Methoxy End Groups Research Articles

Modulating Surface Cation Concentration via Tuning the Molecular Structures of Ethylene Glycol-Functionalized PEDOT for Improved Alkaline Hydrogen Evolution Reaction.

The sluggish catalytic kinetics of nonprecious metal-based electrocatalysts often hinder them from achieving efficient hydrogen evolution reactions (HERs). Poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have been promising materials for various electrochemical applications. Nevertheless, previous studies have demonstrated that PEDOT coatings can be detrimental to HER performance. In this study, we investigated the alkaline HER efficiency of nickel foam coated with three types of ethylene glycol (EG)-functionalized EDOT. Specifically, EDOT derivatives bearing hydroxyl (-OH) and methoxy (-OCH3) end groups on the EG side chain and molecules containing two EDOT units are interconnected via EG moieties. EG groups are selected due to their strong interaction with alkali metal cations. Intriguingly, improved HER performance is observed on all electrodes coated with EG-functionalized EDOTs. Electrochemical impedance spectroscopy, electrochemical quartz crystal microbalance with dissipation, and XPS analysis are employed to explore the origin of enhanced HER efficiency. The results suggest the EG moieties can induce locally concentrated ions near the electrode surface and facilitate water dissociation through noncovalent interactions. The influence of EG chain length is systematically investigated by synthesizing molecules with di-EG, tetra-EG, and hexa-EG functionalities. This study highlights the importance of molecular design in modifying electrode surface properties to promote alkaline HER.

Kidney functional stages influence the role of PEG end-group on the renal accumulation and distribution of PEGylated nanoparticles.

Modification with polyethylene glycol (PEG), or PEGylation, has become a popular method to improve the efficiency of drug delivery in vivo using nanoparticle-based delivery systems. The PEG end-group plays an important role in the in vivo fate of PEGylated nanoparticles through its interactions with proteins in the serum and the cell membrane. However, the effects of PEG end-groups on the renal clearance of PEGylated nanoparticles remain unclear. Kidney function may also affect the renal accumulation and distribution of nanoparticles. Herein, we demonstrate that the accumulation and distribution of PEGylated nanoparticles in kidneys are significantly affected by both the PEG end-group and kidney function damage. Interestingly, compared to PEG with an amino or methoxy end-group, PEG with maleimide as the end-group markedly enhanced the accumulation of PEGylated nanoparticles in normal kidneys, which may improve renal clearance. However, obvious enhancements in the renal accumulation and medullary distribution of PEGylated nanoparticles are detected in kidneys with functional impairment. Damage to renal function further affects how the PEG end-group influences the accumulation and distribution of PEGylated nanoparticles in kidneys in vivo. Collectively, the findings provide deep insights into the interactions between PEGylated nanoparticles and kidneys in vivo.

Ring opening polymerization of d,l-lactide and ε-caprolactone catalysed by (pyrazol-1-yl)copper(ii) carboxylate complexes.

1,2-Bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L) reacts with [Cu(OAc)2] and C6H5COOH, 4-OH-C6H4COOH, 2-Cl-C6H4COOH and (3,5-NO2)2-C6H3COOH to afford the copper complexes [Cu2(C6H5COO)4(L)2] (1), [Cu2(4-OH-C6H4COO)4(L)2] (2), [Cu2(2-Cl-C6H4COO)4(L)2]n (3) and [Cu{(3,5-NO2)2-C6H3COO}2L]n (4) which are characterised by IR, mass spectrometry, elemental analyses, and X-ray crystallography. The structural data revealed two geometries that are adopted by the complexes: (i) paddle wheel in 1, 2·7H2O, 3 and (ii) regular chains in 3 and 4. Magnetic studies show strong antiferromagnetic couplings in the paddle wheel complexes and a weak antiferromagnetic coupling in the monometallic chain one. Catalysis studies performed with these complexes (1–4) showed that they initiate ring opening polymerization (ROP) of ε-caprolactone (ε-CL) under solvent-free conditions and d,l-lactide in toluene at elevated temperatures. Polycaprolactone (PCL) and poly(d,l-lactide) (PLA) obtained from the polymerization reactions are of low molecular weights (858 for PCL and 602 Da for PLA for initiator 1) and polydispersity indices (typically 2.16 for PCL and 1.64 for PLA with 1 as the initiator). End group analysis of the polymers, determined by MALDI-ToF MS, indicates that the polymers have benzoate, hydroxyl, methoxy and cyclic end groups.

