Contrasting acrylate versus methacrylate crosslinking reactions and the impact of temperature
May 20-25, 2018
Divinyl monomers containing multiple vinyl groups are commonly used in polymerization reactions to introduce crosslinked networks. The reactivity of the second vinyl group in a crosslinker monomer decreases once it becomes incorporated in a polymer chain. This Reduced Reactivity Parameter (Ψ) depends on the monomer-crosslinker pair. To date, our group has developed this concept exclusively from methacrylate-based copolymerization systems1,2. Acrylate co-monomers introduce another level of complexity from a competing mechanism toward gel content and macromolecular network development; long chain branching from chain transfer to polymer. The later form networks via α-hydrogen abstraction, which is a prominent reaction with acrylates. Moreover, the differences in reactivity ratio between acrylates and methacrylates add another layer of heterogeneity through the polymerization which also impacts the kinetics and ultimate network structure. In this work, we compare the network formation reaction and the Ψ-parameters for 1,4 butanediol dimethacrylate (BDDMA, containing methacrylate groups) with its acrylate-based counterpart (BDDA, containing acrylate groups) in copolymerization reactions with either n-butyl methacrylate (nBMA) or n-butyl acrylate (nBA). The Ψ-parameter for all systems is estimated by comparing the experimental results with Monte Carlo simulations of the polymerization reactions. The goal of the work is to decouple the contributions of pendent-vinyl based crosslinking and long-chain branching (α-hydrogen abstraction) from the resulting kinetic profile that the Ψ parameter is determined from. Moreover, we contrast the balance of contributions from propagation, chain transfer, reactivity ratios, and utility of the pendent vinyl groups for crosslinking between reactions at either 60 or 70 °C. Even this seemingly small shift in temperature has a marked impact on the kinetics and resulting network for the different pairs of (meth)acrylate comonomers.
- Tripathi, A.K.; Neenan, M.L.; Sundberg, D.C.; Tsavalas, J.G., "Influence of n-Alkyl Ester Groups on Efficiency of Crosslinking for Methacrylate Monomers Copolymerized with EGDMA: Experiments and Monte Carlo Simulations of Reaction Kinetics and Sol-Gel Structure", Polymer (2016), 96, 130–145, DOI:10.1016/j.polymer.2016.04.017
- Tripathi, A.K.; Tsavalas, J.G.; Sundberg, D.C., “Monte Carlo Simulations of Free Radical Polymerizations with Divinyl Crosslinker: Pre- and Post-Gel Simulations of Reaction Kinetics and Molecular Structure", Macromolecules (2015) 48, 184−197, DOI: 10.1021/ma502085x
Chang Liu, John Tsavalas, Yung-Chun Lin, and Amit Tripathi, "Contrasting acrylate versus methacrylate crosslinking reactions and the impact of temperature" in "Polymer Reaction Engineering X (PRE 10)", John Tsavalas, University of New Hampshire, USA Fouad Teymour, Illinois Institute of Technology, USA Jeffrey Stubbs, HP Inc., USA Jose R. Leiza, University of the Basque Country, Spain Eds, ECI Symposium Series, (2018). http://dc.engconfintl.org/prex/6