Backbone Chain Length Research Articles

Network Polymer Properties Engineered Through Polymer Backbone Dispersity and Structure.

Dispersity (Ð or Mw/Mn) is an important parameter in material design and as such can significantly impact the properties of polymers. Here, polymer networks with independent control over the molecular weight and dispersity of the linear chains that form the material are developed. Using a RAFT polymerization approach, a library of polymers with dispersity ranging from 1.2-1.9 for backbone chain-length (DP) 100, and 1.4-3.1 for backbone chain-length 200 were developed and transformed to networks through post-polymerization crosslinking to form disulfide linkers. The tensile, swelling, and adhesive properties were explored, finding that both at DP 100 and DP 200 the swelling ratio, tensile strength, and extensibility were superior at intermediate dispersity (1.3-1.5 for DP 100 and 1.6-2.1 for DP 200) compared to materials with either substantially higher or lower dispersity. Furthermore, adhesive properties for materials with chains of intermediate dispersity at DP 200 revealed enhanced performance compared to the very low or high dispersity chains.

Dependence of Intramolecular Hydrogen Bond on Conformational Flexibility in Linear Aminoalcohols.

Intramolecular hydrogen bonds (H-bonds) are abundant in physicochemical and biological processes. The strength of such interaction is governed by a subtle balance between conformational flexibility and steric effect that are often hard to predict. Herein, using linear aminoalcohols NH2(CH2)nOH (n = 2-5) as a model system, we demonstrated the dependence of intramolecular H-bond on the backbone chain length. With sensitive photoacoustic Raman spectroscopy (PARS), the gas-phase Raman spectra of aminoalcohols were measured in both N-H and O-H stretching regions at 298 and 338 K and explained with the aid of quantum chemistry calculations. For n = 2-4, two conformers corresponding to the O-H···N intramolecular H-bond and free OH were identified, whereas for n = 5, only the free-OH conformer was identified. Compared to free OH, a striking spectral dependence was observed for the intramolecular H-bonded conformer. According to the red shift of the OH-bonded band, the strongest intramolecular H-bond yields in n = 4, but the favorable chain length to form an intramolecular hydrogen bond at room temperature was observed in n = 3, which corresponds to a six-membered-ring in 3-aminopropanol. This is in good agreement with statistical analysis from the Cambridge Structural Database (CSD) that the intramolecular hydrogen bond is preferred when the six-membered ring is formed. Furthermore, combined with the calculated thermodynamic data at the MP2/aug-cc-pVTZ//M062X/6-311++G(d,p) level, the origin of decrease in intramolecular hydrogen-bond formation was ascribed to an unfavorable negative entropy contribution when the backbone chain is further getting longer, which results in the calculated Gibbs free energy optimum changing with increasing temperature from n = 4 (0-200 K) to n = 3 (200-400 K) and to n = 2 (above 400 K). These results will provide new insight into the nature of intramolecular hydrogen bonds at the molecular level and the application of intramolecular hydrogen bonds in rational drug design and supramolecular assembly.

Global lipid remodelling by hypoxia aggravates migratory potential in pancreatic cancer while maintaining plasma membrane homeostasis

Hypoxia plays an important role in pancreatic cancer progression. It drives various metabolic reprogramming in cells including that of lipids, which in turn, can modify the structure and function of cell membranes. Homeostatic adaptation of membranes is well-recognized, but how and if it is regulated in hypoxic pancreatic cancer and its relation to aggressive phenotype and metastasis remains elusive. Here we show hypoxia-induced extensive global lipid remodelling spanning changes in lipid classes, unsaturation levels, glyceryl backbone and acyl chain lengths. No major modulation of plasma membrane biophysical properties revealed a decoupling of lipidome modulation from membrane properties under hypoxia. This was supported by observing minor changes in the lipidome of plasma membranes under hypoxia. Further, hypoxia increased migration and invasion underpinned by reduced actin volume, cell cortical stiffness and facile tether dynamics. In conclusion, we demonstrate buffering of the lipidome alterations leading to a homeostatic membrane response. These findings will help to understand the hypoxic regulation of pancreatic membrane homeostasis and identify tangible theranostic avenues.

