Effect Of Polymer Architecture Research Articles

Effects of Polymer Architecture and Charged Molecular Crowders on Hydrophobic Polymer Collapse

Effects of Polymer Architecture and Charged Molecular Crowders on Hydrophobic Polymer Collapse

Polymeric surfactants at liquid–liquid interfaces: Dependence of structural and thermodynamic properties on copolymer architecture

Polymeric surfactants are amphiphilic molecules with two or more different types of monomers. If one type of monomer interacts favorably with a liquid, and another type of monomer interacts favorably with another, immiscible liquid, then polymeric surfactants adsorb at the interface between the two liquids and reduce the interfacial tension. The effects of polymer architecture on the structural and thermodynamic properties of the liquid–liquid interface are studied using molecular simulations. The interface is modeled with a non-additive binary Lennard-Jones fluid in the two-phase region of the phase diagram. Block and gradient copolymer surfactants are represented with coarse-grained, bead-spring models, where each component of the polymer favors one or the other liquid. Gradient copolymers have a greater concentration at the interface than do block copolymers because the gradient copolymers adopt conformations partially aligned with the interface. The interfacial tension is determined as a function of the surface excess of polymeric surfactant. Gradient copolymers are more potent surfactants than block copolymers because the gradient copolymers cross the dividing surface multiple times, effectively acting as multiple individual surfactants. For a given surface excess, the interfacial tension decreases monotonically when changing from a block to a gradient architecture. The coarse-grained simulations are complemented by all-atom simulations of acrylic-acid/styrene copolymers at the chloroform-water interface, which have been studied in experiments. The agreement between the simulations (both coarse-grained and atomistic) and experiments is shown to be excellent, and the molecular-scale structures identified in the simulations help explain the variation of surfactancy with copolymer architecture.

Effect of Polymer Architecture on the Adsorption and Coating Stability on Heterogeneous Biomimetic Surfaces

Effect of Polymer Architecture on the Adsorption and Coating Stability on Heterogeneous Biomimetic Surfaces

Effect of polymer architecture on the adsorption behaviour of amphiphilic copolymers: A theoretical study

HypothesisPolymer architecture is known to have significant impact on its adsorption behaviour. Most studies have been concerned with the more concentrated, “close to surface saturation” regime of the isotherm, where complications such as lateral interactions and crowding also additionally affect the adsorption. We compare a variety of amphiphilic polymer architectures by determining their Henry’s adsorption constant (kH), which, as with other surface active molecules, is the proportionality constant between surface coverage and bulk polymer concentration in a sufficiently dilute regime. It is speculated that not only the number of arms or branches, but also the position of adsorbing hydrophobes influence the adsorption, and that by controlling the latter the two can counteract each other. MethodologyThe Self-consistent field calculation of Scheutjens and Fleer was implemented to calculate the adsorbed amount of polymer for many different polymer architectures including linear, star and dendritic. Using the adsorption isotherms at very low bulk concentrations, we determined the value of kH for these. FindingsIt is found that the branched structures (star polymers and dendrimers) can be viewed as analogues of linear block polymers based on the location of their adsorbing units. Polymers containing consecutive trains of adsorbing hydrophobes in all cases showed higher level of adsorption compared to their counterparts, where the hydrophobes were more uniformly distributed on the chains. While increasing the number of branches (or arms for star polymers) also confirmed the known result that the adsorption decreased with the number of arms, this trend can be partially offset by the appropriate choice of the location of anchoring groups.

Polymer Architecture Effects on Poly(N,N-Diethyl Acrylamide)-b-Poly(Ethylene Glycol)-b-Poly(N,N-Diethyl Acrylamide) Thermoreversible Gels and Their Evaluation as a Healthcare Material.

Thermoreversible gels which transition between liquid-like and solid-like states when warmed have enabled significant novel healthcare technologies. Poly(N,N-diethyl acrylamide) (PDEA) is a thermoresponsive polymer which can be used as a trigger to form thermoreversible gels, however its use in these materials is limited and crucial design principles are unknown. Herein ABA copolymers with the structure PDEA-b-poly(ethylene glycol) (PEG)-b-PDEA are synthesized to give four block copolymers with varied molecular weight of PDEA and PEG blocks. Rheometry on solutions of the block copolymers reveals that high molecular weight PEG blocks are required to form thermoreversible gels with predominantly solid-like behavior. Furthermore, small-angle X-ray scattering elucidates clear differences in the nanostructure of the copolymer library which can be linked to distinct rheological behaviors. A thermoreversible gel formulation based on PDEA (20kDa)-b-PEG (10kDa)-b-PDEA (20kDa) is designed by optimizing the polymer concentration and ionic strength. It is found that the gel is mucoadhesive, stable, and non-toxic, as well as giving controlled release of a hydrophobic drug. Overall, this study provides insight into the effect of polymer architecture on the nanostructure and rheology of PDEA-b-PEG-b-PDEA and presents the development of a highly functional thermoreversible gel with high promise for healthcare applications.

