Inorganic-organic hybrid polymers by polymerization of methacrylate- or acrylate-substituted oxotitanium clusters with methyl methacrylate or methacrylic acid

Inorganic-organic hybrid polymers were prepared by radical polymerization of methacrylic acid or methyl methacrylate with 0.5-2 mol % of the (meth)acrylate-substituted oxotitanium clusters Ti6O4(OEt)8(OMc)8 (OMc = methacrylate), Ti6O4(OPr)8(OAcr)8 (OAcr = acrylate), and the new clusters Ti4O2(OPri)6(OOCR)6 (OOCR = methacrylate or acrylate). A small cluster proportion is sufficient for an efficient cross-linking of the polymers. Glassy (PMMA) or powdery polymers (PMA) were obtained. With an increasing proportion of cluster, the surface area of the PMA powders increased considerably. The obtained hybrid polymers exhibit a higher thermal stability than the parent polymers because the thermal depolymerization is inhibited or at least retarded. The swelling index of cluster-cross-linked PMMA in organic solvents correlates with the cluster proportion. Small-angle scattering investigations showed that Ti6O4(OPr)8(OAcr)8 in PMMA and PMA and Ti4O2(OPri)6(OMc)6 in PMA is more evenly distributed than Ti4O2(OPri)6(OMc)6 in PMMA. In the latter polymer, the clusters appear to aggregate and to exhibit a kind of discotic structure. Size and/or shape of the clusters and the number of polymerizable surface groups per cluster play a small but significant role in the fine-tuning of the polymer structure and the properties of the hybrid polymers.