Polymerisation kinetics

Since at -40 °C the hexene polymerisation is living, the addition of 10 equivalents of propene to species 66 led to the complete consumption of propene and formation of a Zr-PP-fo-PH block (without further conversion of any unreacted Zr-Me precursor). The identification of the Zr-(propene)j.-(hexene)j, polymer was confirmed by isotopic labelling (l- C-propene, l,T-D-2,3- C-propene) and H, 

Application of Singleton s method of using NMR to determine kinetic 

By contrast to the polymerisation of hexene with 64, which can be followed conveniently by variable-temperature NMR, the polymerisation of smaller monomers like ethene and propene illustrate the limitations of spectroscopic methods since with most metallocene catalysts they are too fast. The kinetic behavior of (SBI)ZrMe2/AlBu 3/[CPh3][CN B(C6F5)3 2] at 25 °C was therefore investigated by quenched-flow techniques to estimate the rates of initiation, chain propagation and chain termination [SBI = rac-Me2Si(Ind)2] [97]. The results are summarised here for comparison with the results on 1-hexene polymerisation discussed above. 

NMR analysis of the polymer also detected low levels of stereo-errors due to enchained 2,1-misinsertions (cf Section 8.9), about 1 in 500. The data suggested that 2,1-insertion is slow but is responsible for the accumulation of dormant states carrying Zr-sec-alkyl chains. 

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G. D. Cooper, J. G. Bennett, Jr., and A. Eactor, Polymerisation Kinetics and Technology, Advances in Chemistry Series, No. 128, American Chemical... 

A. R. Marsh, G. Klein, and T. Vermeulen, Polymerisation Kinetics and Equilibria of Silicic Acid in Aqueous Systems, No. LBL 4415, National Technical Information Service, Springfield, Va., 1975. 

Emulsion Polymerization. Emulsion SBR was commercialised and produced in quantity while the theory of the mechanism was being debated. Harkins was among the earliest researchers to describe the mechanism (16) others were Mark (17) and Elory (18). The theory of emulsion polymerisation kinetics by Smith and Ewart is still vaUd, for the most part, within the framework of monomers of limited solubiUty (19). There is general agreement in the modem theory of emulsion polymerisation that the process proceeds in three distinct phases, as elucidated by Harkins (20) nucleation (initiation), growth (propagation), and completion (termination). 

R. MUkovich, in J. E. McGrath, A., Anionic Polymerisation Kinetics, Mechanisms, and Synthesis, ACS Symposium Series, No. 166, American Chemical Society, Washington, D.C., 1981, p. 41. 

Polymerisation kinetics will be dealt with here only to an extent to be able to illustrate some points of technological significance. This will involve certain simplifications and the reader wishing to know more about this aspect of polymer chemistry should refer to more comprehensive studies. 

A major difference between both kind of syntheses lies in polymerisation kinetics in the former case there is a chain mechanism (initiation, propagation, termination), in the latter case there is no chain reaction and each step is equiprobable. Main comparison points are highlighted in Table 4 [9]. 

Kinetics of radical chain polymerisation. Kinetics calculations on radical chain polymerisation are based on the three steps mechanism with notations as shown in Figure 19. 

E. van Steen and H. Schulz, Polymerisation kinetics of the Fischer-Tropsch CO hydrogenation using iron and cobalt based catalysts, Appl. Catal. A, 1999, 186, 309-320. 

No general procedures can be outlined for endgroup analysis in addition polymers due to the variety of type and origin of the endgroups. When the polymerisation kinetics is known analysis can be done for initiator fragments containing identifiable... 

Fig Gel permeation chromatography data for polystyrene to a molecular-weight distribution curve calculated from polymerisation kinetics. 

An analysis is presented in this paper of the influence exerted on polymerisation kinetics by the complexing of carbocations with monomers. This had been brewing in the author s mind for a long time and had been mentioned in earlier works, and most other workers were aware of it to some extent. Curiously, few if any others had drawn the electrochemical conclusion that such a process would make meaningless the estimates of the population of paired cations in the reaction mixtures, because of the increase in the size of the cations resulting from such an association. 

The relevance to polymerisation kinetics of the Keele group s polarographic measurements on various triarylmethylium ions in different solvents 137 is explained. 

More recently, Landis et al. studied the polymerisation kinetics of 1-hexene with (EBI)ZrMe( t-Me)B(C5F5)3 64 as catalyst in toluene [EBI = rac-C2H4(Ind)2]. Catalyst initiation was defined as the first insertion of monomer into the Zr-Me bond, 65 (Scheme 8.30). Deuterium quenching with MeOD was used to determine the number of catalytically active sites by NMR. The time dependence of the deuterium label in the polymer was taken as a measure of the rate of catalyst initiation. This method also provides information of the type of bonding of the growing polymer chain to zirconium, as n-or sec-alkyl, allyl etc. Hexene polymerisation is comparatively slow, with high regio- and stereoselectivity there was no accumulation of secondary zirconium alkyls as dormant states [96]. 

Chain transfer reactions in homogeneous olefin polymerisation systems with metallocene catalysts, which terminate individual polymer chains, in some instances can also terminate the polymerisation kinetic chain. For example, chain transfer with the monomer in propylene oligomerisation or polymerisation, which involves a bond metathesis reactions between the Mt-C species of the growing polymer chain and the C H species of methyl [scheme (45)] or vinyl [scheme (46)] groups in the monomer, gives rise to temporally inactive metal allyl or metal-vinyl species respectively [177, 241, 264] ... 

The rate of copolymerisation of ethylene and odd-membered ring cycloolefins is higher than the rate of copolymerisation involving even-membered cycloolefins [467]. This indicates that both the polymerisation kinetics and the spatial configuration of the copolymer are influenced by steric factors [2]. 

Both the intramolecular and the intermolecular secondary metathesis reactions affect the polymerisation kinetics by decreasing the rate of polymerisation, because a fraction of the active sites that should be available as propagation species are involved in these non-productive metathesis reactions. The kinetics of polymerisation in the presence of metal alkyl-activated and related catalysts shows in some cases a tendency towards retardation, again due to gradual catalyst deactivation [123]. Moreover, several other specific reactions can influence the polymerisation. Among them, the addition of carbene species to an olefinic double bond, resulting in the formation of cyclopropane derivatives [108], and metallacycle decomposition via reductive elimination of cyclopropane [109] deserve attention. 

M. Morton and M. Wu in Ring-Opening Polymerisation Kinetics, Mechanisms and Synthesis, Ed., J.E. McGrath, ACS Symposium Series No.286, American Chemical Society, Washington, DC, USA, 1985, p.175. 

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