Primary Chain Length Research Articles

Dynamic Chalcogen Squares for Material and Topological Control over Macromolecules

AbstractHerein we introduce chalcogen squares via selenadiazole motifs as a new class of dynamic supramolecular bonding interactions for the modification and control of soft matter materials. We showcase selenadiazole motifs in supramolecular networks of varying primary chain length prepared through polymerization using tandem step‐growth/Passerini multicomponent reactions (MCRs). Compared to controls lacking the selenadiazole motif, these networks display increased glass transition temperatures and moduli due to the chalcogen bonding linkages formed between chains. These elastomeric networks were shown to autonomously heal at room temperature, retaining up to 83 % of the ultimate tensile strength. Lastly, we use post‐polymerization modification via the Biginelli MCR to add selenadiazole motifs to narrowly dispersed polymers for controlled topology in solution. Chalcogen squares via selenadiazoles introduce an exciting exchange mechanism to the realm of dynamic materials.

Dynamic Chalcogen Squares for Material and Topological Control over Macromolecules.

Herein we introduce chalcogen squares via selenadiazole motifs as a new class of dynamic supramolecular bonding interactions for the modification and control of soft matter materials. We showcase selenadiazole motifs in supramolecular networks of varying primary chain length prepared through polymerization using tandem step-growth/Passerini multicomponent reactions (MCRs). Compared to controls lacking the selenadiazole motif, these networks display increased glass transition temperatures and moduli due to the chalcogen bonding linkages formed between chains. These elastomeric networks were shown to autonomously heal at room temperature, retaining up to 83 % of the ultimate tensile strength. Lastly, we use post-polymerization modification via the Biginelli MCR to add selenadiazole motifs to narrowly dispersed polymers for controlled topology in solution. Chalcogen squares via selenadiazoles introduce an exciting exchange mechanism to the realm of dynamic materials.

Synthesis and Crystallographic Characterization of Helical Hairpin Oligourea Foldamers.

Oligomers designed to form a helix-turn-helix super-secondary structure have been prepared by covalently bridging aliphatic oligourea foldamer helices with either rigid aromatic or more flexible aliphatic spacers. The relative helix orientation in these dimers has been investigated at high resolution using X-ray diffraction analysis. In several cases, racemic crystallography was used to facilitate crystallization and structure determination. All structures were solved by direct methods. Well-defined parallel helical hairpin motifs were observed in all cases when 4,4'-methylene diphenyl diisocyanate was employed as a dimerizing agent, irrespective of primary sequence and chain length.

SARS‐CoV‐2 spike protein capture by peptide functionalized networks

AbstractCoronavirus disease 2019 (COVID‐19) has significantly impacted human health, the global economy, and society. Viruses residing on common surfaces represent a potential source of contamination for the general population. Spike binding peptide 1, SBP1 is a 23 amino acid peptide, which has micromolar binding affinity (1.3 μM) towards the spike protein receptor‐binding domain. We hypothesize that if we can covalently immobilize this SBP1 peptide in a covalent crosslinked network system, we can develop a surface that would preferentially bind spike protein and, therefore, which could limit viral spread. A series of covalently crosslinked networks of hydroxy ethyl acrylate (HEA) with different primary chain lengths and crosslinker density was prepared. Later, this network system was functionalized using 2% SBP1 peptide. Our study found that with a shorter chain length and lower crosslinker density, the HEA network system alone could capture almost 80% of the spike protein. We reported that the efficiency could be enhanced almost by 17% with higher crosslinker density.

Controlling Dynamics of Associative Networks through Primary Chain Length

Controlling Dynamics of Associative Networks through Primary Chain Length

Linear Relationship between Mean‐Square Radius of Gyration and Graph Diameter, and Its Application to Network Polymers

AbstractMean‐square radius of gyration Rg2 and the graph diameter D of the random crosslinked network polymers are investigated to find a linear relationship, Rg2 = a D. The proportionality coefficient, a is dominated by the cycle (circuit) rank, or the number of intramolecular crosslinks kc, and a convenient equation is proposed for the relationship between a and kc. This relationship makes it possible to estimate Rg2 based on D and kc, which can reduce the required computational time to determine the Rg2‐values greatly. This new method is applied to find that the contraction factor g decreases with kc, and the differences in the primary chain length distribution that constitute the network polymers vanish for large kc‐values.

PET-RAFT Increases Uniformity in Polymer Networks.

