Bulk Polymerization Of Methyl Methacrylate Research Articles

Heterogeneities at the Onset of Reaction Acceleration during Bulk Polymerization of Methyl Methacrylate Investigated by Small-Angle Neutron Scattering

During bulk free-radical polymerization of methyl methacrylate below the glass-transition temperature of poly(methyl methacrylate), the relative fraction of monomer and polymer changes as the reaction proceeds. The liquid monomer is eventually converted to a solid glassy polymer. In other words, polymerization-induced vitrification or glass transition occurs. This process was traced by small-angle neutron scattering (SANS). The scattering profile discontinuously changes at the vicinity of vitrification. This discontinuous change was correlated with a sudden reaction acceleration known as the Trommsdorff effect. Ornstein–Zernike analysis revealed that the intensity at q = 0 (I(0)) and the correlation length of concentration fluctuation (ξ) suddenly increase at the discontinuous change of the scattering profile. The obtained data implies that the increased heterogeneity (i.e., microscopic concentration fluctuation) is intimately related to the Trommsdorff effect.

Probe into effect of the initiator on the thermal runaway hazards of methyl methacrylate bulk polymerization

The bulk polymerization of methyl methacrylate (MMA) is of great importance in chemical industry, but the polymerization process is highly hazardous, and few reports have focused on the effect of initiators on its thermal hazards. In this work, to thoroughly explore the thermal hazard characteristics, the runaway behavior of MMA bulk polymerization is investigated by a combination of thermodynamics experimental and kinetics theoretical methods. The results indicate that the presence of initiator exhibits an undesirable thermal hazard to the MMA bulk polymerization, and its exothermic behavior is also greatly influenced by the type and concentration of initiator. For azobisisoheptanenitrile (ABVN), azodiisobutyronitrile (AIBN) and dibenzoyl peroxide (BPO) initiators as examples, the AIBN-initiated reaction has the shortest adiabatic induction period (39.51 min), whereas the BPO-initiated polymerization exhibits the strongest maximum temperature-rising rate and maximum pressure-rising rate. Under adiabatic runaway, the temperature and pressure change significantly with increasing AIBN concentration, revealing a great potential risk of thermal runaway. Kinetic parameters are calculated to further understand the thermal runaway mechanisms, showing a strong agreement with the adiabatic experimental data. Finally, based on the cooling failure scenario, severity grading is determined by the evaluation criteria. The current work provides extensive data as a reference and guidance for the process design and optimization of MMA bulk polymerization from the perspective of safety.

Analysis of the glass effect and Trommsdorff effect during bulk polymerization of methyl methacrylate, ethyl methacrylate, and butyl methacrylate

Analysis of the glass effect and Trommsdorff effect during bulk polymerization of methyl methacrylate, ethyl methacrylate, and butyl methacrylate

Study of the radical polymerization mechanism and its application in the preparation of high-performance PMMA by reactive extrusion.

In this study, the mechanism of radical polymerization was further explored by pre-dissolving different polymers and studying the kinetics of the bulk polymerization of methyl methacrylate (MMA) under shear-free conditions. Based on the analysis of the conversion and absolute molecular weight, it was found that, contrary to the shearing effect, the inert polymer with viscosity was the key factor to preventing the mutual termination of radical active species and reducing the termination rate constant k t. Therefore, pre-dissolving the polymer could increase the polymerization rate and molecular weight of the system simultaneously, making the polymerization system enter the automatic acceleration zone faster and greatly reducing the generation of small molecular weight polymers, leading to a narrower molecular weight distribution. When the system entered the auto-acceleration zone, k t decreased rapidly and greatly and entered the second steady-state polymerization stage. Then, with the increase in the polymerization conversion, the molecular weight gradually increased, while the polymerization rate gradually decreased. In shear-free bulk polymerization systems, k t can be minimized and radical lifetimes maximized, but the polymerization system is at best a long-lived polymerization rather than a living polymerization. On this basis, by using MMA to pre-dissolve ultrahigh molecular weight PMMA and core-shell particles (CSR), the mechanical properties and heat resistance of the PMMA with pre-dissolved polymer obtained by reactive extrusion polymerization were better than for pure PMMA obtained under the same conditions. Compared with pure PMMA, the flexural strength and impact strength of PMMA with pre-dissolved CSR were up to 166.2% and 230.5%. With the same quality of CSR, the same two mechanical properties of the samples obtained by the blending method were just improved by 29.0% and 20.4%. This was closely related to the distribution of CSR in the pre-dissolved PMMA-CSR matrix with a distribution of spherical single particles 200-300 nm in diameter, which enabled PMMA-CSR to exhibit a high degree of transparency. This one-step process for realizing PMMA polymerization and high performance shows extremely high industrial application prospects.

