Phase Behavior Of Poly Research Articles

Phase Behavior of Poly(Ethylene Oxide) Studied by Modulated‐Temperature DSC—Influence of the Molecular Weight

Melting and crystallization behavior of poly(ethylene oxide) (PEO) with different molecular weight was investigated by modulated‐temperature differential scanning calorimetry (MT‐DSC)—step‐scan alternating DSC. It was found that by separating the reversing and nonreversing components of the (total) heat flow, PEO 10000, which exhibits the highest degree of crystallinity, shows the smallest nonreversing signal during crystallization. This effect can be attributed to the favorable structural features associated with spacial alignment. On the other hand, the crystallization process of PEO with molecular weight of 3400 is hindered by a relatively high content of end groups that may cause defects in the crystal lattice. For PEO 35000, low segmental mobility and chain entanglements lower the rate of crystallization. The area of the reversing component of PEO melting for different molecular weight fractions confirms that for PEO 10000, recrystallization is less intensive than for both the lower and higher molecular weight analogues.

Phase Behavior of Poly(methyl methacrylate)/Poly(vinylidene fluoride) Blends in the Presence of High‐Pressure Carbon Dioxide

AbstractPrevious efforts have demonstrated that high‐pressure CO2 can markedly influence the phase behavior of amorphous polymer blends. In this work, we examine the effect of high‐pressure CO2 on the miscibility of blends composed of glassy poly(methyl methacrylate) (PMMA) and semicrystalline poly(vinylidene fluoride) (PVDF). Blends of this type are known to exhibit lower critical solution temperature (LCST) behavior with partial miscibility up to ≈50–60 wt.‐% PVDF at ambient conditions. Two miscible PMMA/PVDF blends have been systematically exposed to high‐pressure CO2 at 35 °C and pressures below and above the critical pressure. Small‐angle X‐ray scattering reveals that the scattering intensity at high scattering angles shows little dependence on pressure at low CO2 pressures, but increases substantially at relatively high CO2 pressures. Transmission electron microscopy and differential scanning calorimetry analyses confirm that the blends are initially quasi‐homogeneous with diffuse PVDF‐rich dispersions and a single glass transition temperature. After exposure to relatively high CO2 pressures, however, the PVDF is found to crystallize within the PMMA‐rich matrix. Thermal recycling of these blends promotes homogenization, indicating that such CO2‐altered phase behavior is reversible.SAXS patterns acquired from the 69/31 w/w PMMA/PVDF blend.magnified imageSAXS patterns acquired from the 69/31 w/w PMMA/PVDF blend.

Theoretical consideration on phase behaviors of poly(ethylene oxide-block-propylene oxide)/LiCF 3SO 3 systems in lithium battery

A new thermodynamic model is developed based on the extended perturbed hard sphere chain (PHSC) model and melting point depression theory to describe the phase behaviors of copolymer electrolyte/salt systems. The phase behaviors of poly(ethylene oxide-block-propylene oxide)/LiCF 3SO 3 systems are investigated by thermo-optical analysis (TOA) technique. Quantitative descriptions according to the proposed model are in good agreement with experimental data. The obtained results show that monomer ratio and sequence type of copolymers play a great role in determining eutectic points of the given systems.

Phase behavior of poly(ethylene-co-norbornene) in C6 hydrocarbon solvents: Effect of polymer concentration and solvent structure

Phase behavior information is necessary for accomplishing homogeneous copolymerization to obtain high yield of copolymers and prevent a fouling problem. Cloud-point data to 160oC and 1,450 bar are presented for five C6 hydrocarbon solvents, normal hexane, 2,2-dimethyl butane, 2,3-dimethyl butane, 2-methyl pentane, and 3-methyl pentane, with poly(ethylene-co-53 mol% norbornene) (PEN53). The pressure-concentration isotherms measured for PEN53/n-hexane have maximums that range between 5 and 12 wt% PEN53. The cloud-point curves for PEN53 all have negative slopes that decrease in pressure with temperatures. The single-phase region of PEN53 inn-hexane is larger than the regions in 2,2-dimethyl butane, 2,3-dimethyl butane, 2-methyl pentane, and 3-methyl pentane. The cloud-point curve of PEN53 in 2,2-dimethyl butane is located at higher temperatures and pressures than the curve in 2,3-dimethyl butane due to the reduced dispersion interactions with and limited access of 2,2-dimethyl butane to the copolymer. Similar cloud-point behavior is observed for PEN53 in 2-methyl pentane and 3-methyl pentane.

