The influence of side chains on formation of inclusion complexes prepared with polyolefin and cyclodextrins

We investigated the formation of inclusion complexes (ICs) between cyclodextrins (CDs) with different cavity size and polyolefin (PO) with different side chains by using Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry. The analysis of FTIR spectra revealed that the resultants were complexes of CD and PO, and the analysis of WAXD revealed that the molecules of CD had a channel structure due to the formation of ICs. We found that IC could not be obtained when the cavity size of CD was small for PO molecules to thread and it was too large for cross-sectional area of PO molecules. Thus, it was found that PO1 with few side chains could form IC with α-CD, and PO2 with ethyl side chain could form IC with β-CD and γ-CD, while the PO3 with 2-methyl-propyl side chain could form IC with γ-CD. These results suggest that the cross-sectional areas of polymer and the cavity size of CDs play critical roles in the formation of ICs. It is only possible to form ICs when the polymer chains can tread into cavities of CDs, and the space between the polymer and CD is suitable to provide enough intermolecular interaction to keep the structure of IC stable.     

Synthesis and characterization of soluble polymer ligands possessing sulfide side chains

Soluble polymer ligands possessing aryl monosulfide side chains [poly(4-vinylphenylmethyl sulfide) (PVPMS)], alkyl monosulfide side chains [poly(4-vinylbenzylmethyl sulfide) (PVBMS)] and branched tetrasulfide side chains [poly(7-(4′-vinylbenzyloxy)-2,5,9,12-tetrathiatridecane) (PTeSSD)] were prepared by radical polymerization of the corresponding monomers. These polymer ligands had specific binding abilities for soft acids only, such as Ag(I) and Hg(II) ions. The tetrasulfide-type polymer ligand, PTeSSD, bound the metal ion only by the tetrasulfide side chain itself. The monosulfide-type polymer ligands, PVPMS and PVBMS, bound the metal ion by co-operative interaction between their monosulfide side chains. The resulting polymer-Ag(I) complexes were soluble in organic solvents. Interestingly, a polyester cloth coated with the polymer-Ag(I) complex exhibited significant antibacterial activity against Staphylococcus aureus.     

An easy approach of preparing strongly luminescent carbon dots and their polymer based composites for enhancing solar cell efficiency

We report a one-step approach for synthesis of carbon dots (CDs) under mild conditions. By using (N-(2-aminoethyl)-3-aminopropyl)tris-(2-ethoxy) silane (KH791) as catalyzer, stabilizing and passivation agent, the resultant CDs are allowed to be self-assembled in solution and exhibit excitation wavelength independent photoluminescence (PL) performance. When the solvent is removed, luminescent CDs filled polysiloxane composite is readily yielded through hydrolytic condensation between KH791 and CDs. According to this habit, CDs can be conveniently utilized by coating the hybrid solution on proper substrates, etc. On the basis of the luminescent down-shifting behavior of the composite with CDs, power conversion efficiency of polymer-fullerene-based bulk heterojunction solar cell is increased by about 12% due to effective light conversion of near ultraviolet and blue-violet portions of sunlight. The simple preparation, easy processing and unique PL properties of CDs and their polymer composite provide the latter with broad applicability.     

Translocation of polymer chains through interacting nanopores

The effect of the interaction between nanopore and chain segment on the translocation of polymer chains through an interacting nanopore from a confined environment (cis side, high concentration of chain) to a spacious environment (trans side, zero concentration) was studied by using dynamic Monte Carlo simulations. Results showed that a moderate attractive pore–polymer interaction accelerates the translocation of chain. The optimal interaction at which translocation is the fastest increases with the concentration of chain on the cis side. The dependence of microscopic behaviors of chain translocation on the interaction was investigated.     

Macromolecular recognition by cyclodextrins. Interaction of cyclodextrins with polymethacrylamides bearing hydrophobic amino acid residues

The interaction of cyclodextrins (CDs) with poly(N-methacryloyltryptophan) (pMTrp) and with poly(N-methacryloylphenylalanine) (pMPhe) was investigated as a simple model system of macromolecular recognition of proteins. The association constants (K) for the model compounds, sodium salts of tryptophan and phenylalanine, are not so different (i.e. 43 and 16 M⁻¹ for α-CD, 59 and 69 M⁻¹ for β-CD, and 12 and 3 M⁻¹ for γ-CD, respectively). On the other hand, there is a significant difference in the apparent K values for pMTrp and pMPhe (i.e. the K values for pMPhe are considerably smaller than ca. 10 M⁻¹, whereas those for pMTrp are 30, 83, and 11 M⁻¹ for α-, β-, and γ-CDs, respectively). These observations indicate that a subtle difference in polymer side chains can be critical in macromolecular recognition.     

