Thermoset Polymerization Research Articles

Photoinitiated thermoset polymerization through controlled release of metathesis catalysts encapsulated in poly(phthalaldehyde)

Frontal polymerization of dicyclopentadiene initiated by UV-degradable catalyst microparticles with excellent resin stability and tenability.

Nanonetwork Thermosets from Templated Polymerization for Enhanced Energy Dissipation.

Herein, we aim to develop a facile method for the fabrication of mechanical metamaterials from templated polymerization of thermosets including phenolic and epoxy resins using self-assembled block copolymer, polystyrene-polydimethylsiloxane with tripod network (gyroid), and tetrapod network (diamond) structures, as templates. Nanoindentation studies on the nanonetwork thermosets fabricated reveal enhanced energy dissipation from intrinsic brittle thermosets due to the deliberate structuring; the calculated energy dissipation for gyroid phenolic resins is 0.23 nJ whereas the one with diamond structure gives a value of 0.33 nJ. Consistently, the gyroid-structured epoxy gives a high energy dissipation value of 0.57 nJ, and the one with diamond structure could reach 0.78 nJ. These enhanced properties are attributed to the isotropic periodicity of the nanonetwork texture with plastic deformation, and the higher number of struts in the tetrapod diamond network in contrast to tripod gyroid, as confirmed by the finite element analysis.

Simulation approaches for the mechanisms of thermoset polymerization reactions

Abstract Detailed modeling and simulation of the reaction of alcohol and isocyanate moieties to form urethane have provided a reason to question conventional opinions that this is a step-growth polymerization process. In particular, industrial formulations are dominated by catalytic mechanisms, and these chain mechanisms can change the polymer growth mechanism. This paper's research evaluates experimental data of reaction temperature and resin viscosity of urethane gel reactions that substantiate a chain-growth mechanism. One of the artifacts of a chain-growth mechanism is the rapid appearance of relatively large molecules that reduce gel point times earlier with step-growth mechanisms.

Impact of inter- and intra-molecular movements on thermoset polymerization reactions

The large increase in viscosity during thermoset reactions leads to reduced frequencies of reacting moiety collisions with respective reduced reaction rates. Molecular diffusion substantially ends after the gel point; however, reactions continue after the gel point through mechanisms involving local movement (and reacting moiety contact) of polymer sections/branches which is referred to as intra-molecular movement. The impact of inter- and intra-molecular movements was simulated for polyurethane reactions to better understand the impact of mass transfer on polymerization reactions.Inter-molecular reaction mechanisms are dominant prior to the gel point, and intra-molecular mechanisms are dominant after the gel point. Representing the Arrhenius pre-exponential factor as a sum of a viscosity-dependent term and a viscosity-independent term was identified as the most efficient method to model this phenomenon. Good agreement of simulation results for reaction temperature, foam height, and viscosity profile with the experimental data were obtained.

Chemorheology investigation of a glassy epoxy thermoset on tensile plastic flow and fracture morphology

Reproducible and uncharacteristic tensile stress–strain behavior of cured glassy epoxy-amine networks produces distinctive fracture surfaces. Test specimens exhibiting plastic flow result in mirror-like fracture surfaces, whereas samples that fail during yield or strain softening regions possess nominal mirror-mist-hackle topography. Atomic force microscopy and scanning electron microscopy reveal branched nodule morphologies in the 50-nm size scale that may be responsible for the unusual tensile properties. Current hypothesis is that plastic flow of the glassy thermoset occurs through the existence and deformation of these nodular nanostructures. The thermal cure profile of the epoxy-amine thermoset affects the size and formation of the nodular nanostructure. Eliminating vitrification during thermoset polymerization forms a more continuous phase, reduction in size of the nodules, and eliminates the capacity of the material to yield in plastic flow. This maximizes nanostructure connectivity of the glassy epoxy-amine thermoset and reduces strain to failure significantly. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1333–1344.

Modeling impact of catalyst loading on polyurethane foam polymerization

A MATLAB model based on the simultaneous solution of several differential equations was developed to include the impact of catalyst loading for the reactions and physical processes of a urethane box foaming process. Experiments with different amounts of catalyst loading were conducted to fit the model parameters for this thermoset polymerization. Rate constants for the polyurethane foaming reaction were determined by polyol types, catalyst types and reaction temperatures. By combining these factors polyurethane reaction rates during whole foaming process can be calculated in this model and the model can be used to predict the performance of foams which have multiple combinations of isocyanate, polyols, catalysts, chemical blowing agents, and physical blowing agents in recipes when parameters on pure component (e.g. single polyol) performance are behavior.

Effect of orientation on thermoset frontal polymerization

AbstractWe observed that the velocities of descending thermoset polymerization fronts were strongly affected by the orientation of the tube. The front remained approximately perpendicular to the gravitational vector but propagated almost 1.8 times as fast at 75° along the axis of the tube. We performed a study of the velocity and front‐shape dependence on orientation with propagating fronts of triethylene glycol dimethacrylate with peroxide initiator and acrylamide/bisacrylamide polymerization in dimethyl sulfoxide with persulfate initiator. The percentage increase of velocity was independent of the initiator concentration but strongly dependent on the viscosity. Convection under the front flowed away from the tube wall nearest the vertical axis and was stronger as the angle increased. The front shape also changed, becoming significantly distorted near the wall from which the convection originated. We applied a simple geometric argument to explain the angular dependence for small angles on the basis of the assumption that convection did not affect the velocity of propagation normal to the front. The increase in velocity along the tube axis could be explained by a projection of the normal velocity onto the tube axis, following a 1/cosθ dependence. For higher angles, the convection was not sufficiently strong to maintain a level front. When the difference from a 180° orientation was considered, the velocity dependence exactly followed the geometric relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3504–3508, 2002

In-Situ Monitoring of Urethane Formation by FTIR and Raman Spectroscopy

Reactions of 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, and 2-octanol with phenylisocyanate were monitored by FTIR and Raman spectroscopy. The results show that Raman spectroscopy is as effective as FTIR spectroscopy in following urethane reaction kinetics. The activation energies calculated are 10.0, 10.5, 11.9, 12.8, and 14.8 (kcal/mole) for 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, and 2-octanol reacting with phenylisocyanate without catalyst, respectively. The steric hindrance effects of primary, secondary, and tertiary butanol with phenylisocyanate reaction kinetics were observed. The initial reaction rates of these alcohol systems have a typical ratio of 1:0.3:0.1, respectively. The reaction kinetics simulation, based on a simple kinetics model, fits reasonably well with experimental data obtained by Raman spectroscopy. This agreement further demonstrates the effectiveness of Raman spectroscopy in monitoring urethane reaction kinetics and suggests an effective method for verifying the reaction kinetics and mechanism under nonisothermal conditions. The results of this work will form the basis for our future in-situ study of thermoset polymerization kinetics under exposure to radio frequency electromagnetic (RF) fields.

Monitoring thermoset polymerization of PMR-15 by using electric measurements

Monitoring thermoset polymerization of PMR-15 by using electric measurements

Monitoring thermoset polymerization by using piezoelectric measurements

AbstractThe electric impedance of a piezoelectric element placed inside a polymeric system depends on the viscoelastic property of the polymer. Its measurement is a sensitive and nondestructive method for monitoring the curing of such materials. The validity of this new method is shown by comparison with traditional viscoelastic and ultrasonic techniques.

Impulse viscoelasticity: a new method to study polymerization of thermosets

Impulse viscoelasticity: a new method to study polymerization of thermosets