Is a Vitrimer with a High Glass Transition Temperature Available? A Case Study on Rigid Polyimides Cross-Linked with Dynamic Ester Bonds.

Vitrimers, possessing associative covalent adaptable networks, are cross-linked polymers exhibiting malleable (glass-like) feature and recyclable and reprocessable (thermoplastics-like) properties. The dynamic behaviors of vitrimer are dependent on both chain/molecular mobility (glass transition temperature, Tg) and dynamic bond-exchanging reaction rate (topology freezing transition temperature, Tv). This work aims on probing the effect of high Tg on the stress relaxation and physical recyclability of vitrimers, employing a polyimide cross-linked with dynamic ester bonds (Tg: 310 °C) as the example. Due to its high Tg and chain rigidity, the cross-linked polyimide does not exhibit a high extent of stress relaxation behavior at 320 °C (10 °C above its Tg), even though the temperature is much higher than the hypothetical Tv. While raising the processing temperature to 345 °C, the cross-linked polyimide exhibits a stress relaxation time of about 3300 s and physical malleability. Nevertheless, side reactions may occur in the recycling and reprocessing process under the harsh condition (high temperature and high pressure) to alter the thermal properties of the recycled sample. The diffusion control plays a critical role on the topography transition of a vitrimer having a high Tg. The Tg ceiling is noticeable for developments of vitrimers.

Reaction between 1,3,5-Triisopropylbenzene and Elemental Sulfur Extending the Scope of Reagents in Inverse Vulcanization.

Inverse vulcanization utilizes an organic compound as reagent for crosslinking elemental sulfur to result in corresponding polymeric material with a high sulfur content. This work, employing 1,3,5-triisopropylbenzene (TIPB) as the reagent, demonstrates the first attempt on extending the scope of crosslinking agents of inverse vulcanization to saturate compounds. Under nuclear magnetic spectroscopic analysis, the reactions between TIPB and elemental sulfur take places through ring-opening reaction of S8 resulting in sulfur radicals at sulfur chain ends, radicals transferring to isopropyl groups of TIPB, and radical coupling reactions between carbon radicals and sulfur radicals. The obtained products are similar to the sulfur polymers from conventional inverse vulcanization processes and show self-healing property.

Effect on thermal stability of microstructure and morphology of thermally-modified electrospun fibers of polybenzoxazines (PBz) blended with sulfur copolymers (SDIB).

Simple modification by thermal treatment is the commonly used approach to enhance the performance of electrospun fibers. This was investigated in the thermal treatment of polybenzoxazine (PBz) fibers blended with sulfur copolymers (SDIB) to determine the effect of varying treatment conditions on the microstructure and morphology of PBz fibers with the effect of incorporating sulfur functional groups on resulting properties. Mechanical properties of PBz are greatly improved by thermally-induced ring-opening polymerization (ROP) of the oxazine ring. Blending with sulfur copolymers (SDIB) could have beneficial effects on endowed features on fibers but could also affect the resulting properties of SDIB-blended PBz fibers during crosslinking reactions. Fiber mats were fabricated by electrospinning of PBz (10 wt%) blended with SDIB (10 wt%). Physical modification with varying conditions of sequential thermal treatment were evaluated and compared to the conditions applied on pristine PBz fibers. Changes in morphology and microstructure of fibers after modification were analyzed through scanning electron microscopy (SEM) while elemental compositions were identified after varying the conditions of thermal treatment. Adjustment of treatment conditions using two-step temperature sequential thermal treatment with higher temperatures of 160 °C and 240 °C showed significant changes in microstructure and morphology of fibers. Lower temperatures of 120 °C and 160 °C exhibited microstructure and morphology of fibers which affected the fiber diameter and fiber networks. Cross-sectional SEM images also confirmed the adversed effect of high-temperature treatment conditions on fibrous structures while low-temperature treatment retained the fibrous structures with more compact and stiff fiber networks. SDIB-blended PBz fibers were also evaluated by TGA and DSC to correlate the changes in structure and morphology with the thermal stability and integrity of blended SDIB/PBz fibers as compared to pristine PBz with the effect of change in treatment conditions. Fiber strength indicated slower weight loss for blended fibers and higher onset temperature of degradation which resulted in more thermally stable fibers.

