Search

Raspberry-like hollow hybrid nanoparticles were facilely prepared via simultaneous miniemulsion sol–gel reaction/free radical polymerization of tetraethyl orthosilicate, 3-methacryloxypropyl trimethoxysilane (MEMO) and styrene (ST). MEMO played an important role in controlling their morphologies from dense silica nanoparticles to raspberry-like and raspberry-like hollow hybrid nanoparticles. The hybrid nanoparticles were obtained from the miniemulsion reaction technique with 2 wt% MEMO with or without ST exhibit raspberry-like hollow nanoparticles. The corresponding number-average diameter of hybrid nanoparticles increased from 112 to 126 nm as the ST concentration increased from 0 to 5 wt%. The (raspberry-like hollow) porous silica particle sizes after calcination are 47, 76, 78 and 85 nm for the runs with 0, 1, 2 and 5 wt% ST, respectively. Moreover, for constant level of MEMO at 2 wt%, the highest specific surface area (800 m2 g–1) was achieved for the runs with the ST concentration = 0–1 wt%. Then, it steadily decreased from ca. 710 to 510 m2 g–1 when the ST concentration increased from 1.5 to 20 wt%. As for constant level of ST at 0.5 wt%, the specific surface area is ca. 626, 797 and 580 m2 g–1 for the runs with 1, 2 and 3 wt% of MEMO, respectively.

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with barbituric acid (BTA) in dimethyl sulfoxide (DMSO) were investigated. The polymerization of BMI with BTA in DMSO was characterized by using differential scanning calorimeter (DSC), electron spin resonance (ESR) and 1H-NMR techniques. The polymerization was primarily governed by the Michael addition reaction and aza- Michael addition reaction mechanisms. By contrast, free radical polymerization mechanism of BMI/BTA could be ruled out in DMSO medium. Model-free (isoconversional) method in combination with model-fitting method were used to determine triplet kinetic parameters for the polymerization of BMI with BTA in DMSO. Average activation energy (Eα) and pre-exponential factor (Aα) were ca. 51 kJ mol−1 and 1.33 × 106 min−1 in the fractional conversion (α) range 0.1–0.9, respectively. The polymerization of BMI with BTA was primarily reaction-controlled [f(α) = (1 − α)].

Bismaleimides modified through fluorosubstitution constitute two new electrolyte additives that have been successfully synthesized and used in lithium ion batteries. Fluorosubstitution significantl...

We developed a simple effective approach to prepare poly(N-isopropylacrylamide-co-acrylamide-co-N,N′-methylenebisacrylamide) (PNIPAM/AM/MBA) microgel core–silica shell particles with narrow particle size distribution via the sol–gel reaction of silica precursor deposited directly on the microgel particle surface in the presence of 3-glycidyloxypropyltrimethoxysilane (GLYMO). MBA was used as the cross-linking agent for the formation of microgel with the cross-linked network structure and GLYMO used as a coupling agent. The morphology of hybrid core–shell particles including the shape, core size, shell thickness and surface roughness was governed by the key components of AM and GLYMO. PNIPAM/AM/MBA microgel core–silica shell particles show desirable spherical shape, distinct core–shell structure and raspberry-like particle morphology. In contrast, PNIPAM/MBA microgel core–silica shell particles formed without resort to AM and GLYMO result in very poor silica encapsulation, thereby leading to undesired particle morphology. Incorporation of AM units into PNIPAM/MBA microgel particles increases the lower critical solution temperature (LCST). Furthermore, encapsulation of PNIPAM/AM/MBA microgel particles by silica does not affect the LCST to an appreciable extent, but it greatly reduces the thermo-sensitivity of the hybrid core–shell particles. Finally, the feasibility of using these PNIPAM-based core–silica shell particles as drug carriers was demonstrated.

