Length Of Side Groups Research Articles

Structure and dynamics heterogeneity in poly(vinyl acetal)s: The effect of side group length

Understanding on the structure and dynamics of poly(vinyl acetal)s is insufficient due to the complicated chemical structure and amorphous nature of this type of polymers. In this work, we investigate the effect of side group length on structure and dynamics heterogeneity at different length scales spanning from side group, segment, and polymer network by combing dynamic mechanical analysis (DMA), dielectric relaxation spectroscopy (DRS), solid-state NMR, and differential scanning calorimetry analysis (DSC). By increasing the length of acetal side group, its intrinsic dynamics slows down. Taking into account the scale of segment and networks, with the increase of acetal group length, the formation of cross-linking sites formed by the hydroxyl-rich domain is suppressed, the relaxation distribution of the segment widens, and the volume fraction of rigid component decreases. The effect of side group length on the structure and dynamics heterogeneity of poly(vinyl acetal)s at different scales results in significant changes in material properties such as the non-monotonic change in loss factor value (tan δ) and a monotonous reduction in glass transition temperature (Tg).

Designable Photo-Responsive Micron-Scale Ultrathin Peptoid Nanobelts for Enhanced Performance on Hydrogen Evolution Reaction.

The development of high-reactive single-atom catalysts (SACs) based on long-range-ordered ultrathin organic nanomaterials (UTONMs) (i.e., below 3nm) provides a significant tactic for the advancement in hydrogen evolution reactions (HER) but remains challenging. Herein, photo-responsive ultrathin peptoid nanobelts (UTPNBs) with a thickness of ≈2.2nm and micron-scaled length are generated using the self-assembly of azobenzene-containing amphiphilic ternary alternating peptoids. The pendants hydrophobic conjugate stacking mechanism reveals the formation of 1D ultralong UTPNBs, whose thickness is dictated by the length of side groups that are linked to peptoid backbones. The photo-responsive feature is demonstrated by a reversible morphological transformation from UTPNBs to nanospheres (21.5nm) upon alternative irradiation with UV and visible lights. Furthermore, the electrocatalyst performance of these aggregates co-decorated with nitrogen-rich ligand of terpyridine (TE) and uniformly-distributed atomic platinum (Pt) is evaluated toward HER, with a photo-controllable electrocatalyst activity that highly depended on both the presence of Pt element and structural characteristic of substrates. The Pt-based SACs using TE-modified UTPNBs as support exhibit a favorable electrocatalytic capacity with an overpotential of ≈28mV at a current density of 10mA cm-2. This work presents a promising strategy to fabricate stimuli-responsive UTONMs-based catalysts with controllable HER catalytic performance.

Side group dependent room temperature crystallization-induced phosphorescence of benzil based all organic phosphors.

In this work, we report alkoxy substituted benzil based all organic room temperature phosphors which showed crystallization induced phosphorescence (CIP). Nine title compounds were prepared with various alkyl lengths (OCnH2n+1: n = 8-16) and the effect of alkyl side group length on the phosphorescence performance was investigated, as compared to p-anisil. It was found that both phosphorescence quantum yield and lifetime increased concomitantly as the alkyl length increased up to nonyloxy (BZL-OC9). Further increase in the carbon number caused the phosphorescence performance to deteriorate due to greater conformational freedom of the side groups. An incredible quantum yield of 70% was achieved for BZL-OC9. A promising finding is that the increased quantum yield was accompanied by the increase in the lifetime relative to p-anisil, which has been historically challenging. Single crystallography coupled with UV-Vis spectroscopy revealed that a higher level of intermolecular π-π interactions was observed from p-anisil while more alkyl interactions with less intermolecular π-orbital overlap were found for BZL-OC8. As a result, molecular rigidification with less phosphorescence quenching was achieved for BZL-OC8 leading to enhanced performance. A precipitation study on a dichloromethane solution as a function of the content of MeOH (poor solvent) proved that the emission of the BZL-OCn system is truly aggregation-induced. The current work demonstrates that strategic side group engineering could be a promising approach to developing high-performance all organic phosphors as well as improving the properties of existing phosphors.

