Phthalonitrile Blends: Simple Way to Improve Physical Properties by Increasing Crosslinking Density

A method to improve the mechanical properties of phthalonitrile (PN) resins at lower postcure temperatures is achieved by blending a second‐generation oligomeric aromatic ether ketone‐based PN resin with 1,1,1‐tris‐[4‐(3,4‐dicyanophenoxy)phenyl]ethane in varying concentrations. Most of the mixtures exhibit a single softening temperature indicating that the two resins are miscibile in one another at the respective concentrations. After various blends are thermally cured to several postcure temperatures yielding crosslinked polymers, the polymers demonstrate superb mechanical properties and thermooxidative stability at lower overall postcure temperatures.     

Synthesis and Properties of a High‐Temperature Naphthyl‐Based Phthalonitrile Polymer

A novel, high‐temperature, naphthyl‐based phthalonitrile polymer is prepared. The phthalonitrile monomer, namely, 2,7‐bis(3,4‐dicyanophenoxy) naphthalene (BDCN), is synthesized from the reaction of 2,7‐dihydroxynaphthalene (DHN) with 4‐nitrophthalonitrile (NPN), and its curing behavior with 1,3‐bis(4‐aminophenoxy) benzene (APB) is investigated by DSC. The high‐temperature BDCN polymer is prepared via a two‐step approach: the preparation of the BDCN prepolymer and the post‐cure of the BDCN prepolymer at elevated temperatures. The BDCN polymer might form a polypyrrole structure as revealed by FTIR spectroscopy, and exhibits a high storage modulus, high glass‐transition temperature, and outstanding thermal stability, along with long‐term oxidative resistance.     

Temperature‐Responsive Electrophoretic Deposition of Sulfone‐Containing Nonionic Poly(N‐isopropylacrylamide)

Recently, it has been found that nonionic aliphatic and aromatic poly(ester sulfone)s show anode selective electrophoretic behavior, and it is shown that the electrophoresis is induced by a partial charge separation of the protic solvent at the dispersion interface. In this paper, the first example of temperature‐responsive electrophoretic deposition (EPD) is reported. Electrophoresis of a nonionic sulfone‐containing poly(N‐isopropylacrylamide) [poly(NIPAM)] is performed above the lower critical solution temperature. The poly(NIPAM) is prepared via reversible addition–fragmentation chain transfer radical copolymerization of NIPAM with a sulfone‐containing methacrylate. After EPD, adhesion of human umbilical vein endothelial cells on the deposited surfaces is also demonstrated, aiming at the subsequent temperature‐sensitive detachment.     

Preparation and Characterization of Fully Furan‐Based Renewable Thermosetting Epoxy‐Amine Systems

Fully furan‐based epoxy/amine thermosetting materials are prepared and investigated using a furanyl epoxy monomer, 2,5‐bis[(2‐oxiranylmethoxy)methyl]‐furan (BOF), and two furanyl amine hardeners, 5,5′‐methylenedifurfurylamine (DFDA) and 5,5′‐ethylidenedifurfirylamine (CH₃‐DFDA). These furan‐based thermosets have shown promising glass transition temperatures (62 and 69 °C, respectively, using tan delta) and room temperature storage moduli (≈3.5 GPa). The BOF/CH₃‐DFDA sample is exhibited higher T_g than the BOF/DFDA system due to the presence of an additional methyl group in CH₃‐DFDA. Used as curing agents for DGEBA, DFDA and CH₃‐DFDA have shown excellent performance with resulting T_gs well above 120 °C. Onset degradation temperature of the fully furan‐based samples is observed around 270 °C with high char yields (≈40 wt%) at 750 °C in argon. Based on their thermal and mechanical properties, the renewable fully furan‐based thermosets are found suitable for coating, adhesive, and composite applications, and are therefore potential replacements for incumbent systems.

