The Recent Advances of Polymer-POSS Nanocomposites With Low Dielectric Constant

This study provides a comprehensive overview of the preparation methods for polyhedral oligomeric silsesquioxane (POSS) monomers and polymer/POSS nanocomposites. It focuses on the latest advancements in using POSS to design polymer nanocomposites with reduced dielectric constants. The study emphasizes exploring the potential of POSS, either alone or in combination with other materials, to decrease the dielectric constant and dielectric loss of various polymers, including polyimides, bismaleimide resins, poly(aryl ether)s, polybenzoxazines, benzocyclobutene resins, polyolefins, cyanate ester resins, and epoxy resins. In addition, the research investigates the impact of incorporating POSS on improving the thermal properties, mechanical properties, surface properties, and other aspects of these polymers. The entire study is divided into two parts, discussing systematically the role of POSS in reducing dielectric constants during the preparation of POSS composites using both physical blending and chemical synthesis methods. The goal of this research is to provide valuable strategies for designing a new generation of low dielectric constant materials suitable for large-scale integrated circuits in the semiconductor materials domain.

Syndiospecific Copolymerization of Styrene with para-Methoxystyrene Catalyzed by Functionalized Fluorenyl-Ligated Rare-Earth Metal Complexes

The development of efficient catalysts for the copolymerization of nonpolar monomers with polar monomers remains a great challenging task in polymer synthesis. A one-pot reaction of anhydrous LnCl₃ with pyridyl-methylene-functionalized octamethylfluorenyl lithium OctFlu-CH₂PyLi in a 1:1 molar ratio, followed by alkylation with 2 equiv of LiCH₂SiMe₃ in THF afforded the fluorenyl-ligated rare-earth metal bis(alkyl) complexes (OctFlu-CH₂Py)Ln(CH₂SiMe₃)₂(THF) [Ln = Sc (1), Y (2)]. Both complexes were isolated as neutral species and were characterized by NMR spectrum and elemental analysis. Complex 2 was subjected to single-crystal X-ray diffraction, which showed that the whole modified fluorenyl ligand was coordinated to Y³⁺ in the η⁵/κ¹ mode to form a constrained geometry configuration. In the presence of excess AlⁱBu₃, and on activation with 1 equiv of [Ph₃C][B(C₆F₅)₄] in toluene, complexes 1 and 2 became active for both styrene (St) and para-methoxystyrene (pMOS) polymerization, giving polymers with high syndiotacticity (rrrr > 99%) without solvent extraction. Moreover, the ternary catalyst system composed of complex 2/AlⁱBu₃/[Ph₃C][B(C₆F₅)₄] was highly effective for the syndiospecific copolymerization of styrene with pMOS, producing random copolymers with high molecular weights and narrow molecular weight distributions. The contents of pMOS in the copolymers could be easily tuned in a wide range (11-93 mol %) by simply changing the pMOS-to-St feed ratios.

Isospecific Polymerization of Halide- and Amino-Substituted Styrenes Using a Bis(phenolate) Titanium Catalyst

Isospecific polymerization of polar styrenes is a challenge of polymer science. Particularly challenging are monomers bearing electron-withdrawing substituents or bulky substituents. Here, we report the coordination polymerization of halide- and amino-functionalized styrenes including para-fluorostyrene (pFS), para-chlorostyrene (pClS), para-bromostyrene (pBrS), and para-(N,N-diethylamino)styrene (DMAS) using 2,2′-sulfur-bridged bis(phenolate) titanium precursor (1). The combination of 1 and [Ph3C][B(C6F5)4] and AliBu3 provides crystalline poly(pFS)s with perfect isotacticity (mmmm > 95%) and high molecular weights (≤16.0 × 104 g mol−1). Upon activation with a large excess of DMAO, 1 reaches polymerization activity of 5.58 × 105 g molTi−1 h−1 producing isotactic poly(pFS)s featuring higher molecular weights (≤39.6 × 104 g mol−1). The distinguished performance of the 1/DMAO system has been extended to the polymerization of pClS and pBrS, both usually involve halogen abstraction during the polymerization, to produce isotactic and high molecular weight (Mn = 32.2 × 104 vs. 13.7 × 104 g mol−1) polymers in good activities (2.18 × 105 vs. 1.31 × 105 g molTi−1 h−1). Surprisingly, 1/DMAO is nearly inactive for DMAS polymerization, on contrary, the system 1/[Ph3C][B(C6F5)4]/AliBu3 displays isoselectivity (mmmm > 95%) albeit in a moderate activity.