Small molecule diffusion in poly-(olygo ethylene glycol methacrylate) based hydrogels studied by fluorescence correlation spectroscopy

Understanding just how solutes such as small molecules, polymers or proteins diffuse in “smart” hydrogels is a key factor in developing potential applications. In this work, we used fluorescence correlation spectroscopy (FCS) to study how structural parameters (length of side groups, network density) influence the diffusion of small dye molecules in poly (oligo (ethylene glycol) methyl ether methacrylates) (POEGMAs) hydrogels. Two diffusion components were found and attributed to (i) Fickian-like diffusion slowed only by steric effects, and (ii) diffusion slowed by interactions with the polymer. The relationship between the diffusion component (i) and the polymer concentration showed two regimes with different slopes in both hydrogels and solutions of non-crosslinked polymers, additionally studied for reference. The threshold between these regimes depended on the polymer hydrophilicity/hydrophobicity and the presence of cross-links. The release time of the model drug (ibuprofen) proved to be shorter in the case of denser hydrogel networks than for looser ones. This means that the drug affinity to the polymer network is the crucial parameter determining release processes, while the diffusion factor is of secondary and minor importance.

Influence of lipid bilayer composition on the activity of antimicrobial quaternary ammonium ionenes, the interplay of intrinsic lipid curvature and polymer hydrophobicity, the role of cardiolipin

Incorporation of hydrophobic component into amphiphilic polycations structure is frequently accompanied by an increase of antimicrobial activity. There is, however, a group of relatively hydrophilic polycations containing quaternary ammonium moieties along mainchain, ionenes, which also display strong antimicrobial and limited hemolytic properties. In this work, an influence of a hydrophobic side group length on antimicrobial mechanism of action is investigated in a series of novel amphiphilic ionenes. High antimicrobial activity was found by determination of minimum inhibitory concentration (MIC) and minimum bactericidal, and fungicidal concentration (MBC and MFC) in both growth media and a buffer. Biocompatibility was estimated by hemolytic and mammalian cells viability assays. Mechanistic studies were performed using large unilamellar vesicles (LUVs) with different lipid composition, as simplified models of cell membranes. The investigated ionenes are potent and selective antimicrobial molecules displaying a decrease of antimicrobial activity correlated with increase of hydrophobicity. Studies using LUVs revealed that the cardiolipin is an essential component responsible for the lipid bilayer permeabilization by investigated ionens. In contrast to relatively hydrophilic ionenes, more hydrophobic polymers showed an ability to stabilize membranes composed of lipids with negative spontaneous curvature in a certain range of polymer to lipid ratio. The results substantially contribute to the understanding of antimicrobial activity of the investigated class of polymers.

Hydration in thermo-responsive oligoether methacrylate hydrogels studied by FT-IR spectroscopy

Hydration in thermo-responsive polymer hydrogels, such us poly(oligo(ethylene glycol) methyl ether methacrylates) (POEGMAs) is a key factor in understanding their thermo-responsivity. The hydration of POEGMAs with different length of side groups was comprehensively studied for the first time. The comparative studies have shown that hydration of different hydrophilic centres in various POEGMAs is similar and independent of oligoether chain length. Only some quantitative differences in bound water structure, especially at the first stage of hydration have been found. However, the crystallinity (if it occurs) significantly impacts on the hydration process. Finally, the water structure is the closer to the bulk water structure in the fully swollen PMEO2MA hydrogel than in other POEGMA systems with longer oligoether side groups.

