Solid-state F MAS and H→F CP/MAS NMR study of the phase transition behavior of vinylidene fluoride-trifluoroethylene copolymers: 1. Uniaxially drawn films of VDF 75% copolymer

The changes in the phase structures and molecular mobility caused by the ferroelectric-paraelectric phase transition of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer, P(VDF₇₅/TrFE₂₅), were analyzed using variable temperature (VT) solid-state ¹⁹F MAS and ¹H→¹⁹F CP/MAS NMR spectroscopy. The CF₂ signal of the VDF chain sequence and the CHF signal at the head-to-head linkage of VDF-TrFE sequence showed higher frequency shift in the temperature range 43-92 °C, whereas no change was found for the CHF signal at the head-to-tail linkage of VDF-TrFE up to 92 °C. Hence, VT ¹⁹F MAS spectra revealed that the VDF-TrFE head-to-tail sequence is the most stable part in polymer chains against trans-gauche conformational exchange motions below the phase transition temperature (Curie temperature, T_c) on heating. However, all chain sequences including TrFE units undergo conformational exchange at around T_c. The phase transition behavior is clearly recognized in the ¹⁹F spectral shapes, in which the broad signals of the ferroelectric immobile phase disappeared between 115 and 119 °C. In addition, T_1ρ^F for all peaks decreased to a unique value (ca. 20 ms) at 119 °C, indicating that uniform molecular motion accompanied by a full chain rotation occurred at the temperature. The significantly longer T_1ρ^F for all peaks (ca. 20 ms) in the paraelectric phase (119 °C) than that in the amorphous domain (<4 ms) at ambient temperature supports the conclusion that there is restricted rotational motion of polymer chains around the chain axis in the paraelectric phase. On cooling from 119 to 85 °C, a gradual decrease in gauche conformers in the paraelectric phase was confirmed by the low-frequency displacement of CF₂ signals in VDF sequences accompanied by slight decreases in T₁^F and T_1ρ^F. The phase transition was observed between 85 and 77 °C on cooling, in which the characteristic signals of the paraelectric phase disappeared, the T_1ρ^F values of all peaks quickly increased, and the broad crystalline signals abruptly appeared at 77 °C.     

Structural correlation between crystal lattice and lamellar morphology in the ferroelectric phase transition of vinylidene fluoride-trifluoroethylene copolymers as revealed by the simultaneous measurements of wide-angle and small-angle X-ray scatterings

Intimate correlation has been detected between the crystal structure change and the morphological change of stacked lamellae in the ferroelectric phase transition of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymers on the basis of simultaneous measurement of wide-angle (WAXS) and small-angle X-ray scattering (SAXS) patterns in the heating process. The VDF content of copolymers investigated was 65 and 73 mol%. For both of the copolymers, a cold-drawn sample showed the WAXS pattern of the regular low-temperature phase and the four-points SAXS pattern corresponding to the stacking structure of lamellae tilted by about 30° from the draw axis. When the sample was heated above the Curie transition point T_c, the low-temperature phase changed to the conformationally-disordered paraelectric high-temperature phase and the stacked lamellae reoriented into the direction closer to the draw axis. It was also found that the thickness and long period of the lamellae increased remarkably above T_c. These large changes in lamellar stacking mode occurred in parallel with the trans-to-gauche conformational change of the molecular chains in the crystal lattice. In this way, the morphological change was found to relate intimately with the crystal structural change, both of which are considered to be caused commonly as a result of the trans-gauche conformational change and the translational motion of the thermally-activated molecular chains along the chain axis.     

N.m.r. study of the ferroelectric phase transition in a 7030mol% copolymer of vinylidene fluoride (VF2) and trifluoroethylene (TrFE)

Nuclear magnetic resonance (n.m.r.) studies of ¹⁹F nuclei in a $\text{70}\text{30}\text{mol}\text{\%}$ random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T₂ components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T₁ appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T₁ were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals.     

