We present a straightforward method to prepare amphiphilic graft copolymers consisting of hydrophobic poly(3-hydroxyalkanoates) (PHAs) backbone and hydrophilic α-amino-ω-methoxy poly(oxyethylene-co-oxypropylene) (Jeffamine®) units. Poly(3-hydroxyoctanoate)-co-(3-hydroxyundecenoate) (PHOU) was first methanolyzed to obtain the desired molar mass. The amino end groups of Jeffamine were converted into thiol by a reaction with N-acetylhomocysteine thiolactone and subsequently photografted. This “one-pot” functionalization prevents from arduous and time-consuming functionalization of the hydrophilic precursor or tedious modifications of PHAs, thus simplifying the process. The amphiphilic nature of modified PHAs leads to water-soluble copolymers exhibiting thermoresponsive behavior.