Macromolecular Backbone Research Articles

Well-Defined Poly(γ-benzyl-l-glutamate)-g-Polytetrahydrofuran: Synthesis, Characterization, and Properties

The synthesis of well-defined graft copolymers of poly(γ-benzyl-l-glutamate)-g- polytetrahydrofuran, PBLG-g-PTHF, has been achieved via controlled termination of living PTHF branch chains with −NH– functional groups along PBLG macromolecular backbone. The PBLG backbone with different molecular weights (Mn = 2000–45000 g·mol–1) were prepared by anionic ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydrade (BLG-NCA). Living PTHF chains with predictable chain length (Mn = 720–7000 g·mol–1) were prepared by living cationic ring-opening polymerization of THF with methyl triflate (MeOTf) as an initiator. The grafting efficiency (GE) of living PTHF chains onto PBLG backbone via controlled termination reached to near 100%. The grafting density (GD) along PBLG backbone and average number of PTHF branches (Nb,PTHF) in PBLG-g-PTHF graft copolymers could be mediated by changing the molar ratio of living PTHF chains to −NH– functional groups. Circular dichroism (CD) and FTIR spectra show that some of the graft copolymers maintain α-helical structure from PBLG, and the strength of CD signals for α-helical structure of the graft copolymers also decreased with increasing GD. The crystallization degree and spherulitic growth rate of the PBLG-g-PTHF graft copolymers decreased with increasing GD. The obvious phase separation and reticular state of aggregation morphology in PBLG-g-PTHF graft copolymers could be observed. PBLG-g-PTHF graft copolymers have no cytotoxicity and even conducive for cell survival. These graft copolymers had extremely low bibulous rate, and all the water absorption ratios were kept around 1.02 to maintain the shape and dimensional stability.

P(VDF-TrFE) nanorod assemblies with anisotropic piezoelectric properties investigated by piezoelectric response microscopy

Highly ordered assemblies of the copolymer of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) nanorods with anisotropic piezoelectric response were fabricated on different substrates by using a template-free self-organization method. The significant difference in vertical and lateral piezoelectric responses of the nanorods in piezoresponse force microscopy (PFM) revealed that their molecular dipoles were preferentially oriented parallel to the substrate plane. In addition, dipole orientation distribution map in the nanorods was derived by analyzing the vertical and lateral PFM amplitude and phase images. Infrared reflection spectra further showed that the macromolecular backbones were oriented perpendicularly relative to the substrate. A flat-on lamellar structure and a confined crystallization of dewetted melt phase nanorod formation mechanism were proposed. The highly anisotropic piezoelectric response of the assemblies of nanorods may be promising for nanoscale devices for application in energy harvesting, etc. More importantly, the results demonstrated that self organization could be used for fabricating P(VDF-TrFE) nanostructures by controlling the surface energy of the substrates.

Check your metal - not every density blob is a water molecule

Metals play vital roles in both the mechanism and architecture of biological macromolecules, and are the most frequently encountered ligands (i.e. non-solvent heterogeneous chemical atoms) in the determination of macromolecular crystal structures. However, metal coordinating environments in protein structures are not always easy to check in routine validation procedures, resulting in an abundance of misidentified and/or suboptimally modeled metal ions in the Protein Data Bank (PDB). We present a solution to identify these problems in three distinct yet related aspects: (1) coordination chemistry; (2) agreement of experimental B-factors and occupancy; and (3) the composition and motif of the metal binding environment. Due to additional strain introduced by macromolecular backbones, the patterns of coordination of metal binding sites in metal-containing macromolecules are more complex and diverse than those found in inorganic or organometallic chemistry. These complications make a comprehensive library of "permitted" coordination chemistry in protein structures less feasible, and the usage of global parameters such as the bond valence method more practical, in the determination and validation of metal binding environments. Although they are relatively infrequent, there are also cases where the experimental B-factor or occupancy of a metal ion suggests careful examination. We have developed a web-based tool called CheckMyMetal [1](http://csgid.org/csgid/metal_sites/) for the quick validation of metal binding sites. Moreover, the acquired knowledge of the composition and spatial arrangement (motif) of the coordinating atoms around the metal ion may also help in the modeling of metal binding sites in macromolecular structures. All of the studies described herein were performed using the NEIGHBORHOOD SQL database [2], which connects information about all modeled non-solvent heterogeneous chemical motifs in PDB structure by vectors describing all contacts to neighboring residues and atoms. NEIGHBORHOOD has broad applications for the validation and data mining of ligand binding environments in the PDB.

