Comparison of glass transition and interpretation on miscibility in blends of amorphous poly(vinyl methyl ether) with highly crystallizable versus less‐crystallizable polyesters

Various phase behavior of blends of poly(vinyl ether)s with polyesters of two types (highly crystalline and less crystalline with different main‐chains) were examined using differential scanning calorimetry (DSC) and optical microscopy (OM). Effects of varying the main‐chain polarity of the constituent polyesters on the phase behavior of the blends were analyzed. Miscibility in PVME/polyester blends was found only in polyesters with backbone CH₂/CO ratio = 3.5 to 7.0). T_g‐composition relationships for blends of PVME with highly crystalline polyesters (PBA, PHS) were found to differ significantly from those for PVME blends with less‐crystalline polyesters (PTA, PEAz). Crystallinity of highly crystalline polyester constituents in blends caused significant asymmetry in the T_g‐composition relationships, and induced positive deviation of blends' T_g above linearity; on the other hand, blends of PVME with less crystalline polyesters exhibit typical Fox or Gordon‐Taylor types of relationships. The χ parameters for the miscible blends were found to range from ?0.17 to ?0.33, reflecting generally weak interactions. Phase behavior was analyzed and compared among blends of PVME with rapidly crystallizing vs. less‐crystallizing polyesters, respectively. Effects of polyesters' crystallinity and structures on phase behavior of PVME/polyester blends are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2899–2911, 2007     

Synthesis and characterization of wholly aromatic polyesters derived from 1-phenyl-2,6-naphthalene-dicarboxylic acid and aromatic diols

A series of new wholly aromatic polyesters was synthesized by melt polycondensation of 1-phenyl-2,6-naphthalenedicarboxylic acid (PNDA) and diacetates of various aromatic diols. The aromatic diols studied are hydroquinone (HQ), methylhydroquinone (MHQ), phenylhydroquinone (PHQ), (α-phenylisopropyl)hydroquinone (PIHQ), 2,6-naphthalenediol (2,6-ND), 1,4-naphthalenediol (1,4-ND), and 4,4′-biphenol (BP). These polyesters were characterized for their crystallinity, glass transition temperature (T_g), melting temperature (T_m), liquid crystallinity, and thermal stability. In general, crystallinity of the polyesters are very low and the T_g values of the polyesters range from 150 to 172°C depending on the structure of aromatic diols. All of the polymers formed nematic phases above their T_m or T_g. The polyesters derived from PHQ and PIHQ are soluble in chlorinated hydrocarbon solvents. The initial decomposition temperatures of the polyesters are above 400°C under N₂ atmosphere. © 1996 John Wiley & Sons, Inc.     

The phase behavior of tetramethyl bisphenol-A polyarylate/aliphatic polyester blends

The phase behavior of blends of tetramethyl bisphenol-A polyarylate (TMPAr) with various linear aliphatic polyesters characterized by the ratio of aliphatic carbons to ester groups in the repeating unit, CH₂/COO = 3 ∼ 9, was examined by differential scanning calorimetry and dynamic mechanical analysis. TMPAr/aliphatic polyester blends prepared by solvent casting were found to be miscible when the CH₂/COO ratio of aliphatic polyesters was larger than 4 and up to 9. The thermodynamic interaction parameter, B for the miscible blends was determined by the analysis of the depression of the melting point of polyester using the Hoffman-Weeks method. From the analysis of the heat of mixing data using a binary interaction model, it was concluded that strong unfavorable intramolecular interaction exists between the  CH₂ and  COO units in aliphatic polyesters and that four substituted methyl groups produces more favorable effects on the miscibility TMPAr with aliphatic polyesters. © 1998 John Wiley & Sons, Inc. J Polym Sci 36 : 201–212, 1998     

Which Polyesters Can Mimic Polyethylene?