Microporous Structure Formation of Poly(methyl methacrylate) via Polymerization-Induced Phase Separation in the Presence of Poly(ethylene glycol).

It has been demonstrated that nano- or micro-structured polymeric materials have huge potential as advanced materials. However, most of the current fabricating methods have limitations either in cost or in size. Here, we investigate the bulk polymerization of methyl methacrylate in the presence of poly(ethylene glycol) (PEG). We found that phase separation occurs during bulk polymerization. After removal of PEG via sonication, microscopic structures of poly(methyl methacrylate), including porous structures, co-continuous monolith structures, or particle aggregation structures, are formed. These structures can be controlled by the amount of PEG added and the reaction temperature. The results are summarized in phase diagrams. The addition of PEG significantly affects the reaction kinetics. Phase separation is coupled with the reaction acceleration known as the Trommsdorff effect. As a result, the reaction completes in a shorter time when the PEG amount is higher. We demonstrate surface coating to fabricate an amphiphobic surface, repelling both water and oil. The methods presented here have the potential to fabricate microscopic structures in large areas cost-effectively.

Using following heroes operation in multi-objective differential evolution for fast convergence

In this study, a new hybrid variant of multi-objective differential evolution is developed to improve the extent and the speed of convergence by combining the ability of DE/rand/1 strategy (NSDE1) to retain only better solutions in the selection operation with the ability of Following Heroes operation from adaptive social evolution algorithm to rapidly propagate the effect of the best solutions to the entire population. Such an algorithm is quite useful for fast convergence, particularly in solving computationally intensive multi-objective optimization problems for which it is highly desirable to obtain the better quality optimal solutions in a limited number of function calculations. The performance of the algorithm is first analyzed on thirty multi-objective test problems from ZDT, DTLZ, and WFG test suites for a limited number of function calculations, and the results are compared with four well-established multi-objective optimization algorithms: real-coded elitist non-dominated sorting genetic algorithm (RNSGA-II), non-dominated sorting particle swarm optimization (NSPSO), adaptive social evolution (ASE) and non-dominated sorting differential evolution with DE/rand/1 strategy (NSDE1) and found to be superior. The analysis is further extended to model-based algorithms, Pareto efficient global optimization (ParEGO), kriging for expensive evaluation Pareto (KEEP), and surrogate optimization of computationally expensive multi-objective problems (SOCEMO) which are commonly used for computationally intensive problems. These involve an additional computational cost of evolving the surrogate models. The performance of the proposed algorithm is found to be better than these, though, it has a relatively simple algorithmic structure and does not involve any additional computational cost. The algorithm is then evaluated on computationally intensive multi-objective optimization of bulk polymerization of methyl methacrylate. The numerical results obtained for this problem show better convergence for a limited number of function calculations.

The Trommsdorff effect under shear and bulk polymerization of methyl methacrylate via reactive extrusion

In this study, a concentric-cylinder and double-walled reactor accurately controlling shear rates was established to conduct the free radical bulk polymerization of methyl methacrylate, and the kinetics of Trommsdorff effect under constant shear was investigated. The results showed that increasing shear rate significantly enhanced the termination rate constant (kt), and thus effectively weakened and postponed the Trommsdorff effect. However, the polymerization rate during the “quasi-steady state” was almost not affected by shear rate. Differing from the classical theory, the chain initiation rate (Ri) also increased with shear rate, which was due to the improving initiation efficiency of polymerization reaction. On the other hand, it was found that the critical viscosity when Trommsdorff effect occurred was about 1000 ± 100 Pa·s, independent of shear rates, temperatures and initiator concentrations. Based on utilizing the Trommsdorff effect, polymethyl methacrylate (PMMA) was further synthesized via reactive extrusion, with superior performance comparing to commercial product.

