Polystyrene Chains Research Articles

Supramolecular additive-induced conformational transition of polymer chains via π-π interaction

Controlling the conformation of polymer chains throughout melt processing is a critical factor in the development and optimization of polymer materials for a variety of applications. In this study, we present a supramolecular strategy for modulating the conformational transition of polymer and investigate the structural evolution with supramolecular additive. It is found that minute amounts (0.07–0.9 wt%) of supramolecular nucleating agent, N, N′-dicyclohexylterephthalamide (DCHT), enable polystyrene (PS) chains to adopt more gauche conformation than the trans mode when processed from the melt, resulting in higher PS chain mobility and improved PS film transmittance. The conformational transition of PS chains shows dependence on the π-π interactions between PS and DCHT molecules. By controlling the critical assembly concentration and the self-assembly behavior of DCHT in PS, it is possible to tailor the ratio of gauche to trans states and the corresponding properties of PS. We anticipate that this study will advance the design and development of supramolecular additives for tailoring the structure and properties of other polymers.

Superacid-Assisted Degradation of Polystyrene

We report the degradation pathway of polystyrene in a low-temperature environment by superacid. Polystyrene is a thermoplastic resin widely used in packaging, disposable products, and structural materials. However, economically viable upcycling of polystyrene has yet to be established because of the high cost of chemical recycling and the low value of products. To understand the degradation pathway of polystyrene and establish competitive upcycling practices, we investigated the transformation of normal and deuterated polystyrene chains into small compounds by triflic acid at 20 °C. The degradation study of deuterated polystyrene showed the high stability of the hydrogens at the α carbons of polymerized styrene against triflic acid, which suggests the known β-scission degradation pathway of polystyrene by α-proton abstraction is unlikely. Rather, the polystyrene degradation proceeds through three distinct stages: (i) intrachain cross-linking that forms polymer nanoparticles and simultaneous transformation of polymerized styrene to indan units, (ii) degradation of the polymer nanoparticles into small molecular weight compounds, and (iii) formation of polycyclic aromatic hydrocarbons. The stepwise degradation pathway of polystyrene we report may enable the design of efficient and profitable upcycling processes for end-of-life polystyrene products in low-temperature environments.

Light scattering study of intrachain conformational relaxation of hyperbranched polystyrene chains in a marginal solvent

So far, much less attention has been paid to the dynamic behavior of branched polymers under marginal solvent condition. This work reports the first study of the intrachain conformational relaxation of hyperbranched polystyrene (PS) chains under the marginal solvent condition in the dilute regime. Specifically, the solvents of ethyl acetate (EA) and toluene (Tol) are selected for comparison. By a combination of static and dynamic light scattering measurements, a few findings have been revealed: 1) the weight average of molar masses (Mw) of hyperbranched PS chains are determined to be 7.33 × 107 and 8.02 × 107 g/mol in Tol and EA, respectively, implying the single chain state under both solvent conditions; 2）the value of reduced first cumulant (Γ*) at very high q-regime, i.e., Γ*(∞), is determined to be around 0.026 ± 0.002 in EA, which is not only smaller than the smallest Γ*(∞) ≈ 0.052 ± 0.002 reported for linear chains in literature under theta and good solvent conditions, but also much smaller than the reported Γ*(∞) ≈ 0.033 ± 0.003 for hyperbranched chains in literature under good solvent condition, and the result implies the reduced hydrodynamic interactions. Although the excluded volume effect is relatively weak in the marginal solvent, the present study supports that the existence of weak binary interactions between segments still influence the conformational behavior significantly.

The Effect of Divinylbenzene on the Structure and Properties of Polyethylene Films with Related Radiation Chemical Grafted Polystyrene and Sulfocationite Membranes.

In the present work, the effect of divinylbenzene (DVB) on the kinetics of post-radiation chemical graft polymerization styrene (St) on polyethylene (PE) film and its structural and morphological features were investigated. It has been found that the dependence of the degree of polystyrene (PS) grafting on the DVB concentration in the solution is extreme. An increase in the rate of graft polymerization at low concentrations of DVB in the solution is associated with a decrease in the mobility of the growing chains of PS. A decrease in the rate of graft polymerization at high concentrations of DVB is associated with a decrease in the rate of diffusion of St and iron(II) ions in the cross-linked network structure of macromolecules of graft PS. A comparative analysis of the IR transmission and multiple attenuated total internal reflection spectra of the films with graft PS shows that graft polymerization of St in the presence of DVB leads to the enrichment of the film surface layers in PS. These results have been confirmed by the data on the distribution of sulfur in these films after sulfonation. The micrographs of the surface of the grafted films show the formation of cross-linked local microphases of PS with fixed interfaces.