Self‐metathesis of erucic acid by [(PCy₃)(η‐C‐C₃H₄N₂Mes₂)Cl₂Ru = CHPh] (Grubbs second‐ generation catalyst) followed by catalytic hydrogenation and purification via the ester yields 1,26‐hexacosanedioate (>99% purity). Polyesterification with 1,26‐hexacosanediol, generated from the diester, affords polyester‐26,26, which features a T_m of 114 °C (T_c = 92 °C, ΔH_m = 160 J g⁻¹). Ultralong‐chain model polyesters‐38,23 (T_m = 109 °C) and −44,23 (T_m = 111 °C), generated via multistep procedures including acyclic diene metathesis polymerization, underline that melting points of such aliphatic polyesters do not gradually increase with methylene sequence chain length. Available data suggest that to mimic linear polyethylenes thermal properties, even longer sequences, amounting to at least four times a fatty acid chain, fully incorporated in a linear fashion are required.     

Linear polyesters containing isocyanurate rings

Two series of linear polyesters containing isocyanurate rings have been prepared to determine the effect of structural variations on thermal and solubility properties. The polyesters were prepared by the polycondensation reaction of isocyanurate containing difunctional acid and ester monomers with linear diols. The substituent on the isocyanurate ring and the length of the acid side chain have been shown to have considerable effect on the glass transition temperature T_g. Different solubility properties were observed for the series of polyesters in which the pendant substituent was ? C₆H₅ and the acid side-chain was ? CH₂CO₂H. These polymers were insoluble in THF, and the polyester prepared from 1,6-hexanediol was also insoluble in chloroform. Thermal gravimetric analysis (TGA) indicated that structural differences had no significant effect on the thermal stability of these linear polyesters.     

Synthesis and characterization of aliphatic unsaturated polyesters from trans-4-octene-1,8-dioic and trans-3-hexene-1,6-dioic acids

The influence of the double bond on the thermodynamic parameters, T_m, ΔH_m and ΔS_m of some unsaturated aliphatic polyesters has been found to depend on the number of —CH₂— groups separating the double bond from the ester linkage. Thus, T_m's of the polyesters derived from trans-4-octene-1,8-dioic acid (OD) are lower than those for the corresponding saturated polyesters; no such effect has been observed by comparing T_m's of polyesters derived from trans-3-hexene-1,6-dioic acid (HD) and adipic acid respectively. X-ray investigation has shown, for polyesters of the OD series, the presence of the two polymorphic forms.     

Novel initiators for oxazoline polymerization: generation of polydiacetylene-polyoxazoline networks

A series of bolaform polyoxazolines (POZO) with 1,3-diacetylene cores ((POZO)_m-(CH₂)_n-C≡C-C≡C-(CH₂)_n-(POZO)_m) were synthesized by the living polymerization of 2-methyl-1,3-oxazolines initiated by triflate esters derived from bis(ω-hydroxyalkyl)-1,3-diacetylenes. The chain length of the alkylspacers within the diacetylene core as well as the length of the attached polyoxazoline chains was varied between n = 1 and 4; m = 5, 10 and 15. The thermally induced 1,4-addition process yielding polydiacetylenes (PDA) was studied leading to highly conjugated POZO-PDA hybrid materials.     

Morphology and Temperature Phase Transitions in α,ω-Alkanediols with Different Chain Lengths

A comparative analysis of phase transitions in diols with various chain lengths [(CH₂)₄₄(OH)₂ and (CH₂)₂₂(OH)₂] and changes in their absorption spectra with temperature have been investigated by DSC and FTIR. Analysis of the DSC data has led to the conclusion that the low-temperature phase transition of (CH₂)₂₂(OH)₂ in a solid state (T_s-s = 367.1 K) is a phase transition of the first order, while the high-temperature phase transition (T_m = 376.3 K) is of the second order, i.e., a transition of the order-disorder type. Splitting of the IR absorption bands into doublets at 720-730 cm⁻¹ and 1463-1473 cm⁻¹ indicates that crystalline subcells in the lamellae of both diols are orthorhombic lattices with the parameters typical of hydrocarbons. IR spectra showed that at the phase transition temperature T_s-s transformation of an orthorhombic subcell into a hexagonal one occurs. This type of molecular chain packing remains the same up to the melting temperature T_m. In a (CH₂)₄₄(OH)₂ diol, the ortho-hexagonal subcell transition occurs only at the melting temperature (390.0 K). The wide IR band in the region from 3000 cm⁻¹ to 3600 cm⁻¹ shows that end hydroxyl groups of diol molecules form, on the surfaces of lamellar crystals, long (polymer) regular sequences consisting of intermolecular hydrogen bonds.     

