You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Synthesis of long-circulating, backbone degradable HPMA copolymer-doxorubicin conjugates and evaluation of molecular-weight-dependent antitumor efficacy. Backbone degradable, linear, multiblock N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin (DOX) conjugates are synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization followed by chain extension via thiol-ene click reaction. The examination of molecular-weight-dependent antitumor activity toward human ovarian A2780/AD carcinoma in nude mice reveals enhanced activity of multiblock, second-generation, higher molecular weight conjugates when compared with traditional HPMA copolymer-DOX conjugates. The examination of body weight changes during treatment indicates the absence of non-specific adverse effects.
{"Chemical": ["DOX", "N-(2-hydroxypropyl)methacrylamide", "HPMA", "thiol", "doxorubicin"]}