PMMA cross-link temperature
According to this thesis, the polymerization is determined by thermal initiator that is used in PMMA mixture. The polymerization (corsslinking) starts when the initator is added to the mixture, but it is really slow at low temperature. Higher temperature lowers hardening time (speeds up the crosslinking). Since the dustsheet does not provide the information about the initiator, I would suggest to determine the cross-linking temperature experimentally. Some material related to the polymerization process:http://www.chemistry2011.org/,

BULK POLYMERIZATION OF METHYL METHACRYLATE IN A KNEADER
REACTOR
P.-A. Fleury
LIST AG
CH-4422 Arisdorf,

High conversion polymerization of methyl methacrylate
in the presence of poly(methyl methacrylate) of different relative
molecular mass
J. BARTOŇ, V. PASTUŠÁKOVÁ, V. VAŠKOVÁ, and P. AMBROVIČ
Polymer Institute, Centre of Chemical Research, ChemicalPapers