Synthesis and thermoresponsive behavior of double hydrophilic graft copolymer based on poly(2-methyl-2-oxazoline) and poly(2-ethyl-2-oxazoline)

A recent challenge in polymer self-assembly is the utilization of double hydrophilic graft copolymers (DHGC) in view of biomedical applications. Here we describe, for the first time, a platform of biocompatible DHGC fully based on poly(2-alkyl-2-oxazoline) leading to stimuli-responsive self-assemblies. This original DHGC platform was composed of backbone poly(2-methyl-2-oxazoline-co-2-pentyl-2-oxazoline) (P(MeOx-co-PentOx)) and poly(2-ethyl-2-oxazoline) (PEtOx) grafts. A “grafting onto” approach based on the combination of cationic ring-opening polymerization (CROP) technique and “click chemistry” CuAAc reaction, was successfully used to synthesize poly(2-methyl-2-oxazoline-co-2-pentyl-2-oxazoline)-g-poly(2-ethyl-2-oxazoline) (P(MeOx-co-PentOx)-g-PEtOx) copolymer conjugates of varying backbone and side chain lengths. These purely hydrophilic copolymers demonstrated self-assembling behavior in aqueous solution, showing a characteristic double hydrophilic behavior originating from building blocks immiscibilities. Self-associated structures with spherical morphologies have been evidenced by DLS and cryo-TEM. The sizes and the efficiency of self-association were mainly controlled by the concentration of the graft copolymer and by the molar ratio of the different hydrophilic compounds. In addition, thermoresponsive properties of these copolymers were studied by turbidimetry and DLS. From purely hydrophilic at low temperature, the copolymers showed amphiphilic characters at temperatures close to the cloud points (CP). Interestingly, cloud points were not controlled by the PEtOx graft length as it has been reported for PEtOx homopolymers but it depended mainly upon the PEtOx content of the copolymer, with a critical value around 75 PEtOx wt%. Addition of a kosmotropic salt (Na2SO4) allowed to trigger CPs from 80 °C till 26 °C. The self-assembling properties of this family of hydrophilic and biocompatible copolymers may offer promising prospect in the field of biomedical applications as bioreactors.

Synergistic Engineering of Side Chains and Backbone Regioregularity of Polymer Acceptors for High‐Performance All‐Polymer Solar Cells with 15.1% Efficiency (Adv. Energy Mater. 3/2022)

All-Polymer Solar Cells In article number 2103239, Bumjoon J. Kim, Yun-Hi Kim and co-workers develop a series of polymer acceptors with controlled backbone regioregularities and side chain structures. All-polymer solar cells based on a RRg-C20 acceptor which has a regioregular backbone and optimal side chain length achieve a high power conversion efficiency of 15.12%, attributed to high electron mobility and optimal blend morphology.

Synergistic Engineering of Side Chains and Backbone Regioregularity of Polymer Acceptors for High‐Performance All‐Polymer Solar Cells with 15.1% Efficiency

AbstractTuning the aggregation and crystalline properties of polymers is critical for realizing all‐polymer solar cells (all‐PSCs) with optimal blend morphology and high power conversion efficiency (PCE). In this study, a series of polymerized small‐molecule acceptors (PSMAs) is developed to investigate important relationships among their crystalline/aggregation properties, the blend morphology, and the device performance of the resulting all‐PSCs. A series of PSMAs (regiorandom (RRd)‐C12, RRd‐C20, RRd‐C24, regioregular (RRg)‐C20, and RRg‐C24) with simultaneously‐engineered i) side chain lengths of C12, C20, and C24, and ii) backbone regioregularities of RRd and RRg are synthesized to regulate their crystalline/aggregation properties. As a result, the highest PCE of 15.12% is obtained with all‐PSCs based on RRg‐C20 PSMA having regioregular backbone and optimal side chain length, attributed to high PSMA crystallinity and electron mobility as well as optimal blend morphology with a polymer donor. Thus, this study demonstrates the importance of simultaneous engineering of the backbone regioregularity and side‐chain structures of PSMAs to enhance electron mobility, optimize blend morphology and, thus, achieve highly efficient all‐PSCs.

