Sigmoidal Chemorheological Models of Chip-Underfill Materials Offer Alternative Predictions of Combined Cure and Flow

Prior rheology results on chip-underfill epoxy resins have been re-analyzed by a sigmoidal model that contains three variable physical parameters, including the terminal cured viscosity of the gel, an induction or dwell time and a time factor associated with the speed of conversion as viscosity undergoes large dynamic changes during rapid crosslinking. The analyses were conducted with resins that were originally cured between 150 and 180 °C and show obvious non-linearity, even on a semi-log plot of dynamic viscosity. The sigmoidal models more accurately represent a wider range of dynamic viscosity than power-law-based rheological models, which are both more common and more generally accepted for practical application. If total flow is the critical design parameter in terms of chip underfill, perhaps these alternative sigmoidal models need to be more thoroughly evaluated to gauge their practical use and validity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/61221/1/832_ftp.pd

Chemorheology of photopolymerizable acrylates using a modified Boltzmann sigmoidal model

Experiments were conducted to evaluate the influence of ambient photoconversion on rheology for a range of photopolymerizable urethane dimethacrylate (UDMA) resins containing varying amounts of three comonomers including 1,6 hexane diol-dimethacrylate (HDDMA), an alkoxylated cyclohexane dimethanol diacrylate monomer (CD-582), and hydroxyethyl methacrylate (HEMA). Experiments were performed both as a function of composition and time-dependent dose varying the intensity using a photorheometer. A semilog-based sigmoidal model allowed the determination of four physical model parameters to define the relationship between reaction kinetics and its dynamic influence on viscosity. We have observed induction times and viscosity changes associated with the model that shows a trend in reaction kinetics in the following order from most to least reactive: UDMA > CD582 > HDDMA > HEMA. With increasing amounts of reactive diluent included in the formulation, the kinetics of reaction was more sluggish. The value of this sigmoidal model is that it could help define formulation and process conditions most likely to control crosslinking to maximize dimensional stability or other thermophysical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2319–2325, 2008Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/61230/1/21563_ftp.pd

Kinetic modelling of phenols consumption during polyethylene thermal oxidation

Irganox 1010 stabilized PE was monitored by carbonyl build-up and DSC under oxygen. A scheme for PE stabilization by phenols was implemented and its kinetic parameters were calculated from experimental results. This model was validated from its ability to simulate kinetics curves for carbonyl build up, induction period changes with stabilizer concentration, and stabilizer depletion curve in thermal ageing. The use of OIT measurement for quantifying stabilizer is also discussed. Kinetic analysis showed that OIT is actually proportional to stabilizer concentration in virgin samples but this is not true for aged samples because of negative influence of oxidation unstable by-products. The model was also employed for discussing some scenarii proposed as explanation of heterogeneity observed during thermal oxidation of stabilized polyolefins

MMA bulk polymerization and its influence on in situ resin viscosity comparing several chemorheological models

Earlier published rheological data of methyl methacrylate (MMA) heated and isothermally polymerized at temperatures between 50 and 80°C have been reanalyzed using three semiempirical models of viscosity advancement including a modified Boltzmann sigmoidal model, a microgel model for cure, and a first-order isothermal kinetic model. These alternative models possessed few fitting parameters and could be used without requiring more experiments to be run. For each dataset as a function of temperature, the analysis resolved time constants associated with both the induction time for polymerization and the rate of viscosity rise, which were inversely related to the polymerization temperature. We found the sigmoidal model the most robust to accommodate nonlinearities in viscosity advancement with radical polymerization of MMA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83197/1/33214_ftp.pd