Divinyl Monomers of Different Reactivity

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 

An alternative expression to Eq. (7.92) for the gel point conversion can be derived in terms of the reactivity ratios of the two types of vinyl groups in A and BB. Let represent the relative reactivity of an A monomer and a B monomeric group, when reacting with a free radical of type A, and r2, the relative reactivity of a B group and an A group, when reacting with a B-type radical, i.e., 

The composition equation for initial copolymer in terms of monomer group concentration [B]o becomes [cf. Eq. (7.11)]  

If we ignore the drift of residual monomer composition with conversion and assume a random distribution of crosslinks, we may predict gelation to occur at a conversion pc given by 

Thus when the double bonds of the divinyl monomer are more reactive than that of the vinyl monomer (r2 ri), gelation occurs at lower conversions. Gelation is delayed until the later stages if ri T2- 

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Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

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 ... 

Atom transfer radical polymerization (ATRP) was selected as an exemplary CRP technique to systematically study the kinetics and gelation behavior during the concurrent copolymerization of monovinyl monomers and divinyl cross-linkers (Scheme 2). The effect of different parameters on the experimental gelation was studied, including the initial molar ratio of cross-linker to initiator, the concentrations of reagents, the reactivity of vinyl groups present in the cross-linker, the efficiency of initiation, and the polydispersity of primary chains. Experimental gel points based on the conversions of monomer and/or cross-linker at the moment of gelation, were determined and compared with each other in order to understand the influence of each parameter on the experimental gel points. 

In the FRC of vinyl and multivinyl monomers, a drift in the instantaneous copolymer composition throughout the reaction will be undergone due to the different reactivities of the vinyl groups. This compositional drift is caused by the fact that the more reactive monomer will be consumed faster than the less reactive ones. In the simplest instance, assuming equal reactivity of the vinyl groups in mono-and divinyl monomers present in the reaction system, the reactivity of the crosslinker would be twice that of the monovinyl monomer, and therefore, the polymer chain... 

As a natural consequence of the crosslinking reaction process, the density of the primary polymer differs depending on the time of this primary polymer formation. That is, in the case of the copolymerization of vinyl and divinyl monomers, the generally formed inhomogeneous crosslink formation can be regarded as a natural consequence of the mechanism of crosslink formation. This is true except for die special reaction conditions by favorable timing of the incorporation of divinyl monomer in the polymer chain (formation of pendant double bonds) and consumption of pendant double bonds (formation of crosslinks). These special reaction conditions are used by Flory as simplified conditions when the Flory-Stockmayer theory is applied to the copolymerization of vinyl and divinyl monomers. Flory s simplified conditions include die following three assumptions (1) the reactivities of the monomer and die double bonds in the polymer are all equal (2) any double bond reacts independently and (3) there will be no intramolecular reactions (cyclization) within the finite size molecules (sols). 

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... 

Multiarm polymers (11) can be prepared that still have the reactive functional groups (Z) close to the core. As these are still active, they can be used as sites to initiate the growth of more arms by adding either the same monomer used to prepare (11) or a second monomer to prodnce mikto-arm star polymers, in which the arms have different chemical structures. Thus, an active ended poly(t-butyl acrylate), prepared by ATRP, can be coupled with divinyl benzene to form a multiann star polymer. This structure can be converted to a mikto-arm star polymer by reacting the living ends still present with n-butyl acrylate, and so propagate poly(n-butyl acrylate) chains from the core outward. 

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