Single-crystal-to-single-crystal synthesis of a pseudostarch via topochemical azide–alkyne cycloaddition polymerization

There is high demand for polysaccharide-mimics as enzyme-stable substitutes for polysaccharides for various applications. Circumventing the problems associated with the solution-phase synthesis of such polymers, we report here the synthesis of a crystalline polysaccharide-mimic by topochemical polymerization. By crystal engineering, we designed a topochemically reactive crystal of a glucose-mimicking monomer decorated with azide and alkyne units. In the crystal, the monomers arrange in head-to-tail fashion with their azide and alkyne groups in a ready-to-react antiparallel geometry, suitable for their topochemical azide–alkyne cycloaddition (TAAC) reaction. On heating the crystals, these pre-organized monomer molecules undergo regiospecific TAAC polymerization, yielding 1,4-triazolyl-linked pseudopolysaccharide (pseudostarch) in a single-crystal-to-single-crystal manner. This crystalline pseudostarch shows better thermal stability than its amorphous form and many natural polysaccharides.

Prudent crystal engineering allows head-to-tail arrangement of inositol monomer molecules pre-organizing azide and alkyne units of adjacent monomers in a ready-to-react manner. On heating regiospecific SCSC polymerization yields a starch-like polymer.     

ESR study of the diacetylene polymer 4BCMU

Electron Spin Resonance (ESR) measurements of the polydiacetylene 4BCMU in the solid-state indicate the presence of a thermally activated paramagnetic center with g ≈ 2.002 and first-derivative peak-to-peak linewidth of ≈ 17G. An abrupt and irreversible decrease in ESR signal intensity is observed at ca. 400 K, and appears to be associated with the solid-state planar-nonplanar conformational transformation manifested by an irreversible color change from metallic brown to red.     

Single-crystal-to-single-crystal structural transformations of two sandwich-like Cu(ii) pyrazolate complexes and their excellent catalytic performances in MMA polymerization

Reactions of Cu(OAc)(2)·H(2)O with dmnpzH in EtOH produce a heptanuclear copper(ii) pyrazolate complex [Cu(7)(OH)(2)(OAc)(6)(dmnpz)(6)(EtOH)(6)], which is able to undergo a SCSC structural transformation from a lower symmetry structure to a higher symmetry structure via replacement of ligated-EtOH molecules with MeOH; both complexes along with the solvent-free species exhibit high catalytic activity in the polymerization of MMA.     

Investigation of the structure of polymer diacetylene Langmuir-Blodgett films

Abstract

The structure of Langmuir-Blodgett (LB) diacetylene films CH₃?(CH₂)₁₁?C≡C?C≡C?(CH₂)₈?COOCd_1/2 (DA1) and CH₃?(CH₂)₂₀?CO₂?CH₂?C≡C?C≡CH₂OH (DA2) was studied by X-ray small angle scattering and electron diffraction methods prior to and upon their polymerization. It has been established that Langmuir films have layer packing. The periods of the constituent layers were determined as 58 Å (for DA1) and 69 Å (for DA2). This indicates the existence of a vertical bilayered packing of molecules. It has also been established that polymerization of LB diacetylene films due to the action of UV irradiation does not change the layer thickness appreciably and the structural rearrangement reduces to a slight redistribution of the electron density along the molecules which is explained by a break of the triple bonds during the UV irradiation.     

High ability of a blue phase polymer based on a diacetylene alcohol derivative

The effect of prolonged UV irradiation and high temperature on a blue phase polymer film prepared by the Langmuir–Schaefer method based on 11-hydroxyundeca-6,8-diyn-1-yl N-(4-methoxyphenyl)carbamate was evaluated. The high stability of the polymer under extreme external influences was revealed. The transition of a monolayer to a bilayer with increasing surface pressure during the Langmuir layer formation was confirmed by atomic force microscopy.     