The Effects of Perfluoroalkyl and Alkyl Backbone Chains, Spacers, and Anchor Groups on the Performance of Organic Compounds as Corrosion Inhibitors for Aluminum Investigated Using an Integrative Experimental-Modeling Approach

The ability of surfactant-like compounds to inhibit the corrosion of aluminum in NaCl solution was systematically investigated. The basic idea of this study was to scrutinize the effect of type of backbone chain (alkyl and perfluoroalkyl), length of backbone chain (number of carbon atoms 7, 10, and 17), various anchor groups (carboxylic, thiol, and imidazole) and presence of alkylene and benzene spacers between perfluoroalkyl chain and anchor group. To tackle these effects, three model studies were designed for alkaline etched, superhydrophilic aluminum surface and then approached experimentally and by density functional theory modeling. This enabled us to decouple the adsorption affinity of selected anchor groups on the hydroxylated aluminum surface from the lateral intermolecular cohesive interactions between hydrophobic backbone chains. Fourteen compounds were used to study the changes in the surface composition, wettability and the electrochemical barrier properties. For the carboxylic anchor group, the length and type of chain are important for barrier properties and also for tuning the wettability of the surface. The addition of alkylene spacer to perfluoroalkyl chain significantly affects the properties of the modified surface. Thiol and imidazole anchor groups, however, are not efficient inhibitors regardless the type and length of backbone chains.

Influence of Side-Chain Length and Relative Rigidities of Backbone and Side Chains on Glass Formation of Branched Polymers

Influence of Side-Chain Length and Relative Rigidities of Backbone and Side Chains on Glass Formation of Branched Polymers

Effect of Branch Point Distribution on the Radius of Gyration in Batch Free‐Radical Polymerization with Chain Transfer to Polymer

AbstractFree‐radical polymerization is irreversible, and the primary chains formed earlier are expected to possess larger branching density compared with those formed later, leading to a branching density distribution (BDD) among primary chains. In addition to the BDD, the primary chain length distribution (CLD) may change during polymerization. For a primary CLD with a shift toward smaller chain length during polymerization, the expected g‐ratio for a given number k of branch points can be approximated reasonably well with that for the random branched polymers having the accumulated primary CLD. On the other hand, when the primary CLD moves toward larger chain length during polymerization, the expected g‐ratio may become smaller than the corresponding random branched polymers, due to an “unnatural” combination in the length of backbone and branch chains. The compactness of branched architecture could be controlled through the consideration of the maximum end‐to‐end path length.

Depolymerization of Bottlebrush Polypentenamers and Their Macromolecular Metamorphosis.

The depolymerization of bottlebrush (BB) polymers with varying lengths of polycyclopentene (PCP) backbone and polystyrene (PS) grafts is investigated. In all cases, ring closing metathesis (RCM) depolymerization of the PCP BB backbone appears to occur through an end-to-end depolymerization mechanism as evidenced by size exclusion chromatography. Investigation on the RCM depolymerization of linear PCP reveals a more random chain degradation process. Quantitative depolymerization occurs under thermodynamic conditions (higher temperature and dilution) that drives RCM into cyclopentenes (CPs), each bearing one of the original PS grafts from the BB. Catalyst screening reveals Grubbs' third (G3) and second (G2) generation catalyst depolymerize BBs significantly faster than Grubbs' first generation (G1) and Hoveyda-Grubbs' second generation (HG2) catalyst under identical conditions while solvent (toluene versus CHCl3) plays a less significant role. The length of the BB backbone and PS side chains also play a minor role in depolymerization kinetics, which is discussed. The ability to completely deconstruct these BB architectures into linear grafts provides definitive insights toward the ATRP "grafting-from" mechanism originally used to construct the BBs. Core-shell BB block copolymers (BBCPs) are shown to quantitatively depolymerize into linear diblock polymer grafts. Finally, the complete depolymerization of BBs into α-cyclopentenyl-PS allows further transformation to other architectures, such as 3-arm stars, through thiol-ene coupling onto the CP end group. These unique materials open the door to stimuli-responsive reassembly of BBs and BBCPs into new morphologies driven by macromolecular metamorphosis.

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties.

