Polymerization continued second-stage

During the second stage of these block polymerizations, aMeSt or MVE was added slowly and continuously to charges containing quasiliving poly (IBVE) dications. 

Exclusive polymerization of St continues until the St conversion attains about 50 %. This critical St conversion was constant regardless of f and it corresponds to the equilibrium concentration of poly-St in the particle. Therefore, the second stage is considered to come to end when all of the St droplets disappear. 

Preparation of latex Samples. Two-stage latex samples were prepared by emulsion polymerization of the second-stage monomer mix in the presence of the first-stage polymer latex. The first-stage latexes were either in-situ or separately made using an externally prepared polystyrene latex seed. The mode of polymerization was a semi-continuous process for both stages. 

This is perhaps the most well-known method of polymerization, and as the name implies, involves the continuous addition of monomer units to a growing free-radical chain.The general mechanism of this process in relation to the polymerization of a vinyl monomer is shown in Scheme 1. As Scheme 1 shows, initiation is a two-stage process in which, first a free radical is formed, and second this radical adds on to a monomer unit. The second stage is essentially the same for... 

In the second stage of the manufacture of polymer, the t nperature is raised further, and reaction takes place between the hydroxyethyl end groups to prbduce polymer and ycol. Vacuum is applied slowly and the temperature rmsed to remove the glycol and to continue the reactioiL The final polymerization is usually accomjfiished at 260-300 C under a vacuum of 0.1-10 mm of mercury. 

The presence of chain transfer agents during the second-stage polymerization will produce a decrease in the molar mass of the shell polymer, which will result in more chain mobility and fieedom to achieve the equilibrium morphology, even under conditions where kinetically controUed particle morphologies (i.e. semi-continuous monomer addition) would normally dominate [57,67]. 

Specifically for the PS bead suspension process, Villalobos et al. [9] reported that the end of the first stage occurred at approximately 30% monomer conversion, corresponding to a critical viscosity of about 0.1 Pa s. They also found that the second stage extended up to about a 70% monomer conversion. In the vinyl chloride monomer (VCM) powder polymerization, it has been shown that, at monomer conversions around 10-30%, a continuous polymer network is commonly formed inside the polymerizing monomer droplets that significantly reduces the drop/particle coalescence rate [10]. CeboUada etal. [11] reported that the PSD was essentially estabhshed at monomer conversions of about 35-40% (i.e., end of the second stage). 

Table IX gives the recipe used for these pol3nnerizations. The polybutyl acrylate seed latex was prepared by heating the ingredients for 24 hours at 70° the styrene, water, and potassium persulfate were then added and polymerized for another 8 hours at 70°. Three methods of adding the styrene monomer were used in the second-stage polymerization (i) batch polymerization (ii) equilibrium swelling of the seed latex particles followed by batch pol3nneriza-tion (iii) starved semi-continuous pol3nnerization. The particle growth was essentially stoichiometric, i.e., no new particles were initiated. All three latexes formed transparent continuous films upon drying, whereas a 50 50 mixture of polybutyl acrylate and...

---