Main Chain Monomer Research Articles

Improvement in Cohesive Properties of Adhesion Systems Using Movable Cross-Linked Materials with Stress Relaxation Properties.

A strong, tough, and stable adhesion system used in various environments must be developed. A long-lasting adhesion system should effectively perform in the following five aspects: adhesion strength, toughness, energy dissipation property, self-restoration property, and creep resistance property. However, these properties are difficult to balance using conventional adhesives. Here, a new topological adhesion system using single-movable cross-network (SC) materials [SC(DMAAm) Adh] was designed. 3-(Trimethoxysilyl) propyl acrylate was used as the anchor, N,N-dimethyl acrylamide (DMAAm) was used as the main chain monomer, and γ-cyclodextrin (γ-CD) units acted as movable cross-links. The movable cross-links provided SC(DMAAm) Adh with energy dissipation properties, thereby improving its toughness. The γ-CD units also acted as bulky stoppers that provided a high adhesion strength and self-restoration properties. Moreover, the combination of the movable cross-links and bulky stoppers provided creep resistance to SC(DMAAm) Adh. The performance of the adhesion systems under different mobilities of the polymer chains was examined by adjusting the water content. In proper water-containing states, all mechanical properties of SC(DMAAm) Adh were better than those of the adhesion systems using homopolymers [P(DMAAm) Adh] and polymers with covalent cross-linking points [CP(DMAAm) Adh].

Hybridizing a Dual-Cross Network and a Linear Glassy Polymer for Dynamic Contributions to High Mechanical Toughness Based on Phase-Separated Structures

Bulk copolymerization of alkyl acrylate and cyclodextrin (CD) host monomers forms a single movable cross network (SC), in which the CD units act as movable cross-linkers. Moreover, the bulk copolymerization of the CD monomer and main chain monomer in the presence of SC results in dual-cross-network (DC) elastomers. DC elastomers result in good toughness (Gf). Here, to improve Gf and Young’s modulus (E), we hybridized DC elastomers with tertiary glassy polymers, which are called DCP elastomers. We prepared the DCP elastomers by photopolymerization of N,N-dimethylacrylamide (DMAA) and poly(2-methoxyethyl acrylate) (MEA) in the presence of DC. A DCP elastomer with a suitable weight percent (wt %) of the glassy polymer shows high Gf (108.4 MJ m–3) and E (223.4 MPa) values. Dynamic mechanical analysis (DMA) and in situ small-angle X-ray scattering (SAXS) measurements under uniaxial stretching indicate multiple deformations based on phase-separated structures. We suggest that the phase-separated structures of DCP elastomers cause a large stress dissipation, which contributes to high toughness.

Study on the dispersion mechanism of the polycarboxylic acid dispersant for disperse dyes

Taking C.I. Disperse Blue 79 as the simulation object, the dispersion mechanism of polycarboxylic acid dispersant (poly(SMA-g-IP-MPEG)) for disperse dyes was studied by molecular dynamics simulations. The results show that the hydrophilicity of the dispersant mainly depends on the maleic acid residues; the ionized carboxylate groups of the maleic acid residues provide negative charges that make the dyes repel each other; the hydrophobicity of the styrene residues is the driving force that makes the dispersants adsorb to the dye surfaces; the branched chains grasp the dye crystals like claws, which make the dispersants combine with the dye crystals better. When the ratio of main chain monomer is 3:1 and the branched chain length is larger than 12, the branched chain tends to wrap around the main chain. The repulsion between dyes decreases, thus the dispersion performance becomes worse. When the ratio of main chain monomer is 1:1, the dispersion effect increases with the increase of branched chain length. But when the branched chain length increases to 16, the longer branched chain can adsorb with two dye crystals at the same time, which leads to the decrease of dispersion effect. In general, the main chain monomer ratio had little influence on the dispersion effect. The dispersant with the main chain monomer ratio of 1:1 and the branch chain length of 12 had the best dispersion effect on the dye. The experimental results verified the correctness of the simulation results. The design of polymeric dispersants for disperse dyes should consider not only the improvement of hydrophilicity and charge repulsion to maintain the dispersion stability of disperse dyes in water, but also the binding force between dispersants and disperse dyes. The two interactions determine the dispersion performance of the dispersant for disperse dyes.