     

A Highly Efficient One‐Pot Method for the Synthesis of Carbon Black/Poly(4,4′‐Diphenylether‐1,3,4‐Oxadiazoles) Composites

A series of polyoxadiazoles (PODs) based composites containing carbon black (CB) are prepared through a fast polycondensation reaction of hydrazine sulfate and dicarboxylic acid monomers using poly(phosphoric acid) (PPA) as reaction medium. In order to achieve a homogeneous dispersion of CB, a predispersion step is applied to the CB prior to the synthesis. The moderate acidic nature and high viscosity of the PPA medium promote the oxidation of the CB and suppress reaggregation after dispersion. The carboxylic groups generated on the surface of the CB effectively anchored the growing of POD chains, improving the interfacial interaction between the CB and the surrounding matrix. An increase of 22% in storage modulus at 100 °C is observed. The tensile strength increases up to 48% with the CB addition and the elongation at break increases up to 118% at a low concentration of CB (0.5 wt.‐%). The resultant CB/POD composites, which can be cast as dense films, are soluble in several polar aprotic solvents and their POD matrix have molecular weights in the range of 10⁵ g · mol⁻¹. The high‐performance, high‐temperature light‐weight materials obtained are thermally stable at temperatures as high as 450 °C.

     

Characterization of Eumelanin as an Additive in High-Temperature Phthalonitrile-Based Resin Blends

Bio-manufactured eumelanin is investigated as a sustainable high-char carbon additive for use with moldable high temperature resins. Blends of Bisphenol A poly-ether-ether-ketone (PEEK)-based phthalonitrile (PN) with 0–30 wt% melanin are prepared and characterized for their compositional, thermal, and mechanical properties. Although the char yield increases from 10 to 30 wt% melanin loading, the presence of melanin decreases the thermal stability compared to PN resin alone. Despite this, the melanin-PN resins still maintain a very high char yield (>64%) up to 1000 °C under nitrogen. Rheology, thermal analysis, and mechanical measurements suggest off-gassing of the melanin and increased crosslinking between the melanin and PN, leading to a lower flexural strength resin with higher additive loadings. Spectroscopic studies suggest possible interaction between melanin and PN during co-curing, which ultimately can affect the processing and final properties of melanin-additive composite materials.     

Preparation and Characterization of Highly Bio‐Based Epoxy Amine Thermosets Derived from Lignocellulosics

The development of chemicals from renewable sources as replacements for current toxic and unsustainable petrochemicals is an area of expanding study and interest. Phenolic epoxies derived from lignin, an underutilized resource generated as waste by the pulp and paper industry, and furanyl–amine epoxy curing agents derived from cellulosic biomass, are already proven independently to yield thermosetting resins possessing adequate thermal and thermomechanical properties. In this work, the union of the aforementioned technologies is examined to determine the properties and characteristics of such highly bio‐derived epoxy and amine thermosets. Resins with bio‐derived carbon content greater than 97% are synthesized and characterized via Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Lignin‐derived epoxy resins are found to be compatible with a cellulose‐derived furanyl diamine curing agent to produce thermosetting resins with good thermomechanical and thermogravimetric properties, rivaling the levels of properties exhibited by similar commercial petroleum‐derived systems, indicating viability for replacing petroleum‐based polymers in high‐temperature applications.

     

Reconfigurable Poly(urea‐urethane) Thermoset Based on Hindered Urea Bonds with Triple‐Shape‐Memory Performance

Thermoset shape memory polymers (SMPs) have a series of advantages in practical applications when compared with thermoplastic SMPs. However, the reprocessing and reshaping of thermosets are difficult due to the covalent crosslinking which severely limits the reconfiguration of polymer networks even under high temperature. Here, hinered urea bond (HUB), a urea bearing a bulky substituent on its nitrogen atom that can reversibly dissociate to the corresponding bulky amine and isocyanate, is integrated into the poly(urea‐urethane) (PUU) crosslinked networks, enabling the networks to topologically reconfigure to other structures. Instead of having to cure the thermoset in a mold, the incorporation of HUBs can decouple the synthesis and shape‐forming steps, which is a huge advantage for the processing of thermoset materials compared to conventional thermosets. This new PUU thermoset shows a broad glass transition behavior and exhibits excellent triple‐shape‐memory performance. With the incorporation of this dynamic urea bonds, permanent shapes can be flexibly tuned via the network reconfiguration, which is often neglected but significant to the practical application of SMPs.     