Molecular-Weight-Dependent Infiltration and Adsorption of Polymers into Nanochannels.

The mesoporous silica shell coating hydrogenolysis nano-catalysts alters the molecular weight distributions of cleaved polymer chains compared to catalysts without a shell. The shell, composed of radially aligned narrow cylindrical nanopores, reduces the formation of low-valued gaseous products and increases the median molecular weight of the product, thus enhancing the value of the products for polymer upcycling. To understand the role of the mesoporous shell, we have studied the spatial distribution of polystyrene chains, used as a model polymer, in the nanochannels in both the melt phase and solution phase. In the melt, we observed from small-angle X-ray scattering experiments that the infiltration rate of the polymer into the nanochannels is inversely proportional to the molecular weight, which is consistent with theory. In theta solution experiments using UV-vis spectroscopy, we found that the shell significantly enhances polymer adsorption compared to nanoparticles without pores. In addition, the degree of polymer adsorption is not a monotonic function of molecular weight but initially increases with the molecular weight before eventually decreasing. The molecular weight for the peak adsorption increases with the pore diameter. This adsorption behavior is rationalized as resulting from a balance between the mixing entropy gain by surface adsorption and the conformational entropy penalty incurred by chains confined in the nanochannels. The spatial distribution of polymer chains in the nanochannels is visualized by energy-dispersive X-ray spectroscopy (EDX), and inverse Abel-transformed data reveals a less uniform polymer distribution along the primary pore axis for longer chains.

Coarse-grained modeling of polystyrene-modified CNTs and their interactions with lipid bilayers

In the present work, we describe Martini3 coarse-grained models of polystyrene and carboxyl-terminated polystyrene functionalized carbon nanotubes (CNTs) and investigate their interactions with lipid bilayers with and without cholesterol (CHOL) using molecular dynamics simulations. By changing the polystyrene chain length and grafting density at the end ring of the CNTs at two different nanotube concentrations, we observe the translocation of nanoparticles as well as changes in the lipid bilayer properties. Our results show that all developed models passively diffuse into the membranes without causing any damage to the membrane integrity, although high concentrations of CNTs induce structural and elastic changes in lipid bilayers. In the presence of CHOL, increasing CNT concentration results in decreased rates of CHOL transmembrane motions. On the other hand, CNTs are prone to lipid and polystyrene blockage, which affects their equilibrated configurations, and tilting behavior within the membranes. Hence, we demonstrate that polystyrene-functionalized CNTs are promising drug-carrier agents. However, polystyrene chain length and grafting density are important factors to consider to enhance the efficiency of drug delivery.

Microscopic mechanism of distinct mechanical properties of divinylbenzene reinforced cross-linked polystyrene revealed by molecular dynamics simulations

Molecular dynamics method was employed to establish the model of three-dimensional cross-linked polystyrene (PS) formed by divinylbenzene (DVB) and PS chains. Density, radial distribution function, free volume fraction, mean square displacement of systems with different cross-linking degrees (DVB contents of 0%, 3.8%, 7.1% and 11.1%) were studied, as well as macroscopic properties such as glass transition temperature, elastic mechanical properties, uniaxial tensile deformation. The results showed that cross-linking algorithm proposed was feasible for constructing cross-linked PS. With the increase of cross-linking degree, cross-linked PS became denser, and glass transition temperature increased, indicating an increase of heat resistance. Compared with uncross-linked PS, elastic modulus of three cross-linked systems increased by 19.26%, 29.56% and 40.19%; bulk modulus increased by 2.9%, 20.98% and 44.03%; and shear modulus increased by 21.05%, 29.82% and 42.98%. Tensile stress-strain curves showed that network structure formed by adding DVB improved yield stress and tensile resistance of PS.