Blends of different linear polyamides with hyperbranched aromatic AB2 and A2 + B3 polyesters

To explore the possible applications of hyperbranched polymers for modifying linear polyamides, two hyperbranched aromatic polyesters characterized as high T_g polymers possessing phenolic end groups were used in melt mixing with partly aromatic polyamide and commercially available aliphatic polyamide‐6, respectively. Different amounts of both hyperbranched polyesters (from 1 wt % up to 20 wt %) were added to the polyamides, and the influence of these hyperbranched polyesters on the properties of the polyamides was investigated. The hyperbranched polyester based on an AB₂ approach was found to be the most effective modifier. A significant increase of the glass transition temperature of the final blend was detected. However, a remarkable reduction of crystallinity as well as complex melt viscosity of those blends was also observed. The use of an A₂+B₃ hyperbranched polyester as melt modifier for the polyamides was less effective for changing the thermal properties, and the complex melt viscosity of the final material increased since heterogeneous blends were formed. In contrast to that, generally, the addition of the AB₂ hyperbranched polyester to the polyamides resulted in homogeneous blends with improved T_g and processability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3558–3572, 2009     

Reversible Transformation between Amorphous and Crystalline States of Unsaturated Polyesters by Cis–Trans Isomerization

An aliphatic polyester has been prepared from ethylene oxide and maleic anhydride that undergoes reversible transformation between amorphous (T_g=18 °C) and crystalline (T_m=124 °C) states through cis–trans isomerization of the C=C bonds in the polymer backbone without any change in either the molecular weight or dispersity of the polymer. A similar transformation was also observed in chiral unsaturated polyesters formed from enantiopure terminal epoxides, such as epichlorohydrin, phenyl glycidyl ether, and (2,3‐epoxypropyl)benzene. These unsaturated polyesters with 100 % E‐configuration in the crystalline state were prepared by quantitative isomerization of their Z‐configuration analogues in the presence of a catalytic amount of diethylamine, while in the presence of benzophenone, irradiation with 365 nm UV light resulted in the transformation of about 30 % trans‐alkene to cis‐maleate form, thereby affording amorphous polyesters.     

Ab initio molecular dynamics study for C–Br dissociation within BrH<Subscript>2</Subscript>C–C≡C<Subscript>(ads)</Subscript> adsorbed on an Ag(111) surface: a short-time Fourier transform approach

The reaction dynamics for C–Br dissociation within BrH₂C–C≡CH_(ads) adsorbed on an Ag(111) surface has been investigated by combining density functional theory-based molecular dynamics simulations with short-time Fourier transform (STFT) analysis of the dipole moment autocorrelation function. Two possible reaction pathways for C–Br scission within BrH₂C–C≡CH_(ads) have been proposed on the basis of different initial structural models. Firstly, the initial perpendicular orientation of adsorbed BrH₂C–C≡CH_(ads) with a stronger C–Br bond will undergo dynamic rotation leading to the final parallel orientation of BrH₂C–C≡CH_(ads) to cause the C–Br scission, namely, an indirect dissociation pathway. Secondly, the initial parallel orientation of adsorbed BrH₂C–C≡C_(ads) with a weaker C–Br bond will directly cause the C–Br scission within BrH₂C–C≡CH_(ads), namely, a direct dissociation pathway. To further investigate the evolution of different vibrational modes of BrH₂C–C≡CH_(ads) along these two reaction pathways, the STFT analysis is performed to illustrate that the infrared (IR) active peaks of BrH₂C–C≡CH_(ads) such as vCH₂ [2956 cm^?1(s) and 3020 cm^?1(as)], v≡CH (3320 cm^?1) and vC≡C (2150 cm^?1) gradually vanish as the rupture of C–Br bond occurs and then the resulting IR active peaks such as C=C=C (1812 cm^?1), ω-CH₂ (780 cm^?1) and δ-CH (894 cm^?1) appear due to the formation of H₂C=C=CH_(ads) which are in a good agreement with experimental reflection adsorption infrared spectrum (RAIRS) at temperatures of 110 and 200 K, respectively. Finally, the total energy profiles indicate that the reaction barriers for the scission of C–Br within BrH₂C–C≡CH_(ads) along both direct and indirect dissociation pathways are very close due to a similar rupture of C–Br bond leading to a similar transition state.     