Role of Architecture on Thermorheological Properties of Poly(alkyl methacrylate)-Based Polymers

Oil-soluble poly(meth)acrylate-based polymers play a vital role in the thermorheological modification of a wide variety of lubricants and formulated consumer products, where increased viscosity at elevated temperatures ensures sufficient viscosity over a broad temperature range. The assumed mechanism of viscosity modification for many such polymers is based on temperature-induced swelling due to marginal solvent quality. Although this mechanism is widely accepted, direct and consistent experimental proof is limited due to a lack of structural characterization over a wide temperature range. Additionally, the effect of polymer architecture on the temperature-dependent solution behavior is not fully understood, despite the trend toward branched polymers in recent years. Here, we provide a comprehensive set of data relying on detailed temperature-dependent viscosity measurements, dynamic light scattering (DLS), and small-angle neutron scattering (SANS) experiments to confirm the existence of temperature-induced coil expansion for industrially relevant poly(stearyl methacrylate-co-methyl methacrylate) (p(SMA-co-MMA)) polymers with various architectures including linear, randomly branched, and star-shaped topologies. Compared to the linear and randomly branched polymers, the degree of coil expansion for the star-shaped additives is significantly lower. Regardless of the polymer architecture, the propensity to undergo temperature-induced chain swelling proved to be highly specific toward the type of base oil, underlining the sensitive interplay between polymer and oil chemistry required for designing successful thermorheological modifiers.

Mixed Matrix Membranes Based on Fluoropolymers with m- and p-Terphenyl Fragments for Gas Separation Applications.

Novel mixed matrix membranes (MMMs) based on fluoropolymers with m- and p-terphenyl fragments and NaX zeolites were prepared. The fluoropolymers were synthesized by a one-pot, room-temperature, metal-free superacid-catalyzed stoichiometric and nonstoichiometric step polymerization of 2,2,2-trifluoroacetophenone with two multiring aromatic nonactivated hydrocarbons (p-terphenyl and m-terphenyl). MMMs were characterized by scanning electron microscopy (SEM) and infrared (Fourier transform infrared (FTIR)) spectroscopy and used in gas permeability tests. SEM analysis showed interfacial voids in MMMs prepared in N-methyl-2-pyrrolidone (NMP), The interfacial adhesion in the polymer–zeolite system was considerably improved when chloroform was used as a solvent. Permeability coefficients for pristine polymer membranes were 1.3-fold higher in CHCl3 than in NMP for p-terphenyl fragment and 2.0 times higher in NMP than in CHCl3 for the polymer with m-terphenyl fragment. The incorporation of NaX zeolites in the polymeric matrices improved the gas permeability coefficients compared to the pristine membranes. The effects of polymer architecture, casting solvent, and interaction between the organic matrix and the inorganic particles on the gas separation performance of the developed MMMs were investigated.

Surface Diffusion of Dendronized Polymers Correlates with Their Transfection Potential.

Successful intracellular delivery of therapeutics requires interactions at several liquid-solid interfaces, including cell surface, endosomal membranes, and-depending on the therapeutic-the nuclear membrane. Understanding the dynamics of polymer kinetics at the liquid-solid interface is fundamental for the design of polymers for such biomedical delivery applications. However, the effect of polymer architecture and charge density on polymer kinetics is not readily investigated using routine techniques, and the role of such parameters in the context of gene delivery remains unknown. We adopted a synthetic strategy which enabled the systematic manipulation of charge density, flexibility, and molecular weight using a dendronized linear polymeric architecture. High-speed atomic force microscopy (HS-AFM) was used as a label-free method to directly observe the polymers' dynamic properties, such as velocity, displacement, and diffusion, in physiologically relevant conditions. Importantly, we found that the physical parameters measured by HS-AFM relate to the transfection potential of the individual polymers and may be a valuable tool in screening structural polymer variants.

