Segmented Copolymers Research Articles

Microphase separation/crosslinking competition-based ternary microstructure evolution of poly(ether-b-amide).

The temperature dependence of the rheological properties of poly(ether-b-amide) (PEBA) segmented copolymer under oscillatory shear flow has been investigated. The magnitude of the dynamic storage modulus is affected by the physical microphase separation and irreversible crosslinking network, with the latter spontaneously forming between the polyamide segments and becoming the dominant factor in determining the microstructural evolution at temperatures well above the melting point of PEBA. From the rheological results, the initial temperature of the rheological properties dominated by the microphase separation and crosslinking (Tcross) structures were determined, respectively. Based on the two obtained temperatures, the microstructure evolution upon the heating can be separated into the ternary microstructure domains: homogenous (temperature below ), microphase separation dominating (between and Tcross), and crosslinking dominating domains (above Tcross). When the PEBA is heated to above Tcross, the content of crosslinking network increases with time and temperature, leading to an irreversible and non-negligible influence on the rheological, crystallization, and mechanical properties. A more pronounced strain-hardening phenomenon during the uniaxial stretching is observed for the sample with a higher content of crosslinking network.

Hydration influences on the phase heterogeneity of segmented copolymers.

We elucidate the influences of hydration on the morphological heterogeneity of the class of hard-soft segmented copolymers by experimenting on three model members selected from this group. For influences on phase segmentation, we quantify the degree of phase separation, segment boundary diffusiveness and extent of interphase mixing. Qualitative variations induced by hydration in hydrogen bonding within the phases are also mapped. An inverse relationship between the degree of segmentation and inherent water miscibility of the polymer backbones is observed, that is, high miscibility reducing the degree of segmentation, whereas poor miscibility increasing it. We then quantify hydration induced variations in the size, volume fraction and interaction pair potentials of individual hard segments. The influences on hard segment assemblies are assessed by quantifying their size, volume fraction, interaction pair potential and intrasegment adhesion. This quantification reveals a complex interplay between the volume expansion of individual hard segments and simultaneous swelling and disassembly of their assemblies. Finally, we integrate the segmentation parameters with observed alterations in hydrogen bonding and the inherent polarizability of segments to present a mechanism that reasonably describes the hydrated state morphology. Besides revealing the influences of hydration on the morphological heterogeneity of this class of polymers, our insights give strategies for new synthesis methods for water contact applications and aids in predicting their hydration induced thermomechanical property alterations.

ВЛИЯНИЕ НАПОЛНИТЕЛЕЙ НА АБРАЗИВНЫЙ ИЗНОС СЕГМЕНТИРОВАННОЙ ПОЛИУРЕТАНМОЧЕВИНЫ

As an object of research, we have chosen a well-known elastic polymer material – polyetherurethane urea SKU-PFL, which is a typical segmented block copolymer. Powdered microdispersed fillers capable to improve wear resistant such as calcium stearate and molybdenum disulfide were added to this material at the manufacturing stage in varying amounts (up to 1.5% by weight). The found level of the optimal filler concentration for the investigated elastomers in the region close to 0.5 wt% makes it possible to consider calcium stearate and molybdenum disulfide as not only effective but also economical components of promising wear-resistant polymeric materials.

The influence of spacer composition on thermomechanical properties, crystallinity, and morphology in ionene segmented copolymers.

