Copolymerizable Rubber Flexibilizers

The addition of the rubber component resulted in a decrease in the modulus and yield stress. However, toughening and an improvement in the impact behavior were observed. The phase separation and formation of the rubbery domains played an important role. 

In a previous contribution [74], a hydroxyl-terminated polybutadiene rubber was transformed into an isocyanate-terminated polybuta ene. That modification changed the morphology of the thus-modified UPR and resulted in an enhancement of toughness. 

Cured vinyl ester resins are fragile after curing like standard UPRs and thus need flexibilization. The flexibilization of vinyl ester resins is made using the known reactive rubber vinyl-terminated liquid elastomeric butadiene-acrylonitrile copolymer (VTBN) [76]. The macrostructure of the VTBN flex- 

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