Electrochemical activation of polymer chains mediated with radical transfer reactions.

This work demonstrates a general and effective approach to activate inert polymer chains for further reactions through electrochemically driven radical generation and radical transfer reactions. The generated radical-containing polymer chains show capacity for further polymer reactions and preparation of polymer hybrids.

Effect of a direct sulfonation reaction on the functional properties of thermally-crosslinked electrospun polybenzoxazine (PBz) nanofibers.

Electrospun nanofibers of polybenzoxazines (PBzs) were fabricated using an electrospinning process and crosslinked by a sequential thermal treatment. Functionalization by the direct sulfonation process followed after the post-electrospinning modification treatment. The first stage of experiment determined the effects of varying the concentration of sulfuric acid as the sulfonating agent in the sulfonation reaction under ordinary conditions. The second stage examined the mechanism and kinetics of the sulfonation reaction using only concentrated H2SO4 at different reaction time periods of 3 h, 6 h, and 24 h. The mechanism of the sulfonation reaction with PBz nanofibers was proposed with only one sulfonic acid (-SO3H) group attached to each of the repeating units since only first type substitution in the aromatic structure occurs under this condition. The kinetics of the reaction exhibited a logarithmic correlation where the rate of change in the ion exchange capacity (IEC) with the reaction time increased rapidly and then reached a plateau at the reaction time between 18 h and 24 h. Effective sulfonation was confirmed by electron spectroscopy with a characteristic peak associated with the C-S bond owing to the sulfonate group introduced onto the surface of the nanofibers. ATR-FTIR spectroscopy also confirmed these results for varying reaction times. The SEM images showed that sulfonation has no drastic effects on the morphology and microstructure of the nanofibers but a rougher surface was evident due to the wetted fibers with sulfonate groups attached to the surface. EDX spectra exhibited sulfur peaks where the concentration of sulfonate groups present in the nanofibers is directly proportional to the reaction time. From surface wettability studies, it was found that the nanofibers retained the hydrophobicity after sulfonation but the inherent surface property of PBz nanofibers was observed by changing the pH level of water to basic, which switches its surface properties to hydrophilic. The thermal stability of the sulfonated nanofibers showed almost the same behavior compared to non-sulfonated nanofibers except for the 24 h sulfonation case, which has slightly lower onset temperature of degradation.

A Sulfur Copolymers (SDIB)/Polybenzoxazines (PBz) Polymer Blend for Electrospinning of Nanofibers.

This study demonstrated the processability of sulfur copolymers (SDIB) into polymer blend with polybenzoxazines (PBz) and their compatibility with the electrospinning process. Synthesis of SDIB was conducted via inverse vulcanization using elemental sulfur (S8). Polymer blends produced by simply mixing with varying concentration of SDIB (5 and 10 wt%) and fixed concentration of PBz (10 wt%) exhibited homogeneity and a single-phase structure capable of forming nanofibers. Nanofiber mats were characterized to determine the blending effect on the microstructure and final properties. Fiber diameter increased and exhibited non-uniform, broader fiber diameter distribution with increased SDIB. Microstructures of mats based on SEM images showed the occurrence of partial aggregation and conglutination with each fiber. Incorporation of SDIB were confirmed from EDX which was in agreement with the amount of SDIB relative to the sulfur peak in the spectra. Spectroscopy further confirmed that SDIB did not affect the chemistry of PBz but the presence of special interaction benefited miscibility. Two distinct glass transition temperatures of 97 °C and 280 °C indicated that new material was produced from the blend while the water contact angle of the fibers was reduced from 130° to 82° which became quite hydrophilic. Blending of SDIB with component polymer proved that its processability can be further explored for optimal spinnability of nanofibers for desired applications.

Polymerization of Meldrum's Acid and Diisocyanate: An Effective Approach for Preparation of Reactive Polyamides and Polyurethanes.

