First and last unit of polyethene Is a hydrogen atom bonded to the first and the last unit of polyethene?
If yes, where does the hydrogen come from?
Yes, in The Characterization of Linear Polyethylene SRM 1475. II. Determination of Total Methyl Content by Infrared Spectrophotometry and references cited therein, it is confirmed that the polymer chains terminate with methyl groups (the repeating unit plus an additional hydrogen as you phrase it).