Polystyrene repeat unit structure

Figure 1.1. Calculation of glass transition temperature Tg and density p at room temperature of polystyrene as an example of the application of group contribution techniques, (a) The structure of a polystyrene repeat unit, (b) Fonnal breakdown of this structure into two "groups", (c) Each group makes a contribution to the molecular weight M of the repeat unit, to the "molar glass transition function" Yg, and to the amorphous molar volume V [3a], M, Yg and V arc sums of these contributions ...

Polymer Structures and Properties. Synthetic polymers are mixtures of compounds composed of the same repeating structural units but differing in molecular weight. Thus polystyrene has the repeat unit structure... 

Ellison CJ, Mundra MK, Torkelson JM (2005) Impacts of polystyrene molecular weight and modification to the repeat unit structure on the glass transition-nanoconfinement effect and the cooperativity length scale. Macromolecules 38 1767-1778... 

Monomers are generally simple organic molecules from which the polymer molecule is made. The structure of the repeating unit of a polymer is essentially that or closely related to that of the monomer molecule(s). The formula of the polystyrene repeating unit (II) is thus seen to be essentially the same as that of the monomer styrene CH2 =CH-C6Hs. 

Other macromolecular architectures, such as linear polymers, and any comparisons that have been made were performed with polydisperse samples of significantly different repeat unit structure. For example, the unique melt viscosity behavior of polyether dendrimers was compared with linear polystyrene and not with monodisperse linear analogs containing the same number of polyether repeat units based on 3,5-dihydroxybenzyl alcohol (2). Because of this, important issues, such as i) effect of the numerous chain end functional groups, ii) the effect of branching and, iii) the development of a well defined three-dimensional architecture cannot be addressed and the underlying reason for these inherent differences remains a mystery. 

The history of polymers, including the beginning of addition and of radical polymerization, is recormted by Morawetz. The repeat unit structure (1) of many common polymers, including polystyrene (PS), poly(vinyl chloride) (PVC), and poly(vinyl acetate) (PVAc), was established in the latter half... 

Some of the mechanical and thermal characteristics of polymers are a function of the ability of chain segments to experience rotation in response to applied stresses or thermal vibrations. Rotational flexibility is dependent on repeat unit structure and chemistry. For example, the region of a chain segment that has a double bond (C=C) is rotationaUy rigid. Also, introduction of a bulky or large side group of atoms restricts rotational movement. For example, polystyrene molecules, which have a phenyl side group (Table 14.3), are more resistant to rotational motion than are polyethylene chains. 

Figure 5.1. Molecular structures of the chemical repeat units for common polymers. Shown are (a) polyethylene (PE), (b) poly(vinyl chloride) (PVC), (c) polytetrafluoroethylene (PTFE), (d) polypropylene (PP), (e) polyisobutylene (PIB), (f) polybutadiene (PBD), (g) c/5-polyisoprene (natural rubber), (h) traw5-polychloroprene (Neoprene rubber), (i) polystyrene (PS), (j) poly(vinyl acetate) (PVAc), (k) poly(methyl methacrylate) (PMMA), ( ) polycaprolactam (polyamide - nylon 6), (m) nylon 6,6, (n) poly(ethylene teraphthalate), (o) poly(dimethyl siloxane) (PDMS).

Polymer means many parts and designates a large molecule made up of smaller repeating units. Thus the structure of polystyrene can be written... 

A linear polymer is one in which each repealing unit is linked only to two others. Polystyrene (1-1), poly(methyl methacrylate) (1-34), and poly(4-methyl pentene-1) (1-35) are called linear polymers although they contain short branches which arc part of the monomer structure. By conirast, when vinyl acetate is polymerized by free-radical initiation, the polymer produced contains branches which were not present in the monomers. Some repeating units in these species are linked to three or four other monomer residues, and such polymers would therefore be classified as branched. 

The styrene molecule is the monomer, and the resulting structure, enclosed in square brackets, is the polymer polystyrene. The unit in square brackets is called the repeating unit. Some polymers are derived from the mutual reaction of two or more monomers. For example, poly(hexamethylene adipamide) or nylon-6,6 is made from the reaction of hexamethylenediamine and adipic acid, as shown in the following equation ... 

The number of repeating units in the polystyrene structure (1) is indicated by the index n. This is known as the degree of polymerization (DP). It specifies the length of the polymer chain. Oligomer is a very low... 

The principles of nomenclature for copolymers are based on their structure and are given in Table 1.2, where A and B represent the names of repeating units. For example, a statistical copolymer of ethylene and propylene would be called poly(ethylene-stat-propylene), and a triblock copolymer of styrene (A) sand isoprene (B) would be called polystyrene-Z)/oeA -polyisoprene- /ocA -polystyrene. In some cases it is necessary to introduce square brackets in the nomenclature to clarify the notation. Let us see an example An alternating copolymer of styrene and maleic anhydride would be called poly[styrene-a/ (maleic anhydride)]. 

Positive interactions between cationic species, including protons, with aromatic structures comprise an intensively examined and already well-documented phenomenon [142, 143], In the hypercrosslinked polystyrene these interactions may well be enhanced by a possible presence of condensed aromatic systems. As was shown in Chapter 6, Section 4.4, anthracene-type structures may easily be formed by the condensation of two chloromethylated styrene repeating units, followed by a subsequent oxidation. However, the early elution of pure HCl in Fig. 12.1 does not imply any retentive interactions between protons and the polymer. The retention of HCl occurs only in the presence of a salt. But why would the properties of HCl in the polymeric phase change so dramatically in the presence of metal chlorides, while no association of HCl with LiCl or CaCl2 takes place in solution The version (i) of attractive interactions of protons with the polystyrene phase thus cannot be accepted without serious doubt. 

Pig. 2.1 Chemical structure of (a) polyethylene, (/>) polystyrene, (c) polyvinyl chloride. To illustrate various ways to present such structures, panels (a"), (/> ), and (o ) show the same polymers in various other notations. For instance, hydrogen atoms are usually not shown, carbon atoms may not be explicitly shown as well (a and c"), and only one repeat unit can be shown instead of the chain (b"). 

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