The synthetic problems associated with melt polymerizations to form homopolyesters of isosorbide (ISB) and rigid diacids could potentially be solved by using catalyst systems with acetic anhydride (Ac 2 O). A catalyst consisting of dibutyltin oxide, germanium oxide, and Ac 2 O exhibited excellent performance characteristics in syntheses of a highmolecular-weight homopolyester of ISB and cis/trans-1,4-cyclohexanedicarboxylic acid (CHDA), also referred to as poly(isosorbide cis/trans-1,4-cyclohexanedicarboxylate) (PICD). The acetylation of ISB using Ac 2 O during esterification decreased the steric hindrance of ISB and accelerated the chain growth of PICD. Gel permeation chromatography data confirmed the formation of a highmolecular-weight PICD (71 100 weight-average molecular weight and 14 300 number-average molecular weight) using 0.02 mol of Ac 2 O. The glass transition temperature of PICD was almost 131°C at 0.02 mol of Ac 2 O and decreased with increasing amounts of Ac 2 O due to the breaking of the rigid ring of ISB at higher concentrations of Ac 2 O. The structure of opened ring ISB was confirmed using two-dimensional nuclear magnetic resonance (NMR) and distortionless enhancement by polarization transfer NMR. ■ INTRODUCTION1,4:3,6-Dianhydrohexitol, a biobased material that can be derived from biomass such as wheat, sugar, and corn, has been used in various polymer preparations, pharmaceuticals, and cosmetics. 1−6 It has three stereoisomers which are isosorbide (ISB), isomannide, and isoidide, respectively obtained from glucose, mannose, and fructose. 7,8 Among its three stereoisomers, ISB is the most easily accessible and affordable monomer for polymer synthesis 8,9 and is one of the most favorable candidates for renewable monomers used in addressing environmental issues and the depletion of petroleum resources. 10 When ISB is used as a monomer of polyester, the resulting polyester is not only environmentally desirable, but also has superior thermal and optical properties due to its molecular rigidity and the chirality of its asymmetrical hydroxyl groups. Several reports describe attempts to synthesize various polymers containing ISB, including polyesters, 11−24 polyurethanes, 25−29 epoxy, 30,31 polyamides, 32,33 polycarbonates, and liquid crystalline polymers. 34−38 In homopolyesters made with ISB, the incorporation of terephthalic acid (TPA), an aromatic diacid, results in materials with high thermal stability and desirable mechanical properties. However, the formation of a homogeneous system during polymerization is problematic because both TPA and ISB are solid powders and TPA does not dissolve in ISB melts. 13 Furthermore, the low reactivity and volatility of ISB make it difficult to obtain a high-molecular weight polymer. Previous studies by Quintana et al. 10 describe syntheses of polyterephthalates from ethylene glycol (EG), 1,4-cyclohexanedimethanol (CHDM), and ISB. They reported the number-average molecular weights (M n ) and weight-average molecular weights (M w ) of PE(CIs)T terpolyester conta...

Poly(ε‐caprolactone) (PCL) nanocomposites were prepared using two different types of organically modified nanosilicates by melt intercalation with an internal mixer. Dynamic mechanical analysis revealed possible structural changes in the nanocomposites even during the small deformation occurring during shear oscillatory measurements, as evidenced by a V‐shaped modulus change in the plot of the dynamic storage modulus as a function of stepwise increased temperature. X‐ray diffraction patterns were recorded at different simulated temperatures during the various stages of dynamic measurements. The X‐ray data indicate that the structural changes can be ascribed to a further intercalation of the PCL matrix chains into the silicate layers. This further intercalation is a consequence of the heat treatment during the dynamic mechanical measurements. Furthermore, there is a considerable vertical shift in addition to the horizontal shift in the higher temperature regime, which allows the mapping of a master curve through the application of the time‐temperature superposition principle to the dynamic storage and the loss modulus data obtained at various isothermal temperatures. The present study is also concerned with the relative molecular mobility of both PCL nanocomposites in the given experimental conditions considering the Williams‐Landel‐Ferry (WLF) equation and the Arrhenius relationship between the horizontal shift factor and the activation energy of flow. Moreover, the extent of the vertical shift as a function of temperature made it possible to determine the apparent activation energy of the further intercalation of PCL into the silicate layers. This intercalation is caused by the additional exposure to heat during the dynamic mechanical measurements after mixing, which led to a comparison of the relative diffusivity of the PCL matrix in the two nanocomposites.Dynamic shear storage moduli G′ of PCLOC25A and PCLOC30B as a function of temperature with increase increments of 20 °C from 60 to 260 °C. The G′ data were obtained from isothermal frequency sweep G′(ω) data at ω = 1 rad · s−1 at the corresponding temperatures.magnified imageDynamic shear storage moduli G′ of PCLOC25A and PCLOC30B as a function of temperature with increase increments of 20 °C from 60 to 260 °C. The G′ data were obtained from isothermal frequency sweep G′(ω) data at ω = 1 rad · s−1 at the corresponding temperatures.

IntroductionIn the past few decades, layered silicate-based polymer nanocomposites have attracted considerable attention because of their dramatically increased strength, modulus, thermal resistance and gas permeability barrier, which is obtained with a much lower silicate content than that used in conventional filled polymer composites. [1] Layered silicates have layers with thicknesses on the order of 1 nm and have very high aspect ratios (e.g., 10-1 000), and interlayer spacings between the stacked layers of about 1 nm. [2] The distinctive features of the layered silicates result in the nanocomposites having two possible structures, namely intercalated or exfoliated structures. The intercalated nanocomposites show regularly alternating silicate and polymer layers with a repeat distance of Full PaperPoly(e-caprolactone) nanocomposites, PCLOC25A and PCLOC30B, with organoclays (OCs) having nonpolar and polar organic modifiers, respectively, were prepared by the melt mixing method and additional heat treatment. WXRD analysis revealed that both nanocomposites were exfoliated, irrespective of the OC polarity. However, WXRD failed to show the degree of exfoliation of the nanocomposites, because the d 001 peaks disappeared. Thus, dynamic mechanical analysis (DMA) was carried out to compare the degree of exfoliation of the PCL nanocomposites. From DMA, PCLOC30B showed higher elasticity, storage moduli, viscosity, and activation energy than PCLOC25A, indicating that PCLOC30B had a more exfoliated structure than PCLOC25A. This is due to the polar interaction in PCLOC30B, as verified by the plots of a T versus temperature. Thus, it was confirmed that DMA provides an alternative approach to evaluating the degree of exfoliation of nanocomposites. 627 a few nanometers, whereas the individual layers in the exfoliated nanocomposites are irregularly delaminated and dispersed in a continuous polymer matrix. [3] Such structural differences play a key role in the enhancement of the nanocomposite properties. Exfoliated nanocomposites generally have superior mechanical properties to intercalated nanocomposites, because of the larger surface area that exists between the reinforcement phase and the polymer matrix. [4] Giannelis et al. reported that the thermodynamically stable equilibrium states of the nanocomposites, such as the intercalated and exfoliated systems described above, are dependent on various entropic and enthalpic factors. [5] Since the total entropy change in the system was small, the change in enthalpic factors such as the intermolecular interactions determined the structure of the nanocomposites. [5] Thus, the layered silicate structure depended on the establishment of very favorable polymer-surface interactions to overcome the penalty of the confinement condition, and specific interactions, driven by polar interactions or hydrogen bonding, played a significant role in promoting the dispersion of the layered silicate. [6,7] Finally, the silicate structure, depending on polymer-surface interactions, can have influence...