Thermally Rearrangeable PIM-Polyimides for Gas Separation Membranes

Membrane gas separations require materials with high permeability and good selectivity. For glassy polymers, the gas transport properties depend strongly on the amount and distribution of free volume, which may be enhanced either by engineering the macromolecular backbone to frustrate packing in the solid state or by thermal conversion of a soluble precursor to a more rigid structure of appropriate topology. The first approach gives polymers of intrinsic microporosity (PIMs), while the second approach is used in thermally rearranged (TR) polymers. Recent research has sought to combine these approaches, and here a new range of thermally rearrangeable PIM-polyimides are reported, derived from dianhydrides incorporating a spiro center. Hydroxyl-functionalized polyimides were prepared using two different diamines: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (bisAPAF) and 4,6-diaminoresorcinol (DAR). Thermal treatment at 450 °C under N2 for 1 h yielded polybenzoxazole (PBO) polymers, which showed increas...

Solubility and solution rheology of acrylamide-sulfobetaine copolymers

The copolymer of acrylamide and 3-[N-(2-methacryloxylethyl)-N,N-dimethylammonio]-propane sulfonate (PAM-MDMPS) was prepared via free radical copolymerization. Solubility of the copolymers was studied by turbidimetric titration method under different conditions. It was found for the first time that the critical salt concentration to dissolve the copolymer showed a plateau over one order of magnitude up to the critical overlap concentration. Rheological behavior and chain conformation of the copolymers in 1 M NaCl solution were also studied. The concentration regions according to scaling theory were found the same as neutral polymers in good solvent. The specific viscosities could be normalized by the overlap parameter. According to the Huggins relation, the copolymers adopted a more compact conformation in 1 M NaCl with increasing MDMPS content due to the hydrophobic association of the betaine unit in the macromolecular backbone, which was stabilized by the strongly hydrated dipolar pendant chains.

Synergistic Effect of Functionalized Silica Nanoparticles and a β‐Nucleating Agent for the Improvement of the Mechanical Properties of a Propylene/Ethylene Random Copolymer

In the current study, neat (SiO2) and methacrylate‐modified silica nanoparticles (SiO2‐MAA) are added simultaneously with a β‐nucleated agent in propylene/ethylene random copolymer (PPR). From Fourier transform infrared (FTIR) spectra, it is found that modified silica can be joined covalently with PPR macromolecular backbones with the help of poly(propylene‐g‐maleic anhydride) copolymer, improving dispersion of nanoparticles and increasing their adhesion with the PPR matrix. The formation of β‐phase crystals was evaluated by X‐ray diffraction (XRD) along with the crystallinity, crystal size and d‐spacing values. Tensile tests and dynamic mechanical analysis confirmed the reinforcement effect of the nanoparticles as well as the effect of β‐crystals on the final properties of the nanocomposites.

Application of isotopic labeling, and gas chromatography mass spectrometry, to understanding degradation products and pathways in the thermal-oxidative aging of Nylon 6.6

Abstract Nylon 6.6 containing 13C isotopic labels at specific positions along the macromolecular backbone has been subjected to extensive thermal-oxidative aging at 138 °C for time periods up to 243 days. In complementary experiments, unlabeled Nylon 6.6 was subjected to the same aging conditions under an atmosphere of 18O2. Volatile organic degradation products were analyzed by cryofocusing gas chromatography mass spectrometry (cryo-GC/MS) to identify the isotopic labeling. The labeling results, combined with basic considerations of free radical reaction chemistry, provided insights to the origin of degradation species, with respect to the macromolecular structure. A number of inferences on chemical mechanisms were drawn, based on 1) the presence (or absence) of the isotopic labels in the various products, 2) the location of the isotope within the product molecule, and 3) the relative abundance of products as indicated by large differences in peak intensities in the gas chromatogram. The overall degradation results can be understood in terms of free radical pathways originating from initial attacks on three different positions along the nylon chain which include hydrogen abstraction from: the (CH2) group adjacent to the nitrogen atom, at the (CH2) adjacent the carbonyl group, and direct radical attack on the carbonyl. Understanding the pathways which lead to Nylon 6.6 degradation ultimately provides new insight into changes that can be leveraged to detect and reduce early aging and minimize problems associated with material degradation.

