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Synthetic and natural silica‐aluminates as inorganic acidic catalysts in ring opening polymerization of cyclosiloxanes
Author(s) -
VallejoMontesinos Javier,
Villegas Antonio,
JacoboAzuara Araceli,
Martínez J. Merced,
RamírezOliva Eulalia,
RomeroIzquierdo Araceli,
Cervantes Jorge
Publication year - 2012
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.2873
Subject(s) - chemistry , dispersity , catalysis , polymerization , polymer chemistry , ring opening polymerization , molar mass distribution , monomer , bentonite , silica gel , nuclear chemistry , chemical engineering , organic chemistry , polymer , engineering
Ring opening polymerization (ROP) of hexamethylcyclotrisiloxane (D 3 ) and octamethylcyclotetrasiloxane (D 4 ) was promoted by acid‐treated synthetic and natural silica‐aluminates. Silica‐alumina (1:3 Si/Al molar ratio) was obtained using a simple and economic route from precipitation of aluminum sulfate solutions. The material was treated in an acidic medium to improve the content of acid sites and successfully tested as inorganic acidic catalyst for ROP of D 3 or D 4 cyclosiloxanes. Natural bentonite was treated and used in a similar manner. Once the ROP reaction completed, the catalyst was easily removed and it was found that the recovered synthetic silica‐alumina was active in a second ROP reaction. The effect of the concentration and type of catalyst in respect to the molecular weight and polydispersity of polydimethylsiloxanes was analyzed: increasing the amount of silica‐alumina in ROP of D 4 from 0.05 to 0.1 g decreased the average molecular weight ( M n = 13–1.8 kDa) associated with an increase in the polydispersity (2.95 vs. 1.81). Analogous results were found with bentonite. These values suggest that an increase in the catalyst concentration led to a lower M n , with a more homogeneous molecular chain dimension. Copyright © 2012 John Wiley & Sons, Ltd.