Linear Polymer Chains Research Articles

Synthesis of Star Polymers by RAFT Polymerization as Versatile Nanoparticles for Biomedical Applications

The precise control of polymer chain architecture has been made possible by developments in polymer synthesis and conjugation chemistry. In particular, the synthesis of polymers in which at least three linear polymeric chains (or arms) are tethered to a central core has yielded a useful category of branched architecture, so-called star polymers. Fabrication of star polymers has traditionally been achieved using either a core-first technique or an arm-first approach. Recently, the ability to couple polymeric chain precursors onto a functionalized core via highly efficient coupling chemistry has provided a powerful new methodology for star synthesis. Star syntheses can be implemented using any of the living polymerization techniques using ionic or living radical intermediates. Consequently, there are innumerable routes to fabricate star polymers with varying chemical composition and arm numbers. In comparison with their linear counterparts, star polymers have unique characteristics such as low viscosity in solution, prolonged blood circulation, and high accumulation in tumour regions. These advantages mean that, far beyond their traditional application as rheology control agents, star polymers may also be useful in the medical and pharmaceutical sciences. In this account, we discuss recent advances made in our laboratory focused on star polymer research ranging from improvements in synthesis through to novel applications of the product materials. Specifically, we examine the core-first and arm-first preparation of stars using reversible addition–fragmentation chain transfer (RAFT) polymerization. Further, we also discuss several biomedical applications of the resulting star polymers, particularly those made by the arm-first protocol. Emphasis is given to applications in the emerging area of nanomedicine, in particular to the use of star polymers for controlled delivery of chemotherapeutic agents, protein inhibitors, signalling molecules, and siRNA. Finally, we examine possible future developments for the technology and suggest the further work required to enable clinical applications of these interesting materials.

Ring polymer chains confined in a slit geometry of two parallel walls: the massive field theory approach

The investigation of a dilute solution of phantom ideal ring polymer chains confined in a slit geometry of two parallel repulsive walls, two inert walls, and for the mixed case of one inert and the other one repulsive wall, was performed. Taking into account the well known correspondence between the field theoretical O(n)-vector model in the limit and the behaviour of long-flexible polymer chains in a good solvent, the investigation of a dilute solution of long-flexible ring polymer chains with the excluded volume interaction (EVI) confined in a slit geometry of two parallel repulsive walls was performed in the framework of the massive field theory approach at fixed space dimensions d = 3 up to one-loop order. For all the above mentioned cases, the correspondent depletion interaction potentials, the depletion forces and the forces which exert the phantom ideal ring polymers and the ring polymers with the EVI on the walls were calculated, respectively. The obtained results indicate that the phantom ideal ring polymer chains and the ring polymer chains with the EVI due to the complexity of chain topology and because of the entropical reason demonstrate completely different behaviour in confined geometries than linear polymer chains. For example, the phantom ideal ring polymers prefer to escape from the space not only between two repulsive walls but also in the case of two inert walls, which leads to the attractive depletion forces. The ring polymer chains with less complex knot types (with the bigger radius of gyration) in a ring topology in the wide slit region exert higher forces on the confining repulsive walls. The depletion force in the case of mixed boundary conditions becomes repulsive in contrast to the case of linear polymer chains.

Effects of multifunctional cross-linkers on rheology and adhesion of soft nanostructured materials.

