Morphology and Thermal Properties of Poly[bis(β-phenoxyethoxy)phosphazene]

The structure and thermal properties of poly[bis(-phenoxyethoxy)phosphazene)] (PBPEP) newly synthesized by us were investigated. The crystallization from the melt, the volumetric relaxation in the amorphous phase in the upper vicinity of the glass transition temperature (T _g) and the enthalpy of relaxation of the glass in the lower vicinity of the T _g were shown to be very slow. These slow rates may be related to the low chain mobility due to the bulky side chain. Two kinds of crystal forms, called and forms were found in the melt-crystallized sample. These forms were clearly seen as individual types of spherulites by optical microscopy. The melting temperature of these crystals were analyzed by the Hoffmann–Weeks plot. The so-called T(1) transition that had often been detected in many crystalline polyphosphazenes as the transition from the crystal phase to the mesophase was not observed by x-ray diffraction at elevated temperatures.     

Mesomorphic phase formation of plasticized poly(l‐lactic acid)

The effects of the crystallization temperature, T_c, on the crystal structure as well as its thermal behavior of plasticized poly(l ‐lactic acid) were investigated by means of wide‐angle X‐ray diffraction (WAXD), Fourier‐transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). PLLA blended with succinic acid‐bis[2‐[2‐(2‐methoxyethoxy)ethoxy]ethyl] ester (SAE) showed clear difference in T_c dependence of crystalline form compared to PLLA homopolymer. PLLA with 26 wt % SAE crystallized into orthorhombic α form for T_c above 80°C, while a peculiar disordered structure (mesophase) was obtained for T_c at 40°C. A detailed FTIR analysis of the mesophase of PLLA, focusing on the intra‐ and inter‐chain interaction in the structure, indicated that mesophase had a large degree of disorder in 10/3 helical conformation as well as its packing manner of disordered 10/3 helical chain. Upon heating, mesophase showed a steep exothermic peak at 80°C in DSC thermogram, indicating the phase transformation from mesophase to a form crystal. FTIR results showed that the degree of interchain interaction of C=O in PLLA started to decrease above 60°C, followed by steep increase at 80°C due to the recrystallization into a form. Melt‐recrystallization process in mesophase‐α transformation was clarified. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39762.     

Thermal analysis of poly(bisphenoxyphosphazene); single crystals and melt crystallized samples

High-molecular-weight polyphosphazenes are of considerable interest because of their potential use as relatively high temperature materials that also possess low glass temperature. A number of authors have examined the thermal properties of a wide range of polyphosphazenes. These studies, however, have usually been limited to compression-molded samples or to samples where the morphology or thermal history are poorly understood or highly complex. This article reports the thermal behavior of a single polymer, poly(bisphenoxyphosphazene) starting with the simplest morphological entity—the single crystal. The result of crystallization from the mesomorphic state [above T(1)] and from the melt were also examined, together with the influence of thermal cycling and heating rate. The effects of a variety of parameters on T(1) are reported. This work clearly demonstrates the importance of morphology–crystallization conditions in determining T(1) and suggests the presence of two crystal forms for this polymer.     

Mesophase formation in poly(propylene-ran-1-butene) by rapid cooling

The effect of random insertion of low amount of 1-butene of less than about 11 mol% into the isotactic polypropylene chain on structure formation at non-isothermal crystallization at different rate of cooling was investigated by X-ray scattering, density measurements, and atomic force and polarizing optical microscopy. Emphasis is put on the evaluation of the condition of crystallization for replacement of lamellar crystals by mesomorphic nodules on increasing the cooling rate/supercooling. In the polypropylene homopolymer, mesophase formation occurs on cooling at rates larger about 150–200 K s⁻¹, while in case of poly(propylene-ran-1-butene) mesophase formation is observed on cooling at a lower rate of about 100 K s⁻¹. It is suggested that the lowering of the critical rate of cooling for mesophase formation in poly(propylene-ran-1-butene) is due to a reduction of the maximum rate of formation of monoclinic/orthorhombic crystals at low supercooling, compared to the homopolymer. The data of the present study allowed the establishment of a non-equilibrium phase diagram which shows ranges of existence of phases as a function of the cooling rate on solidification the quiescent liquid and the concentration on 1-butene co-units.     

