Regular block copolymers

Copolymers are categorized by the placement of the mers, as Figure 1-3 shows. For example, in a random copolymer, mers can appear anywhere in the chain whereas, in the block copolymer, regular runs of the mers appear. The graft copolymer attaches the other mers as branches. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Fig. 24.1. (a) A copolymer of vinyl chloride and vinyl acetate the "alloy" pocks less regularly, has a lower Tg, and is less brittle than simple polyvinylchloride (PVC). (b) A block copolymer the two different molecules in the alloy ore clustered into blocks along the chain. 

Thus, the problem on the growth of a block copolymer chain in the course of the interphase radical copolymerization may be formulated in terms of a stochastic process with two regular states corresponding to two types of terminal units (i.e. active centers) of a macroradical. The fact of independent formation of its blocks means in terms of a stochastic process the independence of times ta of the uninterrupted residence in every a-th stay of any realization of this process. Stochastic processes possessing such a property have been scrutinized in the Renewal Theory [75]. On the basis of the main ideas of this theory, the set of kinetic equations describing the interphase copolymerization have been derived [74],... 

The first report of ROMP activity by a well-characterized Mo or W species was polymerization of norbornene initiated by W(CH-t-Bu)(NAr)(0-f-Bu)2 [122]. In the studies that followed, functionality tolerance, the synthesis of block copolymers, and ring-opening of other monomers were explored [30, 123]. Two important issues in ROMP concern the cis or trans nature of the double bond formed in the polymer and the polymer s tacticity. Tacticity is a consequence of the presence of two asymmetric carbons with opposite configuration in each monomer unit. The four ROMP polymers (using polynorbornene as an example) that have a regular structure are shown in Scheme 3. 

Three major topics of research which are based on phase transfer catalyzed reactions will be presented with examples. These refer to the synthesis of functional polymers containing functional groups (i.e., cyclic imino ethers) sensitive both to electrophilic and nucleophilic reagents a novel method for the preparation of regular, segmented, ABA triblock and (A-B)n alternating block copolymers, and the development of a novel class of main chain thermotropic liquid-crystalline polymers, i.e., polyethers. 

Block copolymers are named by using dashes (double-length hyphens) for the bonding of bloeks with each other and with junction units. With graft and star polymers, the grafts or the arms, respectively, are eonsidered to be substituents to the main chain, and the structure is named in the same way as a regular or irregular polymer. Table 8 lists some examples. 

Block copolymers in which the sequential arrangement of regular bloeks is known are named by using dashes for the bonding of blocks with each other and with junetion units ... 

Rule 4.3.1 The formulae of block copolymers ([1], Definition 3.35) consisting of a sequenee of regular blocks ([1], Definition 3.15) and, if known, junction units ([6], Definition Rule 5.5) in known sequential arrangement are written as, e.g.,... 

Rule 4.3.2 The formulae of block copolymers consisting of sequences of regular blocks... 

Because of the geometric regularity present, gutta-percha (/ra/w-polyi-soprene) and stretched NR from Hevea brasitiensis (c/s-polyisoprene) are crystalline. Random copolymers are usually amorphous, but some may be crystalline if the comonomers, such as ethylene and tetrafluoroethylene, are similar in size. Block copolymers may have crystalline domains if either of the com-... 

Folkes, M. J, and Keller, A. (1973). The morphology of regular block copolymers. In The physics of glassy polymers, (ed. R. N. Haward). Applied Science, London. Fredrickson, G. H. and Bates, F. S. (1996). Annual Reviews of Materials Science, 26, 501. Goodman, I. (ed.) (1982). Developments in block copolymers, Vol. 1. Applied Science, London. 

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