Synthesis and characterization of a new conjugated polymer: Polytrifluoromethylacetylene

Polytrifluoromethylacetylene (PTFMA) was synthesized from trifluoromethylacetylene (TFMA) using a PdCl₂/DMF catalyst solution or the anionic initiator n-butyl lithium. Although PdCl₂ proved to be an effective catalyst for the polymerization of TFMA, long reaction times and poor yields made characterization of the resultant polymer difficult. The use of n-butyl lithium, on the other hand, resulted in high yields of PTFMA in relatively short reaction times. The results of thermal analysis and the effects of n- and p-type doping on the electrical conductivity of the polymer are discussed.     

Automated parallel anionic polymerizations: Enhancing the possibilities of a widely used technique in polymer synthesis

Anionic polymerization techniques have been implemented successfully in a commercial automated synthesizer. The main problems for a successful adaptation of the experimental technique in the automated synthesizer are addressed, as well as some simple potential applications, such as the anionic polymerization of styrene, isoprene, and methyl methacrylate. The obtained results were reproducible and in concordance with literature knowledge. The apparent rate constant of the anionic polymerization of styrene in cyclohexane initiated by sec‐butyllithium could be determined at two different concentrations of the monomer and initiator in a temperature range of 10–60 °C. All the synthesis and characterization experiments of the polymers were performed within a short time period. Moreover, the syntheses of poly(styrene‐b‐isoprene) and poly(styrene‐b‐methyl methacrylate) block copolymers were also successfully carried out within the automated synthesizer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4151–4160, 2005     

Electrochemically nanopatterned conducting coronas of a conjugated polymer precursor: SPM parameters and polymer composition

Here we describe the formation of precisely controlled corona-type nanopatterns on electroactive polymer precursor films using scanning probe microscopy (SPM) methods. The binary composition of electroactive groups in the polymer triggers the formation of corona-type nanopatterns at particular voltages and tip writing speeds through the electrooxidation of the polymer precursor film. Various parameters such as tip speed and applied bias were explored in the nanopatterning process, and the formation of a conductive nanopattern was investigated using conducting atomic force microscopy (C-AFM). The formation of the nanopattern was attributed to the flow of electrons from the AFM tip to the polymer film in a controlled electric field distribution. We also report a new method to distinguish the polymer composition and distribution of a polymer blend film by characterizing biasing differences in the patterning of a polymer film.     

Synthesis of a novel highly conjugated conducting polymer

The new conjugated polyacetylene derivative dehydrated poly(4-hydroxy-4-phenyl-1-butyne) [dehydrated poly(HPB)] was synthesized from poly(4-hydroxy-4-phenyl-1-butyne) [poly(HPB)], which was obtained by the polymerization of 4-hydroxy-4-phenyl-1-butyne. The resulting dehydrated poly(HPB) was soluble in common organic solvents. The dehydrated poly(HPB) was found to have extended conjugated polyene structure. The dehydrated poly(HPB) was thermally stable up to 300°C. The electrical conductivity of I₂-doped dehydrated poly(HPB) was 10⁻² S cm⁻¹. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 949–953, 1998     

Pyroelectric effect in crystals of the bis-toluene sulphonate diacetylene monomer and polymer

The pyroelectric properties of the monomer and partially and fuly polymerized crystals of the bis(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol (TS) were measured along their b axes from 100 to 300 K. Two peaks in the pyroelectric current of monomer crystals were found at 192 and 151 K. It is concluded that these crystals lack a centre of symmetry.     

