Block copolymer toughened polyimides and quantitative evaluation of cure kinetic models
Abstract
Polyimides have a number of excellent engineering properties, especially for high temperature aerospace applications, but a major challenge is to improve the fracture toughness. In order to improve fracture toughness, polymeric nanoparticulates were introduced by adding 5% by weight of PnBA-PDMAEMA block copolymer to a PMR-15 polyimide thermoset. The block copolymer was created by ATRP synthesis, followed by mixing with the amic acid form of the PMR-15 imide, then fully imidized in a vacuumed oven and crosslinked in a heat press into the cured thermoset material. Using DLS it was determined that the block copolymer phase separated into spherical domains with diameters from 500 to 2500 nm. The fracture toughness as determined by ASTM D 5054 was increased by 83% for the PMR-15 with the 5% of block copolymer. There is an extensive history of modeling epoxy cure kinetics, where a candidate model is typically fit to a limited set of experimental cure data. However for these models to be valid outside of experimental data conditions a complete understanding of the parameter uncertainty is required. Two phenomenological and three microkinetic cure models have been examined for describing the cure kinetics of Epon 825 with 3-Aminophenyl Sulfone. The evolution of the cure is measured via DSC for a number of dynamic thermal histories and epoxy/amine stoichiometric ratios. The experimental data was first pretreated to address baseline correction and baseline drift. The experimental data was analyzed with respect to each of the cure models, using two separate statistical methods - nonlinear optimization and Bayesian analysis. While there are fundamental differences in how the parameters and uncertainty are determine for each statistical method, both determined that the microkinetic model with an effective ter-molecular reaction as the initial mechanistic step is the most accurate cure model for this epoxy system.
Degree
M.S.Ch.E.
Advisors
Won, Purdue University.
Subject Area
Chemical engineering
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