Bismaleimide-4,4′-diphenylmethane Research Articles

Modification of hydrogenated nitrile rubber with N,N′‐bismaleimide‐4,4′‐diphenylmethane to improve its resistance to heat aging and reduce its compression set

AbstractThis paper delves to improve the upper‐limit temperature of hydrogenated nitrile rubber (HNBR) through regulation of the vulcanization process, filler system and cross‐linking additive. The tensile test and scanning electron microscope images showed that the aging at 180°C significantly accelerated the deterioration in the property of HNBR compared with 150°C aging. The results showed that a higher dosage of bis(1‐(tert‐butylperoxy)‐1‐methylethyl)‐benzene curing agent reduced the compression set of HNBR without sacrificing its tensile strength. Carbon black N539‐filled HNBR exhibited high tensile strength, while carbon black N774‐filled HNBR showed high heat resistance and low compression set. When the HNBR sample was reinforced with 20 phr of N539 and 20 phr of N774 carbon black, it achieved low compression set, high tensile strength, and heat resistance simultaneously. Then, N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) was introduced into the HNBR composite as a cross‐linking assistant agent. The residual strength of BMI‐modified HNBR was 20.3 MPa (the retention rate of 92.3%), and its compression set was as low as 19.2% after aging at 180°C for 72 h. Even after aging the composite at 180°C for 168 h, its strength retention rate remained at 83.2% (18.3 MPa). The approach provided here increased the upper‐limit temperature range of HNBR to 180°C.

Bifunctional coating layer on Ni-rich cathode materials to enhance electrochemical performance and thermal stability in lithium-ion batteries

In this study we use N,N′-bismaleimide-4,4′-diphenylmethane (BMI), trithiocyanuric acid (TCA), and Jeffamine®-M1000 (molar ratio: 2:1:1; BTJ211) as a novel hybrid oligomer additive and surface modifier for coating (at concentrations of ca. 0.5–2 wt.%) of the cathode material LiNi0.80Co0.15Al0.05O2 (NCA) for lithium-ion batteries (LIBs). Qualitative analysis (1H NMR spectroscopy) confirms the polymerization of the BTJ additive. Morphological analyses (scanning electron microscopy/energy dispersive spectroscopy and high-resolution transmission electron microscopy) reveal that the hybrid oligomer is coated uniformly on the surface of the NCA, forming a BTJ@NCA powder material. Coin-type cells incorporating the 1 wt% BTJ@NCA electrode exhibit a significantly improved capacity retention (CR%) of 80.3%, relative to that of the bare NCA electrode (62.1%), at 1 C for 100 cycles at an upper voltage of 4.5 V. Electrochemical impedance spectroscopy and cyclic voltammetry reveal that this superior electrochemical performance originated from a lower charge transfer resistance (678.3 Ω vs. 349.6 Ω), improving Li+ ion diffusivity, and a lower polarization potential (242.9 mV vs. 368.9 mV). Furthermore, operando microcalorimetry of the cells containing the BTJ@NCA electrodes reveals that the modified electrodes can effectively decrease heat release by 69.6% when charging.

Facile fabrication of single-component flame-retardant epoxy resin with rapid curing capacity and satisfied thermal resistance

With the increasing demand of industry, the fabrication of single-component epoxy (EP) systems with satisfactory flame retardancy and thermal stability is of great significance. Herein, a novel phosphorus/nitrogen-containing single-component EP (EP/DOPO/BDM/BICP) system was synthesized via incorporating N,N′-bismaleimide-4,4′-diphenylmethane (BDM), benzimidazolyl-substituted cyclotriphosphazene (BICP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) into EP. In our previous work, we found that DOPO could promote the decomposition of BICP to produce dissociative benzimidazoles under heating, which endowed the as-fabricated epoxy thermoset with rapid curing speed. However, the addition of DOPO reduced the glass transition temperature (Tg) of epoxy thermosets. To deal with this problem, bismaleimide with superior heat resistance was added. The results indicated that the addition of BDM improved the thermal stability, flame retardancy and smoke suppression of EP/DOPO/BDM/BICP. The obtained thermoset exhibited UL94 V-0 rating, limiting oxygen index (LOI) of 40.5% and low total smoke production (TSP) of 10.4 m2 due to the synergetic flame-retardant effect of phosphaphenanthrene, polybismaleimide and cyclotriphosphazene. This research offers a viable approach to develop single-component EPs with improved flame retardancy, thermal stability and rapid-curing ability.