Oligomer Electrolytes for Light-Emitting Electrochemical Cells: Influence of the End Groups on Ion Coordination, Ion Binding, and Turn-on Kinetics.

The electrolyte is an essential constituent of the light-emitting electrochemical cell (LEC), since its operating mechanism is dependent on the redistribution of mobile ions in the active layer. Recent developments of new ion transporters have yielded high-performance devices, but knowledge about the interactions between the ionic species and the ion transporters and the influence of these interactions on the LEC performance is lacking. We therefore present a combined computational and experimental effort that demonstrates that the selection of the end group in a star-branched oligomeric ion transporter based on trimethylolpropane ethoxylate has a paramount influence on the ionic interactions in the electrolyte and thereby also on the performance of the corresponding LECs. With hydroxyl end groups, the cation from the salt is strongly coordinated to the ion transporter, which leads to suppression of ion pairing, but the penalty is a hindered ion release and a slow turn-on for the LEC devices. With methoxy end groups, an intermediate coordination strength is seen together with the formation of contact ion pairs, but the LEC performance is very good with fast turn-on. Using a series of ion transporters with alkyl carbonate end groups, the ion transporter:cation coordination strength is lowered further, but the turn-on kinetics are slower than what is seen for devices comprising the methoxy end-capped ion transporter.

Cleavage of Organosiloxanes with Dimethyl Carbonate: A Mild Approach To Graft-to-Surface Modification.

In this work, we explore the depolymerization of poly(dimethylsiloxane) (PDMS-100) and poly(methylphenylsiloxane) (PMPS) using dimethyl carbonate (DMC) and develop a surface functionalization method by utilizing the DMC-imparted active methoxy end groups of the partially depolymerized polysiloxanes. The efficiency of dimethyl carbonate as a reagent for organosiloxane cleavage was confirmed by means of 1H NMR spectroscopy, size-exclusion chromatography, and viscosity measurements. The reaction of fumed silica with organosiloxanes (PMPS, PDMS-50) in the presence of DMC was investigated using the ζ-potential, 29Si and 13C solid-state NMR spectroscopy, IR spectroscopy, CHN analysis, contact angle goniometry, thermogravimetric analysis, scanning and transmission electron microscopy (TEM), and rheology. It was found that the interaction of PMPS/DMC with an SiO2 surface produced hydrophobic and thermally stable moieties (up to 550 °C) with a densely packed (average 2.2 groups/nm2) alkylsiloxane network for SiO2/PMPS + DMC in comparison with SiO2/PMPS (average 1.4 groups/nm2). Surface functionalization was successfully attained at a relatively moderate temperature of 200 °C. Scanning electron microscopy data show that the average size of aggregates of PMPS/DMC-modified silica nanoparticles is smaller than that of the initial silica and silica modified with neat PMPS. TEM images reveal uniform distribution of the PMPS/DMC mixture across the SiO2 surface. Rheology studies show thixotropic behavior in industrial oil (I-40A), a fully reversible nanostructure and shorter structure recovery time for fumed silica modified in the presence of DMC.