Behavior of supramolecular cross-links formed by host-guest interactions in hydrogels responding to water contents

Reversible or movable cross-links based on host-guest interactions in supramolecular materials create functions such as enhanced mechanical properties and stimulus responsiveness. A supramolecular complex on a polymer side chain achieves the described functions as a reversible cross-link. Generally, 1:1 complex is utilized as a cross-link for the host-guest interaction based-supramolecular materials, but herein, the 1:2 complex between γ-cyclodextrin (γCD) and methyl viologen terminated undecyl acrylate (VC11) was chosen to cross-link three polymeric chains. The obtained supramolecular hydrogels γCD-VC11 (x, y) (x and y represent the mol% of the γCD and VC11 units in feeding, respectively) was prepared by radical copolymerization with acrylamide as a mainchain monomer. Tensile test revealed that toughness (Gf) of γCD-VC11 (x, y) maximized at water content (Wc) ≈ 40 wt.%. The maxima of Gf depended on the amount of γCD and VC11 units. Through dynamic mechanical analysis, Arrhenius style plots between horizontal shift factors and temperature determined activation energies (Ea) of each γCD-VC11 (x, y) and MBAAm (0.5). Ea of MBAAm (0.5) monotonically decreased with the increasing Wc. On the other hand, slope of Ea of γCD-VC11 (x, y) changed at Wc ≈ 40 wt.%. Simultaneously considering results of the tensile tests and DMA, the reversible cross-links formed by γCD and VC11 in γCD-VC11 (x, y) function effectively at appropriate Wc.

The thermal properties of a UV curable acrylate composite prepared by digital light processing 3D printing

Digital light processing (DLP) 3D printing is a potential alternative to traditional thermal curing due to its short curing time and free design customization in the absence of a mold. With this in mind, the present work is aimed at identifying the optimum composition of a printable photopolymer resin with butyl acrylate as the main-chain monomer and diurethane dimethacrylate as a crosslinker to generate a thermal interface material. In particular, the influence of the crosslinker-to-monomer ratio upon the mechanical properties of the printed material is investigated. In addition, aluminum nitride (AlN) is used as the filler due to its excellent thermal conductivity, electrical insulation, and cost effectiveness. The thermal conductivity of the printed material with 30 wt% AlN is shown to be 1.43 W/mK in the in-plane direction and 0.35 W/mK in the through-plane direction. These values are respectively 477 and 350% higher than those of pure acrylate resins, and are attributed to the creation of an efficient thermal transport pathway via dispersion of the AlN particles throughout the layered acrylate resin.

Preparation of hydrophilic polymeric materials with movable cross-linkers and their mechanical property

Hydrophilic polymeric materials with movable cross-linkers were obtained by the bulk copolymerization of a hydrophilic cyclodextrin monomer (γCDAAmMe) and liquid acrylamide monomers. A 2D 1H-NOESY NMR study revealed that the main chains penetrated the CD ring units, which acted as movable cross-linking points. Copolymerization of γCDAAmMe with N,N-dimethyl acrylamide (DMAA) as a small main chain monomer results in hydrophilic movable cross-linked materials (pDMAA-γCDAAmMe (x)). On the other hand, using 4-acryloylmorpholine (ACMO) or N,N-dimethylaminopropyl acrylamide (DMAPAA) as a bulky main chain monomer disfavours the formation of movable cross-links due to steric hindrance between γCDAAmMe and the side chains. In the water content range of approximately 40–80 wt%, the Young's moduli of pDMAA-γCDAAmMe (1)s are similar to those of pDMAA-MBAAm (1). However, the fracture energy of movable cross-linked materials is higher than that of than materials covalently cross-linked with N,N′–methylenebis(acrylamide) (MBAAm). An addition of water enhanced the mobility of the main chain polymers, allowing the movable cross-linking points.

Self-assembly of an amphiphilic macromolecule under spherical confinement: An efficient route to generate hollow nanospheres

In general, bio-macromolecules are composed of hydrophilic and hydrophobic moieties and are confined within small cavities, such as cell membranes and intracellular organelles. Here, we studied the self-organization of macromolecules having groups with different affinities to solvents under spherical nano-scale confinement by means of computer modeling. It is shown that depending on the interaction parameters of monomer units composed of side- and main-chain monomer groups along a single linear macromolecule and on cavity size, such amphiphilic polymers undergo the conformational transitions between hollow nanospheres, rod-like and folded cylindrical structures, and a necklace conformation with and without a particular ordering of beads. The diagram of the conformations in the variables the incompatibility parameter of monomer units and the cavity radius is constructed.

