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Polymers Containing Pendent Pesticide Substituents
Published in Agis F. Kydonieus, Controlled Release Technologies: Methods, Theory, and Applications, 2019
Vinyl pesticide monomers have been polymerized by bulk-, solution-, and emulsion-free radical techniques.1–8 Bulk polymerization is the simplest method for preparing polymers. The monomer(s) is simply mixed with a small amount (<1%) of a free radical initiator, such as azobisisobutyronitrile (AIBN), and heated for several hours. The complete conversion of monomer to polymer, however, is seldom accomplished. Thus, the product is often contaminated with unreacted monomer, which can be very difficult to remove. The polymerizations are also usually exothermic, which can lead to problems with heat control. In fact, bulk polymerizations of vinyl monomers are seldom carried out with large amounts of material due to the danger of explosions.
Superporous Hydrogel Composites: A New Generation of Hydrogels with Fast Swelling Kinetics, High Swelling Ratio and High Mechanical Strength
Published in Raphael M. Ottenbrite, Sung Wan Kim, Polymeric Drugs & Drug Delivery Systems, 2019
Kinam Park, Jun Chen, Haesun Park
Polymerization of monomers in the absence of any other solvent is called bulk polymerization. Bulk polymerization of monomers, such as hydrox-yethyl methacrylate (or HEMA), leads to the production of a glassy, transparent polymer matrix that is very hard. When immersed in water, such a glassy matrix swells to become relatively soft and flexible. Although it allows the transfer of water and some low molecular weight solutes, this kind of swollen polymer matrix (i.e., hydrogel) is considered nonporous. The pores between polymer chains are in fact the only spaces available for mass transfer, and the pore size is within the range of molecular dimensions (a few manometers or less) [14]. Under a scanning electron microscope, the surface of the dried hydrogels appears completely nonferrous. In this case, the transfer of water or other solutes is achieved by a pure diffusional mechanism [14]. This restricts the rate of absorption and to some extent the size of the species that are absorbed [15]. The homogeneous hydrogels have been used widely in various applications, especially in the controlled drug delivery area where limited diffusional characteristics are required [16].
Characteristics of Polymers and Polymerization Processes
Published in Manas Chanda, Plastics Technology Handbook, 2017
Polymerization in bulk, that is, of undiluted monomer, minimizes any contamination of the product. But bulk polymerization is difficult to control because of the high exothermicity and high activation energies of free-radical polymerization and the tendency toward the gel effect (in some cases). By carrying out the polymerization of a monomer in a solvent (solution polymerization), these disadvantages of the bulk process can be avoided. The solvent acting as a diluent reduces the viscosity gain with conversion and allows more efficient agitation or stirring of the medium, thereby enabling better transfer and dissipation of heat. Solution polymerization is, however, advantageous only if the polymer formed is to be applied in solution (avoiding the need for solvent removal at the end), such as for making coating (lacquer) grade poly(methyl methacrylate) resins from methyl methacrylate and related monomers.
Recent advances in the synthesis of and sensing applications for metal-organic framework-molecularly imprinted polymer (MOF-MIP) composites
Published in Critical Reviews in Environmental Science and Technology, 2023
Yongbiao Hua, Deepak Kukkar, Richard J. C. Brown, Ki-Hyun Kim
Bulk polymerization is frequently used to prepare conventional MIPs in bulk form due to its simple operation (Arabi et al., 2020). If small particles are needed, the bulk MIPs should be subject to post-treatments such as mechanical crushing, grinding, and sieving (Pichon et al. 2020). However, such crushing and grinding can alter the MIP particles, causing irregular morphology (and the loss of fine polymer particles) or lowering the binding affinity through the destruction of the imprinted cavities (Arabi et al., 2020; Azizi & Bottaro, 2020). Therefore, some methods have been developed to yield MIP particles with a regular morphology such as precipitation polymerization (Barciela-Alonso et al., 2017), pickering emulsion polymerization (Pan et al., 2013; Sun et al., 2016), and suspension polymerization (S. Chen et al., 2019). Despite the high selectivity for the target species, the extensive sensing application of MIPs network is often restricted for the rapid and efficient detection of analytes due to their demeritiful properties (e.g., poor conductivity (Liang et al., 2017), poor cavities accessibility, and low mass transfer rate (Hatamluyi et al., 2020a)). Therefore, it is of great importance to design novel MIP materials with good conductivity and high surface area to overcome such limitations.
A detailed description of methyl methacrylate free radical polymerization using different heating policies under isothermal and non-isothermal conditions: a kinetic Monte Carlo simulation
Published in International Journal of Modelling and Simulation, 2021
Ramin Bairami Habashi, Mohammad Najafi, Peyman Mostafaei, Behrouz Shojaei
Free radical polymerization (FRP) is one of the most widely used methods in synthesizing a variety of polymers for a wide range of applications. The advantages of this method are the low sensitivity to various impurities, usually mild process temperatures, and applicability to many available polymerization processes such as bulk, solution, suspension, and emulsion. Owing to the absence of any other solvents and additives, the product obtained from the bulk polymerization process is almost completely pure. Because of the high viscosity during the polymerization process, mixing process, heat transfer, and mass transfer are confronted with serious problems, and the gel effect occurs at lower conversions, which usually causes molecular weight distribution to broaden [1–4].
Ring opening polymerization of lactide: kinetics and modeling
Published in Chemical Engineering Communications, 2019
Sangeeta Metkar, Vivek Sathe, Imran Rahman, Bhaskar Idage, Susheela Idage
The 1H NMR spectra of synthesized PLLA are illustrated in Figures 1 and 2 respectively. It shows the peaks for the methine (-CH) proton at 5.14 ppm and 5.22 ppm for the L-lactide and PLLA respectively. The peaks of methyl (-CH3) proton for the L-Lactide (1.7 ppm) and PLLA (1.6 ppm) are as shown in Figure 1 respectively. The decrease in intensity of monomer methine proton (right quartet) and rise in the intensity of the polymer methine proton (left quartet) with time were observed as shown in Figure 2. The plot of Y = ln[M0/M] versus time for L-lactide (M) ROP kinetics with Sn(Oct)2 (C) and 1-pyrene butanol (ROH) [M:C = 5620:1 and ROH:C = 17:1 at temperatures 150–180 °C] is shown in Figure 3 respectively. [M0] and [M] are the initial and unreacted monomer concentrations respectively. This plot is linear at conversion <95%. The livingness of polymerization and assumption of constant number of polymer chains are proved by linear behavior of the semi logarithmic plot (Figure 3). It also indicates that L-lactide polymerization follows the first order dependence on monomer concentration. The absence of induction period confirms that the initiation is fast. The slope of line shown in Figure 3 is equal to the product of kp and [C0] and thus kp is readily evaluated. The estimated kp values are shown in Table 1 respectively. It was observed that replacing [M] by ([M]-[Meq]) had negligible effect on the calculated values of kp (Wang et al., 2014). Meq is the monomer equilibrium concentration. On the basis of kp, it is proved that the bulk polymerization rate increases with an increase in the temperature. The obtained kp values are matching with the reported values (Yingchuan et al., 2011).