A series of segmented ammonium ionenes with varying weight fractions of 2000 g mol-1 poly(ethylene glycol) (PEG) or poly(tetramethylene oxide) (PTMO) soft segments were synthesized, and a simplified coarse-grained model of these materials was implemented using molecular dynamics simulations. In addition to varying soft segment type (PTMO vs. PEG), charge density and soft segment content were varied to create a comprehensive series of segmented ammonium ionenes; thermogravimetric analysis reveals that all segmented ionenes in the series are thermally stable up to 240 °C. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) show the formation of phase separated microdomains at low soft segment content. In particular, DSC shows that the hard and soft domains have distinct glass transition temperatures. Similarly, simulations show that reduced soft segment content induces stronger microphase separation, reduces soft segment mobility, and increases ionic aggregate connectivity and size. These increased ionic associations result in elastomeric behavior, as evidenced by the higher rubbery plateau moduli observed at lower soft segment contents through DMA. Moreover, simulations show that ionic aggregation increases when switching from PEG to the less polar PTMO repeat units, which is consistent with DMA results showing higher plateau moduli for PTMO-based ionenes relative to PEG ionenes. DSC and X-ray diffraction determined that the degree of crystallinity increased with soft segment content regardless of segment type. Overall, these results suggest a semi-crystalline microphase-separated morphology strongly influenced by charge density, the degree of ionic aggregation, and the resulting level of confinement and mobility of the soft segments.

Fabrication and characterization of high flux poly(vinylidene fluoride) electrospun nanofibrous membrane using amphiphilic polyethylene‐block‐poly(ethylene glycol) copolymer

AbstractElectrospun nanofiber membranes (ENM) made of polymers such as polysulfone and poly(vinylidene fluoride) (PVDF) have a much higher contact angle (CA) and also more hydrophobic when compared to the virgin polymers. For water treatment applications, membranes with hydrophilic nature are highly desirable in order to achieve high flux and less fouling potentials. Hence, in the present study, highly hydrophilic electrospun nanofiber membranes (ENMs) were prepared by blending PVDF polymer with amphiphilic polyethylene‐block‐poly (ethylene glycol) (PE‐b‐PEG) copolymer. Resulting amphiphilic ENMs were highly porous (77%–92%) and the breaking elongation of 140% with a young's modulus of 2.55 MPa was observed. When compared with the control PVDF membrane, PE‐b‐PEG blended ENMs revealed higher water permeation flux owing to the enrichment of the hydrophilic PEG segments at the membrane surface, which was confirmed by using X‐ray photoelectric spectroscopy and Energy‐dispersive spectroscopy measurements. When compared to the phase inversion process (CA of 97.3°) blended ENM had CA of 0°, which indicates that besides hydrophilic block copolymer segments, the nature of membrane formation also contributes its role in influencing the hydrophilicity of the membrane. This improved hydrophilicity in combination with larger pore sizes of the PVDF/ PE‐b‐PEG membranes have contributed to enhancement of pure water flux, protein solution permeability and water flux recovery, which can be applied potentially for water treatment applications.

Hydrophilic (AB)n Segmented Copolymers for Melt Extrusion‐Based Additive Manufacturing

AbstractSeveral manufacturing technologies beneficially involve processing from the melt, including extrusion‐based printing, electrospinning, and electrohydrodynamic jetting. In this study, (AB)n segmented copolymers are tailored for melt‐processing to form physically crosslinked hydrogels after swelling. The copolymers are composed of hydrophilic poly(ethylene glycol)‐based segments and hydrophobic bisurea segments, which form physical crosslinks via hydrogen bonds. The degree of polymerization was adjusted to match the melt viscosity to the different melt‐processing techniques. Using extrusion‐based printing, a width of approximately 260 µm is printed into 3D constructs, with excellent interlayer bonding at fiber junctions, due to hydrogen bonding between the layers. For melt electrospinning, much thinner fibers in the range of about 1–15 µm are obtained and produced in a typical nonwoven morphology. With melt electrowriting, fibers are deposited in a controlled way to well‐defined 3D constructs. In this case, multiple fiber layers fuse together enabling constructs with line width in the range of 70 to 160 µm. If exposed to water the printed constructs swell and form physically crosslinked hydrogels that slowly disintegrate, which is a feature for soluble inks within biofabrication strategies. In this context, cytotoxicity tests confirm the viability of cells and thus demonstrating biocompatibility of this class of copolymers.

