Amorphous state, polyamide

The polymers mostly used in pharmaceutical packaging are polyethylene, polypropylene, PVC, polyamide, polystyrol, nylon, cellulose acetate, polyethylene terephthtalate, and blends thereof. Copolymers and rubbers are also used. The DSC melting curve of polyethylene used for packaging purposes is characteristic. Low- and high-density polyethylene are differentiated by their melting points. " Melting point and density of polyethylene are linearily correlated. " Crystallinity may be determined as described above for amorphous state. 

One of the most important uses of polyurethanes is in fabrics with elastic properties, such as spandex (Lycra ). These materials are block copolymers in which some of the polymer segments are polyurethanes, some are polyesters, and some are polyamides. The blocks of polyurethane are soft, amorphous segments that become crystalline on stretching (Section 28.7). When the tension is released, they revert to the amorphous state. 

Linear aliphatic homopolyamides are partially crystalline materials. Therefore they are characterized by both an unordered amorphous state and an ordered crystalline state. The latter may exhibit polymorphism. The extent to which each state or specific modification is represented depends, for a given chemical structure, considerably on processing conditions and treatment operations. It affects the properties of the shaped polyamide product. Thus the corresponding structure parameters are of importance for optimizing fiber processes as well as for assessing the performance of fiber products in particular applications. 

Certain thermoplastics, e.g., PET, can be frozen in the amorphous state below the Tg by quench-cooling of the melt. The occurrence of different crystal forms (polymorphism of polyamides (PA), as an example) and melting gaps caused by tempering can be read from the DSC curve. If recrystallisation is studied, crystal growth rate and supercooling can be measured. 

A.2. Infrared Spectrometry. Theoretical studies of the effect of the degree of crystallinity on vibration spectra account only partially for the appearance or the disappearance of certain absorption bands when comparing amorphous polymers with semicrystalline ones. However, these differences are admittedly related both to the appearance (or the disappearance) of intra- or intermolecular interactions and also to stricter selection rules for the crystalline state. In the latter case, absorption bands corresponding to interactions are better defined and thus narrower they are fewer due to stricter rules of selection. For example, in the case of polyamide-6,6, a linear variation of the intensity of two characteristic absorption bands is observed as a function of the density and hence degree of crystallinity (Figure 6.26). One band is due to the crystalline state, and the other one is due to the amorphous state. 

PEBA exhibit a two-phase (crystalline and amorphous) structure and can be classified as a flexible nylon. Physical, chemical, and thermal properties can be modified by appropriate combination of different amounts of polyamide and polyether blocks [149], Hydrophilic PEBAs can be prepared which can have specific applications in medical devices. Similarly to other thermoplastic elastomers, the poiyamide-based ones find applications in automotive components, sporting goods conveyor belting, adhesives, and coatings [150]. In recent years the world consumption was approximately 6400 tons per year with about 80% in Western Europe and the rest equally split between the United States and Japan [143],... 

Many solid-state NMR studies of oriented polymer fibers or film other than silk have been described. Orientation-dependent chemical shielding tensors especially serve as probes with which the relative orientations of specific bond vectors can be determined [10]. This analytical method can be applied to obtain structural information from oriented polyamide fibers such as poly (p-phenylene terephthalamide) (PPTA) [11], poly(m-phenylene isophthalamide) (PMIA) and poly(4-methyl-m-phenylene terephthalamide) (P4M-MPTA) fibers without isotope labeling of the samples [12] (Chapter 12). Oriented carbonyl carbon labeled poly (ethylene terephthalate) (PET) films have also been analyzed with this method [13] (Chapter 14). Especially, more quantitative structural information will be obtained for a locally ordered domain which has been recognized as an amorphous domain in X-ray diffraction analysis in heterogeneous polymer samples. 

Since Holmes observation of the X-ray diffraction of nylon [1], many fruitful studies have been presented using X-ray diffraction, infrared absorption and other techniques. It can be expected that solid-state NMR provides useful information about the structure and dynamics of the crystalline and noncrystalline components of polyamides [2, 3]. Actually, solid-state H, and NMR have been successfully used to clarify various crystalline and amorphous components. 

This is used when polymers are readily melted without degradation and the molten polymer is forced through a spiimeret comprising 50 to 1000 fine holes. On emerging from the holes, the threads sohdify, often in an amorphous glassy state, and are wound into a yam. Orientation and crystallinity are important requirements in fibers, and the yam is subjected to a drawing procedure that orients the chains and strengthens the fiber. This technique is applied to polyesters, polyamides, and polyolefins. 

The crystalline and noncrystalline phases in polyamide fibers do not appear to be governed by what may be defined as thermodynamie equilibria, nor is there evidenee for definite boundaries between a phase, characterized by a simple or complex state of order and an essentially amorphous phase. It is therefore quite obvious that the morphological structure of nylons cannot be described adequately in terms of a simple two-phase model according to which ideally ordered crystallites exist together with eompletely amorphous domains. This model constitutes merely one of the two limiting cases the other is that of a paracrystal according to which all deviations from the ideal crystal are ascribed to defects and distortions of the crystal lattice [275-277]. 

Although solid-state polymerizations of polyamides and polyesters (which are crystalline polymers), have been known since 1939 and 1962 (13,14), until now, it has been considered impossible to produce polycarbonate by solid-state polymerization, because polycarbonates are amorphous polymers and become molten at the temperatures necessary to effect polymerization. The key technology in solid-state polymerization of polycarbonate is the crystallization of the amorphous piepolymer. It has been found that the low molecular weight amorphous prepolymer is easily crystallized, and the obtained crystallized prepolymer retains its solid-state when it is heated to the temperatures necessary for polymerization. 

The stress-strain curve in Fig. 7.24b first of all exhibits elastic and preplastic behaviour. It then reaches a maximum whose sharpness depends on the polymer and also the deformation rate. Beyond this point, the stress remains almost constant over a certain region, before suddenly increasing to fracture. This is brittle fracture, perpendicular to the load. Many semi-crystalline polymers, such as polyethylene, polypropylene, polyamide 6 and polyamide 6,6 exhibit this type of behaviour at ambient temperature. However, among amorphous polymers in the glassy state, polycarbonate is one of the rare examples to behave in this way. 

The highly intractable chemical stmcture vMch. inq)arts the outstanding mechanical properties also makes the PATs very difficult to process (4, 5). In the ftilly imidized form PAI is not processable hence a poly(amic acid) (PAA) precursor is the usual form in which they are supplied and bricated. The precursors themselves have very hi viscosities in the melt state and hence the flow characteristics tend to be very poor. Semicrystalline and amorphous polyamides (6) and aromatic sulfone polymers such as poly(phenylene sulfide), poly(ether sulfone) and polysulfone (7) have been blended with the precursor to PAI, to obtain better flow characteristics. 

The PEBA are produced by a aiolten state polycondensation reaction of a dicarboxylic polyamide and a polyether diol. The reaction of the rigid polyamide (hard) segments and amorphous polyether (soft) segments in the presence of heat, vacuum and catalyst yields the polyether block amide with the general formula shown below. 

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