Meldrum's acid (MA) is utilized as a monomer to polymerize with diisocyanates to result in polyamides, containing MA moieties at polymer chains. This reaction is also employed to prepare isocyanate-terminated polyamide segments which are utilized as a precursor for preparation of MA-containing polyurethanes. Based on the thermolysis reaction of MA groups, followed by ketene dimerization reaction, the reactive polyamides and polyurethanes show self-cross-linkable features. The cross-linked polyurethanes exhibit good film formability, thermal stability, and mechanical properties. A new MA-based polymerization method and a novel synthesis route for preparation of reactive polyamides and polyurethanes are demonstrated.

Impact of Computer-Based and Pharmacist-Assisted Medication Review Initiated in the Emergency Department.

OBJECTIVES: Whether early medication reconciliation and integration can reduce polypharmacy and potentially inappropriate medication (PIM) in the emergency department (ED) remains unclear. Polypharmacy and PIM have been recognized as significant causes of adverse drug events in older adults. Therefore, this pilot study was conducted to delineate this issue. DESIGN: An interventional study. SETTING: A medical center in Taiwan. PARTICIPANTS: Older ED patients (aged ≥65 years) awaiting hospitalization between December 1, 2017, and October 31, 2018 were recruited in this study. A multidisciplinary team and a computer-based and pharmacist-assisted medication reconciliation and integration system were implemented. MEASUREMENTS: The reduced proportions of major polypharmacy (≥10 medications) and PIM at hospital discharge were compared with those on admission to the ED between pre- and post-intervention periods. RESULTS: A total of 911 patients (pre-intervention = 243 vs post-intervention = 668) were recruited. The proportions of major polypharmacy and PIM were lower in the post-intervention than in the pre-intervention period (-79.4% vs -65.3%; P < .001, and - 67.5% vs -49.1%; P < .001, respectively). The number of medications was reduced from 12.5 ± 2.7 to 6.9 ± 3.0 in the post-intervention period in patients with major polypharmacy (P < .001). CONCLUSION: Early initiation of computer-based and pharmacist-assisted intervention in the ED for reducing major polypharmacy and PIM is a promising method for improving geriatric care and reducing medical expenditures. J Am Geriatr Soc 67:2298-2304, 2019.

Preparation of Cross-Linkable Zwitterionic Polybenzoxazine with Sulfobetaine Groups and Corresponding Zwitterionic Thermosetting Resin for Antifouling Surface Coating.

This work demonstrates a cross-linkable zwitterionic polymer, the corresponding zwitterionic thermosetting resin, and their application for antifouling surface coating. The tertiary amine-containing benzoxazine group is utilized as a precursor to react with 1,3-propane sultone to introduce sulfobetaine moiety to benzoxazine group. The reaction route provides an effective approach for preparation of sulfobetaine-functionalized benzoxazines and the corresponding sulfobetaine-functionalized thermosetting resins of benzoxazines. The sulfobetaine-functionalized polybenzoxazine has been utilized as a coating material for ceramic porous membranes to impart protein-repelling characteristic to the membrane surface. In a filtration test on a Bovine serum albumin (BSA) aqueous solution, the sulfobetaine resin modified membrane shows a 96.2% of rejection rate and a 1680 ± 9 Lm2-h-1 of permeation flux at the first cycle test. In cycled measurements with membrane washing, the membrane shows a total flux decline ratio (Rt) and a reversible flux decline ratio (Rr) of about 46.9% and 43.1%, respectively. A high ratio of reversible fouling (Rr/Rt) of 91.9% is found, which supports the statement that the sulfobetaine-functionalized polybenzoxazine is an effective material to impart antifouling characteristic to porous materials for bioseparation and filtration.

[Indirect pulp therapy for deciduous teeth with deep caries lesions].

Deciduous teeth are the first dentition of humans and play an important role in children's physical and mental development. Dental caries are one of the most common oral diseases in children. According to the data of the World Health Organization, 60%-90% of school children worldwide develop dental caries. In China, dental caries of primary teeth feature high incidence and low rate of visits. Without timely treatment, the deep caries lesions of primary teeth can lead to teeth defect, pulpitis, apical periodontitis, and maxillofacial space infection. Moreover, the premature loss of deciduous teeth can cause malocclusion and eruption disorder of subsequent permanent teeth. These conditions all cause considerable effects on children's oral health and physical and mental development. Performing active and effective measures to treat deciduous teeth with deep caries lesions is important to maintain the integrity and normal physiological function of dentition and facilitate normal eruption of permanent teeth. The current situation of indirect pulp therapy in China was studied in this paper. Basic concepts, including indirect pulp capping, interim therapeutic restoration, partial caries removal, stepwise caries removal, and atraumatic restorative therapy, have been defined by consulting domestic and foreign literature. A theoretical basis for improving the clinical pathway of deciduous teeth with deep caries lesions is provided by explaining the technical connotation and therapeutic importance of indirect pulp therapy in primary teeth.

