Crosslinkable polymer compositions

An in situ crosslinkable composition comprising a polysiloxane having two or more alkoxy groups, a silanol compound having two or more silanol groups, a catalyst for catalyzing a reaction between the alkoxy groups and the silanol groups, a silica filler, and an imaging agent comprising a radiopaaue agent, the comDosition being confirured for injection into a vasculature of a patient such that movement of bodily fluid within the patient is controlled and (a) the composition having a viscosity as measured by oscillatory rheology at 0.1 Hz and 1% strain at 25° C. that is at least ten-fold greater than a viscosity as measured by flow rheology at a frequency of 30 Hz at 25° C., (b) the composition curing when measured at 37° C. within a time period of 1 minute to 120 minutes, (c) after being allowed to anneal for a time period of 7 days at 70° C., the composition having a viscosity as measured using oscillatory rheology at a frequency of 0.1 Hz and a strain of 1% at 25° C. or 37° C. is in the range of 3,000 to 40,000 Pa*s, (d) the composition having a combination of properties (a) and (b), (e) the composition having a combination of properties (a) and (c), (f) the composition having a combination of properties (b) and (c), or (g) the composition having a combination of properties (a), (b) and (c).