Copolymer binary

Heal resistance is regarded to be one of the well-studied properties of copolymers. Many different empirical correlations are known [314-316] between glass transition temperature Tg and fractions P(U2) = P(MjMj) of the diads (M Mj) in macromolecules. We have chosen the simplest form of such a dependence  

Some interesting results have been obtained by Russian scientists [320, 321] who studied the influence of composition inhomogeneity on some service properties and supermolecular structures of copolymers. Two samples of copolymers of butyl acrylate with methacrylic acid were synthesized which had a similar average 

Since the dispersion a2 of composition distribution is regarded to be a measure of such an inhomogeneity, it is straightforward to suppose that when a2 exceeds its critical value ofr. the polymer becomes turbid. So, the unequality a2 o2r can be considered as a sufficient condition for the copolymer to lose its transparency. The value of a2r can be approximately considered as a universal parameter of the system which depends only on temperature [134,6], To verify this assumption, the conversions p+, at which the system becomes turbid, were experimentally 

In order to elucidate the effect of temperature, the authors of Refs. [310,210] determined experimentally the boundary points x x = 0.08 and XgX = 0.65 of the transparency region for the (ST + HA) system at complete conversion, p = 1, when in the course of synthesis the temperature was increased in a given way from 28 °C to 78 °C. Despite a noticeable difference between such a regime and the isothermal one (see Fig. 24), it was found that the regions, in which at p = 1 turbid copolymers were formed, practically coincide. The same could be said about the calculated values of dispersion cr2(l) at the boundary points of the mentioned regions. This might be associated with a rather weak dependence of the reactivity ratios on temperature. A similar practical independence of the turbidity region 

In order to prove that the high composition inhomogeneity was the only reason for microphase separation both (ST + HA) and (ST + MA) copolymers, some of their samples with the same compositions prepared, however, at low conversions (p 0.10) of monomers with their subsequent distillation were studied [310,210]. All these copolymers whose dispersion is by one or two orders of magnitude less than that of the products of complete conversion (p = 1), turn out to be dear. 

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It may be noted here that it is frequently possible to polymerise two monomers together so that residues from both monomers occur together in the same polymer chain. In addition polymerisation this normally occurs in a somewhat random fashion and the product is known as a binary copolymer. It is possible to copolymerise more than two monomers together and in the case of three monomers the product is referred to as a ternary copolymer or terpolymer. The term homopolymer is sometimes used to refer to a polymer made from a single monomer. 

Binary copolymers are commonly referred to simply as copolymers. 

The first approach has been important commercially. The monomer most commonly used is a-methylstyrene (see Section 16.11), whose polymer has a Tg of about 120°C. The heat distortion temperature of the resultant-ABS type polymer will depend on the level of replacement of styrene by the a-methyl-styrene. (It may be noted in passing that a-methylstyrene-acrylonitrile binary copolymers have been available as alternatives to styrene-acrylonitrile materials but have not achieved commercial significance.)... 

Labeled initiators have been used in evaluating the relative reactivity of a wide range of monomers towards initiating radicals.159 The method involves determination of the relative concentrations of the end groups fanned by addition to two monomers (e.g. 119 and 120) in a binary copolymer formed with use of a labeled initiator. For example, when AlBMe-a-13C is used to initiate copolymerization of MMA and VAc (Scheme 3.99),157 the simple relationship (eq. 14) gives the relative rate constants for addition to the two monomers. Copolymerizations studied in this way arc summarized in Tabic 3.13. 

The overall composition at low conversion of binary copolymers formed in the presence of a chain transfer agent can be predicted analytically using an expression analogous to that used to describe terpolymerization where one monomer does not undergo propagation (Section 7.3.2.4),2j6 Making the appropriate substitutions, eq. 37 becomes eq. 70 ... 

Extensive work on radical copolymerization has shown that the composition in a binary copolymer, consisting of monomers Mi and M2, is determined by four rate constants ky for a propagating chain ending with adding to monomer Mj. 