Simultaneous reactions of sulfonation and condensation for high-yield conversion of polystyrene into carbonaceous material

Polystyrene (PS) was chemically treated with sulfuric acid to prepare stabilized precursors, which were converted into carbonaceous materials with high yield via subsequent carbonization. In addition to sulfuric acid, paraformaldehyde (PFA) was used to increase the crosslink density within the sulfonated PS chain networks by forming methylene bridges between phenyl rings via condensation. This transformed PS into a black glassy powder with increased crosslinking points. The carbon yield of the stabilized PS obtained after carbonization showed was considerably higher (45.3 wt%) than those of pristine PS (0 wt%) and sulfonated PS without PFA (22.4 wt%). This was attributed to its superior degree of crosslinks and the additional contribution of sulfur bridges to its thermal stability during carbonization. Further thermal treatment up to 2800 °C resulted in the formation of an intermediate structure between hard and soft carbons, which was directly revealed by microscopic images. These simultaneous reactions of sulfonation and condensation can be universally applied to various PS wastes, regardless of their shape and morphology. This suggests that the solid-to-solid transformation from PS to carbonaceous substances can be an effective and affordable method of upcycling general PS wastes.

Flow behavior of partially disentangled polystyrene chains in confined channels of anodic aluminum oxide templates

Flow behavior of partially disentangled polystyrene chains in confined channels of anodic aluminum oxide templates

Physical Aging of Polystyrene Confined in Anodic Aluminum Oxide Nanopores.

We investigated the glassy dynamics of polystyrene (PS) confined in anodic aluminum oxide (AAO) nanopores by differential scanning calorimetry. Based on the outcome of our experiments, we show that the cooling rate applied to process the 2D confined PS melt has a significant impact on both the glass transition and the structural relaxation in the glassy state. A single glass transition temperature (Tg) is observed in quenched samples, while slow-cooled PS chains show two Tgs corresponding to a core-shell structure. The former phenomenon resembles what is observed in freestanding structures, while the latter is imputed to the adsorption of PS onto AAO walls. A more complex picture was drawn for physical aging. In the case of quenched samples, we observed a non-monotonic trend of the apparent aging rate that in 400 nm pores, reaches a value almost twice as larger than what is measured in bulk and decreases upon further confinement in smaller nanopores. For slow-cooled samples, by adequately varying the aging conditions, we were able to control the equilibration kinetics and either separate the two aging processes or induce an intermediate aging regime. We propose a possible explanation of these findings in terms of distribution in free volume and the presence of different aging mechanisms.

Synthesis of Supramolecular A8Bn Miktoarm Star Copolymers by Host‐Guest Complexation

AbstractWe report a new synthetic method to construct supramolecular A8Bn (n=1, 2, 4) miktoarm star copolymers by host‐guest complexation between a resorcinarene‐based coordination capsule possessing eight polystyrene chains and 4,4‐diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A8Bn (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size‐exclusion chromatography (SEC), and diffusion‐ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase‐separated in the bulk. The micro‐Brownian motion of the A8B4 structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.

Synthesis of Supramolecular A8 Bn Miktoarm Star Copolymers by Host-Guest Complexation.

We report a new synthetic method to construct supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers by host-guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size-exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in the bulk. The micro-Brownian motion of the A8 B4 structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.

Three-Component Bolaform Giant Surfactants Forming Lamellar Nanopatterns with Sub-5 nm Feature Sizes

Nanopatterns with a sub-5 nm line width are of great interest due to their potential applications in nanotechnology. Herein, we report the design and synthesis of three-component bolaform giant surfactants that can assemble into three-phase-four-layer lamellar (LAM3) structures with sub-5 nm feature sizes. These samples consist of central linear polystyrene (PS) chains with oligodimethylsiloxane-functionalized polyhedral oligomeric silsesquioxane (SiPOSS) at one end and perfluoroalkyl-functionalized POSS (FPOSS) at the other end. Phase separation occurs among three mutually incompatible components, leading to LAM3 structures with relatively sharp interfaces and d-spacings of 12–19 nm. While the lamellar periodicity can be facilely tuned by changing the chain length of PS, the pitch widths of the POSS domains remain largely constant. Energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) were used to analyze the elemental distribution of the LAM3 structures. After oxygen plasma treatment, the morphology converts into a hierarchical lamellar structure with extremely small Si-rich layers (∼2 nm in thickness). This work suggests that these bolaform giant surfactants are versatile counterparts of traditional triblock copolymers capable of undergoing rapid and strong phase separation at relatively low molecular weights toward unconventional nanostructures with small feature sizes.