Cylindrical molecular brushes with a loose grafting density

AbstractA cylindrical molecular brush with a low graft density was synthesized by two steps. Firstly, free radical alternating copolymerization of styrene (St) and N‐[2‐(2‐bromoisobutyryloxy)ethyl] maleimide (BiBEMI) gave a macroinitiator where pendant initiating sites for atom transfer radical polymerization (ATRP) being positioned along the backbone with an interval of four CC bonds. The backbone‐to‐be with an alternating sequence was verified by elemental analysis (EA). Secondly, grafting poly(tert‐butyl acrylate) chains from the macroinitiator by ATRP produced the novel molecular brush. Size exclusion chromatography, static light scattering (SLS), and 1H NMR and atomic force microscopy (AFM) were used to characterize the macroinitiator and the molecular brush. The results show that the backbone contains an average 730 repeat units (1 repeat unit = a pair of St and BiBEMI) and the absolute molecular weight of the brush, Mw,SLS, was 4.88 × 106 Da. The brush reveals a number average length Ln to be 96 nm under AFM observation on carbon coated mica, corresponding to the length per main chain monomer unit (Lunit) of 0.066 nm, indicating a less extended conformation due to the low grafting density. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5527–5533, 2009

The Role of Configuration Entropy in Boundary Lubricants Based on the n-Perfluoropropylene Oxide Main Chain Structure

We have investigated the resistance of a novel end-functionalized perfluoropolyether (PFPE) lubricant film to slider–disk interactions caused by low-flying sliders. The PFPE lubricant is based on the CF2CF2CF2O main chain monomer unit. Both slider–disk interactions and the formation of lubricant moguls are significantly reduced compared to the Fomblin Z backbone, (CF2O) p –(CF2CF2O) q . These results are interpreted on the basis of ab initio quantum chemical computations that show that the barrier to internal rotation about the C–O bond in the CF2CF2CF2O monomer unit is significantly larger than in the CF2O monomer unit that is bordered by another CF2O monomer unit, ~8 kcal/mol compared to <2 kcal/mol, respectively. It is proposed that main chains containing CF2O monomer units will be very flexible and hence their physical properties will be more sensitive to adhesive and cohesive interactions, while main chains containing CF2CF2O and CF2CF2CF2O monomer units will be comparatively stiffer and hence their physical properties will be less sensitive to adhesive and cohesive interactions.

Conformation of Cylindrical Brushes in Solution: Effect of Side Chain Length

The conformation of cylindrical brush polymers with a polymethacrylate main and polystyrene side chains (6 ≤ ≤ 33, with the number-average degree of polymerization of the side chains) were studied by combined light and small-angle neutron scattering experiments. The results reveal that the main chain stiffness expressed in terms of the Kuhn statistical segment length, lk, increases with side chain length but does not follow scaling predictions which most probably is due to the limited length of the side chains investigated experimentally. In this respect the present work addresses the transition regime from flexible coils to stiff cylindrical brushes as a function of side chain length. In detail, the increase of lk is stronger in toluene, a very good solvent for the side chains, than in the poor solvent cyclohexane and does not level off for the longest side chains investigated ( = 33). In contrast to earlier work, the cylinder length per main chain monomer is found to be independent of side chain length ...

On the shape of bottle-brush macromolecules: Systematic variation of architectural parameters

We measured the form factor of bottle-brush macromolecules under good solvent conditions with small-angle neutron scattering and static light scattering. The systems under investigation are brushes, synthesized via the grafting-from route, built from a poly(alkyl methacrylate) backbone to which poly(n-butyl acrylate) side chains are densely grafted. The aim of our work is to study how the systematic variation of structural parameters such as the side chain length and backbone length change the conformation of the polymer brushes in solution. All spectra can be consistently described by a model, considering the bottle-brush polymers as flexible rods with internal density fluctuations. Parameters discussed are (1) the contour length per main chain monomer l(b), (2) the fractal dimension of the side chains Ds, as well as (3) the fractal dimension D, and (4) the Kuhn length lambdak of the overall brush. l(b)=0.253+/-0.008 nm is found to be independent of the side chain length and equal to the value found for the bare main chain, indicating a strongly stretched conformation for the backbone due to the presence of the side chains. The fractal dimension of the side chains is determined to be Ds=1.75+/-0.07 which is very close to the value of 10.588 approximately 1.70 expected for a three-dimensional self-avoiding random walk (3D-SAW) under good solvent conditions. On larger length scales the overall brush appears to be a 3D-SAW itself (D=1.64+/-0.08) with a Kuhn-step length of lambdak=70+/-4 nm. The value is independent of the side chain length and 46 times larger than the Kuhn length of the bare backbone (lambdak=1.8+/-0.2 nm). The ratio of Kuhn length to brush diameter lambda(k)d>or=20 determines whether lyotropic behavior can be expected or not. Since longer side chains do not lead to more persistent structures, lambda(k)d decreases from 8 to 4 with increasing side chain length and lyotropic behavior becomes unlikely.

