Low Molecular Weight Polystyrene Research Articles

A new viewpoint on aging degradation of polystyrene: From the perspective of molecular weight

In the photo-oxidative aging experiments, the observed trend of the molecular weight of polystyrene (PS) differs from the expected results. By utilizing techniques such as GPC, XPS, SEM, and UV–Vis, it has been demonstrated that the molecular weight of the PS surface decreases during the initial stages of aging, but remains stable in the later stages. The stability in molecular weight is closely associated with the presence of degradation products on the surface of PS. During the experiment, the low molecular weight PS short chains dissolve in the droplets produced by the aging machine, resulting in a reduction of low molecular weight PS chains on the surface. This phenomenon contributes to the maintenance of a stable molecular weight in the later stages. Additionally, this paper introduces a novel method for describing the degree of PS aging, which offers a more intuitive understanding of the degradation process. This method focuses on the number of special patterns obtained through etching away the degradation products, having reference value.

Tri-block segmented thermoplastic elastomers of N-(aminohexyl)-N-hexylterephthalamide (6T6M) and functionalised polystyrene: Synthesis, characterization and thermal property

Abstract Low molecular weight polystyrene (PSt) containing 1,6-hexamethylenediisocyanate (HMDI) is prepared and used as soft segment. Hard segments (HS) n-(aminohexyl)-n-hexylterephthalamide (6T6M) is prepared and used for the preparation of thermoplastic elastomer. The molecular weight of the copolymer increased by increasing the hard segment content and thereby varied the HS content from 24 to 8 wt%. Inherent viscosity results prove that the synthesized polymer showed expected molecular weight and linear relationship is obtained between inherent viscosity and molecular weight of the copolymer. The 1HNMR spectrum showed expected peak which confirms the product formation. Temperature dependent FT-IR studies of the polymer reveals that the crystallinity of the HS is very high (about 90%) and the hydrogen bonding highly reversible. The thermogravimtric analysis confirms that the polymer is stable upto 420 °C. Differential calorimetric analysis showed two transition namely Tg of soft segment Tm of HS. The XRD analysis confirms the formed material is semicrystalline in nature. Swelling behaviors and solvent resisitivity confirms that the copolymer showed excellent resistivity than the PSt. Therefore the prepared copolymer is highly thermal stable with excellent solvent resisitivity.

Preparation and modification of monodisperse large particle size crosslinked polystyrene microspheres and their application in high performance liquid chromatography

The traditional seed preparation method of polystyrene was improved. Firstly, low molecular weight polystyrene seed microspheres with molecular weight of about 10,000 were successfully prepared by adding copolymer inhibitor and adjusting initiator azodiisobutyronitrile. Then, the polystyrene-divinylbenzene microspheres with large particle size were successfully prepared by the method of seed swelling polymerization, using divinylbenzene as crosslinking agent. Polystyrene-divinylbenzene polymer microspheres were characterized by scanning electron microscopy and gel permeation chromatography. The results showed that the molecular weight of polystyrene seed microspheres decreased with the increase of initiator AIBN dosage. Catechol and potassium iodide could significantly reduce the molecular weight of polystyrene seed microspheres. The size of the expanded microspheres prepared from low molecular weight seeds was controllable (up to 10 μm), with uniform particle size distribution and good monodispersity. Large size polystyrene-divinylbenzene microspheres can be used as stationary phase filler for reversed-phase chromatography, and have a good effect in the purification of industrial phytol. Sulfonated-polystyrene-divinylbenzene can be used as hydrophilic chromatographic filler to separate inosine and uridine. In addition, the baseline separation of cytosine, uracil and thymine was successfully achieved by sulfonated-polystyrene-divinylbenzene column in sodium phosphate buffer/acetonitrile mobile phase.

The role of solvent solubility parameters in the formation of intermittent low and high molecular weight polystyrene rich structures in a thin film resulting from water vapor induced phase separation

The water vapor-induced phase separation of self-similar polymer chains to form highly organized polystyrene thin films was investigated. The Hansen solubility of a set of polystyrenes was determined as a function of molecular weight. The solvent choice for the phase separation of polystyrene in thin films was investigated. Solvents with high hydrogen bonding promote the formation of intermittent phases of polystyrene film. Methyl ethyl ketone and 1,4-dioxane were found to form highly ordered structures.