Stretch‐induced molecular ordering in amorphous/crystalline polylactide blends

The effect of amorphous poly(D ,L ‐lactide) (PDLLA) on the molecular orientation and crystallization of crystalline poly(L ‐lactide) (PLLA) on stretching is reported in this study. It is indicated that the presence of PDLLA in its miscible blends with PLLA is not favorable for either cohesive mesophase formation below T_g or strain‐induced crystallization above T_g at strains beyond the segmental extensibility limit. Because of lack of constraints imposed by cohesive mesophase or crystals, oriented segments are liable to slide each other or recoil, responsible for low‐molecular orientation in the stretched blends. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Phase behavior of poly (pyromellitimide)s having flexible (n-alkyloxy)methyl side chains

Summary Phase behavior of poly(pyromellitimide)s having (n-alkyloxy)methyl side chains (-CH₂OC_mH_2m+1, m=4, 6, 8) has been studied by wide angle X-ray scattering, differential scanning calorimetry and ¹³C solid-state NMR. While there are no observable transitions in the polymers bearing short side chain(m=4, 6), there is one transition in the polymer bearing the longest side chain(m=8), which is assigned to mesophase-mesophase transition. All the samples show layered mesophase at room temperature, in which the side chains are amorphous but the main chains form two-dimensional crystals in each layer. In the polymer bearing the longest side chain(m=8), it shows another layered mesophase at high temperature. In the high temperature mesophase, the main chains do not form two-dimensional crystals in each layer; only the lateral packing of the main chains remains undisrupted. Received: 7 July 2000/Accepted: 22 September 2000     

Some aspects of nonisothermal crystallization of polymers. II. Consideration of the isokinetic condition

In the previous paper a practical method has been applied for an analysis of non-isothermal crystallization in terms of data of isothermal crystallization. The fundamental equation was written on the assumption of the isokinetic conditions in the following form: where X(t) is the degree of phase transformation at time t, and n is the Avrami index determined in the isothermal experiments; K(T) is connected with the crystallization rate constant of the isothermal crystallization, k(T), through the relation K(T) = k(T)^1/n. The equation is derived on the basis of the well-known theory of phase transformation. Experiments of nonisothermal crystallization of high-density polyethylene were carried out under various cooling conditions. The change in crystallinity during the process was followed by using the above equation in the course of the primary crystallization. A procedure of the analysis of the whole, including both the primary and secondary processes, is suggested as an eminently practical one on a more general assumption.     

Influence of mesophase–crystal transition on thermal and mechanical properties of stretched poly(L‐lactide)

The mesophase in the as‐stretched poly(L ‐lactide) (PLLA) exhibits low thermal stability and undergoes melting around T_g. As a consequence, without constraints as‐stretched PLLA can recover to its original (unstretched) length while being held above T_g. Upon constrained annealing at 70°C mesophase is transformed into highly oriented crystals, responsible for little free shrinkage and superior dimensional stability. At the same time, molecular orientation in the amorphous phase first decreases significantly due to thermodynamic relaxation, and then increases moderately with the advent of cold crystallization. It correlates well with the change of yield strength with respect to annealing time. POLYM. ENG. SCI., 53:2568–2572, 2013. © 2013 Society of Plastics Engineers     

Crystal behavior of semicrystalline polystyrene‐block‐poly(l‐lactide) diblock copolymer in thin films with various structures