Effect of Polymer Architecture on the Phase Behavior and Structure of Polyelectrolyte/Microemulsion Complexes (PEMECs)

We studied polyelectrolyte/microemulsion complexes (PEMECs) formed by the biopolymer sodium hyaluronate (NaHA) and cationic oil-in-water (O/W) microemulsion droplets. Around equimolar charge condit...

Effect of polymer architecture and hard/soft segment ratio on the surface morphology and mechanical properties of polyurethane films for potential orthodontic treatment

AbstractIn this study, polyurethane (PU) films are prepared by using 1,4‐butanediol and trimethylolpropane as chain extender and crosslinking agent, respectively. A series of prepolymers are synthesized by varying the feeding molar ratios of methylene diisocyanate to polytetramethylene ether glycol, which are hard and soft segments, respectively. The influence of polymer architecture, chemical composition, and artificial saliva treatment on the surface morphology and mechanical strength of PU films are studied. The crosslinking polymer architecture and higher content of hard segment correlates with enhanced tensile strength and less decrease of tensile strength in the condition of artificial saliva, but reduced elongation at break. The in vitro cytotoxicity study demonstrates that PU films have excellent cytocompatibility.

Brushes, Graft Copolymers, or Bottlebrushes? The Effect of Polymer Architecture on the Nanotribological Properties of Grafted-from Assemblies

Surface-grafted polyzwitterions (PZW) have gained a foothold in the design of synthetic materials that closely mimic the lubricious properties of articular joints in mammals. Besides their chemical composition, the architecture of PZW brushes strongly determines their morphological, nanomechanical, and nanotribological characteristics. This emerges while comparing the properties of linear poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) brushes with those displayed by graft copolymer and bottlebrush brushes, either featuring a low or a high content of PMPC side chains. Surface-initiated atom transfer radical polymerization (SI-ATRP) enabled the synthesis of different branched-brush architectures from multifunctional macroinitiators via multiple grafting steps, and allowed us to modulate their structure by tuning the polymerization conditions. At relatively low grafting densities (σ), long PMPC side segments extend at the interface of bottlebrush and graft copolymer brushes, providing both morphology and lubrication properties comparable to those shown by loosely grafted, linear PMPC brushes. When σ > 0.1 chains nm-2 the effect of the branched-brush architecture on the nanotribological properties of the films became evident. Linear PMPC brushes showed the lowest friction among the studied brush structures, with a coefficient of friction (μ) that reached 1 × 10-4, as measured by atomic force microscopy (AFM). Bottlebrush brushes showed comparatively higher friction, although the high content of hydrophilic PMPC side chains along their backbone substantially improved lubrication compared to that displayed by the more sparsely substituted graft copolymer brushes.

Rationalizing the Phase Behavior of Triblock Copolymers through Experiments and Molecular Simulations

In this paper, we develop a new coarse-grained model, under the MARTINI framework, for Pluronic block copolymers that is able to describe the self-assembly mechanism and reproduce experimental micelle sizes and shapes. Previous MARTINI-type Pluronic models were unable to produce realistic micelles in aqueous solution, and thus our model represents a marked improvement over existing approaches. We then applied this model to understand the effects of polymer structure on the cloud point temperature measured experimentally for a series of Pluronics, including both normal and reverse copolymers. It was observed that high polyoxypropylene glycol content leads to dominant hydrophobic interactions and a lower cloud point temperature, while high hydrophilic polyoxyethylene glycol content shields the micelles against aggregation and hence leads to a higher cloud point temperature. As the concentration increases, the effect of polymer architecture (normal versus reverse) starts to dominate, with reverse Pluronics showing a lower cloud point temperature. This was shown to be due to the increased formation of cross-links between neighboring micelles in these systems, which promote micelle aggregation. Our results shed new light on these fascinating systems and open the door to increased control of their thermal responsive behavior.

Effect of Polymer Architecture on the Nanophase Segregation, Ionic Conductivity, and Electro-Osmotic Drag of Anion Exchange Membranes

Anion exchange membranes (AEMs) are considered an attractive alternative to proton exchange membranes in fuel cell applications because they can operate with nonprecious metal electrodes. However, ...

