Copolymerization with divinyl monomers

Consider the copolymerization of vinyl monomer A with divinyl monomer BB where all of the vinyl groups (i.e., the A group and both B groups) have... 

Disulfide Formation in Polystyrene Networks. Polymer-bound thiols were prepared by copolymerizations of bis -vinylbenzyl)disulfide with other divinyl monomers followed by diborane reduction (Scheme 5) (fiS). The initially formed thiols were juxtaposed for reoxidation to disulfides. Polymer-bound thiols were prepared also by copolymerization of p-vinylbentyl thiolacetate with divinyl monomers followed by hydrolysis (Scheme 6). llie latter thiols were distributed randomly throughout the polymer network. The copolymer reactivity ratios for p-vinylbenzyl thiolacetate and styrene are unknown, but should be similar to those of styrene (Mi) and p-vinyl-bentyl chloride (M2) ri = 0.6, r2 = 1.1 (fifi). Copolymeiizations with equal volumes of monomers and 1/1 acetonitrile/toluene product macroporous 40-48% DVB-cross-linked networks (651. 

The arm-first synthesis of star microgels by initiating polymerization or copolymerization of a divinyl monomer such as diviny lbenzene or a bis-maleimide with a polystyryl alkoxyamine was pioneered by Solomon and coworkers.692 693 The general approach had previously been used in anionic polymerization. The method has now been exploited in conjunction with NMP,692 6 ATRP69 700 and RAFT.449 701 702 The product contains dormant functionality in the core. This can be used as a core for subsequent polymerization of a monoene monomer to yield a mikto-arm star (NMP ATRP704). 

Nonlinear addition polymers are readily obtained by copolymerizing a divinyl compound (e.g., divinylbenzene) with the vinyl monomer (e.g., styrene), as already mentioned. Products so obtained exhibit the insolubility and other characteristics of space-network structures and are entirely analogous structurally to the space-network polymers produced by the condensation of polyfunctional compounds. Owing to... 

Hydroxyl containing polymers may be cross-linked with diisocyanates. Fordyce and Ferry cross-linked styrene-maleic anhydride copolymers through the action of glycols. The copolymerization of divinyl with vinyl monomers may be looked upon as a method of cross-linking chain polymers. The cross-linkages are introduced simultaneously with the growth of the linear polymer chains, rather than afterwards, but this difference is secondary. 

Fig. 2. Formation of various structures in radical crosslinking copolymerization of monovinyl -divinyl monomers with or without using a solvent (diluent).

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 ... 

The complexity of the copolymerization involving a divinyl monomer with unequal or dependent groups is in general at least that of a three-component system and will not be discussed here. 

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)...

The free-radical copolymerization of a vinyl monomer with a small amount of a divinyl monomer offers one of the simplest routes to the preparation of polymer networks and gels. Examples are... 

An example of this case is a vinyl (A2 ) - divinyl (A4) polymerization. The assumption of an ideal polymerization means that we consider equal initial reactivities, absence of substitution effects, no intramolecular cycles in finite species, and no phase separation in polymer- and monomer-rich phases. These restrictions are so strong that it is almost impossible to give an actual example of a system exhibiting an ideal behavior. An A2 + A4 copolymerization with a very low concentration of A4 may exhibit a behavior that is close to the ideal one. But, in any case, the example developed in this section will show some of the characteristic features of network formation by a chainwise polymerization. 

Although Eqs. (1) and (2) eannot generally be applied to chain reactions, the latter has been extended to the speeial ease of chain polymerizations of symmetrieal divinyl eompounds by Stockmayer [2], He applied Flory s procedure to a mixture of polyfiinetional components with a generalized distribution of funetionality and obtained an expression, Eq. (3), for predicting the gel point in addition copolymerizations of monovinyl and divinyl monomers, in which it was assumed that the structure of both monomers is so closely related that all double bonds present have the same reaetivity and moreover, cyclization is ruled out. 

Consider the copolymerization of a vinyl monomer X with a divinyl monomer YY where all of the vinyl groups (i.e., the X group and both Y groups) have the same reactivity. [Methyl methacrylate (MMA)-ethyleneglycol dimethacrylate (EGDMA), vinyl acetate-divinyl adipate (DVA), and to an extent styrene-p- or m-divinylbenzene (DVB) are examples of this type of polymerization system (Odian, 1991). In MMA-EGDMA system. 

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. 

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],... 

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... 

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