Microgel unsaturated polyester

Microgels by Emulsion Copolymerization of Self-Emulsifying Unsaturated Polyesters and Comonomers... 

By emulsion copolymerization (ECP) of self-emulsifying unsaturated polyesters (EUP) and bifunctional monomers, such as styrene (S), microgels may be prepared which have a rather uniform diameter [109]. This uniformity of size is due to a special mechanism of particle formation involved in using EUP as comonomers. 

The parameters which influence the particle size of microgels have been studied during self-emulsifying, seeded emulsion copolymerization of an unsaturated polyester and butyl acrylate [134]. 

Epoxy resins have been toughened by in situ copolymerization of microgels consisting of unsaturated polyesters and bifunctional comonomers [382,383]. 

Microgels which have been prepared in emulsions or microemulsion have a more compact structure than those obtained by polymerization in solution. For microemulsion copolymerization, preferentially self-emulsifying comonomers, such as unsaturated polyesters, are used as polymerizable surfactants, because no emulsifier must be removed after the reaction. By choosing suitable monomer combinations the composition, size and structure of microgels can be widely varied, thus adjusting these macromolecules to special applications. 

For some particular formulations (e.g., unsaturated polyesters formulated with a high styrene concentration), the primary chains that are first generated are not miscible with the unreacted monomers. In this case, there is a phase separation phenomenon characterized by the appearance of relatively large polymer-rich particles. These microgels are formed by a thermodynamic driving force and their sizes are large enough to be detected in both the course of polymerization and the final materials. 

As in most chainwise polymerizations, q -> 1, the first observation arising from Eq. (3.180) is the very low value of the gel conversion. In actual systems, intramolecular cyclization and microgel formation produce an increase in the gel conversion. But reported values of xgei for the free-radical polymerization of systems containing multifunctional monomers are usually below 0.10. This is the case for the crosslinking of unsaturated polyesters (Af) with styrene (A2 ). 

From unsaturated polyesters with carboxylic end groups at both chain ends, after neutralization they are efficient emulsifiers for lipophilic monomers [95], and with styrene as comonomer microgels can be prepared with rather uniform diameter [96]. By using lipophilic initiators, such as 2,2 -azobis(isobutyronitrile) (AiBN), in the microemulsion copolymerization, diffusion of monomers is too slow compared with the reaction rate. Therefore, copolymerization is confined to the coherent, lipophilic phase [97,98] and very small microgel particles with a rather uniform size result. Research work by Funke and cited by Funke [76] indicates the usefulness of microemulsion copolymerization to convert unsaturated polyesters into microgels. 

Liu, S. B., and Yu, T. L., Study of the microgelation of unsaturated polyester resins by dynamic light scattering, Macromol. Chem. Phys., 196, 1307, 1995. 

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