Photoluminescence effects of graphitic core size and surface functional groups in carbon dots: COO− induced red-shift emission

We present a simple molecular approach to control the lipophilic/hydrophilic nature of photoluminescent carbon dots (CDs) based on pyrolysis of alkyl gallate precursors. Depending on the gallic acid derivative used, CDs with different alkyl groups (methyl, propyl, lauryl) on the surface can be obtained by isothermal heating at 270 °C. This precursor-derived approach allows not only the control of lipophilicity but also the length of the particular alkyl chain enables the control over both the size and photoluminescence (PL) of the prepared CDs. Moreover, the alkyl chains on the CDs surface can be readily converted to carboxylate groups via a mild base hydrolysis to obtain water dispersible CDs with a record biocompatibility. The observed differences in PL properties of CDs and time-resolved PL data, including contributions from carbogenic cores and surface functional group, are rationalized and discussed in detail using time-dependent density functional theory (TD-DFT) calculations.     

Simultaneous construction of polymer backbone and side chains by terpolymerization. Synthesis of polyethers with the allyl side chains from dialdehydes, alkylene bis(trimethylsilyl) ethers, and allyltrimethylsilane

Polyethers with allyl side chains were synthesized by the simultaneous acid-catalyzed reaction of dialdehydes (1), alkylene bis(trimethylsilyl) ethers (2), and allyltrimethylsilane (3). The reactions of 1, 2 and 3 were carried out in the presence of 10 mol% of triphenylmethyl (trityl) perchlorate at −55°C to yield polyethers having allyl groups in the side chains. When the dialdehyde having the ester moieties as 1, ethylene bis(trimethylsilyl) ether and 1,4-bis(trimethylsiloxy)cyclohexane as 2 were used, high molecular weight polymers were obtained. In the polymerizations at ambient temperature, the polymer was precipitated during the reaction because of crosslinking between the aromatic rings via a trityl perchlorate assisted Friedel-Crafts reaction. The soluble polyether with the allyl side chains reacted with 1,2-ethanedithiol in the presence of a radical initiator in benzene at 60°C to yield a crosslinked polymer quantitatively within 1 h. This polymer synthesis is unusual in that it concurrently constructs both the polymer backbone and the functional side chains from three monomers.     

Properties of branched polymer chains adsorbed on a patterned surface

The aim of this study was to investigate the properties of polymer chains strongly adsorbed on a planar surface. Model macromolecules were constructed of identical segments, the positions of which were restricted to nodes of a simple cubic lattice. The chains were in good solvent conditions, thus, the excluded volume was the only interaction between the polymer segments. The polymer model chain interacted via a simple contact potential with an impenetrable flat surface with two kinds of points: attractive and repulsive (the latter being arranged into narrow strips). The properties of the macromolecular system were determined by means of Monte Carlo simulations with a sampling algorithm based on the local conformational changes of the chain. The structure of adsorbed chains was found to be strongly dependent on the distance between the repulsive strips, whenever this distance was very short. The mobility of the chains was also studied and it was found that diffusion across repulsive strips was suppressed for large distances between the strips.     

Highly efficient synthesis of cylindrical polymer brushes with various side chains via click grafting-onto approach