Rechargeable lithium-ion batteries (LIBs) involving lithium metal oxides, liquid electrolyte and graphite have been widely used in portable electronic devices due to their relatively high energy density and long cycle life. These desirable features make LIBs very attractive as the power source for electronic devices, hybrid electric vehicles (HEVs) and electric vehicles (EVs) applications [1, 2]. For future EV applications, higher energy density of LIBs up to 360 Wh kg-1 is required. Currently, the energy density of the state-of-the-art LIBs using conventional graphite anode, LiFePO4 (denoted as LFP) or LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes and 1-1.2 M LiPF6 in organic carbonate electrolytes provide practically achievable energy densities of up to around 200-260 Wh kg−1 [3]. When commercial graphite anodes are used, LiNi0.8Co0.15Al0.05O2 (NCA), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.5Mn1.5O4 (LNMO) and LiNiPO4 (LNP) cathode based batteries with high-voltage provide energy densities of 354, 338, 351 and 414 Wh kg-1, respectively. However, LIBs using these high-voltage cathode materials and the organic carbonate electrolytes exhibit quite low thermal stability and tend to catch fire or even explode when abnormal charge/discharge cycling or accidental penetration of cells occurs, which greatly limits the automotive applications. When replacing graphite with a Li metal anode, the energy densities of all battery systems can be enhanced significantly due to the highest theoretical specific energy density (3860 mAh g-1) among all anode materials for rechargeable LIBs. Nevertheless, commercial LIBs are prone to cause safety problems due to the safety concern arising from Li dendrite growth in liquid organic electrolytes [4-6]. The promising solid-state LIBs offer high thermal stability (i.e., low risk in catching fire), high energy density, wide electrochemical stability window and less environmental impact. A competent electrolyte is the key component of solid-state LIBs. The solid-state electrolyte materials are mainly classified as solid polymer electrolytes (SPEs), inorganic solid electrolytes (ISEs), and organic/inorganic composite electrolytes. ISEs include oxide-based and sulfide-based materials [7, 8], which show very high ionic conductivity (10-2 – 10-3 S cm-1). Furthermore, the lithium ion transference number is close to 1. However, the major limitation factors of practical solid-state LIB applications are the large interfacial impedance between electrode and ISE and the difficulty of processing [9]. Considering processability, mechanical flexibility, interfacial compatibility and electrochemical stability, one prefers SPEs to the inorganic ceramic electrolytes. Nevertheless, SPEs have low ion conductivities (10−7 − 10−5 S cm−1 near room temperature) and most of the Li+ transference numbers are lower than 0.5 [10, 11]. The major requirements for SPEs include high ionic conductivity and transference number at room temperature, wide electrochemical potential window, high mechanical strength and excellent thermal stability. However, the ion conductivity is the most important (> 10-4 S cm-1 at room temperature desired) and should be considered first. The coordinating groups of a good polymeric host are expected to interact with Li+ and facilitate dissociation. In this study, we prepared various novel acrylonitrile-based polymers (e.g., acrylonitrile/acrylate copolymer and polymer with two pendant groups b-cyano ethyl ether (-O-CH2CH2-CN) sulfonate alkyl ether (-O-(CH2)3SO3Li). The corresponding SPEs comprising acrylonitrile-based polymer and ca. 50 wt.% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with high ionic conductivity (up to 10-3 S cm-1) at room temperature, high ion transfer number (up to 0.45) and large electrochemical potential window (oxidation stability > 5 V vs. Li+/Li) achieved. The selected SPEs were used as the separator in solid-state batteries with LiFePO4 as the cathode and Li foil as the anode; and long-term cycle stability of solid-state LIB was achieved. The polymers and corresponding SPEs were characterized by using DSC, SEM, XRD and FTIR measurements. Ionic conductivities of SPEs were determined from electrochemical impedance spectroscopy results. The linear sweep voltammetry technique was adopted to measure the oxidation stability window of SPE, and the Evans-Vincent-Bruce method was used to determined ion transfer number. References [1] J.B. Goodenough, Energy Environ. Sci. 7 (2014) 14−18. [2] M. Armand, et al., Nature 451 (2008) 652-657. [3] F. Wu, et al., Chem Soc Rev 49 (2020) 1569-1614. [4] Q. Wang, et at., J Power Sources 208 (2012) 210-224. [5] A.W. Golubkov, et al., RSC Adv 5 (2015) 57171-57186. [6] Z. Wang, et al. Nat Energy 3, (2018) 227–235. [7] L. Fan, et al., Adv. Energy Mater. 2018, 8, 1702657. [8] G. Kim, et al., J Power Sources 282 (2015) 299-322. [9] P. Knauth, Solid State Ion 180 (2009) 911-916. [10] C. Ma, et al., J Power Sources 2016; 317 :103–11. [11] N.K. Karan, et al., Solid State Ion 179 (2008) 689–696. Figure 1

LCST phase transition kinetics of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions was studied by using non-isothermal differential scanning calorimeter (DSC) and isothermal dynamic light scattering (DLS) techniques. The DSC data obtained from 5 and 10 wt% PNIPAM solutions were used in isoconversional kinetics analysis. The resultant large activation energy (Eα) and pre-exponential factor indicated that the phase transition occurred by cooperatively breaking multiple hydrogen bonds. Eα decreased with increasing temperature approximately in a hyperbola form. Theoretical nucleation and growth models were used to adequately describe the temperature dependent Eα. Furthermore, the phase transition process obeyed Avrami–Erofeev nucleation and growth models. As to the 0.05 wt% PNIPAM solution using the isothermal DLS technique, the reaction rate constant was determined at different temperatures, and the Avrami–Arofeev nucleation and growth models adopted to predict the phase transition process.

A cationic lipid-embedded poly(acrylic acid) (PAAc) gel layer coated on chitosan/superparamagnetic iron oxide nanoparticle (SPION) nanohybrid surfaces effectively modulates drug release and MR imaging contrast by pH-responsive morphological transformation and hierarchical alignment of the lipid assemblies.

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with 2-thiobarbituric acid (TBTA) were investigated. Competition among free radicals polymerization, Michael addition reaction and aza-Michael addition reaction mechanisms for the BMI/TBTA reaction system was characterized by using differential scanning calorimeter (DSC), electron spin resonance (ESR) and 1H-NMR techniques. Both radical polymerization and (aza) Michael reaction mechanisms played an important role in the reaction system. Model-free (isoconversional) method was used to determine triplet kinetic parameters for the polymerization of BMI with TBTA. Average activation energy (Eα) and pre-exponential factor (Aα) are ca. 71 kJ mol−1 and 17.85 × 107 min−1 in the fractional conversion (α) range 0.1–0.9, respectively. The polymerization of BMI with TBTA is primarily reaction-controlled [f(α) = (1−α)].