The crystal behavior of a semicrystalline polystyrene‐block‐poly(l ‐lactide) diblock copolymer in phase‐separated thin films with various thicknesses at different crystal temperatures has been investigated using atomic force microscopy and transmission electronic microscopy. Parallel and perpendicular lamellae could be obtained by annealing the thin films for different periods of time as reported previously (Chen et al., Macromolecules 40:6631 (2007)). At different temperatures, crystallization in thin films with parallel lamellar structure in the melt state gives dendrite crystals with orthorhombic structure, and the ordered structure in the melt is destroyed after crystallization. When crystallization occurs in thin films with perpendicular lamellar structure, crystal morphology and structure are greatly affected by the crystallization temperature (T_c). When T_c < T_g,ps, where T_g,ps is the glass transition temperature of a polystyrene block, crystallization is hardly confined within the lamellae. The morphology is preserved but the long period of the perpendicular lamellae is increased after crystallization. When T_c > T_g,ps, rod‐like crystals dominate the final morphology, and crystallinity destroys completely the structure in the melt.© 2012 Society of Chemical Industry     

Morphology and molecular mobility of plasticized polylactic acid studied using solid‐state 13C‐ and 1H‐NMR spectroscopy

MAS ¹³C‐NMR measurements were used for the study of morphology and molecular mobility in amorphous quenched and triacetine‐plasticized PLA samples and PLA samples which underwent cold crystallization during annealing at 80 and 100 °C. The single pulse MAS ¹³C‐NMR spectra indicate that plasticizer promotes cold crystallization which results in the decrease of the temperature of crystallization and formation of more perfect crystalline domains. The T₁(¹³C) spin‐lattice relaxation times show that the presence of plasticizer molecules leads to an increase of local mobility in PLA chains but plasticized PLA after annealing at 100 °C shows more rigid structure. The series of broad line ¹H‐NMR spectra performed at temperatures up to 100 °C provided information on the changes in relaxation processes and morphology of the studied samples. The interpretation of the results obtained using the techniques of NMR spectroscopy were supported by WAXD and DSC measurements. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43517.     

Determination of microphase structure and scale and scale of mixing in poly-ε-caprolactone (PCL)/poly(vinyl chloride) (PVC) blend by high-resolution solid-state 13C-NMR spectroscopy with magic angle spinning and cross polarization

High-resolution solid-state, pulsed Fourier-transform (FT) ¹³C-nuclear magnetic resonance (NMR) spectroscopy with magic angle spinning (MAS) and cross polarization (CP) was applied to a mechanical blend of poly-ε-caprolactone (PCL) and poly(vinyl chloride) (PVC) with 50/50 weight ratio (%) whose composition results in very complex morphology and phase structure in the solid state. Proton spin-lattice relaxation times, T₁(¹H) and T_1ρ(¹H), were used as a probe to determine the microphase structure, the degree of homogeneity in terms of the domain size, and the state of mixing of the blend. In particular, T_1ρ(¹H) was shown to be able to distinguish the separated domains at a level of a few nanometers; the scale of mixing was evaluated from the approximation based on spin-diffusion phenomenon to be ～ 4.7 nm below which two polymers were partially mixed and above which they were homogeneously mixed. Treatment of the T_1ρ(¹H) data with two exponential decay functions resulted in a resolution of individual T_1ρ(¹H) into rigid and mobile components, from which more detailed information on the phase structure and state of mixing were obtained. © 1994 John Wiley & Sons, Inc.     

Structure,Phase Transition,and Electronic Properties of K1−xNaxNbO3 Solid Solutions from First‐Principles Theory

With extensive first‐principles calculations, we investigated the geometric structure, phase transition, and electronic properties of orthorhombic, monoclinic, and tetragonal K_1?xNa_xNbO₃ (KNN) as functions of the Na content. We found that KNN undergoes an orthorhombic‐to‐monoclinic‐to‐orthorhombic phase transition when the Na content is gradually increased. We also found that the polarization vector of the monoclinic phase can be rotated more easily than those of the orthorhombic and tetragonal phases, giving rise to an enhanced piezoelectric response of the monoclinic KNN. Furthermore, our calculations provide an interpretation for the experimentally observed unusual broad peak of the KNN piezoelectric parameters.     

