Gelation Of Poly Research Articles

Block length and topology affect self-assembly and gelation of poly(l-lysine)-block-poly(S-benzyl-l-cysteine) block copolypeptides

We report the self-assembly and hydrogelation of linear and star-shaped poly(l-lysine)-block-poly(S-benzyl-l-cysteine) (PLL-b-PBLC) block copolypeptides with degrees of polymerization (DPs) between 15 and 70, driven by the amphiphilic balance between PLL and PBLC segments as well as both aromatic and hydrogen bonding interactions between PBCL segments. The hydrogelation ability, molecular assembly, and mechanical strength of PLL-b-PBLC could be tuned by manipulating the non-covalent interactions via varying polypeptide chain length and arm number. The confinement of PLL chains due to the packing of hydrophobic, sheet-like PBLC segment led to the percentage of β-sheet/turn conformation much higher than the mole fraction of PBLC segment, faciliating polypeptide self-assembly and hydrogelation. Due to the differences in the degree of freedom for linear and star-shaped polypeptides to self-assembly, the linear PLL-b-PBLC would undergo morphological transformation of the nano-assemblies from 2D bilayers to 3D spherical aggregates upon hydrogelation, but not for the star-shaped counterparts. This study clearly illustrated that the sheet-like PBCL segment is an excellent hydrogelator to trigger hydrogelation of these block copolypeptides.

Hydrophobic and heat-resistant poly(methylphenylsiloxane)-modified resorcinol–formaldehyde composite xerogel monoliths and the carbonized derivatives

Resorcinol–formaldehyde (RF) aerogels are widely used as thermal insulation materials. The present investigation of RF aerogels emphases on improving hydrophobic property and high-temperature residual yields. In this study, polysiloxane-modified RF composite xerogel monoliths were prepared by gelation of poly(methylphenylsiloxane) prepolymer with RF in cosolvent and ambient pressure drying. The influence of phenyl content on structure and thermal property of xerogels was investigated. The as-prepared RF composite monoliths were lightweight and hydrophobic with density lower than 0.300 g/cm3 and water contact angles approaching 130°. Morphology analyses indicated that polysiloxane grew and formed a continuous layer on RF porous skeleton with controlled reaction parameter. Thermogravimetry analyses (TGA) certified that the controlled incorporation of polysiloxane in composite xerogels enhanced the thermal degradation temperature at which the weight loss of RF xerogels reaches 5% (T5%) and increased the residual yields at 1000 °C. The carbonized derivatives were obtained for further enhancing the thermal stability by removal of small molecules during carbonization. Xerogel monoliths preserved hydrophobic property till 500 °C carbonization due to the thermal stability of poly(methylphenylsiloxane). The heat-resistant composite xerogels remained monolith structure after 800 °C treatment under nitrogen condition.

Direct Patterning of Highly Conductive PEDOT:PSS/Ionic Liquid Hydrogel via Microreactive Inkjet Printing.

The gelation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has gained popularity for its potential applications in three dimensions, while possessing tissue-like mechanical properties, high conductivity, and biocompatibility. However, the fabrication of arbitrary structures, especially via inkjet printing, is challenging because of the inherent gel formation. Here, microreactive inkjet printing (MRIJP) is utilized to pattern various 2D and 3D structures of PEDOT:PSS/IL hydrogel by in-air coalescence of PEDOT:PSS and ionic liquid (IL). By controlling the in-air position and Marangoni-driven encapsulation, single droplets of the PEDOT:PSS/IL hydrogel as small as a diameter of ≈260 μm are fabricated within ≈600 μs. Notably, this MRIJP-based PEDOT:PSS/IL has potential for freeform patterning while maintaining identical performance to those fabricated by the conventional spin-coating method. Through controlled deposition achieved via MRIJP, PEDOT:PSS/IL can be transformed into different 3D structures without the need for molding, potentially leading to substantial progress in next-generation bioelectronics devices.