Modulated temperature DSC studies on the phase transitions of poly(ethylene oxide). Effect of temperature step

Phase behaviour of poly(ethylene oxide) (PEOX) was investigated by modulated temperature differential scanning calorimetry (DSC)-step scan alternating DSC at different temperature steps. Additional features of reversible and non-reversible components during phase transitions can be found. By increasing the temperature step between subsequent isothermal segments the reversible component of the melting process was decreasing. This effect is due to a shift of the equilibrium state of melting-recrystallization reversible processes towards higher degree of conversion that hinders molecular nucleation and recrystallization. Analysis of the non-reversible component during crystallization showed that an increase in the step caused a very distinct increase in the non-reversible component signal due to enhanced crystallization of the less-defected structures which was facilitated by larger temperature gradient.

Phase Behavior of Poly(methyl methacrylate)/Poly(vinylidene fluoride) Blends with and without High-Pressure CO2

ADVERTISEMENT RETURN TO ISSUECommunication to the...Communication to the EditorNEXTPhase Behavior of Poly(methyl methacrylate)/Poly(vinylidene fluoride) Blends with and without High-Pressure CO2Teri A. Walker, Yuri B. Melnichenko, George D. Wignall, and Richard J. SpontakView Author Information Departments of Chemical Engineering and Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina 27695, and Condensed Matter Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 Cite this: Macromolecules 2003, 36, 12, 4245–4249Publication Date (Web):May 23, 2003Publication History Received11 February 2003Published online23 May 2003Published inissue 1 June 2003https://doi.org/10.1021/ma030103cCopyright © 2003 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views347Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (86 KB) Get e-AlertsSUBJECTS:Differential scanning calorimetry,Fluoropolymers,Organic compounds,Polymers,Scattering Get e-Alerts

The influence of competitive interactions on multiple eutectic phase behavior in poly(ethylene oxide) molecular complexes

Binary mixtures of poly(ethylene oxide) and resorcinol exhibit two eutectic phase transitions at 40 and 80 °C, which are separated by a single-phase stoichiometric complex at ≈33 mol% resorcinol. These eutectic temperatures increase slightly at higher molecular weights of poly(ethylene oxide). The eutectics and the molecular complex are absent in ternary mixtures with either 25 or 40 wt% poly(2-vinylpyridine) because both polymers contain electron-pair donors which participate in hydrogen bonding interactions with the hydroxyl groups of the small-molecule aromatic. In contrast, 25 wt% polystyrene does not disrupt the bi-eutectic phase behavior of poly(ethylene oxide) and resorcinol because polystyrene is inert in these ternary mixtures. The lightest lanthanides with the largest ionic radii in the first-row of the f-block, like LaCl 3(H 2O) 6 and CeCl 3(H 2O) x , are more effective than neodymium, terbium and ytterbium trichloride hexahydrates from the viewpoint of (i) competing with resorcinol, (ii) interacting with poly(ethylene oxide), (iii) eliminating eutectic melting, and (iv) disrupting the 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol. High-resolution 13C solid state NMR spectroscopy identifies resorcinol in several different molecular environments. Multiple resonances are observed for chemically equivalent, but morphologically and crystallographically inequivalent, 13C sites in the solid state. The isotropic chemical shift of the phenolic 13C site in this small-molecule aromatic is very sensitive to the strength of intermolecular interactions in various phases. For example, self-association of resorcinol in pure crystalline phase γ yields a phenolic carbon chemical shift at 155 ppm. The formation of a 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol in co-crystallized phase β is identified by a phenolic carbon chemical shift at 158 ppm. When resorcinol and poly(2-vinylpyridine) interact in a homogeneous amorphous phase, the phenolic carbon resonance appears at a chemical shift of 160 ppm. A resorcinol-rich disordered crystalline phase in ternary mixtures with poly(ethylene oxide) and poly(2-vinylpyridine) yields a phenolic carbon resonance at 159 ppm. Temperature-composition projections of the binary and ternary phase diagrams, constructed via differential scanning calorimetry, allow one to interpret 13C NMR spectra of these strongly interacting blends and complexes in the solid state.