Macromolecular Engineering and Additive Manufacturing of Poly(styrene-b-isobutylene-b-styrene)

Although polyisobutylene (PIB)-based thermoplastic elastomers (TPEs) possess a combination of unique properties (i.e., low permeability, high environmental and chemical stability, and excellent biocompatibility), they have not been explored for 3D printing. Poly(styrene-b-isobutylene-b-styrene) (SIBS) is one of the most important PIB-based TPEs used in biomedical applications. Herein, we report, for the first time, the development of an efficient and low-cost 3D printing strategy of SIBS by fine-tuning its microstructure and properties. We discovered that blending the polystyrene (PS) homopolymer with SIBS leads to significant changes in its microphase-separated structure. The amount and molecular weight of the added PS significantly affect the micromorphology and 3D printability of SIBS/PS blends. In particular, SIBS/PS blends with high molecular weight PS at relatively high weight fractions show a unique hierarchical salami micromorphology with appropriate properties (improved hardness, modulus, and thermal stability) for 3D printing by fused filament fabrication. SIBS/PS blends with PS molecular weight close to or higher than that of SIBS show better printability than blends with low molecular weight PS. Blending the PIB block copolymer with the homopolymer of its hard block is an efficient and cost-effective strategy for additive manufacturing of PIB-based elastomers with widely tunable properties.

Solid-state polymer adsorption for surface modification: The role of molecular weight

HypothesisSolid-state polymer adsorption offers a distinct approach for surface modification. These ultrathin, so-called Guiselin layers can easily be obtained by placing a polymer melt in contact with an interface, followed by a removal of the non-adsorbed layer with a good solvent. While the mechanism of formation has been well established for Guiselin layers, their stability, crucial from the perspective of materials applications, is not. The stability is a trade-off in the entropic penalty between cooperative detachment of the number of segments directly adsorbed on the substrate and consecutively pinned monomers. ExperimentsExperimental model systems of Guiselin layers of polystyrene (PS) on silicon wafers with native oxide layer on top were employed. The stability of the adsorbed layers was studied as a function of PS molecular weight and polydispersibility by various microscopic and spectroscopic tools as well as quasi-static contact angle measurements. FindingsAdsorbed layers from low molecular weight PS were disrupted with typical spinodal decomposition patterns whereas high molecular weight (>500 kDa) PS resulted in stable, continuous layers. Moreover, we show that Guiselin layers offer an enticing way to modify a surface, as demonstrated by adsorbed PS that imparts a hydrophobic character to initially hydrophilic silicon wafers.

Enhancing response time of micro-patterned thermoresponsive hydrogels by incorporation of pores

Micro-patterned hydrogels have received increasing attention in various research fields that need a fine structure and advanced functions compared to bulk hydrogels. For enhancing their performance, control of the size and distribution of pores in hydrogels is crucial. In particular, for the application of thermoresponsive hydrogels to a soft actuator, the characteristics of pores play an important role in enhancing the response time. We formed a porous structure in micro-patterns of polydiethylacrylamide (PDEAM), a thermoresponsive hydrogel, and analyzed the effect of pore size on the response time of the patterned hydrogels. Micro-patterned thermoresponsive hydrogels are fabricated by photo-crosslinking PDEAM copolymerized with benzophenone photo-crosslinker and polystyrene (PS) as a porogen. Pores sufficiently smaller than patterned objects, between a few micrometers to a few tens of micrometers, are successfully formed by controlling the content and molecular weight of PS. As the size and number of pores increase, the response time is improved, and the response time for swelling and deswelling is improved by up to 52 and 43% by blending PDEAM with 50 vol% of low molecular weight PS (5 kg/mol). This simple way to form a sub-millimeter scale hydrogel structure with controlled pores can be utilized in the emerging research fields, including 3D cell scaffolds, targeted drug delivery, and soft robotics.

Experimental and Numerical Analyses of n-Pentane Solubility and Diffusivity in Polystyrene/Poly(methyl methacrylate) Blends

The solubility and diffusivity of n-pentane in blends of a low-molecular weight polystyrene (PS) and a high-molecular weight poly(methyl methacrylate) (PMMA) were investigated through experimental ...