Comb and bottlebrush polymers present a wide range of rheological and mechanical properties that can be controlled through their molecular characteristics, such as the backbone and side chain lengths as well as the number of branches per molecule or the grafting density. This review investigates the impact of these characteristics specifically on the zero shear viscosity, strain hardening behavior, and plateau shear modulus. It is shown that for a comb polymer with an entangled backbone and entangled side chains, a maximum in the strain hardening factor and minimum in the zero shear viscosity η0 can be achieved through selection of an optimum number of branches q. Bottlebrush polymers with flexible filaments and extremely low plateau shear moduli relative to linear polymers open the door for a new class of solvent-free supersoft elastomers, where their network modulus can be controlled through both the degree of polymerization between crosslinks, nx , and the length of the side chains, nsc , with .

Relationships between surface chemistry, nanotopography, wettability and ice adhesion in epoxy and SU-8 modified with fluoroalkylsilanes from the vapor phase

The objective of this work was to elucidate how ice adhesion to solid substrates is related to surface wettability, which, in turn, results from surface chemical composition and nanotopography. The study was carried out using microscopically smooth surfaces of epoxy and SU-8, a negative epoxy-based photoresist. Epoxy resins are known for their outstanding physicochemical properties. They are often used as surface coatings for outdoor devices and can face harsh environmental conditions, such as icing. SU-8 is extensively used in microfabrication of surface topographical structures. Some of these structures are designed to be superhydrophobic and, in some cases, icephobic. In the present study, we focused on the role of surface physicochemical modifications of these materials in controlling their wetting and icing properties. A homologous series of fluoroalkyl silanes (FAS), which contained 3, 8, 10, and 12 carbon atoms in a molecule, was used to make epoxy and SU-8 surfaces hydrophobic. The FAS deposition process was carried out from vapor phase at atmospheric pressure (AP-VPD). The modified substrates exhibited a significantly increased surface nanoroughness, as a result of etching in oxygen radio frequency (RF) plasma and subsequent silanization. The coatings obtained by the AP-VPD contribute to surface roughness because the FAS vapors and atmospheric water are abundant during deposition processes. Such conditions favor vertical polymerization and formation of clustered deposits. The resulting nanoroughness was shown to affect wettability of modified surfaces. The influence of FAS backbone chain length on resulting surface nanotopography and how it affects surface wettability was investigated. Finally, the relationship between wettability and ice adhesion was examined. The strength of adhesion between frozen sessile droplets and modified substrates was investigated in tensile mode. A linear correlation between the ice-substrate adhesion strength and the macroscopic work of water-substrate adhesion was found.

Advanced designer amines for CO2 capture: Interrogating speciation and physical properties

Large scale and affordable CO2 capture is currently limited by absorbents with somewhat non-optimised chemical and physical properties. Cyclic designer amines with multiple amine groups and tunable molecular structure are proposed to contribute favorably to improve absorbent performance and robustness for CO2 capture. In this work the impact of cyclic structure on absorbent performance has been investigated using 4-amino-1-methylpiperidine (4-A1MPD) as a model designer amine and is compared with its linear di-amine analogue N,N-dimethyl-1,3-propanediamine (N,N-DM13PDA). The benchmark absorbent monoethanolamine (MEA) was investigated in parallel. To illustrate the significance of the cyclic structural feature, adoption of other structural changes such as methyl and propyl groups, and C2 to C3 backbone chain lengths were also investigated for comparison using the cyclic di-amine 4-amino-1-propylpiperidine (4-A1PPD) and linear di-amine N,N-dimethyl-1,2-ethanediamine (N,N-DM12EDA). CO2 absorption and desorption experiments were performed at 40 and 90 °C with analysis of the solutions to determine the speciation including carbamate(s), and carbonates, performed using 13C/1H NMR spectroscopy. The results in terms of the observed CO2 absorption rate, equilibrium CO2 solubility, CO2 desorption rate and cyclic capacity affirm that the cyclic structure strongly influences the general performance of the absorbents evaluated here. The mild steric hindrance induced by the proximity of the primary amine group to the ring acts to destabilize the carbamate and promote formation of bicarbonate resulting in 70% and 78% more bicarbonate in 4-A1MPD and 4-A1PPD than that in MEA while the values for N,N-DM12EDA and N,N-DM13PDA are 47% and 31%. Furthermore, the cyclic capacity was promoted to 215%, 160%, 81% and 65% for 4-A1PPD, 4-A1MPD, N,N-DM13PDA and N,N-DM12EDA in comparison with MEA solution. Density and viscosity of 2 mol·L−1 di-amines and 4 mol·L−1 MEA solutions were investigated over the temperature range 20–80 °C and found to decrease with increasing temperature for all absorbents. The order of the densities can be ranked as: MEA > 4-A1MPD > 4-A1PPD >N,N-DM12EDA >N,N-DM13PDA while the viscosities follow the trend 4-A1PPD > 4-A1MPD >N,N-DM13PDA >N,N-DM12EDA > MEA.