Structure-property relationships of novel phosphonate-functionalized networks and gels of poly(β-amino esters)

pH sensitivity, biodegradability and high biocompatibility make poly(β-amino esters) (PBAEs) important biomaterials with many potential applications including drug and gene delivery and tissue engineering, where their degradation should be tuned to match tissue regeneration rates. Therefore, we synthesize novel phosphonate-functionalized PBAE macromers, and copolymerize them with polyethylene glycol diacrylate (PEGDA) to produce PBAE networks and gels. Degradation and mechanical properties of gels can be tuned by the chemical structure of phosphonate-functionalized macromer precursors. By changing the structure of the PBAE macromers, gels with tunable degradations of 5–97% in 2 days are obtained. Swelling of gels before/after degradation is studied, correlating with the PBAE identity. Uniaxial compression tests reveal that the extent of decrease of the gel cross-link density during degradation is much pronounced with increasing amount and hydrophilicity of the PBAE macromers. Degradation products of the gels have no significant cytotoxicity on NIH 3T3 mouse embryonic fibroblast cells.

Nanostructure of organic-inorganic composite materials based on polymer hydrogels

The initial stage of gelation of organic-inorganic hybrid hydrogels based on poly(N-vinylpyrrolidone) and the products of hydrolytic polycondensation of tetramethoxysilane has been studied by capillary viscometry. The development of strong bonds between polymer molecules and silica particles in aqueous solutions is proved by the electrokinetic sonic amplitude method. The molecular mass of poly(N-vinylpyrrolidone), the concentration of starting components, and their total amount affect the onset time of gelation in poly(N-vinylpyrrolidone)-water-tetramethoxysilane systems. The general scheme of formation of three-dimensional networks in such systems under the conditions of mutual penetration of poly(Nvinylpyrrolidone) coils is suggested. According to this scheme, nanoparticles of the general formula SiOx(OH)y(OR)z linking poly(N-vinylpyrrolidone) macromolecules serve as junctions of the gel network due to the formation of hydrogen bonds between hydrogens of silanol groups of organosilanes and oxygens of carbonyl groups of poly(N-vinylpyrrolidone).

NIR light‐triggered gelling in situ of porous silicon nanoparticles/PEGDA hybrid hydrogels for localized combinatorial therapy of cancer cells

ABSTRACTPorous silicon‐based nanocomposite hydrogels were readily constructed with the gelation of poly(ethylene glycol) double acrylates (PEGDA) macromers, due to the initiation of singlet oxygen photosensitized with porous silicon nanoparticles (PSiNPs) under near‐infrared (NIR) light irradiation. Multifunctional PSiNPs/PEGDA nanocomposite hydrogels showed strong fluorescence, excellent biodegradability, significant photothermal effect, and sustained drug release with high efficiency (>80%). Finally, in situ growth of PSiNPs/PEGDA hybrid hydrogels on cancer cells was also achieved by NIR light, and then their biodegradation, drug release and synergistic chemo‐phototherapeutic efficacy were further demonstrated, which could provide a significant localized inhibition for the viability, adherence, and migration of cancer cells in vitro. Thus, we suggested that these resultant hybrid hydrogels would have important potential on local cancer therapy in future clinical practice. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47443.

Gelation of Poly(Vinylidene Fluoride) Solutions in Native and Organically Modified Silica Nanopores.

The purpose of this study is to highlight the surface and size effects of the nanopores on the thermodynamics and kinetics of gelation. The effects have been probed by applying differential scanning calorimetry to poly(vinylidene fluoride) solutions in tetraethylene glycol dimethyl ether (tetraglyme) and γ-butyrolactone. Nanoconfinement has been accomplished by introducing gels into native and organically modified silica nanopores (4–30 nm). Nanoconfinement has produced two major effects. First, the heat of gelation has decreased three to four times compared to that for the bulk systems. Second, the temperature of gelation has increased by ~40 °C (tetraglyme based systems) and ~70 °C (γ-butyrolactone based systems), the increase being stronger in native nanopores. The effects are discussed in terms of acceleration of gelation due to heterogeneous nucleation at the confining surface, and retardation of gelation due to constricted polymer chain mobility in the middle of the pore volume. Calorimetric data have been subjected to isoconversional kinetics analysis. The obtained temperature dependencies of the activation energies of gelation have been interpreted in the frameworks of the nucleation model of Turnbull and Fisher. The results suggest that nanoconfinement leads to a lowering of both the free energy of nucleation and activation energy of diffusion.

