Rj Rafaël Sablong

Incorporation of Isosorbide into Poly(butylene terephthalate) via Solid-State Polymerization

The biomass-based monomer isosorbide was incorporated into poly(butylene terephthalate) (PBT) by solid-state polymerization (SSP) using the macrodiol monomer BTITB-(OH) 2, which consists of isosorbide (I), terephthalic acid (T), and 1,4-butandiol (B) residues. This macromonomer can be synthesized by a simple one-pot, two-step reaction. Polymers with number-average molecular weights up to 100,000 g x mol (-1) were readily synthesized from various ratios of PBT/BTITB-(OH) 2. Their molecular weights, thermal properties, and colors were compared with corresponding copolyesters that were obtained by melt polycondensation. We found that T m, T c, and especially T g were superior for materials that were obtained by SSP. This is ascribed to differences in the microstructures of both types of copolyesters; the SSP products exhibit a more blocky structure than do the more random melt-polymerized counterparts. The SSP method resulted in much higher molecular weights and much less colored polymers, and it seems to be the preferred route for incorporating biobased monomers that exhibit limited thermal stability into engineering plastics.

Chemoselective Alternating Copolymerization of Limonene Dioxide and Carbon Dioxide: A New Highly Functional Aliphatic Epoxy Polycarbonate

The alternating copolymerization of biorenewable limonene dioxide with carbon dioxide (CO2 ) catalyzed by a zinc β-diiminate complex is reported. The chemoselective reaction results in linear amorphous polycarbonates that carry pendent methyloxiranes and exhibit glass transition temperatures (Tg ) up to 135 °C. These polycarbonates can be efficiently modified by thiols or carboxylic acids in combination with lithium hydroxide or tetrabutylphosphonium bromide as catalysts, respectively, without destruction of the main chain. Moreover, polycarbonates bearing pendent cyclic carbonates can be quantitatively prepared by CO2 insertion catalyzed by lithium bromide.

Bio-derived polymers for coating applications : comparing poly(limonene carbonate) and poly(cyclohexadiene carbonate)

Two fully bio-based polycarbonates, poly(cyclohexadiene carbonate) (PCHDC) and poly(limonene carbonate) (PLC), are synthesised from carbon dioxide and cyclohexadiene oxide and limonene oxide. The low molecular weight polycarbonates are cross-linked by a photoinitiated reaction with trimethylolpropane tris(3-mercaptopropionate), via thiol–ene reactions. The cross-linking reactions are monitored using Raman spectroscopy and the reaction temperatures and times are optimised. Kinetic analyses of the cross-linking process suggest diffusion-controlled reactions for both polymers, despite the differences in the nature of alkene moieties (terminal vs. internal alkene). The resulting materials are evaluated for coating applications, they show promising solvent resistance and hardness and may be used in the future to prepare scratch-resistant coatings.

Coordination chemistry and X-ray studies with novel sterically constrained diphosphonite ligands

The coordination of two novel, sterically constrained diphosphonite ligands towards different palladium, platinum and rhodium precursors has been studied. Complexes of this hitherto unexplored class of diphosphonites, based on rigid xanthene backbones, have been characterized by X-ray crystallography as well as by NMR and IR spectroscopy. A short and concise overview is given on the scarce literature on phosphonite related chemistry. Structural differences in the complexes obtained due to steric influences of the ligands are discussed. Ligand 1, bearing 2-tert-butylphenolate groups, led to orthometallated complexes cis-[MCl{1-κ3C,P,P}] (M = Pd, Pt) and to trans-[RhCl(CO)(1)]. These complexes were compared with those formed with ligand 2, bearing 2,2′-dioxo-3,3′-di-tert-butyl-5,5′-dimethoxy-1,1′-biphenyl groups, preventing orthometallation. The complexes trans-{PdCl2(2)], cis-[PtCl2(2)] and trans-[RhCl(CO)(2)] were structurally characterized. Valuable data were collected on chemical shifts, Pt–P coupling constants, as well as CO stretch frequencies of Rh–CO complexes as important tools for structural characterization of such complexes.

Isocyanate-free approach to water-borne polyurea dispersions and coatings

Here, an isocyanate-free approach to produce polyureas from diamines and dicarbamates as monomers is reported. A side reaction limiting the molecular weight during the diamine/ dicarbamate polymerization, that is, N-alkylation of amine end groups, is investigated. Mitigation of the N-alkylation, either by enhancing the carbamate aminolysis rate or by substitution of dimethylcarbamates with more sterically hindered diethylcarbamates, affords polyureas with sufficiently high molecular weights to assure satisfactory mechanical properties. Stable polyurea dispersions with polyamines as internal dispersing agents are prepared, and the properties of the corresponding coatings are evaluated.