Copolymers basic principles

The term ABS was originally used as a general term to describe various blends and copolymers containing acrylonitrile, butadiene and styrene. Prominent among the earliest materials were physical blends of acrylonitrile-styrene copolymers (SAN) (which are glassy) and acrylonitrile-butadiene copolymers (which are rubbery). Such materials are now obsolete but are referred to briefly below, as Type 1 materials, since they do illustrate some basic principles. Today the term ABS usually refers to a product consisting of discrete cross-linked polybutadiene rubber particles that are grafted with SAN and embedded in a SAN matrix. 

Generalities about block copolymer micelles have been reviewed by Ham-ley [2] and Riess [14], based on previous works from the 1980s and 1990s. This topic will not be covered in detail, but the basic principle, as well as some important practical issues, will be reviewed. The essential experimental techniques used for block copolymer micelle characterization will also be outlined briefly. 

Block copolymer micelles have been the subject of an enormous body of work during the last 30 years. Although the basic principles of block copolymer mi-cellization have been already discovered and experimentally investigated in the 80s, intense research on this topic has been performed since the mid-90s by many research groups. Because it was not possible to include every contribution to that field in the frame of the present review, only selected examples were discussed. 

The two principal in-situ syntheses of branched copolymers are by step growth or radical chemistry. It should be noted that crosslinking of the same phase can also occur in addition to branching. This crosslinking is the basic principle of IPN formation. Hence, in this section, we will only refer to reports where crosslinking of the same phase appears to be a side reaction and not the expected one. 

Poly( inyl chloride), poly(acrylonitrile) and the high acrylonitrile copolymers have presented the major problems with respect to reducing the residual monomer content to extremely low levels. These are in the glas state tmder the conditions where monomer removal must be carried out. In principle, the temperature should be raised above the glass temperature to facilitate monomer removal. In practice, however, the systems are usually lattices or slurries of suspension polymer and coagulation could become a problem. In any case, both the rubbery and glassy states must be considered in any discussion of the monomer removal problem. The basic principles of the transport of gases in both situations have been presented briefly and with appropriate literature references in the introductory section of this review. 

The basic principles regarding the selection of a plasticizer remain the same with a latex system as with the other polymer systems if only end properties of the final film are to be considered. The vinyl latexes require very little reorientation of thought with respect to compounding philosophy. As the copolymers are introduced, each system will have to be considered on its own merits based on the chemistry of the polymers under study. 

Although investigated in lesser detail earlier, the science and technology of polymer blends had its emergence in the 1970 s. Many of the basic principles existed prior to that time e.g., Flory-Huggins thermodynamic principles as well as contributions by Guggenheim and Prigogine). Commercial blends existed for decades before, however the concept of miscibility, phase behavior, and the basic nature of polymer blends was not well understood or appreciated. An initial review of polymer blends [Bohn, 1968] listed only 12 miscible polymer pairs, some of which were minor variations in copolymer structure. The review also noted that UCST (upper critical solution... 

With respect to sweUing in non-solvents, toluene-modified styrene— DVB copolymers have much in common with hypercrosslinked polystyrenes [330]. Both are prepared in accordance with the same basic principle, the formation of rigid networks in strongly solvated state. It will be shown in detail in Chapter 7 that rigid expanded networks possess a relaxed favorable conformation only in their swollen state and, therefore, exhibit a marked tendency to acquire this state by sweUing and incorporating any liquid, even non-solvating one. 

Figure 12.5 shows some of the possible types of compatibiliser, which are all forms of block or graft copolymers. The basic principle is that the... 

Block copolymers are efficient reinforcers of weak interfaces, but they are costly and difficult to get to the interface. Other reinforcing strategies, which may in some cases be more practical, do exist. Two examples are the use of reactive grafting at interfaces and the use of random copolymers. In both of these methods one uses the same basic principle of reinforcement as that which operates in block copolymers a single, covalently bonded molecule straddles the interface in such a way that it is well entangled with the homopolymers on both sides of the interface. 

Before reviewing in detail the fundamental aspects of elastomer blends, it would be appropriate to first review the basic principles of polymer science. Polymers fall into three basic classes plastics, fibers, and elastomers. Elastomers are generally unsaturated (though can be saturated as in the case of ethylene-propylene copolymers or polyisobutylene) and operate above their glass transition temperature (Tg). The International Institute of Synthetic Rubber Producers has prepared a list of abbreviations for all elastomers [3], For example, BR denotes polybutadiene, IRis synthetic polyisoprene, and NBR is acrylonitrile-butadiene rubber (Table 4.1). There are also several definitions that merit discussion. The glass transition temperature (Tg) defines the temperature at which an elastomer undergoes a transition from a rubbery to a glassy state at the molecular level. This transition is due to a cessation of molecular motion as temperature drops. An increase in the Tg, also known as the second-order transition temperature, leads to an increase in compound hysteretic properties, and in tires to an improvement in tire traction... 

Chapter 22 presents the different types of polymers produced from ethylene, propylene, and copolymers of these olefins with other monomers, along with some basic principles that apply to polyolefin synthesis and characterization. The basic features of the mechanism of the polymerization are presented first to provide a framework for the description of different catalysts and materials. After presenting different types of catalysts that have been used for the polymerization of these monomers, a more detailed description of several features of the mechanism is presented. Finally, an overview of ethylene oligomerization, as well as diene polymerization and oligomerization, is presented. The primary journal literature and patent literature on olefin polymerization is immense. Fortunately, many reviews of olefin polymerization have been published. The coverage of olefin polymerization and oligomerization in this chapter is selective, and the reader is directed to review articles for more comprehensive coverage of these topics. " ... 

The assembly of amphiphilic block copolymers to generate discrete nanoscale structures is primarily driven by the hydrophobic effect, with micelle size and shape governed by a set of basic principles rooted in surfactant phase-separation behavior [22-28]. Important parameters that control the size of micelles are the degree of polymerization of the polymer blocks and the Flory-Huggins interaction parameter [28]. 

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