Synthesis, thermal properties and curing kinetics of fluorene diamine-based benzoxazine containing ester groups

A novel diamine-based benzoxazine monomer containing ester and bulky fluorene groups (BABPF-p) was successfully synthesized by the reaction of 9,9-bis-[4-(4-aminobenzoyloxy)phenyl]fluorene with paraformaldehyde and phenol. The chemical structure of monomer was confirmed by Fourier-transform infrared (FTIR) and 1H and 13C nuclear magnetic resonance spectroscopy (1H and 13C NMR). The polymerization behavior of monomer was analyzed by FTIR. The curing kinetics was studied by differential scanning calorimetry (DSC), and the kinetic parameters were determined. The autocatalytic model and Kamal model showed good agreement with the experimental results. The thermal and mechanical properties of poly(BABPF-p) were evaluated with DSC, dynamic mechanical thermal analysis (DMTA), and thermogravimetric analysis (TGA). The cured polymer exhibited the higher glass transition temperature (Tg) than diaminodiphenylmethane-based benzoxazine (P-ddm) and fluorene diamine-phenol-based polybenzoxazine (poly(BF-p)). The incorporation of flexible ester carbonyl linkages into the macromolecular backbone had slight effect on the thermal stability of fluorene-containing polybenzoxazine.

Epoxidation of syndiotactic 1,2-polybutadiene with peracids

The epoxidation of syndiotactic 1,2-polybutadiene (84 and 16% 1,2 and 1,4 units, respectively) with carboxylic peracids prepared in situ and m-chloroperbenzoic acid was studied. In the course of epoxidation in the presence of carboxylic peracids, oxirane groups are formed only through epoxidation of double bonds in the macromolecular backbone, whereas m-chloroperbenzoic acid is responsible for the chemical modification of 1,2 and 1,4 units of polybutadiene. The basic kinetic parameters of 1,2-polybutadiene epoxidation with peracids of various chemical structures were determined.

Characterizing polymer macrostructures by identifying and locating microstructures along their chains with the kerr effect

In this brief report, we demonstrate that Kerr effect measurements, which determine the excess birefringence con- tributed by polymer solutes in dilute solutions observed under a strong electric field, are highly sensitive to and capable of determining their microstructures, as well as their locations along the macromolecular backbone. Specifically, using atactic triblock copolymers with the same overall composition of sty- rene (S) and p-bromostyrene (pBrS) units, but with two differ- ent block arrangements, that is, pBrS90-b-S120-b-pBrS90 (I) and S60-b-pBrS180-b-S60 (II), which are indistinguishable by NMR, we detected a dramatic difference in their molar Kerr constants (mK), in agreement with those previously estimated. Although similar in magnitude, their Kerr constants differ in sign, with mK(II) positive and mK(I) negative. In addition, S/pBrS random and gradient copolymers synthesized by reversible addition- fragmentation chain-transfer (RAFT) polymerization exhibit a heretofore unexpected enhanced enchainment of racemic (r) pBrS-pBrS diads. Comparison of their observed and calculated mKs suggests that the gradient S/pBrS copolymers possess an unanticipated additional gradient in stereosequence that paral- lels their comonomer gradient, that is, as the concentration of pBrs units decreases from one end of the copolymer chain to the other, so does the content of r diads. This conclusion could only be reached by comparison of observed and calculated Kerr effects, which access the global properties of macromole- cules, and not NMR, which is only sensitive to local polymer structural environments, but not to their locations on the co- polymer chains. Molar Kerr constants are characteristic of entire polymer chains and are highly sensitive to their constitu- ent microstructures and their distribution along the chain. They may be used to both identify constituent microstructures and locate them along the polymer chain, thereby enabling, for the first time, characterization of their complete macrostructures. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 735-741

Nanoparticles Synthesis from Corn Cob (Xylan) and Their Potential Application as Colon‐Specific Drug Carrier

AbstractSummary: Corn Cob based Xylan, a natural polysaccharide extracted from agro‐waste may be used as a tool to deliver drugs especially to the colon because of their timely retention in the physiological environment of stomach and small intestine and can only be degraded in colon by vast anaerobic microflora like bifidobacterium. The objective of present research study is to incorporate the drug namely 5‐aminosalicylic acid (5‐ASA) into xylan macromolecular backbone, either by surface adsorption or by intermolecular covalent bond formation so that absorption of drugs is prevented in upper gastrointestinal tract (GIT). To achieve the above objective, xylan prodrug of 5‐ASA was synthesized via activation of carboxylic acid with N,N‐carbonyldiimidazole. The structure of obtained xylan prodrug was evaluated by means FT‐IR spectroscopy. The ester carbonyl absorption band was observed at 1690 cm−1 in addition to the bands originated from 5‐ASA and xylan. The resulting prodrug and xylan itself assembled into spherical nanoparticles were analyzed by scanning electron microscopy. The prodrug of 5‐ASA was synthesized which might be active against inflammatory bowel diseases, a novel thought towards advanced drug delivery from xylan based nanoparticles will be presented.

