Influence Of Polymer Structure Research Articles

Tough supramolecular hydrogels of poly(N,N-dimethylacrylamide)-grafted poly(methacrylic acid) with cooperative hydrogen bonds as physical crosslinks.

Incorporating associative interactions as the energy dissipation units has been recognized as an effective strategy to develop tough hydrogels. For hydrogen-bond associations, however, it is highly challenging to stabilize them under aqueous conditions. Although affording cooperativity can enhance and stabilize the hydrogen bonds, it usually requires stepwise polymerization to form these cooperative associations between different polymers and networks. Here, we report a series of tough supramolecular hydrogels with robust hydrogen-bond associations between grafted polymers that are synthesized by polymerization of a macromonomer of poly(N,N-dimethylacrylamide) (PDMAA) and a small monomer of methacrylic acid. The grafted chains of PDMAA form cooperative hydrogen bonds with the main chain of poly(methacrylic acid) (PMAAc), forming supramolecular hydrogels with high toughness and good stability. The tough and stiff hydrogels are in a glassy state, exhibit forced elastic deformation at room temperature, and remain stable over a wide pH range. In contrast, hydrogels prepared by the copolymerization of DMAA and MAAc are swollen and weak in water due to the lack of successive hydrogen donor/acceptor units and the absence of cooperative hydrogen bonds. In addition, these tough hydrogels exhibit good recyclability and shape memory properties, owing to the supramolecular nature of the network and the temperature-dependent mechanical properties. The influence of polymer structure on the associative interactions and macroscopic properties of the hydrogels should be informative for the design of tough soft materials with versatile applications.

(Invited) Microwave Dielectric Relaxation Spectroscopy: A Technique to Inform Ion Transport in Hydrated Polymer Membranes

Providing sustainable supplies of purified water and energy is a critical global challenge for the future, and polymer membranes will play a key role in addressing these clear and pressing global needs for water and energy. Polymer membrane-based processes dominate the desalination market because they are more energy efficient than thermal desalination processes, and polymer membranes are crucial components in several rapidly developing power generation and energy storage applications that rely on membranes to control, selectively, rates of ion transport. Much remains unknown about the influence of polymer structure on basic intrinsic transport properties, and these relationships are important for designing next generation polymer membrane materials.Key to controlling ion transport in membranes for water purification and energy applications is engineering interactions between ions and the solvated polymer matrix. Microwave dielectric relaxation spectroscopy is a tool that enables study of hydrated polymer membranes because water molecule dipoles can be probed in the microwave frequency region. This technique can provide unique insight into hydrated polymer dielectric permittivity (or dielectric constant) properties, which are critical in emerging thermodynamic modeling of ion transport in hydrated polymers. This presentation discusses the use of microwave dielectric relaxation spectroscopy to uncover structure property relationships in hydrated polymers and, more broadly, presents an overview of research aimed at further understanding fundamental structure/property relationships that govern small molecule transport in polymeric materials considered for desalination and electric potential field-driven membrane applications that can help address global needs for clean water and energy.

Reactive Multilayers and Coatings Fabricated by Spray Assembly: Influence of Polymer Structure and Process Parameters on Multiscale Structure and Interfacial Properties

Reactive Multilayers and Coatings Fabricated by Spray Assembly: Influence of Polymer Structure and Process Parameters on Multiscale Structure and Interfacial Properties

Influence of Polymer Structure and Architecture on Drug Loading and Redox-Triggered Release.

Disulfide cross-linked nanoassemblies have attracted considerable attention as a drug delivery vehicle due to their responsiveness to the natural redox gradient in biology. Fundamentally understanding the factors that influence the drug loading capacity, encapsulation stability, and precise control of the liberation of encapsulated cargo would be profoundly beneficial to redox-responsive materials. Reported herein are block copolymer (BCP)-based self-cross-linked nanogels, which exhibit high drug loading capacity, high encapsulation stability, and controllable release kinetics. BCP nanogels show considerably higher loading capacity and better encapsulation stability than the random copolymer nanogels at micromolar glutathione concentrations. By partially substituting thiol-reactive pyridyl disulfide into the unreactive benzyl or butyl group, we observed opposite effects on the cross-linking process of BCP nanogels. We further studied the redox-responsive cytotoxicity of our drug-encapsulated nanogels in various cancer cell lines.