Quantitative analyses of electric field–induced phase transition in (Na,K)0.5Bi0.5TiO3:Eu ceramics by photoluminescence

Most reported results about phase transition probed by the photoluminescence (PL) spectra of Eu³⁺ ions are qualitative, but the quantitative analyses of phase transition were presented in this work. We fabricated (Na_0.8, K_0.2)_0.5Bi_0.497Eu_0.003TiO₃ (NKBT20:Eu) ferroelectric ceramics and investigated the phase structures and the PL spectra of NKBT20:Eu ceramics before and after poling at different electric fields. The PL spectra indicate a phase transition from tetragonal phase (T phase) to rhombohedral phase (R phase) within NKBT20:Eu ceramics after poling, consistent with the analyses by X-ray diffraction (XRD). Moreover, the emission intensity ratios of the “hypersensitive” transition to the magnetic dipole transition could be used to calculate the fractions of the phase transition quantitatively, which were further confirmed by XRD Rietveld refinements. This study provides a different perspective to investigate the phase transition induced by electric field for NKBT20:Eu ceramics, qualitatively and quantitatively, and the method is expected to be useful in more cases of phase analyses.     

Phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) from I: A proposition for the ferroelectric Curie point

A phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) form I has been found by means of differential scanning calorimetry (d.s.c.) and infra-red (i.r.) vibrational spectroscopy. An endothermic d.s.c. shoulder has been observed at a temperature about 10°C below the melting point, in the vicinity of which the i.r. crystalline trans bands decrease in intensity steeply and the crystalline gauche bands increase in intensity, indicating the conformational change from all-trans to T₃GT₃G type. These observations have been found to be detectable more clearly for samples subjected to the poling treatment under a d.c. high voltage. The transition shows the characteristic behaviour essentially identical to those observed for ferroelectric copolymers of vinylidene fluoride and trifluoroethylene, except for the irreversibility of the structural change, suggesting that the phase transformation revealed here may be a ferroelectric-to-paraelectric phase transition of polar form I crystal and the the Curie point may be about 172°C. It is consistent with Micheron's measurement of the temperature dependence of the dielectric constant. Other structural changes in the form I sample occurring in the temperature range from 20° to 170°C have also been discussed based on the i.r. spectral measurements.     

Crystallographic changes characterizing the Curie transition in three ferroelectric copolymers of vinylidene fluoride and trifluoroethylene: 2. Oriented or poled samples

The effects of uniaxial drawing or poling on the structural changes involved in the ferroelectric-to-paraelectric phase transition in copolymers of vinylidene fluoride and trifluoroethylene were examined and compared to the behaviour of as-crystallized films. The compositions studied were $\text{65}\text{35}$, $\text{73}\text{27}$ and $\text{78}\text{22}\text{mol}\text{\%}$ vinylidene fluoride/trifluoroethylene, all of which crystallize from the melt with a molecular conformation and packing analogous to those of the common piezoelectric β-phase of poly(vinylidene fluoride). Contrary to the previously described behaviour of a $\text{52}\text{48}\text{mol}\text{\%}$ copolymer, orientation did not induce any significant changes in the structure of these copolymers or in its variation with temperature, primarily because these already crystallize directly from the melt in well-ordered, compact unit cells. On the other hand, electrical poling caused the all-trans chains of the ferroelectric phase to be packed more compactly and to survive to higher temperatures, thus shifting the Curie transition closer to the melting points of these copolymers. As a result, competition from melting interfered with the later stages of this solid-state transformation in the $\text{73}\text{27}\text{mol}\text{\%}$ composition, and aborted it at a very early point in the $\text{78}\text{22}\text{mol}\text{\%}$ samples. The Curie temperature was found to exhibit hysteresis between heating and cooling parts of the thermal cycle, to extend over a broad range of temperatures, and to involve intramolecular changes to the same disordered conformation found in melt-crystallized samples. Our results have allowed reasonable implications to be made concerning the existence and nature of a Curie transition in the piezoelectric β-phase of poly(vinylidene fluoride).     