Synthesis and Solution Properties of Hydrophobically Modified Polysaccharides

Hydrophobically modified polymers are amphiphilic macromolecules mainly constituted of a hydrophilic backbone and hydrophobic side groups. In aqueous solutions these polymers undergo inter- or intra-molecular hydrophobic association, which results in unusual properties useful for a number of practical applications. The areas of application of these polymers include associative thickeners for enhanced oil recovery, pharmaceuticals, personal care formulations, coatings, adhesives, surfactants, emulsifiers, etc. This review presents the analysis of a literature data on preparation of hydrophobically modified polysaccharides (HMP) and their properties in aqueous solutions. Some of the synthetic methods used for hydrophobic modification of non-ionic (cellulose ethers, starch, dextran, pullulan, etc.), anionic (carboxymethylcellulose, hyaluronic<br />acid, pectic acid, alginic acid, heparin) and cationic olysaccharides (chitosan) are presented. The methodology used for the investigation of solution properties of hydrophobically modified polysaccharides is discussed. Special attention is paid to aggregate and micelle formation in solutions of hydrophobically<br />modified polysaccharides, solubilization of hydrophobic compounds, their rheological properties and surface activity. The effects of polymer architecture (level of hydrophobic substitution, nature of hydrophobic groups, molecular weight of a hydrophilic backbone, etc.), concentration, temperature, presence of inorganic salts and organic solvents on solution properties of hydrophobically modified polysaccharides are discussed. Some applications of hydrophobically modified polysaccharides are briefly highlighted.

Effect of Polymer Architecture on the Structure and Interactions of Polymer Grafted Particles: Theory and Simulations

We use Langevin dynamics simulations and Polymer Reference Interaction Site Model (PRISM) theory to study polymer grafted nanoparticles specifically to explain the impact of comb polymer architecture on the grafted layer structure and effective interparticle interactions in solvent and in matrix polymer. First, we use simulations to study a single particle grafted with comb polymers with varying comb polymer design (i.e., spacing and length of side chains along the comb polymer backbone), grafting density (i.e., polymer chains/particle surface area), and particle curvature in implicit solvent at the athermal limit. We find that increasing side chain length or decreasing side chain spacing along the comb polymer effectively swells and extends the polymer backbone due to the increasing side chain monomer crowding. For particles at finite curvature with increasing side chain monomer crowding, the monomer concentration profile of the comb polymer backbone at short distances from the surface resembles the concentration profile of a semiflexible linear polymer and at farther distances resembles that of flexible linear polymers grafted to a flat surface. As the particle curvature decreases to zero (i.e., flat surface), increasing side chain crowding has a simpler effect of expanding the grafted layer without changing the overall shape of the concentration profile. To understand how architecture affects the interactions of the comb polymer grafted particles, we use PRISM theory to calculate the potential of mean force (PMF) between comb polymer grafted particles in implicit solvent, explicit solvent, and explicit matrix of athermal linear polymers. On the basis of the PMFs calculated for a wide range of design parameters (grafting density, comb polymer design), we find that, compared to linear polymers, the comb polymers exhibit stronger effective attraction in the PMF between the grafted particles in both small molecule solvent and polymer matrix due to the increased crowding in the grafted layer from the comb polymer side chains. Interestingly, the PMF between the grafted particles in a small molecule solvent is more sensitive to the comb polymer design (i.e., side chain length and spacing) than the PMF between the grafted particles in a polymer matrix.

Effect of Polymer Architecture on the Ionic Conductivity. Densely Grafted Poly(ethylene oxide) Brushes Doped with LiTf

Densely grafted poly(ethylene oxide) (PEO) brushes on a poly(hydroxylstyrene) (PHOS) backbone (PHOS-g-PEO) as well as block copolymers with polystyrene (PS) (PS-b-(PHOS-g-PEO)) are designed as model systems for Li ion transport. This macromolecular design suppresses the propensity of PEO chains for complex crystal formation with LiTf as well as for crystallization. Li ion conductivities similar or even exceeding those in the archetypal electrolyte poly(ethylene oxide)/lithium triflate (PEO/LiCF3SO3 (LiTf)) are obtained for a range of temperatures and LiTf compositions. At the same time, PHOS-g-PEO and PS-b-(PHOS-g-PEO) show improved mechanical stability. Typically, at 333 K, the ionic conductivity is ∼6 × 10–5 S/cm and the modulus at ∼2 × 106 Pa for a [EO]:[Li+] = 8:1 composition. In the endeavor for suitable solid polymer electrolytes macromolecular architecture seems to play a decisive role.

