Initial monomers

Figure 6.3 shows some data which constitute a test of Eq. (6.26). In Fig. 6.3a, Rp and [M] are plotted on a log-log scale for a constant level of redox initiator. The slope of this line, which indicates the order of the polymerization with respect to monomer, is unity, showing that the polymerization of methyl methacrylate is first order in monomer. Figure 6.3b is a similar plot of the initial rate of polymerization—which essentially maintains the monomer at constant con-centration—versus initiator concentration for several different monomer-initiator combinations. Each of the lines has a slope of indicating a half-order dependence on [I] as predicted by Eq. (6.26).

The copolymer composition equation relates the r s to either the ratio [Eq. (7.15)] or the mole fraction [Eq. (7.18)] of the monomers in the feedstock and repeat units in the copolymer. To use this equation to evaluate rj and V2, the composition of a copolymer resulting from a feedstock of known composition must be measured. The composition of the feedstock itself must be known also, but we assume this poses no problems. The copolymer specimen must be obtained by proper sampling procedures, and purified of extraneous materials. Remember that monomers, initiators, and possibly solvents are involved in these reactions also, even though we have been focusing attention on the copolymer alone. The proportions of the two kinds of repeat unit in the copolymer is then determined by either chemical or physical methods. Elemental analysis has been the chemical method most widely used, although analysis for functional groups is also employed. 

Usually, free-radical initiators such as azo compounds or peroxides are used to initiate the polymerization of acrylic monomers. Photochemical (72—74) and radiation-initiated (75) polymerizations are also well known. At a constant temperature, the initial rate of the bulk or solution radical polymerization of acrylic monomers is first order with respect to monomer concentration and one-half order with respect to the initiator concentration. Rate data for polymerization of several common acrylic monomers initiated with 2,2 -azobisisobutyronittile (AIBN) [78-67-1] have been determined and are shown in Table 6. The table also includes heats of polymerization and volume percent shrinkage data. 

The following conditions are stipulated the catalyst decomposition rate constant must be one hour or greater the residence time of the continuous reactor must be sufficient to decompose the catalyst to at least 50% of the feed level the catalyst concentration must be greater than or equal to 0.002 x Q, where the residence time, is expressed in hours. An upper limit on the rate of radical formation was also noted that is, when the rate of radical formation is greater than the addition rate of the primary radicals to the monomers, initiation efficiency is reduced by the recombination of primary radicals. 

Basic Components. The principal components in emulsion polymerization are deionized water, monomer, initiator, emulsifier, buffer, and chain-transfer agent. A typical formula consists of 20—60% monomer, 2—10 wt % emulsifier on monomer, 0.1—1.0 wt % initiator on monomer, 0.1—1.0 wt % chain-transfer agent on monomer, various small amounts of buffers and bacteria control agents, and the balance deionized water. 

The formation of polymer can be considered as a quasi-living polymerization. After the polymerization is complete, it can be reinitiated with the addition of more monomer to the unquenched polymer. However, the degree of polymerization cannot be predicted by the monomer/initiator molar ratio, the polydispersity is 1.5-2.0, and water, or even carboxylic acids, act as inhibitors and do not terminate the polymerization [10]. 

The molecular weights of the polymers are much larger than would be predicted from the monomer/initiator ratio, as seen in Fig. 4. However, this effect is most evident for the polymerization of ethyl cyanoacrylate alone. 

Monosized polystyrene particles in the size range of 2-10 /am have been obtained by dispersion polymerization of styrene in polar solvents such as ethyl alcohol or mixtures of alcohol with water in the presence of a suitable steric stabilizer (59-62). Dispersion polymerization may be looked upon as a special type of precipitation polymerization and was originally meant to be an alternative to emulsion polymerization. The components of a dispersion polymerization include monomers, initiator, steric stabilizer, and the dispersion medium... 

Monomer Initiator Stabilizer/co-stabilizer Medium P. Size (/Ltm) Reference... 

Charge-transfer photopolymerizations of electron-donating monomers initiated by electron-accepting initia-... 

Kinetics and mechanism of polymerization of vinyl monomers initiated by ylides. 

