Crystallization kinetics and morphology of the mesomorphic form of syndiotactic polypropylene

For the first time the kinetics of formation of syndiotactic polypropylene mesophase close to 0 °C through differential scanning calorimetry has been investigated. The calorimetric data have been analyzed through the well‐known Avrami analysis. We have obtained Avrami coefficients less or at most equal to 2, which are likely to indicate a nearly bidimensionality of the crystallites. The morphology of the mesophase, not known up to now, has been examined through atomic force microscopy (AFM): lamellar structures have been observed. The fractal dimension of the AFM images has been evaluated through the box counting method. It resulted about 2, in a very good agreement with the calculated Avrami coefficients. An infrared and diffractometer analysis on samples kept for increasing times at 0 °C has also been performed to confirm the calorimetric data. The experimental results allow one to better clarify the kinetics of mesophase‐formation. It has been found that a time of 3 h at 0 °C is actually necessary for the complete crystallization of the trans‐planar mesophase, a longer time is needed to stabilize the mesophase domains when the sample is extracted from 0 °C at room temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 936–944, 2007     

Equilibrium thermal behavior and morphology of organophilic montmorillonite/poly(ε‐caprolactone) nanocomposites

With differential scanning calorimetry, we have demonstrated a peculiar behavior under equilibrium conditions of neat poly(ε‐caprolactone) and its organophilic montmorillonite nanocomposites. In particular, in the determination of the equilibrium melting temperature by the extrapolation of the data of the melting temperature (T_m) versus the crystallization temperature (T_c), a bimodal trend has been observed. At the lower T_c's, the data of T_m follow a constant trend, whereas at the higher ones, the usual increasing trend has been obtained. Morphological observations by atomic force microscopy (AFM) have provided evidence of two different crystalline morphologies for the lower and higher T_c ranges. Moreover, AFM has shown that the thermal treatments strongly influence the clay dispersion in the polymer matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 22–32, 2006     

Solvent induced polymorphism of quenched syndiotactic polypropylene in different liquids

The solvent induced crystallization phenomenon (SINC) was studied for syndiotactic polypropylene quenched from the melt at 0 °C and kept at this temperature a for long time. In these conditions a mesophase having the chains in trans-planar conformation was formed. The interaction polymer-solvent with liquids having different solubility parameters, derived by both the swelling and the weight uptake, considerably varies among the different liquids, showing a maximum corresponding to carbon tetrachloride ('=8.6). A smaller maximum was found for chloroform ('=9.3). These two maxima were attributed to interaction either with the amorphous phase or with the trans-planar mesophase. Infrared analysis showed that all the liquids induce a conformational transition from trans-planar to helix, and only a small residual fraction of chains in trans-planar conformation was detected for the samples immersed in the liquids and vacuum dried for many hours. The X-ray analysis showed that the quenched sample undergoes in the solvents a complex transformation, partially crystallizing into the helical form I and partially into the helical form II. All the liquids induced the same transformation, in spite of very different levels of interaction.     

Practical generation of 3,5‐dimethoxybenzyllithium: application to the synthesis of 5‐substituted‐resorcinols

Reductive lithiation of 3,5‐dimethoxybenzyl methyl ether was successfully performed with lithium wire and a catalytic amount of naphthalene in dry tetrahydrofuran at ?15°C, leading to the quantitative generation of 3,5‐dimethoxybenzyllithium. This organometallic compound, which can be stored for at least 24 h, was trapped with a variety of different electrophiles, including, besides aldehydes, non‐functionalized and functionalized alkyl halides and an epoxide. Accordingly, it is a useful intermediate in the synthesis of 5‐substituted natural and non‐natural resorcinols. Copyright © 2003 John Wiley & Sons, Ltd.     

Transport properties of mesomorphic syndiotactic polystyrene

Amorphous syndiotactic polystyrene (sPS) films were annealed at 110° and 115°C for 24 h. The annealing at the higher temperature produced the mesomorphic form of sPS, characterized by conformational order, as shown both by the presence of the zigzag band in the infrared spectrum and by the presence of characteristic peaks in the x-ray diffractogram. The crystalline form was not formed at the investigated temperatures. Differential scanning calorimetry of the mesomorphic sample shows that the transformation of the mesophase into the crystalline phase occurs during the heating run. The transport properties of dichloromethane show that the mesophase is impermeable to the vapors at low activity and becomes permeable at higher activities. At low activity it is therefore possible to derive the fraction of impermeable phase, which corresponds to the fraction of mesophase. This fraction was about 50%.     

Liquid–liquid equlibria of polyethylene glycol (PEG) 400 and CO2 with common organic solvents

Liquid polyethylene glycol (PEG), in combination with carbon dioxide (CO₂) and common organic solvents, enables the coupling of a homogeneous reaction with a heterogeneous separation. This is important for the application of homogenous catalysts, which offer superior reactivity but are difficult to separate and recycle. CO₂ can act as a miscibility switch to shift the system from homogeneous at atmospheric conditions to heterogeneous under CO₂ pressure. This allows for extraction of the products into the organic solvent phase and immobilization of the homogeneous catalyst in the PEG phase. This work examines the phase behavior of PEG and carbon dioxide with 1,4-dioxane and acetonitrile at 25 and 40 °C and pressures ranging from 5 to 8 MPa. The experimental data are compared to theoretical calculations using the Sanchez–Lacombe equation of state.     

Cubature rule associated with a discrete blending sum of quadratic spline quasi-interpolants

A new cubature rule for a parallelepiped domain is defined by integrating a discrete blending sum of C¹ quadratic spline quasi-interpolants in one and two variables. We give the weights and the nodes of this cubature rule and we study the associated error estimates for smooth functions. We compare our method with cubature rules based on the tensor products of spline quadratures and classical composite Simpson’s rules.