Relation of glass transition temperature to the hydrogen bonding degree and energy in poly( N-vinyl pyrrolidone) blends with hydroxyl-containing plasticizers: 3. Analysis of two glass transition temperatures featured for PVP solutions in liquid poly(ethylene glycol)

The phase behaviour of poly( N-vinyl pyrrolidone)–poly(ethylene glycol) (PVP–PEG) blends has been examined in the entire composition range using Temperature Modulated Differential Scanning Calorimetry (TM-DSC) and conventional DSC techniques. Despite the unlimited solubility of PVP in oligomers of ethylene glycol, the PVP–PEG system under consideration demonstrates two distinct and mutually consistent glass transition temperatures ( T g) within a certain concentration region. The dissolution of PVP in oligomeric PEG has been shown earlier (by FTIR spectroscopy) to be due to hydrogen bonding between carbonyl groups in PVP repeat units and complementary hydroxyl end-groups of PEG chains. Forming two H-bonds through both terminal OH-groups, PEG acts as a reversible crosslinker of PVP macromolecules. To characterise the hydrogen bonded complex formation between PVP ( M w=10 6) and PEG ( M w=400) we employed an approach described in the first two papers of this series that is based on the modified Fox equation. We evaluated the fraction of crosslinked PVP units and PEG chains participating to the complex formation, the H-bonded network density, the equilibrium constant of complex formation, etc. Based on the established molecular details of self-organisation in PVP–PEG solutions, we propose a three-stage mechanism of PVP–PEG H-bonded complex formation/breakdown with increase of PEG content. The two observed T gs are assigned to a coexisting PVP–PEG network (formed via multiple hydrogen bonding between a PEG and PVP) and a homogeneous PVP–PEG blend (involving a single hydrogen bond formation only). Based on the strong influence of coexisting regions on each other and the absence of signs of phase separation (evidenced by Optical Wedge Microinterferometry) we conclude that the PVP–PEG blend is fully miscible on a molecular scale.

Phase behavior of poly(ether imide) in mixtures of N-methyl-2-pyrrolidinone and methylene chloride

The phase behavior of poly(ether imide) (PEI) in solutions composed of N-methyl-2-pyrrolidone (NMP) and methylene chloride (MC) was studied at 25°C. The pair of solvents used to dissolve PEI has been selected for the purpose to perform a cononsolvent system. From the observed phase behavior, PEI was soluble in either NMP or MC individually but liquid–liquid demixing was observed in mixtures of NMP and MC. However, no cononsolvency was found by the theoretical prediction on the basis of Flory–Huggins formalism including three binary interaction parameters. Therefore, attempts were made to correlate the phase behavior of a cononsolvent system with the modified Flory–Huggins theory using a ternary interaction parameter. A good prediction was obtained when a composition-dependent ternary interaction parameter was included into calculations. In addition, the mechanism of cononsolvency and its relation with the ternary interaction parameter in the cononsolvent systems were discussed. Based on the analysis of IR spectroscopy, the ternary interaction parameter correlates well with a more intermolecular complexation of NMP with MC in the presence of PEI. Thus, the driving force for cononsolvency results from the formation of the NMP–MC complexes favoring over NMP–MC–PEI contacts, leading to exclude PEI segments in the vicinity of the NMP–MC complexes.

Binary Miscible Blends of Poly(Methyl Methacrylate)/Poly(α-Methyl Styrene-co-Acrylonitrile). IV. Relationship Between Shear Flow and Viscoelastic Properties

The effect of simple shear flow on the phase behavior of poly(methyle methacrylate), PMMA, and poly(α-methyl styrene-co-acrylonitrile), PαMSAN, exhibiting an LCST-type phase diagram, has been analyzed on the basis of a generalized Gibbs free energy of mixing, , modified by a stored energy term, E s . The value of the E s (the energy stored by the polymeric molecules during shear flow) was experimentally determined as a function of composition and shear rate from the viscoelastic material functions of the blend by using two different methods proposed by Marrucci and Wolf. The evaluated E s (proposed by Marrucci) from the entanglement plateau modulus, , and dynamic shear viscosity at a given shear rate, η(), were found to well describe the behavior of shear-induced mixing for the present system; i.e., a negative deviation of E s from the linear-mixing rule has been detected, which is a necessary condition for the elevation of the cloud points to higher values under shear flow. However, on the other hand, the calculated E s from the viscoelastic relaxation time, τ0 and zero shear viscosity, η0 (Wolf model), predicted both shear-induced mixing and shear-induced demixing for the large and small concentration range of PαMSAN, respectively; i.e., negative and positive deviation of E s from the linear-mixing rule was observed dependent on the concentration of PαMSAN. It is concluded that the viscoelastic material functions of the blend are very helpful for qualitatively anticipating the phase behavior of the blend under the effect of shear flow.

