Polymers, Copolymers and Blends

Copolymers are polymeric materials with two or more monomer types in the same chain. A copolymer that is composed of two monomer types is referred to as a bipolymer, and one that is formed by three different monomer groups is called a terpolymer. Depending on how the different monomers are arranged in the polymer chain, one distinguishes between random, alternating, block or graft copolymers. The four types of copolymers are schematically represented in Fig. 1.18. 

A common example of a copolymer is an ethylene-propylene copolymer. Although both monomers would result in semi-crystalline polymers when polymerized individually, the melting temperature disappears in the randomly distributed copolymer with ratios between 35/65 and 65/35, resulting in an elastomeric material, as shown in Fig. 1.19. In fact, EPDM rubbers are continuously gaining acceptance in industry because of their resistance to weathering. On the other hand, the ethylene-propylene block copolymer maintains a melting temperature for all ethylene/propylene ratios, as shown in Fig. 1.20. 

Melting and glass transition temperature for random ethylene-propylene copolymers. 

Another widely used copolymer is high impact polystyrene (PS-HI), which is formed by grafting polystyrene to polybutadiene. Again, if styrene and butadiene are randomly copolymerized, the resulting material is an elastomer called styrene-butadiene-rubber (SBR). Another classic example of copolymerization is the terpolymer acrylonitrile-butadiene-styrene (ABS). Polymer blends belong to another family of polymeric materials which are made by mixing or blending two or more polymers to enhance the physical properties of each individual component. Common polymer blends include PP-PC, PVC-ABS, PE-PTFE and PC-ABS. 

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For substrates of WORM and EOD(PCR) disks the industry in the future wants polymers that have a markedly improved resistance to heat softening compared to BPA-PC and, if possible, a lower water absorption and lower birefringence, but otherwise maintain the good characteristics in toughness, production, and cost (194). This goal is being approached in different ways further modification of BPA-PC, newly developed polymers, improvement of the processing characteristics of uv-curable cross-linked polymers, and development of special copolymers and polymer blends, eg,... 

A more complex but faster and more sensitive approach is polarization modulation (PM) IRLD. For such experiments, a photoelastic modulator is used to modulate the polarization state of the incident radiation at about 100 kHz. The detected signal is the sum of the low-frequency intensity modulation with a high-frequency modulation that depends on the orientation of the sample. After appropriate signal filtering, demodulation, and calibration [41], a dichroic difference spectrum can be directly obtained in a single scan. This improves the time resolution to 400 ms, prevents artifacts due to relaxation between measurements, and improves sensitivity for weakly oriented samples. However, structural information can be lost since individual polarized spectra are not recorded. Pezolet and coworkers have used this approach to study the deformation and relaxation in various homopolymers, copolymers, and polymer blends [15,42,43]. For instance, Figure 7 shows the relaxation curves determined in situ for miscible blends of PS and PVME [42]. The (P2) values were determined... 

Homogeneous and Heterogeneous Rubbery-Rubbery Diblock Copolymers and Polymer Blends A Unified View... 

In view of the utility of the aromatic polyesters and the demonstrated effectiveness of the aromatic polyphosphonates as flame retardants, the combination of these two polymers was chosen for this study. In addition, this system provided a composition in which both copolymers and polymer blends could be prepared with identical chemical compositions. The polyesters were prepared from resorcinol with an 80/20 m/m ratio of iso-phthaloyl and terephaloyl chlorides while the polyphosphonates were resorcinol phenylphosphonate polymers. Copolymerized phosphorus was incorporated by replacement of a portion of the acid chloride mixture with phenylphosphonic dichloride. 

Monitoring the composition of copolymers and polymer blends in an extruder... 

It is important to mention that the structure/properties relationships which will be discussed in the following section are valid for many polymer classes and not only for one specific macromolecule. In addition, the properties of polymers are influenced by the morphology of the liquid or solid state. For example, they can be amorphous or crystalline and the crystalline shape can be varied. Multiphase compositions like block copolymers and polymer blends exhibit very often unusual meso- and nano-morphologies. But in contrast to the synthesis of a special chemical structure, the controlled modification of the morphology is mostly much more difficult and results and rules found with one polymer are often not transferable to a second polymer. 

A simple, even though empirical, alternative treatment in use for the permeability of copolymers and polymer blends is 93)... 

Surface adsorption site energy and density are very important. Most biomaterial surfaces have very high site densities, making it difficult to study the mechanisms governing adsorption. Low site density surfaces are available. Heterogeneous surfaces, such as block copolymers and polymer blends, may have very unique adsorption properties. If one of the phases or domains tends to dominate the surface, it may act as a homogenous surface. If both phases are present on the surface, then two or more... 

