UPDATE 1-Chesapeake IPO prices at top-underwriter

* Prices at $21/unit vs $19-$21 range-underwriter

* Sells 21.25 mln units, raises about $446.25 mln

* Molycorp, Envestnet expected to price IPOs on Wed

By Clare Baldwin

NEW YORK, July 28 (Reuters) - Chesapeake Midstream Partners LP (CHKM.N), a natural gas limited partnership between Chesapeake Energy Corp (CHK.N) and Global Infrastructure Partners, priced units in its initial public offering at the top of the expected range on Wednesday, according to an underwriter.

The company sold 21.25 million units for $21 each, raising about $446.25 million. It had planned to sell units for $19 to $21 each.

Two other companies, rare earth oxides miner and processor Molycorp Inc (MCP.N) and investment technology platform provider Envestnet Inc (ENV.N) also are expected to price their IPOs on Wednesday night.

Chesapeake Midstream plans to treat, compresses and transports natural gas from wellheads to third-party pipelines. Its systems consist of 2,800 miles of gathering pipelines, servicing about 4,000 natural gas wells.

The company's two largest customers are Chesapeake Energy and Total SA (TOTF.PA), Chesapeake's upstream joint venture partner in the Barnett Shale region.

The underwriters were led by UBS Investment Bank, Citi and Morgan Stanley. The shares are expected to begin trading on the New York Stock Exchange on Thursday under the symbol "CHKM". (Reporting by Clare Baldwin; editing by Carol Bishopric)