Correlation between the secondary structure and hydrogen bonding in optically active polyurethane and its effect on infrared emissivity

Optically active polyurethanes (PUs) with different specific rotations were synthesized using a hydrogen transfer addition polymerization procedure with isocyanate–phenols of varying enantiomeric excess. The optical activities of the PUs were enhanced with an increase in the enantiomeric excess of the monomers. A helical secondary structure in the PUs with a more compact arrangement of the macromolecular backbones facilitated interchain hydrogen bonding, and the infrared emissivity of the corresponding polymers decreased. The results indicated that the level of order and number of hydrogen bonds in the macromolecule played significant roles in controlling the infrared emissivity.

Synthesis and characterization of poly(ethylene glycol)‐b‐poly(ε‐caprolactone) copolymers with functional side groups on the polyester block

AbstractThis study reports the successful synthesis of amphiphilic MPEG‐b‐PCL based‐block copolymers bearing benzyloxy and hydroxyl side groups on the PCL block by ring‐opening polymerization of 4‐benzyloxy‐ε‐caprolactone (4‐BOCL) and ε‐caprolactone (ε‐CL) with methoxy PEG (550 g mol−1) as the initiator and Tin(II) 2‐ethylhexanoate (SnOct2) as the catalyst. These copolymers were characterized by differential scanning calorimetry (DSC), 1H NMR, and gel permeation chromatography. The thermal properties (Tg and Tms) of the block copolymers depend on the polymer composition. Incorporating a greater amount of 4‐BOCL and/or ε‐CL was incorporated into the macromolecular backbone causes a decrease Tg, and an increase in Tms. The micellar characteristics in the aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). A lower critical micelle concentration (CMC) was observed in MPEG12‐b‐PBOCL12‐b‐PCL series, which have higher hydrophobic components in the copolymers. However, contrasting results were observed for MPEG12‐b‐PBOCL27‐b‐PCL systems. The micelle exhibited a spindle shape, with an average size of less than 200 nm. A weak drug entrapment efficiency and drug‐loading ability of these micelles were observed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thiol-ene “clickable” carbon-chain polymers based on diallyl cyclopropane-1,1-dicarboxylate

A novel type of clickable polymers with a very high local density of allyl side groups was developed. These polymers were obtained by the anionic ring-opening (co)polymerization of diallyl cyclopropane-1,1-dicarboxylate using as an initiating system a protic precursor whose acid–base reaction with the t-BuP4 phosphazene base generated the initiator in situ. The obtained polymers display geminated allyl groups on every third carbon alongside the macromolecular backbone. Homopolymers as well as block and statistical copolymers have been synthesized, with controlled molecular weights and narrow molecular weight distributions. The coupling of mercaptans with the allyl CC double bonds has been investigated both thermally and photochemically, with the influence of the type of initiation on the efficiency of the polymer modification being discussed in comparison with other “clickable” systems. Further functionalization by several thiols was performed, leading to a range of functional poly(cyclopropane-1,1-dicarboxylate)s.

Self assembling nanocomposites for protein delivery: Supramolecular interactions of soluble polymers with protein drugs

Translation of therapeutic proteins to pharmaceutical products is often encumbered by their inadequate physicochemical and biopharmaceutical properties, namely low stability and poor bioavailability. Over the last decades, several academic and industrial research programs have been focused on development of biocompatible polymers to produce appropriate formulations that provide for enhanced therapeutic performance. According to their physicochemical properties, polymers have been exploited to obtain a variety of formulations including biodegradable microparticles, 3-dimensional hydrogels, bioconjugates and soluble nanocomposites. Several soluble polymers bearing charges or hydrophobic moieties along the macromolecular backbone have been found to physically associate with proteins to form soluble nanocomplexes. Physical complexation is deemed a valuable alternative tool to the chemical bioconjugation. Soluble protein/polymer nanocomplexes formed by physical specific or unspecific interactions have been found in fact to possess peculiar physicochemical, and biopharmaceutical properties. Accordingly, soluble polymeric systems have been developed to increase the protein stability, enhance the bioavailability, promote the absorption across the biological barriers, and prolong the protein residence in the bloodstream. Furthermore, a few polymers have been found to favour the protein internalisation into cells or boost their immunogenic potential by acting as immunoadjuvant in vaccination protocols.

