Amorphous phase flexible-chain polymers

The highest values of crystallinity achieved after annealing of fibers of CPE-1 and CPE-2 are 35 and 25%, respectively. Both copolymers under study appear to be semicrystalline materials. In contrast to the majority of flexible-chain polymers, the non-crystalline phase of both stiff-backbone copolyesters is not an amorphous but a mesomorphous one. It was shown that this structure may be identified as an ordered LC smectic state. However, the main difference between the non-crystalline structures of CPE-1 and CPE-2 consists in periodic or aperiodic packing of layers within the LC smectic phase, respectively. 

Linear polymers in the semi-crystalline state are metastable nanostructured systems with the complicated morphology, which are divided into nano-, submicro-, or microphases with crystalline, amorphous, and intermediate (mesophase and other) molecular packing. These different phases are connected in the flexible-chain polymers, such as PE, POM, poly(ethylene terephthalate) (PET), and many others, via strong covalent coupling between crystallites and disordered regions since the typical polymer molecules of l-lOOpm in contour length participate in several nanophases. Due to the multilevel structure, polymers with rather high levels of crystallinity may show up unique dynamics and properties which vary with the thermal and mechanical histories of materials. This has been confirmed by different techniques (DMA, DSC, NMR, DRS, and others) in numerous studies. 

Special attention should be turned to the sharp transition from a narrow concentration corridor to a broad heterophase region, mentioned above, which takes place for low positive values of parameter x- It is int esting to compare the appearance of this broad region with the phenomenon of decomposition of solutions of flexible-chain polymers into two phases with the formation of two liquid (amorphous) phases with values of x in the limit (with infinitely high molecular weight of the polymer) of 0.5. TTie phase equilibrium diagrams (in coordinates v-x) for a rigid-chain polymer with an axial ratio of x = 150 and 350... 

However, it was recently found that many flexible-chain polymers containing no mesogenic groups are capable of forming thermotropic ordered phases in thermodynamic equilibrium and intermediate in structure and properties between crystalline and amorphous without any additional orienting effect of external fields. 

The discussion of the influence of the interphase need not be limited to just linear polyethylenes. Interphases of several nm have been reported in polyesters and poly-hydroxy alkanoates. One major difference between the interphase of a flexible polymer like polyethylene and semi-flexible polymers like PET, PEN and PBT is the absence of regular chain folding in the latter materials. The interphase in these semi-flexible polymers is often defined as the rigid amorphous phase (or rigid amorphous fraction, RAF) existing between the crystalline and amorphous phases. The presence of the interphase is more easily discerned in these semi-flexible polymers containing phenylene groups, such as polyesters. 

Linear Polymers Long chains are necessary to confer the mechanical properties of fibers, plastics, and elastomers that make polymers so valuable. Fibers such as cellulose and polyester arc semicrystalline materials in which the same chemical stmeture exists in both rigid microcrystalline and flexible amorphous phases. Plastics may be either semicrystalline, such as poly(ethylene terephthalate) (the same polyester of fibers is also the PET of beverage bottles), or completely amorphous and glassy, such as polystyrene or poly(methyl methacrylate) (PMMA, Plexiglas or Lucite ). Elastomers are completely amorphous and flexible and would flow as a viscous mbbery liquid except that the polymer chains are cross-hnked to prevent macroscopic flow but allow reversible stretching. As an example, poly(dimethylsiloxane)... 

---