Removing ammonium from water using porous resins: influence of polymer structure, ion exchange capacity and porosity

This study describes the synthesis of polymeric resins based on styrene (STY), glycidyl methacrylate (GMA) and divinylbenzene (DVB), modified chemically through sulfonation reactions during different time intervals, to learn the influence of the materials’ structure on their adsorption capacity and evaluate their potential for application in the removal of ammonium from wastewater to levels compliant with the technical standard NT202, R-10 (INEA, 1986). The results showed that besides the duration of the sulfonation reaction, factors such as surface area and pore diameter also contributed significantly to the ammonium absorption process. The efficiency of the formulations was in decreasing order DVB(7:3)(2)S, DVB(7:3)(24)S, STY-DVB(7:3)(2)S and GMA-DVB(7:3)(2)S. Of these, DVB(7:3)(2)S had the greatest surface area but had low ion exchange capacity. The resin with the greatest exchange capacity was STY-DVB(7:3)(2)S, but it had efficiency about 20% lower than the former resin, showing a result very near that of GMA-DVB(7:3)(2)S.

Influence of polymer structure and amount on microstructure and properties of polyethylene-modified asphalt binders

In recent years, the use of polyethylene (PE) for asphalt modification has been gaining increased attention due to the environmental sustainability and cost-saving benefits. To optimize the performance of the PE-asphalt blends, it is necessary to understand the polymer-binder interactions and their impact on the properties of the modified asphalt binder. In this study, low-density polyethylene (LDPE) with low and high melt flow index (MFI), i.e., LDPE4 and LDPE70, were blended with Pen 60-70 asphalt binder in dosages ranging from 1 to 5 wt.%. PE Wax was also added to the binder or the PE-binder blend to enhance dispersion. The dispersion of PE in the binder and the phase stability of the modified binder were investigated by optical microscope. The equivalent diameter of PE domains increased with time and the polymer dosage level. The addition of PE wax improved the polymer dispersity in the LDPE4 blends. The polymer dispersity in LDPE70 blends was good without adding PE Wax, attributed to the higher MFI value (low molecular weight) of LDPE70. In addition, to understand the stability of polymer modified binder, the steady shear viscosity-temperature profile of these binders was studied using a rotational viscometer. The dynamic rheological properties and performance of the PE-binder blends were evaluated using the dynamic shear rheometer. Based on the microstructure, all other rheological and performance properties, it was concluded that the 3% LDPE70 binder has better polymer dispersity, better low and high temperature performance characteristics.

Influence of polymer structure on the electrical resistivity of nanocomposite materials

In this work, the influence of polymer structure on the electrical resistivity of polymer composites filled with carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), or carbon black (CB) was investigated. An amorphous polymer, polystyrene (PS), and a semi-crystalline polymer, polypropylene (PP), of similar viscosities were selected to investigate the effect of polymer matrix structure on the composites’ electrical resistivity. The composites were prepared by melt mixing in a small batch mixer. CNT dispersion in PS was better than that in PP, and the electrical resistivity of CNT/PS was lower than that of CNT/PP. For example, the electrical resistivity of the 1 vol% CNT/PS and 1 vol% CNT/PP were 13 Ω cm and 120 Ω cm, respectively. However, no significant difference in the electrical resistivity and state of dispersion for both CB-based and GNP-based composites were observed. For the CNT-based composites, it can be speculated that the better dispersibility of CNT particles within the PS matrix has greater influence on the construction of the three-dimensional network than the volume exclusion effect possessed by the PP semi-crystalline polymer.

Phase behavior and hot storage characteristics of asphalt modified with various polyethylene: Experimental and numerical characterizations

Phase behavior is crucial to multi-phase materials, which intensively affects macro-performance of materials. Polymer modified asphalt is a typical multi-phase material and widely applied in paving industry. This paper presents the fundamental understanding of phase behavior and hot storage characteristics of polyethylene (PE) modified asphalts. The influence of polymer structure on phase behavior was studied by experimental and numerical approaches. Experimentally, four typical PE modified asphalts were selected to prepare thin film slides of asphalt, which were subjected to isothermal annealing and observed under fluorescence microscopy (FM). The morphology evolutions were evaluated by statistical size distribution. Storage stability was further evaluated by tube test. Numerically, microstructure evolutions and storage stability were described by phase field method. The results showed that the scope of PE phase size distribution becomes wider during annealing. Linear low-density PE shows a relative slow separation. Phase-field model perfectly describes the experimental microstructure evolution. Polyethylene structural parameters significantly affect the phase behavior. Lower crystalline, higher melt flow index (MFI) as well as more branched molecule promotes the swelling of PE particle and the interaction of constituents. Moreover, differences in density and viscosity between PE and asphalt greatly accelerate the separation in the vertical direction.