Crystallographic changes characterizing the Curie transition in three ferroelectric copolymers of vinylidene fluoride and trifluoroethylene: 1. As-crystallized samples

Copolymers of vinylidene fluoride/trifluoroethylene of molar composition $\text{65}\text{35}$, $\text{73}\text{27}$ and $\text{78}\text{22\%}$ respectively, are ferroelectric and undergo a Curie transition to the paraelectric state at high temperatures. In contrast to the irregular structure found earlier for the $\text{52}\text{48}\text{mol}\text{\%}$ copolymer, the structures of these three compositions in the low-temperature state are all well ordered and analogous to that of β-poly(vinylidene fluoride): they consist of molecular chains in a polar trans conformation whose order is improved with increasing vinylidene fluoride content, packed pseudo-hexagonally in unit cells whose dimensions decrease with increasing vinylidene fluoride content. In their paraelectric phase, the chains assume a partly disordered conformation consisting of irregular TG, T? and TT sequences and are packed on an expanded pseudo-hexagonal lattice. The Curie transitions were found to occur over a broad temperature range, encompassing ～30°C, and in the case of the $\text{78}\text{22}\text{mol}\text{\%}$ copolymer to extend into the melting region; they were also found to exhibit hysteresis by occurring at much lower temperatures upon cooling than upon heating.     

Electrical performance and ferroelectric phase transition characteristic in different oriented 0.73PMN-0.27PT single crystals

The electrical and optical properties of (001)- and (110)-oriented 0.73 Pb(Mg_1/3Nb_2/3)O₃-0.27PbTiO₃ single crystals are systematically investigated at various temperatures, both of which present a series of ferroelectric phase transition processes. Dielectric performance measurements reveal that the ferroelectric phase transition occurs over a temperature range, rather than at one temperature point. By testing the ferroelectric hysteresis P–E curves as well as bipolar and unipolar electric field-induced strain S–E curves, the values of remnant polarization, coercive field, maximum strain, and converse piezoelectric constant d₃₃^* change considerably near the phase transition temperatures. Simultaneously, the 0.73PMN-0.27PT single crystals with (001)- and (110)-orientations under a low electric field show ultrahigh d₃₃^* values of 3540 and 2817 pm/V, respectively, which can be attributed to the electric field-induced monoclinic and orthorhombic phases, respectively. The series of ferroelectric phase transitions upon heating, that is, from rhombohedral ferroelectric to monoclinic/orthorhombic, followed by from monoclinic/orthorhombic to tetragonal, and finally from tetragonal to cubic paraelectric, are further investigated via polarized light microscopy and Raman spectroscopy.     

Structure, phase transition and electric properties of poly(vinylidene fluoride-trifluoroethylene) copolymer studied with density functional theory

The geometry, energy, internal rotation, vibrational spectra, dipole moments and molecular polarizabilities of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) of α- and β-chain models were studied with density functional theory at B3PW91/6-31G(d) level and compared with those of the poly(vinylidene fluoride) (PVDF) homopolymer. The chain length and the trifluoroethylene (TrFE) concentration were examined to discuss the copolymer chain stabilities, chain conformations and electric properties. The asymmetrical internal-rotation potential energy curve shows that the angles for the g and g′ conformations in the α-chain (tg and tg′) models are 53° and −70°, respectively, and the β-chain (ttt) conformation is a slightly distorted all-trans plane with dihedral angle at 177°. The energy differences, E_β − E_α(g) and E_β − E_α(g′), between the β- and the α-conformation are 2.1 and 7.8 kJ/mol, respectively. These values are smaller than that in PVDF (8.4 kJ/mol), suggesting that the β-conformation in the copolymer will be more stable than in PVDF. The energy barriers for β → α(g) and β → α(g′) transitions are 16.2 and 5.8 kJ/mol, respectively. The former is almost twice of the energy barrier in PVDF by 8.2 kJ/mol and the latter is slightly smaller (by 2.4 kJ/mol) than that in PVDF. The respective energy barriers for α(g) → β and α(g′) → β transitions are 18.3 and 13.6 kJ/mol compared with the value 16.3 kJ/mol in PVDF. The asymmetrical energy barriers may be one of the reasons for the copolymers with 0.5-0.6 (mole fraction) VDF exhibiting complicated phase transition behavior. The conformation of α-chain P(VDF-TrFE) exhibits from a helical (containing higher TrFE) to a nearly beeline (containing lower TrFE). This behavior is different from that in the PVDF and the nearly beeline conformation might be responsible for the increasing crystallizability. The helical might also be associated with the complicated phase transition behavior and the larger lattice strain in the P(VDF-TrFE)s with higher TrFE concentration. The energy difference per monomer unit between the β- and α-chain decreases with increasing TrFE content. The ideal β-chain is curved with a radius of about 30 Å, which is similar to that in PVDF. The chain curvature and the TrFE content will affect the dipole moment contribution per monomer. The chain length and TrFE content will not significantly affect the mean polarizability. The calculations indicated that there are some additional characteristic vibrational modes that may be used in identification of the α- or β-phase P(VDF-TrFE)s with different TrFE contents.     