Pyrrolyl-silicon compounds with different alkyl spacer lengths: Synthesis, electrochemical behavior and binding properties

This work reports a joint experimental-theoretical investigation of pyrrolyl-silicon compounds with different alkyl spacers, namely propyl, butyl and hexyl side chains carrying silicon-based end groups. For the electrochemical study, the monomers with methoxysilyl end groups spaced through butyl and hexyl chains were ad-hoc synthesized. Structurally different oligomeric domains are promoted during electropolymerization as a result of irreversible hydrolysis of methoxy end groups by acid intermediate σ-oligomers. The onset of OH-π stabilizing interactions and the charge pinning action of silanol promotes mixed n-p doping behavior of the hybrid films. The more important charge trapping in the case of propyl spacer is attributed to effective (through bond) inductive effects and conformational restrictions. MD simulations of chemisorption of hydrolyzed oligo-pyrroles onto γ-Al2O3 surface confirmed the propyl spacer as the optimum alkyl chain length for stratification and interpenetration of adsorbed hybrid layers.

Structurally Stable Attractive Nanoscale Emulsions with Dipole-Dipole Interaction-Driven Interdrop Percolation.

This study introduces an extremely stable attractive nanoscale emulsion fluid, in which the amphiphilic block copolymer, poly(ethylene oxide)-block-poly(ϵ-caprolactone) (PEO-b-PCL), is tightly packed with lecithin, thereby forming a mechanically robust thin-film at the oil-water interface. The molecular association of PEO-b-PCL with lecithin is critical for formation of a tighter and denser molecular assembly at the interface, which is systematically confirmed by T2 relaxation and DSC analyses. Moreover, suspension rheology studies also reflect the interdroplet attractions over a wide volume fraction range of the dispersed oil phase; this results in a percolated network of stable drops that exhibit no signs of coalescence or phase separation. This unique rheological behavior is attributed to the dipolar interaction between the phosphorylcholine groups of lecithin and the methoxy end groups of PEO-b-PCL. Finally, the nanoemulsion system significantly enhances transdermal delivery efficiency due to its favorable attraction to the skin, as well as high diffusivity of the nanoscale emulsion drops.

Characterization of the Cathode Electrolyte Interface in Lithium Ion Batteries by Desorption Electrospray Ionization Mass Spectrometry.

The solid electrolyte interface (SEI) formed via electrolyte decomposition on the anode of lithium ion batteries is largely responsible for the stable cycling of conventional lithium ion batteries. Similarly, there is a lesser-known analogous layer on the cathode side of a lithium ion battery, termed the cathode electrolyte interface (CEI), whose composition and role are debated. To confirm the existence and composition of the CEI, desorption electrospray ionization mass spectrometry (DESI-MS) is applied to study common lithium ion battery cathodes. We observe CEI formation on the LiMn2O4 cathode material after cycling between 3.5 and 4.5 V vs Li/Li(+) in electrolyte solution containing 1 M LiPF6 or LiClO4 in 1:1 (v/v) ethylene carbonate (EC) and dimethyl carbonate (DMC). Intact poly(ethylene glycol) dimethyl ether is identified as the electrolyte degradation product on the cathode surface by the high mass-resolution Orbitrap mass spectrometer. When EC is paired with ethyl methyl carbonate (EMC), poly(ethylene glycol) dimethyl ether, poly(ethylene glycol) ethyl methyl ether, and poly(ethylene glycol) are found on the surface simultaneously. The presence of ethoxy and methoxy end groups indicates both methoxide and ethoxide are produced and involved in the process of oligomerization. Au surfaces cycled under different electrochemical windows as model systems for Li-ion battery anodes are also examined. Interestingly, the identical oligomeric species to those found in the CEI are found on Au surfaces after running five cycles between 2.0 and 0.1 V vs Li/Li(+) in half-cells. These results show that DESI-MS provides intact molecular information on battery electrodes, enabling deeper understanding of the SEI or CEI composition.