Effect of different lengths of side groups on the thermal, crystallization and mechanical properties of novel biodegradable poly(ethylene succinate) copolymers

To explore the effect of different lengths of side groups, the thermal, crystallization, and mechanical properties were systematically investigated for three novel poly(ethylene succinate) (PES) based copolyesters containing methyl, butyl, and octyl as side groups, respectively, in this research. Relative to linear PES, the presence of side groups did not modify the crystal structure, while increasing the length of side groups slightly decreased the crystallinity of the copolymers. Despite the length of side groups, they all displayed high thermal decomposition temperatures. Increasing the length of side groups gradually decreased the melting point temperatures of PES copolymers. The glass transition temperature of poly(ethylene succinate-co-1,2-propylene succinate) slightly increased; however, those of poly(ethylene succinate-co-1,2-hexamethylene succinate) and poly(ethylene succinate-co-1,2-decamethylene succinate) gradually decreased with an increase in the length of side groups. PES and its copolymers displayed the same crystallization mechanism; however, the crystallization time increased as the length of side groups increased at the same degree of supercooling. The elongation at break increased while the Young's modulus decreased with increasing the length of side groups. The dynamic mechanical analysis results revealed that the storage modulus and tan δ gradually decreased as the length of side groups increased. In brief, the length of side groups significantly influenced the thermal, crystallization, and mechanical properties of PES based copolymers.

New Poly(imide)s Bearing Alkyl Side-Chains: A Study on the Impact of Size and Shape of Lateral Groups on Thermal, Mechanical, and Gas Transport Properties.

A set of five new aromatic poly(imide)s (PIs) incorporating pendant acyclic alkyl moieties were synthesized. The difference among them was the length and bulkiness of the pendant group, which comprises of linear alkyl chains from three to six carbon atoms, and a tert-butyl moiety. The effect of the side group length on the physical, thermal, mechanical, and gas transport properties was analyzed. All PIs exhibited low to moderate molecular weights (Mn ranged between 27.930–58.970 Da, and Mw ranged between 41.760–81.310 Da), good solubility in aprotic polar solvents, except for PI-t-4, which had a tert-butyl moiety and was soluble even in chloroform. This behaviour was probably due to the most significant bulkiness of the side group that increased the interchain distance, which was corroborated by the X-ray technique (PI-t-4 showed two d-spacing values: 5.1 and 14.3 Å). Pure gas permeabilities for several gases were reported (PI-3 (Barrer): He(52); H2(46); O2(5.4); N2(1.2); CH4(1.1); CO2(23); PI-t-4 (Barrer): He(139); H2(136); O2(16.7); N2(3.3); CH4(2.3); CO2(75); PI-5 (Barrer): He(44); H2(42); O2(5.9); N2(1.4); CH4(1.2); CO2(27); PI-6 (Barrer): He(45); H2(43); O2(6.7); N2(1.7); CH4(1.7); CO2(32)). Consistent higher volume in the side group was shown to yield the highest gas permeability. All poly(imide)s exhibited high thermal stability with 10% weight loss degradation temperature between 448–468 °C and glass transition temperature between 240–270 °C. The values associated to the tensile strength (45–87 MPa), elongation at break (3.2–11.98%), and tensile modulus (1.43–2.19 GPa) were those expected for aromatic poly(imide)s.

Significantly Enhanced Molecular Stacking in Ternary Bulk Heterojunctions Enabled by an Appropriate Side Group on Donor Polymer.

Ternary strategy is a promising approach to broaden the photoresponse of polymer solar cells (PSCs) by adopting combinatory photoactive blends. However, it could lead to a more complicated situation in manipulating the bulk morphology. Achieving an ideal morphology that enhances the charge transport and light absorption simultaneously is an essential avenue to promote the device performance. Herein, two polymers with different lengths of side groups (P1 is based on phenyl side group and P2 is based on biphenyl side group) are adopted in the dual‐acceptor ternary systems to evaluate the relationship between conjugated side group and crystalline behavior in the ternary system. The P1 ternary system delivers a greatly improved power conversion efficiency (PCE) of 13.06%, which could be attributed to the intense and broad photoresponse and improved charge transport originating from the improved crystallinity. Inversely, the P2 ternary device only exhibits a poor PCE of 8.97%, where the decreased device performance could mainly be ascribed to the disturbed molecular stacking of the components originating from the overlong conjugated side group. The results demonstrate a conjugated side group could greatly determine the device performance by tuning the crystallinity of components in ternary systems.

