Comonomer effect

Narrow composition distribution Absence of high comonomer fraction ease processesing and comonomer effective in reducing m.p. sharp m.p. Heat seal layers in composites films... 

Cqpolymerization of MCM with traditional monomers is the main technique of metal insertion into a polymer chain, and it is more widely used than their homopolymerization. However, ocpolymerization laws in such systems are difficult to analyze because of their raultiparameter dependence of the kinetics and copolymerization characteristics on the process, parameters such as pH, solvent nature and even concentration ratio (30). The metal-containing giroup in MCM is, as a rule, an electron-donor substituent (scheme Q-e). The copolymerization yields complexes of different comonomers, effecting the polymer composition and structure. In our view, the most remarkable one is cqpolymerization of transition metal diacrylates with MMA, styrene, etc. (37), as well as vinylpyridine and vinylimidazole MX complexes and formation of ternary copolymers of the following composition (38) ... 

Hence, video microscopy analysis is not only a tool for screening of supported catalysts [66] but is also useful for the assignment of a given (industrial) catalyst system to the appropriate kinetic profile and the describing mathematical model. Finally, it is possible to explain certain aspects of crystalline homopolymer growth versus amorphous copolymer growth and the comonomer effect [63-66]. 

Olefin polymerization kinetics are considered and discussed in many reviews [ 1-6]. In this section, the influence of the main parameters such as the concentrations of catalysts and cocatalysts and time of polymerization on polymerization rate, and the main reactions in the olefin polymerization process will be briefly reviewed. We also consider the problems of deviation from the linear law of polymerization rate with changing monomer concentration, the effect of hydrogen in the ethene and propene polymerizations, as well as the nature of the comonomer effect, which are under discussion in the literature and the natures of which are not yet completely clear. 

One of the features of olefin copolymerization kinetics is the effect of comonomer on the rate of ethene or propene polymerization during ethene/a-olefin or propene/ a-olefin copolymerization, i.e., the so-called comonomer effect (CEF). The rate enhancement of ethene or propene polymerization in the presence of a comonomer is observed for conventional ZN catalysts [80, 113-123] and for homogeneous [124-133] and supported metallocenes [134—136] and post-metallocenes catalysts [137-140]. The increase in activity was remarked in the presence of such comonomers as propene, 2-methylpropene, 1-butene, 3-methylbutene,4-methylpentene-l, 1-hexene, l-octene,l-decene, cyclopentene, styrene, and dienes. 

Numerous studies have shown that the magnitude of effect depends on the catalyst nature, the comonomer type, and the experimental conditions. Examples of the comonomer effect for various catalysts and comonomers are shown in Tables 3,4, and 5 as the ratio of copolymerization rate to the ethylene (or propylene) homopolymerization rate. 

For understanding the nature of the comonomer effect, it is also very important that the rate enhancement takes place in the sequential processes of homo- and copolymerization, i.e., when the ethene homopolymerization is carried out after the a-olefin homopolymerization or ethene/a-olefin copolymerization [122, 123] (Table 6). 

Table 3 Comonomer effect in ethene/a-olefin copolymerization using heterogeneous and supported ZN catalyst systems...

CEF - comonomer effect, Rcop - rate of ethene insertion in ethene/a-olefin copolymerization Rpol -rate of ethene homopolymerization... 

Due to the diversity and complexity of the considered polymerization processes, the different causes for manifestation of the comonomer effect or their combination may appear, depending on conditions. 

Table 6 Comonomer effect in the two-step process of homo- and copolymerization of ethene and ...

Further experimentation needs to be undertaken to study the effect of the hydrophobic comonomer, effect of dilution of the pol3nnerization mixture and the effect of different crosslinking agents on swelling and mechanical properties in order to understand the exact interactions and the consequent change in the physical properties of polymers. 

Table 4 compares the activities and incorporation of norbomene by different catalysts. Under special conditions, the polymerization rate of a 1 1 molar mixture of ethene and norbomene is higher than the homopolymeiization of ethene (comonomer effect) [24]. 

Like 3-butenyl-Si(CH3)3, the polymerization performance of 4-pentenyl-Si(CH3)3 (silane monomer of one methylene longer) was slightly different to that obtained for 1 -alkenes (Table 7, compare runs 11-12 with runs 14—15) [23]. First of all, no sign of positive comonomer effect was observed, and the comonomer uptake was poorer. In addition, the H-NMR spectra showed that the resonances at 5.2-5.5 ppm appeared more clearly in the spectmm of polyethylene-co-4-pentenyl-Si(CH3)3 than in the spectrum of polyethylene-co-l-alkene (Fig. 22c versus Figs. 21a and... 

Finally, the polymerization performance of 5-hexenyl-Si(CH3)3 resembles well that obtained for 1-alkenes (Table 7, compare runs 12-13 with runs 14—15). Both of the comonomers resulted in similar results regarding the catalyst activities (positive comonomer effect) and the comonomer uptake. Also, the molar masses were decreased as much when compared with the molar mass of the homopolyethylene (Table 7, run 1) [23]. 

Comonomer effect. It was found during the copolymerization reactions studied that styrene protects the TTC moiety from decomposition and depending on the amount in the initial composition, improved the reaction controlled character. 

Table 12.1 lists the data on the copolymerization of propylene with 1-butene and 1-pentene in liquid propylene medium. It is seen that different initial concentrations of the MC catalyst significantly affect the activity of the MC-MAO catalytic system (experiments 1, 8). A decrease in the concentration of the MC-based complex during its formation, as was shown in Ref. [25], brings about an increase in the activity of the catalytic system by a factor of nearly 2 from 240 kg PP/(mol Zr h) (experiment 1) to 440 kg PP/(mol Zr h) (experiment 8). Addition of the comonomers influences the activity and molecular mass of the polymers. Thus, even at small contents of 1-butene (below 3.4 mol%) and 1-pentene (below 1.4 mol%) in the monomer mixture, the activity of the catalytic system increases appreciably. In the case of copolymerization with 1-butene, the 5deld of the copolymer increases by a factor of 2-3 relative to that for the homopolymerization of propylene for copolymerization with 1-pentene, the 5deld of the copolymer increases by a factor of 1.5. A further increase in the concentration of these comonomers decreases the rate of polymerization. The activation effect of small additives of less reactive comonomers is referred to as the comonomer effect. ... 

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