  Irreversible aggregation processes involving reactive and frozen clusters are
investigated using the rate equation approach. In aggregation events, two
clusters join irreversibly to form a larger cluster, and additionally, reactive
clusters may spontaneously freeze. Frozen clusters do not participate in merger
events. Generally, freezing controls the nature of the aggregation process, as
demonstrated by the final distribution of frozen clusters. The cluster mass
distribution has a power-law tail, F_k ~ k^{-gamma}, when the freezing process
is sufficiently slow. Different exponents, gamma=1, 3 are found for the
constant and the product aggregation rates, respectively. For the latter case,
the standard polymerization model, either no gels, or a single gel, or even
multiple gels may be produced.
