Commercialized pha [CH-CH2--C-OIn R-Methyl, PHA=Polyhydroxy butyrate(PHB) CH First generation of pha -[CH--CH2--C--On R=Ethyl, Pha-Polyhydroxy valerate(PHv [CH-CH2--C--Ola-[CH--CH2--C--O]b- CHs Second generation of phas PHBVCommercialized PHA —[CH—CH2—C—O]n— O CH3 R=Methyl，PHA=Polyhydroxy￾butyrate(PHB) —[CH—CH2—C—O]n— C2H5 O R=Ethyl，PHA=Polyhydroxy￾valerate (PHV) —[CH—CH2—C—O]a——[CH—CH2—C—O]b— O O CH3 C2H5 First Generation of PHA Second Generation of PHA: PHBV