Studies on the nature of the macromolecular condensed state of "nascent" ultra high molar mass polyethylene

Ultra high molar mass polyethylene (UHPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, b y DSC, effect of annealing the recrystallized specimen at 120 similar to 13 0 degreesC, morphology by polarizing optical microscopy and small angle X-r ay scattering. Based on the experimental results obtained the macromolecula r condensed state of the nascent UHPE powder is a rare case of a multi-chai n condensed state of non-interpenetrating chains, involving interlaced exte nded chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC, possibly higher than 300 degreesC, the exact tem perature is however not sue because of chain degradation at such high tempe ratures. The recrystallization process from the melt is a crystallization f rom a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent st ate has its origin in the decrease both of the crystalline chain stem lengt h and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120 similar to 130 degreesC.