Pendant Chain Length Research Articles

Tuning Crystallinity and Stacking of Two-Dimensional Covalent Organic Frameworks through Side-Chain Interactions.

Two-dimensional covalent organic frameworks (2D COFs) form as layered 2D polymers whose sheets stack through high-surface-area, noncovalent interactions that can give rise to different interlayer arrangements. Manipulating the stacking of 2D COFs is crucial since it dictates the effective size and shape of the pores as well as the specific interactions between functional aromatic systems in adjacent layers, both of which will strongly influence the emergent properties of 2D COFs. However, principles for tuning layer stacking are not yet well understood, and many 2D COFs are disordered in the stacking direction. Here, we investigate effects of pendant chain length through a series of 2D imine-linked COFs functionalized with n-alkyloxy chains varying in length from one carbon (C1 COF) to 11 carbons (C11 COF). This series reveals previously unrecognized and unanticipated trends in both the stacking geometry and crystallinity. C1 COF adopts an averaged eclipsed geometry with no apparent offset between layers. In contrast, all subsequent chain lengths lead to some degree of unidirectional slip stacking. As pendant chain length is increased, trends show average layer offset increasing to a maximum of 2.07 Å in C5 COF and then decreasing as chain length is extended through C11 COF. Counterintuitively, shorter chains (C2-C4) give rise to lower yields of weakly crystalline materials, while longer chains (C6-C9) produce greater yields of highly crystalline materials, as confirmed by powder X-ray diffraction and scanning electron microscopy. Molecular dynamics simulations corroborate these observations, suggesting that long alkyl chains can interact favorably to promote the self-assembly of sheets. In situ proton NMR spectroscopy provides insights into the reaction equilibrium as well as the relationship between low COF yields and low crystallinity. These results provide fundamental insights into principles of supramolecular assembly in 2D COFs, demonstrating an opportunity for harnessing favorable side-chain interactions to produce highly crystalline materials.

Morphology transition of amphiphilic homopolymer self-assemblies in water triggered by pendant design and chain length

In this paper, we examined self-assembly of amphiphilic homopolymers bearing the double brush side chains of a hydrophilic PEG and various hydrophobic units including butyl, octyl, dodecyl, octadecyl, and oleyl groups in water. Analyzed by size exclusion chromatography coupled with multiangle laser light scattering, those homopolymers formed uniform micelles, unimer micelles, and large aggregates like rod micelles in water; the morphology depended on the hydrophobic side chains and changed at a certain threshold degree of polymerization (DPth). The homopolymer comprising butyl groups folded into compact micelles via intramolecular association in water, independent of molecular weight. In contrast, the homopolymer carrying octyl groups formed either uniform micelles via multichain association (<DPth) or unimer micelles via single chain folding (>DPth). The homopolymers carrying dodecyl, octadecyl, and oleyl groups exclusively undergo multichain association in water but form either uniform micelles (<DPth) or large aggregates (>DPth). Uniquely, those DPth values decreased with increasing the hydrophobicity of the pendants; more hydrophobic homopolymers tend to form large aggregates at shorter polymer chains. Additionally, those homopolymers with broad molecular weight distribution induced chain length-dependent self-sorting to simultaneously produce uniform micelles and large aggregates in water.

Triptycene‐based fluorescent polymers with pendant alkyl chains: interaction with fullerenes and morphology of thin films

AbstractWe report unique triptycene‐based alternating copolymers bearing long alkyl chains as pendants. Syntheses utilized 2,6‐diethynyltriptycene and appropriate alkyloxyarene monomers polymerized via Sonogashira cross‐coupling reaction to yield triptycene‐based poly(phenylene ethynylene)s. Resulting polymers are soluble in organic solvents and were characterized using various techniques. Experimental results suggest the polymers are thermally stable and fluorescent. The fluorescence emission is quenched in the presence of fullerenes (C60 and C70) suggesting strong host–guest interactions. The magnitude of the binding constant between the polymers and these fullerenes was determined to be of the order of 105 mol L−1. The effects of chain length on the morphology and wettability of the polymers on silicon substrates were studied using atomic force microscopy. Three distinct dewetting patterns, i.e. spherical domains, fractal structures and ring structures, were observed with variation in the pendant chain length. This ability to control the thin‐film morphology of the polymers may have potential technological applications, which include but are not limited to sensors, fluorescent coatings and organic electronics. © 2018 Society of Chemical Industry

Fluorinated Polyacrylic Resins for the Protection of Cultural Heritages: The Effect of Fluorine on Hydrophobic Properties and Photochemical Stability

Two new water-repellent methyl methacrylate-based resins were synthesized changing the fluorinated pendant chain length of the co-monomers adopted, 2,2,2-trifluoroethyl acrylate and 1H,1H,2H,2H-perfluorooctyl methacrylate. The macromolecular and hydrophobic properties of the resultant polymers were investigated and their photochemical stability was estimated via an accelerated UV aging test. This work demonstrates that a polymeric protective prepared from a co-monomer bearing a short fluorinated pendant chain is characterized by more satisfactory hydrophobic and durability features than those of long fluorinated pendant chain-based polymers.