Mechanisms and kinetics of isothermal polymerization of N,N′ -bismaleimide-4,4′-diphenylmethane (BMI) with 5,5-dimethylbarbituric acid (55BTA) in the presence of triphenylphosphine (Ph 3 P, as a base catalyst for aza-Michael addition reaction) were investigated. Both model-free and model-fitting methods were used to determine triplet kinetic parameters, and comparable kinetic parameters obtained. Based on the model-free method, average activation energy (E α ) and pre-exponential factor (A α ) are 33 ± 1 kJ mol −1 and 8267 ± 2 min −1 in the α range 0.1–0.9, respectively, with g(α) = [(1 − α) −0.1 − 1]/0.1 [i.e. f(α) = (1 − α) 1.1 ]. As to the model-free method, overall activation energy (E) and pre-exponential (A) are 32 ± 1 kJ mol −1 and 4583 ± 1 min −1 with the g(α) = [(1 − α) −0.1 − 1]/0.1. Aza-Michael addition reaction mechanism played an important role in the polymerization of BMI/55BTA in the presence of Ph 3 P at low temperature. By contrast, free radical polymerization predominated in the BMI/55BTA system at higher temperature.

Monodisperse silica nanoparticles were prepared via miniemulsion sol–gel reaction of tetraethyl orthosilicate (TEOS). Hexadecane (HD) or hexadecyltrimethoxysilane was used as costabilizer to effectively retard the Ostwald ripening process involved in TEOS miniemulsion. The Ostwald ripening behavior was characterized by dynamic light scattering (DLS), and it was adequately described by the modified Kabal’nov equation. The miniemulsion sol–gel reaction of TEOS/HD with a volume fraction (φ c) of 0.024 at 80 °C is stable in the pH range 6–10. By contrast, gelation of reacting miniemulsions occurs at 70 and 100 min at pH 4 and 5, respectively. The weight-average silica particle size (d w) of colloidal products prepared at 80 °C and pH 7 decreases from 59 to 36 nm with low polydispersity index (PDI, in the range 1.02–1.03), determined by transmission electron microscopy, when the φ c of HD increases from 0.024 to 0.23. At constant φ c (0.024), the resultant silica nanoparticles show larger d w (83 nm) and PDI (1.35) for the TEOS/HD system at pH 10 as compared to the counterpart of pH 7. Furthermore, for the TEOS/HD system at pH 7 and low φ c (0.024), d w increases significantly with temperature being increased from 25 to 80 °C. By contrast, the effect of temperature on silica nanoparticle size becomes insignificant when a high level of HD (φ c = 0.23) is used. Zeta potential measurements and field emission scanning electron microscopy were used to characterize the surface charge density and morphology of resultant silica nanoparticles.

Kinetics of polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with cyanuric acid (CA) in N-methyl-2-pyrrolidone (NMP) was investigated. Both model-free and model-fitting methods were used to determine the relevant kinetic parameters. For the model-free method, the average activation energy (Eα) and pre-exponential factor (Aα) are 23 ± 1 kJ mol−1 and 162 ± 2 min−1 in the α range 0.1–0.9, respectively. The Aα value obtained is a result of the model assumption with g(α) = −ln(1 − α) [i.e. f(α) = (1 − α)], which is based on 1H NMR measurements. As to the model-fitting method, the overall activation energy (E) and pre-exponential (A) are 23 kJ mol−1 and 166 min−1 with g(α) = [(1 − α)0.15 − 1]/0.15 {i.e. f(α) = (1 − α)1.15}. The polymerization kinetics and mechanism of BMI/CA in NMP were characterized by DSC. Furthermore, complementary 1H NMR and 13C NMR techniques were used to identify the chemical structure of CA in the reaction medium and, therefore, the reaction mechanism (model) was predicted.

Lithium-ion battery (LIB) releases significant heat when the lithium metal oxide cathode is subjected to abnormal heating originating from irreversible chemical reactions of the electrode with electrolyte (often accompanied by gaseous combustion), thereby leading to thermal runaway and ultimately disastrous explosion [1-3]. Thermal runaway of LIBs can be triggered by several factors such as over-charge, over-temperature, mechanical damage, etc. In an attempt to resolve the safety issue of LIBs, several protection techniques have been employed externally or internally. The external protection mechanisms include the current interruptive devices, positive temperature coefficient devices, current limiting fuses and diodes (blocking/bypass). By contrast, the internal protection mechanisms focus on the individual components such as electrodes, separators and electrolytes with an aim to make the battery system intrinsically safer against hazard [4-6]. Recently, in order to overcome the disastrous thermal runaway problem of LIBs, a self-terminated oligomer was prepared by the polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with barbituric acid (BTA). This unique oligomer was then coated on the pellet surface of cathode active materials to greatly reduce the risk of thermal runaway [7, 8]. However, the discharge capacity of LIBs with such oligomer being coated on the cathode active materials was lower than that of LIBs without the oligomer inside [7, 8]. Thus, how to balance between the reduction in the risk of thermal runaway and the maintenance of the satisfactory electrochemical performance of LIBs becomes a crucial issue. In this study, we prepared novel reactive oligomer from polymerization of BMI with nucleophile (e.g., cyanuric acid (CA)) was coated on the pellet surface of cathode active materials (LiNi0.6Co0.2Mn0.2O2, denoted as NCM622) for improved performance properties and high safety of LIB. The NCM622 pellets modified by 0.5-1 wt% BMI/CA oligomer exhibited much higher discharge capacity as compared to the native NCM622 at 25 and 55 oC. The solid electrolyte interface (SEI) formed on the cathode active material pellets after charge/discharge cycling was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). A small amount of BMI/CA oligomer (as the cathode additive) greatly reduced undesirable side reactions between the electrode and electrolyte, thereby leading to relatively stable LIBs performance. Finally, the thermal stability of coin-cell LIBs were evaluated at 150 oC via open-circuit voltage (OCV) decay. The thermal stability of the coin-cell LIB associated with 0.5-1.0 wt% BMI/CA coated NCM622 cathode material is better than that of the coin-cell LIB with pristine NCM622 cathode material. References [1] N. Nitta, F. Wu, J.T. Lee, Mater. Today 18 (2015) 252-264. [2] A.W. Golubkov, D.Fuchs, J. W. H.Wiltsche, et al., RSC Adv. 4 (2014) 3633-3642. [3] A.W. Golubkov, S. Scheikl, R. Planteu, G. et al., RSC Adv. 5 (2015) 57171-57186. [4] W.S. Wu, Q.T. Pham, C.C. Yang, et al., Chem Eng J. 405 (2021) 126727 [5] K. Liu, C. Liu, P.C. Hsu, et al., ACS Cent. Sci. 4 (2018) 894−898. [6] M.C. Smarta, F.C. Krauseb, C Hwang, et al., ECS Transactions, 35 (2011) 1-11. [7] C.C. Lin, H.C. Wu, J.P. Pan, et al. Electrochimica Acta 101 (2013) 11– 17. [8] H.M. Liu, D.S., H.C. Wu, C.Y. et al., RSC Adv. 4 (2014) 56147-56155.

