Well-defined difunctional POSS macromers and related organic-inorganic polymers: Precision synthesis, structure and properties

Polyhedral oligomeric silsesquioxanes (POSS) are a class of well-defined organic-inorganic stereo molecules comprising inorganic Si-O-Si cores and peripheral organic moieties. Since they were first reported in 1946 by Scott et al., there have been a great number of investigations on the use of POSS macromers as the building blocks to access the organic-inorganic composites with polymers. In most of cases, monofunctional POSS macromers are employed and the linear hybrid polymers are obtained. Under this circumstance, POSS cages act as the side or end groups whereas the main chains of the polymers remain unchanged. Occasionally, octafunctional POSS macromers are involved, resulting in the generation of crosslinked (or network-like) hybrids. Recently, well-defined difunctional POSS macromers have increasingly provoked a considerable attention of investigators. From the synthetic methodology of POSS macromers to the approaches to introduce them into polymers, difunctional POSS macromers have the features quite different from mono- (or octa-) functional POSS. More importantly, the related organic-inorganic hybrids possess the different morphologies and properties. In the past years, there has been a rapid increase in the number of literatures on the studies on well-defined difunctional POSS and the related organic-inorganic hybrids. Nonetheless, the related review is lacking. In this contribution, we would summarize the recent progress in this regard, from the synthesis of POSS macromers, the approaches of introducing the POSS macromers into polymers to the correlation of morphologies with properties of the organic-inorganic hybrids. In addition, perspectives and challenges for the further advancement are envisaged and discussed.