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pH - responsive composite microspheres , consisting of a core of Fe3O4 nanoparticle , a sandwiched layer of mesoporous silica and a shell of crosslinked poly ( methacrylic acid ) ( PMAA ) , were successfully synthesized via distillation precipitation polymerization .
 Chemical: Fe3O4; Chemical: silica; Chemical: poly ( methacrylic acid ); Chemical: PMAA
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: Fe3O4; Chemical: silica; Chemical: poly ( methacrylic acid ); Chemical: PMAA