The work described herein was initiated in order to generate resin characterization data that could describe a B‐staged epoxy material via the viscosity‐time‐temperature interactions that are inherently related to the nature of thermoset processing. The technique of chemorheology is explored as a means of characterizing the viscosity‐time‐temperature behavior of the B‐staged epoxy resins. The resins studied are typical of those available as glass‐impregnated prepreg bonding sheets used to manufacture multilayer printed wiring boards. The B‐staged resins were characterized isothermally at various curing temperatures. Their isothermal behavior was correlated via an empirical viscosity expression in the form of a dual Arrhenius model. Experiments were then conducted in a nonisothermal temperature mode, measuring viscosity as a function of both time and temperature. The viscosity model was taken into the nonisothermal temperature mode by introducing a time‐temperature integral. Good correlations between measured and predicted dynamic viscosity profiles are presented. Deviations are explained in terms of resin chemistry. The generalizations of behavior are discused. Calculations are presented which allow the comparison of the various B‐staged resins in terms of their viscosity behavior under the influence of an actual lamination thermal profile.

Over the past decade great strides have been made in the measurement, modeling and application of the rheology or viscosity history of curing thermosets. This paper will review the work that lead to the formulation of a simple predictive model to simulate the viscosity path of curing epoxies and to the use of the model in the understanding of the epoxy lamination process. Subsequent work by others that has clearly refined, extended, and simplified the method will be discussed.

synopsisA high-temperature linear amorphous hydrocarbon polymer synthesized cationically from 2,5-norbornadiene (bicyclo [2.2. I] hepta-2,5-diene), was studied thermomechanically with respect to physical transitions and stability in nitrogen. The glass transition temperature was determined to be 32OOC (at less than 1 cps), which is probably the highest known for a linear hydrocarbon addition polymer. The thermomechanical technique of torsional braid analysis, together with thermogravimetric analysis, differential thermal analysis, infrared analysis, and solubility studies, was used to investigate the sequential events of the glass transition and degradation. The polymer is of particular interest since it is a high-temperature plastic which in the bulk form would probably need to be processed a t high speeds in the vicinity of To in an inert atmosphere. The presence of tertiary hydrogen atoms should render it amenable to degradation by the earth's environment.

Aspects of the present status of structure‐property correlations for linear polycarboranesiloxanes which contain rigid carborane cages and flexible siloxane in‐chain linkages are discussed. Low temperature secondary transitions, glass transitions, crystallization and melting transitions, and high temperature chemical transformations in inert and air atmospheres are emphasized. The linear polymers serve as the basis for new high‐temperature elastomers.

A torsional pendulum which operates throughout the temperature range — 180° ⇄ +650°C, and permits the examination of specimens which conform to ASTM standard D2236 is reported. The same apparatus is used for torsional braid analyses for which a composite specimen is prepared by impregnating a multifilament glass braid with a solution of polymer and thermally removing the solvent. A linear‐with‐angle no‐drag optical transducer which employs the linear transmission region of a pair of polarizers is described. The apparatus has been used for examining thermo‐hysteresis effects in polymers. Hysteresis can arise in polymers from physical time‐dependent phenomena such as crystallization ⇄ fusion, dry atmosphere ⇄ water vapor, annealing ⇄ cracking, and from chemical reactions. Thermally‐induced chemical reactions can be regulated so as to freeze out preferentially longer range relaxations, thereby extending the glassy state behavior to higher temperatures. A comparison of the thermomechanical behavior of a commercially available polyimide film and of a polyimideforming varnish is reported using torsional pendulum and torsional braid analyses.