Though much attention has been paid to synthesis of cylindrical polymer brushes, it is still not easy to prepare well-defined brushes by a general approach. Herein, well-defined cylindrical polymer brushes with various side chains were synthesized via grafting-onto approach by CuAAC click chemistry. Narrowly dispersed polymer backbones functionalized with azide groups were obtained by post-modification of poly(glycidyl methacrylate) (PGMA) which was prepared by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization. The alkyne-terminated side chains, polystyrene, polyacrylates, polymethacrylates and poly(N-alkyl acrylamide)s, were synthesized by RAFT mediated radical polymerization with alkyne-containing chain transfer agents (CTAs). The CuAAC reactions between the backbone and side chain polymers were conducted with an equivalent feed of alkyne-terminated side chains and azide groups under mild conditions. Influences of reaction conditions and chemical composition of polymer side chains on grafting efficiency and molecular weight distribution of the polymer brushes were investigated. It is demonstrated that the side chains of polystyrene, polyacrylates and poly(N-alkyl acylamide)s were grafted at a density above 85% while that of polymethacrylates decreased to ca. 50%. The polymer brushes synthesized under the optimized reaction conditions had well-defined chemical composition and narrow distribution of molecular weight, and their wormlike morphology was visualized by atomic force microscopy (AFM).     

Conformations and mobility of polyethylene and trans-polyacethylene chains confined in α-cyclodextrins channels

Conformational properties and mobility of two polymeric chains containing 30 repeating units of either polyethylene (PE) or trans-polyacethylene (PA) confined into the channel formed by eight α-cyclodextrins (αCDs) are studied by Molecular Dynamics simulations performed at 500 K and compared with the behavior exhibited by the same chains when they stand alone in vacuum. The rotaxane structure (i.e. polymeric chains threaded into the αCDs channel) is stabilized with respect to the separated chain and αCDs mostly because of van der Waals interactions. As it might be expected, large differences are observed in the molecular characteristics of the isolated chains as compared to their confined counterparts. The differences are in the sense of decreasing the conformational mobility in favor of extended conformations in the case of confined chains. Comparison of the results obtained for confined PE and PA chains indicates a noticeably larger mobility of the PA chain. Molecular dimensions obtained for the isolated PE chain agree with the results published in the literature.     

Preparation and evaluation of hydrophobic surfaces of polyacrylate-polydimethylsiloxane copolymers for anti-icing

Two series of polyacrylate-polydimethylsiloxane (PDMS) copolymers, namely, polyacrylate-b-PDMS and polyacrylate-g-PDMS with three different molecular weights of PDMS blocks or side chains, were synthesized for formation of hydrophobic surfaces for anti-icing. The main purpose of this paper was to investigate the relationship between ice adhesion strength and the surface structure of the copolymers, and to find out how the prepared PDMS-containing polyacrylate copolymers are potentially used for anti-icing. The microphase-separated structure and the surface chemical composition were analyzed by transmission electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy, and ice adhesion strength was measured using a universal testing machine in a pull off mode. Results suggested that microphase separation appeared clearly in all the copolymers, especially for the block ones. The PDMS chains aggregated on the top of the polymer surfaces caused by microphase separation could weaken the interaction between the polymer surface and water, mainly hydrogen bond, which was demonstrated because of decrease of water contact angle hysteresis. Then, ice adhesion strength was decreased by the contribution of PDMS in the block copolymers or the graft copolymer with longer PDMS side chains. It is suggested that the polyacrylate-b-PDMS or polyacrylate-g-PDMS copolymers would have practical applications in preparation of anti-icing coatings.     

Tailoring side chains of low band gap polymers for high efficiency polymer solar cells

High efficiency organic solar cells (OSCs) require conjugated polymers with a low band gap, broad absorption in visible and IR region, high carrier mobility, and relatively high molecular weight as p-type donor materials. Flexible side chains on the rigid polymer backbone are crucial for the solubility of conjugated polymers. In this work, four polymers with the main chain structure of fluorene-thiophene-benzothiadiazole-thiophene and flexible side chains located on fluorene, thiophene, and benzothiadiazole moiety, respectively, have been synthesized by Suzuki-Miyaura-Schlüter polycondensation. Photovoltaic device measurements with a device configuration of ITO/polymer:PC₇₁BM blends/LiF/Al show that P1 carrying octyloxy chains on benzothiadiazole rings gives the best performance, with a power conversion efficiency of 3.1%.     

