Kinetics Macromonomer

There is a considerable body of evidence (kinetic studies, chemical and NMR analysis) indicating that transfer to VAc monomer involves largely, if not exclusively, the acetate methyl hydrogen to give radical 111 (Scheme 6.29).171,172 This radical (111) initiates polymerization to yield a reactive macromonomer (112). 

Stein166 has indicated that the reactivity of the terminal double bond of the macromonomer (112) is 80% that of VAc monomer. The kinetics of incorporation of 112 have also been considered by Wolf and Burchard175 who concluded that 112 played an important role in determining the time of gelation in VAc homopolymerization in bulk. 

ESI mass spectrometry ive mass spectrometry ESR spectroscopy set EPR spectroscopy ethyl acetate, chain transfer to 295 ethyl acrylate (EA) polymerizalion, transfer constants, to macromonomers 307 ethyl methacrylate (EMA) polymerization combination v.v disproportionation 255, 262 kinetic parameters 219 tacticity, solvent effects 428 thermodynamics 215 ethyl radicals... 

In this review we summarize and discuss the amphiphilic properties of polyoxyethylene (PEO) macromonomers and PEO graft copolymer molecules, the aggregation of amphiphilic PEO macromonomers into micelles, the effect of organized aggregation of macromonomers on the polymerization process, and the kinetics of radical polymerization and copolymerization of PEO macromonomer in disperse (dispersion, emulsion, miniemulsion, microemulsion, etc.) systems [1-5]. 

We begin by describing the current understanding of the kinetics of polymerization of classical unsaturated monomers and macromonomers in the disperse systems. In particular, we note the importance of diffusion-controlled reactions of such monomers at high conversions, the nucleation mechanism of particle formation, and the kinetics and kinetic models for radical polymerization in disperse systems. 

Kinetics of Radical Polymerization of Conventional Monomer and Amphiphilic Macromonomers in Disperse Systems... 

Table 1. Variation of kinetic, molecular weight, and colloidal parameters of dispersion copolymerization of PMA macromonomer and styrene...

The rate of polymerization was found to be independent of emulsifier concentration around CMC (1.8x10 4mol dm 3) and up to ca. 10 3 mol dm 3 and then strongly increased with increasing emulsifier concentration (Fig. 5). It can be seen that, for this system, the break in the dependence of the rate on surfactant concentration does not coincide with the CMC of either the surfactant or the surfactant/PEO-MA macromonomer. In fact, these two values are identical at room temperature at 50 °C the CMC of the surfactant is lower than at 20 °C. The kinetics of particle nucleation for the present nonionic polymerization of BA may not follow a micellar mechanism. 

The rate of dispersion (co)polymerization of PEO macromonomers passes through a maximum at a certain conversion. No constant rate interval was observed and it was attributed to the decreasing monomer concentration. At the beginning of polymerization, the abrupt increase in the rate was attributed to a certain compartmentalization of reaction loci, the diffusion controlled termination, gel effect, and pseudo-bulk kinetics. A dispersion copolymerization of PEO macromonomers in polar media is used to prepare monodisperse polymer particles in micron and submicron range as a result of the very short nucleation period, the high nucleation activity of macromonomer or its graft copolymer formed, and the location of surface active group of stabilizer at the particle surface (chemically bound at the particle surface). Under such conditions a small amount of stabilizer promotes the formation of stable and monodisperse polymer particles. 

Such hydrophilic macromonomers (DPn=7-9) were radically homopolymer-ized and copolymerized with styrene [78] using AIBN as an initiator at 60 °C in deuterated DMSO in order to follow the kinetics directly by NMR analysis. The macromonomer was found to be less reactive than styrene (rM=0.9 for the macromonomer and rs=1.3 for styrene). Polymerization led to amphiphilic graft copolymers with a polystyrene backbone and poly(vinyl alcohol) branches. The hydrophilic macromonomer was also used in emulsion polymerization and copolymerized onto seed polystyrene particles in order to incorporate it at the interface. 

Radical homopolymerization kinetics of some typical macromonomers, such as those from PSt, 23,24 [30,31], and PMMA, 25 [32,33], have been studied in detail by means of ESR methods. 

Table 1 [1] summarizes the relevant kinetic parameters. Clearly, the polymerization of macromonomers, 23-25, is characterized by very low kt values and by less reduced kp values, compared to those of the corresponding conventional monomers such as styrene and MMA. This means that the propagation involving the macromonomer and the multibranched radical is slightly less favored... 

Table 1. Kinetic parameters of some macromonomers in radical polymerization as compared with conventional monomers ...

The copolymerization of Surfmers with monomers differs from the copolymerization of conventional monomers because of, among other reasons, the comparatively large size of the Surfmers molecules. The kinetics and reactivity of non-surface-active macromonomers have been reviewed [47, 48] and it is believed that the factors affecting the reactivity of macromonomers will play a similar role in the reactivity of Surfmers. These factors are ... 

Capek, I. andAkashi, M. (1993) On the kinetics of free-radial polymerisation of macromonomers. JMS-Rev. Macromol. Chem. Phys. C33(4), 369M36. 

The homopolymerization of o)-(4-vinylbenzyl)polystyrene macromonomers was also investigated kinetically by Asami21) under quite different conditions, namely very high amounts of initiator and high overall concentrations. Thus, the molecular weights (even if underestimated) are very low. Under these conditions, the rate of polymerization does not depend on the length of the side chains. However, these particular conditions which favour initiation and termination processes cannot be illustrative of regular polymerizations. 

Revillon and Hamaide 119) studied the kinetics of the copolymerization of butyl acrylate (BA) with an to-styrylpolyoxyethylene macromonomer by means of high-resolution GPC to characterize the amounts of graft copolymer formed and of the macromonomer and comonomer consumed. In this case, the rather low molecular... 

Kinetic analyses were done for several copper-catalyzed copolymerizations of MMA/nBMA,263 nBA/ styrene,264 266 and nBA/MMA.267 All these studies show that there were no significant differences in reactivity ratio as well as in monomer sequence between the copper-catalyzed and conventional radical polymerizations. Only a difference was observed in the copolymerizations between MMA and ometh-acryloyl-PMMA macromonomers where the reactivity of the latter is higher in the metal-catalyzed polymerizations.267 However, this can be ascribed not to the different nature of the propagating species but to the difference in the time scale of monomer addition or other factors. Simulation has also been applied for the copolymerization study.268... 

The synthesis of polystyrene-g-polytetrahydrofurane [188] was achieved by ATR copolymerization of methacrylic PTHF macromonomer, MA-PTHF, with styrene (Scheme 105). The PTHF macromonomer was synthesized by cationic ring opening polymerization of THF with acrylate ions, formed by the reaction of methacryloyl chloride and AgC104. The polydispersity indices of the graft copolymers determined by SEC ranged between 1.3-1.4. Kinetic studies revealed that the relative reactivity ratio of the macromonomer to St was independent of the molecular weight of PTHF. 

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