Effect of the melting temperature on the crystallization behavior of a poly(l‐lactide)/poly(d‐lactide) equimolar mixture

The effect of the final melting temperature (T_f) on the crystallization of poly(l ‐lactide) (PLLA)/poly(d ‐lactide) (PDLA) was studied via a combination of differential scanning calorimetry, wide‐angle X‐ray scattering, polarized optical microscopy, and Fourier transform infrared (FTIR) spectroscopy. We observed that a residual stereocomplex (SC) crystal induced the formation of SC crystals during cooling from a T_f (230°C) just above the melting peak of the SC crystals. On cooling from a T_f (240°C) just above the endset temperature of SC crystal melting [T_m(S)(E)], the possible order structure and the strong interchain interaction promoted the preferential crystallization of SC crystals; this enhanced the formation of α crystals. During cooling from a T_f (≥250°C) far above T_m(S)(E), the crystallization peaks of α and SC crystals converged. The FTIR results indicated that the residual SC crystals, possible ordered structure, and interchain interactions in the melt might have been the key factors for the different crystallization of PLLA/PDLA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43015.     

Influence of grape marc extract on tuning the intermolecular interactions in the high-density polyethylene

Intermolecular interactions and molecular dynamics in thin films of high-density polyethylene (HDPE) containing a high loading of Grape Marc Extract (GME) were analyzed by solid-state NMR. Optical microscopy (OM), Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) studies were used to corroborate the findings. The OM and SEM images and ¹H-¹³C RAMP CP/MAS (ramped amplitude cross-polarization/magic-angle spinning) spectra of HDPE, HDPE-GME, and GME confirmed the incorporation of the GME into the HDPE structure. The results were compared to those for an unfilled HDPE film. The influence of GME on enhancing the amorphous nature of HDPE, altering the crystalline melting behavior and possible intermolecular interactions were evident from the DSC and FTIR. The NMR spin-diffusion and T₁(¹H), T₂(¹H), T_1ρ*(¹³C), T_1ρ(¹H) relaxation and variable contact time experiments revealed the interactions and dynamics at the sub-micron level.     

Crystallization and vitrification effect in a poly(styrene)-g-poly(ethylene oxide) graft copolymer

Crystallization and solid state structure of a poly(styrene)-graft-poly(ethylene oxide) (PS-g-PEO) graft copolymer with crystallizable side chains were studied using simultaneous small angle X-ray scattering/wide angle X-ray scattering/differential scanning calorimetry (SAXS/WAXS/DSC). It is found that the glass transition temperature (T_g) of PS main chain is remarkably higher than that of PS homopolymer. The start cooling temperature (T_o) has a great influence on crystallization of the PEO side-chain. When the graft copolymer is cooled from the temperature above T_g, phase separation is suppressed due to the low mobility of the PS main chain and the homogeneous melt is vitrified. The unfavorable conformation of the rigid main chain results in a single crystallization peak and lower crystallinity. When PS-g-PEO is only heated to a temperature lower than the T_g and then cooled, phase separation is retained. Both the PEO side chains with high and low crystallizability can crystallize in the phase-separated state, leading to double crystallization peaks and higher crystallinity. The effect of solvent on crystallization of the graft copolymer was also examined. It is observed that addition of toluene reduces the T_g of the PS main chain and leads to the disappearance of the vitrification effect.     

