Initial polymerization rates

Fig. 13. Chain-effect polymerization of DL-phenylalanine NCA in nitrobenzene solution at 25°C with different polymeric initiators. Rate coefficient kj (eqn. (57)) as a function of position of the reaction site i in the polymer chain. Initiators 1 Polysarcosine diethylamide, 2 Poly(Al-ethylglycine)diethylamide, 3 Poly(iV-n-propyl-glycine)diethylamide. Sisido et al. [75].

Keywords acrylate- and methacrylate guanidines radical polymerization polymerization initial rates... 

Figure 2. The dependence of AG polymerization initial rate (curve 1) ([APS] = 5x103 mole l 1 60°C) and intrinsic viscosity of resulted polymers (curve 2) (LVNaCl solution in ff20 30°C) on monomer concentration.

It is obvious from Figures 4 and 5 that for mentioned monomer salts AG and MAG the non-linear increase of relative viscosity (r rei) is naturally observed with the rise of monomer concentration in initial reaction solution. (As it was already mentioned the solution remained transparent.) Thus, there is definite correlation in the character of polymerization initial rate change and values of r rei.. 

The obtained data (namely the non-linearity of change of Vp on [M]) may be explained by the fact that due to comparatively high values of r rei of initial solutions of monomer salts (at [M] > 1 mole l1) the constant of chains bimolecular termination rate kt even at conditions of very small conversions is turned to be sensitive to the viscosity of initial reaction solutions and consequently to monomer concentration. Mentioned change of values of relative viscosity with the rise of initial monomer concentration should lead to symbatic reduction of constant kt and thus to mentioned non-linear increase of polymerization initial rate. The suggested explanation may be checked experimentally. If we assume that in the studied system the constant kt is naturally depended on monomer solution viscosity then in accordance with North s conceptions [4, 5] we should take that k0 rf1. Then polymerization rate may be calculated by equation 1... 

Figure 6.3 shows some data which constitute a test of Eq. (6.26). In Fig. 6.3a, Rp and [M] are plotted on a log-log scale for a constant level of redox initiator. The slope of this line, which indicates the order of the polymerization with respect to monomer, is unity, showing that the polymerization of methyl methacrylate is first order in monomer. Figure 6.3b is a similar plot of the initial rate of polymerization—which essentially maintains the monomer at constant con-centration—versus initiator concentration for several different monomer-initiator combinations. Each of the lines has a slope of indicating a half-order dependence on [I] as predicted by Eq. (6.26).

C with AIBN and measured the initial rates of polymerization for the ... 

Usually, free-radical initiators such as azo compounds or peroxides are used to initiate the polymerization of acrylic monomers. Photochemical (72—74) and radiation-initiated (75) polymerizations are also well known. At a constant temperature, the initial rate of the bulk or solution radical polymerization of acrylic monomers is first order with respect to monomer concentration and one-half order with respect to the initiator concentration. Rate data for polymerization of several common acrylic monomers initiated with 2,2 -azobisisobutyronittile (AIBN) [78-67-1] have been determined and are shown in Table 6. The table also includes heats of polymerization and volume percent shrinkage data. 

The units oi sp are /mofh U Initial rate of polymerization is calculated from and the concentration of AIBN using the following equation ... 

Thus the thiol 0 2 25511 is capable of terminating a growiug chain and also initiating a new chain. If the initiation-rate constant, k is not much slower than the propagation-rate constant, the net result is the growth of a new chain without any effect on the overall polymerization rate (retardation). That represents a tme chain transfer, ie, no effect on the rate but a substantial decrease iu molecular weight (12). 

The rate equations of MMA polymerization initiated by peroxide amine systems are listed in Table 4. It shows that No. 1, 2, 3, 8, 9 are in good agreement with the... 

Pavlinec and Lazar [39] reported that organic hydroperoxide and piperidine(PD) could be used as an initiator for MMA polymerization. In our laboratory, we also found that TBH-NMMP, TBH-NEMP [20], TBH-PD(piperidine) [31], TBH-NEP(N-ethylpiperdine) [31], TBH-TMDAPM (N,N -tertramethyl-diamin-odiphenyl-methane), and TBH-TMEDA(MN.NW -tera-methylethylenediamine) [15] systems could initiate MMA to polymerize. The kinetic equation of MMA polymerization initiated with CHP-DMT system has been investigated in our laboratory and the rate equation of polymerization is shown as follows ... 

