Pseudo-interpenetrating polymer networks based on tetrafunctional epoxy resins and poly(methyl methacrylate)

Abstract

Pseudo-interpenetrating polymer networks (p-IPNs) of an epoxy resin and poly(methyl methacrylate) (PMMA) were synthesized simultaneously. Methyl methacrylate (MMA) was polymerized with benzoyl peroxide in the presence of an oligomeric epoxy resin, which contained stoichiometric amounts of either a tetrafunctional [i.e., ethylenediamine (EDA)] or hexafunctional [i.e., triethylenetetramine (TETA)] crosslinking agent. The resulting materials would be useful for aerospace, automotive, medical, and dental applications. The structure of the epoxy resin (i.e., tetraglycidyl 4,4′-diamine diphenyl methane) was confirmed by elemental analysis and IR and NMR spectroscopies. The thermal, mechanical, and kinetic behaviors of the polymeric networks produced from this oligomeric epoxy resin and the p-IPNs of this crosslinked epoxy with linear PMMA were compared. Time-resolved IR spectroscopy of the cyclic ether group in the epoxy at 906 cm−1 revealed kinetic information between 40 and 80°C for a complex reaction scheme. In the absence of MMA, the asymptotic final conversion of epoxide groups was achieved after (1) 60 min of chemical crosslinking at 50°C and (2) 30 min of crosslinking at 80°C with tetrafunctional EDA. In the presence of 10 wt % MMA, asymptotic final conversions of the epoxide group were achieved after (1) 150 min at 40°C, (2) 80 min at 50°C, and (3) 30 min at 80°C. In agreement with other kinetic studies based on the same epoxy resin but different crosslinking agents, these solvent-free polymerizations were diffusion-controlled during the later stages of chemical crosslinking because the apparent reaction order was very close to unity, via an unsteady state batch reactor model with lumped-parameter kinetics. The thermal expansion coefficients of the crosslinked epoxy resin increased at higher concentrations of PMMA, but hexafunctional TETA produced a higher crosslink density and reduced the thermal expansion relative to the same networks and p-IPNs prepared with tetrafunctional EDA. Elastic modulus, fracture stress, and toughness increased synergistically when the epoxy resin was crosslinked with EDA at 40°C in the presence of 10 wt % MMA. This p-IPN exhibited minimal shrinkage, on the order of 0.15%, during the actual polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1858–1868, 2003