Supramolecular polymer

A polymer comprising monomeric units linked via 4 H-bridges and bound within said polymer via a different bond. The bond via the H-bridges is much stronger than with known supramolecular polymers

Phosphorus-Containing Polyisocyanurate Elastomers for Flame Retardant Application

Polyurethane (PU) is one of the most common and versatile polymers in many applications especially in the construction and automotive industry where the improvement of thermal stability and flame retardancy is crucial. As polyisocyanaurate (PIR) is well known to have a high decomposition temperature and phosphorus motifs are usually used as flame retardants in polymers, the introduction of PIR and phosphorus motifs in polyurethanes can lead to PUs with high thermal stability and flame retardancy. We investigated a synthetic pathway to introduce polyisocyanurate (PIR) and phosphorus motifs in polyurethanes via co-trimerization of 4,4′-methylene diphenyl diisocyanate (4,4′-MDI) and monoisocyanate, which was synthesized from the reaction between diethyl (hydroxymethyl)phosphonate (DEHP) and 4,4′-MDI. The resulting PIR-DEHP prepolymer was used to prepare PIR-DEHP elastomers in both solvent and solvent-free conditions. The elastomer with polyester polyol and 15 wt % 1,4-butanediol in the polyol component showed high char formation (25.5 wt %) and 55% reduction in the total heat release (THR) relative to the reference elastomer without PIR and phosphorus content. It is expected that the use of the PIR-DEHP prepolymer can be extended to other applications, such as rigid PU foams and compact thermosets where the flame retardancy and bulk reaction conditions are required

Methodological lessons and findings from an impact evaluation of a WASH project in Indonesia

Internationally, there is growing emphasis on evaluations that aim not only at output and performance data but also show the project’s impacts. This paper reports on the experiences, findings and lessons from the impact evaluation of the Second Water and Sanitation for Low Income Communities Project (WSLIC-2) in the Ministry of Health of Indonesia. During project formulation an impact study was planned using the strongest model of a double difference evaluation (differences between before and after situations and practices in project and matched control villages). In this paper, the team that designed and implemented the study reports on the problems and how they were addressed, followed by a brief summary of the findings. It concludes that the classical double difference study is becoming ever harder to practice in development research and suggests ways to address the challenge

Sorption induced relaxations during water diffusion in S-PEEK

This paper presents an analysis of the sorption kinetics of water vapor and liquid water in the glassy polymer sulfonated poly(ether ether ketone) (S-PEEK). Sorption isotherms are determined experimentally using a gravimetric sorption balance, and the relative contributions of Fickian diffusion and relaxational phenomena are quantified as a function of the water concentration in the polymer using the model of Hopfenberg and Berens.Analysis of the sorption isotherms and determination of the sorption kinetics prove the occurrence of both Fickian sorption behavior and relaxational phenomena already at very low water concentrations in the polymer. With increasing water concentration, the relative importance of relaxation phenomena increases, whereas the relative contribution of Fickian diffusion decreases.Based on the water vapor sorption kinetics only, the Fickian diffusion coefficient increases over two orders of magnitude with increasing water vapor concentration. Taking also the diffusion kinetics from liquid water sorption experiments into account reveals a change of even three orders of magnitude of the Fickian diffusion coefficient when the water concentration in the polymer increases

Siloxane polymers with quadruple hydrogen bonding units

The invention relates to the synthesis of siloxane polymers containing self-complementary quadruple hydrogen bonding groups (4H-units). The resulting polymers show unique new characteristics that result from the reversible, physical interactions between the polysiloxane chains that are based on the (supramolecular) interactions between the 4H-units. The polysiloxanes in this invention show unprecedented bulk material properties and are used as gelling agents for silicone fluids. The resulting gels are clear and display good material properties, while having unparalleled high silicone fluid contents

Synthesis of polyisocyanurate prepolymer and the resulting flexible elastomers with tunable mechanical properties

Polyurethane (PU) is used in a wide range of applications due to its diverse chemical and physical properties. To meet the increasing demands on thermal and mechanical properties of PU materials, polyisocyanurates(PIRs) have been introduced in PU materials as crosslinkers and due to their high decomposition temperature. We prepared a liquid PIR prepolymer with high PIR content by co-trimerization of 4,4’-methylene diphenyl diisocyanate (4,4’-MDI) and mono-isocyanates. The mono-isocyanate was synthesizedvia reaction between a 4,4’-MDI and a 2-ethyl-1-hexanol. The PIR prepolymer obtained was further reacted with long chain polyols and chain extenders in both solvent and solvent-free conditions, leading to PIR elastomers that exhibited good thermal stability with high char formation, and improvedmechanical properties with much higher Young’s modulus. This work demonstrates that the liquid PIR prepolymer can potentially be used in various large-scale industrial applications