Controlling the properties of radiation-synthesized thermoresponsive oligoether methacrylate hydrogels by varying the monomer side-chain length; self-composite network containing crystalline phase

A series of thermo-responsive hydrogels have been synthesized by radiation-induced crosslinking polymerization in bulk based on; oligoether methacrylates (OEGMAs) of side chain lengths of 2–19 EG; monomer units. Side chain lengths have been shown to have a pronounced effect on synthesis parameters (monomers of longer side chains are more easily crosslinked, and the inert atmosphere promotes crosslinking more than air) and hydrogel properties (the thermal stability of obtained networks and their swelling capacities, as well as the temperature of Volume Phase Transition (VPT), increase with increasing oligoether side group length, while the VPT becomes less narrow). Networks based on oligoether methacrylates of sufficiently long side chains (over 7 monomer units) are capable of partial crystallization, forming self-composites, and the crystalline phase is chemically linked to a continuous, coherent polymer network.

Self-Assembly into Strands in Amphiphilic Polymer Brushes.

The self-assembly of amphiphilic macromolecules end-grafted to a plane surface is studied using mean-field theory and computer simulations. Chain backbones are built from hydrophobic groups, whereas side groups are hydrophilic. The brush is immersed in a solvent, which can be good or poor, but on average is not far from θ conditions. It is demonstrated that the strong amphiphilicity of macromolecules at a monomer unit level leads to their self-assembly into a system of strands with a 2D hexagonal order in a cross-section parallel to the grafting plane. The structure period is determined by the length of side groups. In theory, this effect is explained by the orientation of strongly amphiphilic monomer units at a strand/solvent boundary that leads to an effective negative contribution to the surface tension. Computer simulations with molecular dynamics (MD) are used for a detailed study of the local brush structure. The aggregation number of strands grows with the increase of the grafting density and side group length.

Role of Dynamic Asymmetry on the Collective Dynamics of Comblike Polymers: Insights from Neutron Spin-Echo Experiments and Coarse-Grained Molecular Dynamics Simulations

We investigate the collective dynamics of comblike polymers displaying nanosegregation in side groups and main-chain rich domains, where side groups and backbones are dynamically equivalent. Neutron spin-echo experiments on poly(alkylene oxide)s with increasing side-group length have been focused on the decay of inter- and intradomain correlations and are complemented with molecular dynamics simulations on a coarse-grained model. In general, a good qualitative agreement between simulation and experiment is found. The collective times at inter- and intradomain levels converge with decreasing temperature, implying a common glass transition, and separate at high temperatures, revealing an increasing role of connectivity. The features of collective relaxations—regarding stretching, characteristic time, and temperature dependence—are independent of branching. The standard stretching for side-group motions and the closeness of collective and self-motions show that the anomalies exhibited by dynamically asymmetr...

Synthesis and characterisation of reactive liquid crystals containing an azo group

A new series of liquid crystal (LC) monomers – not only contain a double bond but also contain an azo group – were designed and synthesised. The length of side groups in the LC monomers containing azobenzene ester varied from 1 to 2 methylene units, and the length of the substituted groups in the main chain varied from 1 to 3 methylene units. The molecular structures of the intermediates and target compounds were confirmed by Fourier transform infrared, ultraviolet and visible spectrum and nuclear magnetic resonance (NMR) spectroscopy. The thermal phase behaviour of the LC monomers was investigated by polar optical microscopy coupled with hot stage and differential scanning calorimetry (DSC). In this paper, the effect on the LC zone with the substituents were investigated, and with the increased methylene of main chain, the melting point and the phase transition temperature of the substance will be lowered and LC regions will be narrower.

