Structural engineering of polyurethane coatings for high performance applications

“Life is branched” was the motto of a special issue of Macromolecular Chemistry and Physics1 on “Branched Polymers”, indicating that branching is of similar importance in the world of synthetic macromolecules as it is in nature. The significance of branched macromolecules has evolved over the last 30 years from just being considered as a side reaction in polymerization or as a precursor step in the formation of networks. Important to this change in perception of branching was the concept of “polymer architectures”, which formed on new starand graft-branched structures in the 1980s and then in the early 1990s on dendrimers and dendritic polymers. Today, clearly, controlled branching is considered to be a major aspect in the design of macromolecules and functional material. Hyperbranched (hb) polymers are a special type of dendritic polymers and have as a common feature a very high branching density with the potential of branching in each repeating unit. They are usually prepared in a one-pot synthesis, which limits the control on molar mass and branching accuracy and leads to “heterogeneous” products with a distribution in molar mass and branching. This distinguishes hyperbranched polymers from perfectly branched and monodisperse dendrimers. In the last 20 years, both classes of dendritic polymers, dendrimers as well as hb polymers, have attracted major attention because of their interesting properties resulting from the branched architecture as well as the high number of functional groups.2 The challenging synthesis of the dendrimers attracted especially scientists with a strong organic chemistry background and led to beautifully designed macromolecules, which allowed a deeper insight into the effect of branching and functionality. Dendrimers have been considered as perfect “nano-objects” where one can control perfectly size and functionality, which is of high interest in nanotechnology and biomedicine. hb polymers, however, were considered from the beginning as products suitable for larger-scale application in typical polymer fields like coatings and resins, where a perfect structure is sacrificed for an easy and affordable synthetic route. Thus, the first structures that were reported paralleled the chemistry used for linear polymers like typical polycondensation for polyester synthesis. More recently, unconventional synthetic methods have been adopted also for hb polymers and related structures. Presently, a vast variety of highly branched structures have been realized and studied regarding their properties and potential application fields. Excellent reviews appeared covering synthesis strategies, properties, and applications, like the very recent tutorial by Carlmark et al.,3 the comprehensive book on hyperbranched polymers covering extensively synthesis and application * E-mail: voit@ipfdd.de; lederer@ipfdd.de. Chem. Rev. 2009, 109, 5924–5973 5924

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Hyperbranched and highly branched polymer architectures--synthetic strategies and major characterization aspects.

https://cyberleninka.org/article/n/1310744.pdf

Poly(amidoamine), polypropylenimine, and related dendrimers and dendrons possessing different 1 → 2 branching motifs : An overview of the divergent procedures

Fifteen years of research on hyperbranched polymers in the group of Brigitte Voit are described, with a focus first on hyperbranched polyester synthesis and then on the addition and cycloaddition reactions used for the preparation of the hyperbranched structure. The characterization of structural details and bulk, solution, and thin-film properties is highlighted, and steps toward the elucidation of a general property profile of hyperbranched polymers are discussed. Some effects of hyperbranched polymers in reactive formulations and blends and in thin films are addressed that can lead to applications in coatings, as additives, and in microelectronics or sensorics. The great progress possible in the last years is shown, but open questions and unsolved problems are also pointed out. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2679–2699, 2005

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pola.20821

Hyperbranched polymers—All problems solved after 15 years of research?

Macromolecular engineering: From rational design through precise macromolecular synthesis and processing to targeted macroscopic material properties

Dendrigraft polymers: macromolecular engineering on a mesoscopic scale

A new method is presented for the preparation of arborescent copolymers containing polyisoprene (PIP) segments. The technique uses acetyl coupling sites randomly distributed on polystyrene substrates. Isoprene was polymerized with sec-butyllithium in tetrahydrofuran to yield polyisoprenyllithium, and the living polymer was titrated with an acetylated substrate to generate a copolymer. The grafting yield was maximized at 25 °C using 5 equiv of LiCl to attenuate the reactivity of polyisoprenyllithium. Arborescent copolymers were synthesized by grafting PIP side chains with a weight-average molecular weight Mw of either 5000 (PIP5) or 30 000 (PIP30) onto linear, comb-branched (G0), G1, and G2 acetylated polystyrenes. The copolymers with short (PIP5) side chains contain 84−91% w/w polyisoprene. For long (PIP30) side chains, the polyisoprene content varies from 92 to over 97% w/w. The graft copolymers exhibit a geometric increase in branching functionality and molecular weight for successive generations (fw = ...

Synthesis of arborescent polystyrene-graft-polyisoprene copolymers using acetylated substrates

The radius of gyration (Rg) was determined as a function of generation number for arborescent polystyrenes with two different side chain mass average molecular mass (Mw ≈ 5000, 5K, versus 30 000, 30K) by small-angle neutron scattering (SANS) measurements. The Rg values obtained were analyzed in terms of the Zimm−Stockmayer model for randomly branched polymers, the scaling relation Rg ∝ Mwv, and the expansion factor αs = (Rg)goodsolvent/(Rg)ϑsolvent. The Rg and scaling exponent v = 0.26 ± 0.01 found for G0 through G3 polymers with 5K side chains in cyclohexane-d correspond to the values predicted by the Zimm−Stockmayer model. The Rg for G0 through G3 polymers with 30K side chains deviate from the model with v = 0.32 ± 0.02, corresponding to v = 0.33 expected for hard spheres. Deuterated polystyrene (PS-d) side chains were grafted onto G2 and G3 polystyrene (PS) cores. These copolymers, G2PS-graft-PS-d and G3PS-graft-PS-d, were characterized as spheres with a well-defined PS core−PS-d shell structure by the...

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Conformation of Arborescent Polymers in Solution by Small-Angle Neutron Scattering: Segment Density and Core-Shell Morphology

Comparison of the long range polymer chain dynamics of polystyrene and cis-polyisoprene using polymers randomly labeled with pyrene

Arborescent polymers are highly branched macromolecules obtained from successive grafting reactions according to a generation-based scheme. Grafting side chains onto a linear substrate randomly fun...

Steven J. Teertstra

Papers

Dendrigraft polymers: macromolecular engineering on a mesoscopic scale

Synthesis of arborescent polystyrene-graft-polyisoprene copolymers using acetylated substrates

Conformation of Arborescent Polymers in Solution by Small-Angle Neutron Scattering: Segment Density and Core-Shell Morphology

Comparison of the long range polymer chain dynamics of polystyrene and cis-polyisoprene using polymers randomly labeled with pyrene

Viscoelastic Properties of Arborescent Polystyrene-graft-polyisoprene Copolymers