Sulfur Radical Transfer and Coupling Reaction to Benzoxazine Groups: A New Reaction Route for Preparation of Polymeric Materials Using Elemental Sulfur as a Feedstock.

A novel approach to preparing polymeric materials using elemental sulfur as a feedstock through the newly developed sulfur radical transfer and coupling (SRTC) reaction is reported herein. Polybenzoxazines with high sulfur contents are prepared using the SRTC reaction with benzoxazine compounds as the radical acceptors. The reactions between elemental sulfur and benzoxazine rings are analyzed with Fourier transform infrared (FTIR), 1 H NMR, and 13 C DEPT spectroscopies to elucidate the SRTC reaction mechanism. Moreover, the prepared polybenzoxazine-sulfur hybrid materials show attractive repairing properties based on the dynamic S-S linkages. An effective reaction mechanism and the prepared repairable sulfur-possessing polymeric materials are demonstrated.

Effective Synthesis Route for Linear and Cross-Linked Biodegradable Polyesters Using Aliphatic Meldrum's Acid Derivatives as Monomers.

On the basis of the reaction between ketene and alcohol groups to result in an ester linkage and Meldrum's acid as an effective precursor of ketene group, a bifunctional aliphatic Meldrum's acid compound (BisMA) is synthesized and used as a monomer to react with ethylene glycol and glycerol for the preparation of linear and cross-linked aliphatic polyesters, respectively. A 62 and 35 wt % of biodegradation fraction have been recorded on the linear and cross-linked aliphatic polyesters after an 8 week biodegradation test, respectively, to demonstrate the good biodegradability of the synthesized polyesters. In addition to conventional linear biodegradable polyesters, this synthetic route also provides a new and convenient method for preparation of cross-linked biodegradable polyesters. The types of the required monomers and reaction methods for preparation of the cross-linked biodegradable polyesters are similar to those used for conventional thermosetting resins. An integration of biodegradable polymers and thermosetting resins in polymer chemistry has been demonstrated.

2,2,6,6-Tetramethylpiperydinyl-1-oxyl (TEMPO) Functionalized Benzoxazines Prepared with a One-Pot Synthesis for Reactive/Crosslinkable Initiators of Nitroxide Mediated Polymerization.

In this work, the incorporation of a 2,2,6,6-tetramethylpiperydinyl-1-oxyl (TEMPO) group to a benzoxazine ring is performed using a one-pot synthesis for the preparation of TEMPO-functionalized benzoxazine compounds and polymers as reactive and crosslinkable initiators for nitroxide-mediated polymerization (NMP). The TEMPO-functionalization reaction of benzoxazine, traced with 1 H NMR, is conducted with sequential radical transfer and coupling reactions. Moreover, polystyrene-grafted polybenzoxazine copolymers are prepared with the TEMPO-benzoxazine initiator and NMP of styrene. The polymerization system exhibits the characteristics of controlled radical polymerization, including controlled molecular weights of products and ability for sequential polymerization. Moreover, based on the chemical reactivity and crosslinking ability of benzoxazine groups, the synthesis route developed in this work will widen the scope of the design and synthesis of functional and high-performance polymers.

Reactive Hybrid of Polyhedral Oligomeric Silsesquioxane (POSS) and Sulfur as a Building Block for Self-Healing Materials.

This work demonstrates a new reactive and functional hybrid (S-MMA-POSS) of polyhedral oligomeric silsesquioxane (POSS) and sulfur prepared with a direct reaction between a multifunctional methacrylated POSS compound (MMA-POSS) and elemental sulfur (S8 ) through the "inverse vulcanization" process. S-MMA-POSS is an effective building block for imparting self-healing ability to the corresponding thermally crosslinked POSS-containing nanocomposites through a self-curing reaction and co-curing reaction with conventional thermosetting resins. Moreover, S-MMA-POSS is also a useful precursor for preparation of materials with high transparency in mid-infrared region.