共役高分子骨格の電荷輸送特性

共役高分子骨格の電荷輸送特性

General Avenue to Individually Dispersed Graphene Oxide-Based Two-Dimensional Molecular Brushes by Free Radical Polymerization

We present a general strategy for facile synthesis of 2D macromolecular brushes. The ultraflat one-atomic layer of graphene oxide with micrometer-scale sheet topology was employed as the macromolecular backbone; more than 10 types of polymer chains were covalently tethered to the nanosheets through free radical polymerization, producing various 2D molecular brushes with multifunctional arms covering from polar to apolar, water-soluble to oil-soluble, acidic to basic, and functional to common polymers. The resulting molecular brushes are well soluble in desired solvents in the forms of individually dispersed hairy nanosheets. The growing process of 2D molecular brushes was clearly visualized by AFM. The giant 2D brushes with arm density up to 1.59 × 104 arms per μm2 of single side of graphene show high solubility (∼15 mg/mL), low intrinsic viscosity (∼100 mL/g), and fine electrical conductivity (∼8.4 × 10−3 S/cm), and they can possess numerous epoxy and other functional groups at their arms if necessary, promising a luciferous foreground in both scientific research and industrial applications. The polymer-grafted graphene oxide can be well dispersed in free polymer matrix and can be well soluble in solvents again, suggesting that nanocomposite of polymer-grafted graphene oxide and polymer can be readily produced by the solution-processing technique.

Kinetic modeling of the peroxide cross-linking of polymers: From a theoretical model framework to its application for a complex polymer system

Peroxides react with polymers in a variety of ways. The fundamental comprehension and prediction of pertinent kinetics of reactions is consequently indispensable. Based on the mechanisms of reactions of cross-linking process, a new theoretical kinetic model framework was developed. The kinetic model was then applied to the reactions of cross-linking process of various peroxides and a chosen complex polymer compound, namely partially hydrogenated poly(acrylonitrile- co-1,3-butadiene). Whereas the initial macromolecular backbone structure was determined utilizing attached proton test carbon nuclear magnetic resonance, the evolution of overall concentration of cross-links was monitored through viscoelastic characteristics of the system. The model demonstrated good agreement with experimentally measured data and, moreover; the evolution of concentrations of various crucial species inherent to the cross-linking process were predicted. The most significant advantage of the developed kinetic model is that it may be readily applied to an assortment of polymer/peroxide systems.

Synthesis and Characterization of Photochromic Copolymer Grafting Azoaromatic Chromospheres on Pullulan

Preparation of photochromic copolymer grafting 4-(4-nitro phenylazo)-1-naphthol units on a pullulan molecular surface has been accomplished. Surface modification was carried out in aqueous solution by an inverse emulsion polymerization method. Polymerization products were characterized by IR, SEM, XRD and TG-DTA. UV-vis spectroscopy has been used to monitor the photoisomerization of azobenzene moieties on a pullulan molecular surface. The results indicated that functional copolymer has a better photochromism property than its corresponding azobenzene moieties, reflecting the macromolecular backbone of pullulan should actively affect the photoisomerization of azoaromatic moieties.

A moment invariant for evaluating the chirality of three-dimensional objects

Chirality is an important feature of three-dimensional objects and a key concept in chemistry, biology and many other disciplines. However, it has been difficult to quantify, largely owing to computational complications. Here we present a general chirality measure, called the chiral invariant (CI), which is applicable to any three-dimensional object containing a large amount of data. The CI distinguishes the hand of the object and quantifies the degree of its handedness. It is invariant to the translation, rotation and scale of the object, and tolerant to a modest amount of noise in the experimental data. The invariant is expressed in terms of moments and can be computed in almost no time. Because of its universality and computational efficiency, the CI is suitable for a wide range of pattern-recognition problems. We demonstrate its applicability to molecular atomic models and their electron density maps. We show that the occurrence of the conformations of the macromolecular polypeptide backbone is related to the value of the CI of the constituting peptide fragments. We also illustrate how the CI can be used to assess the quality of a crystallographic electron density map.