Covalent and Non-Covalently Coupled Polyester-Inorganic Composite Materials

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Polymers and High Performance Materials


Two types of organic/inorganic materials were synthesized via sol-gel reactions for tetraethylorthosilicate (TEOS) and organoalkoxsilane monomers in the presence of poly(epsilon-caprolactone) (PCL): (1) non-covalent hybrids, in which PCL and silicate, and PCL and organically modified silicate (ORMOSIL), phases are coupled by non-bonded interactions; (2) covalent hybrids in which triethoxysilane-telechelic PCL molecules form chemical bonds with a sol-gel-derived silicate phase. Chemical structures were verified using FTIR and C-13 NMR spectroscopies and MALDI-TOF mass spectrometry. The constant PCL phase T-g for the silicate-PCL hybrids of (1) implies poor organic/inorganic mixing, but dual-melting endotherms varied with silicate content. TGA revealed significant elevation of degradation onset temperature (T-d) of (1) and suppression of the low temperature chain scission process. No PCL glass transition is seen for ORMOSIL-PCL hybrids where diethoxydimethylsilane is the co-monomer and melting occurs in one step, and there are significant increases in T-d. Likewise, no glass transition is seen when acetoxypropyltrimethoxylsilane is the semi-organic co-monomer, but there are dual-melting endotherms. Triethoxysilane-endcapped PCL was synthesized and its microstructure verified by GPC, MALDI-TOF mass spectrometry, FTIR and NMR spectroscopies. T-g for this telechelic PCL that was reacted with a small fraction of TEOS increases relative to hydroxy-telechelic PCL due to formation of phase-linking Si-O-Si bonds through end groups. The temperature/magnitude of the melting transition decreased upon inorganic modification. TGA showed appreciable increase in T-d relative to PCL and both the high and low temperature degradation processes were hindered. Silane-telechelic PCL films have oxygen permeability values less than that of pure PCL, which is totally attributed to a decrease in diffusion coefficient. (C) 2002 Published by Elsevier Science Ltd.

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