A monomer is a reactive molecule that has at least one functional group (e.g. -OH, -COOH, -NH2, -C=C-). Monomers may add to themselves as in the case of ethylene or may react with other monomers having different functionalities. A monomer initiated or catalyzed with a specific catalyst polymerizes and forms a macromolecule—a polymer. For example, ethylene polymerized in presence of a coordination catalyst produces a linear homopolymer (linear polyethylene) ... 

Polymerization of some vinyl monomers initiated by those colored aromatic complexes was described by Scott38 over twenty years ago, and recently the mechanism of this reaction has been elucidated in our laboratory43 where we demonstrated that polymerization initiation is due to an electron transfer to monomer, namely A - -M A-f-M . This system is useful, therefore, in... 

The above treatment only applies to polymerizations where there is negligible conversion of monomer, initiator, and transfer agents. Analytical treatments have been devised to take into account effects of conversion and more complex mechanisms. Discussion of these is beyond the scope of this book. 

The selection of reaction conditions for ATRP is dependent on many factors including the particular monomer, initiator and catalyst. 

RAFT polymerization can be performed simply by adding a chosen quantity of an appropriate RAFT agent to an otherwise conventional radical polymerization. Generally, the same monomers, initiators, solvents and temperatures are used. The only commonly encountered functionalities that appear incompatible with RAFT agents are primary and secondary amines and thiols. 

The molar rate of change of polymeric species of degree of polymerization n in a well-mixed, continuous flow tank reactor is related to the kinetic rate of propagation of unassociated polystyryl anions plus their withdrawal rate in the reactor s effluent. Feed streams are void of polymeric substances, but contain monomer initiator and solvent. 

These TMS-carbamate-mediated NCA polymerizations resemble to some extent the group-transfer polymerization (GTP) of acrylic monomers initiated by organo-silicon compounds [40]. Unlike GTPs that typically require Lewis acid activators or nucelophilic catalysts to facilitate the polymerization [41], TMS-carbamate-mediated NCA polymerizations do not appear to require any additional catalysts or activators. However, it is still unclear whether the TMS transfer proceeds through an anionic process as in GTP [41] or through a concerted process as illustrated in Scheme 14. 

Monomer Initiator Method for assigning initiation rate Temp. C kl/k,)XW l./mole/sec. Bef. 

Fig. 10.—Benzoyl peroxide-initiated polymerization of vinyl-i-j3-phenyl-butyrate in dioxane at 60°C plotted as a first-order reaction. [M]o and [M ] represent concentrations of monomer initially and at time t, respectively. In experiments 1, 2, and 3, respectively, [M]o = 2.4, 7.28, and 5.97 g. of monomer per 100 cc. of dioxane. (Results of Marvel, Dec, and Cooke obtained po-larimetrically.)...

SAMPLE NO. POLYMERIZATION TIME (min) CONVERSION STYRENE IN MONOMER INITIAL STYRENE IN MONOMER GPC 2 CHROMATOGRAM VARIANCE GPC INJECTED INTO TOTAL AMOUNT OF POLYMER INJECTED (mg) VOLUME INJECTED GAUSSIAN FIT TO GPC 2 CHROMATOGRAM... 

Figure 5.60. The temperature change in Fig. 5.59 causes pronounced decreases in the dimensionless concentrations of monomer, initiator, and chain length.

Higher activities may be obtained if the bis(alkoxide) is generated in situ. For example, addition of 100 equivalents L-LA to a 1 2 mixture of Ca(NTMS2)2 and MeOH in THF generates PLA to 97% conversion in 18 min at room temperature (c.f. 66% conversion after 90 min in bulk at 120 °C using commercial Ca(OMe)2).830 Furthermore, no epimerization is observed. Polydispersities are narrow (1.1), with Mn values slightly higher than those predicted from the monomer initiator... 

One of the most widely studied systems for the polymerization of cyclic ethers is the tetra-phenylporphyrinato aluminum system, (TPP)AIX. Most investigations have focused on the chloride complex, (251), which initiates the living ROP of EO, PO, and Et-EO.936 For example, 400 equivalents of EO require 3 hours in CH2C12 at 25 °C to reach 80% conversion. Mn values increase linearly with monomer conversion, with polydispersities typically <1.10, and chain lengths controlled by the initial monomer initiator ratio. 

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