20384
Using this method , oligo ( hydroxyalkanoate ) diols derived from a poly ( 3 - hydroxybutyrate - co - 4 - hydroxybutyrate ) biopolyester [ poly ( 3HB - co - 4HB ) ] and from synthetic atactic poly [ ( R , S ) - 3 - hydroxybutyrate ] ( a - PHB ) were obtained .
 oligo ( hydroxyalkanoate ) diols, poly ( 3 - hydroxybutyrate - co - 4 - hydroxybutyrate ), poly ( 3HB - co - 4HB ), poly [ ( R , S ) - 3 - hydroxybutyrate ], PHB
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 oligo ( hydroxyalkanoate ) diols, poly ( 3 - hydroxybutyrate - co - 4 - hydroxybutyrate ), poly ( 3HB - co - 4HB ), poly [ ( R , S ) - 3 - hydroxybutyrate ], PHB