Crystalline homopolymer

In most ionomers, it is customary to fully convert to the metal salt form but, in some instances, particularly for ionomers based on a partially crystalline homopolymer, a partial degree of conversion may provide the best mechanical properties. For example, as shown in Fig. 4, a significant increase in modulus occurs with increasing percent conversion for both Na and Ca salts of a poly(-ethylene-co-methacrylic acid) ionomer and in both cases, at a partial conversion of 30-50%, a maximum value, some 5-6 times higher than that of the acid copolymer, is obtained and this is followed by a subsequent decrease in the property [12]. The tensile strength of these ionomers also increases significantly with increasing conversion but values tend to level off at about 60% conversion. 

In a partially crystalline homopolymer, nylon 6, property enhancement has been achieved by blending with a poly(ethylene-co-acrylic acid) or its salt form ionomer [24]. Both additives proved to be effective impact modifiers for nylon 6. For the blends of the acid copolymer with nylon 6, maximum impact performance was obtained by addition of about 10 wt% of the modifier and the impact strength was further enhanced by increasing the acrylic acid content from 3.5 to 6%. However, blends prepared using the salt form ionomer (Sur-lyn 9950-Zn salt) instead of the acid, led to the highest impact strength, with the least reduction in tensile... 

In contrast to the substituted PPO s, It Is theoretically possible to obtain the same substituted PECH s by homopolymerization of the corresponding mesogenic oxirane, or by its copolymerization with epichlorohydrin. We have attempted these polymerizations in order to better interpret the thermal behavior of the more complicated copolymers that we have obtained by polymer analogous reactions. Homopolymerization would be instructive because the incorporation of nonmesogenic units into liquid crystalline homopolymers doesn t as a rule change the type of mesophase obtained (5). 

The second requirement is perhaps best illustrated by the cases of isomorphism in isotactic vinyl copolymers (7, 2, 4, 5, 6) only if the helical conformations of the two crystalline homopolymers are not too different, a regular helical conformation is also possible for the copolymer chains. 

The block copolymers obtained are essentially microphase separated systems and form smectic mesophases, analogous to the corresponding liquid crystalline homopolymers. 

The fact that both the neat components and their blends are relatively well characterized with respect to their varying structures and morphologies as a result of the applied mechanical and thermal treatments, permits us to follow the gradual variation of microhardness as a function of structural parameters. In this way one can obtain the H values for material components which are not accessible to direct experimental determination. Furthermore, having the extrapolated values for completely amorphous and fully crystalline homopolymers and starting from a knowledge of the number of components (and/or phases) one can make use of the additivity law (eq. (1.5)) to evaluate the mechanical properties of components which cannot be isolated or do not exist as individual materials. A good example of this are the PET microfibrils studied here (Fig. 5.16(b)). 

In Sections 6.2.1 and 6.2.2 it has been demonstrated that the microhardness technique is very sensitive for detecting structural changes including polymorphic transitions in crystalline homopolymers and copolymers. 

The absence of a allows the material to be processed at much lower temperatures than would be possible with a crystalline homopolymer using only one of the acids. 

Block copolymers and polyallomers require separate treatment in the field of analytical applications of IR spectroscopy to C2-C3 copolymers. Polyallomers are copolymers synthesized from two monomers but exhibiting a degree of crystallinity normally associated only with homopolymers (32) indeed, allomerism denotes constancy of crystalline form with variation in chemical composition. Though crystalline, polyallomers have properties that differ not only from crystalline homopolymers, but also from blends of homopolymers containing the same proportions of the two monomers. The analytical problems are thus somewhat different from those concerning the elastomeric C2-C3 copolymers and a number of methods have been used to determine their composition. 

Furthermore, monomers from which crystalline homopolymer can be produced, such as high-density polyethylene and polypropylene, can be copolymerized to produce resins with controllably reduced crystallinity and thus greater transparency. The ethylene/propylene copolymers may range from partially crystalline plastics to amorphous elastomers. 

The effect of copolymerization on Tm depends on the degree of compatibility of the comonomers. If the comonomers have similar specific volumes, they can replace each other in the crystal lattice (i.e., isomorphous systems), and the melting point will vary smoothly over the entire composition range. On the other hand, if the copolymer is made from monomers each of which forms a crystalline homopolymer, the degree of crystallinity and the crystalline melting point decrease as the second constituent is added to either of the homopolymers. In this case, the T , of the copolymer (i.e., the reduction in the melting point, T ° of the homopolymer due to the addition of the second constituent) is given by Equation 4.11. ... 