Effect of polymer architecture on curcumin encapsulation and release from PEGylated polymer nanoparticles: Toward a drug delivery nano-platform to the CNS

We developed a nanoparticles (NPs) library from poly(ethylene glycol)–poly lactic acid comb-like polymers with variable amount of PEG. Curcumin was encapsulated in the NPs with a view to develop a delivery platform to treat diseases involving oxidative stress affecting the CNS. We observed a sharp decrease in size between 15 and 20% w/w of PEG which corresponds to a transition from a large solid particle structure to a “micelle-like” or “polymer nano-aggregate” structure. Drug loading, loading efficacy and release kinetics were determined. The diffusion coefficients of curcumin in NPs were determined using a mathematical modeling. The higher diffusion was observed for solid particles compared to “polymer nano-aggregate” particles. NPs did not present any significant toxicity when tested in vitro on a neuronal cell line. Moreover, the ability of NPs carrying curcumin to prevent oxidative stress was evidenced and linked to polymer architecture and NPs organization. Our study showed the intimate relationship between the polymer architecture and the biophysical properties of the resulting NPs and sheds light on new approaches to design efficient NP-based drug carriers.

Synthesis and properties of arborescent polyisobutylene derivatives and a paclitaxel conjugate: Towards stent coatings with prolonged drug release

Polyisobutylene (PIB) and its copolymers are used in a wide range of commercial products owing to their high chemical stability, impermeability, elasticity, and biocompatibility. The development of arborescent PIB (arb-PIB) opens many new possibilities for tuning PIB’s properties and for introducing new functionalities. In this work, arb-PIB with short isoprene-rich terminal sequences (arb-PIB-co-IP) was functionalized to provide arborescent epoxide, allylic alcohol, and carboxylic acid derivatives of PIB. The carboxylic acid derivative was used to conjugate the antiproliferative agent paclitaxel (PTX) for investigation as a potential vascular stent coating. The thermal, tensile, and rheological properties of all of the functionalized arb-PIB materials were studied and compared to their linear analogues in order to gain insight into the effects of polymer architecture on these properties as well as to determine their suitability as potential medical device coatings. A coating using the PTX conjugate was found to release PTX much more slowly than control formulations with physically encapsulated drug, yet was still able to prevent cell adhesion and proliferation on their surfaces.

A facile synthesis of catechol‐functionalized poly(ethylene oxide) block and random copolymers

ABSTRACTHerein we develop a facile synthetic strategy for the functionalization of well‐defined polyether copolymers with control over the number and location of catechol groups. Previously, the functionalization of polyethylene oxide (PEO)‐based polymers with catechols has been limited to functionalization of the chain ends only, hampering the synthesis of adhesive and antifouling materials based on this platform. To address this challenge, we describe an efficient and high‐yielding route to catechol‐functionalized polyethers, which could allow the effects of polymer architecture, molecular weight, and catechol incorporation on the adhesive properties of surface‐anchored PEO to be studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2685–2692

Remarkable Effect of Molecular Architecture on Chain Exchange in Triblock Copolymer Micelles

The effect of polymer architecture on molecular exchange in block copolymer micelles has been investigated using time-resolved small-angle neutron scattering (TR-SANS). Narrowly dispersed symmetric PEP–PS–PEP and PS–PEP–PS triblock copolymers were synthesized, where PS and PEP refer to poly(styrene) and poly(ethylene-alt-propylene), respectively. Spherical micelles of the triblocks in squalane, a selective solvent for the PEP blocks, were prepared using a cosolvent method. PEP–PS–PEP forms “hairy” micelles with the PS blocks looped in the cores, while PS–PEP–PS forms “flower-like” micelles with most of the PEP blocks looped in the corona. The micelle structure was characterized by small-angle X-ray scattering, providing in particular the core radius as a function of temperature. TR-SANS experiments were conducted on solutions containing 1 and 6 vol % PEP–PS–PEP, and 0.25 and 0.5 vol % PS–PEP–PEP, using matched pairs of deuterium-labeled (dPS) and normal (hPS) specimens and a mixture of normal and perdeuterated squalane contrast-matched to uniformly mixed hPS/dPS micelle cores. Blends of micelles with initially pure hPS and dPS cores produce scattering intensity that decays with the redistribution of block copolymer chains as a function of time, providing direct access to the rate of molecular exchange. Remarkably, the two triblock architectures display exchange rates that differ by approximately 9 orders of magnitude, even though the solvophobic PS blocks are of comparable size. This discovery is considered in the context of a model that successfully explained the exchange dynamics in PS–PEP diblock copolymer micelles.