Reactive Oligomer Coating Cathode Active Material for Improved Lithium-Ion Battery Performance and Safety

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]. 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) for improved performance properties and high safety of LIB. The LiNi0.6Co0.2Mn0.2O2 pellets modified by 0.5-1 wt% BMI/CA oligomer exhibited much higher discharge capacity as compared to the native LiNi0.6Co0.2Mn0.2O2 at 25 and 55 oC. The solid electrolyte interface (SEI) formed on the cathode active material pellets after 100 charge/discharge cycles was characterized by X-ray photoelectron spectroscopy and scanning electron microscopy. 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 delithiated coin-cell LIBs were investigated at 150 oC. The thermal stability of the coin-cell LIB associated with 1.0 wt% BMI/CA coated LiNi0.6Co0.2Mn0.2O2 cathode material is better than that of the coin-cell LIB with pristine LiNi0.6Co0.2Mn0.2O2 cathode materials.

Reactive Oligomer Coating Cathode Active Materials (LiNi0.6Co0.2Mn0.2O2) for Improved Lithium-Ion Battery Performance and Safety

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.

Kinetics and mechanisms of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with cyanuric acid

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.

Facile construction of one-component intrinsic flame-retardant epoxy resin system with fast curing ability using imidazole-blocked bismaleimide

Latent curing epoxy resin (EP) system with satisfactory flame retardancy has attracted rather considerable interest both in academic and industrial communities over the years. Herein, imidazole-blocked bismaleimide compounds were synthesized through the Michael addition reaction of N,N′-bismaleimide-4,4′-diphenylmethane (BDM) with imidazole (IM), 2-methylimidazole (2MI), and 2-ethyl-4-methylimidazole (EMI), respectively, and were simultaneously used as latent curing agent and flame retardant synergist for 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) based EP (DOPO-EP). The storage stability study disclosed that imidazole-blocked bismaleimide compounds kept chemically inert towards epoxy at room temperature, resulting in long pot life over 40 days. When heated, imidazole-blocked bismaleimide compounds underwent retro-Michael addition reaction to regenerate BDM and the corresponding imidazoles. The fast curing ability was thus achieved via chain polymerization of epoxy initiated by thermally generated free imidazoles. Moreover, polybismaleimide component derived from the homopolymerization of thermally generated BDM was incorporated into the cross-linked EP network, resulted in enhanced thermal and charring performance of epoxy matrix. Compared with the contrast samples EP/2MI-BDM and DOPO-EP/2MI thermosets, DOPO-EP/2MI-BDM thermoset exhibited better flame retardancy with remarkably higher limiting oxygen index (LOI) value and UL94 rating as well as lower peak of heat release rate (pk-HRR), average of heat release rate (av-HRR) and total heat release (THR) from cone calorimeter test. The flame-retardant mechanism study revealed the synergistic flame-retardant effect of phosphaphenanthrene and bismaleimide in condensed phase.

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with barbituric acid in dimethyl sulfoxide

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)].

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with 2-thiobarbituric acid

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 non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with 1,3-dimethylbarbituric acid

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with 1,3-dimethylbarbituric acid (13BTA) were investigated. Competition between free radical polymerization and Michael addition reaction mechanisms for the BMI/13BTA reaction system was characterized by using DSC and 1H NMR technique. Model-free (isoconversional) method was used to determine triplet kinetic parameters for the polymerization of BMI with 13BTA. Average activation energy (Eα) and pre-exponential factor (Aα) are ca. 56kJmol−1 and 65.83×105min−1 in the fractional conversion (α) range 0.1–0.9, respectively. Particle nucleation involved in the polymerization process was satisfactorily predicted by the nucleation Avrami-Erofeev model {f(α)=n(1−α)[−ln(1−α)](n−1)/n} with n=1.46. The z-average particle size of microgel particles was measured by dynamic light scattering, which supported the particle nucleation and growth process.

Mechanisms and kinetics of isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with 5,5-dimethylbarbituric acid in the presence of triphenylphosphine

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 (Ph3P, 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 (Eα) and pre-exponential factor (Aα) are 33±1kJmol−1 and 8267±2min−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±1kJmol−1 and 4583±1min−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 Ph3P at low temperature. By contrast, free radical polymerization predominated in the BMI/55BTA system at higher temperature.

Isothermal polymerization kinetics of N,N′-bismaleimide-4,4′- diphenylmethane with cyanuric acid

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±1kJmol−1 and 162±2min−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 23kJmol−1 and 166min−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.

Kinetics of polymerization of N,N′-bismaleimide-4,4′-diphenylmethane, barbituric acid and aminopropyl phenylsiloxane oligomer

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 CC of BMI in BMI/BTA/APSi MPs is 53mol%, 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 kJmol−1) for the polymerization of BMI/BTA/APSi is higher than that (43 kJmol−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 nucleation-controlled polymerization of N,N′-bismaleimide-4,4′- diphenylmethane/barbituric acid

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=1×10−4t3−1.82×10−2t2+1.044t−2.133 at 100°C.