Characterization of the Cathode Electrolyte Interface in Lithium Ion Batteries By Desorption Electrospray Ionization Mass Spectrometry (DESI-MS)

The solid electrolyte interface (SEI) formed via electrolyte decomposition on the anode of lithium ion batteries is largely responsible for the stable cycling of conventional lithium ion batteries. Similarly, there is a lesser-known analogous layer on the cathode side of a lithium ion battery, termed the cathode electrolyte interface (CEI), whose composition and role are debated. To confirm the existence and composition of the CEI, desorption electrospray ionization mass spectrometry (DESI-MS) is applied to study common lithium ion battery cathodes. As a surface ionization method, DESI does not require matrix addition or high-energy radiation, reducing the perturbation of the surface. We observe CEI formation on both LiMn2O4 and LiCoO2 after running half-cells using 1 M LiPF6 or LiClO4 in ethylene carbonate (EC) with dimethyl carbonate (DMC). Intact poly(ethylene glycol) dimethyl ether is identified as the electrolyte degradation product on the cathode surface by the high mass-resolution Orbitrap mass spectrometer after five cycles between 3.5 and 4.5 V vs. Li/Li+. When EC is paired with ethyl methyl carbonate (EMC), poly(ethylene glycol) dimethyl ether and poly(ethylene glycol) methyl ethyl ether are found on the surface simultaneously. The presence of ethoxy and methoxy end groups indicates both methoxide and ethoxide are produced and involved in the process of oligomerization. Au surfaces cycled under different electrochemical windows as model systems for Li-ion battery anodes are also examined. Interestingly, the identical oligomeric species to those found in the CEI are found on Au surfaces after running five cycles between 2.0 and 0.2 V vs. Li/Li+ in half-cells. These results show that DESI-MS provides intact molecular information on battery electrodes, enabling deeper understanding of the SEI or CEI composition. Figure 1

Molecular-scale charge trap medium for organic non-volatile memory transistors

In this work, we introduce a molecular-scale charge trap medium for an organic non-volatile memory transistor (ONVMTs). We use two different types of small molecules, 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), which have the same triphenylene cores with either hydroxyl or methoxy end groups. The thickness of the small molecule charge trap layer was sophisticatedly controlled using the thermal evaporation method. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) analysis revealed that there were negligible differences in the chemical structures of both small molecules before and after thermal deposition process. The ONVMTs with a 1-nm-thick HHTP charge trap layer showed a large hysteresis window, approximately 20 V, under a double sweep of the gate bias between 40 V and −40 V. The HMTP-based structure showed a negligible memory window, which implied that the hydroxyl groups affected hysteresis. The number of trapped charges on the HHTP charge trap layer was measured to be 4.21 × 1012 cm−2. By varying the thickness of the molecular-scale charge trap medium, it was determined that the most efficient charge trapping thickness of HHTP charge trap layer was approximately 5 nm.

Fine-tuning the mechanofluorochromic properties of benzothiadiazole-cored cyano-substituted diphenylethene derivatives through D–A effect

We synthesized three new benzothiadiazole-cored cyano-substituted diphenylethene derivatives (PT-OMe, PT-H, and PT-CF3) with different methoxy, hydrogen, and trifluoromethyl end groups, and the synthesis confirmed by standard spectroscopic methods. These end groups endowed them with different donor–acceptor (D–A) effects, and they provide them with a peculiar and completely opposite mechanofluorochromic property. Red-shifted mechanofluorochromic features were found in the PT-OMe and PT-H compounds, while on the contrary, PT-CF3 showed blue-shifted mechanofluorochromic behavior. The mechanofluorochromic mechanism was explored and attributed to the metastable state of the ground compounds and the crystalline-amorphous phase transformation between the original and ground states. Moreover, these derivatives showed reversible significant mechanofluorochromic properties and reproducibility between ground and annealed states, making them promising stimuli-responsive and smart luminescent materials for mechanosensors, fluorescence switches and light-emitting device applications. The introduction of the D–A effect strategy demonstrated in this work would provide a new path to fine tune the optical features of mechanofluorochromic materials with unique and diverse fluorescent properties.

