Kinetic polymerization

Polymerization Kinetics Polymerization Reactor Dynamics Emulsion Polymerization (ed. volume)... 

Chain-growth polymerizations are so called because their mechanisms comprise chains of kinetic events. For successful polymerization, the sequence of reactions must first be initiated by some agent, and monomers must be added consecutively to a growing macromolecule. This chain of events may then be terminated by a reaction that is inherent in the system or by the action of impurities. In any case, we can usefully distinguish between at least three different reaction types in a kinetic polymerization chain. These are initiation, propagation, and termination reactions. (Recall that theie is only one reaction involved in step-growth polymerizations where the monomers add to the end of a macromolecule without the intervention of an active center.)... 

The variation of molecular composition of a liquid is described by a kinetic scheme of polymerization a complete scheme includes a great number of different elementary reactions. During analysis of macrokinetics of polymerization processes, i.e. the development of temperature, concentration and hydrodynamic fields in the course of the process, a separate consideration of each step is usually very difficult and ineffective. It is more rational to introduce a unified internal parameter, the conversion P, which characterizes the state of the material [12-14]. For simple kinetic polymerization schemes, the conversion corresponds to the change of concentration of reactive groups or to the conversion of a monomer. 

Fig. 27 Video microscopy kinetics polymerization rate-time profiles for several particles...

Polymers are macromolecules which are composed of smaller molecules linked by covalent bonds. In terms of the reaction kinetics, polymerizations are traditionally classified into several categories stepwise polymerization, free-radical polymerization, ionic polymerization, ring-open polymerization, and coordination polymerization or polyinsertion. Each polymerization method has a combination of requirements for reaction conditions, and they exhibit certain types of product and process features (Caneba, 1992a, 1992b Odian, 1991). Even though in principle, the FRRPP process can be implemented with a wide variety of polymerization mechanisms, its discovery and immediate implementation has occurred in conjunction with free-radical kinetics. 

Keywords polymerization kinetics, polymerization reactors, mathematical modelling, molecular weight distribution (MWD), chemical composition distribution (CCD), Ziegler-Natta catalysts, metallocenes, microstructure, isotacticity distribution, mass transfer resistances, heat transfer resistances, effects of multiple site types. 

Shulz and collaborators in their kinetic polymerizations done anionically in with cumylcesium initiators. Their main concern was to determine the statistics which best described the tactic addition of monomer. By NMR analysis of sequence lengths they concluded that the system obeyed Markovian rather than Bernoulli an statistics. ... 

Kinetic polymerization curves show that autoacceleration takes place essentially from the beginning of the process. 

Keywords kinetics polymerization mechanisms glossary thermodynamics lUPAC Polymer Division. 

Figure 2.34. Kinetic polymerization curves of tetramethylene-dimetacrylate in a matrix of cis-polyisoprene at various values of Xex (I-IV) and ti 8 (1), 24 (2), 48 (3) and 240 (5) hour. Blackened markings show samples after secondary swelling. Explanation is provided in the text, see table 2.5.

The kinetics of this type of polymerization are the same as for simple condensation for this reason, the use of the term polycondensation is perhaps more appropriate. Unless kinetic evidence suggests otherwise, polymerizations involving the formation of chain polymers from cyclic compounds, following ring scission, are classed as condensation polymerizations. Some important con-... 

TMED, (CH3)2NCH2CH2N(CH3)2. B.p. 122 C a hygroscopic base which forms a hydrocarbon-soluble stable chelate with lithium ions and promotes enhanced reactivity of compounds of lithium, e.g. LiAlH4, UC4H9, due to enhanced kinetic basicity of the chelate. Used in polymerization catalysts, tetramethyl lead, TML 5 lead tetramethyl. 

The successful preparation of polymers is achieved only if tire macromolecules are stable. Polymers are often prepared in solution where entropy destabilizes large molecular assemblies. Therefore, monomers have to be strongly bonded togetlier. These links are best realized by covalent bonds. Moreover, reaction kinetics favourable to polymeric materials must be fast, so tliat high-molecular-weight materials can be produced in a reasonable time. The polymerization reaction must also be fast compared to side reactions tliat often hinder or preclude tire fonnation of the desired product. 

Surfactants provide temporary emulsion droplet stabilization of monomer droplets in tire two-phase reaction mixture obtained in emulsion polymerization. A cartoon of tliis process is given in figure C2.3.11. There we see tliat a reservoir of polymerizable monomer exists in a relatively large droplet (of tire order of tire size of tire wavelengtli of light or larger) kinetically stabilized by surfactant. 

Poll Fl-U, Arzt M and Wickleder K-FI 1976 Reaction kinetics in the polymerization of thin films on the electrodes of a glow-discharge gap Eur. Polym. J 12 505-12... 

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

The mechanism of these reactions places addition polymerizations in the kinetic category of chain reactions, with either free radicals or ionic groups responsible for propagating the chain reaction. 

We shall have considerably more to say about this type of kinetic analysis when we discuss chain-growth polymerizations in Chap. 6. 

Although the results presented in Fig. 5.2 appear to verify the predictions of Eq. (5.16), this verification is not free from controversy. This controversy arises because various workers in this field employ different criteria in evaluating the success of the relationships we have presented in fitting experimental polymerization data. One school of thought maintains that an adequate kinetic description of a process must apply to the data over a large part of the time of the experiment. 

The preceding discussions of the kinetics and molecular weight distributions in the step-growth polymerization of AB monomers are clearly exemplified by the esterification reactions of such monomers as glycolic acid or co-hydroxydecanoic acid. Therefore one method for polyester synthesis is the following ... 

The polymerization of j3-carboxymethyl caprolactam has been observed to consist of initial isomerization via a second-order kinetic process followed by condensation of the isomer to polymer ... 

Elsewhere in this chapter we shall see that other reactions-notably, chain transfer and chain inhibition-also need to be considered to give a more fully developed picture of chain-growth polymerization, but we shall omit these for the time being. Much of the argumentation of this chapter is based on the kinetics of these three mechanistic steps. We shall describe the rates of the three general kinds of reactions by the notation Rj, Rp, and R for initiation, propagation, and termination, respectively. 

As with the rate of polymerization, we see from Eq. (6.37) that the kinetic chain length depends on the monomer and initiator concentrations and on the constants for the three different kinds of kinetic processes that constitute the mechanism. When the initial monomer and initiator concentrations are used, Eq. (6.37) describes the initial polymer formed. The initial degree of polymerization is a measurable quantity, so Eq. (6.37) provides a second functional relationship, different from Eq. (6.26), between experimentally available quantities-n, [M], and [1]-and theoretically important parameters—kp, k, and k. Note that the mode of termination which establishes the connection between u and hj, and the value of f are both accessible through end group characterization. Thus we have a second equation with three unknowns one more and the evaluation of the individual kinetic constants from experimental results will be feasible. 

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