Semicrystalline polymer amorphous phase

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Another miscible semicrystalline polymer/amorphous polymer blend SMP is a polyethylene oxide (PEO)/novolac-type phenolic resin blend [24]. The blend was found to be completely miscible in the amorphous phase when the phenolic content is up to 30 wt%, and the crystalline melting temperature (T,f) of the PEO phase working as a transition temperature can be tuned. 

For some blends containing one or more amorphous polymers together with one or more semicrystalline polymers, the phase distribution and the interface are demonstrated using electron microscopic techniques in combination with different preparation methods. Additionally, deformation and fracture structures are presented ... 

In certain high molecular weight materials (e.g. deformed elastomers, amorphous regions in semicrystalline polymers, and phase-separated block copolymers) some characteristics of the mesomorphic state are observed, namely local orientational order in the absence of translational order. In some instances researchers have tried to describe the deviation from isotropy observed on a local scale in these materials with the vocabulary used for liquid crystals. Indiscriminate applications... 

In the model [98] it has been assiuned, that nucleus domain with size u is formed in defect-free part of semicrystalline polymer, that is, in crystallite. Within the frameworks of model [1] and in respect to these polymers amorphous phase structure such region is loosely packed matrix, surrounding a local order region (cluster), whose structure is close enough to defect-free polymer structure, postulated by the Flory felt model [16, 17]. In such treatment the value u can be determined as follows [43] ... 

The well-known heterogeneity of amorphous glassy pol5miers plastic deformation [1,2] allows to assume them nonhomogeneous systems. The same affirmation is valid in respect of semicrystalline pol5miers amorphous phase [3,4], As well nevertheless, both models of continues (let us remind, that Ihe known Dugdale model, often used for crazes characteristics, was developed originally for a metals [5]) and molecular concepts, are applied successfully for both classes polymers behavior description. In this cormection ihe question arises about scale, which can be considered as lower boimdary of models of continua applicability. 

Polymer fibers typically are semicrystalline. The amorphous phase of polymer fibers exhibits glass transition, i.e., a reversible transition from a hard, glassy state... 

Lamellar morphology variables in semicrystalline polymers can be estimated from the correlation and interface distribution fiinctions using a two-phase model. The analysis of a correlation function by the two-phase model has been demonstrated in detail before [30,11] The thicknesses of the two constituent phases (crystal and amorphous) can be extracted by several approaches described by Strobl and Schneider [32]. For example, one approach is based on the following relationship ... 

PTEB-Q) to the annealed ones, owing to the presence of the crystalline phase. Moreover, the temperature of the peak increases with the annealing, as well as the broadness of the relaxation. These results suggest that the liquid crystalline phase gives raise to an a relaxation similar to that of amorphous polymers despite the existence of the two-dimensional order characteristic of smectic mesophases, and it changes following the same trend than that of semicrystalline polymers. 

The chains that make up a polymer can adopt several distinct physical phases the principal ones are rubbery amorphous, glassy amorphous, and crystalline. Polymers do not crystallize in the classic sense portions of adjacent chains organize to form small crystalline phases surrounded by an amorphous matrix. Thus, in many polymers the crystalline and amorphous phases co-exist in a semicrystalline state. 

The crystallization process of flexible long-chain molecules is rarely if ever complete. The transition from the entangled liquid-like state where individual chains adopt the random coil conformation, to the crystalline or ordered state, is mainly driven by kinetic rather than thermodynamic factors. During the course of this transition the molecules are unable to fully disentangle, and in the final state liquid-like regions coexist with well-ordered crystalline ones. The fact that solid- (crystalline) and liquid-like (amorphous) regions coexist at temperatures below equilibrium is a violation of Gibb s phase rule. Consequently, a metastable polycrystalline, partially ordered system is the one that actually develops. Semicrystalline polymers are crystalline systems well removed from equilibrium. 

Basic Equations. Scattering according to Porod s law [18,137] is a consequence of phase separation in materials. In a two-phase system (e.g., a semicrystalline polymer) every point of the irradiated volume belongs to one of two distinct phases (in the example to the crystalline phase or to the amorphous phase). In a multiphase system there are more than two distinct phases. 

In contrast to the mature instrumental techniques discussed above, a hitherto nonexistent class of techniques will require substantial development effort. The new instruments will be capable of measuring the thermal (e.g., glass transition temperatures for amorphous or semicrystalline polymers and melting temperatures for materials in the crystalline phase), chemical, and mechanical (e.g., viscoelastic) properties of nanoscale films in confined geometries, and their creation will require rethinking of conventional methods that are used for bulk measurements. 

The important peculiarity of semicrystalline polymer oxidation is that only the amorphous phase is oxidized [12,13,33,34,42], Hence, the oxidation rate and the parameter a vvt 1/2... 

According to the principles of polycondensation, all of the above reactions will also take place during SSP. The conditions for the latter, however, are different as this process is carried out at lower temperatures in a non-homogeneous environment. In order to examine the kinetics of SSP, some assumptions have to be made to simplify the analysis. These are based on the idea that the reactive end groups and the catalyst are located in the amorphous regions. Polycondensations in the solid state are equilibrium reactions but are complicated by the two-phase character of the semicrystalline polymer. 

As discussed above, many polymers contain some crystalline structures when they are solidified. These polymers are referred to as semicrystalline resins. These crystalline structures can be observed using microscopy as shown in Fig. 2.12 for PP and sPS resins. As shown schematically in Fig. 2.13 and discussed above, not all portions of the polymer chains are incorporated into the crystalline structure. Instead, the portions of the chains that are not crystallized make up the amorphous phase. Solid density is the most commonly used method for measuring the... 

In most cases, however, polymers crystallize neither completely nor perfectly. Instead, they give semicrystalline materials, containing crystalline regions separated by adjacent amorphous phases. Moreover, the ordered crystalline regions may be disturbed to some extent by lattice defects. The crystalline regions thus embedded in an amorphous matrix typically extend over average distances of 10-40 nm. The fraction of crystalline material is termed the degree of crystallinity. This is an important parameter of semicrystalline materials. 

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