On the Proton Conduction Pathways in Polyelectrolyte Membranes Based on Syndiotactic-Polystyrene

When functionalized by the solid-state sulfonation process, the amorphous regions of the semi-crystalline syndiotactic-polystyrene (sPS) become hydrophilic, and thus can conduct protons upon membrane hydration, which increases the interest in this material as a potential candidate for applications with proton exchange membranes. The resistance of sulfonated sPS to oxidative decomposition can be improved by doping the membrane with fullerenes. In previous work, we have described the morphology in hydrated sulfonated sPS films doped with fullerenes on different length scales as determined by small-angle neutron scattering (SANS) and the structural changes in such membranes as a function of the degree of hydration and temperature. In the current work, we report on the relationship between the morphology of hydrated domains as obtained by SANS and the proton conductivity in sulfonated sPS-fullerene composite membranes at different temperature and relative humidity (RH) conditions. Based on this combined experimental approach, clear evidence for the formation and evolution of the hydrated domains in functionalized sPS membranes has been provided and a better understanding of the hydration and conductivity pathways in this material has been obtained.

Recent progress in rare-earth metal-catalyzed sp2 and sp3 C–H functionalization to construct C–C and C–heteroelement bonds

The review presents rare-earth metal-catalyzed C(sp2/sp3)–H functionalization accessing C–C/C–heteroatom bonds and olefin (co)polymerization, highlighting substrate scope, mechanistic realization, and origin of site-, enantio-/diastereo-selectivity.

Synthesis and properties of block copolymers composed of norbornene/higher α-olefin gradient segments using ansa-fluorenylamidodimethyltitanium-[Ph3C][B(C6F5)4] catalyst system

A series of di- and triblock copolymers composed of gradient norbornene (NB)/α-olefin segments were synthesized by a (t-BuNSiMe₂Flu)TiMe₂-based catalyst and their physical and mechanical properties were investigated.

Kenaf fibre treatment and its impact on the static, dynamic, hydrophobicity and barrier properties of sustainable polystyrene biocomposites

Natural fibre-polymer adhesion can be improved by treating the fibre surface or polymer. In this study, resorcinol-hexamethylenetetramine mixture (R-HMT) is used as a chemical treatment for kenaf fibre waste to extend the interfacial adhesion between the fibre-polystyrene matrices. The effect of the untreated and treated kenaf fibre (designated as UK and TK fibre) on the thermal (DSC), viscoelastic, mechanical, hydrophobicity, and barrier properties of polystyrene (PS) was studied. Four different percentages of each type of fibre (10, 20, 30, and 40 wt%) were used. The chemical structure of the TK fibre was confirmed by Fourier-transform infrared spectroscopy (FT-IR) analysis. The compatibility of the fibre-polymer was investigated by scanning electron microscopy (SEM). The results showed that the use of the treated fibre at 30 wt%, enhanced the tensile strength by 148% and 212% compared to neat PS and PS/UK-30, respectively, indicating a good fibre bond adhesion. The DMA data demonstrated that the storage modulus increased significantly, especially for the PS/TK-30 composite. Meanwhile, the glass transition temperature (T_g) shifted to a lower temperature for both types of fibre. Also, the hydrophobicity of the PS composites, which was determined by thickness swelling measurements, was improved when the TK fibre was inserted. Furthermore, water vapor and oxygen transmission rates were determined. A good correlation between most of the properties for the PS composite-based treated fibre was observed, which revealed the possibility of using these materials for sustainable automotive components and gas sensitive packaging applications.

Natural fibre-polymer adhesion can be improved by treating the fibre surface or polymer.

Tethered primary hepatocyte spheroids on polystyrene multi-well plates for high-throughput drug safety testing

Hepatocyte spheroids are useful models for mimicking liver phenotypes in vitro because of their three-dimensionality. However, the lack of a biomaterial platform which allows the facile manipulation of spheroid cultures on a large scale severely limits their application in automated high-throughput drug safety testing. In addition, there is not yet a robust way of controlling spheroid size, homogeneity and integrity during extended culture. This work addresses these bottlenecks to the automation of hepatocyte spheroid culture by tethering 3D hepatocyte spheroids directly onto surface-modified polystyrene (PS) multi-well plates. However, polystyrene surfaces are inert toward functionalization, and this makes the uniform conjugation of bioactive ligands very challenging. Surface modification of polystyrene well plates is achieved herein using a three-step sequence, resulting in a homogeneous distribution of bioactive RGD and galactose ligands required for spheroid tethering and formation. Importantly, treatment of polystyrene tethered spheroids with vehicle and paradigm hepatotoxicant (chlorpromazine) treatment using an automated liquid handling platform shows low signal deviation, intact 3D spheroidal morphology and Z’ values above 0.5, and hence confirming their amenability to high-throughput automation. Functional analyses performance (i.e. urea and albumin production, cytochrome P450 activity and induction studies) of the polystyrene tethered spheroids reveal significant improvements over hepatocytes cultured as collagen monolayers. This is the first demonstration of automated hepatotoxicant treatment on functional 3D hepatocyte spheroids tethered directly on polystyrene multi-well plates, and will serve as an important advancement in the application of 3D tethered spheroid models to high throughput drug screening.

