Kinetics of emulsion polymerization of methyl methacrylate

Abstract

SynopsisThe kinetics of the emulsion polymerization of methyl methacrylate at 500C have been studied in seeded systems using both chemical initiation and y-radiolysis initiation. Both steady-state rates and (for y-radiolysis) the relaxation from the steady state were observed. The average number of free radicals per particle was quite high (e.g., 4 . 7 for mol dm-3 S,Oginitiator). The data are quantitatively interpreted using a generalized Smith-Ewart-Harkins model, allowing for free radical entry, exit, bimolecular termination within the latex particles, and aqueous phase hetero-termination and re-entry. From this treatment, there results (i) the dependence of the termination rate coefficient (k,) on the weight fraction of polymer (wJ, (ii) lower bounds for the dependence of the entry rate coefficient on initiator concentration, and (iii) the conclusion that most exited free radicals undergo subsequent reentry into particles rather than hetero-termination. The results for k,(wJ are consistent with diffusion control at temperatures below the glass transition point. Comparisons are presented of the behavior of methyl methacrylate, butyl methacrylate, and styrene in emulsion polymerization systems.

Cross-Chain Transfer Rate Constants of Styrene-Terminated Radicals to Methyl Acrylate and Methyl Methacrylate

“…In Table 3, we have summarized these results. As can be seen from this table, k tr,M in the homopolymerization of MA is at least a factor of 30 larger than the k tr,M in the homopolymerization of MMA, 47,48 whereas this is reduced to a factor of 3 when the terminal unit of the radical is S. This factor of 3 can easily be attributed to a steric effect in the frequency factor of the reaction, but a factor of 30 solely due to steric effects is highly unlikely. 49 These results strongly suggest that the transfer mechanisms in the cross-transfer reactions to MA and MMA are different to the ones in their respective homopolymerizations.…”

Catalytic chain transfer for molecular weight control in the emulsion homo- and copolymerizations of methyl methacrylate and butyl methacrylate

“…Initiator, I-I, and initiator derived radicals exit. 12 In this case, exit does not affect the over-(until they enter), IMM • , are located in the aqueous all kinetics as there is no net radical loss.…”

A mechanistic investigation of Pickering emulsion polymerization

“…In addition, we make the reasonable assumption that Cp,M is constant (6.6 M for PMMA latexes, according to Gilbert). 54 This means that the reason for the observed increase in Rp has to do with compartmentalization and thus the number of particles and their size. Hence, the nanoparticles play a prime role in the latex particles formation stage of Pickering emulsion polymerization.…”

“…This is in agreement with the behaviour observed in conventional emulsion polymerization of MMA. 54 Ballard and coworkers argued that for low values of ̅ this trend could be quantified with a dimensionless acceleration parameter. Theoretically a value of 0.5 for this parameter is obtained in the case of emulsion polymerization with complete re-entry of desorbed free radicals.…”

“…We obtained calculated values between 0.3-0.6 for all runs with the exception of the silica-free standard emulsion polymerization, in agreement with values obtained from conventional emulsion polymerization reactions. 54 This is logical as the substantially larger particles lead to high values of ̅ for which the theoretical value of 0.5 for the acceleration parameter is no longer valid. We would like to point out that the calculated values for ̅ are sensitive to the values of Np used.…”