Kinetic study of polymerization

The chain termination processes will be described in detail in the following sections, dealing with the kinetic study of polymerization process. 

We describe a mechanistic and kinetic study of polymerization of ethylene and 1-hexene by the homogeneous catalyst Cp2ZrCl2-(MeAlO)x-toluene. 

For a long time this quantity was about the only experimental basis for kinetic studies of polymerization, and only in recent years was it possible to determine the individual rates of the different reaction steps with the aid of an ingenious and modern experimental technique. 

It should be mentioned that simple metal complexes immobilized on polymer supports were initially used for polymerization (1965/1966) in the Solvay catalysts based on titanium complexes bound to macromolecular ligands with C=0, C=N and C=N groups. Until now the data are mainly available in patent literature, and there are few kinetic studies of polymerization processes involving the action of macromolecular complexes. At the same time the use of metal complexes bound to inorganic supports has been extensively developed in polymerization catalysis. This indicates that there has been inadequate study of the application of metal complexes immobilized on polymer supports to the catalysis of polymerization and copolymerization of different monomers, mainly olefins. 

The application of dilatometric method for kinetic studies of polymerization or copolymerization processes is usually based on the determination of the dependences of the speed of the process on the following parameters ... 

Most values of / have been measured at zero or low conversions. During polymerization the viscosity of the medium increases and the concentration of monomer decreases dramatically as conversion increases (i.e. as the volume fraction of polymer increases). The value of / is anticipated to drop accordingly. 32, u 9j % For example, with S polymerization in 50% (v/v) toluene at 70 °C initialed by 0.1 M AIBN the instantaneous" / w as determined to vary from 76% at low conversion to <20% at 90-95% conversion (Figure 3.3).32 The assumption that the rate of initiation (kAf) is invariant with conversion (common to most pre 1990s and many recent kinetic studies of radical polymerization) cannot be supported. 

Recent kinetic studies of this polymerization 14) revealed that some parasitic reactions cause termination and induction periods in the overall process. Their nature is not known yet. It is tentatively suggested that the activated polymers react with the dormant ones yielding some destruction products, although the nucleophile capable of activating the still available dormant chains is regenerated. Alternatively it is possible that the intermediate 3 is labile and may decompose before collapsing into 4 with regeneration of the nucleophile. Whatever the cause of these side reactions, one should stress that the conversion of the monomer into polymer is almost quantitative. 

Kinetic studies of the polymerization of mono-functional polymethyl methacrylate led to the determination of the propagation constants, k , of the sodium, potassium, and cesium salts 29- 35 36) of polymethyl methacrylates anions. Surprisingly, they... 

With stannous octoate-promoted polymerization, the metal species is believed to function as the catalyst and water (added or endogenous), or alcohol, serves as the initiator (Fig. 2). This mechanism is supported by recent kinetic studies of PCL polymerization in the presence of triphenyltin acetate (46). After an induction period, polymerization is zero order with respect to monomer and near first... 

The study of polymerization kinetics allows us to understand how quickly a reaction progresses and the role of temperature on the rate of a reaction. It also provides tools for elucidating the mechanisms by which polymerization occurs. In addition, we are able to study the effect of catalysts on the rates of polymerization reactions, allowing us to develop new and better catalysts based on the measured performance. 

A Kinetic Study of an Anhydride-Cured Epoxy Polymerization... 

In the literature, examples are given of bench-scale equipment designed for special fields such as for polymerizations [186] and for kinetic studies of catalytic reactions [187]. 

It is unfortunate that many workers have not appreciated how essential a clue to the kinetics can be provided by the kinetic order of the whole reaction curve. The use of initial rates was carried over from the practice of radical polymerisation, and it can be very misleading. This was in fact shown by Gwyn Williams in the first kinetic study of a cationic polymerization, in which he found the reaction orders deduced from initial rates and from analysis of the whole reaction curves to be signfficantly different [111]. Since then several other instances have been recorded. The reason for such discrepancies may be that the initiation is neither much faster, nor much slower than the propagation, but of such a rate that it is virtually complete by the time that a small, but appreciable fraction of the monomer, say 5 to 20%, has been consumed. Under such conditions the overall order of the reaction will fall from the initial value determined by the consumption of monomer by simultaneous initiation and propagation, and of catalyst by initiation, to a lower value characteristic of the reaction when the initiation reaction has ceased. 

Abstract. Auto-accelerated polymerization is known to occur in viscous reaction media ("gel-effect") and also when the polymer precipitates as it forms. It is generally assumed that the cause of auto-acceleration is the arising of non-steady-state kinetics created by a diffusion controlled termination step. Recent work has shown that the polymerization of acrylic acid in bulk and in solution proceeds under steady or auto-accelered conditions irrespective of the precipitation of the polymer. On the other hand, a close correlation is established between auto-acceleration and the type of H-bonded molecular association involving acrylic acid in the system. On the basis of numerous data it is concluded that auto-acceleration is determined by the formation of an oriented monomer-polymer association complex which favors an ultra-fast propagation process. Similar conclusions are derived for the polymerization of methacrylic acid and acrylonitrile based on studies of polymerization kinetics in bulk and in solution and on evidence of molecular associations. In the case of acrylonitrile a dipole-dipole complex involving the nitrile groups is assumed to be responsible for the observed auto-acceleration. 