Synthesis and solid state structures of macromolecular cylindrical brushes with varying side chain length

Cylindrical brushes with a macromolecular backbone and well-defined side chains of different length (4≤ P n sc≤38) were synthesized by polymerization of macromonomers. The effect of side chain length on the intermolecular order has been investigated by means of X-ray scattering on the melt-extruded samples. The increase of the side chain molar mass results in an increase of the intermolecular distance d according to d∼( M n sc) 0.476. The contour length of the cylindrical brush polymers per main chain monomer unit, l m, was determined to slightly vary with side chain molar mass M n sc according to l m∼( M n sc) 0.059. The resulting values are much less than the maximum extension, l m =0.25 nm, which is found to be almost independent of side chain molar mass. Also, supermolecular structure formation of a random copolymer brush prepared by radical copolymerization of methacryloyl end functionalized polyvinylpyridine and polymethylmethacrylate macromonomers has been observed and is interpreted as a consequence of intramolecular phase separation.

Biological characterization of a novel biodegradable antimicrobial polymer synthesized with fluoroquinolones.

Biomaterial-related infections continue to represent a significant challenge to the medical community. Several approaches have been utilized to incorporate antimicrobial agents at the surface of implant devices in attempts to delay or eliminate the formation of biofilms. To date, most of these strategies have focused on drug conjugation or diffusion-limited systems for the delivery of such pharmaceutical agents. More recently, work has been presented on the feasibility of incorporating drugs into the backbone of polymers as a main-chain monomer. When sequenced into the backbone of the polymer with other monomers that are hydrolytically sensitive to enzyme-catalyzed breakdown, it is thought that drugs may be able to be selectively released. Specifically, degradable polyurethanes have been synthesized with fluoroquinolone antibiotics and have shown an ability to kill bacteria when released following degradation of the polymer chains by the macrophage-derived enzyme cholesterol esterase. However, specificity of the cleavage sites in the polymer was difficult to control. Since cholesterol esterase has specificity for hydrophobic moieties, it is desirable to alter the formulation of the polyurethanes to incorporate long hydrophobic monomers immediately adjacent to the ciprofloxacin molecule. Hence, the current study focuses on evaluating the enzyme-catalyzed degradation of a degradable polyurethane synthesized with 1,12 diisocyanatododecane as a substitute for 1,6 diisocyanatohexane, which was used in previous work. Validation of specific ciprofloxacin release and the generation of antimicrobial are shown. A preliminary cell study to assess the cytotoxicity of this biodegradable antibiotic polymer shows that the material has no observable effects on cell proliferation or cell membrane structure.

Solvent-Induced Length Variation of Cylindrical Brushes

Polymacromonomers with a main chain much larger than the side-chain length adopt the form of cylindrical brush polymers the contour length per main-chain monomer of which depends on the side-chain length. In the present investigation it is demonstrated that the length per monomer also depends on the solvent quality, i.e., the cylinders are shorter in a poor solvent as compared to a good solvent. It is argued that the repulsion of the side chains represents the extension force, which acts against the entropic contraction force of the main chain. Thus, cylindrical brushes may be suitable as responsive materials for sensors, actuators or soft machines.

Main Chain Conformation and Anomalous Elution Behavior of Cylindrical Brushes As Revealed by GPC/MALLS, Light Scattering, and SFM

High molar mass polymacromonomers based on methacryloyl end-functionalized oligo methacrylates (Mn = 2410 g/mol) adopt the conformation of wormlike cylindrical brushes. Comparison of the absolute molar mass, Mw, determined by static light scattering and the contour length, Lw, of the molecules measured by SFM in the dry state revealed the length per vinylic main chain monomer of the cylindrical structure to be less than 0.1 nm, thus being much shorter than the maximum value of 0.25 nm. In solution this shrinkage could be quantified to 0.071 nm per monomer by Holtzer analysis of the scattering curves which in addition yielded the Kuhn statistical segment length lk = 120 nm. GPC MALLS investigations of such samples showed an anomalous elution effect: After a regular elution at small elution volumes the molar mass of the eluting molecules increased drastically with increasing elution volume. Fractionation by GPC showed that this effect is caused by a fraction of extremely high molar mass molecules which elu...

Molecular mobility of spin-labelled terephthaloyl chloride and 1,10-decanediol copolymer in solution

Intramolecular mobility of spin-labelled terephthaloyl chloride and 1,10-decanediol copolymer in solution was investigated using a polymer in which the label was rigidly attached to the main chain methylene groups. Correlation times and effective segmental dimensions were measured, as were the frequency and amplitude of the high-frequency torsional vibrations of the main chain monomer units. The amplitude of high-frequency torsional vibrations was shown to increase with increasing temperature.