Many studies use infrared spectroscopy for quality control and quality analysis in polymer production. It is particularly used for the determination of the composition of copolymers and polymer blends and also for determination of additive and filler contents [90, 91, 92]. 

Chemical engineers have worked with polymers since the first Bakelite articles were produced early in this century. Since then, the class of polymeric materials has grown to encompass a whole range of thermoset and thermoplastic resins, as well as copolymers and polymer blends, and chemical engineers have played major roles in the rise of these materials to commercial success. From production of the resins (which involves heat and mass transfer, kinetics, fluid dynamics, process design, and control) to the fabrication of final articles (involving many of the same processes, as well as some unit operations not part of traditional chemical engineering, such as extrusion... 

One of the most difficult problems when characterizing copolymers and polymer blends by SEC-viscometry is the accurate determination of the polymer concentration across the SEC elution curve. The concentration detector signal is a function of the chemical drift of the sample under investigation. To overcome this problem, Goldwasser proposed a method where no concentration detector is required for obtaining Mn data [72]. In the usual SEC-viscometry experiment, the determination of the intrinsic viscosity at each slice of the elution curve requires a viscosity and a concentration signal ... 

Recent studies [111,214] indicate that Th-FFF can even be used to determine the relative chemical composition of two components in random copolymer and linear block copolymers whose monomers do not segregate due to solvent effects. However, this application is limited by the unpredictable nature of thermal diffusion. Nevertheless, combining information from Th-FFF with those derived on fractions by independent detectors selective to composition (such as an IR spectrometer) can yield further insight into the dependence of DT on the chemical composition. Even more powerful is the combination of Th-FFF with SEC as, here, the chemical composition (from Th-FFF) can be studied as a function of the molar mass (from SEC). This was demonstrated by van Asten et al. by cross fractionating copolymers and polymer blends with SEC and Th-FFF [358]. 

What is remarkable, however, that this same behavior is exhibited, not only by the crosslinked PS, but also by the great variety of uncrosslinked homopolymers, copolymers and polymer blends shown on Fig. 9. This graph also nicely demonstrates the increase in crazes over deformation zones in the same polymers due to... 

The results demonstrate that coupled chromatographic techniques with multiple detectors permit the determination of average composition data, heterogeneity parameters, and separations of homopolymers and copolymers. The methodology reviewed here enables a distinction to be made between copolymers and polymer blends. 

Several methods can be used for the chromatographic characterization of complex polymers such as copolymers and polymer blends. The... 

Returning now to our more general discussion of cquations-of-state, note that a concise review of cquations-of-state for the PVT behavior of polymers was provided by Zollcr [39], who compared the ability of several equations-of-state (some developed empirically and some developed based on fundamental theoretical considerations) to represent PVT data for homopolymers, copolymers and polymer blends. He concluded [39] that, among theoretically-based equations-of-state, the Simha-Somcynsky equation [40,41] represents the available data best over extended ranges of temperature and pressure. 

Elemental composition and content of some specific elements is an important analytical tool for polymer characterization, mainly for the characterization of copolymers and polymer blends and the determination of molecular weight of homopolymers [2, 3]. 

In this way, EA can be applied to determine monomer composition in copolymers and polymer blends and any other composite material. Although results from EA are comparable to those obtained from spectroscopic techniques such as IR and NMR (nuclear magnetic resonance) spectroscopies, developments in EA are needed to improve the accuracy and precision of the method. 

Similarly, it is not possible with simple methods to identify with certainty such combinations as copolymers and polymer blends. In such cases more sophisticated methods of analysis are required. 

AFM is widely used in the analysis of polymer surfaces, such as morphology and molecidar structure of crystalline and oriented polymers, block copolymers, and polymer blends. The example shown in Figure 10.13(b) is the AFM three-dimensional smface image of the fracture surface of a composite. A lamellar structure is clearly observed, with periodicity of about 200 nm, comparable to values obtained from the SEM micrographs [Figure 10.13(a)]. 

The dichroism technique has been employed in structural and orientation studies on a wide range of polymers, and a detailed discussion of the many results would require considerably more space than is appropriate for this chapter. In Table 2 we have collected together a fairly comprehensive list of references to recent quantitative dichroic studies on individual polymers, copolymers and polymer blends. No references are given to the numerous qualitative dichroic results reported, although it should be mentioned that these have provided valuable information concerning the structure of polymers and their spectral assignments. 

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