Vinyl-divinyl polymerization

Imidazolidin-2-one, 4,5-dihydroxy-4,4-di(p-bromophenyl)-reactions with urea, 5, 406 Imidazolidin-2-one, 1,3-divinyl-polymerization, 1, 280 I midazolidin-2-one, 1 -ethyl-3-vinyl-polymerization, 1, 279 Imidazolidin-2-one, 4-methylene-synthesis, 5, 140... 

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. 

Generalization of Flory s Theory for Vinyl/Divinyl Copolvmerization Using the Crosslinkinq Density Distribution. Flory s theory of network formation (1,11) consists of the consideration of the most probable combination of the chains, namely, it assumes an equilibrium system. For kinetically controlled systems such as free radical polymerization, modifications to Flory s theory are necessary in order for it to apply to a real system. Using the crosslinking density distribution as a function of the birth conversion of the primary molecule, it is possible to generalize Flory s theory for free radical polymerization. 

Covalent polymeric networks which are completely disordered. Continuity of structure is provided by an irregular three-dimensional network of covalent links, some of which are crosslinks. The network is uninterrupted and has an infinite molecular weight. Examples are vulcanized rubbers, condensation polymers, vinyl-divinyl copolymers, alkyd and phenolic resins. 

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. 

In several types of chainwise polymerizations, species with high molar mass are generated from the beginning of the reaction. This is depicted in Fig. 3.2 for an A2 (one double bond per molecule) +A4 (two double bonds per molecule) free-radical polymerization - e.g., a vinyl-divinyl system. 

Let us consider an A2 + A4 chainwise polymerization e.g., a vinyl - divinyl system with af = 0.01 (a very small concentration of the crosslinker in order to keep ideal conditions), and q = 0.999. Figure 3.22 shows the fraction of tetrafunctional crosslinks, nc 4/[A4o], as a function of conversion, for two limiting values of ,. Termination by combination (E, = 1) increases the crosslink concentration with respect to termination by chain transfer or disproportionation (2, = 0). At full conversion, termination by combination leads... 

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... 

Divinyl polymerization, polymers n. Polymerization of a monomer, which contains two vinyl groups. When the two double bonds are conjugated (as in 1,3-dienes) the polymerization is called diene polymerization. 

The relations given above can readily be applied to crosslinking of existing chains, where the concentration of active network chains,, is the independent variable. When networks are formed by vinyl-divinyl crosslinking copolymerization, 4 p, (j)2, M -, and possibly the interaction parameters, JCi-j functions of the polymerization conversion which is now the independent variable of a system characterized by initial concentrations of the mono- and divinyl monomers, the diluent(s), and reactivities of the vinyls. The dependence of d)S on the volqme conversion of njonomer to the crosslinked polymer is simply where... 

Vinyl polymers cross-linked with divinyl monomers, for example, polystyrene polymerized in the presence of divinyl benzene. 

A more complicated behaviour was obtained with divinyl ether due to the formation of both cyclic structures and pendent vinyl groups in the chain. The failure of such olefins as styrene and isopropenylbenzene to give copolymers with 2-fural-dehyde, and in fact to homopolymerize in its presence, was blamed on the strength of the complex formed between the initiator and the aldehyde, believed too stable to initiate polymerization. 

In principle, polymers equivalent to those obtained from vinyl and divinyl monomers may be synthesized by this method. The product in the above example possesses the same chain structure as polyethylene. The polymerization process, notwithstanding the likelihood of a metal alkyl intermediate, should conform satisfactorily to stepwise condensation. However, the product, and those obtained by Friedel-Crafts condensation as well, lack the recurrent functional groups which generally characterize condensation polymers. 

Detailed studies on the lipase-catalyzed polymerization of divinyl adipate and 1,4-butanediol were performed [41-44]. Bulk polymerization increased the reaction rate and molecular weight of the polymer however, the hydrolysis of the terminal vinyl ester significantly limited the formation of the polyester with high molecular weight. A mathematical model describing the kinetics of this polymerization was proposed, which effectively predicts the composition (terminal structure) of the polyester. 

---