Thermodynamic scaling of dynamics in polymer melts: Predictions from the generalized entropy theory

Many glass-forming fluids exhibit a remarkable thermodynamic scaling in which dynamic properties, such as the viscosity, the relaxation time, and the diffusion constant, can be described under different thermodynamic conditions in terms of a unique scaling function of the ratio ρ(γ)∕T, where ρ is the density, T is the temperature, and γ is a material dependent constant. Interest in the scaling is also heightened because the exponent γ enters prominently into considerations of the relative contributions to the dynamics from pressure effects (e.g., activation barriers) vs. volume effects (e.g., free volume). Although this scaling is clearly of great practical use, a molecular understanding of the scaling remains elusive. Providing this molecular understanding would greatly enhance the utility of the empirically observed scaling in assisting the rational design of materials by describing how controllable molecular factors, such as monomer structures, interactions, flexibility, etc., influence the scaling exponent γ and, hence, the dynamics. Given the successes of the generalized entropy theory in elucidating the influence of molecular details on the universal properties of glass-forming polymers, this theory is extended here to investigate the thermodynamic scaling in polymer melts. The predictions of theory are in accord with the appearance of thermodynamic scaling for pressures not in excess of ~50 MPa. (The failure at higher pressures arises due to inherent limitations of a lattice model.) In line with arguments relating the magnitude of γ to the steepness of the repulsive part of the intermolecular potential, the abrupt, square-well nature of the lattice model interactions lead, as expected, to much larger values of the scaling exponent. Nevertheless, the theory is employed to study how individual molecular parameters affect the scaling exponent in order to extract a molecular understanding of the information content contained in the exponent. The chain rigidity, cohesive energy, chain length, and the side group length are all found to significantly affect the magnitude of the scaling exponent, and the computed trends agree well with available experiments. The variations of γ with these molecular parameters are explained by establishing a correlation between the computed molecular dependence of the scaling exponent and the fragility. Thus, the efficiency of packing the polymers is established as the universal physical mechanism determining both the fragility and the scaling exponent γ.

Molecular, conformational, and optical characteristics of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate) in organic solvents

A number of samples of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate)—a comb-like polymer with ionically bound side chains—are obtained by the polymerization of dodecylammonium-2-acrylamido-2-methylpropanesulfonate in an aqueous medium. The samples are obtained in a wide molecular-mass range. Molecular, hydrodynamic, and optical characteristics of the samples are determined by the methods of sedimentation-diffusion analysis, viscometry, and flow birefringence in dilute polymer solutions in chloroform and dimethyl sulfoxide containing small amounts of 0.1 M LiCl. It is shown that conformational and optical characteristics based on hydrodynamic and dynamo-optic investigations agree with the data available for acrylic and methacrylic polymers with the same lengths of side groups. In other words, the character of attachment (covalent or ionic) of long side chains to the backbone has no effect on the conformational and optical characteristics of macromolecules.

Side Chain Effects of Poly(3-alkylthiophene) on the Morphology and Performance of Polymer Solar Cells

Poly(3-alkylthiophene) formed regular, layered arrays and showed liquid crystalline structures in the solid state. To elucidate the nanophase segregation in poly(3-alkylthiophene)/fullerene blends, X-ray diffraction, atomic force microscopy, scanning electron microscopy, and polarized optical microscopy were conducted. The effect of side-chain influence on the photovoltaic properties of solution-processed poly(3-alkylthiophene)/fullerene blends has been studied in this paper. Side chains investigated here include butyl, hexyl, and dodecyl groups. It shows that the photovoltaic performance is strongly affected by the length of side groups, which alters the morphology of the photoactive layer due to changes in solvent solubility, miscibility, and fullerene diffusion rate in the blends.

Substituent Effect on the Electronic Properties and Morphologies of Self‐Assembling Bisphenazine Derivatives

Tuning electronic properties and morphologies: We report a unique design platform of n-type organic semiconductors based on asymmetrically substituted bisphenazines that enable tuning of both electronic properties and morphologies of 1D nanostructures (see figure) by using small substituents with various sizes and electronic demands.This paper reports the synthesis and characterization of novel self-assembling n-type organic semiconductors based on asymmetrically substituted bisphenazines with various functional groups of different size, electron-withdrawing ability, and conjugation length. The overarching objective of this research is to tune electronic properties and morphologies of self-assembled structures of this system simultaneously, which offers a potentially useful platform for future optoelectronic applications. The thermal, optical, and electrochemical properties associated with different substituents were studied by differential scanning calorimetry (DSC), UV-visible and fluorescence spectroscopy, and cyclic voltammetry (CV). Electronic properties were calculated using density functional theory, and results were compared to experimental HOMO, LUMO, and energy gaps. The one-dimensional (1D) self-assembly properties of these new n-type molecules are discussed in terms of the type of peripheral substituents, alkyl side group length, and assembly conditions. This study includes extensive investigations by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Synthesis and mesophase behaviors of 2,5-disubstituted styrene-based random copolymers: Effect of difference in side-group length on liquid crystallinity