Two‐dimensional polymer synthesis through the topochemical polymerization of alkylenediammonium muconate as a multifunctional monomer

Here we demonstrate a unique two‐dimensional polymer synthesis through topochemical polymerization via polymer crystal engineering, which is useful for controlling and designing the polymerization reactivity as well as the polymer chain and crystal structures. We have succeeded in the synthesis of a sheet polymer through the polymerization of alkylenediammonium (Z,Z)‐muconate as a multifunctional 1,3‐diene monomer in the crystalline state under the irradiation of UV and γ‐rays or upon heating in the dark. The photopolymerization reactivity of several muconates and the structural control of the obtained polymer are described. The stereochemical structure of the polymer and the polymerization mechanism are discussed on the basis of the results of IR and NMR spectroscopy, thermogravimetric measurements, and solid‐state hydrolysis for the transformation into poly(muconic acid). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3922–3929, 2004     

Electrochemical tuning of the optoelectronic properties of a fluorene-based conjugated polymer

The electrochemical reduction of a fluorene-based conjugated polymer, poly(9-fluorenone-alt-9,9-dioctylfluorene), was investigated for the first time. The carbonyl group in the fluorenone unit was selectively and quantitatively converted to the methylene group, as determined by (1)H NMR, IR, and energy-dispersive X-ray (EDX) analysis. The optical and electrochemical properties of the polymers were studied by UV-vis, photoluminescence (PL), and cyclic voltammetry (CV) measurements and were found to be tunable by varying the reduction level.     

Cascade polymerizations: recent developments in the formation of polymer repeat units by cascade reactions

Traditionally, most polymerizations rely on simple reactions such as alkene addition, ring-opening, and condensation because they are robust, highly efficient, and selective. These reactions, however, generally only yield a single new C–C or C–O bond during each propagation step. In recent years, novel macromolecules have been prepared with propagation steps that involve cascade reactions, enabling various combinations of bond making and breaking steps to form more complex repeat units. These polymerizations are often challenging, given the requirements for high conversion and selectivity in controlled polymerizations, yet they provide polymers with unique chemical structures and significantly broaden the scope of how polymers can be made. In this perspective, we summarize the recent developments in cascade polymerizations, primarily focusing on single-component cascades (rather than multi-component polymerizations). Polymerization performance, monomer scope, and mechanisms are discussed for polymerizations utilizing radical, ionic, and metathesis-based mechanisms.

Cascade polymerizations provide new routes to unique polymer structures. In this perspective, we summarize their performance, monomer scope, and mechanisms.     

Controlled processing of polymer nanoribbons: Enabling microhelix transformations

Flow‐coated, two‐dimensional polymer ribbon structures undergo a shape‐transformation into a three‐dimensional helix upon their release into a solution. Driven by surface forces and due to geometric asymmetry, the helix radius and spring constant depend upon the ribbon cross‐section dimensions, surface energy, and material elastic modulus. Such spring‐like microhelices offer multiple functionalities combined with mechanical stretching and shape recovery. Fabricating such microhelices requires a sequence of processing steps, beginning with flow‐coating of ribbons on a substrate, followed by etching of a “scum layer” to allow for an independent release into a solution, upon which shape‐transformation occurs. During the deposition‐etch‐release sequence, various control parameters influence the nanoribbon size and geometry, hence the helix properties. The experimental study presented here focuses on the influence of meniscus height, substrate velocity, substrate surface energy, and etch time on nanoribbon size (height and width), scum layer thickness, and helix radius. The results show that meniscus height and contact angle dictate flux toward the meniscus edge and volume available for spatial assembly, allowing control over the aspect ratio of ribbons. We vary the aspect ratio by two orders of magnitude, while maintaining geometric asymmetry needed for helix shape‐transformation. We provide robust scaling for the nanoribbon size and geometry and report the advantages and disadvantages of different parameters, in the control of polymer nanoribbon and helix fabrication. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1270–1278     

Chemosensing of nitroaromatics with a new segmented conjugated quaterphenylene polymer

A new approach for introducing porosity in fluorescent polymer films to increase sensing performance is presented. A novel segmented conjugated polymer composed of p-quaterphenylene segments tethered by their meta positions along the polymer main chain by 2,2-isopropylene spacers was synthesized. The bent nature of its microstructure generates amorphous morphologies that let analytes diffuse rapidly within the films. Fluorescence quenching studies with polymer films and methanol solutions of nitroaromatics showed high sensitivity, fast response and reversibility of the fluorescence quenching. Thus, half of the maximum quench (Q_50%) occurred with nitrobenzene at the micromolar range in less than 1 min in a reversible manner.     