Photoinduced electron/energy transfer (PET)-reversible addition-fragmentation chain transfer polymerization (RAFT) and conventional photoinitiated RAFT were used to synthesize polymer networks. In this study, two different metal catalysts, namely, tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3) and zinc tetraphenylporphyrin (ZnTPP), were selected to generate two different catalytic pathways, one with Ir(ppy)3 proceeding through an energy-transfer pathway and one with ZnTPP proceeding through an electron-transfer pathway. These PET-RAFT systems were contrasted against a conventional photoinitated RAFT process. Mechanically robust materials were generated. Using bulk swelling ratios and degradable cross-linkers, the homogeneity of the networks was evaluated. Especially at high primary chain length and cross-link density, the PET-RAFT systems generated more uniform networks than those made by conventional RAFT, with the electron transfer-based ZnTPP giving superior results to those of Ir(ppy)3. The ability to deactivate radicals either by RAFT exchange or reversible coupling in PET RAFT was proposed as the mechanism that gave better control in PET-RAFT systems.

Dimensions of Network Polymers

AbstractThe mean‐square radius of gyration Rg2 and the graph diameter D of the network polymers formed through the random crosslinking of predetermined primary chains with a fixed number of intermolecular and intramolecular crosslinks are investigated by the numerical calculation based on the graph theory. In the case of ring‐free polymers, D is the longest end‐to‐end path length, sometimes referred to as the maximum span length. The expected Rg2‐value for a given D is found to follow a linear relationship, Rg2 = a D + b, similarly as in the cases of the ring‐free polymers. The proportional coefficient, a decreases approximately linearly with the number of intramolecular crosslinks kc, or the cycle rank in the graph theory, essentially independent of the total number k of crosslinks and the primary chain length distribution. The contraction factor g of the average Rg2 of the whole network polymer system is also governed by kc, and decreases with kc. One may be able to design and control the Rg2‐values of crosslinked polymers through the magnitude of D, which is usually easier to imagine than the complex 3D architecture.

Dimensions of Crosslinked Polymers without Rings

AbstractMean‐square radius of gyration Rg2 and the maximum span length LMS of each polymer molecule formed in the crosslinking of polymer chains that follow the Schulz–Zimm distribution are determined by using the Monte Carlo simulation method for the generation of various crosslinked polymer architecture. For the random crosslinking, it is found that the expected g‐ratio of Rg2 of the crosslinked polymer to that of a linear polymer for a given number of crosslinks k does not change with the crosslinking density up to the gel point. The g‐ratio for a given k is larger for broader primary chain length distribution, and a convenient formula for the relationship between g and k is proposed. The linear relationship, Rg2 = 0.178 LMS applies, at least approximately, regardless of the primary chain length distribution and the crosslinking density. The relationship is essentially the same as for the branched polymers. The effect of nonrandom crosslinking is investigated through the theoretical simulation for the free‐radical vinyl/divinyl copolymerization conducted in a steady‐state continuous stirred tank reactor (CSTR). It is found that the nonrandomness induced by this reaction system does not change either of the universal relationships, g–k and Rg2–LMS.

NMR chemical shifts of carbon atoms and characteristic shift ranges in the oil sample

Application of high resolution 13C nuclear magnetic resonance (NMR) spectroscopy to characterize crude oil was demonstrated. The chemical shifts of 13C NMR functional groups that determine the composition of the oil sample were determined. Molar fractions of primary, secondary, quaternary, tertiary, aromatic groups, aromatic factor and average hydrocarbon chain length of aliphatic hydrocarbons of the oil sample according to 13C NMR spectra were determined. Detailed description of the 13C NMR spectra of the oil sample using a single consideration of three NMR spectra: 13C, 13C Attached Proton Test (APT), 13C with Gated Decoupling (GD) was performed. The different contribution of the studied oil sample in the aliphatic (10–75 ppm) and aromatic (115–165 ppm) areas of the 13C NMR spectra was determined. The presence of all major hydrocarbon components in the studied oil sample was established on the quantitative level, the aromaticity factor and the mean length of the hydrocarbon chain were evaluated. Quantitative fractions of aromatic molecules and functional groups constituting oil hydrocarbons were determined. In this work we demonstrate that the attached proton test and gated decoupling 13C NMR spectroscopy can afford all information to complete the chemical shift assignment of an oil sample, especially for determination of long range 1H–13C coupling constants and 13C multiplicity.

