FRANKFURT/ZURICH, Sept 29 (Reuters) - Family-owned contract manufacturer PolyPeptide is preparing for a 2021 Zurich stock market listing as the company seeks to raise funds for further growth, two people close to the matter said.

The maker of therapeutic peptides, which are used by pharma companies as well as biotechnology groups, could offer shares worth up to 500 million Swiss Francs ($544 million), potentially giving it a market capitalisation of roughly 1.5 billion Francs, they added.

Rothschild is acting as adviser on the initial public offering and has sent out requests for proposals to investment banks hoping to help with the listing, one of the people said on condition of anonymity.

PolyPeptide was not available for comment and Rothschild declined to comment.

PolyPeptide is headquartered in Sweden, but is expected to choose Zurich as a venue for a potential IPO as peers Lonza and Bachem are listed there.

Lonza and Bachem trade at 26 and 32 times their expected core earnings.

Revenue and earnings figures for PolyPeptide could not be learned.

PolyPeptide Group was founded in 1996 and has since expanded through a series of acquisitions, including buying Lonza's peptides business in 2017.

It operates six manufacturing sites: two in the United States, three in Europe and one in India. It employs more than 850 staff.

Peptides are tiny proteins that are used among other in cancer drugs, antibiotics, vaccines or anti-wrinkle agents. ($1 = 0.9200 Swiss francs) (Additional reporting by Abhinav Ramnarayan; Editing by Barbara Lewis)