Optimization of the pendant chain length in partially fluorinated aromatic anion exchange membranes for alkaline fuel cells

Partially fluorinated aromatic polymer-based anion exchange membranes with propylene side chains exhibit high chemical stability and alkaline fuel cell performance.

Well-defined methacrylate copolymer having reactive maleimide pendants for fabrication of thermally-labile crosslinked networks with robust self-healing

The versatility of well-defined methacrylate random copolymer having reactive maleimide pendants (CoPMA) toward robust thermoreversibility and self-healability is reported. The CoPMA is synthesized by a controlled radical polymerization, thus being capable for the control of maleimide pendant density and chain length (i.e. molecular weight). The CoPMA is proved to be an effective polymeric dienophile yielding thermally-labile networks at room temperature with newly-synthesized polyfurans: a small-molecule difunctional furan (DFu) and a polymeric furan (CoPFuMA). The fabricated networks are dynamic at elevated temperatures through retro-Diels/Alder (rDA)/DA reaction, leading to rapid self-healing of micron-sized cuts on CoPMA/DFu films, compared with CoPMA/CoPFuMA films.

The effect of alkyl chain length on material properties of fatty-acid-functionalized amidoamine-epoxy systems

Polyamine crosslinkers functionalized with pendant fatty acids are commercially used in epoxy coatings in part to enhance water barrier properties for corrosion prevention. However, a systematic understanding of the links between monomer molecular structure and material properties of such systems remains elusive, which limits our ability to design newer and more environmentally friendly coating systems. In this work, the effect of n-alkyl chain length in fatty-acid-functionalized polyamines on crosslinked epoxy-amidoamine systems is studied using a combined experimental and simulation-based approach. Both experiments and simulations show that density decreases and volume-expansion coefficients increase with increasing pendant chain length. Furthermore, it is shown that the trends in density and coefficient of volume thermal expansion with chain length obtained from simulations are consistent with an ideal mixing approximation. Interestingly, however, the glass-transition temperature Tg is found to be insensitive to chain length. Molecular simulations reveal that increasing the alkyl chain length from four to ten carbons does not introduce new flexibility mechanisms to the dense thermosets, which explains the Tg insensitivity. This work demonstrates a new way to significantly decrease the density of a thermoset polymer without compromising desirable properties such as high Tg and low coefficient of thermal expansion, and therefore may provide sounder rationale for molecular-based design of epoxy-based coatings.

Morphology and high-performance of in-situ self-assemble epoxy resin with side aliphatic dangling chains

A series of epoxy resins containing side aliphatic pendant chains (abbreviated as EPC-04, EPC-08, EPC-12 and EPC-18) were prepared by the reaction between the diglycidyl ether of bisphenol F (DGEBF) and the single-ended fatty amine with a chain length ranging from C4 to C18. Studies on the film morphology and the physical performance demonstrate that the cured EPC-04, EPC-08, EPC-12 and EPC-18 composites possess excellent mechanical and thermal properties, which are originated from the micro-, submicro- and nano-structured phases distributed in the epoxy matrix. In addition, by adjusting the lengths of the dangling aliphatic chains, the mechanical properties of the cured resins can be tuned in different scales. Consequently, by prolonging the pendant chain length to C18, the cured resin exhibits a striking tensile strength of 90.65MPa, an elongation of 6.1% and a modulus of 2.55GPa.

Guanidinoamidized linear polyethyleneimine for gene delivery

Guanidine was introduced to low molecular weight linear polyethyleneimine (LPEI) via amide groups, to explore the effect of both guanidine degree and pendant chain length on its transfection behavior. The resulting guanidinoamidized LPEIs (GLPEIs) could dramatically reduce LPEI’s toxicity, enhance its DNA-packaging capability, cellular uptake and therefore transfection efficiency. These polyplexes were taken up very efficiently via caveolae-mediated endocytosis and their transfection efficiencies in ovarian cancer cells were significantly improved compared to native LPEI10k polyplexes. Among these GLPEIs, LPEI-C3-G100 showed higher DNA affinity even than LPEI25k and the highest transfection efficiency, probably due to the optimization of polymer chain flexibility. Of notice, LPEI-C3-G100 polyplexes could more effectively accumulate into cytoplasm than LPEI25k, although the transfection efficiency of LPEI-C3-G100 polyplexes was not superior to that of LPEI25k polyplexes, which would be probably attributed to the more efficient release of LPEI25k polyplexes than LPEI-C3-G100 polyplexes in the cytoplasm.

