Polyethylene glycol (PEG) and polypropylene glycol (PPG) are both polyether compounds used in a wide range of applications due to their distinct properties. The key difference lies in their monomeric building blocks. PEG is formed from ethylene oxide molecules, resulting in a polymer that is more flexible, hydrophilic, and suitable for pharmaceutical and medical applications due to its lower toxicity and higher biocompatibility. On the other hand, PPG, derived from propylene oxide, is less hydrophilic and more lipophilic than PEG, which makes it more suitable for industrial applications, such as in surfactants, polyurethane foams, and lubricants. The choice between PEG and PPG depends on the required balance between hydrophilicity, toxicity, and application-specific performance requirements.

Titanium is not brittle. It has a high strength-to-weight ratio. is corrosion resistant. and does not fracture or break easily.

tungsten is harder than titanium. Tungsten has a higher Mohs hardness 7.5 compared to 6.5. It is one of the hardest materials on earth. Titanium has a lower strength to weight ratio making it less dense but very strong.