Defying expectation, investors piled into initial public offerings at a record rate in 2020, and few expect the excitement to wear off soon.Companies raised $167.2 billion through 454 offerings on US exchanges this year through December 24, compared with the earlier full-year record of $107.9 billion at the height of the dot-com boom in 1999, according to Dealogic.The coronavirus pandemic turned the usual flow of the IPO market on its head, with $67.3 million raised in the fourth quarter. That amount is almost six times the total for the first three months of the year.As a result of the scramble, stalwarts of the 21st-century economy including Airbnb Inc., DoorDash Inc. and Palantir Technologies Inc. are now publicly traded, accessible to the average investor.