Abstract
The merits to hybridize the inorganic material with the organic polymer including to reduce the brittleness of inorganic material, to enhance the rigidity and thermal resistance of organic material and to provide unique properties such as in optical, in electronic, in magnetic or others by the proper design and selection of organic and inorganic precursors to hybridize, hence, was the intention to study in this thesis. Three types of silica/polymers hybrid materials, silica/poly(2-hydroxyethyl methacrylate (PHEMA) hybrids, bioactive (3-trimethoxysilyl)propyl methacrylate (MSMA)/HEMA hybrid and pH- sensitive silica/chitosan hydrogel were synthesis through the sol-gel process. System I. Transparent silica/PHEMA hybrid materials The silica/PHEMA hybrids were synthesized by various ways: the tetramethoxysilane (TMOS)/2-hyrdoxylethyl methacrylate (HEMA) hybrid gels were synthesized with acid and base catalysts, via the in situ polymerization of HEMA, with and without co-solvent methanol (TMOS/HEMA); the direct mixing of colloidal silica with PHEMA using methanol as a co-solvent (colloidal silica/PHEMA); and the adding of the inorganic precursor, tetraethyloxysilane (TEOS), to the PHEMA/methanol solution, followed by the sol-gel process with an acid-catalyst (TEOS/PHEMA). With methanol in the TMOS/HEMA sol, the enhanced esterification and depolymerization reactions of the silanols resulted in a slower growth of silica particles. The silica particles that were synthesized with an acid catalyst were less than 40 nm. The thermal resistance of PHEMA chains was enhanced by the addition of colloidal silica. The Fourier transform infrared characterizations and the exothermal peaks on the differential scanning calorimetry traces of these hybrid gels indicated chemical hybridization occurring as a result of condensation of the colloid silica and PHEMA at higher temperatures. Hence, the residual weight content of TMOS in the synthesis with the base catalyst was even higher than the content of TMOS in the hybrid sol. The structure of the colloidal silica/PHEMA hybrid consisted of nano-silica uniformly dispersed in the PHEMA phase with slight inter-molecular hydrogen bonding. The structure of TEOS/PHEMA hybrid was similar to a semi-interpenetrated polymer network (semi-IPN) with PHEMA chains tethered into the nano-silica network by inter- and intra-molecular hydrogen bonding. Consequently, the TEOS/PHEMA hybrid gels exhibited a smoother surface, higher transparency, and better thermal stability than the colloidal silica/PHEMA hybrid gels. System II. Bioactive MSMA/HEMA hybrid materials The MSMA and HEMA monomers were mixed with the molar ratio ranged from 0.05/0.95 to 0.2/0.8, and then hybridized through the free-radical polymerization. Both monomers contained reactive C=C bonds accompanied with the hydrolysis and condensation reactions of trimethoxysilane groups in MSMA resulted in the structure of MSMA/HEMA hybrid as that copolymer chains tethered with nano-silica particles. During the synthesis period, a calcium salt was added into the MSMA/HEMA hybrid sol; therefore, a complex pair of calcium ion and Si-O- was formed and tethered to the copolymer chains. The hybrid gel with calcium ion tethered was immersed in the Kokubo buffer solution for one week, a bone-like hydroxyapatite (HA) layer was found on the surface of hybrid gel and the hybrids with the molar ratios of MSMA/HEMA being 0.1/0.9 and 0.15/0.85 exhibited more stable and larger HA crystals on their surfaces than others. This result indicated that the MSMA/HEMA hybrid was a bioactive material. The mechanism to form HA crystal on the surface of MSMA/HEMA hybrid in the Kukobo solution was due to that the HA nucleation triggered by a catalytic effect of silanol (Si-OH) group and accelerated by the release of calcium ion (Ca2+) from the hybrid material into the solution. System III. pH-sensitive silica/chitosan hybrid materials The TMOS sol and chitosan were mixed with the weight ratio ranged from 2/8 to 6/4, and then hybridized through the sol-gel process. The structure of hybrid was that the chitosan chains extended into the nano-scale silica network. The synthesized hybrid hydrogel exhibited better water uptake content than the pure chitosan, The equilibrium water content of the silica/chitosan hybrid, synthesized from TMOS/chitosan mixture with the weight ratio of 3/7, was double than the pure chitosan. In addition, the hybrid hydrogels showed a reversible swelling and de-swelling behaviors while alternatively placed in the pH 2.2 citric acid solutions and pH 7.4 citric acid/NaHPO4 buffer solutions. This result demonstrated that the TMOS/chitosan hybrids exhibited an excellent pH-sensitive hydrogel behavior.