title: Gel Point Suppression in RAFT Polymerization of Pure Acrylic Cross-Linker Derived from Soybean Oil.
abstract: Here we report the reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylated epoxidized soybean oil (AESO), a cross-linker molecule, to high conversion (>50%) and molecular weight (>100 kDa) without macrogelation. Surprisingly, gelation is suppressed in this system far beyond the expectations predicated both on Flory-Stockmeyer theory and multiple other studies of RAFT polymerization featuring cross-linking moieties. By varying AESO and initiator concentrations, we show how intra- versus intermolecular cross-linking compete, yielding a trade-off between the degree of intramolecular linkages and conversion at gel point. We measured polymer chain characteristics, including molecular weight, chain dimensions, polydispersity, and intrinsic viscosity, using multidetector gel permeation chromatography and NMR to track polymerization kinetics. We show that not only the time and conversion at macrogelation, but also the chain architecture, is largely affected by these reaction conditions. At maximal AESO concentration, the gel point approaches that predicted by the Flory-Stockmeyer theory, and increases in an exponential fashion as the AESO concentration decreases. In the most dilute solutions, macrogelation cannot be detected throughout the entire reaction. Instead, cyclization/intramolecular cross-linking reactions dominate, leading to microgelation. This work is important, especially in that it demonstrates that thermoplastic rubbers could be produced based on multifunctional renewable feedstocks.
authors.affiliation: Chemical and Biological Engineering, Iowa State University , Ames, Iowa, United States.
authors.forename: Mengguo
authors.initials: M
authors.lastname: Yan
authors.affiliation: Chemical and Biological Engineering, Iowa State University , Ames, Iowa, United States.
authors.forename: Yuerui
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Chemical and Biological Engineering, Iowa State University , Ames, Iowa, United States.
authors.forename: Mingjia
authors.initials: M
authors.lastname: Lu
authors.affiliation: Chemical and Biological Engineering, Iowa State University , Ames, Iowa, United States.
authors.forename: Fang-Yi
authors.initials: FY
authors.lastname: Lin
authors.affiliation: Chemical and Biological Engineering, Iowa State University , Ames, Iowa, United States.
authors.forename: Nacú B
authors.initials: NB
authors.lastname: Hernández
authors.affiliation: Chemical and Biological Engineering, Iowa State University , Ames, Iowa, United States.
authors.forename: Eric W
authors.initials: EW
authors.lastname: Cochran
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry*; D003500:Cyclization; D005782:Gels / Q000737:chemistry*; D007700:Kinetics; D058105:Polymerization; D011108:Polymers / Q000737:chemistry*; D013024:Soybean Oil / Q000737:chemistry*; D014783:Viscosity
chemical_list: D003432:Cross-Linking Reagents; D005782:Gels; D011108:Polymers; C554142:epoxidized soybean oil; D013024:Soybean Oil