Vitrimer chemistry for 4D printing formulation

Vitrimerization is one of the new methods under development to convert polymer wastes into high-value compounds. The chemistry of vitrimers is such that the presence of dynamic chemical bonds changes the permanent covalent bonds into covalent adaptable networks, which are reversible. This allows for recycling and reprocessing of polymers by maintaining their initial properties after several cycles, which is included in the preparation of polymer resins to convert polymer waste into materials that can be formulated for three-dimensional (3D) printing resins. Four-dimensional (4D) printing has also been recently introduced as sustainable 3D printing of responsive polymers with dynamic applications, such as soft robotics, medicine, and medicals. Therefore, the synthesis of polymers with dynamic chemistry based on vitrimers can add unique properties such as shape memory, shape recovery, self-healing, and flexibility to the 3D printed products. Vitrimerization chemistry could contribute to polymer waste by producing 4D-printed resins. This article presents the vitrimerization chemistry used in different polymers to produce 4D printing resins with the mentioned capabilities and lists their recipes for the preparation of formulations used in 4D printing so that the researchers can use them in a practical way to possibly achieve simultaneous shape-programmable, self-healing, and recyclable features in printed structures

Study of Slurry Ethylene Polymerization with Ziegler-Natta Catalysts: Kinetics and Investigation on the Rate of Monomer Consumption Equation

In the current work, ethylene polymerization was investigated from a mathematical modeling point of view. The initiation (activation), propagation, termination, and deactivation reactions were taken into account and the relevant equations used in the modeling were obtained from the elementary reactions. Some assumptions including neglecting the transfer and deactivation reactions were considered to simplify the modeling. According to the results obtained, these assumptions were only applicable to the initial stages of the polymerization reaction, namely the first 20 min of the reaction.Finally, transfer to monomer and deactivation reaction was also included in the improved version of the model and a new equation acceptably matching the experimental results was developed for the rate of the polymerization

Adsorption kinetics of methylene blue from wastewater using pH-sensitive starch-based hydrogels

Abstract In this work, starch/poly(acylic acid) hydrogels were synthesized through a free radical polymerization technique. The molar ratios of acrylic acid to N,N′-methylenebisacrylamide were 95:5, 94:6, and 93:7. The samples exhibited an amorphous porous structure, indicating that the size of the pores was contingent upon the amount of cross-linking agent. The quantity of acrylic acid in structure rose with a little increase in the amount of the cross-linking agent, which improved the hydrogels’ heat stability. The swelling characteristics of the hydrogels were influenced by both the pH level and the amount of cross-linking agent. The hydrogel with a ratio of 94:6 exhibited the highest degree of swelling (201.90%) at a pH of 7.4. The dominance of the Fickian effect in regulating water absorption in the synthesized hydrogels was demonstrated, and the kinetics of swelling exhibited agreement with Schott's pseudo-second order model. The absorption of methylene blue by the hydrogels that were developed was found to be influenced by various factors, including the concentration of the dye, the quantity of the cross-linking agent, the pH level, and the duration of exposure. The hydrogel 95:5 exhibited the highest adsorption effectiveness (66.7%) for the dye solution with a concentration of 20 mg/L at pH 10.0. The examination of the kinetics and isotherms of adsorption has provided evidence that the process of physisorption takes place on heterogeneous adsorbent surfaces and can be explained by an exothermic nature

Employing Moment Equations Model to Study the Effect of Different Active Centers on Homopolymerization Kinetics of Ethylene

Ethylene was homopolymerized over Ziegler-Natta catalyst and the homopolymerization was modeled using moment equations. Mechanism was modeled according to five different reaction centers of catalyst. For each center, there are different reaction rate coefficients; therefore the final product of each center would be expected to be different. Modeling results showed good conformity to the experimental results. According to the results obtained, the molecular weight distribution of each active center follows a Schultz-Flory distribution. However, the molecular weight distribution ofpolymer produced is much broader than a Schultz-Flory distribution. Besides, the order of polymerization with regards to monomer concentration is different for each center and it is higher than unity. Moreover, the catalyst active centers deteriorate in the presence of hydrogen and consequently catalyst yield drops. Nevertheless, polymerization kinetics is not affected much by hydrogen. Hydrogen also reduces polymer molecular weight since it is a strong transfer agent in olefin polymerizations. Notwithstanding, it does not affect polydispersity index. Finally, by increasing the cocatalyst concentration the activity of active centers is not changed, while it lessens the molecular weight as a transfer agent