Phase Behavior of Poly(Oxyethylene)–Poly(Oxypropylene)–Poly(Oxyethylene) Block Copolymer in Water and Water–C12EO5 Systems

The binary phase diagram of a triblock copolymer poly(oxyethylene) (PEO) poly(oxypropylene) (PPO) poly(oxyethylene) (PEO), (PEO)37(PPO)58(PEO)37 or P105 in water and the ternary system of P105, water, and pentaoxyethylene dodecyl ether (C12EO5) has been studied to understand the miscibility of a small amphiphile, C12EO5 and a copolymer, as well as the mixing effect on the formed liquid crystalline structures. Phase diagrams, small angle x‐ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to characterize these systems. The phase diagram of the binary system is presented together with the characteristic parameters for founded phases, namely, cubic, hexagonal, and lamellar phases. In the ternary system it was found that the small amphiphile and the block copolymer, despite having very different chain lengths are essentially miscible forming single phases. A large amount of C12EO5 can be solubilized in the P105 aggregates whereas P105 is most difficult to dissolve in the C12EO5 aggregates because of the difference in the molecular size. The copolymer is practically insoluble in the lamellar phase of C12EO5 due to the packing constraint. Hence, two lamellar phases coexist in a surfactant‐rich region, at W s = 0.66, where W s is the weight fraction of the total amphiphile in the system. This indicates that the thickness of the lipophilic part of the C12EO5 lamellar phase is too small to allocate the large lipophilic chain of the P105 triblock copolymer.

Effect of the octadecyl acrylate concentration on the phase behavior of poly(octadecyl acrylate)/supercritical CO2 and C2H4 at high pressures

Pressure–composition isotherms were measured for the CO2/octadecyl acrylate system at 45.0, 80.0, and 100.0°C and at pressures up to 307 bar. This system exhibited type I phase behavior with a continuous mixture-critical curve. The solubility of octadecyl acrylate for the CO2/octadecyl acrylate system increased as the temperature increased at a constant pressure. The experimental results for the CO2/octadecyl acrylate system were modeled with the Peng–Robinson equation of state. A good fit of the data was obtained with the Peng–Robinson equation of state with one adjustable parameter for the CO2/octadecyl acrylate system. Experimental cloud-point data for the poly(octadecyl acrylate)/CO2/octadecyl acrylate system were measured from 36 to 193°C and at pressures up to 2100 bar, and the added octadecyl acrylate concentrations were 11.9, 25.9, 28.0, 35.0, and 40.0 wt %. Poly(octadecyl acrylate) dissolved in pure CO2 up to 250°C and 2100 bar. Also, adding 45.0 wt % octadecyl acrylate to the poly(octadecyl acrylate)/CO2 solution significantly changed the phase behavior. This system changed the pressure–temperature slope of the phase-behavior curves from an upper critical solution temperature (UCST) region to a lower critical solution temperature region as the octadecyl acrylate concentration increased. Cloud-point data to 150°C and 750 bar were examined for poly(octadecyl acrylate)/C2H4/octadecyl acrylate mixtures at octadecyl acrylate concentrations of 0.0, 15.0, and 45.0 wt %. The cloud-point curve of the poly(octadecyl acrylate)/C2H4 system was relatively flat at 730 bar between 41 and 150°C. The cloud-point curves of 15.0 and 45.0 wt % octadecyl acrylate exhibited positive slopes extending to 35°C and approximately 180 bar. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 372–380, 2002

Phase Behavior of Poly(l-lactide) in Supercritical Mixtures of Dichloromethane and Carbon Dioxide

Phase behavior data are presented for poly(l-lactide) in supercritical mixtures of dichloromethane and carbon dioxide. Cloud point pressures were measured using a variable-volume view cell apparatus as functions of temperature, dichloromethane composition in a mixed solvent, and molecular weight of poly(l-lactide) at the polymer concentration of ≈0.05 mass fraction in solution. This system exhibited the characteristics of lower critical solution temperature phase behavior. As the dichloromethane composition in the mixed solvent increased, the cloud point pressure at a fixed temperature decreased significantly. The cloud point pressure increased linearly with a logarithmic increase of the poly(l-lactide) molecular weight.