Tailoring the viscoelasticity of epoxy thermosets

AbstractThis research work is aimed to understand the effect of epoxy resin chemistry on the viscoelasticity of the cured epoxy thermosets. In this article, two model systems are selected based on epoxy‐amine reactants. In the model Systems I, the functionality of the epoxy is varied. In model System II, the pendant (side) chain length in the amine is varied. It is found that by varying the initial properties (e.g., functionality, pendant chain length, mixing ratio (r), aromaticity, etc.) the network properties (crosslink density and flexibility) of the cured (or hardened) epoxy changed. The changes (or shift) in the viscoelastic properties (or viscoelasticity) of the cured epoxy is mainly due the changes in the network properties. Further, to study the time and temperature effects the viscoelastic master curves for the two model systems are generated using Time‐Temperature‐Superposition (TTS) principle. The shift in the viscoelastic master curves is modeled with a simple Kohlrausch‐Williams‐Watts (KWW) fit function. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Controlling the degradation rate of thermoresponsive photo-cross-linked poly(organophosphazene) hydrogels with compositions of depsipeptide and PEG chain lengths

Thermosensitive and photo-cross-linkable poly(organophosphazenes) containing various amounts of isoleucine ethyl ester, AMPEG550, AMPEG750, aminoethyl methacrylate, and depsipeptide were synthesized, characterized, and were investigated for in vitro and in vivo degradation rates. The aqueous solutions of all polymers showed a sol–gel phase transition behavior against the temperature changes. The polymer degradation rate was majorly affected by the type and degree of the side group’s substitutions. The rate of degradation was initially dependent on the degree of photo-cross-linking, and in later stages on the amounts of the depsipeptide and PEG chain lengths in the polymer network. The amount of the pendant depsipeptide and chain length of the α-amino-ω-methoxy-poly(ethylene glycol) had significant impact on the polymer degradation rates. The polymers with high amount of the depsipeptide, and PEG750 showed fast degradation. These results suggest that the degradation rate of the injectable and dual cross-linkable gels can be tuned to the desired extent and may find wide utilities in various biomedical applications, where the gel strength and degradation rate are needed to be tightly regulated.

Ionomeric modification of a metallocene‐based polyolefinic elastomer and its influence on the physicomechanical properties: Effects of the crystallinity and pendent chain length

AbstractA new class of ionomer was developed through the grafting of acrylic acid onto a metallocene‐based poly(ethylene octene) elastomer, followed by its neutralization with zinc acetate. The ionomeric product was characterized through Fourier transform infrared spectroscopy, small‐angle X‐ray scattering, and transmission electron microscopy studies. The effect of the crystallinity and pendent chain length on the ionomeric modification was also studied through the variation of the level and nature of comonomer, respectively. The impact of these ionomeric modifications on various physicomechanical properties was thoroughly investigated with differential scanning calorimetry and mechanical, dynamic mechanical, and thermogravimetric analysis, and the resulting properties were correlated with the structure of the modified elastomers. The ionomerization of the base elastomers caused a significant improvement in the mechanical and thermal properties compared to the corresponding pristine elastomer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Ionomeric modification of metallocene-based polyolefinic elastomers with varied pendant chain length and its influence on physico-mechanical properties

A new class of ionomer was developed through sulfonation of the metallocene-based poly(ethylene–octene) elastomer, followed by its neutralization with zinc acetate. Ionomeric products were characterized through Fourier transform infrared (FT-IR) spectroscopy, small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) studies. The effect of pendant chain length on the ionomeric modification was also studied through the variation of the comonomer. The impact of these ionomeric modifications on various physico-mechanical properties was thoroughly investigated by using differential scanning calorimetry, mechanical, dynamic mechanical, and thermogravimetric analysis. The resultant properties were correlated with structures of the modified elastomers. Ionomerisation of the base elastomers causes a significant improvement in the stress–strain, as well as the thermal properties compared to the corresponding pristine elastomer.