The reaction of hydrazine monohydrate with DPTA yielded the bis(N-aminoimide) that was allowed to react with the dianhydride of 2,2-bis[4-(3,4-dicarboxyphenoxy) phenyl]-propane (dianhydride A) in m-cresol or o-dichlorobenzene to form a crystalline homopolymer (Scheme 1.6). 

The use of two isomeric acids leads to an irregular chain which inhibits crystallization. This allows the polymer to be processed at much lower temperatures than would be possible with a crystalline homopolymer. Nevertheless the high aromatic content of these polyesters ensures a high Tg ( 90°C). The polymer is self-extinguishing with a limiting oxygen index of 34 and a self-ignition temperature of 545°C. The heat-deflection temperature under load (1.8 MPa) is about 175 C. 

A wide range or crystalline homopolymer, from extremely high to extremely low molecular weight can be produced in the loop reactor. 

He X, Zhang H, Yan D, Wang X. 2003. Synthesis of side chain liquid crystalline homopolymers and triblock copolymers with p methoxyazobenzene moieties and poly(ethylene glycol) as coil segments by atom transfer radical polymer zation and their thermotropic phase behavior. J Polym Sci Part A Polym Chem 41 2854 2864. 

Incorporation of another monomer into an otherwise crystalline homopolymer will generally reduce the crystallinity and lower the melting point in a continuous manner. Several theoretical models have been developed addressing the reduction of crystallinity and melting point. In discussing these models, we will designate the major comonomer as the monomer in the base homopolymer, and any others will be minor comonomers. 

The following equation derived by Flory gives the theoretical dependence of the melting point on the amount of minor comonomer added to the crystalline homopolymer [185]... 

Hence, video microscopy analysis is not only a tool for screening of supported catalysts [66] but is also useful for the assignment of a given (industrial) catalyst system to the appropriate kinetic profile and the describing mathematical model. Finally, it is possible to explain certain aspects of crystalline homopolymer growth versus amorphous copolymer growth and the comonomer effect [63-66]. 

In a very real sense, partly crystalline polymers are two-phase materials. While the major theme of this book is the behavior of two-phase materials, each phase being different chemically, the reader will observe a great deal of similarity between partly crystalline homopolymers, such as polyethylene, and the polyblends and composites. Important analogies or contrasts will be mentioned whenever appropriate. Indeed, the concept of highly oriented crystalline polymers as molecular composites has recently generated an exceptional degree of interest from both fundamental and engineering points... 

ANALOGY BETWEEN POLYMER BLENDS AND CRYSTALLINE HOMOPOLYMERS... 

In the earlier discussion of the properties of crystalline homopolymers in the bulk state (Chapter 1), it was shown that such polymers always contain some amorphous material, various segments of the same chain lying in crystalline or amorphous regimes (Krigbaum et al, 1964). If the amorphous portion is above its 7, i.e., is elastomeric, a direct analogy exists between such materials and polymer blends, blocks, and grafts, in which the formation of hard and soft domains is induced by the use of polymer components differing in chemical composition and inherent properties thus, as pointed... 

The mechanical behavior of isomorphic macromolecular systems would be expected to be quite different from the behavior observed in bicomponent or biconstituent systems. Indeed, isomorphic systems would be expected to behave in many respects like crystalline homopolymers, except that such properties as 7 and lattice spacings may be dependent on composition. Because of the single-phase situation, the glass-rubber transition and related properties may be expected to behave as if a random copolymer... 

The dimensions of the crystal and amorphous subsystems vary from nanometers to micrometers, i.e., polymeric materials are nanophase- or microphase-separated and have only a partial crystallinity. If we treat homopolymers as one-component systems, the phase rule of Sect. 2.5.7 does not permit equilibrium between two phases, except at the transition temperature. Partially crystalline homopolymers are, thus, not in equilibrium. The properties of semicrystalline polymers are critically influenced by the interactions between the amorphous and crystalline domains, as is seen in the formation of rigid amorphous fractions, discussed in Sect. 6.1.3 and 6.3.4. 

In the copolymers described in Sect. 3.4, the multiple components of the system are joined by chemical bonds and demixing, needed for complete phase separation of the components, is strongly hindered and may lead to partial or complete decoupling from crystallization. The resulting product is then a metastable micro- or nanophase-separated system with arrested, local equilibria. In some cases, however, it is possible to change the copolymer composition during the crystallization or melting by chemical reactions, such as trans-esterification or -amidation. In this case, the chemical and physical equilibrium must both be considered and a phase separation of the copolymer into either crystalline homopolymers or block copolymers is possible. 

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