Kinetic form , copolymer

Both the mini- and macroemulsion copolymerizations of pMS/MMA tend to follow bulk polymerization kinetics, as described by the integrated copolymer equation. MMA is only slightly more soluble in the aqueous phase, and the reactivity ratios would tend to produce an alternating copolymer. The miniemulsion polymerization showed a slight tendency to form copolymer that is richer in the more water-insoluble monomer. The macroemulsion formed a copolymer that is slightly richer in the methyl methacrylate than the co-... 

Figure 9(a) shows the kinetics for the ak I and the methylene proton peak of (MA-St) in the coil form at af=0.87 and 35°C. Under the assumption of single exponential decay function expressed by Equation (1), ln(l - Mz/Mq) has to be proportional to x. For the phenyl protons, the proportional relationship is apparently well satisfied in a range of x less than 2 sec, and ln(l - Mz/Mq) at x= 0 is very close to the expected value (= In 2), but the kinetics for the methylene protons in styrene is not expressed by Equation (1) in the range of x. Figure 9(b) shows the kinetics for the compact form copolymer at = 0.25. For the peak I, the proportional relationship between ln(l - Mz/Mq) and x is clearly seen in a range of x less than 3 sec, and for the backbone protons the proportionality is apparently found, but not strictly. As described later, the recovery curve with a correlation time is in principle nonexponential because of coupled relaxation, and therefore we made use as before of concept of an effective relaxation time T from the initial perturbation to the time when the deviation from equilibrium falls to about 25 30% of its initial value. A dotted line in Figure 9(a) shows an example of the... 

If the reactor fluid contains two different monomers Mi and M2, both monomers can react with radical sites to form copolymer radicals. If there is no template for the monomer preference to react with the radical site, then the sequence of monomer addition will be based on monomer reactivity rules. Description of copolymerization kinetics differs from that in Fig. 1.3.1 (homopolymerization kinetics) during chain propagation, as shown in Fig. 1.3.4... 

Finally, we would like to emphasize that, in most applications, in-situ formed copolymers are utilized, which are formed by the reaction of appropriately functionalized homopolymer additives at the polymer-polymer interface. A review article [106] cites not a single case where a premade copolymer had been used in a real application. Therefore, the interfacial behavior in such systems should be investigated fundamentally in greater detail in order to probe the effects of the characteristics of the reactive species on the kinetics of interfacial partitioning and the subsequent reaction, as well as on the effect of the resultant (diblock or graft or comb) copolymer on the interfacial tension and, thus, on the morphology of the macrophase-separated polymer blend. 

The characterization of the interfacial chemical reactions and the reaction kinetics are very challenging topics in this area. In fact the quantitative analysis of the interfacial chemical reactions and reaction kinetics has still to be performed for most of the melt reactions despite their crucial importance for the understanding of the relationship between melt reactions, blend phase morphology and ultimate properties. The copolymer generated as a result of the interfacial reactions is difficult to separate and to characterize. Several investigations are still being made to identify and characterize the in situ formed copolymer. 

The possibility of conformational changes in chains between chemical junctions for weakly crosslinked CP in ionization is confirmed also by the investigation of the kinetic mobility of elements of the reticular structure by polarized luminescence [32, 33]. Polarized luminescence is used for the study of relaxation properties of structural elements with covalently bonded luminescent labels [44,45]. For a microdisperse form of a macroreticular MA-EDMA (2.5 mol% EDMA) copolymer (Fig. 9 a, curves 1 and 2), as compared to linear PM A, the inner structure of chain parts is more stable and the conformational transition is more distinct. A similar kind of dependence is also observed for a weakly crosslinked AA-EDMA (2.5 mol%) copolymer (Fig. 9b, curves 4 and 5). 

Knowledge of kui/kii is also important in designing polymer syntheses. For example, in the preparation of block copolymers using polymeric or multifunctional initiators (Section 7.6.1), ABA or AB blocks may be formed depending on whether termination involves combination or disproportionation respectively. The relative importance of combination and disproportionation is also important in the analysts of polymerization kinetics and, in particular, in the derivation of rate parameters. 

Statistical copolymers are formed when mixtures of two or more monomers are polymerized by a radical process. Many reviews on the kinetics and mechanism of statistical copolymerization have appeared1 9 and some detail can be found in most text books on polymerization. The term random copolymer, often used to describe these materials, is generally not appropriate since the incorporation of monomer units is seldom a purely random process. The... 

The success of the multifunctional initiators in the preparation of block and graft copolymers depends critically on the kinetics and mechanism of radical production. In particular, the initiator efficiency, the susceptibility to and mechanism of transfer to initiator, and the relative stability of the various radical generating functions. Each of these factors has a substantial influence on the nature and homogeneity of the polymer formed. Features of the kinetics of polymerizations initiated by multifunctional initiators have been modeled by O Driscoll and Bevington 64 and Choi and Lei.265... 

Unusual reactivities of mechano-radicals have been reported in a few instances. To explain the pseudo first-order kinetics and the high yield of linear block copolymers formed during the mechanochemical degradation of a mixture of... 

This is the simplest of the models where violation of the Flory principle is permitted. The assumption behind this model stipulates that the reactivity of a polymer radical is predetermined by the type of bothjts ultimate and penultimate units [23]. Here, the pairs of terminal units MaM act, along with monomers M, as kinetically independent elements, so that there are m3 constants of the rate of elementary reactions of chain propagation ka ]r The stochastic process of conventional movement along macromolecules formed at fixed x will be Markovian, provided that monomeric units are differentiated by the type of preceding unit. In this case the number of transient states Sa of the extended Markov chain is m2 in accordance with the number of pairs of monomeric units. No special problems presents writing down the elements of the matrix of the transitions Q of such a chain [ 1,10,34,39] and deriving by means of the mathematical apparatus of the Markov chains the expressions for the instantaneous statistical characteristics of copolymers. By way of illustration this matrix will be presented for the case of binary copolymerization ... 

An exhaustive statistical description of living copolymers is provided in the literature [25]. There, proceeding from kinetic equations of the ideal model, the type of stochastic process which describes the probability measure on the set of macromolecules has been rigorously established. To the state Sa(x) of this process monomeric unit Ma corresponds formed at the instant r by addition of monomer Ma to the macroradical. To the statistical ensemble of macromolecules marked by the label x there corresponds a Markovian stochastic process with discrete time but with the set of transient states Sa(x) constituting continuum. Here the fundamental distinction from the Markov chain (where the number of states is discrete) is quite evident. The role of the probability transition matrix in characterizing this chain is now played by the integral operator kernel ... 

For the interbipolycondensation the condition of quasiideality is the independence of the functional groups either in the intercomponent or in both comonomers. In the first case the sequence distribution in macromolecules will be described by the Bernoulli statistics [64] whereas, in the second case, the distribution will be characterized by a Markov chain. The latter result, as well as the parameters of the above mentioned chain, were firstly obtained within the framework of the simplified kinetic model [64] and later for its complete version [59]. If all three monomers involved in interbipolycondensation have dependent groups then, under a nonequilibrium regime, non-Markovian copolymers are known to form. 

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