Title page for ETD etd-383911142975720


Type of Document Master's Thesis
Author Li, Chenghong
URN etd-383911142975720
Title Preparation of Nitrile Containing Siloxane Triblock COpolymers and Their APplication As Stabilizers For Siloxane Magnetic Fluids
Degree Master of Science
Department Chemistry
Advisory Committee
Advisor Name Title
Dillard, John G.
Gibson, Harry W.
McGrath, James E.
Wightman, James P.
Riffle, Judy S. Committee Chair
Keywords
  • polysiloxanes
  • block copolymers
  • stabilizers
Date of Defense 1996-12-11
Availability unrestricted
Abstract
Nitrile containing siloxane block copolymers were developed as stabilizers for siloxane magnetic fluids. The siloxane magnetic fluids have been recently proposed as internal tamponades for retinal detachment surgery. PDMS-b-PCPMS-b-PDMSs (PDMS = polydimethylsiloxane, PCPMS = poly(3-cyanopropylmethylsiloxane) were successfully prepared through kinetically controlled polymerization of hexamethylcyclotrisiloxane initiated by lithium silanolate endcapped PCPMS macroinitiators. The macroinitiators were prepared by equilibrating mixtures of 3- cyanopropylmethylcyclosiloxanes (DxCN) and dilithium diphenylsilanediolate (DLDPS). DxCNs were synthesized by hydrolysis of 3-cyanopropylmethyldichlorosilane, followed by cyclization and equilibration of the resultant hydrolysates. DLDPS was prepared by deprotonation of diphenylsilanediol with diphenylmethyllithium.

It was found that mixtures of DxCN and DLDPS could be equilibrated at 100°C within 5-10 hours. By controlling the DxCN-to-DLDPS ratio, macroinitiators of different molecular weights could be obtained. The major cyclics in the macroinitiator equilibrate are tetramer (8.6 ± 0.7 wt%), pentamer (6.3 ± 0.8 wt%) and hexamer (2.1 ± 0.5 wt%). 2.5k-2.5k-2.5k, 4k-4k-4k, and 8k-8k-8k triblock copolymers were prepared and characterized. These triblock copolymers are transparent, microphase separated and highly viscous liquids. It was found that these triblock copolymers can stabilize nanometer gamma-Fe2O3 and cobalt particles in octamethylcyclotetrasiloxane or hexane. Hence PDMS-b-PCPMS -b-PDMSs represent a class of promising steric stabilizers for silicone magnetic fluids.

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