We investigate the nanostructure, the rheology and the adhesion of soft supramolecular materials elaborated by blending monofunctional and multifunctional poly(isobutene) (PIB) chains. Monofunctional PIB chains (PIBUT) are linear and unentangled polymer chains (Mn ≈ 3 kg mol-1) functionalized in the middle by a bis-urea interacting moiety, able to self-associate by four hydrogen bonds. Covalent coupling of monofunctional PIB allows us to synthesize longer chains bearing two or three interacting moieties. These chains are then added to monofunctional PIB to prepare blends containing up to 10% of multifunctional PIB (M-PIBUT). The influence of M-PIBUT on the supramolecular nanostructure, which results from the self-assembly of stickers, is studied by Atomic Force Microscopy and Small Angle X-ray Scattering at room temperature. Multifunctional and monofunctional chains are shown to interact with each other to form bundles of rod-like aggregates. The consequences of these interactions on the rheology of the blends were studied by shear tests in the linear and non linear regimes, below and above the order-disorder transition temperature. A pronounced strengthening effect of M-PIBUT is observed at room temperature: the supramolecular blends become more elastic and are more resistant to creep with increasing concentration of M-PIBUT. The effects of M-PIBUT on the nanostructure and the rheology suggest that M-PIBUT, which can link with more than one supramolecular aggregate, plays the role of a physical cross-linker. The impact of these supramolecular cross-linkers on the adhesion of the blends is studied by probe-tack tests and discussed by analyzing the in situ deformation through the debonding images.

Colloidal gels tuned by oscillatory shear.

We examine the microstructural and mechanical changes which occur during oscillatory shear flow and reformation after flow cessation of an intermediate volume fraction colloidal gel using rheometry and Brownian Dynamics (BD) simulations. A model depletion colloid-polymer mixture is used, comprising a hard sphere colloidal suspension with the addition of non-adsorbing linear polymer chains. The results reveal three distinct regimes depending on the strain amplitude of oscillatory shear. Large shear strain amplitudes fully break the structure which results in a more homogenous and stronger gel after flow cessation. Intermediate strain amplitudes densify the clusters and lead to highly heterogeneous and weak gels. Shearing the gel to even lower strain amplitudes creates a less heterogonous stronger solid. These three regimes of shearing are connected to the microscopic shear-induced structural heterogeneity. A comparison with steady shear flow reveals that the latter does not produce structural heterogeneities as large as oscillatory shear. Therefore oscillatory shear is a much more efficient way of tuning the mechanical properties of colloidal gels. Moreover, colloidal gels presheared at large strain amplitudes exhibit a distinct nonlinear response characterized largely by a single yielding process while in those presheared at lower rates a two-step yielding process is promoted due to the creation of highly heterogeneous structures.

Residual stresses in colloidal gels.

A combination of experiments and Brownian Dynamics (BD) simulations is utilized to examine internal stresses in colloidal gels brought to rest from steady shear at different shear rates. A model colloidal gel with intermediate volume fraction is chosen where attractions between particles are introduced by adding non-adsorbing linear polymer chains. After flow cessation, the gel releases the stress in two distinct patterns: at high shear rates, where shear forces dominate over attractive forces, the shear-melted gel behaves as a liquid and releases stresses to zero after flow cessation. After low shear rates, though, stresses relax only partially, similar to the response of hard sphere glasses and jammed soft particles. The balance between shear and attractive forces which determines the intensity of structural distortion controls the amplitude of the residual stresses through a universal scaling. Stress decomposition to repulsive and attractive contributions in BD simulations reveals that internal stresses mainly originate from attractive forces. Moreover, analysis of particle dynamics indicates that internal stresses are associated with sub-diffusive particle displacements on average smaller than the attraction range as such short-range displacements are not sufficient to completely erase structural anisotropy caused during the course of shear.

Dynamic self-assembly of ‘living’ polymeric chains

We report a dynamic self-assembly system of ‘living’ polymeric chains sustained by chemistry using reactive molecular dynamics simulations. The linear polymeric chains consist of self-assembled nanoparticles connected by metastable linker molecules. As such, the polymeric chains, once assembled, undergo spontaneous dissociation driven by thermodynamics. However, with a continuous supply of linker molecules and the stored chemical energy therein, the polymeric chains can survive and maintain a steady state averaged chain length. These dynamically self-assembled polymeric chains are analogous to biological systems that both are thermodynamically metastable, yet dynamically stable upon continuous influx of matter and energy.

Semi-Interpenetrating Polymer Networks with Predefined Architecture for Metal Ion Fluorescence Monitoring.

