Suspension polymerization polymer characterization

When the polymer was prepared by the suspension polymerization technique, the product was crosslinked beads of unusually uniform size (see Fig. 16 for SEM picture of the beads) with hydrophobic surface characteristics. This shows that cardanyl acrylate/methacry-late can be used as comonomers-cum-cross-linking agents in vinyl polymerizations. This further gives rise to more opportunities to prepare polymer supports for synthesis particularly for experiments in solid-state peptide synthesis. Polymer supports based on activated acrylates have recently been reported to be useful in supported organic reactions, metal ion separation, etc. [198,199]. Copolymers are expected to give better performance and, hence, coplymers of CA and CM A with methyl methacrylate (MMA), styrene (St), and acrylonitrile (AN) were prepared and characterized [196,197]. 

Water insoluble monomers such as vinyl chloride may be polymerized as suspended droplets (10-1000 nm in diameter) in a process called suspension (pearl) polymerizations. Coalescence of droplets is prevented by the use of small amounts of water-soluble polymers, such as PVA. The suspension process is characterized by good heat control and ease of removal of the discrete polymer particles. 

An additional porous polymer is poly(glycidyl methacrylate-ethyleneglycol dimethacrylate) (see Figure 2.46) that is synthesized by suspension polymerization in the presence of an inert porogen in the polymerization reaction, obtaining a material with an internal macroporous morphology characterized by an interconnected pore network, which permeates the extensively cross-linked polymer matrix [209],... 

Dawkins JV. Aqueous suspension polymerizations, chain polymerization, II, Chapter 14. In Geoffrey A, Bevington JC, editors. Comprehensive Polymer Science. The Synthesis, Characterization Applications of Polymers. Volume 4. Oxford Pergamon Press 1989. 

When water-soluble initiators and surface-active agents are used, relatively stable latices are formed from which the polymer cannot be separated by filtration. In the case of vinyl acetate, the distinctions are more blurred. Our description of Procedure 3-3 above represents a transitional situation between a solution and a suspension process since the product separated from the reaction medium. Between the true suspension and the true emulsion polymerization, we find, according to Bartl [4], the processes for formation of reasonably stable dispersion of fine particles of poly(vinyl acetate) using reagents which are normally associated with suspension polymerization. The product is described as creme-like. The well-known white, poly(vinyl acetate), household adhesives may very well be examples of these creamy dispersions. The true latices are characterized by low viscosities and particles of 0.005-1 /im diameter. The creme-like dispersions exhibit higher viscosities and particle diameters of 0.5-15 fim. 

P. Ding and B. J. Qu, Synthesis and characterization of polystyrene/layered doublehydroxide nanocomposites via in situ emulsion and suspension polymerization. Journal of Applied Polymer Science, 101 (2006), 3758-66. 

A more recent application of ultrasonics has been the characterization of the extent of polymerization in a condensation or radical process. The first observations were made by Sokolov, and subsequent reports of measurements on polystyrene, poly(vinyl chloride) and poly(vinyl acetate) " have confirmed the utility of the method. It is clear that this type of study is still in its infancy however, certain facts emerge which demonstrate the importance of this method. The compressibility of a solution containing monomer and polymer is directly related to the proportion of each component present. It is therefore possible to quantitatively estimate the extent of conversion from the observed velocity of sound. In a suspension polymerization, the glass transition of the polymer forming the bead is itself a function of the extent to which unreacted monomer is retained in the system. In this case, observation of the attenuation can indicate the extent to which polymerization has occurred in the system. Unfortunately the data are not sufficiently extensive to estimate the general validity of the method for the monitoring of polymerization in reactors, although the potential has been clearly demonstrated. 

Polymerization can be catalytic or noncatalytic, and can be homogeneously or heterogeneously catalyzed. Polymers that form from the liquid phase may remain dissolved in the remaining monomer or solvent, or they may precipitate. Sometimes beads are formed and remain in suspension sometimes emulsions form. In some processes solid polymers precipitate from a fluidized gas phase. Polymerization processes are also characterized by extremes in temperature, viscosity, and reaction times. For instance, many industrial polymers are mixtures with molecular weights of 104 to 107. In polymerization of styrene the viscosity increased by a factor of 106 as conversion increased from 0 to 60 percent. The adiabatic reaction temperature for complete polymerization of ethylene is 1800 K (3240°R). Initiators of the chain reactions have concentration as low as 10-8 g-moFL, so they are highly sensitive to small concentrations of poisons and impurities. 

Further in this chapter we will discuss polymerization processes, specifically processes performed in a heterogeneous medium, including suspension, emulsion, and mini emulsion. We shall discuss their preeminent properties, such as the type of nucleating particle, a greater efficiency in the heat exchange, inorganic fillers and their features, and the addition of special characteristics of each process and the analytical methods used in the characterization of polymer/inorganic hybrid. 

To characterize the polymerization behavior of FA and to investigate how the presence of MMT influences this polymerization, FTIR spectra were collected before and during the resiniflcation process. The dispersion of the MMT in the PFA matrix is shown both directly and indirectly. The direct evidence consists of the XRD patterns of the FA-MMT suspension, which was used to monitor the process of intercalation and exfoliation of the MMT at various stages of resinifica-tion. The dispersion is indirectly evidenced in increased thermal stability of the MMT-PFA nanocomposite, as measured by TGA. The thermal stability is discussed and compared to the pure polymer and to the CW-PFA nanocomposites. In addition, the important differences between oxidative and nonoxidative degradation of the NaMMT-PFA nanocomposite is discussed, and a mechanism is proposed to explain the difference in terms of acid-catalyzed degradation. 

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