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with cyanuric acid (CA) were investigated. Competitive free radical polymerization and aza-Michael addition reaction mechanisms involved in the BMI/CA reaction system were characterized by using DSC, 1H-NMR, electron spin resonance (ESR) and gel permeation chromatography (GPC). Free radical polymerization mechanism predominated in the BMI/CA reaction system. Both model-free and model-fitting methods were used to determine the isoconversional activation energy (Eα) and pre-exponential factor (Aα). The values of Eα and Aα for aza-Michael addition reaction evaluated at α = 0.1 were 86 kJ mol−1 and 2.42 × 1010 min−1, respectively, and the reaction model was f(α) = 1.73(1 - α)α0.11. By contrast, Eα gradually decreased with increasing α (decreased from 88 to 48 kJ mol−1) in the α range 0.15−0.9, which was attributed to the inherent multi-step kinetics in free radical polymerization.

Researchers study the solid polymer electrolyte (SPE) to raise the safety and capacity of current lithium ion battery technology to a higher level. We opt to work on the polymer host based on acrylonitrile (PAN), since the nitrile group provides an admirable electrochemical stability and a high polarity, which are critical to the polymeric electrolyte. Yet, the nitrile group is also the origin of high glass transition temperature Tg, which requires synthetic efforts to reduce Tg through tuning the SPE composition. The RAFT mediated polymerization technique is employed to decrease the molecular weight and simultaneously incorporate a substantial amount of thiocarbonate moiety in the backbone. The synthesized PAN copolymer, molecular weight ~1600 g mol−1, contains 43.3% (by mole) carbon, 2.1% sulfur, and 8.7% nitrogen. Copolymerization with dodecyl acrylate increases the free volume of host. Substitution of LiFSI for LiTFSI reduces the glass transition temperature effectively since LiFSI is easier to dissociate and more effective in plasticization. The synthesis efforts result in the highest ion conductivity 6.1 × 10−4 S cm−1 at room temperature and 1.1 × 10−3 S cm−1 at 50 °C. This SPE also displays a lithium transference number 0.318, a high stability when interfacing the lithium metal, and tolerates a potential window of 6.0 V. When sandwiched between lithium anode and NMC622 cathode, the cell of SPE reaches 150 mAh g−1 in charge and discharge.

Non-isothermal polymerization kinetics of N , N′ -bismaleimide-4,4′-diphenylmethane (BMI)/barbituric acid (BTA) was investigated by using DSC. Comparable extents of Michael addition reaction estimated independently by a molecular probe, hydroquinone (HQ), and the deconvolution technique using the Haarhoff-Van der Linde (HVL) function were achieved. Both the model-fitting and model-free methods were employed to determine the kinetic parameters for the polymerization of BMI/BTA. The kinetic parameters of the BMI/BTA system for the three distinct stages were determined by the model-free method with the aid of the deconvolution technique. The particle nucleation involved in the polymerization process was satisfactorily predicted by the nucleation Avrami-Erofeev models {f(α) = n(1 − α)[−ln(1 − α)] (n − 1)/n } with n = 1.61 for Stage 1, n = 2.24 (Stage 2) and n = 2.77 (Stage 3). Microgel particles (MPs) of BMI/BTA were generated during polymerization. The particle size (d, z-average) of MPs was measured by dynamic light scattering (DLS). The least-squares best-fitted d versus t profile attained is d = 1 ×1 0 −4 t 3 − 1.82 × 10 −2 t 2 + 1.044t − 2.133 at 100 °C.

Kinetics of polymerizations of N,N′-bismaleimide-4,4′-diphenylmethane (BMI)/barbituric acid (BTA) [2/1 (mol/mol)] in the presence and absence of 20 wt% aminopropyl phenylsiloxane oligomer (APSi) was investigated. Microgel particles (MPs) of BMI/BTA/APSi and BMI/BTA formed during polymerizations at 100 or 130 °C. The initial particle growth rate of BMI/BTA/APSi MPs is faster than that of pristine BMI/BTA MPs due to the presence of APSi nuclei. The residual C C of BMI in BMI/BTA/APSi MPs is 53 mol%, which is comparable to that of BMI in BMI/BTA MPs. The same kinetic model, characterized by reaction-controlled overall, could be used to describe both polymerization systems. The value of activation energy (54 kJ mol−1) for the polymerization of BMI/BTA/APSi is higher than that (43 kJ mol−1) for the polymerization of BMI/BTA. The thermal stability of the cured BMI/BTA/APSi polymer is better than that of the cured BMI/BTA polymer.

