The Shape Memory Properties Of Polynorbornene

Shape memory polymers?SMPs?are the kind of special intelligent materials which can be deformed and subsequently fixed into a temporary shape,which would remain stable unless they are exposed to an appropriate external stimulus that trigger the polymer to recover to its original shape.Currently,SMPs have become the research hotspot of the scientists.Polynorbornene?PNB?has good shape memory and damping characteristics,as a smart material,which would has very broad range of applications in the future.In this paper,Polynorbornene Rubber?PNR?and Polynorbornene resin?PNB?were used to prepare PNR,PNR/EPDM blends,low oil extended PNB?Lo-PNB?and PNB composites.The scanning electron microscope?SEM?,transmission electron microscope?TEM?,rubber process analyzer?RPA?,differential scanning calorimeter?DSC?,dynamic mechanical analyzer?DMA?and material testing machine were used to rearch the microstructure,dynamic rheological properties,thermal properties,mechanical properties and shape memory properties.The results indicated that when the content of plasticized oil increased from 0 phr to 40 phr,the glass transition temperature?Tg?of the PNR was reduced from-33.5? to-38.9? which was because the content of plasticizer between the molecular chains of PNR and caused the free volume increased.The segments and molecular chains could move more easily and the interaction force between molecular chains was weakened which led to the shape recovery ratio reducing.But the shape fixity ratio was almost unchanged.In the PNB/EPDM blends,due to the transfer of plasticized oil,there was a phenomenon that the two Tgs moved on both sides.The shape memory properties of PNR/EPDM =100/0 were better than that of PNR/EPDM=75/25.Although the shape memory properties were slightly worse after blending,the Tg?26.5??of PNR in the PNR/EPDM= 75/25 as a transition temperature was more suitable for shape memory and the anti-thermal oxygen aging performance was greatly improved.In Lo-PNB,as the recovery temperature increasing,the shape recovery ratio and the recovery rate of the Lo-PNB increased when below 80?.And the degree of recovery was more consistent with the "time temperature equivalent principle".The shape fixity ratio of Lo-PNB could be as high as 99% and the shape recovery ratio was gradually increased in the three shape memory cycle.As the increasing of molding times,the shape recovery of the Lo-PNB gradually increased,which was exactly same as the sequence of the balance relaxation modulus,indicating the higher the balance relaxation modulus,the higher the shape recovery ratio.Four different structures of micro-nanoparticles?carbon black?CB?,carbon nanotube?CNT?,organic montmorillonite?OMMT?,calcium carbonate?Ca CO₃??were used to fill the Lo-PNB to preparate the four PNB composites?CB-PNB,CNT-PNB,OMMT-PNB,Ca CO₃-PNB?.The Tgs of the PNB composites were about 23?,near room temperature which was conducive to practical application.The sequence of the maximum stress relaxation rates and the balance relaxation modulus were Ca CO₃-PNB>CNT-PNB>OMMT-PNB> CB-PNB,same as that of the maximum shape recovery rate and the shape recovery ratio at recovery temperature?Tr?=53?.The sequence of the lowest recovery temperature resulting in over 99.0% of shape recovery ratio was exactly opposite to that of the balance relaxation modulus.They indicated that the faster the maximum stress relaxation rate was,the maximum shape recovery rate.The higher the balance relaxation modulus was,the higher the shape recovery ratio at a same recovery temperature and the lower recovery temperature at the same shape recovery ratio.The shape fixity ratios of the four composites could reach above 99.0% at Tg-15?.The four PNB composites exhibited excellent shape fixity and recovery performance.Ca CO₃-PNB showed the best ordinary shape memory cyclic performance and CB-PNB showed the worst in the four composite.The sequence of the fixity of PNB composites was OMMT-PNB>CNT-PNB>CB-PNB> Ca CO₃-PNB in the reversible plastic shape memory performance.The shape recovery performance was excellent.OMMT-PNB showed the best shape reversible plastic shape memory property.