二维向列型液晶的I-N相变及纹影织构模拟

从液晶的Landau-de Gennes自由能出发进行推导,发现在二维情况下向列型液晶的I-N相变为二级相变,且相变点为NωФ=2;在液晶畸变自由能单一Frank常数假设下,利用元胞动力学方法对二维向列型液晶的Ginzberg-Landau方程进行计算机模拟,得到了其纹影织构图样。     

A Fourier transform infra-red study of the phase behaviour of polymer blends. Ethylene-vinyl acetate copolymer blends with poly(vinyl chloride) and chlorinated polyethylene

Fourier transform infra-red studies of ethylene-vinyl acetate (EVA) blends with poly(vinyl chloride) (PVC) and chlorinated polyethylene (CPE) are presented. Previous studies have demonstrated that these blends are compatible at ambient temperature and exhibit lower critical solution temperatures (LCST) in a range that is readily accessible and below the onset of significant polymer degradation. Infra-red spectra of EVA-PVC and EVA-CPE films cast from solution and recorded at room temperature exhibit the familiar frequency shifts and band broadenings of the carbonyl stretching vibration that are consistent with compatible blend systems. Significantly, at temperatures above the LCST, these spectral features are not observed, which implies phase separation. By monitoring the frequency of the EVA carbonyl stretching vibration in samples of the blends, an estimation of the relative strength of the intermolecular interactions has been obtained as a function of temperature. A non-linear relationship is observed and the temperature at which the relative strength of the intermolecular interaction appears very weak correlates with the LCST. The implications of these results are discussed.     

Phase transition of Eu2Ti2O7 under high pressure and a new ferroelectric phase with perovskite‐like layered structure

Ferroelectrics with perovskite‐like layered (PL) structure are well‐known for their high T_c and the application prospect of high‐temperature‐piezoelectric sensing. In this study, the PL‐structure Eu₂Ti₂O₇ was prepared by 1‐step high‐pressure sintering, which show the pyrochlore structure of Eu₂Ti₂O₇ would change into PL structure at 11 GPa, 1300°C. The PL‐structure Eu₂Ti₂O₇ is metastable, which will change back to pyrochlore structure at about 900°C in the air. The PL‐structure Eu₂Ti₂O₇ was confirmed as a high‐temperature ferroelectric material for the first time. The ferroelectric domain switching was directly observed using piezoelectric force microscope. The piezoelectric constant of the PL Eu₂Ti₂O₇ ceramic was measured as 0.7‐0.9 pC/N and its thermal depoling temperature (T_d) was determined as 800°C, which is associated with the PL‐pyrochlore transition.     