How do hyperbranched polyimides form in polymerizations of N,N’-bismaleimide-4,4′-diphenylmethane with barbituric acid?

The reactivity of the >CH2 and >NH groups of barbituric acid (BTA) toward the two terminal -C=C- groups of N,N’-bismaleimide-4,4′-diphenylmethane (BMI) was studied with the aid of three model compounds (N-phenylmaleimide (PMI) containg one -C=C- group, 1,3-dimethylbarbituric acid (1,3DMBTA) containing 1 >CH2 group and 5,5-dimethylbarbituric acid (5,5DMBTA) containing 2 >NH groups per molecule) and a molecular probe (hydroquinone (HQ)) that was capable of detecting free radical polymerization. Kinetics studies (DSC) and molecular structure characterization (1H-NMR) showed that it was the >CH2 group of BTA that predominated in the isothermal polymerization of BMI with BTA in N-methyl-2-pyrrolidone in the temperature range 373–403 K. On the contrary, the 2 >NH groups of BTA did not contribute to polymerization of BMI with BTA to an appreciate extent.

The synergistic effect of maleimide and phosphaphenanthrene groups on a reactive flame-retarded epoxy resin system

A novel reactive flame-retarded epoxy resin system was prepared by copolymerizing diglycidyl ether of bisphenol-A (DGEBA) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), N,N'-bismaleimide-4,4'-diphenylmethane (BDM) and 4,4'-diamino-diphenyl sulfone (DDS). Curing behavior, thermal and flame-retardant properties of the cured epoxy resins were investigated by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL94 test and cone calorimeter. The results indicated that phosphaphenanthrene group was introduced into the multicomponent system by addition reaction of DOPO with BDM. Compared with traditional DOPO-DGEBA systems, the EP/DDS/BDM/DOPO thermosets showed greatly improved glass transition temperatures (210–223 °C). The results of combustion tests indicated that the addition of BDM or DOPO into DGEBA could improve the flame resistance of the thermosets. Most importantly, the flame-retardant property was further improved when BDM and DOPO coexisted in the epoxy resin systems. For example, compared to the control samples, the EP/DDS/BDM/DOPO-15 thermoset displayed better flame retardancy with higher LOI value and UL94 rating, lower peak of heat release rate (pk-HRR) and average of effective heat of combustion (av-EHC) under the same content of BDM and phosphorus, strongly confirming the synergistic effect of BDM and DOPO. In addition, in a particular proportion, BDM and DOPO synergistically functioned in the condensed-phase and gaseous-phase at the same time. The flame retardant mechanism was studied by TGA and cone calorimeter coupled with the analysis of the char residues.

Effects of initial composition and temperature on the kinetics of polymerizations of N,N′-bismaleimide-4,4′-diphenylmethane with barbituric acid

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.

Kinetics of polymerization of N,N⿲-bismaleimide-4,4⿲-diphenylmethane with barbituric acid

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⿿403K 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 1H-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.

Effect of solvent proton affinity on the kinetics of michael addition polymerization ofn,n′-bismaleimide-4,4′-diphenylmethane with barbituric acid

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, which was correlated quite well with the solvent proton affinity (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

Synthesis and characterization of phenylsiloxane‐modified bismaleimide/barbituric acid‐based polymers with 3‐aminopropyltriethoxysilane as the coupling agent

AbstractThe preparation and characterization of phenylsiloxane (PhSLX)‐modified N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI)/barbituric acid (BTA) (10/1 mol/mol) oligomers are described. 3‐Aminopropyltriethoxysilane (APTES) was used as the coupling agent. The resultant hybrid BMI/BTA‐APTES‐PhSLX polymers were characterized primarily using thermogravimetric analysis in combination with differential scanning calorimetry and Fourier transform infrared measurements. The thermal stability of the BMI/BTA oligomer was improved significantly by incorporation of a small amount (20–30 wt%) of the copolymer of PhSLX and APTES (PASi). After adequate post‐curing reactions, the PASi‐modified BMI/BTA oligomers (HYBRID20 and HYBRID30 containing 20 and 30 wt% PASi, respectively) exhibited greatly reduced thermal degradation rates in the temperature range 300–800 °C and an increased level of residues at 800 °C as compared to the native BMI/BTA oligomer. This was further confirmed by thermal degradation kinetic studies, in which the activation energies for the thermal degradation reactions of the cured PASi‐modified BMI/BTA oligomers were shown to be higher than that of the pristine BMI/BTA oligomer. © 2012 Society of Chemical Industry