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:

In Vivo Degradation and Elimination of Injectable Ricinoleic Acid-Based Poly(ester-anhydride). The in vivo degradation and elimination after subcutaneous implantation of injectable p(SA-RA) 3:7 copolymer in rats, followed by characterization of the polymer matrix composition during hydrolysis and erosion, is reported. Major chemical changes were observed during the first few days post implantation, the anhydride bonds hydrolyzed along with about 45% weight loss and a significant decrease in the molecular weight. (1)H NMR spectral analysis was used to determine the structures and content of ricinoleic acid containing oligomeric chains present in the degraded polymer. The polymer degrades into ester oligomers of 2-4 ricinoleic acid units which further degrade to ricinoleic acid, a natural fatty acid. The polymer hydrolytic degradation process fit the in vitro degradation process.
{"Chemical": ["Ricinoleic Acid", "ricinoleic acid", "p(SA-RA) 3:7", "(1)H", "Poly(ester-anhydride)", "fatty acid"]}