Demixing of colloid-polymer mixtures in poor solvents

The influence of poor solvent quality on fluid demixing of a model mixture of colloids and nonadsorbing polymers is investigated using density functional theory. The colloidal particles are modelled as hard spheres and the polymer coils as effective interpenetrating spheres that have hard interactions with the colloids. The solvent is modelled as a two-component mixture of a primary solvent, regarded as a background theta-solvent for the polymer, and a cosolvent of point particles that are excluded from both colloids and polymers. Cosolvent exclusion favors overlap of polymers, mimicking the effect of a poor solvent by inducing an effective attraction between polymers. For this model, a geometry-based density functional theory is derived and applied to bulk fluid phase behavior. With increasing cosolvent concentration (worsening solvent quality), the predicted colloid-polymer binodal shifts to lower colloid concentrations, promoting demixing. For sufficiently poor solvent, a reentrant demixing transition is predicted at low colloid concentrations.Comment: 6 pages, 3 figure

van der Waals interaction of parallel polymers and nanotubes

We study the mutual interactions of simple, parallel polymers and nanotubes, and develop a scheme to include the van der Waals interactions in the framework of density functional theory (DFT) for these molecules at intermediate to long-range separations. We primarily focus on the polymers polyethylene, isotactic polypropylene, and isotactic polyvinylchloride, but our approach applies more generally to all simple polymers and nanotubes. From first-principle DFT calculations we extract the electron density of the polymers and their static electric response. We derive explicit expressions for the van der Waals interaction energy under simple symmetry assumptions.Comment: 8 pages, 2 figures (2 eps figure files

Use of water-based carbonyl-functional polymers on a cross-linker-free highperformance leather finish

The present paper aims to study a new high-performance coating formulation while avoiding the use of cross-linkers. By using acrylic polymers with carbonyl functional groups, the negative environmental effects of the finishing process can be minimized. These new polymers can give very good physical properties without losing the inherent properties of flexibility and elasticity needed in upholstery leatherPostprint (published version

Functionalized hyperbranched polymers via olefin metathesis

Hyperbranched polymers are highly branched, three-dimensional macromolecules which are closely related to dendrimers and are typically prepared via a one-pot polycondensation of AB_(n≥2) monomers.^1 Although hyperbranched macromolecules lack the uniformity of monodisperse dendrimers, they still possess many attractive dendritic features such as good solubility, low solution viscosity, globular structure, and multiple end groups.^1-3 Furthermore, the usually inexpensive, one-pot synthesis of these polymers makes them particularly desirable candidates for bulk-material and specialty applications. Toward this end, hyperbranched polymers have been investigated as both rheology-modifying additives to conventional polymers and as substrate-carrying supports or multifunctional macroinitiators, where a large number of functional sites within a compact space becomes beneficial

A practical density functional for polydisperse polymers

The Flory Huggins equation of state for monodisperse polymers can be turned into a density functional by adding a square gradient term, with a coefficient fixed by appeal to RPA (random phase approximation). We present instead a model nonlocal functional in which each polymer is replaced by a deterministic, penetrable particle of known shape. This reproduces the RPA and square gradient theories in the small deviation and/or weak gradient limits, and can readily be extended to polydisperse chains. The utility of the new functional is shown for the case of a polydisperse polymer solution at coexistence in a poor solvent.Comment: 9 pages, 3 figure

Renormalized field theory of collapsing directed randomly branched polymers

We present a dynamical field theory for directed randomly branched polymers and in particular their collapse transition. We develop a phenomenological model in the form of a stochastic response functional that allows us to address several interesting problems such as the scaling behavior of the swollen phase and the collapse transition. For the swollen phase, we find that by choosing model parameters appropriately, our stochastic functional reduces to the one describing the relaxation dynamics near the Yang-Lee singularity edge. This corroborates that the scaling behavior of swollen branched polymers is governed by the Yang-Lee universality class as has been known for a long time. The main focus of our paper lies on the collapse transition of directed branched polymers. We show to arbitrary order in renormalized perturbation theory with $\varepsilon$-expansion that this transition belongs to the same universality class as directed percolation.Comment: 18 pages, 7 figure

Density functional approach for inhomogeneous star polymers

We propose microscopic density functional theory for inhomogeneous star polymers. Our approach is based on fundamental measure theory for hard spheres, and on Wertheim's first- and second-order perturbation theory for the interparticle connectivity. For simplicity we consider a model in which all the arms are of the same length, but our approach can be easily extended to the case of stars with arms of arbitrary lengths.Comment: 4 pages, 3 figures, submitte

Nucleic Acid Carriers Based on Precise Polymer Conjugates

Polymer polydispersity, random conjugation of functional groups, and poorly understood structure–activity relationships have constantly hampered progress in the development of nucleic acid carriers. This review focuses on the synthetic concepts for the generation of precise polymers, site-specific conjugation strategies, and multifunctional conjugates for nucleic acid transport. Dendrimers, defined peptide carriers, sequence-defined polyamidoamines assembled by solid-phase supported synthesis, and precise lipopeptides or lipopolymers have been characterized for pDNA and siRNA delivery. Conjugation techniques such as click chemistries and peptide ligation are available for conjugating polymers with functional transport elements such as targeting or shielding domains and for direct covalent modification of therapeutic nucleic acids in a site-specific mode

End-group functionalization of poly(2-oxazoline)s using methyl bromoacetate as initiator followed by direct amidation

Poly(2-alkyl/aryl-2-oxazoline)s (PAOx) are an alluring class of polymers for many applications due to the broad chemical diversity that is accessible for these polymers by simply changing the initiator, terminating agent and the monomer(s) used in their synthesis. Additional functionalities (that are not compatible with the cationic ring-opening polymerization) can be introduced to the polymers via orthogonal post-polymerization modifications. In this work, we expand this chemical diversity and demonstrate an easy and straightforward way to introduce a wide variety of functional end-groups to the PAOx, by making use of methyl bromoacetate (MeBrAc) as a functional initiator. A kinetic study for the polymerization of 2-ethyl-2-oxazoline (EtOx) in acetonitrile (CH3CN) at 140 degrees C revealed relatively slow initiation and slower polymerization than the commonly used initiator, methyl tosylate (MeOTs). Nonetheless, well-defined polymers could be obtained with MeBrAc as initiator, yielding polymers with near-quantitative methyl ester end-group functionality. Next, the post-polymerization modification of the methyl ester end-group with different amines was explored by introducing a range of functionalities, i.e. hydroxyl, amino, allyl and propargyl end-groups. The lower critical solution temperature (LCST) behavior of the resulting poly(2-ethyl-2-oxazoline)s was found to vary substantially in function of the end-group introduced, whereby the hydroxyl group resulted in a large reduction of the cloud point transition temperature of poly(2-ethyl-2-oxazoline), ascribed to hydrogen bonding with the polymer amide groups. In conclusion, this paper describes an easy and fast modular approach for the preparation of end-group functionalized PAOx

Density functional theory and demixing of binary hard rod-polymer mixtures

A density functional theory for a mixture of hard rods and polymers modeled as chains built of hard tangent spheres is proposed by combining the functional due to Yu and Wu for the polymer mixtures [J. Chem. Phys. {\bf 117}, 2368 (2002)] with the Schmidt's functional [Phys. Rev. E {\bf 63}, 50201 (2001)] for rod-sphere mixtures. As a simple application of the functional, the demixing transition into polymer-rich and rod-rich phases is examined. When the chain length increases, the phase boundary broadens and the critical packing fraction decreases. The shift of the critical point of a demixing transition is most noticeable for short chains.Comment: 4 pages,2 figures, in press, PR