Phase behavior of poly( N-isopropylacrylamide) in binary aqueous solutions

In this work, the phase behavior of linear poly( N-isopropylacrylamide) (PNIPA) in water–solvent mixtures was investigated. Several solvents, including low molecular weight alcohols, were selected and phase separation temperatures were determined through cloud point measurements. All the studied systems exhibited the cononsolvency effect, i.e. lower PNIPA compatibility within definite ranges of composition in water-rich mixtures. However, it was first detected that the coexistence of phase separation temperatures—a lower critical solution temperature (LCST) with an upper critical solution temperature (UCST)—at higher solvent concentrations in most systems, depend on the hydrophobic nature of the solvent. The change from a LCST to a UCST was correlated with the competition between polymer–water and polymer–solvent interactions mediated by compositional factors. The effects produced by the different solvents tested were qualitatively compared, considering aspects related to their particular molecular structures, such as the potential to form hydrogen bonds and the implications of the size and shape of non-polar groups for hydrophobic hydration.

Monomer concentration effect on the phase behavior of poly(propyl acrylate) and poly(propyl methacrylate) with supercritical CO2 and C2H4

Experimental cloud-point data to temperature of 186 °C and pressure of ~2,500 bar are presented for ternary mixtures of poly(propyl acrylate)(PPA)-CO2-propyl acrylate (PA) PPA-C2H4-PA and poly(propyl methacrylate) (PPMA)-CO2-propyl methacrylate (PMA) systems. Cloud-point pressures of PPA-CO2-PA system were measured in the temperature range of 32 °C to 175 dgC and to pressures as high as 2,070 bar with PA concentrations of 0.0, 5.0, 11.7 and 30.4 wt%. Adding 34.1 wt% PA to the PPA-CO2 mixture significantly changes the phase behavior. This system changes the pressure-temperature slope of the phase behavior curves from U-LCST region to LCST region as the PA concentration increases. Cloud-point data to 170 °C and 1,400 bar are presented for PPA-C2H4-PA mixtures and with PA concentration of 0.0, 5.7, 15.5 and 22.2 wt%. The cloud-point curve of PPA-C2H4 system shows relatively flat at 730 bar for temperatures between 41 and 150 °C. With 15.5 and 22.2 wt% PA the cloud-point curve exhibits a positive slope that extends to 35 °C and ~180 bar. Also, the ternary PPMA-CO2-PMA system was measured below 186 °C and 2,484 bar, and with cosolvent of 5.2-20.1 wt%. PPMA does not dissolve in pure CO2 to 233 °C and 2,500 bar. Also, when 41.5 wt% PMA is added to the PPMA-CO2 solution, the cloud-point curve shows the typical appearance of a lower critical solution temperature (LCST) boundary.

Miscibility and Phase Structure of Blends of Poly(ethylene oxide) with Poly(3-hydroxybutyrate), Poly(3-hydroxypropionate), and Their Copolymers

The miscibility and phase behavior of poly(ethylene oxide) (PEO) blends with poly(3-hydroxybutyrate) (P(3HB)), poly(3-hydroxypropionate) (P(3HP)), and poly(3-hydroxybutyrate-co-3-hydroxypropionate)s (P(3HB-co-3HP)s) have been investigated by differential scanning calorimetry (DSC) and high-resolution solid-state 13C nuclear magnetic resonance (NMR). Four bacterial P(3HB-co-3HP) samples with 3HP contents of 15, 25, 46, and 76 mol % have been used in order to investigate possible influence of the sequence structure of P(3HB-co-3HP)s on the miscibility and phase behavior of blends. These four P(3HB-co-3HP) samples have different thermal properties and crystallizability depending on the 3HP contents. The DSC thermal behavior of the blends revealed that the blends of PEO with P(3HB), P(3HP), and P(3HB-co-3HP)s were miscible over the whole composition range but the crystallization of blend components followed by phase separation exerted much influence on the phase structure of the blends. The results from solid-state NMR spectroscopy showed that the 50/50 binary blends of P(3HB)/PEO, P(3HB-co-15%3HP)/PEO, P(3HB-co-25%3HP)/PEO, and P(3HP)/PEO were phase-separated due to the presence of crystalline phase but miscible to some extent. Two components in these blend were found to be mixed on a range greater than 30−40 nm, with two crystalline phases and an amorphous phase of miscible two components coexisting.

