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Synthesis & Characterization of block co-polymers derived from germanium dicarboxylic acid and amino Propyl terminated Polydimethyl Siloxanes

Gill, Rohama (2009) Synthesis & Characterization of block co-polymers derived from germanium dicarboxylic acid and amino Propyl terminated Polydimethyl Siloxanes. PhD thesis, Quaid-i-Azam University, Islamabad .

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Abstract

Block copolymers having polyamide with a trichlorogermyl pendant, (-COR'- CO–NH-Ar-NH-CO-R'-CO-)x as hard segment and aminopropyl-terminated polydimethylsiloxane H2N(CH2)3SiO(CH3)2(CH3)2SiO)ySi(CH3)2(CH2)3NH2], (PDMS) as the soft segment of general formula [(-CO-R'-CO-HN-Ar-NH)x-CO-R′- CO-NH(CH2)3SiO(CH3)2(Me2SiO)ySi(CH3)2(CH2)3NH2]n , [n = 4.37 to 1175.0; x = 5 to 8; y = 360] where R′ = CH2CH(CH2GeCl3); CH2CHGeCl3CH2; CH2CH(GeCl3); CH(CH3)CH(GeCl3); CH(CH3)CH(GeCl3) and Ar = C6H4 ; (-C6H3-CH3)2 ; (-C6H3- OCH3)2 ; 2,5-(CH3)2-C6H2 and C6H4-O-C6H4 were prepared by polycondensation reaction. A series of trichlorogermyl-substituted dicarboxylic acids of general formula HOOC-R-COOH where R = -CH2CH(GeCl3)CH2- (1), - CH(CH2GeCl3)CH2- (2), -CH(GeCl3)CH2- (3), –CH(CH3)CH(GeCl3)- (4) – CH(GeCl3)CH(CH3) (5) were synthesized by the hydrogermylation reaction of unsaturated acids such as itaconic, trans-glutaconic, fumaric, mesaconic and citraconic acid with HGeCl3 which was produced in situ by the reaction of GeO2 with 37% HCl in presence of NaH2PO2.H2O. The synthesized trichlorogermyl substituted dicarboxylic acids were characterized by melting point, elemental analysis, FTIR, 1H NMR and 13C NMR. X-ray crystal structures of the trichlorogermyl substituted itaconic acids (1) and trans-glutaconic (2) were analyzed to show supramolecular structures in which central Ge atom in each of these structures is four-coordinated with a slightly distorted tetrahedral geometry. The trichlorogermyl substituted dicarboxylic acids were then converted into their respective acid chloride using dry, distilled SOCl2 and condensed with slightly less than the required stoichiometric amounts of various para-substituted aromatic diamines dissolved in dry THF in the presence of an organic base Et3N under strict inert conditions to yield respective chloro terminated polyamide which were copolymerized in situ with aminopropyl-terminated polydimethylsiloxane (PDMS) dissolved in dry THF to obtain various series of seventeen new block copolymers PA 1 to PA 17. These block polymers were structurally characterized by elemental analysis, FT-IR, 1H NMR, solid state 13C NMR and molecular weight determination. Their molecular weights as determined by Laser Light Scattering technique were found in range 1.71×105 to 331×105 g/mol. The thermal stability of these copolymers was investigated by using various thermal analyses techniques such as TGA and DSC. These block copolymers show two Tgs, at ca -120oC and the other between 350oC to 400oC indicating presence of soft component of PDMS and hard component polyamide with average decomposition temperature at 500oC. TG-FTIR studies indicate that initial decomposition of these block copolymers starts with the evolution of CO. The pyrolysis of these polymers under inert conditions was done and the GCMS studies of the gases thus evolved revealed the presence of the oligomeric cyclic products of general formula [(CH3)2SiO]n where n 3-7 and the polyamide fragments. Scanning electron microscopy (SEM) was used to study the surface morphology. Thermodynamic and kinetic parameters such as Ea, ∆H, ∆S, and n were calculated from Tg curves using Horowitz/Metzger methods. The values of activation energy so obtained fall in the range of 38.30 kJ/mol to 76.12 kJ/mol. Hydrogen bonding and inter-chain linkage give them increased activation energy and high stability. Due to the presence of polar site of polyamide block the copolymers absorb 5-17% moisture when soaked in water, using standard procedures at room temperature. The block copolymers were used for the covalent assembly of Layer by Layer (LbL) multilayers adopting a dipping technique for the deposition onto preactivated Silicon or quartz substrates. Primarily, by using PDMS with a molar mass of about 2,500 g/mol and about 27,000 g/mol, the conditions (such as concentration of polymers, dipping time, rinsing etc.) for covalent layer-by-layer assembly were optimized to the point of identifying reaction conditions for this surface reaction that led to the construction of multilayers with a linear growth increment with respect to the number of layers chemisorbed and embedding of macromolecules with only 2 functional end-groups. As LbL multilayer assemblies are formed by the alternate deposition of polymers, therefore in the present study poly(ethylene-alt-maleic anhydride (PEMA) was used along with PDMS. Polyethylenimine (PEI) layer was deposited onto the substrate as the precursor layer. Thus the LbL film architecture was PEI(PEMA/PDMS)n where n = number of layer pairs deposited. The thickness of each layer pair was measured using an ellipsometer, while AFM, SAXR and UV Spectroscopy were also employed for the characterization of LbL nanofabricated multilayers. Aminopropyl terminated PDMS having only two functional groups have been successfully adsorbed onto PEMA utilizing the LbL technique resulting into multilayer buildup.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Synthesis. Characterization. block, co-polymers, derived, germanium, dicarboxylic, acid, amino Propyl, Polydimethyl Siloxanes
Subjects:Physical Sciences (f) > Chemistry(f2)
ID Code:6500
Deposited By:Mr. Javed Memon
Deposited On:27 Jun 2011 14:58
Last Modified:27 Jun 2011 14:58

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