Synthesis and self-assembly of fluorene-vinylene alternating copolymers in “Hairy-Rod” architecture: side chain – mediated tuning of conformation,microstructure and photophysical properties

In the present work, we demonstrate that the side chain choice, as a tunable parameter, is an effective strategy to drive molecular ordering, packing motifs and overall microstructure of a conjugated polymer. By applying Wittig polycondensation novel ‘rod-coil’ structures, in ‘hairy-rod’ architecture, based on fluorenylene vinylene copolymers with well-defined oligomeric side chains were synthesized using ‘T’-shaped or ‘Cross’-shaped p-terphenyl macromonomers. The overall character of the copolymers was systematically varied by attaching of hydrophilic PEG 2000, hydrophobic polar oligo-ε-caprolactone or hydrophobic and non-polar oligostyrene side chains. Self-assembling of the copolymers by simple direct dissolution method was achieved in various solvents by modifying their selectivity in relation to the side chain or main chain. The morphology investigations demonstrated that unique nanofeatures obtained in each case (helical foldamers, vesicles, disks, or helical turns) depend on the nature, number, and position of the side chains which influence the photophysical properties. The ‘hairy-rod’ topology is also responsible for the self-assembly of the materials in molten state, as thermal analysis revealed, and the propensity of the new synthesized conjugated main chain for helical folding was evidenced, as well.     

Radical crossover reactions of a dynamic covalent polymer brush for reversible hydrophilicity control

Reversible hydrophilicity control of a radically exchangeable polymer brush with dynamic covalent linkages was successfully demonstrated. A polymer brush with alkoxyamine units was prepared via surface-initiated atom transfer radical polymerization, and reversible surface hydrophilicity control was achieved via dynamic covalent exchange reactions of alkoxyamines. Exchange reactions between alkoxyamine units in the side chains of the polymer brush and the terminal of poly(4-vinylpyridine) (P4VP) were carried out in order to prepare a side-chain functionalized polymer brush. Subsequent quaternization of P4VP chains with iodomethane was carried out to prepare a more hydrophilic surface. In addition, a de-grafting reaction of the quaternized P4VP side chains was performed to confirm reversibility of the alkoxyamine via radical exchange reactions on the surface. All the composition and wettability changes were investigated via X-ray photoelectron spectroscopy and contact angle measurements.     

“Grafting-from” polymerization for uniformly bulk modification of pre-existing polymer materials via a supercritical-fluid route

A novel approach to uniformly bulk graft modification of pre-existing polymer materials without ungrafted homopolymers was achieved at relatively low temperature by means of gamma (γ)-rays pre-irradiation-induced “grafting-from” polymerization with supercritical carbon dioxide (scCO₂) both as solvent and as swelling agent. The polymer substrates were first irradiated with γ-rays originated from cobalt-60 resource under nitrogen atmosphere at ambient temperature, and thereby leading to uniform formation of trapped radicals on polymer backbone. Then, the produced polymer-trapped radicals were utilized to initiate graft polymerization of vinyl monomers dissolved in scCO₂ within polymer substrates. A combination of transmission electron microscopy, scanning electron microscopy and elemental analysis shows that side graft chains covalently bonded to polymer substrate backbone in nanometer scale are uniformly dispersed within polymer membranes with a thickness of 5 mm. Altering the experimental conditions can easily control the grafting yield with regard to side graft-chain length. This method can also be applied to various functional polymer chains covalently attached to different polymer substrates, even with high viscosity or limited solubility. The novel graft-polymer materials produced by this method are not formed in the absence of scCO₂ and are impossible to prepare by conventional methodologies.     

The Effect of the Structural Elements on the Properties of Side Chain Mesomorphic Polymers

The thermal properties of mesomorphic polymers depend on the relative amounts of the different structural elements (hard core, flexible chains, main chain) of the polymer. Literature data are compared with the conclusions obtained from the three-component thermodynamic model of side chain mesomorphic polymers. The effects of the different soft elements (main chain, spacer and p-alkyl or alkoxy chain) depend first of all on the length of the spacer and its interaction with the main chain. The thermal properties of the polymer can be well regulated by varying the different structural elements of the homo- and co-polymers. The glass transition temperature (T_g) of the polymer can be reduced by building O and N atoms into the main chain and/or by binding the side chains on 3rd, 4th, etc. atoms of the main chain. The T_g can be further reduced by increasing the length of the spacer. If the spacers are long enough, the layer type structures are favored, with p-alkoxy chains behaving also as a plasticizer of the main chain. The clearing point can be influenced by copolymerization of monomers with different hard cores. The three-component thermodynamic model of side-chain mesomorphic polymers well explains the effect of different structural elements on the structure and properties of these polymers.     

