Vinyl/divinyl copolymerization

In the case of vinyl/divinyl copolymerization, the subscript 1 is used to designate mono-vinyl monomer, 2 is used for divinyl monomer. f Q indicates the initial mole fraction of divinyl monomer in the monomer mixture, instantaneous mole fraction of monomer i bound in the polymer chain. 

Intramolecular reactions always accompany Intermolecular crossllnk-Ing. Their Intensity depends on the structure of the constituent units and very much on the reaction mechanism. Thus, if the network is built up by step reactions from low functionality components, cycllzatlon is relatively weak. On the contrary, chain vinyl-divinyl copolymerization yields highly cycllzed products just in the beginning of the polymerization especially if the concentration of the polyvinyl monomer is higher. This case will be briefly commented on later in this article. 

Let us consider first the copolymerization of a divinyl monomer bearing independent vinyls of the same reactivity with a monovinyl monomer the reactivity of which may be different. The vinyl-divinyl copolymerization can be described by the normal copolymerization equation ... 

Fig. 2. Composition of the monomers, of the polymer and the crosslinking density as a function of conversion in vinyl-divinyl copolymerization, 1 molar fraction of the divinyl monomer in the monomer mixture, 2 molar fraction of reacted monovinyl units from all vinyl units reacted (J,), 3 molar fraction of all divinyl molecules in the polymer, 4 molar fraction of divinyl molecules that reacted with only one vinyl bond in the polymer, 5 the crosslinking density. Fig. 2 A = rt = 1, f = 0.5 Fig. 2B rt =1, r, = 0.5, / = 0.5 Fig. 2C r, = 0.5, r, = 1, / = 0.5 Fig. 2D rt — 0.2, ra = 1.8, /f = 0.8 (Calculations by K. DcSek)...

Nonlinear polymer formation in emulsion polymerization is a challenging topic. Reaction mechanisms that form long-chain branching in free-radical polymerizations include chain transfer to the polymer and terminal double bond polymerization. Polymerization reactions that involve multifunctional monomers such as vinyl/divinyl copolymerization reactions are discussed separately in Sect. 4.2.2. For simplicity, in this section we assume that both the radicals and the polymer molecules that formed are distributed homogeneously inside the polymer particle. 

Assuming that classical chemical kinetics are valid and that the crosslinking reaction rate is proportional to the concentrations of polymer radicals and pendant double bonds, it was shown theoretically that the crosslinked polymer formation in emulsion polymerization differs significantly from that in corresponding bulk systems [270,316]. To simplify the discussion, it is assumed here that the comonomer composition in the polymer particles is the same as the overall composition in the reactor, and that the weight fraction of polymer in the polymer particle is constant as long as the monomer droplets exist. These conditions may be considered a reasonable approximation to many systems, as shown both theoretically [316] and experimentally [271, 317]. First, consider Flory s simplifying assumptions for vinyl/divinyl copolymerization [318] that (1) the reactivities of all types of double bonds are equal, (2) all double bonds... 

A second case in vinyl-divinyl copolymerization is the copolymerization of A and BB in which the reactivities of the vinyl groups A and B are not equal, while the two B groups are equally reactive. If the B groups are r times as reactive as the A groups, they enter the copolymer r times as rapidly and hence the ratio of B and A groups in the copolymer, d [Bj/d [a], is... 

J. Malinsky, J. Klaban and K. Dusek, Vinyl-divinyl copolymerization Copolymerization and network formation from styrene and p- and wi-divinylbenzene, J. Macromol. Sci.-Chem., 1971, A5, 1071. 

FRC of a vinyl monomer with a small amount of divinyl monomer represents one of the simplest methods for synthesizing polymer networks. In these systems, the divinyl monomer acts both as a comonomer and as a crosslinker. One of the most common and studied systems of this type is the copolymerization of styrene (STY) and divinylbenzene (DVB). Poly(STY-cri-DVB) copolymers are widely used as ion-exchange resins and separation media for size-exclusion chromatography, although several other vinyl/divinyl copolymerization systems have also been smdied [18],... 

Although they lack commercial importance, many other poly(vinyl acetal)s have been synthesized. These include acetals made from vinyl acetate copolymerized with ethylene (43—46), propjiene (47), isobutjiene (47), acrylonitrile (48), acrolein (49), acrylates (50,47), aHyl ether (51), divinyl ether (52), maleates (53,54), vinyl chloride (55), diaHyl phthalate (56), and starch (graft copolymer) (47). 

In this paper, the pseudo-kinetic rate constant method in which the kinetic treatment of a multicomponent polymerization reduces to that of a hcmopolymerization is extensively applied for the statistical copolymerization of vinyl/divinyl monomers and applications to the pre- and post-gelation periods are illustrated. 

Crosslihkinq Density Distribution. Let us consider the statistical copolymerization of vinyl/divinyl monomers without chain transfer to polymer for simplicity. In this case the crosslinking density p is defined as follows. 

The previous concepts may be illustrated with the experimental determination of the evolution of reaction rate, measured by DSC at T = 60°C, for the copolymerization of methyl methacrylate (MMA) with variable amounts of ethylene glycol dimethacrylate (EGDMA), a vinyl-divinyl system (Sun et al., 1997). The reaction was initiated with 2,5-dimethyl-2,5-bis(2-ethylhexanoyl)peroxy hexane. 

Fig. 26 MC simulation results that show bimodal MWDs in the emulsion copolymerization of vinyl/divinyl monomers [270]...

Predict the extent of reaction at which gelation would occur in the following two vinyl-divinyl systems, both containing 1 mol% of the divinyl component (a) styrene-ethylene glycol dimethacrylate and (b) methyl methacrylate-divinyl benzene. Assume that the reaction conditions for the two systems are such as to yield the same DP. of 1000 for the uncrosslinked polymer. Take the r and T2 values from Table 7.1 for the analogous vinyl-vinyl copolymerizations. [Ans. (a) Pc = 0.015 (b) p, = 0.012.]... 

Zhu and Hamielec [94] studied the FRC of vinyl monomers with chain transfer to polymer and the copolymerization of vinyl/divinyl monomers using a multiradical approach. They used the method of moments and focused on the pre-gelation period. They concluded that... 

TABLE 12.6 Elementary Reactions in the Nitroxide-Mediated Radical Copolymerization of Vinyl/Divinyl Monomers... 

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