Structure and properties of crystalline polymers

Starting with a structural study of the crystallization behaviour of poly(vinyl alcohol), the author has been analysing the crystal and molecular structures of crystalline polymers for the past 35 years. One of the characteristic points of the methods used is the co-operative use of X-ray diffraction and infrared and Raman spectroscopy (normal coordinate treatment). There are many examples of the application of this technique to a series of polyethers, polythioethers, polyesters, polymer complexes etc. Furthermore, the intra- and intermolecular energy calculations have succeeded in accelerating the structural analyses of important but complicated polymer materials and in revealing the factors governing the stable crystal structure and molecular conformation of a polymer. Poly(ethylene oxygenzoate) x form and double-stranded helices of isotactic poly(methyl methacrylate), the first double helix ever found for synthetic polymers, are used as typical for the application of this method. The structural interpretation of the mechanism of optical compensation in racemic polymers is also a good example. The energy calculations have developed to the stage where the stability of two crystal forms of polyethylene can be discussed in terms of free energy. Utilizing the structural data thus accumulated and the spectroscopically obtained interaction parameters, the structure-property relationship has been clarified quantitatively by lattice dynamical theory. The calculated crystallite moduli of polymer chains agree well with the observed ones for many polymers such as poly-p-phenylene terephthalamide, etc. The study has been advanced by a new method of calculation of the three-dimensional elastic constant tensor and its application to polyethylene, poly(vinyl alcohol), nylon 6 etc. As an extension the general method of calculating the piezoelectric constant tensor has also been derived and successfully applied to poly(vinylidene fluoride) form I, resulting in the interpretation of the origin of macroscopic piezoelectricity of this polymer.     

Magnetic phase transition and magneto-dielectric analysis of spinel chromites: MCr2O4 (M = Fe,Co and Ni)

In this work, we present magnetic phase transition temperatures and magneto-dielectric coupling in MCr₂O₄ (M = Fe, Co and Ni) ceramics, synthesized using sol–gel auto-combustion route. In order to develop their respective crystalline textures, all these chromites were calcined at 650?°C for 2?h. X-ray diffraction patterns confirmed that FeCr₂O₄ had a rhombohedral structure while NiCr₂O₄ and CoCr₂O₄ exhibited a spinel-type cubic structure. The presence of relevant elements in the specific stoichiometric ratios was confirmed using energy dispersive X-ray spectroscopy. The shapes and sizes of the grains for all the samples were determined using the images obtained from a field emission scanning electron microscope. Temperature dependent magnetic analysis have shown that FeCr₂O₄, CoCr₂O₄ and NiCr₂O₄ are ferromagnetic at 5?K and their magnetic phase transition temperatures were measured as 80, 83 and 90?K, respectively. Spin-orbit interference was also studied through magneto-dielectric coupling for these chromites using a modified impedance analyzer set-up.     

Structural study of a series of ethylene-tetrafluoroethylene copolymers with various ethylene contents, Part 1: Structure at room temperature investigated for uniaxially-oriented samples by an organized combination of 2D-WAXD/SAXS and IR/Raman spectra

The X-ray fiber diagrams, polarized infrared/Raman spectra, and small-angle X-ray scattering data have been successfully measured for a series of uniaxially-oriented ethylene (E)-tetrafluoroethylene (TFE) random copolymers. The difference in crystal structure and morphology has been investigated. All the samples of E/TFE copolymer were found to take the planar-zigzag conformation at room temperature except pure polytetrafluoroethylene case. The layer line intensities of the X-ray fiber diagram and the 00l reflection intensities were found to change systematically. From this, the E and TFE sequences were considered to be included commonly in a crystal lattice. The detailed investigation of the polarized infrared and Raman spectra allowed us to assign the bands to some characteristic structures. These can be used effectively in the study of structural changes occurring in the phase transition of these copolymer samples. The 2-dimensional small-angle X-ray scattering patterns were compared among the copolymers and the difference in stacked lamellar structure has been discussed.     

Aliphatic polyesters as models for relaxation processes in crystalline polymers: 2. Dielectric relaxation in copolymers of adipic acid with 1,6 and 2,5-hexanediols