Microwave-Assisted Reaction in Green Solvents Recycles PHB to Functional Chemicals

An efficient microwave-assisted process for chemical recycling of poly(3-hydroxybutyrate) (PHB) in green solvents was demonstrated. Previously, PHB has been thermally recycled to crotonic acid and unsaturated oligomers. Our aim was to utilize green solvents (water, methanol, and ethanol) under alkaline conditions to achieve fast hydrolysis and monomeric or oligomeric degradation products with carboxyl and hydroxyl or methoxy or ethoxy end groups. Preliminary screening confirmed that the most efficient degradation process was obtained in alkaline methanol. In addition, sample amount, sodium hydroxide concentration, and degradation time all influenced the degradation process and final degree of degradation. Comparison with pure thermal degradation clearly demonstrated the effectiveness of the microwave-assisted process as the time and temperature needed for complete degradation was significantly reduced. Several characterization techniques were utilized for mapping the degradation processes and resulting degradation products. After optimization of the process, complete degradation of PHB to monomeric degradation products (3-hydroxybutanoic acid, 3-methoxybutanoic acid, and crotonic acid) was reached after only 20 min of microwave heating at 110 °C. Functional chemicals for synthesis or modification of biopolymers are thus obtainable from microwave-assisted degradation of PHB in green solvents. This offers new possibilities for retaining the material value of PHB via chemical recycling.

Synthesis of Telechelic Poly(ether sulfone) Oligomers by Chain-Growth Condensation Polymerization

The synthesis of telechelic poly(ether sulfone)s with methoxy end groups is reported. Molecular weights ranging from 1600 to 2800 g mol −1 and polydispersities of 1.1–1.2 are synthesized by chain-growth condensation polymerization. The initiator is chosen by using semiempirical calculations and 19 F NMR spectroscopy measurements. The polymers are characterized by NMR spectroscopy and matrix-assisted laser desorption/ionization time of fl ight (MALDI-TOF) mass spectrometry (MS), and are terminated by a methoxy group at one end and a fl uorine at the other, and up to approximately 20% polymer of similar mass but slightly higher polydispersity, methoxy terminated at both ends, is present, along with less than 5% of polymer terminated at both ends by fl uorine atoms. These do not need to be separated, and can be converted to methoxy-ending telechelic blocks, yielding polyvalent, reactive rigid building blocks for copolymer synthesis.

Polymer Nanocomposite Hydrogels Exhibiting Both Dynamic Restructuring and Unusual Adhesive Properties

Polymer nanocomposite (NC) hydrogels exhibiting both dynamic restructuring and unusual adhesive properties in wet and dry states have been prepared in an efficient and straightforward way via free radical polymerization of poly(ethylene glycol) methyl ether acrylate (PEG) in the presence of silane-modified sodium montmorillonite (NaMMT). The dynamic restructuring of the NC gel has been demonstrated by almost instant recovery of mechanical properties, such as storage modulus, loss modulus, and damping tan δ (at 0.025 strain) by 60-110% after being stressed to the point of gel failure. Furthermore, the dry NC gel showed exceptional thermal and mechanical stability during a heating and cooling cycle between 25 and 110 °C, with only slightly decreases followed by at least 30% increases in both moduli, while tan δ remained nearly unchanged. The NC gel in dry state could repeatedly adhere to various surfaces such as steel, glass, plastic, etc., and detach from the surface without being broken and leaving little contamination behind. This unique adhesive characteristic was characterized by high storage modulus, loss modulus (kPa), and tan δ (>0.6) corresponding to high cohesive, adhesive, and tacking properties of pressure-sensitive adhesives (PSAs). Finally, a reversible network structure formed by PEO interpenetrating within 3-dimentional (3-D) silica network was proposed to be responsible for the dynamic restructuring and the unique adhesive behaviors observed in the NC gel, and the 3-D network structure was investigated by XRD, FTIR, and DSC measurements. For this 3-D network structure, we suggest that the flexibility of PEO could allow PEO side chains to contact with various surfaces by either PEO segments or methoxy end groups via weak physical interactions, such as van der Waals interactions or hydrogen bonding, whereas the reversible network structure contributes to the recovery of strength and shape after the gel failure.