Study on the performance of methyl methacrylate polymerization: Comparison of partially oxidized tri-n-butylborane and benzoyl peroxide with aromatic tertiary amines.

In this study, we examined the polymerization performance of methyl methacrylate (MMA) initiated with partially oxidized tri-nbutylborane (TBBO) compared to that initiated with benzoyl peroxide and aromatic tertiary amine (BPO/amine) system. In the bulk polymerization of MMA at 37°C, conversion initiated with TBBO after 3 h was nearly quantitative, whereas the conversion with the BPO/amine system was low (~20%). The number-averaged and weight-averaged molecular weight of the TBBO-initiated polymer was more than twice as high as that of the BPO/amine-initiated polymer. Electron spin resonance (ESR) analysis of MMA polymerization indicated that the TBBO-initiated system maintained its radical intensities for a longer period than the BPO/amine-initiated system. Furthermore, the radical fragments in the TBBO-initiated PMMA after 72 h were still active as a polymerization initiator for MMA. These findings suggest that the polymerization mechanism of MMA initiated by TBBO functions as a living-like polymerization initiator.

Methyl methacrylate as solvent for the thermal decomposition of the cyclic molecule pinacolone diperoxide: Toward the polymerization process

ABSTRACTThe decomposition rate constant (kd) of pinacolone diperoxide (PDP, 3,6‐diterbutyl‐3,6‐dimethyl‐1,2,4,5‐tetraoxacyclohexane) in methyl methacrylate (MMA) is determined by the kinetic study of its thermal decomposition at temperatures from 110 °C to 140 °C. The calculated kd values for PDP are higher than the corresponding values previously determined and reported for diethyl ketone triperoxide (DEKTP, 3,3,6,6,9,9‐hexaethyl‐1,2,4,5,7,8‐hexaoxacyclononane), for example, at 140 °C the kd for PDP is 75.4 × 10−5 s−1, while for DEKTP, it is 50.6 × 10−5 s−1. The difference in the kd between 130 °C and 140 °C indicates that the decomposition mechanism, sequential and/or concerted, is a function of temperature. The conformations of both initiators justify the higher kd for PDP in MMA than DEKTP, where one single conformer is found for PDP, whereas 212 conformers are found for DEKTP. Bulk polymerization of MMA using PDP as the initiator reveals also the presence of an induction period, such as in DEKTP case. This work provides mechanistic insights into the interactions among the bifunctional cyclic peroxide PDP and the MMA monomer and their influence on the polymerization kinetics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 997–1007

Phase separation during bulk polymerization of methyl methacrylate

We report on the phase separation of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) during bulk free-radical polymerization. The phase separation is induced when the reaction is initiated at room temperature by the redox reaction of benzoyl peroxide in the presence of an amine. During the reaction, the ratio of MMA and PMMA changes continuously. Separation into MMA-rich and PMMA-rich phases coincides with the onset of the Trommsdorff effect. At room temperature, the interface between the two phases remains, even after drying the remaining monomer. When the sample is annealed above the glass transition temperature Tg, the interface disappears. Due to the frozen dynamics of the polymer chains, subsequent cooling below Tg does not result in further phase separation. This result provides evidence for the existence of rich, thermodynamically stable states, which are typically suppressed due to the frozen dynamics of polymers at temperatures below the Tg, after thermal processing above the Tg. When bulk polymerization of MMA is conducted at room temperature, polymerization-induced phase separation occurs. Separation into MMA-rich and PMMA-rich phases coincides with the onset of the Trommsdorff effect. The highlighted region of the phase diagram represents a part of the phase state that depends upon the processing path: in one case (path 1), there are two phases present, in the other (path 2), the material is single-phase.