Linear aliphatic polyesters are interesting model systems for studying relaxation processes in crystalline polymers because they show both γ and β relaxations in a prominent way whereas in many highly crystalline linear polymers (LPE, POM etc.) the β process is suppressed and, unlike branched polyethylene which also has a prominent β process, the polyesters have no chemical structural complications due to branches. To study the hypothesis that variations in the appearance of the β (glass-rubber) relaxation are due to varying degrees of immobilization of long-range segmental motion in the amorphous fraction by the presence of the crystal phase measurements are made of dielectric relaxation in a series of the title copolymers that span the crystallinity range of zero (homopolymer with 2,5-hexanediol) to ≈60% (homopolymer with 1,6-hexanediol). The data are analysed in terms of the effect of degree of crystallinity on both kinetic parameters (activation energies and relaxation width) and equilibrium parameters (dipole correlation factor deduced from relaxation strength). In the latter case special care is taken to properly assess composite mixture effects on the relaxation strength. The shape of the β process is extremely sensitive to the degree of crystallinity, broadening greatly with the onset of the presence of crystallinity and increasing in broadness with increasing degree of crystallinity. Although less sensitive than the width, the β relaxation dipole correlation factor depends on crystallinity also, the availability of chain configurations within the amorphous fraction being noticeably reduced in the crystalline specimens. The γ process kinetic parameters are relatively insensitive to the presence of the crystal phase, a behaviour consistent with a localized motion mechanism. The γ relaxation strength correlates with the process having an amorphous phase origin if it is assumed that the 2,5 diol units contribute less to relaxation strength than the 1,6 diol units; a result also consistent with the localized motion concept.     

Simultaneous enhancement of emission and thermal sensitivity via phase transition in Gd2(MoO4)3:Yb3+/Er3+ crystals

The effects of site symmetric distortion induced by the phase transition on up-conversion emission and thermal sensing performance of Gd₂(MoO₄)₃:Yb³⁺/Er³⁺ (GMO) crystals were elaborately studied by minimizing interference from many factors. Monoclinic GMO showed a much stronger fluorescence intensity and larger fluorescence intensity ratio under the irradiation of 980 nm laser in comparison to the orthorhombic counterpart. These remarkable up-conversion properties stemmed from the low site symmetry with large site symmetric distortion in monoclinic GMO. Moreover, the thermal sensing property of the samples was assessed based on the fluorescence intensity ratio technique, where monoclinic GMO exhibited much higher maximum absolute sensitivity (S_a = 0.0257 K⁻¹ at 510 K) due to the site symmetric distortion, which was further explained by the Judd–Ofelt theory and polarizability of the chemical bond volume model. Results opened an efficient avenue for achieving highly sensitive thermometry in many daily scenarios via finely tailoring the local site symmetry.     

H NMR study of temperature-induced phase transitions in D2O solutions of poly(N-isopropylmethacrylamide)/poly(N-isopropylacrylamide) mixtures and random copolymers

¹H NMR spectroscopy was used to investigate temperature-induced phase transitions in D₂O solutions of poly(N-isopropylmethacrylamide) (PIPMAm)/poly(N-isopropylacrylamide) (PIPAAm) mixtures and P(IPMAm/IPAAm) random copolymers of various composition on molecular level. While two phase transitions were detected for PIPMAm/PIPAAm mixtures, only single phase transition was found for P(IPMAm/IPAAm) copolymers. The phase transition temperatures of PIPAAm component (appears at lower temperatures) are not affected by the presence of PIPMAm in the mixtures; on the other hand, the temperatures of the phase transition of PIPMAm component (appears at higher temperatures) are affected by the phase separation of the PIPAAm component and depend on concentration of the solution. For P(IPMAm/IPAAm) random copolymers, a departure from the linear dependence of the transition temperatures on the copolymer composition was found for a sample with 75 mol% of IPMAm monomeric units.     

Polymerization of Lactams: 57. G.l.c. and n.m.r. analysis of the anionic copolymers of 2-pyrrolidone with 6-caprolactam and 8-octanelactam

The activated anionic copolymerization of 2-pyrrolidone (PD) with 6-caprolactam (CL) or 8-octanelactam (OL) proceeds even above the ceiling temperature for PD homopolymerization. At high temperatures, the copolymerizations are accompanied by the depolymerization of PD sequences, which is more pronounced with the copolymers with CL. The copolymers obtained probably exhibit a constitutional heterogeneity and contain considerable amounts of low-molecular weight fractions. This may be the reason why the content of comonomers in the prepared copolymers determined by g.l.c. did not agree with that found by ¹H n.m.r. or ¹³C n.m.r. spectroscopy. The copolymers with CL had in part a block structure and also an alternating character, depending on temperature and polymerization time, while random copolymers were obtained at high temperatures. The copolymers with OL tended mostly to alternation.