I was researching and came across your post. Its an interesting qtn that is asked from so many. without websense or surfcontrol, or another subscription based service for web filtering - its quite difficult to satisfy this requirement.
However I am looking in web chat based blocking, and without getting too granular I have compiled an IP addr list of "all or most" web based chat servers associated with chat infrastructure. It should be stated that this can be a moving target:
64.4.45.62
65.55.206.154
69.147.115.128
64.12.161.0/24
64.12.161.185
64.12.200.0/24
205.188.153.0/24
205.188.179.0/24
64.12.202.116
69.147.112.160
66.163.181.12
64.4.13.128/26
207.46.96.0/19
64.4.13.128/25
216.136.175.143
216.136.175.144
216.136.175.145
216.136.225.0/25
216.136.226.209
216.136.226.210
216.136.227.166
216.136.227.167
78.141.177.7
204.9.163.162
--------------------------------
hth