Polymerization batch anionic

Telechelic PS are of interest for making block copolymers. These materials are usually prepared in the laboratory using batch anionic polymerization since FR polymerization usually leads to less than the desired end-grouje functionality of 2. However, commercial production of telechelic PS likely will require the lower cost of solution FR polymerization chemistry. The success of solution FR chemistry for making these polymers requires the development of highly efficient functionalized initiators. 

As an example, consider the batch anionic polymerization represented by Equations 16.1 and 16.3 for very fast initiation and no terminations, the system can be described by Equations. However, for very rapid termination. Equation 16.4 may be replaced by ... 

Integration of Equations 16.26-16.29 along with the monomer balance will describe the monomer conversion and molecular weight distribution as a function of time for the batch anionic polymerization. Addition of the enthalpy balance will allow the simulation to be done nonisothermally. 

The manufacture of siHcone polymers via anionic polymerization is widely used in the siHcone industry. The anionic polymerization of cycHc siloxanes can be conducted in a single-batch reactor or in a continuously stirred reactor (94,95). The viscosity of the polymer and type of end groups are easily controUed by the amount of added water or triorganosUyl chain-terminating groups. 

Emulsion Polymerization. Emulsion polymerization uses soaps and anionic surfactants to create two-phase systems that have having long-term stability. The key steps in a batch emulsion polymerization are the following ... 

Hawker et al. 2001 Hawker and Wooley 2005). Recent developments in living radical polymerization allow the preparation of structurally well-defined block copolymers with low polydispersity. These polymerization methods include atom transfer free radical polymerization (Coessens et al. 2001), nitroxide-mediated polymerization (Hawker et al. 2001), and reversible addition fragmentation chain transfer polymerization (Chiefari et al. 1998). In addition to their ease of use, these approaches are generally more tolerant of various functionalities than anionic polymerization. However, direct polymerization of functional monomers is still problematic because of changes in the polymerization parameters upon monomer modification. As an alternative, functionalities can be incorporated into well-defined polymer backbones after polymerization by coupling a side chain modifier with tethered reactive sites (Shenhar et al. 2004 Carroll et al. 2005 Malkoch et al. 2005). The modification step requires a clean (i.e., free from side products) and quantitative reaction so that each site has the desired chemical structures. Otherwise it affords poor reproducibility of performance between different batches. 

Two batches of PVN, prepared by emulsion polymerization, had molecular weights of 510,000 and 720,000 and were used for the blends and grafts, respectively. Both polystyrene (PS, Mw = 150,000) and poly-4-vinylbiphenyl (PVB, Mw = 450,000) were prepared by anionic polymerization. A low molecular weight (Polyglycol E4000, Dow Chemical Co.) and a high molecular weight PEO (WSR-35, Union Carbide Chemicals Co.) were used as received. 

K-Resin SBC synthesis is a batch anionic solution polymerization of styrene and 1,3-butadiene using an n-butyllithium (NBL) initiator in a process referred to as living polymerization . Although often referred to as a catalyst, each NBL gives rise to a distinct polymer chain. Polymer chains grow by adding monomer... 

Step Polymerization 356 Chain Polymerizations Reactions 360 Modeling a Batch Polymenzation Reactor 368 Molecular Weight Distribution 370 Anionic Polymerization 375... 

The concept of living polymerizations started in 1956 when Szwarc found that in the anionic polymerizations of styrene (St) the polymer chains grew until all the monomer was consumed [9], and that the chains continued growing when another batch of monomer was added. The addition of another monomer resulted in the formation of block copolymers. These polymerizations proceeded without termination or chain transfer occurring in the system. Prior to this work, the conditions used for the polymerizations had not been stringent enough to keep the active species alive and allow observation of this type of behavior. The polymer molecular weights were predictable based on the ratio of... 

Ionic polymerization systems of commercial importance employ mostly batch and continuous solution polymerization processes. Suitable monomers for ionic polymerization include conjugated dienes and vinyl aromatic. Among these, the anionic polymerization of styrene-butadiene (SB) and styrene-isoprene (SI) copolymers and the cationic polymerization of styrene are the most commercially important systems. 

Figure 13.15 Reactor and termination stage in batch and semicontinuous anionic polymerization. I Recycle stream from fractionator and II polymer product stream to devolatilization fractionation [100],...

In a conventional anionic polymerization of styrenes in polar solvents in a batch macroreactor, major drawbacks include the requirement of low temperature such as —78°C. In contrast, Nagaki et al. reported that controlled anionic polymerization of styrene can be conducted under easily accessible conditions such as 0°C in a polar solvent using a flow microreactor to obtain the polystyrene with narrower molecular weight distribution (M = 1,200-20,000, MJM = 1.09-1.13) (Fig. 9) [146]. Moreover, the molecular weight can be easily controlled by changing the flow rates of monomer and initiator solutions. Furthermore, these methods can be... 

Controlled anionic polymerization of alkyl methacrylates initiated by 1,1-diphenyUiexyllithium using a flow microreactor gives the corresponding poly (aUcyl methacrylate)s with high level of control of molecular weight under easily accessible temperatures compared with conventional batch macropolymerization, e.g., —28°C for methyl methacrylate (MMA) (MJMn = 1.16), 0°C for butyl methacrylate (BuMA) MJM = 1.24), and 24°C for tert-butyl methacrylate (f-BuMA) (Mw/Mn = 1.12). Precise control of the reaction temperature and fast mixing of a monomer and an initiator seem to be responsible (Fig. 16) [161]. 

Much of nylon 6 is used in producing fibers. Polycaprolactam prepared by water-catalyzed polymerizations is best suited for this purpose. It can also be used in molding, though anionically polymerized caprolactam can be used as well. The polymerizations are carried out both in batch and in continuous processes. Often, tubular flow reactors are employed. 

The group of Yoshida [12] investigated the effect of using a micro-reactor for the anionic polymerization of methacrylates. Compared to a corresponding batch... 

In considering batch polymerization systems, the kinetics of polymerization can be used directly. For anionic polymerization with chain transfer, the kinetic chain length (x) can be shown to be a function of the monomer concentration ... 

Block Copolymerization. A polymerization with long chain lives can be used to make block copolsrmers (qv). An important commercial example is styrene/butadiene blocks produced by anionic polymerization (qv). A solution polymerization is done in a batch reactor, starting with one of the two monomers. That monomer is reacted to completion and the second monomer is added while the catalytic sites on the chains remain active. This produces a block copolymer of the AB form. Early addition of the second monomer produces a tapered block. If the second monomer is reacted to completion and replaced by the first monomer, an ABA triblock is obtained. This process is not easily converted to continuous operation because polsrmerizations inside tubes rarely approach the piston-flow environment that is needed to react one monomer to completion before adding the second monomer. Designs using static mixers (also known as motionless mixers) are a possibility. 

Because of facile cross-propagation, statistical (or nearly random) copolymerization is very easily achieved in free-radical systems, in contrast to ionic reactions. The reactivity of many comonomers are relatively similar. For example, in RP, methacrylates have similar reactivity to styrene and are 3 times more reactive than acrylates. However, in anionic polymerization acrylates are 100 times more reactive than methacrylates and the latter much more reactive than styrene. In cationic polymerization the opposite reactivity order is observed. The copolymerization of monomers with similar reactivity should result in statistical copolymers with no compositional variation during the pol5unerization. This has been observed for copolymerization of the same type of monomers such as various styrenes, various methacrylates, and various acrylates. This is the case for both CRP and conventional RP. However, in batch copol5unerizations of different classes of comonomers there is a continuous change of residual monomer composition in the reaction because one comonomer reacts faster than the other one. 

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