Segregation of Maghemite Nanoparticles within Symmetric Diblock Copolymer and Triblock Terpolymer Patterns under Solvent Vapor Annealing.

Block copolymers (BCPs), through their self-assembly, provide an excellent guiding platform for precise controlled localization of maghemite nanoparticles (MNPs). Diblock copolymers (di/BCP) represent the most applied matrix to host filler components due to their morphological simplicity. A series of nanocomposites based on diblock copolymer or triblock terpolymer matrices and magnetic nanoparticles were prepared to study and compare the influence of an additional block into the BCP matrix. MNPs were grafted with low molecular weight polystyrene (PS) chains in order to be segregated in a specific phase of the matrix to induce selective localization. After the mixing of the BCPs with 10% w/v PS-g-MNPs, nanocomposite thin films were formed by spin coating. Solvent vapor annealing (SVA) enabled the PS-g-MNPs selective placement within the PS domains of the BCPs, as revealed by atomic force microscopy (AFM). The recorded images have proven that high amounts of functionalized MNPs can be controllably localized within the same block (PS), despite the architecture of the BCPs (AB vs. ABC). The adopted lamellar structure of the “neat” BCP thin films was maintained for MNPs loading approximately up to 10% w/v, while, for higher content, the BCP adopted lamellar morphology is partially disrupted, or even disappears for both AB and ABC architectures.

Additive-Triggered Chain Transfer to a Solvent in Coordination Polymerization

Low-molecular-weight polystyrene (LMPS) is the precursor of a brominated styrene oligomer that is used for small, precise, thin electrical components and an environmentally benign flame-retardant m...

Wet Brush Homopolymers as “Smart Solvents” for Rapid, Large Period Block Copolymer Thin Film Self-Assembly

The spontaneous formation of periodic nanopatterns through the self-assembly of block copolymer (BCP) thin films offers an enticing path to engineer functional material properties over large areas, but the prohibitively slow ordering of ultrahigh molecular weight BCPs that generate large pattern periods (>100 nm) severely restricts the design space in which BCPs may be used. Here, we demonstrate that blending lamellae-forming polystyrene-block-poly(methyl methacrylate) diblock copolymers with very low molecular weight polystyrene and poly(methyl methacrylate) homopolymers can reduce by an order-of-magnitude the times required to form ordered large period patterns through solvent vapor annealing. Using in situ grazing-incidence small-angle X-ray scattering and ex situ electron microscopy, we show that the added homopolymer plasticizers act as a “smart solvent”: They increase the mobility of the long BCP chains by amplifying the dilution effect during solvent vapor annealing but segregate to like domains du...

Polymer-Polymer Interfacial Perturbation on the Glass Transition of Supported Low Molecular Weight Polystyrene Thin Films.

Clarifying interfacial perturbation on polymer relaxation is important for polymer material development. Herein we investigated polymer-polymer interfacial perturbation on low molecular weight (MW) polystyrene (PS) thin film (15-180 nm) glass transition by depositing various polymers atop PS films. Overall, rubbery topcoats induced Tg depression of PS thin film (below 60 nm), whileglassy topcoats induced Tg elevation of PS thin film (below 30 nm). Importantly, for the rubbery topcoat, Tg perturbation strength is largely dependent on the Tg difference between interfacial polymers and a larger Tg difference would induce stronger perturbation, while for the glassy topcoat this dependence is inconspicuous. Meanwhile, the interfacial perturbation length during PS glass transition by rubbery topcoats is estimated to be around 8 nm, while it is considered to be about 3.5 nm for glassy topcoats. The different interfacial perturbation length induced by disparate topcoats was accounted for by their different perturbation strength on adjacent PS molecules and disparate interfacial roughness. The results can promote the understanding of polymer interfacial perturbation and benefit the design and development of polymer-based materials.

Anomalous viscosity decrease of polycarbonate by addition of polystyrene

The shear viscosity of binary blends comprising polycarbonate (PC) and low-molecular-weight polystyrene (L-PS) was examined. It was found that the viscosity of PC significantly decreases by the addition of L-PS. Although the dynamic mechanical properties indicated that L-PS is immiscible with PC, the morphology observation of the extruded strand clarified that shear-induced phase-mixing occurs. Furthermore, the viscosity decrease was found to be pronounced in the high shear stress condition, which is much more obvious than that by the addition of low-molecular-weight PC. Consequently, the addition of L-PS improves the flowability at injection-molding greatly.