A critical survey of the literature on free radical polymerizations in the presence of phase transfer agents indicates that the majority of these reactions are initiated by transfer of an active species (monomer or initiator) from one phase to another, although the exact details of this phase transfer may be influenced by the nature of the phase transfer catalyst and reaction medium. Initial kinetic studies of the solution polymerization of methyl methacrylate utilizing solid potassium persulfate and Aliquat 336 yield the experimental rate law ... 

The observed catalytic effect of the crown ether appears to be dependent on the nucleophile employed in both polymerization and corresponding model reactions. Not surprisingly, it appears that the stronger the nucleophile employed, the smaller the catalytic influence of the crown ether. For example, with potassium thiophen-oxide yields of polymer or model products were almost quantitative with or without catalyst. By contrast, the reaction of PFB with potassium phthalimide, a considerably weaker nucleophile, affords 6 in 50% with catalyst and in 2-3% without catalyst under identical conditions. However, it may be that this qualitative difference in rates is, in fact, an artifact of different solubilities of the crown complexed nucleophiles in the organic liquid phase. A careful kinetic study of nucleophilicity in catalyzed versus non-catalyzed reactions study is presently underway. 

Whatever previously listed monomer is considered, the living character of the polymerization has been confirmed by kinetic studies, where polymerization is first order in both monomer and initiator. Moreover, the molecular weight can be predicted by the monomer-to-initiator molar ratio, the molecular weight distributions are narrow (PDI=1.05-1.20), and the monomer resumption... 

Few structural tools are available to assess the structure of crosslinked networks directly. A frequent approach is to derive such information from kinetic study of unreacted monomer during the polymerization process (4). The possibilities for deriving structural information by characterizing network fragments has not been fully explored. 

Kinetic study of this reaction usually requires sampling the polymerizing mixture and analyzing for the concentrations of the various reaction species at different polymerization times. Vofsi and Tobolsky in 1965 reported the use of radioactively tagged initiator (10), while Saegusa amd coworkers in 1968 developed a "phenoxy end-capping" method in which the oxonium ion is trapped with sodium phenoxide and the derived phenyl ether at the polymer chain end quantitatively determined by UV spectrophotometry (11). 

We found this method to be extremely useful for kinetic in-situ study of polymerizations without disturbing the system. Subsequently we applied to follow the polymerization initiated... 

Lactam polymerizations (nonassisted as well as assisted) are usually complicated by heterogeneity, usually when polymerization is carried out below the melting point of the polymer [Fries et al., 1987 Karger-Kocsis and Kiss, 1979 Malkin et al., 1982 Roda et al., 1979]. (This is probably the main reason why there are so few reliable kinetic studies of lactam polymerizations.) An initially homogeneous reaction system quickly becomes heterogeneous at low conversion, for example, 10-20% conversion (attained at a reaction time of no more than 1 min) for 2-pyrrolidinone polymerization initiated by potassium t-butoxide and A-benzoyl-2-pyrrolidinone. The (partially) crystalline polymer starts precipitating from solution (which may be molten monomer), and subsequent polymerization occurs at a lower rate as a result of decreased mobility of /V-acyl lactam propagating species. 

Langsdorf BL, Zhou X, Lonergan MC. Kinetic study of the ring-opening metathesis polymerization of ionically functionalized cyclooctatetraenes. Macromolecules 2001 34 2450-2458. 

Plasson, R., Biron, J. P, Cottet, H., Commeyras, A., and Taillades, J. (2002). Kinetic study of the polymerization of alpha-amino acid N-carboxyanhydrides in aqueous solution using capillary electrophoresis. J. Chromatogr. A, 952, 239-48. 

The diethylzinc-alcohol (1 2) system was also extensively studied by Tsuruta and his co workers (85,86). Amorphous zinc dialkoxide was concluded to be an active species, because crystalline zinc alkoxide prepared from zinc chloride and lithium alkoxide proved to have only a very small catalytic activity. Based on kinetic studies of the polymerization of propylene oxide with the ZnEt2-CH3OH (1 2) catalyst system, the catalytically active species was concluded to be the complex formed by coordination of one molecule of monomer to the catalyst. In the polymerization of propylene oxide with the catalyst system, it was concluded that the monomer was polymerized by ring opening brought about by cleaving the CH2-0 bond (87). 

Fig. 8. The apparatus for kinetic studies of living polymerizations under an electric field. Reproduced, with permission, from Ise, Hirohara, Makino, and Sakurada J. Phys. Chem. 72, 4543 (1968)...

Imai, Saegusa, Furukawa et al. (48,66) carried out kinetic studies of THF polymerization in bulk and in cyclohexane solution at 0° C. They used a ternary catalyst system consisting of AlEt3-H20(2 l)-epichloro-hydrin (ECH). They obtained high molecular weight polymer and noticed no evidence for either termination or transfer. Their polymerizations were preceded by an induction period as shown in Fig. 13 but after that their data could be fitted to an equation of the same form as equation 42. This time [f0] was defined as the concentration of propagating species ([P ]) determined from the amount and the molecular weight of product polymer. 

Such products are found to undergo continued inorganic polymerization resulting from pendant hydroxy groups forming bridges between adjacent metal centers. Kinetic studies of this reaction mechanism indicate that a general rate law may be written as... 

To avoid interference from the alkylation of the titanium cyclopentadienyl compound with aluminum alkyl, Cp2Ti(R)Cl has been used in place of Cp2TiCl2 as a catalyst component. Reichert and Meyer 641 made a detailed kinetic study of the polymerization of ethylene with the soluble Cp2Ti(C2H5)Cl/Al(C2H5)Cl2 catalyst in toluene at 10 °C. Figure 3 shows the polymerization rate as a function of time at... 

---