Random Addition Copolymerizations

In this chapter we review and discuss random (nonequimolar) MA copolymerizations, covered by the condition r r2 — 1, and provide a comprehensive patent coverage on uses for these materials. Some attention is also given to discussing copolymerizations of MA-based monomers, such as maleates and fumarates, since over the years substantial study has been devoted to trying to find uses for these monomers and polymers. Chapter 10 covers the very frequent conditions for MA copolymerizations where 1 2 — 0. 

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Mechanistic Aspects of Cationic Copolymerizations The relative reactivities of monomers can be estimated from copolymerization reactivity ratios using the same reference active center. However, because the position of the equilibria between active and dormant species depends on solvent, temperature, activator, and structure of the active species, the reactivity ratios obtained from carbocationic copolymerizations are not very reproducible [280]. In general, it is much more difficult to randomly copolymerize a variety of monomers by an ionic mechanism than by a radical. This is because of the very strong substituent effects on the stability of carbanions and carbenium ions, and therefore on the reactivities of monomers substituents have little effect on the reactivities of relatively nonpolar propagating radicals and their corresponding monomers. The theoretical fundamentals of random carbocationic copolymerizations are discussed in detail and the available data are critically evaluated in Ref. 280. This review and additional references [281,282] indicate that only a few of the over 600 reactivity ratios reported are reliable. 

As an option, the polymer can then be fed to a fluidized bed gas-phase reactor, operated in series vith the MZCR, where additional copolymerization can take place to yield high-impact copolymer PP. This gas-phase reactor may be bypassed when homopolymer or random copolymers are produced. In this reactor, the elastomeric phase (ethylene/propylene rubber) is generated within the porous homopolymer matrix that resulted from the first reaction stage. The pores, developed inside the polymer particle in the MZCR upstream, allow the rubber phase to develop without the formation of agglomerates resulting from the sticky nature of the rubber. 

The second approach for site-specific double PPM was performed using the polythiolactones prepared by random RAFT copolymerization of NIPAAM and thiolactone acrylamide monomer 7 (Scheme 12) [52]. The respective copolymers were subjected to additive-free nucleophilic amine-thiol-ene conjugation. A chloroform solution of the poly thiolactone at a concentration of 10 wt% was treated with the desired acrylate, followed by addition of the primary amine. Both reagents were used in a fivefold excess with respect to the number of thiolactone units (Scheme 15). 

Styrene-butadiene rubber is prepared from the free-radical copolymerization of one part by weight of styrene and three parts by weight of 1,3-butadiene. The butadiene is incorporated by both 1,4-addition (80%) and 1,2-addition (20%). The configuration around the double bond of the 1,4-adduct is about 80% trans. The product is a random copolymer with these general features ... 

GopolymeriZation Initiators. The copolymerization of styrene and dienes in hydrocarbon solution with alkyUithium initiators produces a tapered block copolymer stmcture because of the large differences in monomer reactivity ratios for styrene (r < 0.1) and dienes (r > 10) (1,33,34). In order to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such as tetrahydrofuran or an alkaU metal alkoxide (MtOR, where Mt = Na, K, Rb, or Cs). In contrast to Lewis bases which promote formation of undesirable vinyl microstmcture in diene polymerizations (57), the addition of small amounts of an alkaU metal alkoxide such as potassium amyloxide ([ROK]/[Li] = 0.08) is sufficient to promote random copolymerization of styrene and diene without producing significant increases in the amount of vinyl microstmcture (58,59). 

Another important consequence of the limitations concerning cross-addition is that anionic polymerization is not suited for the synthesis of random copolymers. If a mixture of two anionically polymerizable monomers is reacted with an initiator, the most electrophilic monomer will polymerize while the other is left almost untouched 30). In other words, a general feature of anionic binary copolymerization is that one of the reactivity ratios is extremely high while the other is close to zero. 

In addition, the incorporation of fluoroether units in a regular sequence in the above fluoropolyethers is almost impossible owing to the random nature of the copolymerization process. In this article we describe a novel method for making perfectly alternating fluoropolyethers from functional fluoropolymers that are prepared by base-catalyzed homopolymerization of hydroxy-containing fluoro-monomers. 

Random copolymerization of one or more additional monomers into the backbone of PET is a traditional approach to reducing crystallinity slightly (to increase dye uptake in textile fibers) or even to render the copolymer completely amorphous under normal processing and use conditions (to compete with polycarbonate, cellulose propionate and acrylics in clear, injection molded or extruded objects). 

Smith et al. [64] prepared a series of PET/PTT copolyesters, and found that addition of the other component suppressed the melting point of the respective homopolymer. Between 37 and 60 % PTT content, the copolymers became amorphous and did not show any melting endotherms in the differential thermal analyzer scans. A similar behavior was observed by Balakrishnan and coworkers [102] in PET/PTT copolyesters prepared by the transesterification of PET with PDO, and by the copolymerization of EG and PDO with DMT [103, 104], The non-crystallizing behavior of copolymers with intermediate contents of the respective component is similar to that of a eutectic mixture, indicating formation of random copolyesters. The 7 g and solubility temperature of the copolyesters were, however, continuous and went through minima with increasing PTT content [64],... 

In many copolymerizations growth is influenced by the terminal (active) monomer unit. This can be described by Markov trials Zero order (or Bernoullian mechanism) means that the terminal unit of the growing chain does not influence the addition (rate, stereoregularity, etc.) of the next monomer molecule. Such copolymerizations often are called random . 

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