Advances in catalytic production processes of biomass-derived vinyl monomers

This review provides a summary and perspective for three bio-derived vinyl monomers – acrylic acid, methacrylic acid and styrene.

The Multilevel Structure of Sulfonated Syndiotactic-Polystyrene Model Polyelectrolyte Membranes Resolved by Extended Q-Range Contrast Variation SANS

Membranes based on sulfonated synditoactic polystyrene (s-sPS) were thoroughly characterized by contrast variation small-angle neutron scattering (SANS) over a wide Q-range in dry and hydrated states. Following special sulfonation and treatment procedures, s-sPS is an attractive material for fuel cells and energy storage applications. The film samples were prepared by solid-state sulfonation, resulting in uniform sulfonation of only the amorphous phase while preserving the crystallinity of the membrane. Fullerenes, which improve the resistance to oxidation decomposition, were incorporated in the membranes. The fullerenes seem to be chiefly located in the amorphous regions of the samples, and do not influence the formation and evolution of the morphologies in the polymer films, as no significant differences were observed in the SANS patterns compared to the fullerenes-free s-sPS membranes, which were investigated in a previous study. The use of uniaxially deformed film samples, and neutron contrast variation allowed for the identification and characterization of different structural levels with sizes between nm and μm, which form and evolve in both the dry and hydrated states. The scattering length density of the crystalline regions was varied using the guest exchange procedure between different toluene isotopologues incorporated into the sPS lattice, while the variation of the scattering properties of the hydrated amorphous regions was achieved using different H2O/D2O mixtures. Due to the deformation of the films, the scattering characteristics of different structures can be distinguished on specific detection sectors and at different detection distances after the sample, depending on their size and orientation.

Organolithium-Initiated Polymerization of Olefins in Deep Eutectic Solvents under Aerobic Conditions

Despite their ubiquitous presence in synthesis, the use of polar organolithium reagents under environmentally benign conditions constitutes one of the greatest challenges in sustainable chemistry. Their high reactivity imposes the use of severely restrictive protocols (e.g., moisture- and oxygen-free, toxic organic solvents, inert atmospheres, low temperatures, etc.). Making inroads towards meeting this challenge, a new air- and moisture-compatible organolithium-mediated methodology for the anionic polymerization of different olefins (e.g., styrenes and vinylpyridines) was established by pioneering the use of deep eutectic solvents (DESs) as an eco-friendly reaction medium in this type of transformation. Fine-tuning of the conditions (sonication of the reaction mixture at 40 °C in the absence of protecting atmosphere) along with careful choice of components of the DES [choline chloride (ChCl) and glycerol (Gly) in a 1:2 ratio] furnished the desired organic polymers (homopolymers and random copolymers) in excellent yields (up to 90 %) and low polydispersities (IPD 1.1-1.3). Remarkably, the in situ-formed polystyril lithium intermediates exhibited a great resistance to hydrolysis in the eutectic mixture 1ChCl/2Gly (up to 1.5 h), hinting at an unexpected high stability of these otherwise highly reactive organolithium species in these unconventional reaction media. This unique stability can be exploited to create well defined block-copolymers.

Syndiospecific Coordination Polymerization of Si-H-Containing Styrenes Catalyzed by Scandium Complex and Synthesis of Styrene-Based Triblock Copolymers

The controlled syndiospecific polymerization of three Si-H-containing styrenes, that is, 4-(methylhydrosilyl)styrene (FSt-1), 4-(dimethylhydrosilyl)styrene (FSt-2) and 4-(diisopropylhydrosilyl)styrene (FSt-3), is realized in the presence of (C₅ Me₄ SiMe₃ )Sc (CH₂ C₆ H₅ )₂ (THF)/[Ph₃ C][B(C₆ F₅ )₄ ]. Then a series of FSt-b-styrene-b-FSt triblock copolymers (FSt-St-FSt) are synthesized facilely via a sequential monomer feeding process (FSt-2, styrene, and FSt-2, respectively) during the polymerization. The syndiotactic polystyrene (sPS) block in the middle endows the copolymer with high melting point above 250 °C, whereas the Si-H groups on monomer FSt-2 introduce functional pendants to the end-blocks (with Si-H content of 31-63 mol%). Finally by a mild and high-effective hydrosilylation reaction, novel polar-group functionalized sPS is obtained.

BN Polystyrenes: Emerging Optical Materials and Versatile Intermediates

BN polystyrenes are an emerging class of polyolefins functionalized with aromatic side chains in which at least one CC bond is replaced with a BN bond. This class of structures exhibits unusual photophysical properties relative to organic polymers. BN polystyrenes serve as intermediates in the preparation of functional polymers, including stereoregular polar polyolefins. The consequences of BN for CC bond substitution on reactivity and properties are highlighted.