Fully aromatic thermotropic liquid crystalline homopolyesters of 3,4′-benzophenone dicarboxylic acid

A series of fully aromatic, thermotropic homopolyesters, derived from 3,4′-benzophenone dicarboxylic acid and various aromatic diols, was prepared by the melt polycondensation method and examined for thermotropic behavior by a variety of experimental techniques. The aromatic diols used in the study were hydroquinone, 2,6-, 1,4-, 1,5-, 2,3-, and 2,7-naphthalenediol isomers. All of the homopolyesters of 3,4′-benzophenone dicarboxylic acid with aromatic diols (except that with 2,7-naphthalenediol) formed a nematic LC phase in the melt. They had the glass transition temperatures (T_g) in the range of 133–164°C, the melting transitions (T_m) in the range 305–360°C and the high thermal stabilities (T_d) in the range of 410–483°C. The 2,6-naphthalenediol based homopolymer had the highest T_m (360°C) and the 2,3-naphthalenediol based homopolymer had the lowest T_m (305°C) among all of the homopolymers of naphthalenediol isomers. © 1994 John Wiley & Sons, Inc.     

Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity

Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC-based pincer ligands—which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC-n)(C₂H₄)][BAr^F₄] (n=12, 14, 16; Ar^F=3,5-(CF₃)₂C₆H₃)—have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr’ (Ar’=3,5-tBu₂C₆H₃) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3-enynes by C−C bond reductive elimination through the annulus of the ancillary ligand. The intermediates are formed with orthogonal regioselectivity, with E-alkenyl complexes derived from HC≡CtBu and gem-alkenyl complexes derived from HC≡CAr’, and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HC≡CtBu, E-tBuC≡CCH=CHtBu is produced via direct reductive elimination from the corresponding rhodium(III) alkynyl E-alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductive elimination of Ar'C≡CC(=CH₂)Ar’ is encumbered relative to head-to-head coupling of HC≡CAr’ and it is only with the largest macrocyclic ligand studied that the two processes are competitive. These results showcase how macrocyclic ligands can be used to interrogate the mechanism and tune the outcome of terminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC-Me)(C₂H₄)][BAr^F₄] and solvent effects.     

Synthesis and properties of thermotropic liquid-crystalline polyesters containing 9,10-diphenylanthracene moiety in the main chain

We synthesized thermotropic liquid-crystalline polyesters in which 9,10-diphenylanthracene moieties are incorporated into the main chain type of polyester forming the chiral smectic C (Sm C*). The polymers were prepared by the isopropyltitanate-catalyzed reaction of biphenyldicarboxylic acid and the corresponding diols, with different ratios of diol of 9,10-diphenylanthracene moiety to the alkane diols (1, 5, and 10 mol %) under nitrogen atmosphere. The polymers exhibited thermotropic liquid crystals despite the presence of a bulky diphenylanthracene moiety in the main chain. The circular dichroism spectra revealed that a Sm C* phase was formed in the polymer with 1 mol % of anthracene moiety, although only an Sm A phase was formed in the other polymers. This is the first example of a Sm C* polyester containing a diphenylanthracene moiety in the main chain. Furthermore, we measured the optical properties of the polymers and found that they exhibited very high fluorescent efficiency. The fluorescence spectra of the thin film differed from that of a CH₂Cl₂ solution.     