Gel Point Properties in Batch Free‐Radical Vinyl/Divinyl Copolymerization

AbstractGelation is a critical phenomenon, and various simple relationships are expected to hold. On the other hand, it is important to clarify the required conditions for the validity of the relationships. In this theoretical study, the effects of the primary chain connection statistics and the primary chain length distribution change during batch free‐radical vinyl/divinyl copolymerization on the gel point properties are investigated systematically. The weight fraction distribution at the gel point always conforms to the power‐law distribution,W(P)∝P−αwith α = 1.5, as long as the classical chemical kinetics is valid in a closed reaction system. When the primary chain connection statistics is independent of chain length, the cross‐linking density, ρg, of the gel molecule right at the gel point is given by , where is the weight‐average chain length of all primary chains. The random cross‐linking is a special case that belongs to this category. The distribution of the pendant double bonds among polymer molecules having different molecular weights is nonrandom, except for the special cases with equal reactivity of all types of double bonds for which the random cross‐linking applies.

Controllable Power‐Law Distribution in Free‐Radical Vinyl/Divinyl Copolymerization by Using a Continuous Stirred Tank Reactor

AbstractIt has been believed that the power‐law molecular weight distribution is formed at the gel point, and the power exponent falls in a category of universality in critical phenomena, and therefore, it cannot be changed. It is found that the power‐law weight fraction distribution W(P) ∝ P−α, capable of controlling the exponent α, can be synthesized by using a continuous stirred tank reactor (CSTR). The exponent is governed by a single non‐dimensional parameter, ξ that is equivalent to the Damköhler number, representing the ratio of timescales between the mean residence time and the crosslinking reaction. For small ξ’s, the non‐critical transition of the weight‐average molecular weight to infinity is observed, and the exponent approaches α = 2. For large ξ’s, the system shows similar behavior to that in a closed system and the exponent is the same as for the batch polymerization, with α = 1.5. At the gel point, the product of the average crosslinking density and the weight‐average primary chain length satisfies the relationship, . The crosslinking density of the gel molecule at the gel point is found to be .

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.

Architectural control of polystyrene physical properties using branched anionic polymerization initiated at ambient temperature

AbstractAmbient temperature‐initiated anionic polymerization has generated branched polystyrenes of varying molecular weights and architectures by inclusion of a distyryl branching comonomer into a conventional sec‐Butylithium‐initiated polymerization of styrene. Primary chain length control within the branched polymers, and restriction of the branching points to varying segments of the primary chains, led to variations of glass transition temperature with no direct correlation to the branched polymer molecular weight but a strong relationship to the length of individual chains comprising the branched macromolecules.

Random Branching of Polymer Chains with Schulz–Zimm Distribution. 2. Radius of Gyration and Maximum Span Length

AbstractMean‐square radius of gyration Rg2 and the maximum span length LMS of each polymer molecule are investigated for the random branching of primary chains that follow the Schulz–Zimm distribution, by using the Monte Carlo simulation method. It is found that the expected g‐ratio of Rg2 of the branched molecule to that of a linear molecule for a given number of branch points k does not change with the branching density. The expected g‐ratio becomes larger for the primary chains with broader distribution. An approximate formula for the relationship between g‐ratio and k that accounts for the distribution breadth is proposed. The relationship between the weight fraction of the maximum span chain LMS/(degree of polymerization) and k shows the analogous behavior with that for g‐ratio and k. The magnitude of Rg2 is proportional to LMS, with Rg2 = 0.18 LMS, irrespective of the breadth of the primary polymer chain length distribution.

H2 roaming chemistry and the formation of H3+ from organic molecules in strong laser fields

Roaming mechanisms, involving the brief generation of a neutral atom or molecule that stays in the vicinity before reacting with the remaining atoms of the precursor, are providing valuable insights into previously unexplained chemical reactions. Here, the mechanistic details and femtosecond time-resolved dynamics of H3+ formation from a series of alcohols with varying primary carbon chain lengths are obtained through a combination of strong-field laser excitation studies and ab initio molecular dynamics calculations. For small alcohols, four distinct pathways involving hydrogen migration and H2 roaming prior to H3+ formation are uncovered. Despite the increased number of hydrogens and possible combinations leading to H3+ formation, the yield decreases as the carbon chain length increases. The fundamental mechanistic findings presented here explore the formation of H3+, the most important ion in interstellar chemistry, through H2 roaming occurring in ionic species.

