Copolymerization statistical copolymers

State Correlation Diagram (SCO) approach 27-8 statistical copolymerization see copolymerization statistical copolymers sea also copolymers definition 333... 

Statistical copolymers are formed when mixtures of two or more monomers are polymerized by a radical process. Many reviews on the kinetics and mechanism of statistical copolymerization have appeared1 9 and some detail can be found in most text books on polymerization. The term random copolymer, often used to describe these materials, is generally not appropriate since the incorporation of monomer units is seldom a purely random process. The... 

One of the major advantages of radical polymerization over most other forms of polymerization, (anionic, cationic, coordination) is that statistical copolymers can be prepared from a very wide range of monomer types that can contain various unprotected functionalities. Radical copolymerization and the factors that influence copolymer structure have been discussed in Chapter 7. Copolymerization of macromonomers by NMP, ATRP and RAFT is discussed in Section 9.10.1. 

The form of the distribution (Eq. 101), as shown in Fig. 7, qualitatively differs from that exhibited by this distribution for the products of homophase copolymerization. This distinction takes place both in real systems (ri < l,r2 < 1), where statistical copolymers are formed and in hypothetical systems (ri l,r2 1), where the formation of multiblock copolymers is expected. Essentially, the composition distribution in the latter systems... 

Direct Copolymerization of Sulfonated Monomers To Afford Random (Statistical) Copolymers... 

The copolymerization of a mixture of monomers offers a route to statistical copolymers for instance, a copolymer of overall composition XXXV is synthesized by copolymerizing a mixture of the four monomers... 

Secondary metathesis reactions are sometimes encountered during metathesis copolymerization, leading to a reshuffling of the units in the chain and eventually to a random distribution for example in the copolymerization of 248 and 258 using RUCI3 as catalyst, statistical copolymers are produced no matter whether the monomers are mixed initially or added sequentially576. See also the copolymers of 128 Section Vm.B.6. 

The first important question we need to answer is how the monomer feed composition x(p) will be changed with conversion at various initial values 5° and the parameters of kinetic copolymerization model. When such a trajectory x(p) is known, on the base of the formulae (5.1), (5.3), and (5.7) one can find the main statistical copolymer characteristics at any number of its components within the framework of the chosen kinetic model. 

As it follows from the present review, a rather complete and experimentally well-grounded quantitative theory of radical copolymerization of an arbitrary number of monomers has been developed. This theory allows one to calculate various statistical copolymers characteristics using the known values of reactivity ratios. The modern stage of the development of this theory is characterized by new approaches applying, for example, the apparatus of graph theory and theory of the dynamic systems which permit to widen the area of theoretical consideration involving the multicomponent copolymerization at high conversions. 

The composition of instantaneously generated chains is not sufficiently described by the copolymerization equation which only informs us about the mean populations of monomers in a statistical copolymer. This problem was studied by Goldfinger and Kane [190] based on the following considerations. 

There exist many alternating copolymerizations ethylene or propene with alkyl acrylates [244], vinyl acetate with maleic anhydride [245], styrene with acrylonitrile [246], styrene with fumaronitrile [247], vinyl carbazol with fumaronitrile, vinyl ferrocenne with diethylfumarate [248], and further pairs or systems of three monomers [238, 249-253]. External conditions can support or hinder alternation. At not too high temperatures, vinyl acetate forms a donor—acceptor complex with maleic anhydride. Under these conditions (and in the presence of a radical initiator), an alternating copolymer is formed. The concentration of the complex decreases with increasing temperature above 363 K the complex cannot exist. Under these conditions, copolymerization yields a statistical copolymer whose composition depends on the composition of the monomer mixture [245]. 

Extremely hydrophobic monomers do not polymerize well via macroemulsion polymerization due to their very low rates of monomer transport across the aqueous phase. Obviously, these monomers can be polymerized much more effectively in a miniemulsion system. One example of this is provided by Landfester et al. [320]. In this paper,fluoroalkyl acrylates are polymerized in a miniemulsion with low levels of a protonated surfactant. When fluorinated monomers were copolymerized with standard hydrophobic and hydrophilic monomers, either core-shell structures or statistical copolymers were formed. 

SAN is constituted of styrene and acrylonitrile units copolymerized statistically in the ratio 80 20 mol%. Previous studies on the photooxidation of PS [7,8] and PAN [3] have shown that the photooxidation rates of these polymers were very different PS degrades about 20 times faster than PAN. Consequently, the first steps of photooxidation of the copolymer SAN is presumed to involve mainly the styrene units. SAN samples have been irradiated and analyzed under the same conditions as PS samples. 

Statistical copolymers were reported for N-vinylimidazole and 13b [50], for acrylamide with 9a [11], 9b [12], and 9c [13], and for terpolymers of acrylamide, sodium acrylate, and 9b [51]. Several hydrolytically stable am-monioacetate and pyridiniocarboxylate monomers based on isobutylene with variable length of hydrophobic side chains did not homopolymerize, but these monomers with surfactant properties are suited for copolymerization with electron-poor monomers [52]. 

Polymers and copolymers were laboratory-prepared samples. Samples W4 and W7 of the diblock copolymer AB poly(styrene-fo-tetramethylene oxide) (PS—PT) were synthesized by producing a polystyrene prepolymer whose terminal group was transformed to a macroinitiator for the polymerization of THF. Samples B13 and B16 of the diblock copolymer AB poly[styrene-h-(dimethyl siloxane)] (PS-PDMS) were prepared by sequential anionic polymerization. Samples of statistical copolymers of styrene and n-butyl methacrylate (PSBMA) were produced by radical copolymerization. Details of synthetic and characterization methods have been reported elsewhere (15, 17-19). 

A distinctive advantage of radical polymerization is that a variety of monomer pairs can readily be copolymerized into true random/statistical copolymers. 

A mixture of two monomers that can be homopo-lymerized by a metal catalyst can be copolymerized as in conventional radical systems. In fact, various pairs of methacrylates, acrylates, and styrenes have been copolymerized by the metal catalysts in random or statistical fashion, and the copolymerizations appear to also have the characteristics of a living process. The monomer reactivity ratio and sequence distributions of the comonomer units, as discussed already, seem very similar to those in the conventional free radical systems, although the detailed analysis should be awaited as described above. Apart from the mechanistic study (section II.F.3), the metal-catalyzed systems afford random or statistical copolymers of controlled molecular weights and sharp MWDs, where, because of the living nature, there are almost no differences in composition distribution in each copolymer chain in a single sample, in sharp contrast to conventional random copolymers, in which there is a considerable compositional distribution from chain to chain. Figure 26 shows the random copolymers thus prepared by the metal-catalyzed living radical polymerizations. 

Inclusion compounds allow the realization of copolymerization in the crystal state (1-6). This is a further difference with respect to typical solid state reactions. Both block- and statistical copolymers can be obtained the former involves a two-step process, with subsequent inclusion and polymerization of two different monomers (21) the latter requires the simultaneous inclusion of two guests. This phenomenon has a much wider occurrence than thought at first, especially when a not very selective host such as PHTP is used. Research with this host started with mixtures of 2-methylpentadiene and 4-methylpentadiene, two almost exactly superimposable molecules (22), but was successfully extended to very dissimilar monomers, such as butadiene and 2,3-dimethylbutadiene. 

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