Controlling the degree of branching in vinyl polymerization

Branching is an important tool for a synthetic polymer chemist in order to control the macroscopic properties of polymers. In condensation polymers, branching can be controlled by copolymerization of an AB? type monomer with an AB type monomer. However, in Vinyl polymerizations, it was not until very recently that the degree of branching could be controlled. Two different approaches, namely, Self-Condensing Vinyl Polymerization (SCVP) and Atom Transfer Radical Polymerization (ATRP) were developed for controlling the degree of branching in vinyl systems. This review article highlights recent advances in the science and technology in these two industrially very important approaches. A brief summary at the end highlights the advantages and disadvantages of each methodology. (C) 2000 Elsevier Science Ltd. All rights reserved

Synthesis and characterization of N-substituted hyperbranched polyureas

N,N'-disubstituted hyperbranched polyureas with methyl, benzyl, and allyl substitutents were synthesized starting from AB(2) monomers based on 3,5-diamino benzoic acid. Carbonyl azide approach, which generates isocyanate group in situ on thermal decomposition, was used for the protection of isocyanate functional groups. The N-substituted hyperbranched polymers can be considered as the new class of internally functionalized hyperbranched polyureas wherein the substituent can function either as receptor or as a chemical entity for selective transformations as a tool to tailor the properties. The chain-ends were also modified by attaching long chain aliphatic groups to fully realize the interior functionalization. This approach opens up a possible synthetic route wherein different functional substituents can be used to generate a library of internally functionalized. hyperbranched polymers. All the hyperbranched polyureas were characterized by FTIR, H-1-NMR, DSC, TGA, and size exclusion chromatography. Degree of branching in these N,N'-disubstituted hyperbranched polyureas, as calculated by H-1-NMR spectroscopy using model compounds, was found to be lower than the unsubstituted hyperbranched polyurea and is attributed to the lower reactivity of N-substituted amines compared to that of unsubstituted amines. (C) 2004

An efficient route for the synthesis of hyperbranched polymers and dendritic building blocks based on urea linkages

A highly efficient synthetic route, based on the quantitative reaction between amine and isocyanate functionalities, was used successfully for the synthesis of hyperbranched polymers and dendritic building blocks based on urea linkages. The thermal decomposition of 3,5-diamino benzoyl azide or 5-amino isophthaloyl azide generated in situ the corresponding phenyl isocyanates, which were then polymerized to give wholly aromatic hyperbranched polyureas. Hyperbranched polyurea with amine chain ends was soluble in common organic solvents. The degree of branching, as calculated with H-1 NMR, was 0.55. Diethyl 5-amino isophthalate and Boc-protected 5-amino isophthaloyl azide were used for the successful stepwise synthesis of dendritic wedges based on urea linkages. The thermal generation of the isocyanate functionality with gaseous nitrogen as the side product and its quantitative reaction with amine groups were the salient features of this convergent synthesis. This eliminated the use of chromatographic purification, an inherent part of other convergent growth approaches, and made it a very efficient synthetic route for the synthesis of dendritic wedges. The products were characterized by H-1 NMR, C-13 NMR, and electron spray mass spectroscopy (ESMS) techniques. (C) 2001 , Inc

Controlled functional group presentations in dendrimers as a tool to probe the hyperbranched architecture

The layer-by-layer incorporation of monomers in the synthesis of dendrimers allows for variations in the functionalities between one layer and the next. However, incorporation of different functionalities in combination with the above would lead to the introduction of sequences in dendrimers. We review the three complementary synthetic methods we have developed for sequencing the dendrimers. We also illustrate the utility of these methodologies in identifying certain fundamental properties of dendrimers. More specifically, we have probed the intermediate layers of the dendrimers by incorporation of spectroscopic probes in precise locations within dendrimers. Similarly, we have utilized this method to identify the true architectural advantages of dendrimers as light harvesters in solar energy applications

Self-assembly of facially amphiphilic dendrimers on surfaces

Facially amphiphilic dendrimers have been shown to provide significant difference in surface behavior due to subtle changes in structure. The monodendrons are capable of providing hydrophobic surfaces, while the didendrons provide superhydrophobic surfaces. This provides an example of how a molecular level change could result in significant changes in surface behavior. This difference is attributed to the conformational differences exhibited by these dendrimers on surfaces

Smaller building blocks form larger assemblies: Aggregation Behavior of biaryl-based dendritic facial amphiphiles

Synthesis and micellar behavior of biaryl-based benzyl ether dendritic molecules prepared from a new biaryl building block are described. The key objective of the study is to tune the size of individual dendritic molecules and investigate its effect on aggregation behavior of the resulting micelle-like assemblies. We show that the functional group placement in the building block influences flexibility of the dendritic backbone and interior volume available for packing the hydrophobic groups, which is reflected in different aggregation behavior and aggregate size of the two types of micellar assemblies

Synthesis and characterization of functionalized 3,4-propylenedioxythiophene and its derivatives

A functionalized monomer based on 3,4-propylenedioxythiophene, namely ProDOT-OH, was synthesized easily in a single step from commercially available starting materials and was successfully polymerized electrochemically resulting in the formation of an electroactive conjugated film on the working electrode. The presence of the free hydroxyl group makes ProDOT-OH as the material of choice due to ease of derivatization. This has been shown successfully for pre-polymerization functionalization wherein various derivatives were synthesized starting from ProDOT-OH. All the monomers were characterized by H-1, C-13 NMR, GC-MS and elemental analysis. The polymers were characterized by cyclic voltammetry, spectroelectrochemistry and in situ conductance measurements

Rational design of an electrochromic polymer with high contrast in the visible region: dibenzyl substituted poly( 3,4-propylenedioxythiophene)

A dibenzyl substituted poly(3,4-propylenedioxythiophene) was designed and synthesized, and exhibited a contrast of 89% at 632 nm with switching speeds of 400 ms and coloration efficiency of 575 cm(2) C-1