The development of new synthetic approaches for the preparation of efficient 3D luminescent chemosensors for transition metal ions receives considerable attention nowadays, owing to the key role of the latter as elements in biological systems and their harmful environmental effects when present in aquatic media. In this work, we describe an easy and versatile synthetic methodology that leads to the generation of nonconjugated 3D luminescent semi-interpenetrating amphiphilic networks (semi-IPN) with structure-defined characteristics. More precisely, the synthesis involves the encapsulation of well-defined poly(9-anthrylmethyl methacrylate) (pAnMMA) (hydrophobic, luminescent) linear polymer chains within a covalent poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) hydrophilic polymer network, derived via the 1,2-bis-(2-iodoethoxy)ethane (BIEE)-induced crosslinking process of well-defined pDMAEMA linear chains. Characterization of their fluorescence properties demonstrated that these materials act as strong blue emitters when exposed to UV irradiation. This, combined with the presence of the metal-binding tertiary amino functionalities of the pDMAEMA segments, allowed for their applicability as sorbents and fluorescence chemosensors for transition metal ions (Fe3+, Cu2+) in solution via a chelation-enhanced fluorescence-quenching effect promoted within the semi-IPN network architecture. Ethylenediaminetetraacetic acid (EDTA)-induced metal ion desorption and thus material recyclability has been also demonstrated.

Improved operational stability of Pebax-based gas separation membranes with ZIF-8: A comparative study of flat sheet and composite hollow fibre membranes

Polymer-based hollow fibre composite membranes are composed of a porous support coated with a highly permeable gutter layer, and a thin selective top layer. They are promising candidates for industrial gas separation, but there are challenges in maintaining their performance under high pressure or during long-term operation. To tackle this, we incorporated ZIF-8 into Pebax-1657 (polyamide-polyether copolymer) for gas separation membrane fabrication. To fully understand the behaviour of hollow fibre composite membranes, special attention was paid to the effect of ZIF-8 on the Pebax chain structure using dense film flat sheet membranes. The presence of porous ZIF-8 disrupted the original well-packed polymer chain structure, leading to higher fractional free volume and gas permeability. However, the introduced microvoids were non-continuous and the gas selectivity was only slightly reduced. On the other hand, the stable structure of ZIF-8, together with the hydrogen bonds between ZIF-8 organic ligands and polyamide chains, significantly improved the linear glassy polymer chain stiffness, ensuring good operational stability under elevated pressure for both flat sheet and hollow fibre membranes. Finally, good long-term operational stability was observed with the hollow fibre membrane, indicating the ZIF-8/Pebax coating overcame the aging previously observed for the poly[1-(trimethylsilyl)-1-propyne] (PTMSP) gutter layer.

Syntheses, supramolecular structures, and thermal behavior of heteronuclear gold(III)–mercury(II) dithiocarbamatochloride complexes [Au{S2CN(CH3)2}2]2[HgCl4] and ([Au{S2CN(C2H5)2}2]2[Hg2Cl6] · OC(CH3)2) n by 13C MAS NMR, X-ray diffraction, and simultaneous thermal analysis data

New heteronuclear gold(III)–mercury(II) compounds are synthesized by the chemisorption reaction of freshly precipitated mercury dimethyl (MeDtc) and diethyl dithiocarbamates (EtDtc) with [AuCl4]− anions in a medium of 2 M HCl. The crystals of complexes [Au{S2CN(CH3)2}2]2[HgCl4] (I) and ([Au{S2CN(C2H5)2}2]2[Hg2Cl6] • OC(CH3)2)n (II) are obtained from solutions in methanol and acetone, respectively. The crystal and supramolecular structures of the preparatively isolated compounds are determined by X-ray diffraction analysis (CIF files CCDC nos. 1452118 (I) and 1452119 (II)). The structure of ionic complex I is built of alternating binuclear [Au2{S2CN(CH3)2}4]2+ cations and [HgCl4]2− anions. A more complicated structure of compound II contains centrosymmetric isomeric [Au{S2CN(C2H5)2}2]+ cations (A and B) and centrosymmetric binuclear [Hg2Cl6]2− anions. The supramolecular structure of compound II is formed due to pairs of Au•••S secondary bonds between the adjacent gold(III) complex cations resulting in the formation of linear polymeric chains [•••A•••B•••]n (directed along the x crystallographic axis). Isomeric cations A and B are alternated along the chains. The character of thermolysis of the complexes is studied and the regeneration conditions of bound gold are revealed by the simultaneous thermal analysis data. The thermal destruction of compounds I and II occurs simultaneously at the cationic and anionic moieties of the compounds to reduce gold(III) accompanied by the release and subsequent sublimation of mercury(II) chloride. The final product of the thermal transformations of the complexes is reduced elemental gold.

