Copolymer changes

Many random copolyesters and polyester-polycarbonates have also been prepared by ester interchange reactions in the molten state. Thus, poly(ethylene terephthalate-co -isophthalates) can be obtained by simple melt blending of PET and poly(ethylene isophthalate) (PEI) homopolyesters at 270°C. The copolymer changes gradually from a block type at the beginning of reaction to a random-type... 

Chemically modified silica fillers with grafted methyl groups or methyl and silicon hydride groups, influenced the micro- and macrostructures of various copolymers. Changes in cross-linking, orderliness, crystallinity, microtacticity and conformation of macromolecules have been detected in the presence of fillers. Surface functionality of the silica filler determines the disposition of macromolecular chains at the interface. 

Erosion rates of poly (anhydride) copolymers are controlled by adjusting their molecular weight and biscarboxyphenoxy propane sebacic acid ratio. Sebacic acid-rich copolymers display much faster degradation rates than biscarboxyphenoxy propane-rich copolymers. Changes in the ratio of the monomers are reported to provide various degradation rates ranging from 1 day to 3 years. 

Incorporation of monofunctional epoxy POSS into an amine-cured epoxy network increased and broadened the Tg without changing the crosslink density and enhanced the thermal properties. Additionally, it was found that the thermal and thermal-mechanical properties of resultant styrene-POSS vinylester resin nanocomposites were dependent on the percentage of POSS incorporated into the resin [171]. Over a range of POSS incorporations, the Tg of the copolymers changed very little, but the flexural modulus increased with increasing POSS content. 

An example of a one-dimensional superlattice structure is structure 1, which is an ordered copolymer. The skeleton is formed by silicon and germanium atoms. A unit cell is three times larger than that of a homopolymer. The band structure of this ordered copolymer changes to the zone-folded profile, which may result in a characteristic absorption spectrum. 

The value of dj in all copolymers changes inconsiderably. In the case of small values of n the interchain distance reached its maximum value (Tables 6.4-6.6). The replacement of a... 

It was realized by Staudinger, as early as 1930, that when two monomers copolymerize, the tendency of each monomer to enter the chain can differ markedly. He found that if an equimolar mixture of vinyl acetate and vinyl chloride was copolymerized, the chemical composition of the product varied throughout the reaction, and that the ratio of chloride to acetate in the copolymers changed from 9 3 to 7 3 to 5 3 to 5 7. 

FIGURE 12.4 Illustration of drift in copol rmer composition with conversion in a batch reactor for two commercially important comonomer pairs. VA content in copolymer increases sharply with conversion in acrylonitrile-vinyl acetate copol merization (i i/iJ2 = 4.05/0.061) and content of MA in copolymer changes very little with conversion in acrylonitrile-methyl acrylate copolymerization (i i/i 2=l 02/0.70). 

Hence, the stated above results have shown, that the introduction of the changed groups in copolymer changes macromolecular coil in solution structure, reducing its fractal dimension, gyration radius and increasing chain rigidity. Within the frameworks of fractal analysis it was demonstrated, that the indicated factors could influence essentially on both polymers synthesis process and polymer effectiveness as flocculator [5],... 

The glass transitions of amorphous copolymers change smoothly with concentration from one pure component to the other, as is shown in Fig. 7.67 for poly(acrylamide-co-styrene), poly(methyl acrylate-co-styrene), and poly(styrene-co-... 

Does the chain sequence distribution of copolymer change with... 

The polarization hysteresis loop measured at room temperature for the P (VDF-TrFE) 68/32 mol% copolymer changes with the irradiation dose (Cheng et al. 2002). With increased dosage, flie near square polarization hysteresis loop, characteristic for a normal ferroelectric material, is transformed to a slim polarization loop (at 75 Mrads). At very high dose (175 Mrads), the polymer becomes a Unear dielectric in which the crystallinity is near zero. 

The early copolymers of vinyl acetate with dibutyl maleate or acrylate esters offered distinct advantages over the homopolymer in their ability to adhere to a vast number of difficult-to-bond surfaces. However, they also had disadvantages, e.g., poor heat resistance, relatively low strength, rather slow setting speed, and comparatively poor machinability. The introduction of vinyl acetate-ethylene copolymers changed this picture considerably. This class of emulsion had all the benefits of homopolymers in strength, machinability and heat resistance in addition to better adhesion characteristics than those of the ester copolymers. 

Figure 11 The structure of micelles of ABA triblock copolymers changes qualitatively with the selectivity of the solvent. A corona of singly anchored A chains is formed in a precipitant for the B blocks (a). A corona of B loops is expected when the solvent is a precipitant for the A blocks (b). In this case, exchange interactions and bridging are possible. When two micelles are at grazing contact, the coronal block can adopt two possible states a loop (b) or a bridge (c).

The crystallinity of propylene-1-butene copolymers changes to a much smaller extent with an increase in the amount of the comonomer relative to the copolymers of another type (propylene-ethylene, propylene-hexene, propylene-octene). This tendency is consistent with the published data, which shows that 1-butene slightly affects the crystallization of the isotactic PP owing to its cocrystallization with propylene in a wide range of copol5mier compositions.The incorporation of 1-pentene entails a more efficient reduction in the degree of crystallinity than the incorporation of 1-butene. 1-pentene, like 1-butene, may undergo cocrystallization with propylene molecules in PP chains. At the same time, 1-hexene and 1-octene are incorporated into pol mier chains in the form of lattice defects, and thus ensure disorder that causes more distinct decreases in T and crystallinity of pol miers. ... 

In reference [10] are summarized the most important empirical models reported in literature to predict the phase inversion that is, the critical composition at which the phases A and B of a binary blend could become co-continuous in A/B uncompatible blend. Sometimes phase inversion covers a window of compositions (with onset and offset limits) rather than a transient point. When a compatibilizer is added or formed in situ by suitable chemical reaction, the situation becomes much more complex and hardly obeying any model as the copolymer changes the interfacial tension and affects the viscoelastic behavior of the blend. 

Hachiboshi et al were able to crystallize random copolymers of ethylene terephthalate/ ethylene isophthalate over the complete composition range. The wide-angle X-ray patterns of these copolymers change systematically with co-unit content and it is concluded that the two units can cocrystallize and can form a new unit cell. A complete phase diagram, involving both the solidus and liquidus composition, was determined and is illustrated in Figure 23. The solidus was determined by... 

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