Popiolek, who is a former London CEO of Gavin Anderson and joined Grandfield two years ago, declined to comment.
However, PRWeek understands he has refused an offer to join Bell Pottinger Corporate & Financial, where Grandfield chairman Charles Cook has been appointed deputy chairman.
Popiolek's clients included hedge fund manager RAB Capital, data recovery firm Kroll Ontrack, Falkland Gold and Minerals, Global Petroleum, Hampson Industries and Parson Consulting. He also worked on Grandfield's campaign for the Londis Shareholders Action Group.
Cook declined to talk about how Grandfield's staff and clients would be affected by the deal but it is thought that the firm's remaining four PROs are expected to join Bell Pottinger C&F.
Similarly, Grandfield's 12 retained clients, which also include Evolution Securities, the Railtrack Private Shareholders Acton Group and Allergy Therapeutics, are to pass to Bell Pottinger C&F.