Sulfonation of metallocene‐based polyolefinic elastomers and its influence on physicomechanical properties: Effect of reaction parameters, styrene grafting, and pendant chain length

AbstractDirect sulfonation and styrene‐mediated sulfonation were carried out onto metallocene‐based poly(ethylene‐co‐octene) (POE) and poly(ethylene‐co‐butene) (PBE) elastomers to impart polarity on the completely nonpolar rubbery matrices and to prepare a new class of elastomer. The influence of styrene‐grafting and pendant chain length on the degree of sulfonation was also studied. The effects of sulfonation, styrene grafting and styrene‐mediated sulfonation at their optimized levels on various physicomechanical properties were thoroughly investigated, and the resultant properties were correlated with structures of the modified elastomers. Higher extent of sulfonic acid groups were introduced through direct sulfonation in comparison with the styrene‐mediated sulfonation, whereas better thermal and mechanical properties were obtained through styrene‐mediated sulfonation in comparison with the direct sulfonation process. PBE had shown higher degree of sulfonation and percentage grafting than POE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8023–8040, 2008

Chemical modification of metallocene-based polyolefinic elastomers by acrylic acid and its influence on physico-mechanical properties: Effect of reaction parameters, crystallinity and pendant chain length

In this investigation, solution grafting of acrylic acid (AA) in presence of benzoyl peroxide (BPO) was carried out onto metallocene-based “poly(ethylene-octene) elastomers” (POE) as well as “poly(ethylene-butene) elastomers” (PBE), to impart polarity on the non-polar rubbery matrix and also to study the effects of crystallinity and pendant chain length on the “grafting percentage” and “percent gel yield” at optimized conditions for all the POE and PBE systems. Reaction parameters were optimized on the basis of the relative proportions of graft and gel formations obtained through %weight gain, Fourier Transform infrared spectroscopy and elemental analysis. The effect of grafting at its maximum level on various physico-mechanical properties was also thoroughly investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC), mechanical, dynamic mechanical (DMTA), and thermogravimetric analysis (TGA) and the properties were correlated with the structure of the modified polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5529–5540, 2007

Polyaniline with ω-hydroxyalkoxy pendant substituent on the meta-position

A series of meta-substituted polyaniline derivatives, poly[3-(ω-hydroxyhexoxy)aniline], poly[3-(ω-hydroxyoctoxy)aniline], poly[3-(ω-hydroxydecoxy)aniline] and poly[3-(ω-hydroxydodecoxy)aniline] have been synthesized via chemical oxidative polymerization. The resulting polymers show enhanced solubility in organic solvent. The polymerization yield is increased and the reaction is accelerated by the addition of aniline. The homopolymers can attain conductivity in the range of 10 −6 to 10 −4 S cm −1 after protonic doping with HCl. Upon doping oxidatively with iodine, the conductivity is ca. 10 −5 to 10 −3 S cm −1. For the copolymers with aniline (15 mol%), the corresponding conductivity is higher, 10 −5 to 10 −3 S cm −1 upon HCl doping and 10 −4 to 10 −2 S cm −1 upon iodine doping. Thermogravimetry (TG) of the polymer depicts two major weight loss steps corresponding to the degradation of side chain and the thermal breakdown of the backbone, respectively. The polymers are largely amorphous but show an increase in crystallinity with increasing pendant chain length. The polymers were also subjected to FT-IR, UV–VIS and X-ray photoelectron spectroscopy (XPS) studies.

Hydrolytic degradation of tyrosine-derived polycarbonates, a class of new biomaterials. Part II: 3-yr study of polymeric devices

The kinetics and mechanisms of in vitro degradation of tyrosine-derived polycarbonates, a new class of polymeric biomaterials, were studied extensively at 37°C. These polymers carry an alkyl ester pendent chain that allows the fine-tuning of the polymer's material properties, its biological interactions with cells and tissue, and its degradation behavior. The polymer carrying an ethyl ester pendent chain, poly(DTE carbonate), has been established as a promising orthopedic implant material, exhibiting bone apposition when in contact with hard tissue. Tyrosine-derived polycarbonates are relatively stable and degrade only very slowly in vitro. Therefore, accelerated studies were conducted at 50 and 65°C to observe the behavior of polymers during the later stages of degradation. Varying the pendent chain length affected the rate of water uptake, initial degradation rate, and physical stability of the polymeric devices. During the 3-yr study, the polymer degraded by random chain cleavage of the carbonate bonds, accompanied by a relatively small amount of pendent chain de-esterification. No mass loss was observed during this period at 37°C, but mass loss was readily evident during the accelerated studies at 50 and 65°C. Thus, it is reasonable to assume that mass loss will occur also at 37°C, albeit only after extensive backbone carbonate cleavage and pendent chain ester hydrolysis. The dimension and surface area of the devices influenced the initial degradation rate, but did not significantly affect the overall rate of degradation. No evidence of “acid dumping” or the release of acidic residues found during the degradation of poly( d, l-lactic acid) were observed for this family of tyrosine-derived polycarbonates.