Use of Doubly Charged Precursors to Validate Dissociation Mechanisms of Singly Charged Poly(Dimethylsiloxane) Oligomers

Collision-induced dissociation of doubly charged poly(dimethylsiloxane) (PDMS) molecules was investigated to provide experimental evidence for fragmentation reactions proposed to occur upon activation of singly charged oligomers. This study focuses on two PDMS species holding trimethylsilyl or methoxy end-groups and cationized with ammonium. In both cases, introduction of the additional charge did not induce significant differences in dissociation behavior, and the use of doubly charged precursors enabled the occurrence of charge-separation reactions, allowing molecules always eliminated as neutrals upon activation of singly charged oligomers to be detected as cationized species. In the case of trimethylsilyl-terminated oligomers, random location of the adducted charge combined with rapid consecutive reactions proposed to occur from singly charged precursors could be validated based on MS/MS data of doubly charged oligomers. In the case of methoxy-terminated PDMS, favored interaction of the adducted ammonium with both end-groups, proposed to rationalize the dissociation behavior of singly charged molecules, was also supported by MS/MS data obtained for molecules adducted with two ammonium cations.

Copper(II) ion-sensing mechanism of oligo-phenylene vinylene derivatives: syntheses and theoretical calculations

Oligo-phenylene vinylene (oligo-PV) with two picolinamide side-groups and six methoxy end-groups was synthesized in order to be a fluorescent sensing molecule. Various metal ion solutions (1.5×10−4 M) were added to the 1.5×10−6 M acetonitrile solution of the fluorescent molecule. The fluorescent emission spectra showed that, at about the same concentration (1.5×10−4 M), only Cu(II) ion can quench the fluorescent emission of the picolinamide-PV solution. Possible metal ion-sensing mechanisms could be either the binding at picolinamide side-groups or methoxy end-groups, or interchain-stacking driven by the metal ions. Hence, oligo-PVs with six methoxy end-groups but without substituted side-groups, and another oligo-PV with six methoxy end-groups and two ethoxy side-groups were synthesized for comparison. These molecules turned out to be inactive to any metal ion solutions. Moreover, quantum calculation was used to confirm the result. Binding energy and conformation were calculated and simulated. It could be concluded that nitrogen and oxygen atoms of the picolinamide group and one oxygen atom from the methoxy group are involved in the metal ion-binding process.

Self-assembled liquid crystals formed by hydrogen bonding between non-mesogenic 1,3,4-oxadiazole-based pyridines and substituted benzoic acids

A series of new supramolecular liquid crystalline complexes have been prepared readily through intermolecular hydrogen bonding between non-mesogenic 1,3,4-oxadiazole-based pyridines and substituted benzoic acids. The liquid crystalline properties of the H-bonded complexes were studied by infrared spectrometry, polarising optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. All the H-bonded complexes exhibited liquid crystalline behaviours with various mesophases such as nematic (N), smectic A and hexagonal columnar mesophases, which are determined by the electronic nature of terminal groups and the number of alkoxy chains of the H-acceptors and H-donors. The rod-like H-bonded complexes 2a/3a, 2a/3b and 2a/3c with an electron-withdrawing end group (NO2, F or CN) fascinate to form an enantiotropic smectic A phase, whereas complex 2a/3d bearing an electron-donating methoxy end group tends to display a monotropic N phase. In contrast, the disc-shaped complexes 2b/3e and 2c/3e with six peripheral decyloxy chains are room temperature liquid crystals exhibiting columnar mesophase. All the complexes 2a/3a, 2a/3b, 2a/3c and 2a/3d in CH2Cl2 solutions exhibited an intense broad absorption peak at ca. 303 nm, and emitted a strong blue emission with λmax at ca. 390 nm and good photoluminescence quantum yields (ΦFL = 0.56–0.81).

