The direct enzymatic polymerization of miniemulsions consisting of lactone nanodroplets represents a new and convenient pathway for the synthesis of biodegradable polymer nanoparticles, where the chemical composition and molecular weight can be varied in a certain range. Oligoesters completely end‐capped with an alkene or diene group can also be prepared by this technique. These building blocks extend polyester application as they allow to impart improved biodegradability to both siloxane and resin chemistry.
TEM image of the polyester particles obtained by enzymatic polymerization in miniemulsion. 相似文献
Discrete-fracture and rock matrix (DFM) modelling necessitates a physically realistic discretisation of the large aspect ratio
fractures and the dissected material domains. Using unstructured spatially adaptively refined finite-element meshes, we find
that the fastest flow often occurs in the smallest elements. Flow velocity and element size vary over many orders of magnitude,
disqualifying global Courant number (CFL)-dependent transport schemes because too many time steps would be necessary to investigate
displacements of interest. Here, we present a higher-order accurate implicit pressure–(semi)-implicit transport scheme for
the advection–diffusion equation that overcomes this CFL limitation for DFM models. Using operator splitting, we solve the
pressure and the transport equations on finite-element, node-centred finite-volume meshes, respectively, using algebraic multigrid
methods. We apply this approach to field data-based DFM models where the fracture flow velocity and mesh refinement is 2–4
orders of magnitude greater than that of the matrix. For a global CFL of ≤10,000, this implies sub-CFL, second-order accurate
behaviour in the matrix, and super-CFL, at least first-order accurate, transports in fast-flowing fractures. Their greater
refinement, however, largely offsets this numerical dispersion, promoting a highly accurate overall solution. Numerical and
fracture-related mechanical dispersions are compared in the realistic DFM models using second-order accurate runs as reference
cases. With a CFL histogram, we establish target error criteria for CFL overstepping. This analysis indicates that for extreme
fracture heterogeneity, only a few transport steps can be sufficient to analyse macro-dispersion. This makes our implicit
method attractive for quick analysis of transport properties on multiple realisations of DFM models. 相似文献
Hydrophobic association and stimuli‐responsiveness is a powerful tool towards water‐based adhesives with strongly improved properties, which is demonstrated based on the example of hydrophobically modified alkali‐soluble latexes (HASE) with modulated association. Their rheological properties are highly tunable due to the hydrophobic domains that act as physical crosslinking sites of adjustable interaction strength. Ethanol, propanol, and butanol are used as water‐soluble model additives with different hydrophobicity in order to specifically target the association sites and impact the viscoelastic properties and stimuli‐responsiveness. The rheological and mechanical property response upon dilution with water can be tailored, and dilution‐resistant or even dilution‐thickening systems are obtained. The investigations are of high importance for water‐based adhesives, as our findings provide insight into general structure–property relationships to improve their setting behavior, especially upon contact with wet substrates.
Mono(cyclopentadienyl)titanium complexes of the general formula Ti(η5-C5R5)X2OR' were designed as structurally well-defined mononuclear initiators for the ring-opening polymerization of four-, six-, and seven-membered lactones. Living pseudo-anionic mechanism with acyl-oxygen cleavage is suggested by various NMR spectroscopic studies as well as the isolation of the mono(insertion) products. The nature of the ancillary ligands lead to significant changes in the polymerization activity and is discussed in terms of electronic and steric effects. 相似文献