Multi-scale coarse-grained molecular dynamics simulation to investigate the thermo-mechanical behavior of shape-memory polyurethane copolymers

Shape-memory polyurethanes (SMPUs) are smart semi-crystalline polymers with heat-induced shape memory. The segmented SMPU copolymer simulated in this study consisted of an isocyanate (hard segment) that acts as a netpoint to stabilize the network, and a polyol (soft segment) that, owing to polymer crystallization, acts as a molecular switch. The ratio of hard to soft segments is a determining factor in the thermo-mechanical behavior and shape-memory performance of SMPU copolymers. However, the limitations of the scale of the conventional all-atom molecular dynamics simulation makes it difficult to observe mesoscale phenomena such as the phase-segregated morphology and polymer crystallization. To address this problem, we have developed a coarse-grained (CG) molecular dynamics (MD) model with fewer degrees of freedom by treating multiple atoms as a single bead. We derived the CG intra- and inter-bead potentials of the CG MD model such that the structural and thermodynamic properties would be identical to those of the all-atom reference model. Consequently, polymer crystallization was verified to occur at room temperature with the developed CG potentials. We subsequently investigated the effects of hard-segment content (HSC) on the thermal transition at SMPU melting temperature. We also investigated the influence of HSC on the thermo-elastic behavior and shape-memory properties of SMPU copolymers by simulating a 4-step thermo-mechanical cycle. The results revealed that the microstructure significantly affects macroscopic shape-memory behavior. We expect that this study will be used to improve the prediction and design of the thermo-mechanical behavior of segmented polyurethane or other semi-crystalline polymers.

Effect of Hydrophilic Monomer Distribution on Self-Assembly of a pH-Responsive Copolymer: Spheres, Worms and Vesicles from a Single Copolymer Composition.

A series of copolymers containing 50 mol % acrylic acid (AA) and 50 mol % butyl acrylate (BA) but with differing composition profiles ranging from an AA‐BA diblock copolymer to a linear gradient poly(AA‐grad‐BA) copolymer were synthesized and their pH‐responsive self‐assembly behavior was investigated. While assemblies of the AA‐BA diblock copolymer were kinetically frozen, the gradient‐like compositions underwent reversible changes in size and morphology in response to changes in pH. In particular, a diblock copolymer consisting of two random copolymer segments of equal length (16 mol % and 84 mol % AA content, respectively) formed spherical micelles at pH >5, a mix of spherical and wormlike micelles at pH 5 and vesicles at pH 4. These assemblies were characterized by dynamic light scattering, cryo‐transmission electron microscopy and small angle neutron scattering.

The role of ionic clusters in the determination of the properties of partially neutralized ethylene-acrylic acid ionomers

Ionomers with different degree of neutralization were prepared from an ethylene-acrylic acid copolymer of 8.5 wt% acrylic acid content. The ionomers were characterized by Fourier transform infrared spectroscopy, small angle X-ray scattering, differential scanning calorimetry and dynamic mechanical thermal analysis measurements as well as rheology and tensile testing. The main relaxing species in ionomers are the methylene groups and the ethylene-acrylic acid copolymer segments. The mobility of these latter decreases upon neutralization and above a critical degree of neutralization a phase consisting of polyethylene segments attached to ionic clusters forms. The crystalline structure of the polymer contains primary and secondary crystallites. The amount and regularity, i.e. lamella thickness, of the latter decrease with increasing neutralization. Multiplets form from ionic species already at a small degree of neutralization and then they associate into clusters with increasing size as ion content increases. The mechanical properties of the ionomers are determined by their crystalline structure and cluster formation. Clusters increase strength and modulus, while decrease deformability. The combined effect of the two factors (crystallinity, cluster size) on stiffness was successfully described by a simple model.

Controlling the Chain Folding for the Synthesis of Single-Chain Polymer Nanoparticles Using Thermoresponsive Polymers

Synthetic polymer single-chain nanoparticles (SCNPs) are an emerging new class of nanomaterials that possess similar folded structures as natural proteins. However, most SCNPs reported so far are p...

