Poly(beta-alanoid-block-beta-alanine)s: synthesis via cobalt-catalyzed carbonylative polymerization and self-assembly

Expanding the "Magic Triangle" of Reinforced Rubber Using a Supramolecular Filler Strategy

A strategy for optimizing the rolling resistance, wet skid and cut resistance of reinforced rubber simultaneously using a supramolecular filler is demonstrated. A β-alanine trimer-grafted Styrene Butadiene Rubber (A₃-SBR) pristine polymer was designed and mechanically mixed with commercially available styrene butadiene rubber to help the dispersion of a β-alanine trimer (A₃) supramolecular filler in the rubber matrix. To increase the miscibility of A₃-SBR with other rubber components during mechanical mixing, the pristine polymer was saturated with ethanol before mixing. The mixture was vulcanized using a conventional rubber processing method. The morphology of the assembles of the A₃ supramolecular filler in the rubber matrix was studied by Differential Scanning Calorimetry (DSC) and Transmission Electron Microscopy (TEM). The Differential Scanning Calorimetry study showed that the melting temperature of β-sheet crystals in the vulcanizates was around 179 °C and was broad. The melting temperature was similar to that of the pristine polymer, and the broad melting peak likely suggests that the size of the crystals is not uniform. The Transmission Electron Microscopy study revealed that after mixing the pristine polymer with SBR, some β-sheet crystals were rod-like with several tens of nanometers and some β-sheet crystals were particulate with low aspect ratios. Tensile testing with pre-cut specimens showed that the vulcanizate containing A₃-SBR was more cut-resistant than the one that did not contain A₃-SBR, especially at a large cut size. The rolling resistance and wet skid were predicted by dynamic mechanical analysis (DMA). DMA tests showed that the vulcanizates containing A₃-SBR were significantly less hysteretic at 60 °C and more hysteretic at 0 °C based on loss factor. Overall, the "magic triangle" was expanded by optimizing the rolling resistance, wet-skid, and cut resistance simultaneously using a β-alanine trimer supramolecular filler. The Payne effect also became less severe after introducing the β-alanine trimer supramolecular filler into the system.

Oligo(β-peptoid)s with Backbone Chirality from Aspartic Acid Derivatives: Synthesis and Property Investigation

Poly(β-peptoid)s (N-substituted poly-β-alanines) are an intriguing class of pseudopeptidic materials for biomedical applications, but the polymers prepared by solution polymerization have restricted diversity and functionality due to synthetic difficulty. Synthesis of structurally diverse poly(β-peptoid)s is highly desirable yet challenging. Herein, we report a new approach to synthesize skeletal chiral β-peptoid polymers from readily available aspartic acid derivatives. Two types of N-substituted β³-homoalanine monomers, i.e., N-(methyl propionate)-Asp-OMe ( ^N MeP-Asp-OMe) and N-(tert-butyl propionate)-Asp-OMe ( ^N tBuP-Asp-OMe), were synthesized in high yield via an aza-Michael addition reaction between l-aspartic acid-1-methyl ester (l-Asp-OMe) and acrylate species. Both N-substituted β³-homoalanines can be readily converted into polymerizable N-substituted β³-homoalanine N-carboxyanhydrides (β-NNCAs). Subsequent ring-opening polymerization (ROP) of these β-NNCA monomers provides access to oligo(β-peptoid)s and mPEG-poly(β-peptoid) diblocks with backbone chirality. Their conformations were preliminarily studied by circular dichroism (CD) spectra and Fourier transform infrared spectroscopy (FT-IR). The synthetic strategy would significantly facilitate the development of novel poly(β-peptoid)s with well-defined and diverse structures.

Chemoenzymatic Synthesis of Nitrogen Polymers with Biomedical Applications Catalyzed by Lipases

The application of Candida antarctica lipase B as catalyst in the synthesis of two examples of nitrogen polymers is described. Firstly, we report a novel linear polyamidoamine oligomer, obtained by polymerization of ethyl acrylate and N-methyl-1,3-diaminopropane, catalyzed by Candida antarctica lipase B immobilized on polypropylene. The second part of the chapter describes an efficient route for the synthesis of a novel β-peptoid oligomer with hydroxyalkyl pendant groups in the nitrogen atom, through the polymerization of ethyl N-(2-hydroxyethyl)-β-alaninate catalyzed by Candida antarctica lipase B physically adsorbed within a macroporous poly(methyl methacrylate-co-butyl methacrylate) resin. Moreover, two derivatives of the β-peptoid oligomer were prepared: by acetylation and by grafting polycaprolactone. This last process was performed through ring-opening polymerization of caprolactone from the β-peptoid pendant hydroxyl groups and afforded a brush copolymer. The products were blended with polycaprolactone to make films by solvent casting. The inclusion of the acyl derivatives of the β-peptoid to polycaprolactone affected the morphology of the film yielding micro- and nanostructured patterns. The obtained products showed biomedical applications.

Peptoid polymers: a highly designable bioinspired material

Bioinspired polymeric materials are attracting increasing attention due to significant advantages over their natural counterparts: the ability to precisely tune their structures over a broad range of chemical and physical properties, increased stability, and improved processability. Polypeptoids, a promising class of bioinspired polymer based on a N-substituted glycine backbone, have a number of unique properties that bridge the material gap between proteins and bulk polymers. Peptoids combine the sequence specificity of biopolymers with the simpler intra/intermolecular interactions and robustness of traditional synthetic polymers. They are highly designable because hundreds of chemically diverse side chains can be introduced from simple building blocks. Peptoid polymers can be prepared by two distinct synthetic techniques offering access to two material subclasses: (1) automated solid-phase synthesis which enables precision sequence control and near absolute monodispersity up to chain lengths of ~50 monomers, and (2) a classical polymerization approach which allows access to higher molecular weights and larger-scale yields, but with less control over length and sequence. This combination of facile synthetic approaches makes polypeptoids a highly tunable, rapid polymer prototyping platform to investigate new materials that are intermediate between proteins and bulk polymers, in both their structure and their properties. In this paper, we review the methods to synthesize peptoid polymers and their applications in biomedicine and nanoscience, as both sequence-specific materials and as bulk polymers.