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 phenyleneethynylene-doped poly(pphenylenebutadiynylene) s for live cell imaging. We developed a new synthetic approach to high molecular weight poly(p-phenylenebutadiynylene) s (PPBs) by increasing backbone flexibility. The introduction of a small amount of flexible units along the backbone improved both the physical and photophysical properties of the polymers. These materials were successfully fabricated into conjugated polymer nanoparticles (CPNs) and used for fluorescent live cell imaging for the first time.
{"Chemical": ["PPBs", "poly(pphenylenebutadiynylene) s", "phenyleneethynylene", "poly(p-phenylenebutadiynylene) s"]}