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Abstract
The KOH-catalyzed depolymerization of vulcanized silicone rubbers to reproduce cyclosiloxane monomers was studied. First, the depolymerization was carried out in toluene with varying amounts of KOH to find that the yield of monomers first increased and then decreased with the increment of KOH, the highest yield was 65% at the molar ratio KOH/(Si – O) units 0.08. At the molar ratio 0.13 in the absence of solvent, the monomers yield was 46%. However, when an acid buffer such as KH PO and KCOOC H COOH was added after the KOH-catalyzed depolymerization was over, the product yield was increased remarkably to more than 80%. q 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Monomer recycling; Silicone rubber; Buffer acid

1. Introduction
The problem of polymer wastes at both post-manufacturerand post-consumer stages is now an https://www.51lunwen.org/liuxuelunwendx/important issue to besolved for the global conservation of environment andcarbon resources particularly in conjunction with theprotection of petroleum resources from depletion. It canbe the primary solution to this problem that polymer wastesare recycled by means of depolymerization to monomers vialow-energy processes because monomers can reproduce thesame polymers compatible with the original ones. Unfortu-nately, up to now, those polymers that are industrially recycledvia monomers are not so many. Since the worldwide annualproduction of organosilicon polymers has now reached severalmillion tons and the polymers have caused the same problemof wastes treatment as other conventional plastics do, theyshould also be recycled repeatedly to the same organosiliconpolymers. Although inorganic silicon resource is abundant,the industrial framework for recycling silicone polymers isparticularly important because a huge amount of energy andcarbon resource are required the production of organosiliconmonomers [1].Poly(dimethysiloxane)s (PDMS) are the most importantorganosilicon polymers, which are produced mainly fromcyclosiloxane monomers such as hexamethylcyclotrisilox-ane (D3) and octamethylcyclotetrasiloxane (D4) by means ofionic ring-opening polymerization catalyzed by acids orbases [2 –4]. It is well known that the polymerizationinvolves a thermodynamic equilibrium between the cyclicmonomers and linear polymers [5–7]. Based on this fact,linear PDMS can be depolymerized to cyclosiloxanemonomers by removing the monomers continuously fromthe equilibrium under acid or base catalysis [8 –12] and,therefore, recycling methods of cross-linked PDMS wastes(vulcanized silicone rubbers) to cyclosiloxane monomershave been already developed [13 – 18].The main problem of recycling vulcanized siliconerubber wastes in the form of monomers is that the rate ofdepolymerization is very slow owing to the networkstructure even catalysts are used. One method to facilitatethe depolymerization is to perform it at a temperature ashigh as or more than 300 8C in an inert gas atmosphere[13 –15]. The other is the use of solvents [16 – 18]. However,the latter method, on one hand, is energetically undesirablebecause代写留学生论文 it requires a solvent-removing process prior to therecovery of monomers. On the other hand, when a high-boiling solvent is used, it is difficult to remove only themonomers from equilibrated depolymerization mixture and,even after th本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。