Branching Analysis of Multivalent Conjugates Using Size Exclusion Chromatography-Multiangle Light Scattering.

Multivalent conjugates (MVCs) (conjugation of multiple proteins to a linear polymer chain) are powerful for improving the bioactivity and pharmacokinetics of a bioactive molecule. Since this effect is highly dependent upon the valency of the conjugated proteins, it is imperative to have a technique for analysis of the conjugation ratio. Studies of MVCs have used size exclusion chromatography-multiangle light scattering (SEC-MALS), which allows for the separate and individual analysis of the protein and biopolymer components based on their specific refractive index increment and UV extinction coefficient constants to determine the number of proteins bound per biopolymer molecule. In this work, we have applied traditional branching analysis to the SEC-MALS data, with the primary assumption that the polymer backbone can be used as the linear counterpart. We demonstrated good agreement between the branching values and the valency determined by traditional analysis, demonstrating that branching analysis can be used as an alternative technique to approximate the valency of MVCs. The branching analysis method also provides a more complete picture of the distribution of the measured values, provides important branching information about the molecules, and lowers the cost and complexity of the characterization. However, since MVC molecules are both conjugate molecules and branched molecules, the most powerful approach to their characterization would be to use both traditional multivalent conjugate analysis and branching analysis in conjunction.

Structure of a coordination polymer based on the bioctahedral [Re12CS14(SO2)3(CN)6]6– cluster anion and ammine complexes of Ni2+

The first coordination polymer containing the [Re12CS14(SO2)3(CN)6]6– cluster anion is obtained and structurally characterized. The [{Ni(NH3)4}3{Re12CS14(μ-SO2)3(CN)6}]∙14H2O compound (1) is obtained by the reaction of NiCl2∙6H2O and K6[Re12CS14(μ-SO2)3(CN)6] in a mixture of NH3/H2O and CH3CN. The compound crystallizes in the triclinic space group P-1 with the unit cell parameters: a = 13.1633(4) A, b = 14.0464(4) A, c = 20.7198(7) A, α = 73.660(1)°, β = 83.101(1)°, γ = 65.102(1)°, V = 3334.6(2) A3, Z = 2, d calc = 3.661 g/cm3. The crystal structure is composed of linear polymeric chains located parallel to the b axis and solvate H2O molecules bound by hydrogen bonds.

A Highly Stretchable and Autonomous Self‐Healing Polymer Based on Combination of Pt···Pt and π–π Interactions

A new self-healing polymer has been obtained by incorporating a cyclometalated platinum(II) complex Pt(C∧ N∧ N)Cl (C∧ N∧ N = 6-phenyl-2,2'-bipyridyl) into a polydimethylsiloxane (PDMS) backbone. The molecular interactions (a combination of Pt···Pt and π-π interactions) between cyclometalated platinum(II) complexes are strong enough to crosslink the linear PDMS polymer chains into an elastic film. The as prepared polymer can be stretched to over 20 times of its original length. When damaged, the polymer can be healed at room temperature without any healants or external stimuli. Moreover, the self-healing is insensitive to surface aging. This work represents the first example where the attractive metallophilic inter-actions are utilized to design self-healing materials. Moreover, our results suggest that the stretchability and self-healing properties can be obtained simultaneously without any conflict by optimizing the strength of crosslinking interactions.