Kinetics of miniemulsion polymerization of 1,6-hexanediol diacrylate (HDDA) was investigated. The particle size of microgel particles remained relatively constant (ca. 270 nm) during polymerization in the temperature range 65–75 °C. The model-fitting method in combination with the model-free method was used to determine the relevant kinetic parameters. The droplet nucleation involved in the miniemulsion polymerization process was satisfactorily predicted by the nucleation Avrami-Erofeyev model {g(α) = [−ln(1 − α)] 1/2 }. The overall activation energy (E = ca. 75 kJ mol −1 ) determined by the model-fitting and model-free methods is quite close to the overall activation energy (ca. 80 kJ mol −1 ) for polymerization initiated by a thermal initiator. By contrast, the conventional model [g(α) = −1/2ln(1 − α)] was incapable of adequately predicting the polymerization kinetic data. The miniemulsion polymerization was characterized by DSC, DLS and TEM.

Soluble amyloid-&beta, oligomers (oA&beta, 42)-induced neuronal death and inflammation response has been recognized as one of the major causes of Alzheimer&rsquo, s disease (AD). In this work, a novel strategy adopting silica-coated iron oxide stir bar (MSB)-based AD therapy system via magnetic stirring-induced capture of oA&beta, 42 into magnetic plaques (mpA&beta, 42) and activation of microglia on cellular plaque clearance was developed. With oA&beta, 42 being effectively converted into mpA&beta, 42, the neurotoxicity toward neuronal cells was thus greatly reduced. In addition to the good preservation of neurite outgrowth through the diminished uptake of oA&beta, 42, neurons treated with oA&beta, 42 under magnetic stirring also exhibited comparable neuron-specific protein expression to those in the absence of oA&beta, 42. The phagocytic uptake of mpA&beta, 42 by microglia was enhanced significantly as compared to the counterpart of oA&beta, 42, and the M1 polarization of microglia often occurring after the uptake of oA&beta, 42 restricted to an appreciable extent. As a result, the inflammation induced by pro-inflammatory cytokines was greatly alleviated.

Hypothesis How to encapsulate poly(N-isopropylacrylamide) (PNIPAM) mesoglobule cores by silica shells greatly affects the resultant nanoparticle structures. Incorporation of acrylamide (AM) unit into PNIPAM in combination with 3-glycidyloxypropyltrimethoxysilane (GLYMO, as a coupling agent) effectively induces nucleation and growth of silica on PNIPAM core surfaces, where the –NH2 of acrylamide reacts with the epoxide of GLYMO while GLYMO further participates in subsequent sol-gel reaction of tetraethyl orthosilicate (TEOS), thereby leading to desirable particle morphology. Experiments PNIPAM-based core–silica shell nanoparticles were prepared by sol-gel reaction of TEOS and GLYMO in the presence of polymeric core particles. The major parameters investigated in a systematic fashion include acrylamide concentration and weight ratio of polymer:GLYMO:TEOS. GPC, DLS, DSC, FE-SEM, TEM, FTIR and TGA were then used to characterize polymeric cores and hybrid nanoparticles. Findings The particle morphology was governed primarily by the acrylamide content and the weight ratio of PNIPAM/AM:GLYMO:TEOS, and desirable hybrid nanoparticles with narrow particle size distribution were achieved. The LCST of PNIPAM-based mesoglobules increases with increasing acrylamide content. Encapsulation of PNIPAM-based mesoglobules with silica also reduces their thermo-sensitivity. This is the first report of developing a novel approach to prepare PNIPAM-based mesoglobule core–silica shell nanoparticles with controllable particle morphologies.

A thermodynamic approach dealing with a regular solution of monomer (styrene (ST) herein) and different polymeric costabilizers as the disperse phase of miniemulsion were used to develop a model that describes the Ostwald ripening behavior involved in such a colloidal system. The validity of this model was verified by the Ostwald ripening rate data obtained from ST miniemulsions stabilized by living polystyrene costabilizer (PSlc) or polystyrene costabilizer (PSc) upon aging at 25 ℃. PSlc is more effective in retarding the Ostwald ripening process than PSc, though PSlc and PSc have comparable number-average molecular weights. The model can be also used to study the mutual interaction between monomer and polymeric costabilizer. Satisfactory modeling results achieved for ST miniemulsions using polymethyl methacrylate as the costabilizer further verify the general validity of the present model. Finally, the values of heat of mixing and interaction parameter between ST and different polymeric costabilizers were also determined.

Kinetics of polymerizations of N,N′-bismaleimide-4,4′-diphenylmethane (BMI)/barbituric acid (BTA) with molar ratios of BMI to BTA equal to 1/1, 2/1 and 4/1 in the temperature range 373–403 K were studied. Both Michael addition polymerization and free radical polymerization mechanisms were operative in such reaction systems. With the knowledge of kinetic parameters of the Michael addition polymerization of BMI with BTA taken from the literature, optimized kinetic parameters for simultaneous free radical polymerization including the overall initiation rate constant and the combined propagation and termination rate constants were achieved. In addition, modeling results along with experimental gelation time data showed that contribution of free radical polymerization was promoted for the polymerization carried out at a higher reaction temperature and/or a larger molar ratio of BMI to BTA. By contrast, Michael addition polymerization was enhanced with a smaller molar ratio of BMI to BTA and/or a lower reaction temperature.

