S. Ramakrishnan

Hyperbranched polyurethanes with varying spacer segments between the branching points

Hyperbranched polyurethanes, with varying oligoethyleneoxy spacer segments between the branching points, have been synthesized by a one-pot approach starting from the appropriately designed carbonyl azide that incorporates the different spacer segments. The structures of monomers and polymers were confirmed by IR and 1 H-NMR spectroscopy. The solution viscosity of the polymers suggested that they were of reasonably high molecular weight. Reversal of terminal functional groups was achieved by preparing the appropriate monohydroxy dicarbonyl azide monomer. The large number of terminal isocyanate groups at the chain ends of such hyperbranched macromolecules caused them to crosslink prior to its isolation. However, carrying out the polymerization in the presence of 1 equiv of a capping agent, such as an alcohol, resulted in soluble polymers with carbamate chain ends. Using a biphenyl-containing alcohol as a capping agent, we have also prepared novel hyperbranched polyurethanes with pendant mesogenic segments. These mesogen-containing polyurethanes, however, did not exhibit liquid crystallinity probably due to the wholly aromatic rigid polymer backbone.

Recent Developments in Polyether Synthesis

Review: Polyethers, both aliphatic, such as poly(ethylene oxide), poly(propylene oxide), etc., and wholly aromatic ones, such as poly(phenylene oxide)s, are commercially important materials. Polymers belonging to the former class are primarily synthesized via a ring-opening polymerization route, while those belonging to the latter are prepared via either oxidative coupling or nucleophilic aromatic substitution approaches. Polyethers that contain both aromatic and aliphatic units in their backbone are far less common. This review will discuss some of the recent advances in the preparation of polyethers, primarily focussing on those where the ether linkage is generated during polymerization. Although the standard ring-opening polymerization (ROP) route toward aliphatic polyethers has witnessed several interesting developments in recent years, it will not be covered in this review. The last section deals with a new melt-transetherification approach for the preparation of poly(xylylene alkylene ether)s developed in our laboratory.

Effect of branching on the crystallization kinetics of poly(ethylene terephthalate)

The effect of branching on the crystallization behavior of poly(ethylene terephthalate) has been examined by nonisothermal crystallization studies, using DSC. It was found that branching causes a significant change in the crystallization behavior, in that the Avrami exponent n lies between 1 and 2, suggesting a rodlike growth process compared to a spherulitic one observed in the case of PET. In addition, the effect of molecular kinks and linear disruptions were also examined; in both these cases, however, the same spherulitic growth, as seen in the case of PET, is observed. Further, the presence of branching, kinks and linear disruptions, in small concentrations, appears to enhance the crystallization process, possibly, by acting to facilitate nucleation. At higher concentrations of such defects, however, the crystallization process is slowed down and the overall crystallinity of the PET copolymers is reduced.

Effect of branching on the thermal properties of novel branched poly(4‐ethyleneoxy benzoate)

Poly(4-ethyleneoxy benzoate) (PEOB) was synthesized by the self-condensation of ethyl 4-(2-hydroxyethoxy) benzoate (E4HEB) under transesterification conditions. Branched PEOB was prepared by the condensation of E4HEB with an

Synthesis and thermal analysis of branched and “kinked” poly(ethylene terephthalate)

AB_2

Poly(alkylene itaconate)s – an interesting class of polyesters with periodically located exo-chain double bonds susceptible to Michael addition

monomer, ethyl 3,5-bis(2-hydroxyethoxy) benzoate (EBHEB), under similar conditions. Varying amounts of branching (0–50%) were introduced into the linear polymer by changes in the composition of the comonomers in the feed. The solution viscosity of the polymers indicated that they had reasonable molecular weights; the extent of branching in these copolymers was established from their

Folding of a Donor-Containing Ionene by Intercalation with an Acceptor

^1H

Phenyl-Ring-Bearing Cationic Surfactants: Effect of Ring Location on the Micellar Structure

NMR spectra. Differential scanning calorimetry studies indicated that, as expected, the introduction of branching drastically affected the percent crystallinity of the copolymers (as seen from their

Self-Adapting Peripherally Heterofunctionalized Hyperbranched Polymers: Formation of Janus and Tripodal Structures

\Delta H_m

Functionalized and Postfunctionalizable Porous Polymeric Films through Evaporation-Induced Phase Separation Using Mixed Solvents

, the enthalpy of melting), and when the extent of the incorporation of the