Innovation in poly(vinyl acetate) water resistant D3 glues used in wood industry

Poly(vinyl acetate) (PVAc) water-resistant glues used in the wood industry and belonging to the class of durability D3 show high resistance to both water and heat compared to the usual PVAc-based thermoplastic products. In conventionally synthesised adhesives this is attained by means of cross-linking (although limited) of the linear polymer chains and moreover by using inorganic salts, such as aluminium chloride.The paper illustrates the limits of these products and presents the prospects in the chemistry of industrial-grade D3-class PVAc adhesives. More in detail, it is shown how the individual roles of both cross-linking agent and aluminium chloride contribute to the occurrence of recurring inconveniences characterising conventional PVAc-D3 glues, which include formaldehyde release during time (mostly related to the curing agent), glueline colouring and indirect staining of wood (both are mostly evident in selected wood species, in the presence of either heat or UV irradiation), acidic pH, and equipment corrosion (related to the presence of aluminium chloride).Understanding those mechanisms has constituted the basis for the development of newly synthesised PVAc-D3 glues, whose characterisation is expressly reported in the present work. Such systems have shown good adhesion to wood surfaces and have exhibited neither corrosive nor chromatic alteration evidences, as well as absence of formaldehyde emissions. All these occurrences were verified by specific tests, such as corrosion on steel, measurements of the formaldehyde content of the dispersion, and emissions from panel boards, and glueline exposure to both temperature and UV irradiation after application in selected wood species.

Surface enrichment driven by polymer topology

We report a molecular dynamics simulation study of free-standing films of a blend of linear and cyclic polymer chains. We find that the composition of linear chains at the interface is enhanced relative to their bulk value for short chains but is depleted for long chains. Our findings are in agreement with recent experimental evidence reported for blends of short linear and cyclic polystyrene chains and highlight the genuine surface behavior in the short chain-length regime where theoretical predictions are more difficult. We highlight surface enrichment at low-energy surfaces as the result of competition between different entropic and enthalpic contributions to the interfacial free energy of the system.

From a ring polymer to a tribridged multicyclic nanoconstruct

Our previous work on macromolecular pyramoids is extended to a nanostructure made of macromolecular rings connected with linear polymeric chains. The example of two and three rings of different molecular weights connected with three linear polymeric segments is explicitly studied. The sizes of the ring parts as well as of the linear connectors are given and utilized to derive indications for large internal volume and surface openings of the macromolecular nanoconstructs. Indications of helical structures are also discussed.

Effect of ionic liquids on the structural, thermal, and in vitro degradation properties of poly(ε‐caprolactone) synthesized in the presence of Candida antarctica lipase B

ABSTRACTThe study provides detailed information on the differences in the structural, thermal and degradation properties of poly(ε‐caprolactone) synthesized in two different ionic liquids, 1‐butyl‐3‐methylimidazolium hexafluorophosphate [bmim][PF6] and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim][NTf2], regarding its further usage in the pharmaceutical field. The polymer structure confirms the presence of both linear polymer chains with end‐functional hydroxyl groups allowing covalent coupling of the therapeutic agents, and cyclic macromolecules, both affecting the degree of crystallinity of polymer. The highest macrocyclic content (64%) after 7 days of polymerization at 80 °C was observed for [bmim][NTf2]. For [bmim][PF6], the macrocyclic content value was not dependent on the reaction time and remained at a similar level (10–14% at 80 °C). The results of degradation test revealed that hydrolytic degradation of ester bonds is more pronounced for PCLs synthesized in [bmim][NTf2], due to their lower degree of crystallinity compared with PCLs obtained in [bmim][PF6]. A high purity, low polydispersity index of the obtained polymers and high yield of the process (ca., 90%) indicate that ionic liquids seem to be promising solvents for the synthesis of biomedical polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43728.

Crystal and Molecular structures of Tris- (3,5 – dinitrobenzoato) Disproziy (III) Dihidrat

In the crystal structure of the Tris(3,5 – dinitrobenzoato) Disproziy (III)dihidrat Dy C H N O H O n n n ( ) ( ) 7 3 2 63 2 2 [ ], disproziy ions are bridged by carboxylate qroups to from linear polymeric chains. The coordination around Dy is eightfold involving six O atoms from tris carboxylate qroups and two water O atoms. Within the polymeric chains, only the bridging type of bonding exists. The Dy-O distances of the bridging carboxylate qroups 2 2964 8 3530 17 . ( ) ( ) and 2. A are shorter than the Dy-O distances 2 441 2 2 509 2 . . ( ) ( ) −   A involving the water molecules.

