Nitroxide-Controlled Free-Radical Copolymerization of Vinyl and Divinyl Monomers. 2. Gelation

Abstract

Some important features of the gel prepared by the nitroxide-mediated free-radical copolymerization of styrene with a small amount of 4,4′-divinylbiphenyl were studied. Owing to the "living" character of this system, the cross-linking reaction in this system proceeds highly homogeneously (randomly) without forming any microgels. The gel prepared by this method showed remarkable differences from the one prepared in the conventional system, in regard to the relative fraction and swelling ratio of the gel studied as a function of monomer conversion. It was also found that the critical number density of cross-links at the gel point agreed with the mean-field theoretical value of Flory and Stockmayer (FS) within a factor 2. This value was exceptionally small compared with those previously reported for the conventional free-radical systems, which are typically 1 or 2 orders of magnitude larger than the FS value. These results, along with the previous study on the reactivity of the pendant vinyl of this system Fukuda, T. Macromolecules 1997, 30, 4268), show that the gels prepared by this method are exceptionally homogeneous compared with those prepared by the conventional free-radical method.

Rigid Macroporous Poly(divinylbenzene) Monoliths with a Well‐Defined Bicontinuous Morphology Prepared by Living Radical Polymerization

“…Under ideal conditions, the living radical polymerization of a multifunctional monomer (or crosslinker) should yield dense 3D networks with no voids other than interatomic interstices. [13,14] However, for real experimental systems, some distribution in the DP leads to the development of primary particles that are interconnected by the subsequent polymerization of vinyl groups located on the particle surfaces. Therefore the gel skeletons consist of agglomerated nanoparticles (estimated to be less than 10 nm in size from field-emission SEM (FESEM) observations) with inter-particle voids.…”

“…[2][3][4][5][6][7][8][9][10][11][12] During the course of conventional free radical polymerization using various monomers and crosslinkers, when a monomer or crosslinker molecule starts to react, it is soon segregated from the solvent by an abrupt increase in the local degree of polymerization (DP) or due to the formation of an intramolecular network (cyclization), and thus phase separation (sometimes termed as "microgel" formation) takes place. [13,14] Although these phase-separation methods yield macroporous structures with a narrow size distribution of pores formed by the interstices between segregated particles, the precise and independent control of pore size and pore volume is rather difficult. The facile and fine control of pore properties has recently become necessary because monolithic porous materials with well-defined pore properties and surfaces have been shown to allow faster transport of liquid and gas molecules; moreover, these structures possess higher mechanical strength [15,16] and are especially suitable as chromatographic separation media, ion exchange resins, [17][18][19] and catalyst supports.…”

Polimerização RAFT em Miniemulsão

“…Conforme já revisado, as técnicas de CLRP [136] permite a síntese de polímeros com arquitetura molecular definida, tendo sido recentemente adaptada para uso em diversos tipos de sistemas dispersos de polimerização, o que torna possível o uso de diversas técnicas de CLRP como rota de síntese de nanogéis com arquitetura molecular complexa e definida [13,[137][138][139][140][141] . De uma forma geral, as técnicas de CLRP em sistemas dispersos são de fato rotas bem atrativas para a síntese de nano-hidrogéis com estrutura molecular bem definida (ex.…”

Thermo-mechanical behavior and specific volume of highly crosslinked networks based on glycerol dimethacrylate and its derivatives

“…In consequence, functional groups differ in reactivity, and the overall conversion is limited due to hindered mobility of reactive groups [16]. Attempts at increasing network homogeneity have been made and these include the atom transfer radical polymerization [17], controlled/living radical polymerization [18,19], or recently applied thiol-ene-methacrylate systems with step growth polymerization mechanism [20].…”