Influences of Hydrogen Bonding and Peripheral Chain Length on Mesophase Structures of Mesogen-Jacketed Liquid Crystalline Polymers with Amide Side-Chain Linkages

A series of mesogen-jacketed liquid crystalline polymers, poly{2,5-bis[(4-alkoxyphenyl)aminocarbonyl]styrene} (P-Cm, where m is the number of carbon atoms in the alkoxy groups, and m = 1, 4, 8, 12), with an amide core and flexible tails of varying lengths on the two ends in the side chain were designed and successfully synthesized via conventional radical polymerization. The mesophase structures of these polymers were dependent on the number of carbon atoms in the peripheral chains. Wide-angle X-ray diffraction and polarized light microscopy results revealed that the polymers with m ≥ 4 could form smectic A phases, while a columnar nematic phase could be formed for the polymer with methoxy end groups (P-C1). The hydrogen bonding among the side-chain amide groups might play an important role in forming and stabilizing these liquid crystalline phases, which was suggested by the results from variable-temperature FTIR and 2D IR analyses.

Tuning Helical Twisting Power of Isosorbide-Based Chiral Dopants by Chemical Modifications

Isosorbide-based chiral dopants (ICD) with various substituent groups were newly synthesized to control their helical twisting powers (HTP). Phase transition behaviors of ICD molecules were first investigated by combined techniques of differential scanning calorimetry, wide-angle X-ray diffraction, and cross-polarized optical microscopy. ICD with n-hexyloxy end groups formed the multiple ordered phases, and those with methoxy or acetoxy end groups exhibited a simple crystal-to-isotropic transition. Energy-minimized chemical conformations of ICD molecules revealed that all the ICDs had twisted conformations and that the extension of the benzoyl ester moiety induced a higher twisted conformation. By varying substitution groups, HTPs of ICDs were controlled from 26.6 to 80.2 μm−1. Particularly, ICD with an acetoxy end group (ICD-2) showed the largest HTP. It was also realized that by controlling the content of ICD-2 from 3.0 to 4.5 mol%, the helical pitch length of cholesteric LC mixture was adjusted to reflect a specific visible light.

A New General Methodology for the Syntheses of End-Functional Polyisobutylenes by Nucleophilic Substitution Reactions

The syntheses of end-functional polyisobutylenes (PIBs) including hydroxy, amino, carboxy, azide, boxy and thymine end groups have been accomplished using nucleophilic substitution reactions. propargyl, methoxy, and thymine end groups have been accomplished using nucleophilic substitution reactions. S N 2 reactions on PIB-Allyl-X (X = Cl or Br), the trans-1,4 addition product of the capping reaction of living PIB with 1,3-butadiene, with different nucleophiles successfully yielded the corresponding PIB-Allyl-OH, PIB-Allyl-OMe, PIB-Allyl-NH 2 , PIB-Allyl-OCH 2 C≡CH, PIB-Allyl-N 3 , and PIB-Allyl-CH 2 COOH with quantitative functionalization as determined by 1 H and 13 C NMR, FT-IR, and matrix-assisted time-of-flight mass spectroscopy. As expected, the rate of substitution was faster with PIB-Allyl-Br compared to PIB-Allyl-Cl. GPC analysis of the precursor PIB-Allyl-X and the products indicated that the polymer chain is unaffected by the substitution reactions. The synthesis of hydroxy telechelic PIBs was also achieved using X-Allyl-PIB-Allyl-X at reaction conditions similar to that employed for the preparation of PIB-Allyl-OH. The methodology was extended to the synthesis of PIB block copolymers by employing polymeric nucleophiles. PIB-b-poly(ethylene oxide) (PEO) was synthesized by the nucleophilic substitution of PIB-Allyl-Cl with PEO-O - Na + .