Semi-continuous monomer addition

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]. 

There are three important processes for preparing PVAc latexes in the presence of PVA as a protective colloid batch, semi-continuous, and delayed addition of monomer [10]. In this Chapter, the effects of the addition of VAc and initiators on the properties of PVAc latexes are discussed using the three methods under the same charge of ingredients for polymerization as shown in Fig. 1 [1,11]. 

Compositional drift in continuous reactor trains can be altered by introducing feed streams of the more reactive monomer between reactors. This procedure is equivalent to programmed addition of the more reactive monomer in a semi-continuous system. 

Bassett and Hoy (7,8) investigated the influence of the method of monomer addition on the alkali-swelling behavior. In this case, carboxyl-containing monomers were fed in three different stages of the semi-continuous polymerization (i) in the... 

A major drawback of conventional microemulsion polymerization is the high surfactant-to-monomer ratio usually needed to form the initial microemulsion. Surfactant can be used more efficiently in semi-continuous or fed polymerization processes. Several polymerization cycles can be run in a short period of time by stepwise addition of new monomer. After each cycle of monomer addition, most of the surfactant is still available to stabilize the growing hydro-phobic polymer particles, or to forms microemulsion again when a polar monomer is used. For instance, in the polymerization of vinyl acetate (VA) by a semi-continuous microemulsion process [21], latexes with a high polymer content of about 30 wt% were obtained at relatively low AOT concentrations of about 1 wt%. Moreover, their particle sizes and molecular weights were much smaller than those obtained by conventional emulsion polymerization. 

Though the continuous addition of monomer via hollow fibers into a Winsor I-Hke system is rather novel, it is not as convenient as the drop-wise addition of monomer under a semi-continuous process. Ming et al [67, 68]... 

The reaction time is 16 hours for the batch procedure. In the semi-continuous procedure a seed latex is first prepared with 1/10 of the monomer amount during 30 minutes at 80 C. The remaining monomer is then added continuously during 2.5 hours.The polymerization is completed by heating the system for an additional 1 hour. 

The semi-continuous emulsion polymerization processes is characterized by continued addition of reaction ingredients such as monomer, emulsifier, initiator, or water to the reaction system throughout the polymerization. In this emulsion polymerization process, two major types of feeds are used for the introduction of ingredients to the reactor neat monomer feed (M) or monomer emulsion feed (ME). In M feed method, the feed contains only monomer and all the other ingredients are initially in the reactor. Otherwise, the major components of the ME feed are a monomer, a part from the emulsifier, and water. But it... 

In addition, the presence of seeding stage in the semi-continuous process (by 10 wt % monomer), the increasing of the feeding time and better control of the initiator feed increased the monomer conversion, the average particle size, and the stabilities of the pol3rmerization and latex of VAc/DOM monomer system. The effect of these reaction variables on the conversion and the particle size of the VAC/DOM latex are given in Table 3 [99]. 

Each of the following six latex preparations was prepared by a semi-continuous, two-step procedure. In step one, 5-10%w of the monomers were added to water containing all of the required surfactant and more than 5-10w% of the catalyst. In step two, additional catalyst was added and the remainder of the monomers was added continuously over several hours. When AMPS sodium salt was one of the monomers, it was added continuously as a separate feed from the other monomers. 

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