Изучение физико-химических свойств новых водорастворимых сополимеров катионного типа на основе N-изопропилакриламида

Novel water-soluble copolymers of cationic type have been synthesized by free-radical copolymerization of N-isopropylacrylamide (NIPAAm) and N-(2-vinyloxyethyl)-N-(2-cyanoethyl)amine (VOECEA) in ethanol solutions, employing 2,2’-azobisisobutyronitrile (AIBN) as radical initiator. The polymerization at 60°C was carried out in ampules in an argon atmosphere for 2 h. After the reaction, the resultant copolymers were precipitated twice in boiling water and was then vacuum-dried for 24 h. The obtained NIPAAm-VOECEA copolymers were characterized by means of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was observed that for copolymers with low moieties of NIPAAm in composition the degradation starts at low temperatures due to thermal decomposition of nitrogen groups of the copolymer. The presence of an oxygen in VOECEA backbone contributes the decomposition of linear copolymers at low temperatures. It was measured the glass transition temperature (Tg) of the synthesized copolymers. It was observed that with increasing the units of NIPAAm in copolymer composition the Tg increases due to the folding of linear polymer chain and the rigidity of NIPAAm moieties.

Ring Polymer Dynamics Are Governed by a Coupling between Architecture and Hydrodynamic Interactions

The behavior of linear polymer chains in dilute solution flows has an established history. Polymers often possess more complex architectures, however, such as branched, dendritic, or ring structures. A major challenge lies in understanding how these nonlinear chain topologies affect the dynamic properties in nonequilibrium conditions, in both dilute and entangled solutions. In this work, we interrogate the single-chain dynamics of ring polymers using a combination of simulation, theory, and experiment. Inspired by recent experimental results by Li et al., we demonstrate that the presence of architectural constraints has surprising and pronounced effects on the dynamic properties of polymers as they are driven out of equilibrium. Ring constraints lead to two behaviors that contrast from linear chains. First, the coil–stretch transition occurs at larger values of the dimensionless flow strength (Weissenberg number) compared to linear chains, which is driven by coupling between intramolecular hydrodynamic in...

Fragility-Confinement Effects: Apparent Universality as a Function of Scaled Thickness in Films of Freely Deposited, Linear Polymer and Its Absence in Densely Grafted Brushes

Ellipsometry measurements as a function of cooling rate are used to study nanoscale confinement effects on dynamic fragility (kinetic fragility), m, in supported films of freely deposited, linear polymer. Polymers include neat polystyrene (PS), neat polycarbonate (PC), and PS + 2 wt % 1,10-bis(1-pyrene)decane (BPD) as small-molecule diluent; in each case, the substrate/polymer interface lacks significant attractive interactions. In terms of both the length scale at which confinement effects become evident and the percentage reduction in m from its bulk value, the magnitude of the m-confinement effect increases with increasing bulk polymer system m. Additionally, for films of linear polymer lacking significant attractive interactions with the substrate surface, m-confinement effects are evident at larger onset thicknesses than those commonly reported in the literature for the glass transition temperature (Tg)-confinement effect. Evans et al. [Macromolecules 2013, 46, 6091] found that the Tg-confinement effect in related films exhibits a universal nature as a function of scaled thickness. Fragility-confinement effects of films of freely deposited, linear polymer chains exhibit a similar universal nature as a function of scaled thickness using shift factors consistent with those used by Evans et al. However, when PS is confined in a dense brush with one end of each chain covalently attached to the substrate surface, both m and Tg are independent of brush thickness. The strong correlation of fragility-confinement and Tg-confinement effects has important implications for understanding the fundamental natures of both the Tg-confinement effect and the glass transition itself.