A Cocatalytic Effect between Meldrum's Acid and Benzoxazine Compounds in Preparation of High Performance Thermosetting Resins.

In this work, a cocatalytic effect between Meldrum's acid (MA) and benzoxazine (Bz) compounds has been explored to build up a self-promoting curing system. Consequently, the MA/Bz reactive blend exhibits a relatively low reaction temperature compared to the required temperatures for the cross-linking reactions of the pure MA and Bz components. This feature is attractive for energy-saving processing issues. Moreover, the thermosetting resins based on the MA/Bz reactive blends have been prepared. The MA component can generate additional free volume in the resulting resins, so as to trap air in the resin matrix and consequently to bring low dielectric constants to the resins. The MA-containing agent is an effective modifier for benzoxazine resins to reduce their dielectric constants.

High flux MWCNTs-interlinked GO hybrid membranes survived in cross-flow filtration for the treatment of strontium-containing wastewater.

Graphene oxide (GO)-based membranes provide an encouraging opportunity to support high separation efficiency for wastewater treatment. However, due to the relatively weak interaction between GO nanosheets, it is difficult for bare GO-based membranes to survive in cross-flow filtration. In addition, the permeation flux of the bare GO membrane is not high sufficiently due to its narrow interlayer spacing. In this study, GO membranes interlinked with multi-walled carbon nanotubes (MWCNTs) via covalent bonds were fabricated on modified polyacrylonitrile (PAN) supports by vacuum filtration. Due to the strong bonds between GO, MWCNTs and the PAN membrane, the membranes could be used for the treatment of simulated nuclear wastewater containing strontium via a cross-flow process. The result showed a high flux of 210.7L/(m2h) at 0.4MPa, which was approximately 4 times higher than that of commercial nanofiltration membranes. The improved water permeation was attributed to the nanochannels created by the interlinked MWCNTs in the GO layers. In addition, the hybrid membrane exhibited a high rejection of 93.4% for EDTA-chelated Sr2+ in an alkaline solution, and could also be used to separate Na+/Sr2+ mixtures. These results indicate that the MWCNTs-interlinked GO membrane has promising prospects for application in radioactive waste treatment.

Radical and Atom Transfer Halogenation (RATH): A Facile Route for Chemical and Polymer Functionalization.

This work demonstrates a new halogenation reaction through sequential radical and halogen transfer reactions, named as "radical and atom transfer halogenation" (RATH). Both benzoxazine compounds and poly(2,6-dimethyl-1,4-phenylene oxide) have been demonstrated as active species for RATH. Consequently, the halogenated compound becomes an active initiator of atom transfer radical polymerization. Combination of RATH and sequential ATRP provides an convenient and effective approach to prepare reactive and crosslinkable polymers. The RATH reaction opens a new window both to chemical synthesis and molecular design and preparation of polymeric materials.

Thermosetting resins with high fractions of free volume and inherently low dielectric constants.

This work demonstrates a new class of thermosetting resins, based on Meldrum's acid (MA) derivatives, which have high fractions of free volume and inherently low k values of about 2.0 at 1 MHz. Thermal decomposition of the MA groups evolves CO2 and acetone to create air-trapped cavities so as to reduce the dielectric constants.

Atom Transfer Radical Addition/Polymerization of Perfluorosulfonic Acid Polymer with the C-F Bonds as Reactive Sites.

This work reports the first demonstration of the chemical reactions on the C-F groups of perfluorosulfonic acid polymers. The Nafion chains show chemical reactivity for atom transfer radical addition onto multiwalled carbon nanotubes and ability to serve as a macroinitiator for atom transfer radical polymerization. The C-F groups and mainchain -CF2 groups have been demonstrated, under a study with 19F NMR, as the active sites responsible for the reactions. The results could certainly extend both the scopes of chemistry and application of perfluorosulfonic acid polymers as well as the windows of atom transfer radical addition/polymerization to fluorinated compounds.