The synthesis and characterization of a mesomorphic brush type polycarbosilane: poly[1,1-bis(4′-biphenyl)silabutane]

Summary Poly[1,1-bis(4-biphenyl)silabutane] (II) has been prepared by the anionic ring opening polymerization of 1,1-bis(4-biphenyl)silacyclobutane. II shows mesomorphic behavior by DSC. The¹³C NMR T₁ relaxation times have been measured. These are found to be smaller than those of poly(1,1-dimethylsilabutane)by an order of magnitude. This may result from interaction of the highly rigid biphenyl side chain moieties. The thermal stability of II is higher than that for other 1,1-disubstituted polysilabutanes.     

Electron beam crosslinking of fluoroalkoxy,methoxyethoxyethoxy, and substituted phenoxy polyphosphazenes: Physical and chemical characterization and comparison to a thermally induced free radical process and ionic complexation

Electron beam, thermal free radical, and cationic complexation mechanisms have been employed to investigate crosslinking in selected polyphosphazenes. In polyphosphazenes functionalized with o‐allylphenol to facilitate free radical crosslinking, maximum crosslink density was achieved after 10 min at 130°C utilizing benzoyl peroxide as an initiator. Electron beam radiation was found to give an increased crosslink density with increased dose. The dose–crosslink density relationship observed for a aryloxyphosphazene terpolymer PPXP also was seen in poly[bis(2,2′‐(methoxyethoxy)ethoxy)phosphazene] (MEEP). However, with two lots of a fluoroalkoxyphosphazene an initial crosslink density was achieved at a lower electron beam exposure with no additional crosslink density observed with increasing dose. These measurements are observations of net crosslinking, which is the result of crosslinking processes balanced by chain scission processes. DSC revealed that neither thermal‐ nor electron beam‐initiated crosslinking cause any significant change in the T_g of the polymer. Metal ion complexation with MEEP consistently gave T_g values that were higher than MEEP. The T_g values measured for both MEEP and the lithium‐complexed MEEP were unaffected by electron beam irradiation. These data suggest the location of lithium complexation may be at the nitrogen lone electron pair on the backbone, representing a new mechanism of lithium complexation in phosphazenes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 55–66, 2000     

Synthesis,characterization, and mesomorphic behavior of side-chain liquid crystalline copolysiloxane polymers I. with an oligo (ethylene oxide) unit and a cyano unit in the side chain

The syntheses and characterizations of poly [4-allyloxy-benzoic acid [4-(2-methoxy) ethoxy] biphenyl]-4-yl ester-co-4-allyloxy-[(4-cyano)-4-phenyl] carboxyl benzoate ester (poly [(MS3BDBE1)-co-(MCN)]_x/y) (where x/y represents the molar ratio of the two structural units on the side chain) were performed in this study. The molar compositions of the structural units on the copolymers side chain were characterized by¹H NMR. The transition temperatures, mesophase texture, and layer spacing (dl) of the polysiloxane polymers and copolymers were determined by differential scanning calorimetry (DSC), polarized optical microscopy, and X-ray diffraction patterns. The effects of the molar composition in the copolymers on the mesophase texture, transition temperatures, enthalpy/entropy change of mesophase/isotropic transition, dl of these copolymers were also discussed.     

Synthesis and phase behavior of new cholesteric liquid‐crystalline copolymers containing chiral mesogenic groups derived from menthol derivatives

The synthesis of a new chiral mesogenic monomer ( M₁ ), a nematic monomer ( M₂ ), and a series of side chain cholesteric copolymers ( P₂ – P₆ ) containing the mesogenic menthyl groups is described. The chemical structures of the compounds were confirmed by FTIR and ¹H NMR. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. M ₁ showed an enantiotropic cholesteric phase, and M₂ revealed a nematic phase. The homopolymers P₁ and P₇ , respectively, displayed a chiral smectic A (S_A) phase and a nematic phase, while the copolymers P₂ – P₆ exhibited the Grandjean texture of the cholesteric phase. T_g, T_i, and ΔT of P₁ – P₇ increased with increasing the concentration of M₂ in the polymers. All of the obtained polymers displayed very good thermal stability and the wide mesophase temperature range. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008