Five series of binary copolymers, poly[2,5-di(ROOC)styrene- co-2,5-di(R′OOC)styrene]s (R = n-C 3H 7–, R′ = C 2H 5–, n-C 4H 9–, and n-C 5H 11–; R = n-C 6H 13–, R′ = n-C 4H 9–, and n-C 5H 11–), were synthesized via free radical polymerization. The random nature of the copolymers was expected on the basis of the assumed similar reactivities of the analogous monomers and proved by 13C NMR analysis. It was also implied by the smoothly varying glass transition temperatures and further supported by the monotonous variation in d spacings for the liquid crystalline copolymers, where both corresponding homopolymers are liquid crystals. Subtle difference of R and R′ was found to have significant impact on the mesomorphic properties of the copolymers. When the pair of the corresponding homopolymers has the same mesogenic structure, a difference of one carbon atom in the alkyl chain can be tolerated over the whole copolymer composition range; however, the liquid crystalline structure soon disappears with the incorporation of a co-unit of an homopolymer that is not liquid crystal. For the copolymers with alkyl chain length differing by two carbon atoms, the liquid crystalline structure is lost with the incorporation of relatively low co-unit content despite the pair of corresponding homopolymers having the same mesogenic structure.

FT‐IR Study of Blends and Complexes of Poly(mono n‐alkyl itaconates) with Poly(N,N‐dimethylacrylamide) and Poly(ethyloxazoline)

AbstractSummary: This paper reports an FT‐IR study of blends and complexes of poly(mono n‐alkyl itaconates) with poly(N,N‐dimethylacrylamide) (PDMA) and poly(ethyloxazoline) (PEOX). Strong hydrogen bonding has been found and both polybases have shown similar acceptor strengths. The extent of the interassociation has been estimated by spectral curve fitting of the polybase carbonyl band. The influences of the solvent medium and alkyl side group length of the poly(mono n‐alkyl itaconate) on the interassociation extents have been discussed. Blend and complex interassociation behavior has been compared too. Results show that media influences the interassociation degree in systems with PDMA, but has negligible influence in systems with PEOX. Moreover, the interassociation degree in blends with PEOX does not depend on the length of the poly(monoalkyl itaconate) side group, while an interassociating ability loss is observed in blends with PDMA as the side group size of the polyacid increases. This different behavior is attributed to the greater interspacing between vicinal carbonyl groups in PEOX. Anyway, this band shows conformational sensitivity and reflects the conformational changes that are forced to adopt as the steric hindrances present in the medium (due to the bulky side groups of the polyacids) increase.Auto scaled carbonyl stretching region for PMBuI/PEOX complexes.magnified imageAuto scaled carbonyl stretching region for PMBuI/PEOX complexes.

Synthesis and curing of rod-like epoxies with alkoxy groups as flexible side chain

A series of aromatic diepoxides consisting of rigid ester unit with different lengths of flexible alkoxy side groups (R = H, OCH 3 , OC 3 H 7 , and OC 8 H 17 ) were synthesized, and their thermal and cure behavior with aromatic diamine were investigated by using a DSC. The values of melting temperatures for the epoxy monomers ranged from 65 to 221°C depending upon the length of side groups. Cure kinetics of an epoxy/4,4'-diaminodiphenylmethane (DDM) system with two different side groups (R = OC 3 H 7 and OC 8 H 17 ) forming homogeneous mixture was examined using a multi-temperature scan method, developed by Ozawa and Kissinger, in order to determine the activation energy (E) and the frequency factor (A). The epoxy monomer having longer side group showed smaller E and larger A, indicating that the introduction of the long flexible side group could accelerate the cure reaction of rod-like epoxy.