# Metal-Coordinated Polymer-Inorganic Hybrids: Synthesis, Properties, and Application
## 2 Methods of Synthesizing Coordinated Polymer-Inorganic Hybrids
### General Synthetic Route for Supramolecular Coordination Complexes (SCCs)
#### 2.3.2 Liquid Phase Infiltration (LPI)  
LPI is analogous to VPI, except a liquid phase inorganic precursor is used during infiltration. LPI involves the selective binding of a metal salt precursor to reactive functional groups within the polymer matrix, often through complexation or electrostatic interactions [83]. Similarly, it can be applied for area-selective infiltration of BCPs where one  
Figure 3: (**a**) Schematic of atomic layer deposition (ALD) and sequential infiltration synthesis (SIS) processes. ALD provides conformal surface coatings layer by layer, while SIS enables in-depth infiltration of precursors into polymer matrices [65]. (**b**) Schematic of vapor phase infiltration (VPI) process [68]. (**c**) Illustration of block copolymer (BCP) templating using annealing techniques as a pre-processing step for vapor phase infiltration (VPI). The self-assembled BCP thin film is annealed to achieve ordered domain structures, which serve as templates for selective infiltration and subsequent material synthesis [79]. (**d**) Schematics of liquid phase infiltration of BCPs: PS-b-P2 VP cylinders are immersed in an acidic metal salt solution, where anionic metal complexes bind to protonated P2 VP. O\({}_{2}\) plasma then removes the polymer, reducing metal salts to nanostructures, replicating the BCP morphology [83]. Adapted with permission from the Royal Society of Chemistry [65; 68] and American Chemical Society [79].  
of the constituent blocks carries functional groups that facilitate this selective binding to create nanostructured inorganics (typically metals or metal oxides) that replicate the morphology of the polymer template [84] (Figure 3d). For BCPs, the metal precursor can be selectively incorporated either before the self-assembly process by mixing the BCP with the metal salt solution [85] or after self-assembly by soaking the formed nanostructures into the precursor-containing solution [34]. Alternatively, a metal salt solution can be directly spin-coated onto the polymer film [86].  
LPI is sensitive to the pH value of the precursor solution due to the Lewis acid-base nature of the reactions. Often, an adjustment is made using hydrochloric acid [38], sodium hydroxide [87], or a buffer solution [88]. The pH alters the reaction time and temperature depending on the polymer and the inorganic precursor used [40; 87; 88]. Furthermore, LPI products can be obtained as a suspension, which requires extraction steps such as separation and freeze-drying [38; 87]. Poly (acrylic acid) [38; 87] and polyethyleneimine [88; 89; 90] are two common polymers used in LPI, and they are often paired with cyanate precursor.  
While LPI can be a good candidate for mitigating vapor pressure limitations, enabling a greater diversity of inorganic precursors, a significant limitation of this method is the slower kinetics (reactions may require 24-72 h to complete [87; 89; 90]) compared to VPI, in which they are completed within minutes [91].