The roles of dibenzyl trithiocarbonate (DBTTC) as both costabilizer and reversible addition–fragmentation transfer (RAFT) reagent in RAFT miniemulsion polymerizations of styrene were investigated. The effectiveness of DBTTC costabilizer in retarding Ostwald ripening involved in the storage stability of miniemulsion is comparable to that of conventional low-molecular-weight costabilizers such as cetyl alcohol, but inferior to that of hexadecane. The major variables chosen for studying kinetics of RAFT miniemulsion polymerizations include the type of initiators and levels of DBTTC and surfactant. At a constant level of DBTTC, the rate of polymerization for benzoyl peroxide (BPO)-initiated polymerization is slower than that for sodium persulfate (SPS)-initiated polymerization. Furthermore, the polymerization rate decreases with increasing level of DBTTC for polymerizations initiated by BPO (or SPS). It is the monomer droplet nucleation that governs BPO-initiated polymerizations. In contrast, for SPS-initiated polymerizations, the probability for homogeneous nucleation to take place is greatly increased, especially for polymerizations with lower levels of DBTTC and higher levels of surfactant. © 2015 Society of Chemical Industry

The modified Kabal'nov equation developed by a thermodynamic approach dealing with a regular solution of monomer and costabilizer as the two-component disperse phase adequately describes the Ostwald ripening rate data in a wide range of the volume fraction of costabilizer for styrene miniemulsions stabilized by a homolog of n-alkane costabilizers (CnH2n+2; n = 10, 12, 16, 18, 20, 24, 32) upon aging at 25 °C. The results show that the costabilizer with the shortest chain length (C10H22) is not hydrophobic enough to effectively retard the Ostwald ripening process. The effectiveness of n-alkanes as costabilizer in suppressing the Ostwald ripening process increases with increasing n-alkane molecular weight. Nevertheless, further increasing the n-alkane chain length from C24H50 to C32H66 does not lead to significant improvement in the effectiveness of n-alkane as costabilizer. The major characteristics of the modified Kabal'nov equation are also discussed in this work.

Non-isothermal polymerization kinetics of reactive N,N′-bismaleimide-4,4′-diphenylmethane/barbituric acid microgel particles (BMI/BTA MPs) and BMI/BTA/hydroquinone (HQ) MPs in N-methyl-2-pyrrolidone (NMP) solution studied. The model-fitting method in combination with the model-free method was used to determine the kinetic parameters for the polymerizations of reactive BMI/BTA MPs and BMI/BTA/HQ MPs. The results show that Michael addition polymerization predominates in BMI/BTA/HQ MPs in the temperature range 95–140 °C. For BMI/BTA MPs, free radical polymerization plays a crucial role in the temperature range 70–95 °C, whereas Michael addition polymerization becomes significant when the temperature is higher than 120 °C. The non-isothermal polymerization processes were satisfactorily predicted by the same contracting cylinder model for both the BMI/BTA MPs and BMI/BTA/HQ MPs.

Isothermal kinetics of polymerizations of N , N ⿲-bismaleimide-4,4⿲-diphenylmethane (BMI) with barbituric acid (BTA) (BMI/BTA = 2/1 (mol/mol)) in N -methyl-2-pyrrolidone in the temperature range 373⿿403 K were studied. A mechanistic model involving the competing Michael addition and free radical polymerization mechanisms was developed. With the knowledge of the kinetic parameters for Michael addition polymerization obtained from our previous work, this kinetic model in combination with experimental data obtained from DSC and 1 H-NMR measurements was used to evaluate the kinetic parameters of free radical polymerization of BMI initiated by BTA. The model adequately predicted the kinetics of polymerization of BMI/BTA at different temperatures. Key kinetic parameters for the free radical polymerization mechanism were then determined. At high temperature, free radical polymerization predominates in the reaction system. By contrast, at low temperature, Michael addition polymerization competes more effectively with free radical polymerization.

The Ostwald ripening behavior of the three-component disperse phase styrene miniemulsions stabilized by mixed costabilizers of cetyl alcohol (CA)/n-alkanes (or dodecyl methacrylate (DMA)/n-alkanes) was investigated. The pseudo-two-component disperse phase miniemulsion model adequately described Ostwald ripening rate data. In addition, the general validity of a universal correlation (i.e., the Ostwald ripening parameter K1 is inversely proportional to the equivalent water solubility of bulk mixed costabilizers) was further confirmed by vast experimental data. For n-alkanes with lower molecular weight ( 226), miniemulsions stabilized by these two types of mixed costabilizers exhibited opposite Ostwald ripening behavior.

A novel drug delivery strategy featured with enhanced uptake of nanoparticles (NPs) by targeted tumor cells and subsequent intratumoral cellular hitchhiking of chemotherapy to deep tumor regions was described. The NP delivery system was obtained from assembly of poly(lactic acid-co-glycolic acid)-grafted hyaluronic acid (HA-g-PLGA) together with an anticancer drug, SN38, in aqueous phase, followed by implementing the NP surface with a layer of methoxypoly(ethylene glycol)-b-poly(histamine methacrylamide) (mPEG-b-PHMA) via hydrophobic association to improve the colloidal stability both in vitro and in vivo. Upon arrival of these PEGylated NPs at the acidic tumor site through the EPR effect, mPEG-b-PHMA became detached from the NP surface by the charge transition of the PHMA blocks from neutral (hydrophobic) to positively charged (hydrophilic) state via acid-induced protonation of their imidazole groups in tumor microenvironment. The exposure of HA shell on the naked NP thus resulted in enhanced uptake of NPs by CD44-expressed tumor cells, including cancer cells and tumor-associated macrophages (TAMs). Along with the TAMs being further chemotactically recruited by hypoxia cells, the engulfed nanotherapeutics was thus transported into the avascular area in which the anticancer action of chemotherapy occurred by virtue of the drug release alongside PLGA degradation, similar to those arising in other tumor nonhypoxia regions.