Single-Chain Conformational Characteristics of Comb-Like Polyelectrolytes: Molecular Dynamics Simulation Study

The single-chain conformation of a model comb polyelectrolyte, in which the electric charges are located on the last monomer of side chains, has been studied using molecular dynamics simulations. The model chain has a hydrophobic backbone and hydrophilic side chains. The influence of parameters such as the length of backbone and side chains, the grafting density of side chains, flexibility of the chain and different strengths of backbone hydrophobicity have been investigated. At high grafting density of side chains, a transition from turn to pearl-necklace and finally to globular conformation is observed by increasing the hydrophobicity. Radius of gyration (Rg) of the backbone depends linearly on the number of backbone monomers at low values of the backbone hydrophobicity, but at high values of the backbone hydrophobicity, because of the appearance of turn-like segments between successive globular sections in the pearl-necklace structure, the scaling exponent of Rg versus N is larger. Also, the chain flexibility affects the backbone conformation significantly. The increase of the persistence length leads to the appearance of the folded and then the extended conformations. In addition to the statistical properties of the chains, the investigation of the relaxation of the chains conformation shows that, the backbone takes almost its final conformation in the early time steps of the simulation for all conditions. It means that the relaxation time of the chain is relatively short (fast relaxation).

The Behavior of Amphiphilic Molecular Brushes with Polyimide Backbone and Poly(methyl methacrylate) and Polystyrene Side Chains in the Vicinity of Θ Point

The behavior of amphiphilic molecular brushes in the vicinity of the Θ point has been studied by the methods of molecular hydrodynamics and optics upon variation of temperature. As objects of investigation, graft copolymers with polyimide main chain and poly(methyl methacrylate) and polystyrene side chains were chosen. The samples studied differed in the backbone and side chain lengths at a similar degree of grafting. The molecular mass of the samples under investigation was varied in a sevenfold range. For comparison, linear poly(methyl methacrylate) and polystyrene have been studied. It has been shown that the behavior of molecular brushes and linear polymers in the vicinity of the Θ point differs significantly. A more rapid gain in intrinsic viscosity of the solutions of graft copolymers in the vicinity of the Θ point is explained by the simultaneous increase in the volume of macromolecules and in their shape asymmetry.

A comparative study of thermodynamic, conformational, and structural properties of bottlebrush with star and ring polymer melts.

Thermodynamic, conformational, and structural properties of bottlebrush polymer melts are investigated with molecular dynamics simulations and compared to linear, regular star, and unknotted ring polymer melts to gauge the influence of molecular topology on polymer melt properties. We focus on the variation of the backbone chain length, the grafting density along the backbone, and the length of the side chains at different temperatures above the melt glass transition temperature. Based on these comparisons, we find that the segmental density, isothermal compressibility, and isobaric thermal expansion of bottlebrush melts are quantitatively similar to unknotted ring polymer melts and star polymer melts having a moderate number ( f = 5 to 6) of arms. These similarities extend to the mass scaling of the chain radius of gyration. Our results together indicate that the configurational properties of bottlebrush polymers in their melt state are more similar to randomly branched polymers than linear polymer chains. We also find that the average shape of bottlebrush polymers having short backbone chains with respect to the side chain length is also rather similar to the unknotted ring and moderately branched star polymers in their melt state. As a general trend, the molecular shape of bottlebrush polymers becomes more spherically symmetric when the length of the side chains has a commensurate length as the backbone chain. Finally, we calculate the partial static structure factor of the backbone segments and we find the emergence of a peak at the length scales that characterizes the average distance between the backbone chains. This peak is absent when we calculate the full static structure factor. We characterize the scaling of this peak with parameters characterizing the bottlebrush molecular architecture to aid in the experimental characterization of these molecules by neutron scattering.

Polyimide Aerogels Using Triisocyanate as Cross-linker.