Thermal properties of thermoplastic polymers: Influence of polymer structure and procedure of radical polymerization

Experimental data prove a significant mutual interference between the chemical nature of the monomer and the particularities of the radical polymerization procedure which influences the thermal decomposition (depropagation) of the corresponding polymer. Results are presented for polystyrene, poly(methyl methacrylate), and poly(α-methylene-γ-valerolactone) which were made via different radical polymerization techniques (thermally self-initiated bulk polymerization at 80 °C, photoinitiated bulk and aqueous heterophase polymerization at 25 °C). Also, experimental data are presented after thermally annealing the polymers at 200 and 300 °C.

Oligosaccharide-crowned hyperbranched poly(ethyleneimine) as an additive to thin-layer chromatography systems for the separation of vitamins, amino acids and β-blocker enantiomers

Impregnation of a stationary phase by organic and inorganic agents in high-performance thin-layer chromatography (HPTLC) may result in higher separation selectivity and resolution. This work is devoted to the application of novel core–shell polymers consisting of hyperbranched (poly(ethyleneimine)) core surrounded by oligosaccharide shell (PEI-OS) as a component of silica stationary phase in HPTLC for the separation of water-soluble vitamins, amino acids, and chiral β-blocker enantiomers. The influence of polymer structure (degree of substitution of PEI terminal amino groups with oligosaccharides and molecular weight of dendritic core [5 or 25 kDa]) as well as the content of PEI-OS in the stationary phase and a method of modification of the stationary phase on the efficiency of vitamin and amino acid determination and on the enantioselectivity factors of β-blockers separation were investigated. It was established that such polymers can be used as modifying agents of HPTLC systems for on-line preconcentrat...

Is Molecular Weight or Degree of Polymerization a Better Descriptor of Ultrasound-Induced Mechanochemical Transduction?

A detailed understanding of the fundamental processes that govern mechanical transduction in covalent polymer mechanochemistry is essential to advance innovation in this field. In contrast to progress in the development of new mechanophores, the influence of polymer structure and composition on mechanochemical activity has received relatively little attention. In order to address this gap in knowledge, a continuous flow system with synchronous UV-vis absorption capabilities was designed to quantify the ultrasound-induced mechanical activation of a spiropyran mechanophore in real-time. Measurements of reaction kinetics with polymer tethers of varying repeating unit structure demonstrate that degree of polymerization is the key descriptor of mechanochemical activity, independent of molecular weight and pendant group constitution. These results have important implications for the rationalization of mechanochemical properties and the design of new mechanochemically active polymer systems.

Structure property relationship for carbazole and benzothiadiazole based conjugated polymers

A series of conjugated polymers with carbazole monomer/dimer/trimer as the donor unit or benzothiadiazole monomer/trimer as the acceptor unit were synthesized and used as donor materials for polymer solar cells (PSCs). The influence of polymer structure on the optical properties and performance of PSCs was investigated in detail. P1 showed a power conversion efficiency (PCE) of 5.8%. The incorporation of longer donor or acceptor unit leads to a blue shift of absorption spectrum and the polymers became more amorphous due to the large torsion angels in the polymer backbone. After increasing the length of donor or acceptor, the PCE decreased dramatically to 0.43% for P2, 0.23% for P3, and 1.23% for P4. Our results have offered a useful insight to structure–property relationship for high performance polymer solar cells.