We report a novel approach based on using polyoxyethylene alkylphenyl ether ammonium sulfate (HS10) as an anion reactive surfactant, which greatly reduced the size of poly(N-isopropylacrylamide-co-acrylamide-co-N,N′-methylenebisacrylamide) [P(NIPAM/AM/MBA)] microgel core – silica shell particles. First, the microgel cores were synthesized by copolymerization of N-isopropylacrylamide (NIPAM), N,N′-methylenebisacrylamide (MBA) with a variation of acrylamide (AM) and HS10 concentration in water. It followed by silica encapsulation of the microgel cores via the addition of 3-glycidyloxypropyltrimethoxysilane (GLYMO) and tetraethyl orthosilicate (TEOS) at alkaline environment (pH 12). It is interesting to note that the size of both PNIPAM-based microgel cores and PNIPAM-based microgel core – silica shell particles were well-controlled by using a small level of HS10. Furthermore, SEM images of the hybrid core – shell particles show the well-defined spherical morphology with monodisperse particle size distribution. As expected, HS10-containing samples are covered by the porous silica shell layer, instead of continuous silica shell obtained from HS10-free samples observed in TEM images. This novel incorporation not only well controls the core size and shell morphology, leading to increase their specific surface area but also does not greatly affect the thermo-sensitivity of final products. The resultant thermo-responsive microgel core – silica shell particles with controlled particle morphology and physicochemical properties are useful for biomedical application fields.

Non-isothermal radical polymerization kinetics for barbituric acid (BTA)/epoxy diacrylate (EA) and benzoyl peroxide (BPO)/EA (serving as the reference) in NMP were investigated. The DSC data showed that the activation energy of the polymerization of EA initiated by BTA was much lower than that initiated by BPO. For polymerizations of BTA/EA and BPO/EA except BPO/EA = 3/100 (w/w), the reaction mechanism involving nucleation, followed by nucleus growth in the first stage was proposed. For the polymerization of BPO/EA [3/100 (w/w)], the reaction system was adequately described by the instantaneous nucleation and nucleus growth mechanisms in the first stage. Moreover, the nucleation and subsequent growth of microgel nuclei were primarily governed by the propagation reaction and diffusion-controlled termination reaction for the polymerization system of BTA/EA or BPO/EA. In the second stage (in the conversion range 0.75–0.90), the diffusion-controlled propagation and termination reactions governed the development of highly crosslinked macrogel (i.e., macroscopic agglomerate).

a b s t r a c t Non-isothermal degradation kinetics of cured polymer samples of barbituric acid (BTA)/bisphenol A diglycidyl ether diacrylate (EA) and benzoyl peroxide (BPO)/EA was investigated. The sample of BTA/EA exhibited an inferior thermal stability as compared to the BPO/EA counterpart (as the reference sample). The degradation kinetics for both cured polymer samples of BTA/EA and BPO/EA were determined by the model-fitting method with the aid of a deconvolution technique. For the sample of BTA/EA, the complex degradation process was described by the diffusion-controlled and reaction-controlled mechanisms in the first and second steps, respectively. For the sample of BPO/EA, the mechanism responsible for the first step of the degradation process was reaction-controlled. By contrast, the degradation process was described by the nucleation-controlled mechanism, followed by the multi-molecular decay law in the second step. Different degradation kinetics and mechanisms between cured polymer samples of BTA/EA and BPO/EA were attributed to their different crosslinked network structures. © 2013 Published by Elsevier B.V.

The effects of the molecular weight of polystyrene (PS) and polymethyl methacrylate (PMMA) costabilizers on the Ostwald ripening behavior at 25 °C of styrene (ST) miniemulsions and the polymerization of these miniemulsions were investigated. The effectiveness of PS and PMMA costabilizers in retarding the diffusional degradation of ST miniemulsions decreases with increasing the molecular weight of PS or PMMA costabilizers. The Ostwald ripening rate data were used to determine the critical chain length of polymeric costabilizers to induce chain entanglements. The resultant critical chain length to induce chain entanglements is 36,387 ± 1475 g mol −1 and 7668 ± 521 g mol −1 for PS and PMMA costabilizer, respectively, which are comparable to those reported in the literature. The polymerization of the ST miniemulsions stabilized by PMMA costabilizers with different molecular weights at 70 °C was then carried out. The polymerization rate decreases with increasing the polymeric costabilizer molecular weight. This was attributed to the reduced number of latex particles (i.e., reaction loci) with the polymeric costabilizer molecular weight. The miniemulsion polymerization kinetics is primarily controlled by the particle nucleation process (the competition between the monomer droplet nucleation and homogeneous nucleation), which is closely related to the effectiveness of these costabilizers in retarding the Ostwald ripening process. Furthermore, the ideal one-to-one copy of homogenized monomer droplets into latex particles cannot be achieved during polymerization.