Efficiency enhancement of polyfluorene: Polystyrene blend light-emitting diodes by simultaneous trap dilution and β-phase formation

By diluting poly(dioctylfluorene) (PFO) with low molecular weight polystyrene (PS), electron trapping and trap-assisted recombination can be strongly suppressed. For polymer light-emitting diodes (PLEDs) consisting of a PFO:PS (1:3) blend, a doubling of the efficiency is expected owing to trap dilution. Experimentally, we observe a much larger efficiency increase of nearly an order of magnitude. The electroluminescence and photoluminescence spectra of the PFO:PS blend show a sharpening of the vibrational peaks with regard to pristine PFO with the emission maximum at 436 nm. This spectral feature is characteristic of the formation of the β-phase in PFO upon PS addition. From the analysis of the absorption spectra, the fraction of the β-phase induced by blending typically amounts to 13%. The strong PLED efficiency enhancement therefore arises from the combined effect of β-phase formation (∼4 times) and trap dilution (∼2 times).

Antimicrobial activities of low molecular weight polymers synthesized through soap-free emulsion polymerization

To evaluate the influence of low molecular weight polymers synthesized through soap-free emulsion polymerization on the indicator microorganism, Micrococcus luteus, methyl methacrylate (MMA) and styrene were polymerized by using various initiators. The MMA polymer colloid was not toxic to M. luteus. High volumes of polystyrene were continuously synthesized, and low-molecular weight polystyrenes were removed from the suspension to the supernatant. During the bioassay test, as the molecular weight of the cationic polystyrene in the supernatant decreased, the inhibition zone against M. luteus grew larger. Low molecular weight cationic polystyrene was toxic to M. luteus. Hence, the supernatant containing low molecular weight cationic polystyrenes (particularly those with molecular weights below 1000 g/mol) obtained from soap-free emulsion polymerization should be treated carefully prior to its discharge to the environment. Moreover, such supernatants should be treated with more care if they are to be discharged into seas or rivers. One solution to reduce the toxicity of the supernatant against M. luteus is the addition of N-vinylacetamide monomers during polymerization.

Impact of Molecular Weight on the Thermal Stability and the Miscibility of Poly(ε-caprolactone)/Polystyrene Binary Blends

Poly(e-caprolactone) (PCL) and two different molecular weight (6K and 650K) of polystyrene (PS) were mixed in solution to prepare binary blends of PCL/PS with various compositions. The impact of the molecular weight of PS in the blends was studied on thermal stability and miscibility by the thermogravimetric analysis (TGA) and the differential scanning calorimetry (DSC) method. The TGA results under dynamic conditions in an inert atmosphere show that the thermal stability of the blends depends on the length of PS molecules. The increase of the low molecular weight PS into the PCL/PS blend reduces the thermal stability while the high molecular weight PS improves the thermal stability. The crystallization peak temperature, enthalpy, and crystallinity of the blends are found molecular weight dependent; these parameters with blend compositions deviate from linearity of additive law for low molecular weight PS, while they do follow the additive law for high molecular weight PS. A significant melting point depression of PCL crystals with composition was observed for the blends with the incorporation of the low molecular weight PS, while the no significant melting temperature depression was observed for the high molecular weight PS. The experimental results clearly indicate that in the PCL/PS blends, the thermal stability and the interaction between the neat components strongly depend on the molecular weight of the PS.

A strategy of improving the imprinting effect of molecularly imprinted polymer: Effect of heterogeneous macromolecule crowding

The topic in the present work is to prepare molecularly imprinted polymer (MIP) in heterogeneous crowding surrounding for improving imprinting effect. For the first time, heterogeneous crowding surrounding was made up of a tetrahydrofuran (THF) solution of low molecular weight polyethene glycol (PEG) and high molecular weight polystyrene (PS). The MIP prepared in heterogeneous crowding surrounding against procyanidin B2 can display apparent imprinting effect (imprinting factor of 5.13) in the situation of difficult imprinting at single crowding surrounding or non-crowding surrounding. The necessity of simultaneous use of low and high molecular weight crowding agents for enhanced imprinting effect was further proved. NMR peak shifts of active hydrogen of procyanidin B2 strongly suggested that the interaction between functional monomer and template can be enhanced due to the effect of heterogeneous crowding in the self-assembly process. The influence of molecular weight and amount of PEG, molecular weight of PS, as well as the ratio of procyanidin B2 to functional monomer on the imprinting factor was investigated. The MIP was then used to extract purify procyanidin B2 from extract of grape seed. The recovery of procyanidin B2 obtained was 87% with relative standard deviation of less than 5%.

