Semi-crystalline state

Fully deuterated linear poly(ethylene) (PE) has been investigated also via various 2H NMR techniques below Tm, i.e. in the semi crystalline state [83, 84]. The crystallinity ratio was measured as a function of temperature and it was shown that the motions are highly restricted in the amorphous regions of PE. It was shown that the onset of 3 and a transitions (at which mobility appears in the crystalline phase) may be observed by 2H NMR on raising the temperature. This onset of local motions in the crystalline phase is related to the chain relaxation process quoted previously. 

In polymer crystallization the challenge is to identify and clarify the transformations by which chain molecules pass from a disordered, molten state to the ordered supra-molecular organization known as the semi-crystalline state. The subject is highly relevant in terms of both basic science and technology it is indeed clear that many modern applications require complete control of the structure and the morphology of polymers from macroscopic dimensions down to below the nanoscale. As a simple example, making the crystallites in a polymer liber equally oriented and reducing the number of chain folds (or hairpins) therein, usually turn out to be very favorable requisites for mechanical performance. 

The only "normal" phase state for polymers, known from the physics of small molecules, is the liquid state, though even here polymers show special properties, like viscoelasticity. The typical states of polymers are the glassy, the rubbery and the semi-crystalline state, all of which are thermodynamically metastable. 

Estimate the diffusivity at 298 K and the activation energy of diffusion for oxygen in PETP, both in the glassy and in the semi-crystalline state. 

Baldwin, D.F. Park, C.B. Suh, N.P. A micro-cellular processing study of poly(ethylene tereph-thalate) in the amorphous and semi-crystalline states. Polym. Eng. Sci. 1996, 35 (4), 1446-1453. 

The mechanical properties of PLA, which have been extensively studied, are dependent on the production process and the amorphous or semi-crystalline state of the sample. Amorphous PLA presents a tensile modulus between 2.05... 

CL-AGE copolymer films of ca. 3-mil-thickness were additionally vacuum-dried for 48 hours. Two sample temperatures, 25°C(semi-crystalline state) and 80°C(melt state), were utilized for irradiation. For the higher temperature of 80°C, a heated steel plate was used as the substrate for the copolymer. The film sample was placed on this temperature-controlled steel plate and passed through the electrocurtain system described below. For the irradiation process which required two passes, following the first pass the sample was again immediately placed on another 80 C steel plate and passed through the electrocurtain system a second time. 

According to this intramolecular-nucleation model, when the melt of long-chain macromolecules is quenched to low temperatures for fast crystallization, each macromolecule may perform multiple local intramolecular nucleation events and hence will be included in several lamellae or several positions of the same lamellae, with only little changes of their unperturbed coil-size scaling. At each position, intramolecular nucleation yields folded-chain clusters. This picture is quite consistent with Hoffman s proposition of a variable-cluster model for the conformation of macromolecules in the semi-crystalline state [50[. 

All PVT diagrams studied so far refer to polymer liquids. Substantial experimental difficulty arises in the extension to the semi crystalline state because of the nonequilibrium nature. No determined attempt at extrapolation to equilibrium data has been made to date, despite the possibility to approximate equilibrium crystal properties from imit cell parameters of X-ray data. 

The glass transition temperature (T ) depends on the polymer chain arrangement T is equal to 67 in an amorphous state, 81 °C in a semi-crystalline state and 125 °C in a crystalline and oriented state. 

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. 

Some of the polymers can exist both in a fully glassy, amorphous state and in a semi-crystalline state. Say which and present explanations. 

Baldwin D F, Park C B and Sub N P, A Microcellular Processing Study of Polyfethylene Terephthalate) in the Amorphous and Semi-Crystalline States Part I Microcell Nucleation , Polym Eng. Sci., 1996, 36, 1437. 

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