Synthesis and Photopolymerization of Thiol‐Modified Triazine‐Based Monomers and Oligomers for the Use in Thiol‐Ene‐Based Dental Composites

Thiol‐ene photopolymerizations combine the unique features of step‐growth reactions and photoinitiated polymerizations, so that they experience a growing interest for applications such as coatings or dental restoratives. Most studies have making use of a relatively flexible ester and the hydrolytically labile derivative pentaerythritoltetra(3‐mercaptopropionate) ( PETMP ) as the thiol component in common. In this study, the performance of hydrolytically stable 1,3,5‐tris(3‐mercaptopropyl)‐1,3,5‐triazine‐2,4,6‐trione ( 4a ), 1,3,5‐tris(2‐methyl‐3‐mercapto‐propyl)‐1,3,5‐triazine‐2,4,6‐trione ( 4b ), and oligomers thereof in thiol‐ene photopolymerizations is investigated. The oligomers are prepared via thiol‐Michael or thiol‐isocyanate additions by using 4a and suitable diacrylates or diisocyanates containing a rigid core structure. Compared with PETMP , the thiol derivative 4a shows better flexural strength and modulus of elasticity in thiol‐ene photopolymerizations with 1,3,5‐triallyl‐1,3,5‐triazine‐2,4,6‐trione ( TATATO ) as the‐ene derivative. This phenomenon becomes especially evident after storage in water at 37 °C for 24 h. Furthermore, the performance regarding the flexural strength, the Young's modulus of elasticity, the polymerization shrinkage stress of 4a , and the polyadducts thereof in dental filling composites is evaluated and discussed.

     

Modification of Solventless‐Synthesized Benzoxazine Resin by Phthalonitrile Group: An Effective Approach for Enhancing Thermal Stability of Polybenzoxazines

Although the solventless method for synthesizing benzoxazine resins has the advantage of low cost, the impurities involved in the products such as oligomers and original phenols significantly weaken the properties of polybenzoxazines. Herein, the commercialized BA‐a (benzoxazine derived from bisphenol‐A, aniline, and formaldehyde) resin obtained from a solventless method is modified by phthalonitrile through the reaction between phenol groups and 4‐nitrophtahlonitrile. The structures of obtained resins have been confirmed by ¹H and ¹³C nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR). In addition, the ring‐opening polymerization behavior of each resin has been studied by differential scanning calorimetry and in situ FTIR. Furthermore, the thermal properties of the cross‐linked thermosets were measured by thermomechanical analysis and thermogravimetric analysis. The phthalonitrile‐functionalized benzoxazine resin shows a low polymerization temperature with the maximum of exothermic peak centered at 218.7 °C, and its corresponding polybenzoxazine exhibits excellent thermal stability, with a high Td₅ value (346 °C) and high char yield (42.78%).     

Synthesis of Functional Sugar‐Based Polyurethanes

Three new polyurethanes (PUs) with multiple pendant allyl groups were synthesized from L ‐arabinitol as versatile materials for the preparation of tailor‐made PUs with varying degrees of functionalization. Their allyl functional groups can take part in thiol‐ene reactions to obtain greatly diverse materials. Thus, six new highly functional PUs were prepared by click chemistry to give polymers with NHBoc [NH‐CO‐OC(CH₃)₃], amino, carboxylic, and 1,2‐dihydroxyethyl side groups. The thermal stability of the novel PUs was investigated by thermogravimetric analysis and differential scanning calorimetry. This strategy provides a simple and versatile platform for the design of new materials whose functionality can be easily modified to anchor diverse biologically active molecules.     