Gelation of poly(vinyl chloride) inside a single screw extruder and its effect on product properties

Two resin formulations were extruded through a single screw extruder, equipped with a single flighted screw, rotating at 10 rpm, at different barrel temperature settings, which resulted in different melt temperatures measured in the adapter zone. The extrudates were subsequently subjected to assessments of the gelation level by three different methods: differential scanning calorimetry (DSC), capillary rheometry (CR), and solvent absorption (SA). The pros and cons of these methods are discussed. It appears that DSC is the most accurate technique for the quantitative determination of the gelation degree (GD), with the drawback that the specimen size is very small. The CR technique, based on measurement of entrance pressure, is also capable of providing reasonable estimates of GD, with some potential inaccuracies as a result of difficulties associated with measurement or assessment of temperature rise. The SA technique provided qualitative assessments of GD in agreement with the other two methods. Ultimate tensile strength, elongation at break, solid density, and color change were also measured and were correlated to melt temperatures and the corresponding GD. Extruded specimens having GDs in the range of 60%–90% possessed satisfactory properties for both resin formulations. J. VINYL ADDIT. TECHNOL., 25:E174–E180, 2019. © 2018 Society of Plastics Engineers

In Situ Silication of Polymer Nanofibers to Engineer Multi‐Biofunctional Composites

AbstractThe critical role of silica in bone homeostasis has motivated the development of silica‐based biomaterials for orthopedic applications. Whereas polymer nanofibers have emerged as promising substrates for orthopedic applications, nanoparticle agglomeration precludes the preparation of silica containing composite nanofibers by electrospinning. This work presents a facile sol‐gel process to fabricate electrospun nanocomposite fibers by in situ silica gelation in poly (ϵ‐caprolactone) (PCL) solution. Citric acid is shown to be more effective than acetic acid as the pH catalyst for gelation by rapidly yielding near uniform nanoparticles (150+50 nm). The composite nanofibers exhibited increased water wettability than neat PCL with sustained release of silicon ions. The composite fibers induced early apatite formation in simulated body fluid. Quantitative characterization of the tubular networks formed by human umbilical cord vascular endothelial cells revealed that the eluted silicon ions and citric acid in fibers synergistically promoted angiogenic activity, which was corroborated by increased gene and protein expressions of several known angiogenic markers. Furthermore, silicate fibers augmented osteogenesis of human mesenchymal stem cells as measured by the increased mineral deposition and increased gene and protein expression of osteogenic markers. Thus, the in situ silicated fibers are promising multi‐biofunctional materials for orthopedic applications.

The role of electrostatic repulsion in the gelation of poly(vinyl alcohol)/borax aqueous solutions

This study examined linear viscoelasticity (LVE) of semidilute non-entangled poly(vinyl alcohol) (PVA) and borax aqueous solutions: one borax molecule dissociates into two B(OH)3 molecules and two B(OH)4- ions, and the latter can crosslink the PVA chains. Gelation was observed with increasing concentration of borax in the solutions. Analysis of LVE with the reversible gelation model reveals that although the number density of crosslinking ions increases with increasing concentration of borax, the fraction of the crosslinking ions decreases, which is attributed to the intensified electrostatic repulsion when more sites of the PVA chains are occupied by the ionic crosslinkers.

Semi‐interpenetrating polymer networks based on crosslinked poly(N‐isopropyl acrylamide) and methylcellulose prepared by frontal polymerization

ABSTRACTIn this work, semi‐interpenetrating gels of poly(N‐isopropyl acrylamide) and methylcellulose were successfully synthesized by using the Frontal Polymerization (FP) technique. The gels were obtained in the presence of dimethyl sulfoxide and trihexyltetradecylphosphonium persulfate, as polymerization solvent and radical initiator, respectively, hence avoiding the formation of bubbles during polymerization. Then, some of the gels containing dimethyl sulfoxide were thoroughly washed with water, hence obtaining the corresponding hydrogels. The effects of the ratio between poly(N‐isopropyl acrylamide) and methylcellulose, the amount of crosslinker and solvent medium (i.e., dimethyl sulfoxide and water) were thoroughly studied, assessing the influence of temperature and velocity of FP fronts on the glass transition temperature values (dried samples), on the swelling behavior and on the dynamic‐mechanical properties (gels swollen both in water and dimethyl sulfoxide). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 437–443

From Weakness to Strength: C-H/π-Interaction-Guided Self-Assembly and Gelation of Poly(benzyl ether) Dendrimers.