Engineering the Properties of Polymer Photonic Crystals with Mesoporous Silicon Templates

The effect of molecular weight on the rate and extent of melt-infiltration of polystyrene into mesoporous silicon-based photonic crystals is investigated as a function of polymer molecular weight. Polymer viscosity and chain end-to-end (Ree) distance correlate with the rate and extent of infiltration. High molecular weight (Mw) polystyrene (200 or 400 kDa) infiltrates the mesoporous material in two distinct phases: a rapid phase where the larger pores of the template are filled, followed by a slower phase during which the smaller pores fill. Low molecular weight polystyrene (20 and 35 kDa) fills the pores more uniformly, progressing into the film as a single, relatively distinct front of liquid polymer. Scanning electron microscope (SEM) analyses of cross sections of the films are consistent with the optical measurements, showing a lower extent of infiltration for the higher molecular weight polymers. Removal of the porous Si templates by soaking in a chemical etchant generates free-standing films of nanostructured polymer. The low molecular weight samples display better replication. Partial removal of the template enables tuning of the hydrophobicity of the free-standing polymer films, which is demonstrated with a flexible and chemically stable polyvinylidene fluoride polymer.

Dramatic Tunability of the Glass Transition Temperature and Fragility of Low Molecular Weight Polystyrene by Initiator Fragments Located at Chain Ends

Important, yet unexplored effects of chemically distinct initiator fragments incorporated at chain ends in linear polymer are investigated in depth. Polystyrene (PS) samples of a wide range of molecular weight (MW) were synthesized by conventional free radical polymerization and controlled radical polymerization using seven different initiators and compared with anionically polymerized PS. The initiator fragments incorporated during polymerization have major consequences on the glass transition temperature (Tg) and dynamic fragility of low MW PS. For example, with ∼4 kg/mol PS, the Tg onset value and fragility can be tuned from ∼334 K and ∼65, respectively, with dodecanethiol and hydrogen atom chain ends to ∼367 K and ∼130, respectively, with cyanopentanoic acid chain ends. A similar high Tg and high fragility were measured with isobutyric acid/SG1 nitroxide chain ends. These remarkable effects, with a greater than 30 K difference in Tg and a factor of 2 difference in fragility, indicate that chain ends i...

Fabrication of cage-like particles via unstable seeded dispersion polymerization: A new concept in the polymerization-induced self-assembly

ABSTRACTThe formation mechanism of hollow micron-sized polystyrene (PS) particles having numerous dents on the surface, so-called cage-like particles, obtained from seeded dispersion polymerization (SDP) of 2-ethylhexyl methacrylate (EHMA) with low molecular weight (MW) PS particles stabilized by poly(vinyl alcohol) (PVA) in the presence of hexadecane droplets was investigated. It was found that association of poly(2-ethylhexyl methacrylate) (PEHMA)/hexadecane phases which occurs due to the instability of the obtained composite particles followed by a diffusion of PS ellipsoidal particles into each other is the main process responsible for the production of such unique morphology. Time course monitoring of the SDP showed that diffusion of hexadecane and/or PS and/or PEHMA phase into PS/PEHMA/hexadecane composite particles through PS shell which happens based on Ostwald ripening is the main phenomenon which results in the formation of the dents on the surface of final particles. Moreover, the experimental results revealed that in this reaction system, the polymerization develops in a faster manner rather than the SDP employing seed particles having higher MWs. Furthermore, it was observed that particles with different surface morphologies can be produced by using different hydrocarbons. The elimination of small particles which are produced in addition to the cage-like ones via decreasing the concentration of the stabilizer was another interesting finding of this research. The acquired results showed that unstable SDP is expected to be a new concept in polymerization-induced self-assembly (PISA) which employs instability of a dispersion for self-assembly of polymeric particles, and therefore, production of polymeric unique objects.