Self-catalyzed polymerization

In the absence of an externally added strong acid the diacid monomer acts as its own catalyst for the esterification reaction. For this case [HA] is replaced by [COOH] and Eq. 2-17 can be written in the usual form [Flory, 1953] 

For most polymerizations the concentrations of the two functional groups are very nearly stoichiometric, and Eq. 2-18 can be written as 

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The polyesterification becomes a much more economically feasible reaction when it is catalyzed by an external acid. The self-catalyzed polymerization is not a useful reaction from the practical viewpoint of producing high polymers in reasonable reaction times. 

Because TPA has a melting point of >300 °C and poor solubility in PDO, direct esterification is preferably carried out in the presence of a heel under a pressure of 70-150kPa and at 250-270 °C for 100-140min. A heel is an oligomeric PTT melt with a degree of polymerization (DP) of 3 to 7, purposely left in the reaction vessel from a previous batch to improve TPA solubility and to serve as a reaction medium. The esterification step is self-catalyzed by TPA. 

Figure 3 Fraction of material in the polymerized state, f, as a function of the mass action variable X relative to its value X at the half-way point f =1/2. Indicated are predictions for the isodesmic and the self-catalyzed nucleated polymerization models. Activation constant of the nucleated polymerization Ka = 10-4.

If the nucleated assembly is self-catalyzed, then this modifies only the role of the equilibrium constant K in the non-self-catalyzed model and has to be replaced by the ratio K/Ka. This means that we again obtain for the fraction polymerized material f=KaNa/(1 + KaNa) but that the degree of polymerization averaged over the active material only now obeys (Ciferri, 2005)... 

The self-catalyzed model is a simplification of the actin polymerization model of Oosawa and Kasai (1962) [and more recent elaborations of it (Niranjan et al., 2003)], and both equilibrium constants K and Kn, and hence the free energies g and ga can in principle be obtained by fitting the theory to assembly experiments. Typical values of g for, for example, actin vary between —10 and —20 kBT and ga between +2 and +3 kBT (Oosawa and Asakura, 1975 Oosawa and Kasai, 1962). For the biomimetic compound oligo(phenylene vinylene) similar to compound 2 shown in Figure 6, dissolved in alkane solvents, similar values were found for g but much larger ones for ga of +8 to +10 kBT, making the supramolecular polymerization of this compound an extremely highly co-operative process (Jonkheijm et al., 2006). 

IfX 1, disordered (nonhelical) assemblies do not form in any appreciable quantities. For h< 0, there is a polymerization transition from monomers to helical assemblies that is of the self-catalyzed nucleation type provided flj 3> 1. In the language of the coarse-grained self-catalyzed nucleated assembly model, the transition takes place near Xp exp [f3h] and we are able to assign an activation constant Ka exp [ 3j + 311], The theory of Section 2 approximately applies. 

Assume that the polymerization i,s self catalyzed [cat] = [COOH], plot the appropriate function of the fraction of functional groups reacted, p, as a function of time in order to obtain a linear plot. Plot the experimental data on the same plot. In what regions do the theory and experiment agree, and in which region do they disagree ... 

Bundgaard H. Polymerization of penicillins 11. Kinetics and mechanism of dimerization and self-catalyzed hydrolysis in aqueous solution. Acta Pharm Succ 1977 14 47-66. 

The self-condensing copper-catalyzed polymerization of macromonomer of poly(tBA) with a reactive C—Br bond (H-6) affords hyperbranched or highly branched poly(tBA).447 Copolymerization of H-1 and TV-cyclohexylmaleimide induced alternating and self-condensing vinyl polymerization.448 The residual C—Cl bond was further employed for the copper-catalyzed radical homopolymerization of styrene to give star polymers with hyperbranched structures. Hyperbranched polymers of H-1 further serve as a complex multifunctionalized macroinitiator for the copper-catalyzed polymerization of a functional monomer with polar chromophores to yield possible second-order nonlinear optical materials.325... 

