Copolymers Addition polymers formed from

Chromosorb Century Series (Johns Manville Corp.) is a range of microporous polymers formed from the co-polymerisation of DVB and styrene, additional vinyl monomers are included to produce a range of co-polymers with varying surface areas and polar characteristics suitable for analysis of a wide range of samples. Table 5.10 summarises the composition of the copolymer, properties and applications. 

In an addition potymerization reaction, the molecules form new linkages by opening existing tt bonds. Polyethylene forms, for example, when the carbon-carbon double bonds of ethylene open up. In a condensation potymerization reaction, the monomers are joined by splitting out a small molecule from between them. The rious kinds of nylon are formed, for example, by removing a vrater molecule from between an amine and a carboxylic acid. A polymer formed from two different monomers is called a copolymer. 

Pathway 2 is generally chosen in the academic literature. In addition to sodium naphthalene, dilithium compounds are often used [146-150]. The following terminators are described for the third pathway silicon tetrachloride and tintetrachloride dicarbonic acid ester [151], divinylbenzene [152], and polymers formed from divinylbenzene [153] containing numerous vinyl groups yielding star-shaped polymers. Block copolymers of styrene and butadiene or isoprene are synthesized commercially in large ranges. 

There are additional factors that may reduce functionality which are specific to the various polymerization processes and the particular chemistries used for end group transformation. These are mentioned in the following sections. This section also details methods for removing dormant chain ends from polymers formed by NMP, ATRP and RAFT. This is sometimes necessary since the dormant chain-end often constitutes a weak link that can lead to impaired thermal or photochemical stability (Sections 8.2.1 and 8.2.2). Block copolymers, which may be considered as a form of end-functional polymer, and the use of end-functional polymers in the synthesis of block copolymers are considered in Section 9.8. The use of end functional polymers in forming star and graft polymers is dealt with in Sections 9.9.2 and 9.10.3 respectively. 

Vinyl copolymers contain mers from two or more vinyl monomers. Most common are random copolymers that are formed when the monomers polymerize simultaneously. They can be made by most polymerization mechanisms. Block copolymers are formed by reacting one monomer to completion and then replacing it with a different monomer that continues to add to the same polymer chain. The polymerization of a diblock copolymer stops at this point. Triblock and multiblock polymers continue the polymerization with additional monomer depletion and replenishment steps. The polymer chain must retain its ability to grow throughout the process. This is possible for a few polymerization mechanisms that give living polymers. 

For example, a PE-fe-poly(ethylene-co-propylene) diblock composed of crystalline PE and amorphous ethylene/propylene copolymer segments was synthesized from ethylene and ethylene/propylene. The addition of MAO and Ti-FI catalyst 40 (Fig. 25) to an ethylene-saturated toluene at 25 °C resulted in the rapid formation of a living PE (Mn 115,000, MJMn 1.10). The addition of ethylene/propylene (1 3 volume ratio) to this living PE formed a PE-/>poly(ethylcnc-co-propylcnc) block copolymer (Mn 211,000, MJMn 1.16, propylene content 6.4 mol%) [30], As expected, the polymer exhibits a high Tm of 123 °C, indicating that this block copolymer shows good elastic properties at much higher temperatures than the conventional random copolymers of similar densities. 

Redistribution and Polymer Structure. The structure of DMP-DPP copolymers is probably determined by the relative rates of the polymerization reaction and the monomer-polymer redistribution reaction. In the DMP-DPP system, structure may be predicted simply by observing the effect on solution viscosity of the addition of one of the monomers to the growing polymer derived from the other monomer. When DPP is added to a DMP reaction mixture, the solution viscosity drops immediately almost to the level of the solvent, as redistribution converts the polymer already formed to a mixture of low oligomers ... 

In addition polymers, by contrast, the recurring units have the same structures as the monomer(s) from which the polymer was formed. Examples are polystyrene (1-1), polyethylene (1-3), styrene-maleic anhydride copolymers (1-26), and so on. 

However, replacement strategies are not straightforward with compromises on either performance and cost having to be addressed. An excellent example of this centres around the chlorine issue. Chlorine imparts a unique set of properties to addition polymers, such as the ability to crystallise on film formation. Vinylidene chloride copolymers have exeellent gas, odour and moisture barrier properties impossible to achieve from non-chlorinated waterborne film forming materials. In the barrier packaging area it has a unique position, with proposed replacements being unable to fully match its overall... 

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