Block copolymers, preparation

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). 

Step-Growth Gopolymerization. A sample of a block copolymer prepared by condensation polymerisation is shown in equation 30 (37). In this process, a prepolymer diol (HO—Z—OH) is capped with isocyanate end groups and chain extended with a low molecular-weight diol (HO—E—OH) to give a so-called segmented block copolymer, containing polyurethane hard blocks and O—Z—O soft blocks. 

In 1978 Hiils (Mumcu et al ) described the properties of a block copolymer prepared by condensation of polytetramethylene ether glycol with laurin lactam and decane-1,10-dicarboxylic acid. The materials were introduced as XR3808 and X4006. The polyamide XR3808 is reported to have a specific gravity of 1.02, a yield stress of 24 MPa, a modulus of elasticity of 300 MPa and an elongation of break of 360%. The Swiss company Emser Werke also introduced similar... 

Using the above method, Bamford and Han [59] have succeeded in synthesizing and characterizing copolymers in which each block is an alternating copolymer. The block copolymers prepared are of general structure ... 

In this chapter techniques of block copolymer preparation involving thermally labile azo compounds are reviewed. Upon heating, aliphatic azo compounds evolve nitrogen thus forming two carbon centered free radicals. 

Table 9.9 Block Copolymers Prepared by Macromonomer RAFT Polymerization under Starved-Feed Conditions.380"595...

Other block copolymers prepared using similar strategies include PEO (anionic) with second block poly(4-vinylpyridme).M ... 

POLYALLOMER RESINS. These are block copolymers prepared by polymerizing monomers in the presence of anionic coordination catalysts. The polymer chains in polyallomers are composed of homopolymerized segments of each of the monomers employed. The structure of a typical polyallomer can be represented as ... 

In this chapter, the focus is largely on experimental and theoretical studies of micellization in a range of solutions of model block copolymers prepared by anionic polymerization. A discussion of both neutral and ionic block copolymers is included, and features specific to the latter type are detailed. The adsorption of block copolymers at the liquid interface is also considered in this chapter. Recent experiments on copolymer monolayers absorbed at liquid-air and liquid-liquid interfaces are summarized, and recent observations of surface micelles outlined. Thus this chapter is concerned both with bulk micellization and the surface properties of dilute copolymer solutions. 

The block copolymers were AB type styrene-butadiene block copolymers prepared by anionic polymerization. Unless specified differently in the text, a block copolymer of number average molecular weight 110,000 containing 70 wt % styrene and 30 wt % butadiene (S30B) was used. Samples of different composition used in one series of experiments had approximately the same molecular weight. 

Top block copolymer prepared by Procedure 2 Center random copolymer prepared by Procedure 1 Bottom a blend of homopolymers... 

Block Copolymers Prepared by the Combination of Different Polymerization Mechanisms... 

Table 8.1 Examples of block copolymers prepared using the SAM technique...

Since 1980, siloxane-urea block copolymers prepared by the reaction of bisaminoalkyl-terminated silicones and diisocyanates [1] have been well known in the literature. Silicone is responsible for the elastomeric behavior and urea for the thermal behavior. Nevertheless, to obtain high-molecular-weights in the polymerization of such copolymers, the starting compounds have to be sufficiently pure [2]. Therefore, one key step in the synthesis of such block copolymers is the preparation of... 

B) (A)2n(B)m an ABA-type triblock copolymer Scheme 15.2. Block copolymer preparation via living polymerization methods. 

In the block copolymers prepared according to system 3, the rubber segments may be arranged in thin layers, in thin cylinders or as a nearly continuous network (14). The thickness of the rubber phase can never be greater than the end-to-end distance of the stretched rubber sequence. I the case of a polyol with a molecular weight of 4000, this end-to-end distance is at most about 200 A. Because the rubber chain will not be fully stretched, the thickness of the rubber phase will even be smaller, viz. about 100 A. Because the resolution of SEM is also about 100 A, the rubber phase in system 3 is hardly distinguishable ("Figure 2C ). 

A wide variety of block copolymers can be obtained by the metal-catalyzed living radical polymerizations, which are now applicable to numerous monomers. Most of them are block copolymers prepared from methacrylates, acrylates, and styrenes combinations are therefore within the same family or between different families. 

Figure 19. Block copolymers prepared via living anionic polymerization.

Figure 25. Block copolymers prepared from commercially available polymers.

Table 1 Examples of polypeptide hybrid block copolymers prepared from macromolecular amine initiators [8,9]. Block architectures are primarily AB diblocks or ABA triblocks, where the polypeptide segment is the A domain, and the macroinitiator is the B domain ...

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