Large Optical Asymmetry in Silver Nanoparticle Assemblies Enabled by CH-π Interaction-Mediated Chirality Transfer.

Transfer of asymmetry from the molecular system to the other distinct system requires appropriate chemical interactions. Here, we show how the CH-π interaction, one of the weakest hydrogen bonds, can be applied to transfer the asymmetry from π-conjugated chiral molecules to the assemblies of plasmonic Ag nanoparticles, where the aliphatic chains of chiral molecules and the polystyrene chains grafted on Ag nanoparticles are served as the hydrogen donor and acceptor, respectively. The optical asymmetry g-factor of the chiral assemblies of plasmonic nanoparticles is strongly dependent on the molecular weight of the polystyrene ligand, the core structure of the molecule, and the aliphatic chain length of the chiral molecule. Importantly, we explore a molecular mixing strategy to enhance the asymmetry g-factor of chiral molecular assemblies, which consequently promotes the g-factor of chiral plasmonics efficiently, reaching a high value of ∼0.05 under optimal conditions. Overall, we rationalize the chirality transfer from chiral molecules to inorganic nanoparticles, providing the guidance for structural design of chiral nanocomposites with a high g-factor.

Solvent-induced assembly of mono- and divalent silica nanoparticles.

Particles with attractive patches are appealing candidates to be used as building units to fabricate novel colloidal architectures by self-assembly. Here, we report the synthesis of one-patch silica nanoparticles, which consist of silica half-spheres whose concave face carries in its center a polymeric patch made of grafted polystyrene chains. The multistage synthesis allows for a fine control of the patch-to-particle size ratio from 0.23 to 0.57. The assembly of the patchy nanoparticles can be triggered by reducing the solvent quality for the polystyrene chains. Dimers or trimers can be obtained by tuning the patch-to-particle size ratio. When mixed with two-patch nanoparticles, one-patch nanoparticles control the length of the resulting chains by behaving as colloidal chain stoppers. The present strategy allows for future elaboration of novel colloidal structures by controlled assembly of nanoparticles.

Assembly of polyelectrolyte star block copolymers at the oil-water interface.

To understand and resolve adsorption, reconfiguration, and equilibrium conformations of charged star copolymers, we carried out an integrated experimental and coarse-grained molecular dynamics simulation study of the assembly process at the oil-water interface. This is important to guide development of novel surfactants or amphiphiles for chemical transformations and separations. The star block copolymer consisted of arms that are comprised of hydrophilic-hydrophobic block copolymers that are covalently tethered via the hydrophobic blocks to one point. The hydrophobic core represents polystyrene (PS) chains, while the hydrophilic corona represents quaternized poly(2-vinylpyridine) (P2VP) chains. The P2VP is modeled to become protonated when in contact with an acidic aqueous phase, thereby massively increasing the hydrophilicity of this block, and changing the nature of the star at the oil-water interface. This results in a configurational change whereby the chains comprising the hydrophilic corona are significantly stretched into the aqueous phase, while the hydrophobic core remains solubilized in the oil phase. In the simulations, we followed the kinetics of the anchoring and assembly of the star block copolymer at the interface, monitoring the lateral assembly, and the subsequent reconfiguration of the star via changes in the interfacial tension that varies as the degree-of-protonation increases. At low fractions of protonation, the arm cannot fully partition into the aqueous side of the interface and instead interacts with other arms in the oil phase forming a network near the interface. These insights were used to interpret the non-monotonic dependence of pH with the asymptotic interfacial tension from pendant drop tensiometry experiments and spectral signatures of aromatic stretches seen in vibrational sum frequency generation (SFG) spectroscopy. We describe the relationship of interfacial tension to the star assembly via the Frumkin isotherm, which phenomenologically describes anti-cooperativity in adsorbing stars to the interface due to crowding. Although our model explicitly considers long-range electrostatics, the contribution of electrostatics to interfacial tension is small and brought about by strong counterion condensation at the interface. These results provide key insights into resolving the adsorption, reconfiguration, and equilibrium conformations of charged star block copolymers as surfactants.