Improved Bloch‐Siegert based B1 mapping by reducing off‐resonance shift

An MRI method based on the Bloch‐Siegert (BS) shift phenomenon was recently proposed as a fast and precise way to map a radio frequency (RF) transmit field (B₁⁺ field). For MRI at high field, the mapping sensitivity of this approach was limited by tissue heating associated with a BS irradiation pulse. To mitigate this, we investigated the possibility of lowering the off‐resonance frequency of this pulse since theoretical analysis indicated that the sensitivity of Bloch‐Siegert based B₁⁺ mapping could be substantially improved when irradiating closer to resonance. Using optimized irradiation pulse shape and gradient crushers to minimize direct excitation effects, in vivo experiments on human brains at 7 T confirmed improved sensitivity with this approach. Improved sensitivity translated into an 80% reduction in B₁⁺ estimation errors without increasing tissue heating. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Synthesis and Properties of Novel Fluorinated Poly(phenylene‐co‐imide)s

A new class of high‐performance materials, fluorinated poly(phenylene‐co‐imide)s, were prepared by Ni(0)‐catalytic coupling of 2,5‐dichlorobenzophenone with fluorinated dichlorophthalimide. The synthesized copolymers have high molecular weights ( = 5.74 × 10⁴–17.3 × 10⁴ g · mol^?1), and a combination of desirable properties such as high solubility in common organic solvent, film‐forming ability, and excellent mechanical properties. The glass transition temperature (T_gs) of the copolymers was readily tuned to be between 219 and 354 °C via systematic variation of the ratio of the two comonomers. The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 66.7–266 MPa, 2.7–13.5%, and 3.13–4.09 GPa, respectively. The oxygen permeability coefficients ( ) and permeability selectivity of oxygen to nitrogen ( ) of these copolymer membranes were in the range of 0.78–3.01 barrer [1 barrer = 10^?10 cm³ (STP) cm/(cm² · s · cmHg)] and 5.09–6.25, respectively. Consequently, these materials have shown promise as engineering plastics and gas‐separation membrane materials.

     

High‐Performance Bio‐Based Benzoxazines from Enzymatic Synthesis of Diphenols

This paper reports the preparation, characterization, and performance of three low viscosity fully bio‐based benzoxazine resins synthesized from bio‐based furfurylamine, paraformaldehyde, and three new enzymatic originated diphenols obtained through a sustainable and highly selective lipase‐catalyzed enzymatic process from p‐coumaric acid, and three bio‐based diols (propanediol, butanediol, and isosorbide, respectively). The enzymatic method is used for the first time, to the authors’ knowledge, to design specific diphenolic structures dedicated to the preparation of benzoxazine thermosetting resins whose precursors exhibit easy handling within a wide processing window (from room temperature up to 200 °C). The resulting cross‐linked materials present high glass transition temperature (T _g > 200 °C) and inherent charring ability upon pyrolysis (≈50 wt% at 1000 °C). These results open a valuable and new pathway to develop enhanced benzoxazines and bring them new properties.     

Joint Effect of Poly(ethyhlene‐co‐1‐octene) Chain Length and 1‐Octene Fraction on High‐Temperature Thermal Gradient Interaction Chromatography

High‐temperature thermal gradient interaction chromatography (HT‐TGIC) fractionates polyolefins based on an adsorption–desorption mechanism. Several factors influence the shape and position of HT‐TGIC chromatograms, notably polymer microstructure, analytical conditions, and, to a lesser extent, solvent type. This article investigates the joint influence of chain length and comonomer content of a series of polyethylene and ethylene/1‐octene copolymers having similar 1‐octene fractions (0–13 mol%) and a wide range of molecular weights on HT‐TGIC fractionation. For each series of copolymers having similar 1‐octene fraction, the elution peak temperature decreases exponentially and the profiles become increasingly broader below a critical number average chain length value. The authors use Monte Carlo simulation and Stockmayer distribution to explain the observed behavior, finding that no simple correlation exists between ethylene sequences in the copolymers and peak elution temperature, but that there is strong evidence that axial dispersion is responsible for symmetrical broadening of the HT‐TGIC profiles. The authors also study the HT‐TGIC of binary blends, finding that components with similar 1‐octene contents and dissimilar chain lengths tend to increase co‐adsorption/co‐desorption effects.