The C-H/π interactions as the key driving force for the construction of supramolecular gels remain a great challenge because of their weak nature. We hereby employed for the first time weak C-H/π interactions for the construction of supramolecular dendritic gels based on peripherally methyl-functionalized poly(benzyl ether) dendrimers. Their gelation property is highly dependent on the nature of the peripheral methyl groups. Furthermore, single-crystal X-ray analysis and NMR spectroscopy revealed that multiple C-H/π interactions between the proton of the methyl group and the electron-rich peripheral methyl-substituted aryl ring played significant roles in the formation of supramolecular nanofibers and organogels. This study uncovers the critical role of weak noncovalent interactions and provides new insights into the further design of self-assembled nanomaterials.

Zmiany strukturalne w plastizolach z poli(chlorku winylu) po ich zelowaniu

Zmiany strukturalne w plastizolach z poli(chlorku winylu) po ich zelowaniu

Self-assembly and gelation of poly(aryl ether) dendrons containing hydrazide units: factors controlling the formation of helical structures.

Self-assembly of AB2 and AB3 type low molecular weight poly(aryl ether) dendrons that contain hydrazide units were used to investigate mechanistic aspects of helical structure formation during self-assembly. The results suggest that there are three important aspects that control helical structure formation in such systems with acyl hydrazide/hydrazone linkage: i) J-type aggregation, ii) the hydrogen-bond donor/acceptor ability of the solvent, and iii) the dielectric constant of the solvent. The monomer units self-assemble to form dimer structures through hydrogen-bonding and further assembly of the hydrogen-bonded dimers leads to macroscopic chirality in the present case. Dimer formation was confirmed by NMR spectroscopy and by mass spectrometry. The self-assembly in the system was driven by hydrogen-bonding and π-π stacking interactions. The morphology of the aggregates formed was examined by scanning electron microscopy, and the analysis suggests that aprotic solvent systems facilitate helical fibre formation, whereas introduction of protic solvents results in the formation of flat ribbons. This detailed mechanistic study suggests that the self-assembly follows a nucleation-elongation model to form helical structures, rather than the isodesmic model.

Synthesis, Chloramphenicol Uptake, and In Vitro Release of Poly(AMPS–TEA-Co-AAm) Gels with Affinity for Both Water and Alcohols

Novel copolymeric gels of poly(AMPS–TEA-co-AAm) with superabsorbency in both water and alcohols were synthesized by neutralizing 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) with triethylamine (TEA) followed by copolymerizing the resulted salt with acrylamide (AAm) in aqueous solutions using N,N′-methylenebisacrylamide (MBAm) as a crosslinker, and ammonium persulfate (APS) as an initiator. By swelling the xerogel of poly(AMPS–TEA-co-AAm) in the drug solution followed by removing the solvent to give drug-polymer conjugate, the incorporation of a model drug, chloramphenicol, into the gels was investigated by using water and alcohols as solvent, respectively. The in vitro drug release profile of the drug-polymer conjugate was investigated in PBS. The results showed that poly(AMPS–TEA-co-AAm) gels exhibited superabsorbency in both water and a series of alcohols; and the alcohol-facilitated uploading of chloramphenicol into the gels was much greater than that achieved in water. The poly(AMPS–TEA-co-AAm) gels exhibited a similar drug release profile with conventional hydrogels; and only part of the drug uptaken by the gels was released as a result of poor aqueous solubility of chloramphenicol.

Rigidity of the crystals of thermo-sensitive gel spheres of poly (N-isopropyl acrylamide) in the deionized aqueous media as studied by the reflection spectroscopy in the sedimentation equilibrium

Reflection spectroscopy of deionized suspensions of the thermo-sensitive gels of poly (N-isopropylacrylamide) with various degrees of cross-linking were made in the sedimentation equilibrium at 20 °C. Rigidity of the crystals increased as sphere concentration increased and increased slightly as the degree of the cross-linking of the gel spheres increased. The fluctuation parameters of the gel crystals were between 0.05 and 0.07 and slightly larger than those of typical hard-sphere systems. These experimental results emphasize that the gel crystals are soft compared with those of typical hard-sphere systems and role of the extended electrical double layers for the crystallization of gel spheres is important but weak compared with that of hard colloidal spheres.