Synthesis of novel copolymer/Mn+ biomimetic adhesives based on temperature strengthened coacervation effect

Synthesis of biomimetic adhesive for achieving robust interface bonding attracts numerous attentions for various applications. Inspired by the metal ions-assisted coacervation mechanism of sandcastle worm glue, novel copolymer/Mn+ complex wet adhesives are synthesized successfully, containing hydrophobic component, bidentate anionic component and temperature sensitive component. The anionic segments in copolymer interacts with different metal ions (Ca2+/Mg2+/Cu2+) in solution through coacervation reaction along with temperature-strengthened dehydration effect, resulting in the formation of biomimetic adhesives. The wet adhesion strength of the biomimetic adhesives is tunable based on the ions species, concentrations and coordination time, while the adhesion mechanisms are analyzed and discussed in details. The biomimetic adhesives not only can be used to tightly bond two solid surfaces underwater, but also is robust and effective in air. For example, current adhesives can firmly bonding various substrates including glass, Si, PTFE and animal bone. More importantly, the biomimetic adhesives are capable of sealing leaky pipes or vessels in harsh wet environment. Due to no dopamine chemistry, current adhesives involve no oxidation problem. We firmly believe this new system would demonstrate promising applications in surface engineering, wet sealing/repairing and tissue engineering.

Analysis of Defects in Biaxially Oriented Polypropylene Films by Micro-Fourier Transform Infrared and Raman Spectroscopies

Abstract A practical method for identification of defects that occur occasionally during the production of biaxial oriented polypropylene (BOPP) films is developed. The size and morphology of the defects in the BOPP film were observed with optical microscopy, and micro Fourier transform infrared (Micro-FTIR) and Raman spectroscopies were employed to identify the chemical composition of the defects. Significant amounts of ethylene and propylene units were found in the defects, and characteristic vibrational bands for crystalline PP were observed by both IR and Raman. However, one defect exhibited IR characteristics for ordered PE whereas the other showed amorphous PE structure. These results indicate that the defects are composed of either ethylene-propylene block copolymers with long sequences of both propylene and ethylene that can form ordered structures, or ethylene-propylene segmented copolymers with long propylene sequences that can crystallize and shorter ethylene sequences that are amorphous. Possible sources of these foreign materials and corresponding mitigation measures were discussed.

Guanidine-phosphate interactions stabilize polyion complex micelles based on flexible catiomers to improve mRNA delivery

Messenger RNA (mRNA) holds great potential as therapeutic agent, though its broad applicability is hampered by its rapid degradation by nuclease attacks and poor access to cells. Polyion complex (PIC) micelles comprising block catiomers are promising mRNA carriers, because of their effective mRNA protection in the PIC core and the capability to promote mRNA cellular uptake. We have recently shown that flexible polycations can promote the interaction between catiomers and mRNA toward improving delivery efficiency, demonstrating that, by engineering the PIC formation, the efficacy of mRNA-loaded PIC micelles (mRNA/m) can be improved. Herein, we focused on the valency between the polycation segment and mRNA, and studied its ability to promote, in collaboration with the flexible catiomers, mRNA stability and delivery efficiency for producing potent nanocarriers. The functionalities of guanidine and primary amine were compared through preparation of two different block copolymers, namely, poly(ethylene glycol)-poly(glycidyl methyl guanidine) (PEG-PGMG) and PEG-poly(glycidyl methyl amine (PEG-PGMA)). mRNA/m from PEG-PGMG (mRNA/mPGMG) showed enhanced stability against biological molecules, including polyanions, urea and nucleases compared to mRNA/m prepared from PEG-PGMA (mRNA/mPGMA), resulting in high efficiency of cellular uptake and protein translation. Our results indicate that multivalent interactions between the guanidine moieties in the polycation segments of block copolymers and the phosphate groups in mRNA are a key factor for stabilizing mRNA/m toward improving mRNA delivery efficiency.