     

Novel Phosphorous‐Containing Aromatic Polyethers – Synthesis and Characterization

Summary: The synthesis of novel phosphorous‐containing aromatic polyethers P‐PEEK and P‐PSU, based on poly(ether ether ketone)s (PEEK) and poly(ether sulfone)s (PSU) was carried out successfully by using phosphorous‐containing aromatic diols instead of bisphenol A in the usual synthesis procedure. The molecular weights of the P‐PEEKs and P‐PSUs obtained reflect both the influence of the different halogen components used and the lower thermal stabilities of the phosphorous‐containing diols compared to bisphenol A. However, polymers with sufficient molecular weights could be obtained, having interestingly high T_gs, high thermal stabilities as well as modified flame retardance properties depending on the diol type incorporated.

Comparison of the molecular weights of the synthesized P‐polyethers.     

Polyhedral Oligomeric Silsesquioxane‐ and Fullerene‐End‐Capped Poly(ε‐caprolactone)

Novel fullerene‐ and polyhedral oligomeric silsesquioxane‐ (POSS) double end‐capped poly(ε‐caprolactone) (PCL) were successfully synthesized. The crystallization behavior of the fullerene‐ and POSS‐ double end‐capped PCL and the effect of aggregation of the POSS and fullerene moieties on the crystallization of PCL were thoroughly studied. The aggregation of the fullerene moieties has much larger confinement effect on the crystallization of PCL than that of POSS. The successful incorporation of two nano‐sized objects, that is, fullerene and POSS, into the PCL matrix may introduce their merits, so that PCL can attain multi‐functional properties.

     

Modification of Oligomeric Cyanate Ester Polymer Properties with Multi‐Walled Carbon Nanotube‐Containing Particles

The properties of an oligomeric cyanate ester polymer were modified by the addition of 0.01–3 wt.‐% multi‐walled carbon nanotube (MWNT) containing particles. The dynamic mechanical behavior and thermal properties of the cyanate ester/MWNT nanocomposites were evaluated. The storage modulus, G′, of the nanocomposite with 1 wt.‐% MWNT particles was nearly 60 and 600% higher than the neat polymer at 100 and 200 °C, respectively. The glass transition temperature of the nanocomposite was also raised by 30 °C and its thermal stability in air and nitrogen was increased by 58 and 25 °C, respectively. The property improvements are attributed to reinforcement of the cyanate ester as a result of good nanotube dispersion and effective polymer‐MWNT interaction.

     

Syntheses of Biaxially Extended Octithiophene‐Based Conjugated Copolymers for High‐Open‐Circuit‐Voltage Photovoltaic‐Cell Applications

Novel biaxially extended octithiophene (8T)‐based conjugated polymers are successfully ­synthesized using Stille coupling reactions of the branched octithiophene moiety with seleno­phene (P8TSe), thiophene (P8TT), and thieno[3,2‐b]thiophene (P8TTT). The 8T moiety can signifi­cantly lower the highest occupied molecular orbital (HOMO) level and leads to an enhanced open‐circuit voltage because of the branched conformation. The power conversion efficiencies (PCE) of the polymer/[6,6]‐phenyl‐C71‐butyric acid methyl ester PC₇₁BM photovoltaic cells are in the range of 1.28–2.30%. In particular, the P8TTT‐based device processed from an o‐dichlorobenzene/1,8‐diiodoctane mixed solvent shows the best PCE among the studied polymers (2.81%), demonstrating that 8T‐based polymers with a low HOMO level can emerge as promising candidates for organic device applications.

     

MR‐monitored focused ultrasound using the acoustic‐coupling water bath as an intrinsic high‐mode dielectric resonator

The conventional set‐up for MR‐monitored focused ultrasound surgery includes a piezoelectric transducer and an acoustic‐coupling water bath integrated into the MR patient table; a large surface RF coil is placed close to the patient or, alternatively, the body coil is used as the MR receiver. Potential disadvantages of this approach are that the body coil has low sensitivity because of its low filling factor and the local RF coil can interfere with and cause reflections of the ultrasound irradiation. In this article, a completely new approach is presented, in which an MR transmit/receive coil is not needed at all. Instead, the dimensions of the water bath are adjusted so that a high‐order dielectric mode is excited, resulting in efficient MR excitation and reception at the transducer focal point. An example of monitoring ultrasound‐mediated heating in a phantom is shown on a 7‐T human system, although the new method can also be applied at lower fields. Copyright © 2014 John Wiley & Sons, Ltd.