Effect of Chain Transfer to Polymer in Conventional and Living Emulsion Polymerization Process

Emulsion polymerization process provides a unique polymerization locus that has a confined tiny space with a higher polymer concentration, compared with the corresponding bulk polymerization, especially for the ab initio emulsion polymerization. Assuming the ideal polymerization kinetics and a constant polymer/monomer ratio, the effect of such a unique reaction environment is explored for both conventional and living free-radical polymerization (FRP), which involves chain transfer to the polymer, forming polymers with long-chain branches. Monte Carlo simulation is applied to investigate detailed branched polymer architecture, including the mean-square radius of gyration of each polymer molecule, <s2>0. The conventional FRP shows a very broad molecular weight distribution (MWD), with the high molecular weight region conforming to the power law distribution. The MWD is much broader than the random branched polymers, having the same primary chain length distribution. The expected <s2>0 for a given MW is much smaller than the random branched polymers. On the other hand, the living FRP shows a much narrower MWD compared with the corresponding random branched polymers. Interestingly, the expected <s2>0 for a given MW is essentially the same as that for the random branched polymers. Emulsion polymerization process affects branched polymer architecture quite differently for the conventional and living FRP.

Effect of alkanol chain length of primary alkanolamines and alkyl chain length of secondary and tertiary alkanolamines on their CO2 capture activities

Abstract The effect of the alkanol chain length in primary alkanolamines and the alkyl chain length in secondary and tertiary alkanolamines on CO 2 absorption and desorption kinetics, equilibrium CO 2 loading, heat duty, cyclic capacity, and pKa were studied. A selection strategy developed in our earlier work was used to identify potential solvents which could be used in a blend. Based on the strategy, alkanolamines that had a combination of high absorption parameter and high desorption parameter should be selected. The results of this study showed that, for absorption parameters, longer alkanol chain lengths of primary alkanolamines and longer alkyl chain lengths of secondary and tertiary alkanolamines led to higher equilibrium CO 2 loading and pKa. However, the influence of mass transfer limitations on these positive effects resulted in a maximum trend for initial rate of CO 2 absorption for secondary and tertiary alkanolamines. On the other hand, for the desorption parameters, the increase in the chain lengths also caused the generation of larger amounts of bicarbonate ions which resulted in higher CO 2 desorption rates and cyclic capacity, but lower heat duty. However, the longer chain alkanolamines also had high viscosities which adversely modified their performance by also introducing mass transfer limitations. Based on chain length alone, BMEA came out as the best overall alkanolamine component which could be used in a blend.

Toward Understanding of Branching in RAFT Copolymerization of Methyl Methacrylate through a Cleavable Dimethacrylate

We report the reversible addition–fragmentation chain transfer (RAFT) solution copolymerization of methyl methacrylate (MMA) with a cleavable divinyl comonomer, bis(2-methacryloyl)oxyethyl disulfide (BMAODS). 2-Cyano-2-propyldodecyl trithiocarbonate was used as a RAFT chain transfer agent and 2,2′-azobis(2-methylpropionitrile) as an initiator. The selective cleavage of BMAODS disulfide bonds was used to collect primary chains for the determination of the branching density (BD). The effects of initial monomer concentration, vinyl/divinyl ratio, and primary chain length on the branching and cyclization reactions were thoroughly investigated. It was found that more than 50% pendent double bonds from BMAODS were consumed in cyclization rather than in branching. The BD increased linearly with the conversion up to approximately 60% conversion. The monomer concentration was found to be the most efficient parameter in promoting branching. Increasing divinyl monomer ratio and primary chain length favored cyclizati...

Pt nanoparticles synthesized with new surfactants: improvement in C1–C3 alcohol oxidation catalytic activity

Platinum electrocatalysts were prepared using PtCl4 as a starting material and 1-decylamine, N,N-dimethyldecylamine, 1-dodecylamine, N,N-dimethyldodecylamine, 1-hexadecylamine, and 1-octadecylamine as surfactants. These surfactants were used for the first time in this synthesis to determine whether the primary and/or tertiary structure and/or chain length of the surfactants, affects the size and/or activity of the catalysts in C1–C3 alcohol electro-oxidation reactions. Electrochemical measurements (cyclic voltammetry and chronoamperometry) indicated that the highest electrocatalytic performance was observed for the Pt nanocatalysts that were stabilized by N,N-dimethyldecylamine, and this has a tertiary amine structure with a short chain length (R = C10H21). The high performance may be due to the high electrochemical surface area, Pt(0)/Pt(IV) ratio, %Pt utility, and roughness factor (Rf). X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy were used to determine the parameters that affect the catalytic activities.