Tuning intermolecular non-covalent interactions for nanowires of organic semiconductors

Anthracene and its derivatives are used to demonstrate a simple way to cast assemble nanowires of organic semiconductors with tuning of intermolecular non-covalent interactions by molecular design. The tuning of intermolecular interactions could be achieved by (i) decreasing intermolecular hydrophobic interactions by linking hydrophilic side chains to anthracene rings, (ii) increasing intermolecular interaction for self-assembly with the assistance of hydrogen bonds, and (iii) enhancing molecular π-π interaction by increasing the conjugated dimension of the compounds.     

Electrorheological behavior of two thermotropic and lyotropic liquid crystalline polymers

A thermotropic liquid crystalline (LC) polymer, consisting of an LC silicone having benzoic acid phenylester LC groups as side chains of the siloxane polymer main chain diluted with dimethylsilicone, and a lyotropic LC polymer solution, consisting of poly(γ-benzyl-L -glutamate) in 1,4-dioxane, both showed a large electrorheological (ER) effect, i.e., an instantaneous increase in shear stress upon the application of an electric field. In the electric field, the thermotropic polymer exhibited Newtoman-like flow and a dynamic viscoelasticity similar to that of low molecular weight liquid crystals, while the lyotropic polymer solution exhibited elastic flow and a dynamic viscoelasticity similar to that of particle-dispersion ER fluids. These differences in ER behavior suggest large differences in their ER mechanisms, with that of the thermotropic polymer dominated by interaction between its LC domains and that of the lyotropic polymer solution by the orientation of the dipoles of its LC groups. © 1996 John Wiley & Sons, Inc.     

Effect of temperature on the selection of semiconducting single walled carbon nanotubes using Poly(3-dodecylthiophene-2,5-diyl)

We report on the investigation of the temperature effect on the selective dispersion of single-walled carbon nanotubes (SWNTs) by Poly(3-dodecylthiophene-2,5-diyl) wrapping. The interaction mechanism between polymer chains and SWNTs is studied by controlling the polymer aggregation via variation of the processing temperature. Optical absorption and photoluminescence measurements including time resolved photoluminescence spectroscopy are employed to study the degree of interaction between the polymer in different aggregation states and the carbon nanotubes. At low processing temperatures, results are consistent with the planarization of the polymer chains and with SWNTs working as seeds for polymer aggregation. The formation of small clusters due to the inter-digitation of alkyl tails between neighboring polymer-wrapped SWNTs allows the formation of the SWNT bundles, as experimentally evidenced and investigated by molecular dynamics simulations. The interaction between the tubes within the bundles, which is reflected in the variation of the photoluminescence dynamics of the polymer, can be suppressed by warming up the sample.     

Nanostructuring and functionalizing polymers with cyclodextrins

We summarize our recent studies employing the cyclic starches called cyclodextrins (CDs) to both nanostructure and functionalize polymers. Two important structural characteristics of CDs are taken as advantages to achieve these goals. First the ability of CDs to form non-covalent inclusion complexes (ICs) with a variety of guest molecules, including many polymers, by threading and inclusion into their relatively hydrophobic interior cavities, which are roughly cylindrical with diameters of ∼0.5 to 1.0 nm for α-, β-, and γ-CD containing 6, 7, and 8 α-1,4-linked glucose units, respectively. When guest polymers are coalesced from the CD-ICs by removing their host CDs, they are observed to solidify with structures, morphologies, and even conformations that are distinct from bulk samples made from their solutions and melts. Molecularly mixed, intimate blends of two or more polymers that are normally immiscible can be obtained from their common CD-ICs, and the phase segregation of incompatible blocks can be controlled (suppressed or increased) in CD-IC coalesced block copolymers. In addition, additives may be more effectively delivered to polymers in the form of their soluble or crystalline CD-ICs or rotaxanes. Secondly, many -OH groups attached to the exterior rims of CDs, in addition to conferring water solubility, provide an opportunity to covalently bond them to polymers either during their syntheses or via post-polymerization reactions. Polymers containing CDs in their backbones or attached to their side chains are observed to more readily accept and retain additives, such as dyes, fragrances, etc. They may also be further reacted or treated through their CDs to cross-link and form networks or to form blends with other polymers having a propensity to thread through their attached CD cavities.