Preparation of Polystyrene Nanocomposite by In Situ Atom Transfer Radical Polymerization: Study of Polymerization Kinetics in the Presence of Clay

Styrene nanocomposites were synthesized by in-situ atom transfer radical polymerization at 110oC. The variations of monomer conversion and the linearity of semilogarithmic kinetic plot, some signs of living polymerizationand constant radical concentration in the reaction medium, were revealed by gas chromatography technique (GC). According to the gel permeation chromatography (GPC) results, the number average molecular weight increased linearly against the monomer conversion indicating the living nature of the polymerization. Weight average molecular weight and polydispersity of nanocomposites were also derived from GPC data. In addition, the PDI value was wider for polymers extracted from nanocomposite samples, and still widened as the clay content increased. Moreover, all the samples experienced a fall in PDI value from nearly 2 to almost 1.1 as the reaction progressed. FTIR results are indications of some interactions between clay surface and monomer, which may be attributed to higher rated in polymerization kinetics. XRD displayed no peak in in-situ synthesized nanocomposites indicating an exfoliated structure in the prepared nanocomposites; conversely, a solution blending technique resulted in an intercalated structure. AFM phase images well displayed the dispersion of nanoclay in the polymeric matrix. The delamination of clay platelets in the polymer matrix of in-situ prepared nanocomposite is demonstrated by TEM images; on the other hand, TEM results revealed the intercalated structure of nanocomposites prepared by solution blending technique

Study of Atom Transfer Radical Polymerization of Styrene and Its Gel Effect by Monte Carlo Simulation Method

Atom transfer radical polymerization (ATRP) of styrene was carried out at 105°C and a Monte Carlo simulation was employed to model the system. The variations of monomer conversion, the initiator concentration, average molecular weight, and molecular weight distribution were evaluated as the reaction proceeded. According to the results obtained, for similar reaction time, monomer conversion is higher when gel effect is taken into account. Also, the concentration of initiator suddenly drops at the initial stages of polymerization, and finally reaches zero. In addition, in the presence of gel effect, bimolecular termination rate constant decreases during the polymerization. Moreover, number- and weight-average molecular weights linearly rise as the polymerization progresses; this also is a confirmation to the living nature of the polymerization. Finally, the molecular weight distribution of polymers synthesized narrows at high monomer conversion. In effect, polydispersity index decreases from about 2 (at the onset of polymerization) to around 1.3 (towards the end of polymerization)

A Comparative Study between FRP and ATRP of Styrene by Monte Carlo Simulation: Effect of Free Radical Mobility

Styrene polymerization through FRP and ATRP methods was carried out at 110oC, while in-depth studies were performed by Monte Carlo simulation.The changes in monomer conversion, initiator concentration, average molecular weight, and polydispersity index were computed over the course of the polymerization. As the results indicate, compared to ATRP, the FRP reaches higher conversion in a similar reaction time. In addition, the concentration of initiator suddenly drops at the early stages of the ATRP and eventually amounts to zero; chain-length dependent termination rate constant also decreases as the polymerization progresses. However, in case of FRP, the concentration of initiator exponentially falls and termination rate constant rises during the reaction. Furthermore, the average molecular weight increases linearly in the course of ATRP, which testifies the living dynamism of the reaction. Finally, the molecular weight distribution of chains obtained byATRP process is much narrower

Effect of Reactant Concentration Variations on the Kinetics of Atom Transfer Radical Polymerization of Acrylonitrile

Polyacrylontrile synthesis, via atom transfer radical polymerization, is studied in various initiator concentrations, transitional metal catalyst and different concentrations of CuBr2. The variations of monomer conversion and the lin-earity of semi-logarithmic kinetic profile which is the evidence of living polymerization and constant radical concentration in the reaction medium, were revealed by gas chromatography technique (GC). Gel permeation chromatography (GPC) studies revealed that, the number average molecular weight increases linearly against monomer conversion, an indicative of living nature of the polymerization process. Additionally, the conversion, apparent rate constant and number average molecular weight increased with increased initiator concentration as well as the transitional metal complex concentration. However, addition of CuBr2 lowered conversion, kapp, and the number average molecular weight of polyacrylonitrile. Molecular weight distribution of synthesized polymers broadened with increased initiator concentration and also transitional metal complex concentration. However, addition of CuBr2 has resulted in narrower molecular weight distribution polyacrylonitrile. Moreover, all the samples experienced a drop in PDI value from nearly 2 to almost 1.1 as the reaction progressed