Hollow hybrid nanogels were prepared first by the coassembly of the citric acid-coated superparamagnetic iron oxide nanoparticles (SPIONs, 44 wt %) with the graft copolymer (56 wt %) comprising acrylic acid and 2-methacryloylethyl acrylate units as the backbone and poly(ethylene glycol) and poly(N-isopropylacrylamide) as the grafts in the aqueous phase of pH 3.0 in the hybrid vesicle structure, followed by in situ covalent stabilization via the photoinitiated polymerization of MEA residues within vesicles. The resultant hollow nanogels, though slightly swollen, satisfactorily retain their structural integrity while the medium pH is adjusted to 7.4. Confining SPION clusters to such a high level (44 wt %) within the pH-responsive thin gel layer remarkably enhances the transverse relaxivity (r2) and renders the MR imaging highly pH-tunable. For example, with the pH being adjusted from 4.0 to 7.4, the r2 value can be dramatically increased from 138.5 to 265.5 mM(-1) s(-1). The DOX-loaded hybrid nanogels also exhibit accelerated drug release in response to both pH reduction and temperature increase as a result of the substantial disruption of the interactions between drug molecules and copolymer components. With magnetic transport guidance toward the target and subsequent exposure to an alternating magnetic field, this DOX-loaded nanogel system possessing combined capabilities of hyperthermia and stimuli-triggered drug release showed superior in vitro cytotoxicity against HeLa cells as compared to the case with only free drug or hyperthermia alone. This work demonstrates that the hollow inorganic/organic hybrid nanogels hold great potential to serve as a multimodal theranostic vehicle functionalized with such desirable features as the guidable delivery of stimuli-mediated diagnostic imaging and hyperthermia/chemotherapies.

The effect of solvent proton affinity on the kinetics of the Michael addition polymerizations of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) and barbituric acid (BTA) in different solvents [N-methyl-2-pyrrolidone (NMP), N,N′-dimethylacetamide (DMAC), and N,N′-dimethylformamide (DMF)] were investigated. This was achieved by the complete suppression of the competitive free radical polymerization via the addition of a sufficient amount of hydroquinone (HQ). A mechanistic model was developed to adequately predict the polymerization kinetics before a critical conversion, at which point the diffusion-controlled polymerization become the predominant factor during the latter stage of polymerization, was achieved. The activation energy (Ea) of the Michael addition polymerization of BMI with BTA in the presence of HQ in increasing order was: NMP DMAC > DMF). By contrast, the frequency factor (A) in increasing order is: NMP < DMAC < DMF. As a result of the compensation effect between Ea and A, at constant temperature, the Michael addition rate constant decreased with increasing solvent proton affinity. POLYM. ENG. SCI., 54:559–568, 2014. © 2013 Society of Plastics Engineers

Styrene miniemulsions stabilized by a series of n-alkane costabilizers (CnH2n+2, n = 10, 12, 16, 18, 20, 24, and 32) were prepared, and the Ostwald ripening behavior of the resultant two-component disperse phase colloids on aging at 25°C characterized with the aid of a semiempirical model developed in our previous work. This versatile model was capable of predicting the Ostwald ripening rate data over a wide range of the volume fraction of n-alkanes within submicron monomer droplets. It was shown that the Ostwald ripening rate (or the water solubility of n-alkane) decreased with increasing n-alkane molecular weight. A correlation between the water solubility and the molecular weight of n-alkanes was established accordingly.

The Ostwald ripening behavior of ST or MMA miniemulsions stabilized by various types of costabilizers upon aging at 25°C was investigated. The general validity of the quadratic empirical model with two parameters K1 and K2 was verified and it showed great potential to describe the general features of the Ostwald ripening process involved in miniemulsions stabilized by a relatively wide range of volume fraction of costabilizer in the disperse phase. The greater the K1/RO,1 (or K2/RO,1) value, the more effective is the costabilizer in stabilizing miniemulsion droplets against the diffusional degradation process. RO,1 is the Ostwald ripening rate corresponding to the single component of ST (or MMA). Some useful correlations of the K1/RO,1 (or K2/RO,1) data with the water solubility (or solubility parameter) of the bulk costabilizer were established. Polymeric costabilizers showed quite different behavior in stabilizing miniemulsions compared to low molecular weight costabilizers. Incorporation of hydrophilic...

With the addition of sufficient hydroquinone to completely suppress the free radical polymerization, the kinetics of Michael addition polymerizations of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) and barbituric acid (BTA) with BMI/BTA = 2/1 (mol/mol) in 1-methyl-2-pyrrolidone was investigated independently. A mechanistic model was developed to adequately predict the polymerization kinetics before a critical conversion (ca. 60%), at which point the diffusion-controlled polymer reactions started to predominate in the latter stage of polymerization. The Michael addition polymerization rate constants and activation energy in the temperature range 383–423 K were determined accordingly. Beyond the critical conversion, a relatively stationary limiting conversion (ca. 69%) independent of the reaction temperature was achieved. A diffusion-controlled polymerization model taken from the literature satisfactorily predicted the limiting conversion data. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Polymeric vesicles attained from the self-assembly of distearin (a diacylglycerol lipid)-conjugated poly(acrylic acid) (PAAc) with various distearin contents in the aqueous phase show the capability of control over the vesicular-wall permeability to hydrophilic solutes of varying sizes by a simple manipulation of the external pH. The pH sensitivity of the vesicle membranes in size-selective permeability is largely dependent upon the lipid content of copolymer. By the addition of CaCl2 in aqueous vesicle suspensions, the pH-evolved assembly structure and the membrane permeability can be immobilized with promoted resistance to further pH alteration, along with an additional counterion screening effect that reduces the pH required for the onset of polar solutes of certain sizes to pass through the membranes. Small-angle X-ray scattering (SAXS) measurements of the vesicle structure in the aqueous phase indicate that the pH-regulated permeability to polar solutes is virtually governed by the extent of hydration and swelling of the vesicle membranes, and the lipid residues within each vesicle wall are packed into the approximate to 4-5 repeating lamellar islet structure surrounded by PAAc segments.