End-Tethered Chains Increase the Local Glass Transition Temperature of Matrix Chains by 45 K Next to Solid Substrates Independent of Chain Length

The local glass transition temperature Tg of pyrene-labeled polystyrene (PS) chains intermixed with end-tethered PS chains grafted to a neutral silica substrate was measured by fluorescence spectroscopy. To isolate the impact of the grafted chains, the films were capped with bulk neat PS layers eliminating competing effects of the free surface. Results demonstrate that end-grafted chains strongly increase the local Tg of matrix chains by ≈45 K relative to bulk Tg, independent of grafted chain molecular weight from Mn = 8.6 to 212 kg/mol and chemical end-group, over a wide range of grafting densities σ = 0.003 to 0.33 chains/nm2 spanning the mushroom-to-brush transition regime. The tens-of-degree increase in local Tg resulting from immobilization of the chain ends by covalent bonding in this athermal system suggests a mechanism that substantially increases the local activation energy required for cooperative rearrangements.

Chain Movements at the Topmost Surface of Poly(methyl methacrylate) and Polystyrene Films Directly Evaluated by In Situ High-Temperature Atomic Force Microscopy.

The surfaces of polymeric materials are thermodynamically unstable, and the glass-transition temperature (Tg) is significantly lower than that in the bulk material. However, the mobility of the chains at the top of the surface has never been directly evaluated. In this study, the movements of the topmost chains of poly(methyl methacrylate) (PMMA) and polystyrene (PS) bulk films were observed in situ at high temperatures with atomic force microscopy in tapping mode. PMMA and PS chains started moving at ∼97 and ∼50 °C, respectively, which were slightly and significantly below the values of their bulk Tg (PMMA, 108 °C; PS, 104 °C), respectively. The activation energies of the apparent diffusion constants of PMMA and PS, derived by particle image velocimetry analysis, were 193 and 151 kJ mol-1, respectively, and reasonable for the glass transition. Movements of isolated PMMA chains deposited on a PMMA film by the Langmuir-Blodgett technique were also observed and confirmed to be essentially the same as those on the PMMA film surface.

Geometry-Modulated Self-Assembly Structures of Covalent Polyoxometalate–Polymer Hybrid in Bulk and Thin-Film States

This work reports the synthesis, characterization, and self-assembled structures of three series of Keggin-type polyoxometalate (POM)-based hybrid molecules KPOM-mPSn (m = 1, 2 and 3), in which one, two, or three polystyrene (PS) chains are covalently attached to a POM head, respectively. The classical “click” reaction was applied to prepare samples with predesigned molecular geometry, which were further purified by C18 reversed-phase high-performance liquid chromatography (RP-HPLC). Strong chemical incompatibility between inorganic POMs and organic PS chains drives the hybrid molecules to microphase separate into versatile nanostructures in both bulk and thin-film states. In thermally annealed bulk samples, four phase morphologies were found depending on both the overall molecular geometry and the volume fractions of PS tails, including lamellae (LAM), hexagonal packed cylinders (HEX), disordered micelles (DM), and body-centered cubic (BCC) packed spheres, as revealed by small-angle X-ray scattering (SAXS). In the thin-film state, LAM, HEX, and BCC structures were observed and proved by transmission electron microscopy (TEM) images and grazing incidence SAXS (GISAXS). This work expands the scope of self-assembled nanostructures of POM-based hybrid materials to spherical phases and provides a platform for the study of the basic physical principles of their self-assembly behavior.

Threading Polystyrene Stars: Impact of Star to POM‐POM and Barbwire Topology on Melt Rheological and Foaming Properties

AbstractPolymer topology highly impacts rheological melt and foaming properties. Grafting sidechains onto a linear polymer typically results in shear thinning and strain hardening in elongation flow. To study the influence of an increasing number of covalently connected polystyrene (PS) starsswith a linear PS chain (Mw,PS= 90 kg mol−1), low‐disperse branched polymers withsranging from one to four are synthesized. Each star contains approximately 12 sidechains with a length ofMw,a≈ 25 kg mol−1. Oscillatory shear measurements indicated that the zero‐shear viscosityη0scales withη0 ≈ atTref= 180 °C. Moreover, uniaxial elongation rheology allows determining the strain hardening factorSHF, which varies betweenSHF= 2–135, with increasings. Foaming experiments revealed that combining viscosity reduction with the improvement of stretchability promotes higher volume expansion ratios (VER= 3.21–10.41) and the formation of larger cells (D= 4.8–14.8 µm).