Copolymers linear/branched/cross-linked

It is possible to classify polymers by their structure as linear, branched, cross-linked, and network polymers. In some polymers, called homopolymers, merely one monomer (a) is used for the formation of the chains, while in others two or more diverse monomers (a,p,y,...) can be combined to get different structures forming copolymers of linear, branched, cross-linked, and network polymeric molecular structures. Besides, on the basis of their properties, polymers are categorized as thermoplastics, elastomers, and thermosets. Thermoplastics are the majority of the polymers in use. They are linear or branched polymers characterized by the fact that they soften or melt, reversibly, when heated. Elastomers are cross-linked polymers that are highly elastic, that is, they can be lengthened or compressed to a considerable extent reversibly. Finally, thermosets are network polymers that are normally rigid and when heated do not soften or melt reversibly. 

Structural types Homopolymers Copolymers (alternating, block, and random) Linear, branched, cross-linked, dendrimeric, etc. Homogeneous SAMs Mixed SAMs Patterned SAMs... 

Know the meaning of homopolymer, copolymer, linear, branched, and cross-linked polymer. For copolymers, know the meaning of alternating, random, block, and graft. 

Network Linear Branched Copolymer Stereopolymer or Cross-link... 

Butadiene and isoprene have two double bonds, and they polymerize to polymers with one double bond per monomeric unit. Hence, these polymers have a high degree of unsaturation. Natural rubber is a linear cis-polyisoprene from 1,4-addition. The corresponding trans structure is that of gutta-percha. Synthetic polybutadienes and polyisoprenes and their copolymers usually contain numerous short-chain side branches, resulting from 1,2-additions during the polymerization. Polymers and copolymers of butadiene and isoprene as well as copolymers of butadiene with styrene (GR-S or Buna-S) and copolymers of butadiene with acrylonitrile (GR-N, Buna-N or Perbunan) have been found to cross-link under irradiation. 

Resins vs. Plastics Thermoplastics vs. Thermoset Homopolymers vs. Copolymers Bifuncrional vs. Polyfunctional Linear vs. Branched vs. Cross-Linked Addition vs. Condensation... 

In this chapter, the big four thermoplastics are covered polyethylene, polypropylene, polyvinyl chloride, and polystyrene. Like most other thermoplastics, they are long-chain polymers that become soft when heated and can be molded under pressure. They are linear- or branch-chained and, except for some exotic copolymers, have little or no cross-linking. Technological advances continue. Research in copolymerization, catalysts, processing, blending, and fabricating continues even as you read this. 

Figuer 9.1 Schematic illustration of various polycation structures used for preparation of polyplexes (A) linear (PEI) (B) randomly branched (PEI) (C) dendrimer (PAMAM) (D) block and graft copolymers (Pluronic-g-PEI and PEO-g-PEI modified with a targeting moiety by one PEO end) (E) nanoscale cross-linked network (PEO-c7-PEI). 

TFFF has been employed for the investigation of linear polymers in various solvents [19, 20, 21], copolymers [22, 23], branched polymers [23], and cross-linked microgels and block-copolymer micelles [24]. Kirkland coupled TFFF with an online viscosity detector [25]. 

Polymers are macromolecules built of smaller units called monomers. The process by which they are formed is called polymerization. They may be synthetic (nylon, Teflon, and Plexiglas) or natural (such as the biopolymers starch, cellulose, proteins, DNA, and RNA). Homopolymers are made from a single monomer. Copolymers are made from two or more monomers. Polymers may be linear, branched, or cross-linked, depending on how the monomer units are arranged. These details of structure affect polymers properties. 

Macromolecular synthesis involves the design of synthetic methodology for the formation of macromolecular architecture, including controlled molecular weight and molecular weight distribution, stereochemistry, topology (linear, branched, and cross-linked), block and graft copolymers, and... 

The configuration of a molecule refers to the fixed arrangement of the atoms in the molecule, which is determined by the chemical bonds that have been formed. The configuration of a polymer chain cannot be altered unless chemical bonds are broken and reformed. The linear, branched, or cross-linked architecture of polymer molecules, and the different types of copolymers discussed in Section 3.3 are all examples of different molecular configurations. Even within a linear homopolymer, there can be different configurations of molecules, as will be explained in Sections 3.6 and 3.7. 

A very large number of morphologies can be found in the world of polymers and copolymers. Polymers can be linear, branched, comb-type, star-like, micelles, macrocyclic or cross-linked, when chains are linked together for copolymers the order can be random, alternating, in block or graft as illustrated in Figure 10.1. The order of the repeating units has to be specified, as different orders result in different properties. 

A polymer is composed of repeating units (i.e., monomers) that are linked together into long chains that can be linear, branched, or cross-linked. If a polymer contains two different types of monomers, it is a copolymer. A linear polymer is a thermoplastic. At elevated temperatures it melts and flows as a liquid. In a cross-linked polymer, the repeat units are actually linked into a three-dimensional network of macroscopic size. It is a thermoset. Once the polymerization is completed, the cross-linked polymer cannot be softened or melted. It is hard, infusible, and insoluble. Hence a thermoset adhesive is the most durable but is also difficult to characterize as compared to a thermoplastic one. 

The formation of synthetic polymers is a process that occurs via chemical connection of many hundreds up to many thousands of monomer molecules. As a result, macromolecular chains are formed. They are, in general, linear but can be branched, hyperbranched, or cross-linked as well. However, depending on the number of different monomers and how they are connected, homopolymers or one of the various kinds of copolymers can result. The chemical process of chain formation may be subdivided roughly into two classes, depending on whether it proceeds as a chain growth or as a step growth reaction (Fig. 3.1). 

PolysUoxanes, [-O-Si(RR )-], are linear resins that can be branched or cross-linked into elastomers. They have high compressibility, permeability to gases, low Tg and viscosity, exceptional weatherability, low surface tension coefficient, and are relatively expensive. Siloxane polymers or copolymers have been incorporated into engineering or specialty resins to improve processability, toughness, HDT, and solvent and weather resistance. 

There are many different types of polymers. In addition to the linear polymers such as polyethylene, there are branched polymers and cross-linked polymers. Copolymers can be prepared by polymerizing one alkene in the presence of another. When styrene and acrylonitrile are polymerized in the same reaction vessel, for example, a copolymer such as 177 is formed. These copolymers can be random copolymers, where there is no deflnite sequence of monomer units, but they can also be regular copolymers, where there is a regular alternating sequence of each monomeric unit. 

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