Statistical characteristics of the second type define the microstructure of copolymer chains. The best known characteristics in this category are the fractions P [/k) (probabilities) of sequences Uk involving k monomeric units. The simplest among them are the dyads U2, the complete set of which, for example, for a binary copolymer is composed of four pairs of monomeric units M2M, M2M2. The number of the types of k-ad in chains of m-component copolymers grows exponentially as mk so that with practical purposes in mind it is generally enough to restrict the consideration to sequences Uk] with moderate values of k. Their calculation turns out to be rather useful... 

The microheterogeneity coefficient was introduced only for the description of the microstructure of binary copolymers with symmetric units. At increased number of unit types and/or when account is taken of structural isomerism, the role of Km will be performed by other parameters analogous to it. A general strategy for the choice of these latter has been elaborated in detail [12], while their values have been measured via NMR spectroscopic techniques for a variety of polycondensation polymers [13]. 

Fig 1 Schematic representation of a globule of a binary copolymer with a fuzzy profile of monomeric units... 

Eigenvalues of the operator Qr are real while the largest of them, Af, equals unity by definition. As a result, in the limit n-> oo all items in the sum (Eq. 38), excluding the first one, Q Q f = Xr/Xfh will vanish. In this case, chemical correlators will decay exponentially along the chain on the scale n 1/ In AAt values n < n the law of the decay of these correlators differs, however, from the exponential one even for binary copolymers. This obviously testifies to non-Markovian statistics of the sequence distribution in molecules (see expression Eq. 11). The closer is to unity, the greater are the values of n. The situation when n 1 corresponds to proteinlike copolymers. 

In the case of statistic copolymers of two monomers (binary copolymers) the glass transition temperature steadily changes with the molar amounts of the two monomers. In many cases, a similar behavior is observed with some mechanical properties (tensile strength, impact strength, stiffness, and hardness) (see Chap. 1). Deviations can occur in copolymers, which contain only a few percent of one comonomer. 

When one wants to determine the compositional heterogeneity of a given binary copolymer, a series of reference samples with different composition are required to... 

T. C. Tranter (36) has studied the binary copolymers based on hexamethylene diamine and -phenylene dipropionic, 3-(/>-carboxy-methyl)phenyl-butyric, 2-(/>-carbomethoxy)phenylpropionic, hydro-quinone diacetic, terephthalic, adipic, or sebacic acids. In spite of the fact that only the copolymers of hexamethylene diamine with/>-phenylene dipropionic and with 2-(/>-carbomethoxy)phenylpropionic acids show a linear softening point composition curve, Tranter claims for isomorphism in the copolymers of all the systems. In fact, their X-ray examination shows that they behave in the same basic manner, the second component dissolving in the lattice of the first until a certain critical concentration is reached, where the lattice structure changes quite abruptly to that of the second component. 

Isomorphous replacement in isotactic polyaldehydes was shown by A. Tanake, Y. Hozumi, K. Hatada, S. Endo, and R. Fujishige (42). These authors studied the binary polymer systems formed by acetaldehyde, propionaldehyde, n-butyraldehyde, iso-butyraldehyde and w-heptanal. All the copolymers are crystalline over the whole range of compositions. In the case of binary copolymers of acetaldehyde, propionaldehyde and K-butyraldehyde the unit cells have the same tetragonal space group UJa, with the same chain axis (4.8 A), while the dimensions of the a axis change continuously as a function of the copolymer composition. In the case of copolymers of isobutyraldehyde with other aldehydes, the continuous variation of the lattice constants a and c were observed. 

This complicated triple sum can be simplified by applying the rooted tree treatment. Here the outline is confined to a binary copolymer the results may easily be generalized to copolymers with r components. 

In the binary copolymer the two molecular weights of the monomeric units are MoA and MoB, the corresponding refractive index increments vA and vB, and the overall composition (mole fractions) nA and nB. This overall composition will in general differ from the composition of individual molecules. Thus, the molecular weight MXI of the i-th isomer with polymerization degree x is given by... 

Figure 3. Copolymer composition diagram of CPT-SOj-AN expressed as a binary copolymer...

The question is, whether such primary structures can be obtained for binary copolymers, not obligatorily of biological origin. It is easy to do this by computer simulation [18], and much more difficult in real experiments. However, in both cases the corresponding procedure should involve the following stages that are schematically depicted in Fig. 1 ... 

Different Methods for die Statistical Description of Binary Copolymers... 

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