Nanoprobe Diffusion in Dehydrating Polyvinyl Alcohol Solutions and Gels

We investigate the effect of dehydration on the diffusion of fluorescent nanoprobes embedded in aqueous solutions and gels of Poly(Vinyl Alcohol) (PVA) polymers. using a custom-made optical chamber and applying fluorescence correlation spectroscopy (FCS), we measured changes in fluorescence intensity and, simultaneously time-correlation functions at various stages during the dehydration of samples of the solutions or gels. The samples were prepared at different concentrations and cross-link densities, with glutaraldehyde being the cross-linker. We have analyzed the data and determined the changes of the concentrations of the nanoprobes and PVA, as well as the apparent diffusion times of the nanoprobes during the dehydration. For rhodamine fluorophores (TAMRA, MW =430 Da), we find that diffusion slows down in both shrinking samples. The drying rates of samples of the solution and gel are different, though both samples were prepared with the same PVA concentrations and subjected to the same conditions. Moreover, the diffusion time and its changes in the drying sample of gel is larger than those in the corresponding drying sample of the solution. We also measured changes of the elastic modulus of samples of dehydrating gels prepared at different concentrations and cross-link density, the goal being to establish whether there is a correlation between the changes of the elastic modulus and those of the nanoprobe diffusion.

Effects of Poly(Propylene Oxide)–Poly(Ethylene Oxide)–Poly(Propylene Oxide) Triblock Copolymer on the Gelation of Poly(Ethylene Oxide)–Poly(Propylene Oxide)–Poly(Ethylene Oxide) Aqueous Solutions

Poly(ethylene oxide)-poly(propylene oxide)–poly(ethylene oxide) ((EO)n–(PO)m–(EO)n) block copolymers, commercially available as Pluronics (BASF Corp.) and Poloxamers (ICI Corp.), have been widely applied in medicine, biochemistry, and other fields because of their ability to form reversible micelles and physical gels in aqueous solution. Generally, for PEO–PPO–PEO block copolymers with higher ethylene oxide concentration, the micellization and gelation in aqueous solution are easier. However, if we introduce the reverse block copolymer PPO–PEO–PPO into PEO–PPO–PEO aqueous solutions, the micellization and gelation of the system will be more complex. In this work, the reverse block copolymer PO14–EO24–PO14 (17R4) was added to the Pluronics EO20–PO70–EO20 (P123), EO100–PO65–EO100 (F127), and EO133–PO50–EO133 (F108) aqueous solutions with different molar ratios. The rheological properties of different mixtures were measured to study the additive effect on the gelation behavior. The sol–gel transition temperature of the P123, F127, and F108 solutions shifted to a higher temperature when 17R4 was added to the solutions. In addition, the existence of 17R4 greatly affected the stability of gels. These results help to better understand the gelation of Pluronic aqueous solutions.

Gelation of Poly(l-lactic acid) Induced by Complex Crystallization with Solvents

Abstract Gels of poly(l-lactic acid) (PLLA) in several solvents, including N,N-dimethylformamide (DMF) were formed by cooling solutions of PLLA. Polarizing optical micrographs showed the formation of spherulites of PLLA in the gels below 70 °C. The storage modulus of the gel decreased abruptly below 70 °C, which suggest that the crystalline structure of PLLA prevented the flow of DMF and induced the gelation. The X-ray diffraction (XRD) patterns of the gels were similar to those of the ε-crystals of PLLA which were induced by the formation of complex crystallization with DMF. The mechanism of the formation of the gel is discussed based on the experimental data.

Study on temperature response in raspberry-form gels of poly (N,N-diethylacrylamide)

Slow swelling and shrinking rates are a significant challenge for some applications of temperature-sensitive hydrogels. This study reports raspberry-form poly N,N-diethylacrylamide (DEAA) gel particles, which are aggregates of single spherical gel particles. The raspberry-form gel particles show improved temperature-response rates especially for swelling. This improvement in the response rate is attributed to two key factors: the free space between the individual gel particles that make up the aggregated gel particle, and the constraints from the contact points between the individual gel particles. During the swelling process, the polymer chain networks can diffuse at the faster rate characteristic of the individual gel particles constructing the raspberry-form gel, and consequently the response rate of the overall raspberry-form gels can be accelerated. During the shrinking process, the constraints from the contact points between the individual gels dominate the polymer chain diffusion and the shrinking rate because of non-zero shear modulus. The shrinking behavior was affected not by the individual particle size, but rather the apparent gel size and shape.