Types of Copolymerization Behavior

Different types of copolymerization behavior are observed depending on the values of the monomer reactivity ratios. Copolymerizations can be classified into three types based on whether the product of the two monomer reactivity ratios r rx is unity, less than unity, or greater than unity. 

A copolymerization is termed ideal when the r rx product is unity. Ideal copolymerization occurs when the two types of propagating species Mf and Mf show the same preference for 

Most ionic copolymerizations (both anionic and cationic) are characterized by the ideal type of behavior. 

When = 2 = 1, the two monomers show equal reactivities toward both propagating species. The copolymer composition is the same as the comonomer feed with a random placement of the two monomers along the copolymer chain. Such behavior is referred to as random or Bemoullian. For the case where the two monomer reactivity ratios are different, that is, 1 and r2 1 or U 1 and r2 1, one of the monomers is more reactive than the other toward both propagating species. The copolymer will contain a larger proportion of the more reactive monomer in random placement. 

The copolymer has the alternating structure I irrespective of the comonomer feed composition. Moderate alternating behavior occurs when either (1) both r and r2 are small ( ] ri — very small, close to 0) or (2) one r value is small and the other r is zero ( ] ri — 0). The copolymer composition tends toward alternation but is not the perfectly 

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Problem 7.11 Predict the type of copolymerization behavior that would be expected for the following monomer pairs ... 

It is necessary to emphasize one principal peculiarity of the copolymerization dynamics which arises under the transition from the three-component to the four-component systems. While the attractors of the former systems are only SPs and limit cycles (see Fig. 5), for the latter ones we can also expect the realization of other more complex attractors [202]. Two-dimensional surfaces of torus on which the system accomplishes the complex oscillations (which are superpositions of the two simple oscillations with different periods) ate regarded to be trivial examples of such attractors. Other similar attractors are fitted by the superpositions of few simple oscillations, the number of which is arbitrary. And, finally, the most complicated type of dynamic behavior of the system when m 4 is fitted by chaotic oscillations [16], for which a so-called strange attractor is believed to be a mathematical image [206]. 

What are the four different types of enthalpy of copolymerization behavior with conversion of copolymerization ... 

In a cross-linked polymer, the junction units are different kinds of monomers than the chain repeat units, so these molecules might be considered to be still another comonomer. While the chemical reactions which yield such cross-linked substances are copolymerizations, the products are described as cross-linked rather than as copolymers. In this instance, the behavior due to cross-linking takes precedence over the presence of an additional type of monomer in the structure. 

These types of behavior characterizes the many different plastics available (Table 7-1). Some tough at room temperature, are brittle at low temperatures. Others are tough and flexible at temperatures far below freezing but become soft and limp at moderately high temperatures. Still others are hard and rigid at normal temperatures but may be made flexible by copolymerization or adding plasticizers. 

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). 

It is important to note that the tendency of a monomer towards polymerization and therefore also towards copolymerization is strongly dependent on the nature of the growing chain end. In radical copolymerization the composition of the copolymer obtained from its given monomer feed is independent of the initiating system for a particular monomer pair, but for anionic or cationic initiation this is normally not the case. One sometimes observes quite different compositions of copolymer depending on the nature of the initiator and especially on the type of counterion. A dependence of the behavior of the copolymerization on the used catalyst is often observed with Ziegler-Natta or metallocene catalysts. 

The difference in reactivity of MPP and DPP in homopolymerization at 25°C is almost as great as that between DMP and DPP. It might therefore be expected that at this temperature, the behavior of MPP and DPP in copolymerization should resemble that of DMP and DPP— that is, simultaneous oxidation of both monomers or oxidation first of the less reactive DPP, followed by addition and oxidation of MPP, should yield random copolymer, while addition of MPP to growing DPP should form a block copolymer. At 60°C, however, MPP and DPP are of comparable reactivity, like DMP and MPP at 25° C, and perhaps only random copolymers could be obtained, no matter what procedure is followed. These expectations have been partially realized. The MPP-DPP copolymerization is more complex than either of the other two systems examined, with four distinguishable types of copolymer produced under different conditions. 

Poly(ethylene oxide) (PEO) macromonomers constitute a new class of surface active monomers which give, by emulsifier-free emulsion polymerization or copolymerization, stable polymer dispersions and comb-like materials with very interesting properties due to the exceptional properties of ethylene oxide (EO) side chains. They are a basis for a number of various applications which take advantage of the binding properties of PEO [39], its hydrophilic and amphipathic behavior [40], as well as its bio compatibility and non-absorbing character towards proteins [41]. Various types of PEO macromonomers have been proposed and among them the most popular are the acrylates and methacrylates [42]. 

The propagating species in the cationic polymerization can be examined from the copolymerization behavior (21). Cyclic ethers such as tetrahydrofuran (THF) or 3,3-bischloromethyloxetane (BCMO), and cyclic esters such as 0-propiolactone (/3-PL) or -caprolactone (c-CL) are classified as oxonium ion type monomers. Copolymerizations between these monomers are observed easily as in the case of BCMO-THF (12, 13), BCMO-/3-PL (14, 15), BCMO-c-CL (16), and THF- -CL (21). 

It is worth mentioning that a set of the types of the dynamic behavior of the system in the case of copolymerization of m monomers is principally wider in comparison with the distillation process of an m-component liquid mixture as it has already been remarked [13]. The reason for this lies in the fact that copolymerization is a non-equilibrium process in contrast to distillation. In a particular case of three-component copolymerization such a possibility is shown... 

The most thorough topological classification of the dynamic behavior of the copolymerization systems suppose to make them out by their kinds, each of them is determined by the types of all SPs as well as by manifolds separating their basins (regions of their attraction). Every kind is characterized by the type of its phase portrait. The case of the binary copolymerization obviously is trivial since each of the types (5.8) consists of only one genus which in its turn includes a single kind. 

All the mentioned types of the nontrivial dynamic behavior are excluded for the systems where the reactivity ratios ry can be described by the expressions of the well-known Alfrey-Price Q-e scheme [20], and as a result they are to follow the simplified terminal model (see Sect. 4.6). In these systems, due to the relations Bj(X)/Bj(x) = ajj/ajj which holds for all i and j, the functions 7e,-(2) according to relations (4.10) are the ratios of the homogeneous polynomials of degree 2. Besides, for the calculations of the coefficients ak of Eq. (5.11) one can use the simple formulae presented in terms of determinants Dj and D [6, p. 265]. The theoretical analysis [202] leads to the conclusion that in such systems even the limited cycles are not possible and all azeotropes are certainly unstable. Hence any trajectory H(p) and X(p) when p -> 1 inevitably approaches the SP corresponding to the homopolymer the number of which can be from 1 to m. The set of systems obtained due to the classification within the framework of the simplified model essentially impoverishes in comparison with the general case of the terminal copolymerization model since some types of systems cannot be principally realized under the restrictions which the Q-e scheme puts on the reactivity ratios r. ... 

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