The effect of hydrogen bonding on the phase behavior of poly(ethylene-co-acrylic acid)-ethylene-cosolvent mixtures at high pressures

Experimental cloud-point data to 260 °C and 2,500 bar are reported to demonstrate the impact of two cosolvents, acetone and methanol, on the phase behavior of polyethylene, poly(ethylene-co-2.4 mol% acrylic acid) (EAA2.4), poly(ethylene-co-3.9 mol% acrylic acid) (EAA3.9), poly(ethylene-co-6.9 mol% acrylic acid) (EAA6.9), and poly(ethylene-co-9.2 mol% acrylic acid) (EAA9.2) in ethylene. In pressure-temperature (P-T) space, the miscibility of EAA copolymers in ethylene decreases significantly with temperature and with increasing acrylic acid content of EAA due to self-association of the acrylic acid segments. Acetone and methanol, both dramatically enlarge the solubility of EAA copolymers due to the hydrogen bonding with acrylic acids in the EAA. At low concentrations, methanol is a better cosolvent than acetone. However, the impact of methanol diminishes rapidly with increasing methanol concentration once all the acrylic acids in the EAA are hydrogen bond with methanol molecules.

Investigation at the chain segmental level of the miscibility of poly(vinyl chloride)/atactic poly(methyl methacrylate) blends

AbstractWe employed high‐resolution 13C cross‐polarization/magic‐angle‐spinning/dipolar‐decoupling NMR spectroscopy to investigate the miscibility and phase behavior of poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) blends. The spin–lattice relaxation times of protons in both the laboratory and rotating frames [T1(H) and T1ρ(H), respectively] were indirectly measured through 13C resonances. The T1(H) results indicate that the blends are homogeneous, at least on a scale of 200–300 Å, confirming the miscibility of the system from a differential scanning calorimetry study in terms of the replacement of the glass‐transition‐temperature feature. The single decay and composition‐dependent T1ρ(H) values for each blend further demonstrate that the spin diffusion among all protons in the blends averages out the whole relaxation process; therefore, the blends are homogeneous on a scale of 18–20 Å. The microcrystallinity of PVC disappears upon blending with PMMA, indicating intimate mixing of the two polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2390–2396, 2001

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

Phase behavior of poly(pyromellitimide)s having (n-alkyloxy)methyl side chains (-CH 2 OC m H 2m+1 , m=4, 6, 8) has been studied by wide angle X-ray scattering, differential scanning calorimetry and 13 C solid-state NMR. While there are no observable transitions in tne 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.

Phase Behavior of Poly(l-lactide) in Supercritical Mixtures of Carbon Dioxide and Chlorodifluoromethane

Phase behavior data are presented for poly(L-lactide) (L-PLA: MW = 2000 g.mol -1 ), a biodegradable polymer, in supercritical solvent mixtures of carbon dioxide (CO 2 ) and chlorodifluoromethane (HCFC-22). Experimental cloud point curves, which were the phase boundaries between single and liquid-liquid phases, were measured using a variable-volume view cell apparatus for various CO 2 compositions up to about 82 mass % (on a polymer-free basis) and for temperatures up to about 393.15 K. The location of the phase transition boundaries between liquid (L) and liquid-vapor (LV) and between liquid-liquid (LL) and liquid-liquid-vapor (LLV) was also investigated as a function of solvent composition for the L-PLA dissolved in mixed solvents of CO 2 and HCFC-22. The cloud point curves exhibited a lower critical solution temperature phase behavior. As the CO 2 content in the solvent mixture increased, the cloud point pressure at a fixed temperature increased significantly. Addition of CO 2 to HCFC-22 caused a lowering of dissolving power of the mixed solvent, A lower critical end point (LCEP) was estimated from the cloud point curve and the L-to-LV and LL-to-LLV phase transition curves. The LCEPs were shifted to lower temperatures as the CO 2 content in the mixed solvent increased.