Effect of Azo and Peroxide Initiators on a Kinetic Study of Methyl Methacrylate Free Radical Polymerization by DSC

Free radical polymerization of methyl methacrylate was investigated in the presence of azo and organic peroxide initiator, such as 2,2′-azobisisobutyronitrile (AIBN), 1,1-bis(tert-butylperoxy)cyclohexane (BTBPC), tert-butyl peroxyneodecanoate (TBPND), and tert-butyl peroxy-2-ethylhexanoate (TBPEH) under isothermal condition (Tiso=60∼90 °C). The reaction heat generated in the bulk polymerization of methyl methacrylate was measured using a differential scanning calorimeter (DSC). The degree of polymerization and its reaction rate were expressed as a function of conversion (α) and its rate (dα/dt), respectively. We confirmed that autoacceleration proceeded predominantly during the autoacceleration regime (τauto) appearing after the onset of autoacceleration of MMA polymerization. In this work, kinetic models consisting of two contributions, such as n th order reaction and a kinetic equation representing autoacceleration, were suggested. The combined kinetic models were simulated and compared with the experimental data to evaluate the reliabilities.

Kinetics and temperature evolution during the bulk polymerization of methyl methacrylate for vacuum-assisted resin transfer molding

Curing reactions of methyl methacrylate (MMA) comprise an induction time of gradual temperature change over tens of minutes, followed by a sudden temperature rise within tens of seconds because of auto-acceleration known as the Trommsdorff effect. These curing effects were investigated as initial initiator and polymer concentrations were varied. A mathematical model combining the reaction kinetics with heat transfer was developed and verified in its ability to simulate the processing kinetics and temperature evolutions throughout thick MMA-based parts. It was further demonstrated that the processing conditions at specific points within a part during manufacture could be actively controlled via the Trommsdorff effect by locally varying the initial concentration of poly(methyl methacrylate) (PMMA) solution. Together, these advancements provide an enhanced ability to design and optimize the manufacture of thick, large-scale PMMA materials by taking advantage of auto-acceleration instead of avoiding it.

Effect of Organic Nano Carboncapsule Incorporated Modified Clay on Fire‐Retardancy of PMMA Nanocomposites

Here we investigate a new type of highly flame retardant poly(methyl methacrylate) (PMMA) nanocomposite by bulk polymerization of methyl methacrylate (MMA) in the presence of organic nano carboncapsule (OCNC/NCNC)‐incorporated modified montmorillonites (CL120, CL42). The morphology of the modified clay was confirmed by X‐ray diffraction (XRD), and Fourier transform infrared (FT‐IR) spectroscopy was used to identify the functional groups in the clay. The nano morphological characterization of the clay in the PMMA matrix was confirmed by XRD and transmission electron microscopy (TEM). The thermal and mechanical properties of the PMMA nanocomposites were investigated by thermogravimetry and dynamic mechanical analysis, respectively. PMMA containing organo nano carboncapsule‐doped CL42 modified cocoamphodipropionate (K2) (P‐O‐CL42) could achieve very high thermal stability compared to pristine PMMA. The 5% thermal decomposition temperature (T5d) increased by 63.2°C. Storage modulus of PMMA nanocomposites measured by DMA analysis. An enhancement of storage modulus and significant reduction in the peak heat release (PHR) rate were observed in the almost all PMMA nanocomposites as compared to pristine PMMA. Moreover, these results suggest that PMMA nanocomposites can have potential applications in the building industry and the medical field.

Optimized on-line control of MMA polymerization using fast multi-objective DE

ABSTRACTOptimized on-line control (OOC) of polymerization reactors combine the optimization with the on-line operation and control. In this, re-optimized control variable trajectories, in the presence of unplanned disturbances, are obtained and implemented on-line to save the batch. Also, the available computational time for the optimization is limited as the re-optimized trajectories need to be implemented in real time on the actual system. In the present study, the OOC of such a system, i.e., bulk polymerization of methyl methacrylate (MMA) in a batch reactor, is carried out in the occurrence of heater malfunction. To solve the underlying multi-objective problem, a multi-objective variant of differential evolution with an improved mutation strategy is developed. The developed algorithm shows faster convergence with respect to other compared algorithms for a large number of benchmark problems. Finally, this algorithm is used to find the optimal temperature trajectories and the OOC with these trajectories found to be successfully countering the effect of heater malfunction.