Characterization and gas transport properties of UV-irradiated polydimethylsiloxane (PDMS)-containing polyimide copolymer membranes

The influence of UV irradiation on gas permeation properties of random segmented poly (imide-siloxane) (PIS) copolymer films was investigated. Random segmented copolymers were synthesized via ester-acid imidization from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) in a 7:3 M ratio with 2,4-diamino mesitylene (DAM) and varying amounts of a diamine terminated polydimethylsiloxane (PDMS) oligomer (Mn = 3000 g/mol). Solvent cast films of these copolymers were UV-irradiated on both sides in air at 365 nm, which induced crosslinking and photooxidation. Pure-gas permeabilities of H2, O2, N2, CH4, and CO2 were measured with upstream pressures ranging from 2 to 18 atm at 35 °C. Gas permeability coefficients of a series of PIS copolymers decreased, and selectivity of all gas pairs increased after UV irradiation due to a decrease in free volume by UV crosslinking and photooxidation.

Effect of ionic liquid segments of copolymer on compatibilization process and dielectric behavior of polylactide/polyvinylidene fluoride blends

AbstractBiodegradable polylactide (PLA) and polyvinylidene fluoride (PVDF) blends containing the copolymer of PEGMA and 1‐vinyl‐3‐ethylimidazolium bromide (PMI) were prepared, and the effects of ionic liquid segments of PMI on the compatibility of PLA and PVDF were investigated by dielectric relaxation spectroscopy (DRS). PMI can obviously improve the compatibility of PLA and PVDF, compared with the copolymer of PEGMA and vinyl imidazole (PMV). DRS showed that the compatibility of PLA and PVDF was related to the relaxation behavior of the blends, which was identified with Maxwell‐Wagner‐Sillars (MWS) interfacial polarization. The ε' of PLA/PVDF/PMI blends was much higher than that of PLA/PVDF/PMV blends in the same temperature, resulting from the stimulation of MWS interfacial polarization by the ion mobility of PMI.

Light emitting, segmented block copolymers containing distyrylbenzene blocks connected through α,ω-nonamethylenedioxy chain spacer for applications in polymer light emitting diodes

Two novel, soluble, semiconducting and light emitting segmented block copolymers, termed as NPPV1 and NPPV2 are synthesized using Horner-Emmons condensation polymerization. The chromophoric groups present in the copolymers are distyrylbenzene (DSB) units substituted with rigid, bulky cyclohexylmethoxy and cyclohexylethoxy groups. The rigid blocks are linked to flexible α,ω-nonamethylenedioxy chain spacer through ether linkage. The structural, morphological, thermal and photo-physical characteristics of the synthesized polymers are studied in detail. Noticeable differences in properties arising through the substituent effects are observed for both the polymers. Detailed studies bring out quite interesting structure-property relationships between the substituents introduced in the synthesized copolymers and their crystalline properties, thermal characteristics, optical properties, photoluminescence emission and fluorescence quantum yield. Polymer light emitting diodes (PLEDs) employing these segmented polymers as emissive layers are assembled and characterized to establish their suitability for lighting applications. Using the architecture, ITO/PEDOT:PSS/NPPV1/LiF-Al, polymer light emitting diodes (PLEDs) are assembled and as the first step of device characterization, their current-voltage characteristics are studied to establish the device behavior and find out the onset voltage. The emission characteristics of the devices are then studied using Ocean Optics USB 2000 spectrometer integrated to a computer using a dedicated program. The assembled devices show Schottky junction like behavior in the current-voltage characteristics and electroluminescence emission in the blue green region with appreciable intensity at the onset voltage of 8.8 V. It is highly desirable to develop polymers showing emission in the high frequency,blue region, using cost-effective synthesis routes. The novel approaches adopted in the synthesis of the monomers and the corresponding copolymers to achieve the anticipated structure-property relationships suitable for the effective designing of polymer light emitting diodes are the highlights of the present work.