Samal et al. [25] reported that Ce(IV) ion coupled with an amide, such as thioacetamide, succinamide, acetamide, and formamide, could initiate acrylonitrile (AN) polymerization in aqueous solution. Feng et al. [3] for the first time thoroughly investigated the structural effect of amide on AAM polymerization using Ce(IV) ion, ceric ammonium nitrate (CAN) as an initiator. They found that only acetanilide (AA) and formanilide (FA) promote the polymerization and remarkably enhance Rp. The others such as formamide, N,N-dimethylformamide (DMF), N-butylacetamide, and N-cyclohexylacetamide only slightly affect the rate of polymerization. This can be shown by the relative rate (/ r), i.e., the rate of AAM polymerization initiated with ceric ion-amide divided by the rate of polymerization initiated with ceric ion alone. Rr for CAN-anilide system is approximately 2.5, and the others range from 1.04-1.11. 

The synthetic methods of macromolecules having an active pendant group include (1) the transformation reactions of polymer and copolymers, and (2) polymerization and copolymerization of functional monomers having active pendant groups. The macromolecules, either in the shape of film or microbeads, can be used as the substrate. As we have mentioned previously, the rate of polymerization initiated with the Ce(IV) ion redox system is much faster than that initiated by Ce(l V) ion alone, as expressed in / r 1. Therefore, the graft... 

The rate of fl-scission of benzoyloxy radicals is such that in most polymerizations initiated by these radicals both phenyl and benzoyloxy end groups will be formed (Scheme 3.4). A reliable value for the rate constant for p-xcission would enable the absolute rates of initiation by benzoyloxy radical to be estimated. Various values for the rale constant for p-scission have appeared. Many of the early estimates are low. The activation parameters (in CCI4 solvent) determined by Chateauneuf et a(.m are log]0 A = 12.6 and Ea = -35.97 kJ mol 1 which corresponds to a rate constant of 9xl06 s 1 at 60 °C. 

For less polar monomers, the most extensively studied homopolymerizations are vinyl esters (e.g. VAc), acrylate and methacrylate esters and S. Most of these studies have focused wholly on the polymerization kinetics and only a few have examined the mierostructures of the polymers formed. Most of the early rate data in this area should be treated with caution because of the difficulties associated in separating effects of solvent on p, k and initiation rate and efficiency. 

In conventional radical polymerization the rate of polymerization is described by eq. 5 (Section 5.2.1). As long as the rate of initiation remains constant, a plot of ln([M]0/[ Vf]t) vs time should provide a straight line. 

As an example, consider the polymerization of methyl methacrylate, initiated by a,a -azobisisobutyronitrile.4 The dependence of the initial rate on the concentration of the initiator is displayed in Fig. 1-1, which shows them on a double logarithmic scale. The points define a straight line with a least-squares slope of0.496. Clearly the reaction is half-order with respect to the concentration of the initiator. 

Some of the results of bulk polymerization of 61 by using different anionic catalysts are summarized in Table 858 It was easily polymerized in the presence of alkali metal compounds above 60 °C. The polymerization at 150 °C was too fast to be controlled. The yield and the viscosity number, i gp/c, of the resulting polyamide increased with the reaction time. The initial rate of the polymerization became higher with the size of the countercation, in analogy to the case of anionic polymerization of e-caprolactam59. The rate increased also with raising temperature as shown in Fig. 658. ... 

Kennedy and co-workers10 studied model cationic polymerization initiation and termination. They determined the effect of halogens in f-BuX and MeX on the rate of reaction between f-BuX and Me3Al. The pseudo second order rate constant decreased (Table 1) as ... 

The effect of f-BuX initiator and MeX solvent on PIB yield was studied in the temperature range from —20° to —60 °C. Results are shown in Table 3. Initial rates of polymerization at —40 °C were determined from time-conversion plots (Fig. 1). 

The initial rate of polymerization was determined from the initial slopes of time-conversion curves (Fig. 1) using f-BuX/Me3 Al/MeCl systems at -40 °C. This... 

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