General considerations on strain induced orientation and crystallization developments

1 General considerations on strain induced orientation and crystallization developments 

The strain induced orientation of the PUs has been studied extensively by using a variety of experimental techniques [5,21, 161,162.169,170,174,348-350]. 

Bonart was amongst the first to identify the orientation of the periodic microphase structure under tensile deformation. Bonart suggested that the hard domains are composed of laterally stacked HS. It was noted that in MDI polyether copolymers, the SS become fully extended along the stretch direction and begin to crystallize at strains of about 150%. In contrast, the HS were found initially to orient transverse to the stretch direction and ultimately to break up to allow orientation of the HS in the stretch direction [14], Similar observations were made by us on DBDI based materials [67], as shown in the following section. 

The PUs mechanical behaviour has been investigated extensively and is intimately linked to the composition of the hard and soft domain and their resulting 

Prisacariu, Polyurethane Elastomers, DOI 10.1007/978-3-7091-0514-6 5, Springer-Verlag/Wien 2011 

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