Selectivity in Bromination of Aromatic Substrates by Molecular Bromine in the Presence of Reusable Zeolites

Bromination of aromatic substrates, namely, toluene, phenol, phenyl acetate and chlorobenzene has resulted predominantly in the formation of para bromo derivatives. While solution bromination of phenyl acetate and chlorobenzene is very slow, zeolite-mediated bromination proceeds smoothly, reflecting the catalytic activity of zeolite in this reaction. A suitable mechanism involving assistance from the sodium ion in generating the active brominating species is proposed. The paraselective bromination of these substrates is also compared with that of nitration and the observed differences are suitably explained.     

Melt characterization of ultra high molecular weight polyethylene using squeeze flow

A method for determining the melt viscosity and molecular weight of ultra high molecular weight polyethylene (UHMWPE) is described. The method, based on squeeze flow, was used to characterize seventeen UHM W-PE samples varying in molecular weight from 0.6 × 10⁶ to 5.1 × 10⁶ and in viscosity from 2.9 × 10⁶ to 3.4 × 10⁹ poise. A correlation between melt viscosity and molecular weight was demonstrated, but the reliability of a molecular weight determination decreased somewhat as molecular weight increased. As a predictor of melt processability, the method provides the speed and simplicity heretofore lacking in UHMW-PE characterization by solution viscosity while retaining high reproducibility.     

Selection of Polyacrylonitrile Fibre Modification Parameters

The studies conducted show that: the efficiency of modification of as-spun PAN fibre is higher than with modification of the conditioned fibre; the fibres obtained can be recommended for fabrication of fire-resistant fabrics for work clothing.     

Oxygen permeation of blends of copolymers of siloxanes and poly(methylmethacrylate)

A series of low molecular weight (≈40000) copolymers of methylmethacrylate (MMA) and 4-(methacryloyloxy)butylpentamethyldisiloxane (MBPD) have been synthesized by free radical polymerization in dimethylformamide solution. The microstructure, as derived from ¹³C NMR spectra, indicates that the copolymers are about 80% syndiotactic with an overall random distribution of mers. At room temperature, copolymers rich in MMA are clear, rigid glasses but become liquid at high MBPD content. Blends of these copolymers with PMMA are all heterogeneous with visible phase separation over most of the composition range. Differential scanning calorimetry studies show the presence of two T_g's when the relative concentration of PMMA to copolymer is high. Blends of two co-polymers of similar siloxane content produce clear films with no indication of phase separation. The permeability to oxygen at 25°C increases from 0.20 for pure PMMA to 3.0 (fmol/m·s·Pa.) for a copolymer of MMA/MBPD of the mole ratio of 3:1. Evaluation of the permeation behaviors of the blends suggests that blends rich in siloxane exist as a layered structure with the PMMA rich component dominating the observed permeability.     

Melting points of synthetic wax esters

Saturated, monoenoic and dienoic wax esters, C₂₆−C₄₀, have been synthesized from even-numbered fatty alcohols and acids. In homologous series of saturated esters, the increments of melting points follow a regular trend except for those esters which have an acid moiety two carbon atoms shorter than the alcohol moiety. These wax esters have melting points higher than interpolation would predict. Monoenoic wax esters with the double bond in the alcohol chain have melting points about 10 C higher than their isomers with the double bond in the acid chain.     

Studies of polymer–polymer solubility using a two-dimensional solubility parameter approach

The two-dimensional solubility parameter approach has been applied to the prediction of solubility of one polymer in another. The solubility parameters of a number of polymers have been calculated and the second dimension shown to improve the agreement between the calculated solubility and that measured using a ternary solution technique. The method proved most useful for predicting the effect of small structural modifications on solubility, and several examples of changing solubility, monitored by calculations and measurements, are given. Structural modifications included copolymer ratio variations and substitutions to affect polymer density or reduce polarity of functional groups. The effects of temperature and molecular weight on solubility are discussed in terms of regular solution theory, which could not account for the decrease in solubilities with increased temperature observed for several polymer–polymer systems.     

Effect of crystallization and interface formation mechanism on mechanical properties of film‐insert injection‐molded poly(propylene) (PP) film/PP substrate

A previous study has shown that the adhesion between the film and substrate of film‐insert injection‐molded poly(propylene) (PP) film/PP substrate was evident with the increases in barrel temperature and injection holding pressure. In this second part of the research work, the crystallinity at the interfacial region (i.e., region between the film and the injected substrate) was extensively studied using FTIR imaging, polarized light microscopy, and DSC in an attempt to determine the level of influence that crystallinity has on the interface and bulk mechanical properties. Consequently, a more thorough and clearer picture of the influence of the inserted film on the interfacial crystallinity and subsequently the substrate mechanical properties, such as peel strength and impact strength, has been revealed. The initial proposition that crystallinity could enhance film–substrate interfacial bonding has been confirmed, judging from the higher peel strength with increasing crystallinity at the interfacial region. Nevertheless, the change in crystallinity was not only confined to the interfacial region. With the film acting as heat‐transfer inhibitor between the injected resin and the mold wall, the total crystal structure of the substrate was substantially altered, which subsequently affected the bulk mechanical properties. The lower impact strength of film‐insert injection‐molded samples compared to that of samples without film inserts provided evidence of how the film could impart inferior properties to the substrate. The difference in cooling rate between the substrate and film might also cause other defects such as warpage and/or residual stress build‐up within the product. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 294–301, 2005     

Sterols,aliphatic hydrocarbons,and fatty acids of a nonphotosynthetic diatom,Nitzschia alba

The unsaponifiable lipids and total fatty acids of a nonphotosynthetic diatom,Nitzschia alba, have been examined. The major fatty acids were found to be 14∶0, 16∶0, 18∶1, and 20∶5; small amounts of 15∶0, 16∶1, 18∶0, 18∶2, 18∶3, and 20∶4 acids also were present. The unsaponifiable lipids consisted mostly of sterols, with only traces (<0.1%) of hydrocarbons (chiefly C₁₆, C₁₈, and C₂₈ normal olefins). The sterols contained brassicasterol (major) and clionasterol (minor), as well as traces of an unidentified sterol; clionasterol was present only in glycosidically bound form.     

Constrained regression in chemical engineering practice

Absolute equality constraints in multiple regression are shown to introduce only minor modifications in the normal equations by a subset of the regression parameters. It is essential that these are ordered such that the subset is observable through the constraints. The constraints are shown to give greater residuals about the regression, but the precision in the parameter estimation is improved.In general power function curve fitting, a quadratically convergent iterative computation of the optimal exponents uses the normal equations as equality constraints. The correlations between the coefficients and the exponents in a sum of power functions become very high, when the number of terms increases such that their individual observability is being greatly reduced. The effect is shown to be a very poor precision in the parameter estimation and a heavy oscillation in the coefficients.The algorithms suggested are illustrated by curve fitting of some binary equilibrium data, where the relative volatility model gives a superior fit to the data.