Miniemulsion polymerizations of n-butyl cyanoacrylate via two routes: towards a control of particle degradation

This study aimed at determining the influence of the mechanism of polymerization on the molar mass and degradation of poly(n-butyl cyanoacrylate) (PBCA) nanoparticles obtained by miniemulsion polymerization. Therefore, nanoparticles of poly(n-butyl cyanoacrylate) were synthesized via radical and/or anionic miniemulsion polymerization stabilized by Brij?78, a POE based surfactant. Polymerization conditions had little influence on the final diameter while it severely affected the final molar masses of PBCA. An increase of the temperature and of the pH of the continuous phase led to higher molar masses. A further increase was observed when a radical initiator was added in the monomer. The evolution of the molar mass of the synthesized poly(n-butyl cyanoacrylate) was followed as a function of time at pH 7.4 by Size Exclusion Chromatography. As expected, the degradation kinetics strongly depended on the polymerization mechanism (anionic or radical).     

Understanding the crystallization process of a diketopyrrolopyrrole-based conjugated polymer in blend films

The film morphology of fullerene and diketopyrrolopyrrole-based conjugated polymers (PDPPs) blends largely influences the device performance in organic solar cells. It is critical to control the morphology of blend films, which usually requires investigations of the crystallization of PDPP-based thin films. Here, we study the influence of marginal solvent additive 1,2-dichlorobenzene (ODCB) and non-solvent additive 1,8-diiodooctane (DIO) on the crystallization of poly[2,5-bis(2-octyldodecyl)pyrrolo-[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2′: 5′,2″: 5″,2″′-quaterthiophene] (PDQT). The blends formed fibril structures in thin films, as revealed by transmission electron microscopy. The fibril density increased and the width decreased with the ODCB amount. The critical ODCB content to achieve constant fibril width is almost proportional to the concentration of PDQT. Higher ODCB content also results in higher fibril density in pure PDQT films. In contrast, the amount of DIO has a negligible influence on the fibril width and density of thin films. Moreover, novel dendritic fibrils were formed in PDQT films upon addition of ODCB. A model based on nucleation and growth is proposed to explain these findings. The heterogeneous nucleation was dominant with the presence of ODCB, while the homogeneous nucleation was prevailing when DIO was used. The results show that initial nucleation density and growth direction are key factors determining the fibril width.     

Photoluminescence spectra of a conjugated polymer: from films and solutions to single molecules

The purpose of this work is to address the issue of applicability of single-molecule spectroscopy (SMS) results for conjugated polymers to "bulk" samples, e.g. conjugated polymer films. Also, some apparent inconsistencies in the literature on SMS regarding the photoluminescence spectral position of conjugated polymers are discussed. We present a series of photoluminescence spectra of thin films of the conjugated polymer poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) with a wide range of varying thickness. The thickness was varied from approximately 20 nm to the value corresponding to well-separated single molecules (SMS sample). The thickness variation resulted in a strong ( approximately 2000 cm(-1)) blue-shift and broadening of the spectrum. The result was reproduced on isolated molecules embedded into a PMMA matrix. This effect cannot be explained by a decrease in energy transfer "freedom" alone. We performed a comprehensive comparison of presented and elsewhere published spectra of MEH-PPV polymer and oligomers in different samples: films, solutions, isolated-molecule coatings and standard SMS samples. The comparison allows that the main reason behind the blue shift is conformational disorder, which is largely dependent on the sample. We also discuss some experimental aspects of SMS, such as representativeness of detected molecules, spectral sensitivity of a setup and temperature. Together with differences in sample preparation method, these issues can explain the existing inconsistencies in the literature.