Gilch Synthesis of Poly(ortho-Phenylene Vinylenes): A Powerful Access to High-Molecular-Weight Blue-Emitting Polymers.

For the first time, the successful Gilch synthesis of poly(ortho-phenylene vinylenes) (ortho-PPVs) is reported. The molar mass of the constitutionally homogeneous ortho-PPVs reaches values as high as Mw ≈ 300 000 Da. The ortho-connectivity of the repeating units forces the chains to assume closely packed conformations even in good solvents. Significant perturbation of the π-electron systems and considerable shortening of the conjugation lengths are the consequences. UV-vis absorption and photoluminescence maxima consequently are shifted clearly toward shorter wavelengths compared to, e.g., classic para-PPVs.

Photoinduced Gilch Polymerization: A Basically New Access to Poly(p-phenylene vinylenes) (PPVs) of Exciting Constitutional Homogeneity.

A novel procedure has been developed for the Gilch reaction leading to poly(p-phenylene vinylenes) (PPVs). In the first step, selective activation of the starting material is achieved at low temperature. Subsequently, controlled chain growth is induced by lighting the α-halo-p-quinodimethane monomer. In contrast to the thermal Gilch polymerization, the photoinduced process allows adjusting crucial parameters such as intensity and energy of light. The progress of PPV formation can be followed visually or by in situ UV-vis spectroscopy. If the polymers are formed under appropriate conditions, they show very high molar masses, polydispersities in the common range, and higher constitutional homogeneity than thermally grown PPVs.

Effect of molecular architecture on single polymer adhesion.

Several applications require strong noncovalent adhesion of polymers to substrates. Graft and branched polymers have proven superior to linear polymers, but the molecular mechanism is still unclear. Here, this question is addressed on the single molecule level with an atomic force microscopy (AFM) based method. It is determined how the presence of side chains and their molecular architecture influence the adhesion and the mobility of polymers on solid substrates. Surprisingly, the adhesion of mobile polymers cannot significantly be improved by side chains or their architecture. Only for immobile polymers a significantly higher maximum rupture force for graft, bottle-brush, and branched polymers compared to linear chains is measured. Our results suggest that a combination of polymer architecture and strong molecular bonds is necessary to increase the polymer-surface contact area. An increased contact area together with intrachain cohesion (e.g., by entanglements) leads to improved polymer adhesion. These findings may prove useful for the design of stable polymer coatings.

Benchtop versus high field NMR: Comparable performance found for the molecular weight determination of lignin.

Lignin is a promising renewable biopolymer being investigated worldwide as an environmentally benign substitute of fossil-based aromatic compounds, e.g. for the use as an excipient with antioxidant and antimicrobial properties in drug delivery or even as active compound. For its successful implementation into process streams, a quick, easy, and reliable method is needed for its molecular weight determination. Here we present a method using 1H spectra of benchtop as well as conventional NMR systems in combination with multivariate data analysis, to determine lignin's molecular weight (Mw and Mn) and polydispersity index (PDI). A set of 36 organosolv lignin samples (from Miscanthus x giganteus, Paulownia tomentosa and Silphium perfoliatum) was used for the calibration and cross validation, and 17 samples were used as external validation set. Validation errors between 5.6% and 12.9% were achieved for all parameters on all NMR devices (43, 60, 500 and 600 MHz). Surprisingly, no significant difference in the performance of the benchtop and high-field devices was found. This facilitates the application of this method for determining lignin's molecular weight in an industrial environment because of the low maintenance expenditure, small footprint, ruggedness, and low cost of permanent magnet benchtop NMR systems.

Water-free synthesis of polyurethane foams using highly reactive diisocyanates derived from 5-hydroxymethylfurfural.

This paper reports on the synthesis of a new highly reactive diisocyanate monomer based on hydroxymethylfurfural. It further describes its catalyst-free conversion to linear-chain thermoplastic polyurethanes as well as to cross-linked polyurethane foams. In addition, a novel strategy for the synthesis of polyurethane foams without the necessity of using water is developed. Nitrogen is utilized herein as blowing agent which is formed during Curtius rearrangement of a new furan based carboxylic azide into its corresponding diisocyanate.

Patchy nanocapsules of poly(vinylferrocene)-based block copolymers for redox-responsive release.

Nanocapsules composed of a poly(vinylferrocene)-block-poly(methyl methacrylate) shell and a hydrophobic liquid core are prepared in water. The nanocapsule shells display a patchy structure with poly(vinylferrocene) patches with sizes of 25 ± 3 nm surrounded by poly(methyl methacrylate). The functional nanopatches can be selectively oxidized, thereby influencing the colloidal morphology and introducing polar domains in the nanocapsule shell. The hydrophobic to hydrophilic transition in the redox-responsive nanopatches can be advantageously used to release a hydrophobic payload encapsulated in the core by an oxidation reaction.