A family of polyimide (PI)-based aerogels is produced using Desmodur N3300A, an inexpensive triisocyanate, as the cross-linker. The aerogels are prepared by cross-linking amine end-capped polyimide oligomers with the triisocyanate. The polyimide oligomers are formulated using 2,2'-dimethylbenzidine, 4,4'-oxydianiline, or mixtures of both diamines, combined with 3,3',4,4'-biphenyltetracarboxylic dianhydride, and are chemically imidized at room temperature. Depending on the backbone chemistry, chain length, and polymer concentration, density of the aerogels ranged from 0.06 to 0.14 g/cm3 and Brunauer-Emmett-Teller surface areas ranged from 350 to 600 m2/g. Compressive moduli of these aerogels were as high as 225 MPa, which are comparable to, or higher than, those previously reported prepared with similar backbone structures but with other cross-linkers. Because of their lower cost and commercial availability as cross-linker, the aerogels may have further potential as insulation for building and construction, clothing, sporting goods, and automotive applications, although lower-temperature stability may limit their use in some aerospace applications.

Synthesis of comb-shaped polymers via controlled cationic polymerization of oxazolines with polyester-type macroinitiator

On the basis of macroinitiators of polyester type, hybrid comb-shaped polymers with poly-2-isopropyl-2-oxazoline side fragments are prepared via ring-opening cationic polymerization. A method for estimating the length of polyoxazoline side chains and their grafting density is proposed. It is shown that, at the given ratio of the length of backbone and side chains, which depends on the chemical structure of the initiator, the graft copolymers are capable of formation of micellar aqueous solutions with a lower critical solution temperature.

Amphiphilic polypeptide-polyoxazoline graft copolymer conjugate with tunable thermoresponsiveness: Synthesis and self-assembly into various micellar structures in aqueous and nonaqueous media

A “grafting onto” approach based on two different controlled ring-opening polymerization (ROP) techniques is developed to synthesize polytyrosine-graft-poly(2-ethyl-2-oxazoline) (PTyr-g-PEtOx) copolymer conjugates of varying main backbone and pendent chain lengths. This approach consists of syntheses of propargyl functionalized polytyrosine (PTyr-O-Pr) by ROP of tyrosine N-carboxyanhydride and azide functional poly(2-ethyl-2-oxazoline) (PEtOx-N3) by cationic ROP separately followed by their grafting using CuAAC reaction to afford the final graft copolymer conjugate (GCC). Owing to the presence of pendent hydrophiphilic PEtOx block, PTyr-g-PEtOx GCC exhibits LCST-type reversible phase transition behavior in water, which is tunable with respect to its concentration and the lengths of the main backbone and the pendent block. Again, the amphiphilic PTyr-g-PEtOx GCC molecules undergo self-assembly into spherical unit micelles and their consequent secondary aggregations into compound micelles both in aqueous and non-aqueous media. Upon increasing the solution temperature above LCST, micelles/compound micelles of PTyr-g-PEtOx GCC undergo further aggregation into higher order micellar agglomerates without any disruption of micellar structures as observed from DLS study. A hydrophobic dye (nile red) can easily be encapsulated into the hydrophobic PTyr core of the PTyr-g-PEtOx micelles in water, which remains stable without any release of the dye even when the temperature is increased above the LCST of the GCC.

Enhancement of Out-of-Plane Mobilities of Three Poly(3-alkylthiophene)s and Associated Mechanism

Poly(3-alkylthiophene) (P3AT) is a popular family of π-conjugated polymers used to study polymer-based flexible electronic devices. To enhance the performance of a smart material for wearable or stretchable-skin devices, it is crucial to optimize both the carrier mobility and the film structure. Here, we present the enhancements of hole mobilities of three P3ATs films along the out-of-plane direction using photoconductivity measurements by rubbing. The three P3ATs have the same conjugated backbone but different alkyl side chain (CnH2n+1) lengths of n = 4, 6, and 12. As the alkyl chain length becomes longer, the hole mobility increased up to 5-fold after rubbing. Polarized absorption and grazing-incidence X-ray diffraction measurements indicate the P3AT (n = 12) film has a highly oriented structure in the in-plane direction and increased π–π stacking in the out-of-plane direction after rubbing due to a low tensile modulus from the long alkyl side chain.