Effect of Dispersed Polymeric Nanoparticles on the Bulk Polymerization of Methyl Methacrylate

We proposed a methodology to investigate the effect of dispersed nanoparticles (NPs) on bulk polymerization of methyl methacrylate (MMA), based on DSC experiments and modeling of the bulk polymerization kinetics. As examples, we have applied it to polymeric NPs, polytetrafluoroethylene (PTFE) and polystyrene (PS), and compared the results with those from linear PMMA and cross-linked PMMA (cPMMA). The presence of dissolved linear PMMA enhances the MMA bulk polymerization kinetics, as if the system was prepolymerized at a conversion equal to the dissolved amount of the linear PMMA. The dispersed cPMMA also enhances the MMA polymerization kinetics, but the enhancement decreases as the cross-linker in the cPMMA increases. The PTFE NPs behave like (inert) dead volume, while the PS NPs do enhance the MMA polymerization kinetics due to their slight swelling in MMA. Therefore, we can conclude that dispersed nonswellable polymeric NPs behave like inert dead volume, and swellable polymeric NPs enhance the MMA bulk ...

Ultrasonically enhanced bulk ATRP of methyl methacrylate at high conversion with good livingness and control

A great challenge in controlled radical polymerization such as atom transfer radical polymerization (ATRP) has been related to keep the livingness and molecular weight control of the reaction at high conversion, especially in bulk polymerization. The objective of this work is to investigate the effects of ultrasound power on the polymerization at high conversion. The initiator for continuous activator regeneration ATRP is used for bulk polymerization of methyl methacrylate (MMA) as the model system. Good livingness and control up to high conversion are obtained through employing ultrasonic waves. By this method, MMA is polymerized in bulk up to “glass state” (88%) at 70°C with polydispersity about 1.2 under an operating frequency of 40 kHz and output power of 100 W. Chain extension reaction proves the livingness of the synthesized polymers at glassy state. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1683–1687, 2016

Diffusion of single molecular and macromolecular probes during the free radical bulk polymerization of MMA – towards a better understanding of the Trommsdorff effect on a molecular level

Diffusional heterogeneities of molecular and macromolecular probes were studied during the radical bulk polymerization of methyl methacrylate using fluorescence microscopy methods.

Modification of nanocrystalline cellulose for application as a reinforcing nanofiller in PMMA composites

Nanocrystalline cellulose (NCC) with particle length of 100–500 nm was prepared from microcrystalline cellulose and modified with a reversible addition–fragmentation chain transfer (RAFT) agent, i.e., 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPADB). From the surface of CPADB-modified NCC, methyl methacrylate (MMA) was grafted to produce poly(methyl methacrylate) (PMMA)-modified NCC. Unmodified NCC, CPADB-modified NCC, and PMMA-modified NCC were further used as reinforcing nanofillers in PMMA composite plates prepared by bulk polymerization of MMA. Regardless of NCC type, the PMMA plates were transparent to visible light at low NCC concentrations but became translucent with increasing NCC concentration. At given NCC concentration, the visible-light transparency of the PMMA/NCC composites decreased in the order PMMA-modified NCC, CPADB-modified NCC, unmodified NCC. PMMA-modified NCC and CPADB-modified NCC showed moderate potential for reinforcing the PMMA matrix, while unmodified NCC detrimentally affected the mechanical properties of the PMMA composites due to more pronounced particle aggregation.

Carbon nanofillers for modification of cold-curable composites based on methyl methacrylate

In bulk polymerization of methyl methacrylate, initiated by the benzoyl peroxide–N,N-dimethylaniline system, introduction of anisodiametric carbon nanofillers leads to an increase in the molecular mass and glass transition point of the resulting polymer. Modified cold-curable highly filled composites based on methyl methacrylate binder and mineral fillers and intended for repairing concrete pavements of roads and airports exhibit enhanced levels of compression strength and bending tensile strength.

Methyl methacrylate polymerization involving a cobalt ortho-iminobenzosemiquinone complex: Determination of the chain transfer constant

We studied the effect of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-ortho-iminobenzosemi-quinono]cobalt(II) on the kinetics of the bulk polymerization of methyl methacrylate at 70°C and on the molecular-weight characteristics of the polymer synthesized. The effective chain transfer constant in the polymerization of methyl methacrylate in the presence of the complex in benzene at 70°C was determined by the Mayo method and by linearizing the macromolecule chain length distribution. The constants obtained were compared with the same parameters available from the literature for a number of known chain-transfer agents, viz., dodecyl mercaptan and cobalt porphyrin and oxime complexes.