The Influence of Polymer Structure on the Physical Characteristic of Intraoral Film Containing BSA-loaded Nanoemulsion

Therapeutic protein has limitation, both in stability and invasive route of administration. Therefore, formulation to optimize the use of therapeutic protein becomes the research focus of interest. The purpose of this study was to develop nanoemulsion as a carrier system for a standard-model protein drug – bovine serum albumin (BSA). BSA-loaded nanoemulsion was then formulated into hydrophilic film for intraoral route. The influence of polymers was evaluated in relation to physical property of the film. Nanoemulsion was prepared using self assembly method with composition of Glyceryl monooleate (GMO), Cremophor RH-40 and Polyethylene glycol (PEG 400), with ratio of 1:8:1. The film was prepared using different polymers and plasticizers with solvent casting technique. Standard characterization of BSA nanoemulsion was including droplets size, size distribution, zeta potential, morphology, and entrapment efficiency. Physical properties of the film containing BSA nanoemulsion was included macroscopic of film, film thickness, film weight uniformity, folding endurance, tear resistance, Tensile strength (TS), percentage of elongation (PE), Elasticity modulus (EM) and film morphology. Based on all evaluated parameters, Carboxy methyl chitosan (CMCs) produced better film suitable for intraoral dosge form. Critical factors such as type and ratio of film-forming polymer, plasticizer, process and BSA concentration influenced the film characteristics.

PEGylation Improves Nanoparticle Formation and Transfection Efficiency of Messenger RNA

Cationic polymers have been intensively investigated for plasmid-DNA (pDNA), but few studies addressed their use for messenger-RNA (mRNA) delivery. We analyzed two types of polymers, linear polyethylenimine (l-PEI) and poly-N,N-dimethylaminoethylmethacrylate P(DMAEMA), to highlight specific requirements for the design of mRNA delivery reagents. The effect of PEGylation was investigated using P(DMAEMA-co-OEGMA) copolymer. The influence of polymer structure on mRNA binding and particle formation was assessed in a side-by-side comparison with pDNA by methods such as agarose-retardation assay and scanning probe microscopy. Transfection studies were performed on bronchial epithelial cells. Binding of cationic polymers inversely correlated with type of nucleic acid. Whereas P(DMAEMA) bound strongly to pDNA, only weak mRNA binding was observed, which was vice versa for l-PEI. Both polymers resulted in self-assembled nanoparticles forming pDNA complexes of irregular round shape; mRNA particles were significantly smaller and more distinct. Surprisingly, PEGylation improved mRNA binding and transfection efficiency contrary to observations made with pDNA. Co-transfections with free polymer improved mRNA transfection. Gene delivery requires tailor-made design for each type of nucleic acid. PEGylation influenced mRNA-polymer binding efficiency and transfection and may provide a method of further improving mRNA delivery.

Study of dynamics of the cross-linking process of hyperbranched polymers

The description of polymer relaxation properties makes it possible to characterize the influence of polymer structure on its useful properties, i.e., stability and resistance. To determine the profile of the relaxation properties of the linear, hyperbranched and dendrite unsaturated polyester resins, the synthesis of the oligoester as the model compounds was performed. The structures of the obtained model compound were confirmed by elemental analysis and 1H NMR and FTIR spectroscopy. The determination of the α relaxation processes for model oligoester allowed us to describe the practical properties of commercial compounds. The description of the relaxation process may facilitate the interpretation of the dependence between useful properties of polyesters and their molecular structure. The results of the experiments allowed us to improve the technology of the synthesis processes and to extend the range of their usage.

Behavior of pressure dependence of melting temperatures in aromatic polyesters: Influence of polymer structure

AbstractThe thermal behavior of three aromatic polyesters in a homologous series, poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) was studied under hydrostatic pressure up to 200 MPa by using a high pressure differential thermal analysis apparatus. Confining fluid high pressure dilatometer was used to establish the volume–temperature curves (in both solid and liquid regions) from which volume change on melting of these polyesters at atmospheric pressure was determined. Single endothermic peak was seen for PET and PTT, whereas PBT showed double peaks above 50 MPa. Pressure coefficient of melting temperature at atmospheric pressure (dTm/dp(0)), was obtained from the quadratic fit. The dTm/dp(0) for PTT was newly determined to be 0.445 KMPa−1, whereas for PET and PBT were 0.503 and 0.455 KMPa−1, respectively, comparable to reported values. The dTm/dp(0) exhibited the odd‐even behavior corresponding to odd and even number of methylene groups in the repeat unit. Enthalpy and entropy of fusion had the most influence on this coefficient. Entropy related to conformational and volume change were evaluated and the former was found to have a significant impact on the value of dTm/dp(0). © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1799–1808, 2009

