The couple previously had given Caltech more then $30 million over the years for projects in environmental science and economics and management studies, among other causes. Their new donation is more open ended, creating an endowment that allows Cal Tech to advance promising initiatives without locking in a specific goal.

“Our philosophy is to allow for flexibility because you can’t know the future, and science is about exploring the unknown,” Ronald Linde said in a statement.

Linde, the vice chair of Caltech’s board of trustees, earned his bachelor’s degree in engineering from UCLA in 1961 and his doctorate in materials science from Caltech in 1964. He later founded Envirodyne Industries and was its chief executive as it grew into an international conglomerate with branches in plastics, packaging and steel. He sold the firm in 1989 and later was in the finance industry.Maxine Linde was general counsel of Envirodyne and previously worked as a scientific programmer at the Caltech-managed Jet Propulsion Laboratory.

In thanking the Lindes, Caltech President Thomas F. Rosenbaum said in a statement that the gift will have “a far-reaching and enduring impact” on the engineering- and science-oriented school. The Lindes “understand deeply the Institute’s fundamental values and appetite for bold research endeavors.”

The largest gift ever received by Caltech was the $600-million pledge in 2001 from Intel Corp. cofounder Gordon Moore and his wife Betty.

By LARRY GORDON

Photo: Ronald and Maxine Linde have made their new pledge to Caltech open-ended. “Our philosophy is to allow for flexibility because you can’t know the future,” Ronald Linde said. (California Institute of Technology)