Equation 20.17 puts the kinetic expression entirely in terms of the initial concentration of monomer, Cq, and is in the form useful for following the rates of linear (only bifunctional monomers) self-catalyzed polycondensations. If 1/p is plotted against t one gets a straight line. Under self-catalyzed conditions, the reaction is third order, and the degree of polymerization (DP, or Xn) is approximately proportional to t. This third-order dependency of the rate of self-catalyzed polycondensations also means that the rate of increase in the molecular weight (degree of polymerization) slows down quite rapidly as the reaction proceeds. 

A bimetallic titanium complex of BINOL derivative can be used to catalyze the asymmetric carbonyl-ene reaction [46]. Insoluble polymeric catalyst 74 was prepared from a self-assembly of Ti(OiPr)4 and non-crosshnked copolymers with (R)-binaphthol pendant groups (Scheme 3.22) [47]. The self-assembled polymeric Ti complex is insoluble in organic solvent and catalyzed the carbonyl-ene reaction of glyoxylate 75 and a-methylstyrene 76. When the reaction of 75 and 76 was carried out with 20mol% of 74 in Gl pCf at room temperature, an 85% yield of the product with 88% ee was obtained. Following its recovery by filtration, this catalyst was reused five times with full retenhon of its activity and enantioselectivity, without further treatment... 

A compilation of enzyme-catalyzed self-condensation polymerizations that have thus far appeared in the literature is given in Table 4.1. 

Apart from species containing OH groups that may be added as catalysts, the epoxy-amine reaction generates OH groups. Therefore, the reaction is self-catalyzed by reaction products, a fact that leads to sigmoidal conversion versus time curves when the polymerization is performed at a constant temperature. 

An efficient one-pot synthesis of core/shell TiO /PANI-NPs from meth-acrylic acid-functionalized TiO -NPs by self-catalyzed hydroamination and oxidative polymerization of aniline was demonstrated by Bae et al. [118]. Core/shell-structured TiO /PANI nanocomposite was also fabricated by grafting aniline on aminobenzoate monolayer that is chemically adsorbed on the TiO nanocrystal surface [119]. Ferromagnetic semiconducting PANI/TiO nanocomposites [96], PANI/TiO nanocomposite photocatalysts [97], as well as composites of self-assembled PANI nanostructures with TiO -NPs [88] or TiO nanotubes [98] were synthesized by... 

Uses Reducing agent in redox-catalyzed polymerization color stabilizer, modifier, catalyst for polyamides antioxidant intermediate for forming metallic salts used as stabilizers accelerator for org. peroxide catalysts improver of polysiloxane resins free radical promoter in emulsion polymerization promoter in polyester resin curing mfg. of self-extinguishing fibers (reacts with polyester resin and polyolefin) color/odor inhibitor, catalyst for some thermoplastics discoloration inhibitor in PE corrosion inhibitor on thin aluminum surfs. lubricity improver in polyphenyl thioether-based lubricants Manuf./Distrib. Akzo Nobel http //www.akzonobel.com, Ferro http //WWW. ferro. com... 

Block-Type Brushes by Sequential Polymerization The sequential hving polymerization of two macromonomers or a macromonomer with a conventional comonomer forms either block-block- or block-coil-type brush structures. For example, giant rod-coil amphiphilic block copolymer bmshes were prepared via a stepwise metallocene-catalyzed polymerization [58]. In the first step, a concentrated solution of methacryloyl end-functionalized PS macromonomer (DP = 18.3, MWD = 1.05) was polymerized by the organosamarium(iii) catalyst in THF. After PS macromonomer was completely consumed, the active center remained living, and tert-butyl methacrylate tert-butyl methacrylate (tBMA) as a comonomer was added to grow the second block. After termination by ethanol, the poly(tert-butyl methacrylate) (PtBMA) coil block was hydrolyzed into a hydrophihc block, poly(methacrylic acid) (PMAA). The final product consisted of a hydrophobic PS brush block and a hydrophihc PMAA coil. The hydrophilic PMAA coil collapsed in nonpolar solvents, which forced the block-coil CPBs to self-assembled into giant micelles with PMAA as the core component and the stiff PS brush block as the shell to stabihze the micelles. 

Two quite different kinetic situations arise from Equation 4.1 depending on the identity of HA, that is, on whether a strong acid is added as an external catalyst providing two different modeling approaches, that of self- and external-catalyzed polymerization. 

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