Phenol adsorption and desorption with physically and chemically tailored porous polymers: Mechanistic variability associated with hyper-cross-linking and amination

Understanding phenol adsorption-desorption mechanisms allows adsorbent tailoring to improve capacity and adsorbent reuse. Amberlite™ XAD4, a commercial styrenic polymer that is convenient to physically and chemically modify, was functionalized with dimethylamine (DMA) or trimethylamine (TMA) and/or hyper-cross-linked with 1,2-dichloroethane. These modifications were applied to enhance individual and/or synergistic phenol adsorption mechanisms, including hydrogen bonding, electrostatic interactions, and π-π dispersion forces. While XAD4-DMA adsorbs more phenol at pH = 6, XAD4-TMA has 23% higher capacity at pH = 11 due to adsorbate deprotonation that increases electrostatic interactions. Combining hyper-cross-linking with amination maximizes adsorption capacity due to synergistic impacts associated with increased micropore volume and surface affinity. Amine groups reduce desorption efficiency by 6-94% due to stronger adsorbate-adsorbent interactions compared to π-π dispersion forces. Isobutanol, which forms hydrogen bonds, is the most efficient desorption solvent, followed by chloroform, which has the same polarity index but does not hydrogen bond. n-Hexane only desorbs phenol removed with π-π dispersion forces and is not appropriate to regenerate aminated polymers. 0.1 N NaOH is an environmentally benign solvent for regenerating as-received XAD4 and XAD4-DMA, but not XAD4-TMA. Understanding phenol adsorption mechanisms allows development of physiochemically modified polymers with increased phenol adsorption capacity and regeneration efficiency.

The emerging applications of click chemistry reactions in the modification of industrial polymers

Click chemistry reactions have been applied to the modification of major industrial polymers by analysing the synthetic approaches and the resulting material properties.

Convenient synthesis of versatile syndiotactic polystyrene materials containing pendant alkenyl groups with a scandium catalyst system

The syndioselective copolymerization of styrene with five alkenyl functionalized styrenic monomers, with the use of a scandium catalyst, produced a new family of versatile syndiotactic polystyrene materials with pendant alkenyl groups.

Highly syndioselective coordination (co)polymerization of isopropenylstyrene

Coordination (co)polymerization of para-isopropenylstyrene (pIPSt) and meta-isopropenylstyrene (mIPSt), initiated by scandium (Sc) based catalysts, afforded new type of products, bearing pendant isopropenyl groups with perfect syndiotacity (rrrr > 99%).

Engineering of Syndiotactic and Isotactic Polystyrene-Based Copolymers via Stereoselective Catalytic Polymerization

This contribution presents an updated overview of the different copolymers containing stereoregular polystyrene blocks. Special emphasis is placed on syndiospecific and isospecific copolymerization of styrene with co-monomers (ethylene and α-olefins, conjugated and non-conjugated dienes, styrene derivatives, etc.). The catalytic systems involved are described and the polymerization mechanisms are discussed. Alternative approaches (simultaneous, living, chain-transfer and graft copolymerization) and the resulting detailed structures and characteristics of the copolymers are also reported.

DFT study on 1,7-octadiene polymerization catalyzed by a non-bridged half-titanocene system

For (η⁵-C₅Me₅)TiCl₂(O-2,6-ⁱPr₂C₆H₃)/MAO system, the selectivity of repeated insertion and intramolecular cyclization of 1,7-octadiene were explored in detail by DFT method.

Stereoselective copolymerization of amino-functionalized styrene with butadiene using a half-sandwich scandium complex

Stereoselective copolymerization of amino-functionalized styrene with butadiene was conducted and the influence of amino groups on the copolymerization performance was investigated.

Syndiotactic Polystyrene/Hybrid Silica Spheres of POSS Siloxane Composites Exhibiting Ultralow Dielectric Constant

Homogeneously dispersed hybrid silica/syndiotactic polystyrene composites were investigated for low-κ dielectric applications. The composites were prepared by a solution blending method, and their microstructures were analyzed by SEM, TEM, and AFM. Crystallization and phase transformation behavior of sPS were investigated using differential scanning calorimetry and wide-angle X-ray diffraction. These composites exhibited improved thermal stability and reduced thermal expansion coefficients. Promising dielectric properties were observed for the composites in the microwave frequency region with a dielectric constant (κ = 1.95) and loss (tan δ = 10(-4)) at 5 GHz.

AB2 Y-shaped miktoarm star conductive polyaniline-modified poly(ethylene glycol) and its electrospun nanofiber blend with poly(ε-caprolactone)

The aim of this study is the synthesis, and characterization of novel type AB₂ Y-shaped miktoarm star conductive polyaniline-modified poly(ethylene glycol), and preparation of its electrospun nanofibers blend with poly(ε-caprolactone).