Unsymmetrically Substituted Aliphatic Diacetylenes Containing Amine Functionalities

A one-pot reaction which combines the Cadiot-Chodkiewicz coupling reaction with the Gabriel synthesis of primary amines is evaluated as a means for the synthesis of unsymmetrically disubstituted aminodiacetylenes of the type CH₂-(CH₂)_n-C≡C-C≡C-CH₂-NH₂ (n=2,3,4,5).     

The template synthesis of mesoporous silicas with the thiourea functional group

Mono- and bifunctional mesoporous silicas containing the thiourea group ≡Si(CH₂)₃NHC(S)NHC₂H₅ or thiourea and various nitrogen-containing groups [≡Si(CH₂)₃NH₂, ≡Si(CH₂)₃NH(CH₂)₂NH₂, or {≡Si(CH₂)₃}₂NH], respectively, in the surface layer were prepared by template syntheses with cetylpyridinium chloride as a template. The synthesized samples had well-developed porous structures (S _sp = 750–1150 m²/g, V _c = 0.51–0.72 cm³/g, and d = 2.4–3.5 nm) and high functional group contents (1.0–2.0 mmol/g). Hydrothermal treatment of the mesophases in a mother liquor at 80°C (24 h) improved the structure-adsorption characteristics of the functionalized mesoporous silicas.     

Determination of interactions between aryl polyesters and poly(ether imide) via glass transition temperatures of separated phases in immiscible blends

Phase behavior in domains of immiscible blends of poly(pentamethylene terephthalate)/poly(ether imide) (PPT/PEI) and poly(hexamethylene terephthalate)/poly(ether imide) (PHT/PEI) were investigated using differential scanning calorimetry (DSC). The measured glass transition temperature (T _g) reveals that aryl polyesters dissolve more in the PEI-rich phase than the PEI does in the aryl polyester-rich phase, for both PPT/PEI and PHT/PEI systems. Additionally, optical microscopy supports the conclusion that PPT (or PHT) dissolves more in the PEI-rich phase than PEI does in the PPT-rich (or PHT-rich) phase in the aryl polyester/PEI blends. Furthermore, the Flory–Huggins interaction parameters (χ₁₂) for the PPT/PEI and the PHT/PEI blends were calculated to be 0.12 and 0.17, respectively. For the blend systems comprising of PEI and homologous aryl polyesters, the value of χ₁₂ exhibits a trend of variation with respect to structure of aryl polyesters. For the PPT/PEI and PHT/PEI blends, investigated in this study, value of the polymer–polymer interaction parameter (χ₁₂) between the aryl polyester and the PEI was found to be positive, which increases with the number of methylene moieties in the repeating unit of the aryl polyester, ultimately resulting in phase separation observed.     

Synthesis,Redox and Optical Properties of Low‐Bandgap Platinum(II) Polyynes with 9‐Dicyanomethylene‐Substituted Fluorene Acceptors

In view of the strong electron‐withdrawing nature of the cyano substituent, a blue donor/acceptor‐type organometallic polymer (trans‐[—Pt(PBu₃)₂—C≡C—R—C≡C—]_n (R = 9‐dicyanomethylenefluorene‐2,7‐diyl)) was prepared in good yield by CuI‐catalyzed polymerization involving the dehydrohalogenating coupling of trans‐[Pt(PBu₃)₂Cl₂] and H—C≡C—R—C≡C—H. The thermal, redox and photoconducting properties of the polymer are reported. Electronic absorption studies indicate that it has a bandgap of 1.58 eV which is the lowest among any of the metal polyyne polymers reported in the literature. The derivatization of the polymer backbone with electron deficient dicyano‐substituted electron acceptor in the side chain is found to be effective to tune the bandgap of this class of materials while maintaining their solubility and processability.     

Papain catalyzed estehification of alanine by alcohols and diols

Papain catalyzed esterification of Boc-Ala-OH with various alcohols and diols under biphasic conditions was investigated. Long-chain diols HO(CH₂)nOH gave good yields of esterification up to n=10 whereas the homologous alcohols C_nH_2n+1OH condensed well only for n = 2, 4, 6. Esterification with functionnalized primary alcohols is also described.