂? °CH₂? segment of the chain. No abnormally short distances among neighboring chain atoms were observed. A typical texture pattern was found in specimens of this polymer that were cold rolled and subsequently annealed. In this texture the c axis of the unit cell is highly oriented in the rolling direction; the a and b axes of the unit cell are oriented preferentially so that the terephthalate residue lies as close as possible to the plane of rolling.     

Crystallization kinetics of the monoclinic modification of poly(3,3-dimethyl oxetane)

Poly(3,3-dimethyl oxetane) fractions ranging in number average molecular weights from 18500 to 130000 have been isothermally crystallized from the relaxed melt state in the temperature range from 12 to 44 °C, where only the monoclinic modification is formed. The influence of molecular weight and undercooling in crystallization kinetics has been analyzed. The level of crystallinity is very slightly dependent on molecular weight but the influence of this parameter on the time scale of the crystallization is relatively pronounced. The crystallization temperature coefficient was determined and it was found a constant value of the product of the interfacial energies in the range of molecular weights which has been analyzed. Growth rate measurements were carried out for fraction ¯M _n=130000 and it was found that the temperature coefficients for overall and growth rates are equal. Finally, the comparison of the experimental results for this polymer with those reported for poly(oxetane) shows two main differences: first, the crystallization rate is slower for poly(3,3-dimethyl oxetane) and second, the temperature coefficient is smaller for this polymer.     

Vibrational spectroscopic studies on modifications of poly(trans-alkenylene)s. I. The orthorhombic modification of poly(trans-pentenylene) and poly(trans-heptenylene)

Experimental results of vibrational spectroscopic studies on the orthorhombic modification of poly(trans-pentenylene) and poly(trans-heptenylene) are discussed on the basis of a normal coordinate analysis for an isolated chain model.     

Structures of poly(p-hydroxybenzoic acid) (PHBA) at ambient temperature

The molecular structure of poly (p-hydroxybenzoic acid) (C₆H₄COO)_x at ambient temperature was determined by x-ray powder diffraction analysis. The diffraction pattern is explained as a mixture of two orthorhombic phases having the same space group Pbc2₁ with four C₆H₄COO chemical repeats in the unit cell and the following cell parameters: a = 7.42 Å, b = 5.70 Å, and c = 12.45 Å for phase I (ρ_calc = 1.51 g cm^?3); and a = 3.83 Å, b = 11.16 Å, and c = 12.56 Å for phase II (ρ_calc = 1.48 g cm^?3). The chain conformation is the same in both phases, involving two benzoyl rings staggered by ca. 120° along the chain. Disorder has been considered in the packing of phase I by giving equal occupancy to the two molecules oriented up or down along the c chain axis. ©1995 John Wiley & Sons, Inc.     

Vibrational spectroscopic studies on different modifications of poly(trans-alkenylene)s

Summary The changes in the state of order in poly(trans-octenylene) and poly(trans-dodecenylene) are studied by Raman and FTIR-spectroscopy in dependence of temperature and applied stress. The observed spectral changes are discussed on the basis of a normal coordinate analysis.

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Zusammenfassung Die Änderungen des Ordnungszustandes in Poly(trans-octenylen) und Poly(trans-dodecenylen) wurden mittels der Raman- und FTIR-Spektroskopie in Abhängigkeit von Temperatur und Reckgrad untersucht. Die beobachteten spektralen Änderungen werden auf der Basis einer Normalkoordinatenanalyse diskutiert.