Angular 4 material chips placeholder not working properly

its an issue with the keywords spelling in ts file. you have defined it as

  keyowords = [];

And the name you are referring to in the html file is keywords. Change the name in ts file to

keywords = [];

This is working stackblitz code for the same :- https://stackblitz.com/edit/angular-rtti3v?file=app%2Fchips-input-example.html