Coarse-Grained Molecular Dynamics Modeling of Segmented Block Copolymers: Impact of the Chain Architecture on Crystallization and Morphology

We extend our recent coarse-grained model describing semicrystalline homopolymers to simulate the morphology and phase transitions of thermoplastic elastomers made of segmented (hard/soft) block copolymers. The generic model is adapted to match the physical characteristics of the two chemical units involved in the copolymer chains by using classic scaling rules. We investigate the crystallization kinetics of the hard segments as well as their phase separation from the soft units in either triblock or pentablock copolymers. We identify the soft segment molecular weight as a key parameter resulting in the following observations when decreasing the temperature from a homogeneous state. On the one hand, the phase separation preceding the crystallization process in triblock copolymers results in a constant temperature of crystallization when varying the soft segment length. On the other hand, the limited phase separation achieved in pentablock copolymers constrains them to crystallize at progressively lower temperatures while increasing the soft segment length. Finally, increasing the soft segment molecular weight was found to lead to a higher relative crystallinity which can be interestingly related to a rise of the loop segment’s content.

Lithium Salt Distribution and Thermodynamics in Electrolytes Based on Short Perfluoropolyether-block-Poly(ethylene oxide) Copolymers

Wide-angle X-ray scattering (WAXS) was used to study the distribution of salt in short-chain disordered block copolymer electrolytes with concentration fluctuations on the length scale of 1 nm. The electrolytes were binary mixtures of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and a short block copolymer comprising perfluoroether (PFE) segments covalently bonded to ethylene oxide (EO) segments. We develop a method to analyze scattering data from mixtures of block copolymers and salt where salt distribution is not known beforehand, using a minimal number of adjustable parameters. The WAXS peak due to scattering from disordered concentration fluctuations is fit to a random phase approximation (RPA) model that includes a parameter to describe the partitioning of salt between the perfluoropolyether (PFPE)-rich and poly(ethylene oxide) (PEO)-rich concentration fluctuations. This method enables quantification of the salt distribution and the effective Flory–Huggins interaction parameter between polymer segments. We posit that attractive interactions between the TFSI– anion and PFPE (fluorous effect) drive some of the salt into the PFPE-rich fluctuations. On the other hand, the attractive interactions between Li+ and EO segments drive the remaining salt molecules into the PEO-rich fluctuations. We use WAXS to quantify LiTFSI partitioning between the PFE and EO segments in the block copolymer. The segregation between blocks, quantified by an effective Flory–Huggins interaction parameter between polymer segments, decreases with increasing salt concentration, behavior that is atypical for block copolymer electrolytes.

Microstructure and Mechanical/Elastic Performance of Biobased Poly (Butylene Furanoate)-Block-Poly (Ethylene Oxide) Copolymers: Effect of the Flexible Segment Length.

The aim of this paper is to extend knowledge on biobased poly(butylene furanoate)–block–poly (ethylene oxide) (PBF-b-PEO) copolymers’ performance by studying the effect of the PEO segment’s molecular weight on the microstructure and materials behavior. As crystallization ability of PEO depends on its molecular weight, the idea was to use two PEO segment lengths, expecting that the longer one would be able to crystallize affecting the phase separation in copolymers, thus affecting their mechanical performance, including elasticity. Two series of PBF-block-PEOs with the PEO segments of 1000 and 2000 g/mol and different PBF/PEO segment ratios were synthesized by polycondensation in melt, injection molded to confirm their processability, and subjected to characterization by NMR, FTIR, DSC, DMTA, WAXS, TGA, and mechanical parameters. Indeed, the PEO2000 segment not only supported the crystallization of the PBF segments in copolymers, but at contents at least 50 wt % is getting crystallizable in the low temperature range, which results in the microstructure development and affects the mechanical properties. While the improvement in the phase separation slightly reduces the copolymers’ ability to deformation, it is beneficial for the elastic recovery of the materials. The investigations were performed on the injection molded samples reflecting the macroscopic properties of the bulk materials.

Synthesis of nano-capsules via aqueous emulsion RCMP-PISA and encapsulation

Synthesis of nano-capsules using aqueous RCMP-PISA and encapsulation of rhodamine-B (Rh-B).