Classifying shape memory polymers classification by polymer structure

3 Classifying shape memory polymers classification by polymer structure 

The main difference between Tg and is that the Tg presents a wide interval of temperatures while has a narrow interval (Behl et al, 

Osada (1995), Kagami (1996) and co-workers have been pioneers in the study of hydrogels as SMMs. Firstly they studied hydrogels from acrylic acid (AA) and stearyl acrylate (SA) copolymers chemically cross-Unked with N,N -methylene-bis(acryl amide) (MBAA) (Osada and Matsuda, 1995). Shape memory was obtained thanks to long hydrophobic regions from stearic acid contained in SA. These regions form a crystalline phase below 50°C and they act as a switching phase. This material has shape memory effect 

In general, polymers with amorphous and crystalline regions can themselves be candidates for SMMs. In this case, the fixity shape is established by the crystals and the switching phase is due to the amorphous chains. 

Through the block copolymerization of two different homopolymers it is possible to obtain a system with separated phases (Lu et al, 2008 Luo et al., 2000 Meng et al, 2009 Min et al, 2005). The co-monomer with the highest transition temperature acts as the fixity phase, while the other one is the switching phase. Also in this case the transition temperature can be Tg or depending on the nature of the co-monomer. Moreover, the copolymerization allows improvement in other properties like biodegradability, hydro-philicity, solvent absorption and diffusion, toughness, transition temperature or activation shape memory time. 

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