Theoretically predicting the solubility of polydisperse polymers using Flory–Huggins theory

Polydispersity affects physical properties of polymeric materials, such as solubility in solvents. Most biobased, synthetic, recycled, mixed, copolymerized, and self-assembled polymers vary in size and chemical structure. Using solvent fractionation, this variety in molecular features can be reduced and a selection of the sizes and molecular features of the polymers can be made. The significant chemical and physical dispersity of these polymers, however, complicates theoretical solubility predictions. A theoretical description of the fractionation process can guide experiments and material design. During solvent fractioning of polymers, a part of the polydisperse distribution of the polymers dissolves. To describe this process, this paper presents a theoretical tool using Flory–Huggins theory combined with molecular mass distributions and distributions in the number of functional groups. This paper quantifies how chemical and physical polydispersity of polymers affects their solubility. Comparison of theoretical predictions with experimental measurements of lignin in a mixture of solvents shows that multiple molecular features can be described well using a single set of parameters, giving a tool to theoretically predict the selective solubility of polymers

Chemistry, Functionality, and Coating Performance of Biobased Copolycarbonates from 1,4: 3,6-Dianhydrohexitols

Biobased polycarbonates were synthesized from 1,4:3,6-dianhydro-D-glucitol, 1,4:3,6-dianhydro-L-iditol, and 1,4:3,6-dianhydro-D-mannitol as the principal diols, using different types of carbonyl sources. The (co)polycarbonates resulting from polycondensation reactions in solution using triphosgene consisted of several types of polymer chains with respect to chain topology (e. g., linear or cyclic chains) and end-group structure (e. g., hydroxyl, chloroformate or alkyl chloride end-groups). The introduction of flexible comonomers seemed to increase the amount of cyclic structures in the product mixtures. The melt polymerization of diphenyl carbonate with 1,4:3,6-dianhydrohexitols required high reaction temperatures and led to almost exclusively hydroxy-functional poly(1,4:3,6-dianhydrohexitol carbonate)s. Copolymerizing the 1,4:3,6-dianhydrohexitols with 1,3-propanediol and diphenyl carbonate at high temperature resulted in the partial loss of 1,3-propanediol. On the other hand, by melt polycondensation of 1,4:3,6-dianhydrohexitol-based bis(phenyl carbonate) monomers in combination with primary diols and/or triols, the insertion of the primary alcohols could be achieved in a more controlled way. OH-functional materials were prepared, having suitable molecular weights, T(g) values, thermal stability, and melt viscosity profiles for (powder) coating applications. These functional biobased (co)polycarbonates were cured with polyisocyanate curing agents, resulting in colorless to pale yellow transparent, glossy coatings with good mechanical performance and solvent resistance. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 1450-1463, 201

Unique Base-Initiated Depolymerization of Limonene-Derived Polycarbonates

The depolymerization of poly­(limonene carbonate) (PLC) initiated by 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD) was investigated. The strong organic base TBD was capable of deprotonating the OH-terminated PLC, leading to fast degradation via backbiting reactions at high temperature. An interesting feature of the base-initiated breakdown of PLC lies in the quantitative depolymerization into the corresponding initial limonene oxide monomer. This result implies the complete back-to-monomer recyclability of the fully biobased PLC, which accordingly can be considered as a really sustainable material. Additionally, the stability of PLC when exposed to TBD was enhanced by an end-capping reaction, which further supported the proposed degradation pathway

Graphene oxide single sheets as substrates for high resolution cryoTEM

CryoTEM is an important tool in the analysis of soft matter, where generally defocus conditions are used to enhance the contrast in the images, but this is at the expense of the maximum resolution that can be obtained. Here, we demonstrate the use of graphene oxide single sheets as support for the formation of 10 nm thin films for high resolution cryoTEM imaging, using DNA as an example. With this procedure, the overlap of objects in the vitrified film is avoided. Moreover, in these thin films less background scattering occurs and as a direct result, an increased contrast can be observed in the images. Hence, imaging closer to focus as compared with conventional cryoTEM procedures is achieved, without losing contrast. In addition, we demonstrate an ∼1.8 fold increase in resolution, which is crucial for accurate size analysis of nanostructures

Nucleation and Growth of Monodisperse Silica Nanoparticles

Although monodisperse amorphous silica nanoparticles have been widely investigated, their formation mechanism is still a topic of debate. Here, we demonstrate the formation of monodisperse nanoparticles from colloidally stabilized primary particles, which at a critical concentration undergo a concerted association process, concomitant with a morphological and structural collapse. The formed assemblies grow further by addition of primary particles onto their surface. The presented mechanism, consistent with previously reported observations, reconciles the different theories proposed to date