Renewable Long-Chain Fatty Acids for Production of Biodegradable Medium-Chain-Length Polyhydroxyalkanoates (mcl-PHAs) at Laboratory and Pilot Plant Scales

Several types of mcl-PHAs were produced by Pseudomonas putida KT2442 at pilot and laboratory scales from renewable long-chain fatty acids (LCFAs) and octanoic acid. These and other mcl-PHAs are now available in sufficient amounts to carry out application and processing studies. We have isolated and purified these polymers in preparative amounts of 10−500 g by solvent recovery and selective enzymolysis. The molecular weights of mcl-PHA copolymers produced from LCFAs were generally similar to those found for octanoic acid based material, but the polydispersity was higher and the degree of polymerization was lower. The polymers showed thermal properties common for amorphous or semicrystalline thermoplastic elastomers above their Tg, which decreased with increasing average pendant chain length. PHAs derived from LCFAs, which contained 3−12 new hydroxyacid comonomers compared to PHA produced from oleic acid, were amorphous, did not crystallize, and showed liquid properties at room temperature. As the number of comonomers and thus the degree of disorder increased in these PHAs, the polymers became more viscous and tacky. PHAs derived from octanoic acid and oleic acid were not affected by the production scale in terms of composition and physical properties. Although different production process control strategies used at lab and pilot scale did influence the process productivity, the substrate yield was not affected by the process control type applied and was always close to the theoretical PHA yield to be expected for fatty acid utilization through the β-oxidation pathway. Isolation and GC−MS analysis of the methanolyzed trimethylsilyl- (TMSI-) derivatives allowed the identification of a large number of previously unknown 3-hydroxy acid PHA components. All purified polymers were subjected to in vitro aerobic biodegradation using a compost isolate. The extent of mineralization varied from 15 to 60% of the theoretical biochemical oxygen demand (ThBOD). The polymer weight loss after 32 days ranged from 40 to 90% for the different mcl-PHAs.

Tyrosine–PEG-derived poly(ether carbonate)s as new biomaterials: Part I: synthesis and evaluation

Tyrosine–PEG-derived poly(ether carbonate)s were prepared by condensation copolymerization with phosgene. The resulting polymers were random copolymers with weight average molecular weights from 40 000 to 200 000 dalton. Chemical structure and purity were confirmed by NMR and FTIR spectral analysis. General structure–property correlations were established. The glass transition temperature decreased with increasing PEG content and increasing pendent chain length. When higher molecular weight PEG blocks were used, the glass transition temperature increased relative to identical polymers having shorter PEG blocks. The tensile modulus increased with decreasing PEG content, decreasing pendent chain length, and when longer PEG blocks were used. Water uptake and the rate of backbone degradation increased with increasing PEG content. Microspheres could be prepared by solvent evaporation techniques from copolymers with low PEG content. Release rate of pNA and FITC-dextran from the microspheres increased with increasing PEG content. While tyrosine-derived polycarbonates were excellent substrates for cell attachment and growth, the presence of only 5 mol% of PEG 1000 led to low or no cell attachment in short-term cell culture with both rat lung fibroblasts and osteoblasts. The polymers were non-cytotoxic.

Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 4. An Extended Pendant−Core Model for Gasoline Composition

The pendant−core concept has been used previously to predict product slates from catalytic cracking. In this concept, alkyl side chains and analogous moieties are defined as “pendants”, which are attached to a cluster of aromatic and/or naphthenic rings which is referred to as the “core”. This work extends the pendant−core concept via a model which correlates feed composition (19 main component types determined by mass spectroscopy) to nine product subclasses (both gasoline and non-gasoline) by adding product distribution functions. These product distribution functions depend upon the feed component class (saturates, aromatics, and sulfur compounds) and upon the core−pendant ratio. For example, the production of light gas and coke increases with the core−pendant ratio since the probability of coke formation increases with core size and the average pendant chain length decreases as the proportion of carbon in pendants decreases. Using these component distribution functions, and the mass spectroscopic analysis of feeds, one can calculate anticipated yields of nine product subclasses: light gas, C3/C4 gas, light cycle oils, heavy cycle oils, coke, and gasoline range: paraffins, olefins, aromatics, and naphthenes. The product distribution functions were developed from data on four feedstocks. For the four feedstocks used in the correlation, plus a fifth feedstock, the predicted product quantities are within 2 wt % of the experimental values. The present form of the model does not address effects of polar (acidic or basic) compounds in feeds on product slate.