Silk-elastinlike recombinant polymers for gene therapy of head and neck cancer: From molecular definition to controlled gene expression

Silk-elastinlike protein polymers (SELP's) are block copolymers of silk-like and elastin-like tandem repeats. With appropriate sequence and composition SELPs can be liquid at room temperature and form hydrogels at body temperature. The influence of polymer structure and concentration on biodegradation in vitro and controlled delivery of adenoviruses carrying reporter genes to head and neck tumors in vivo was evaluated using hydrogels made from three SELP analogs. SELP-815K, with eight silk and fifteen elastin units and a lysine (K) modified elastin, was compared to SELP-415K and SELP-47K. Hydrogels with higher silk content and concentration degraded at a slower rate compared to other analogs. Intratumoral injection of adenoviruses with SELPs enhanced gene expression in tumor tissue up to 10 fold compared to viral injection without polymer. Viruses delivered with SELP-815K at 4 wt.% polymer concentration showed the highest level of gene expression. Tumor to liver ratio of expression was up to 55 fold higher for SELP-mediated systems. This study demonstrates the influence of exquisite control over polymer structure using recombinant techniques on spatial and temporal control over adenoviral delivery and establishes the utility of SELP matrices as biodegradable systems for gene therapy of head and neck cancer.

Improving the Signal-to-Noise Performance of Molecular Diagnostics with PEG-Lysine Copolymer Dendrons

The synthesis, characterization, and use of dendron-like poly(ethylene glycol)-lysine (PEG-Lys) copolymers as an intermediate layer for biomolecular diagnostic signal enhancement is presented. Solid phase Fmoc-peptide synthesis was used to synthesize polymers with one, two, and three PEG-Lys comonomer units in both a linear and first and second-generation dendronic structure directly onto organosilica microspheres. The microsphere surface loadings (number of free amine sites) were modified and quantified through an innovative use of the protecting groups of coupled amino acids. Surfaces with 0.1-100% of the original loading corresponding to 0.3-270 nmol/m2 of free amines were achieved. The influence of polymer structure and surface loading (grafting density) on the signal-to-noise of the microsphere-based molecular diagnostic was assessed measuring the difference in the signal of a model protease digestion assay and reduction in the nonspecific adsorption of bovine serum albumin. Increasing the polymer grafting density and the addition of dendronic branching were both found to increase the assay signal and reduce the nonspecific protein adsorption.

Influence of Polymer Structure in Sulfonated Block Copoly(ether sulfone) Membranes for Fuel Cell Application

Influence of Polymer Structure in Sulfonated Block Copoly(ether sulfone) Membranes for Fuel Cell Application

Heparin–Paclitaxel Conjugates Using Mixed Anhydride as Intermediate: Synthesis, Influence of Polymer Structure on Drug Release, Anticoagulant Activity and In Vitro Efficiency

The heparin-paclitaxel conjugates using amino acid as linker (HD2), with low anticoagulant activity, the similar anticancer activity as paclitaxel, offer great potential for further investigation. Two types of heparin-paclitaxel conjugates (HD) have been developed, in which O-acetylated heparin as carrier conjugates with paclitaxel by direct ester bond (HD1) and by inserting different amino acids as spacers, including valine, leucine, and phenylalanine (HD2a, HD2b, and HD2c), respectively. Specifically, mixed anhydride groups of carrier as activating intermediates mediate the synthesis of prodrugs. The HD conjugates are characterized by (1)H NMR, FT-IR and GPC. The percentage weight of drug and hydrolysis rate for HD are detected by UV and HPLC. The anticoagulant activity and cell cycle of MCF-7 of HD are measured by APTT and FCM, respectively. HD2 conjugates show better solubility and faster hydrolysis rates than those of HD1. Meanwhile, the anticoagulant activity of HD is reduced and FCM analysis show that MCF-7 cells treated with HD are arrested in the G2/M phase of cell cycle. Amino acids as linkers between paclitaxel and carrier are appropriate to facilitate the release of paclitaxel from carrier. Mixed anhydrides mediate the synthesis of prodrugs and HD2 conjugates are expected to further investigate in vivo experiment.