Polypropylene repeat unit structure

PHAs can consist of a diverse set of repeating unit structures and have been studied intensely because the physical properties of these biopolyesters can be similar to petrochemical-derived plastics such as polypropylene (see Table 1). These biologically produced polyesters have already found application as bulk commodity plastics, fishing lines, and for medical use. PHAs have also attracted much attention as biodegradable polymers that can be produced from biorenewable resources. Many excellent reviews on the in vivo or in vitro synthesis of PHAs and their properties and applications exist, underlining the importance of this class of polymers [2, 6, 7, 12, 26-32]. 

Polymer Syntheses. The block copolyether-urethane-ureas were synthesized from polypropylene glycol, methylene bis(4-phenylisocyanate), and ethylenediamine using a two-step solution polymerization (7). The repeat unit structure was ... 

The urethane interface region and polyether segments were modeled with a copolyether-urethane synthesized from polypropylene glycol (1000 MW) and methylene bis(4-phenylisocyanate) using a one-step solution polymerization technique (8). The copolymer has the following repeat unit structure ... 

C13-0049. Draw the structure of polypropylene, showing at least five repeat units. 

The enumeration and geometry of the possible stereoregular structures of polypropylene oxide illustrate the value of the above concepts of symmetry. Propylene oxide monomer has a truly asymmetric carbon, and the repeat unit in the polypropylene oxide chain can be either of the two optical isomeric... 

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).

Linear polymers. A linear polymer is a polymer molecule in which the atoms are more or less arranged in a long chain called the backbone. This is best illustrated with the structure of polyethylene (Fig. 14.1). However, polymers such as polypropylene or poly(l-pentene) in which a small chain called pendant groups presents in the repeating unit, are also designated as a linear polymer. The chains of pendant groups are much... 

A similiar comparison can be made between permeability data of polyesters and polycarbonates containing "polyester-like" monomers. For example, polycarbonates 26 and 27, which contain predominantly bisphenols which are structurally similiar to the repeat unit (circled) of an alkyl terephthalate polymer (PBT), possess essentially the same low permeability as that polyester (Table V). Furthermore, there has been a recent announcement (3 ) that aliphatic polycarbonates, such as polypropylene and polyethylenecarbonate, are being developed as potential gas barrier materials. In summary these results suggest that the relative low permeabilities of commercial polyesters and high permeabilities of commerical polycarbonates are not a direct consequence of the ester or carbonate links, but are due instead to the structure of the monomers they are prepared from, i.e., the aliphatic diol and aromatic bisphenol, respectively. 

For TSCA purposes, SRU names are used only for several types of common polymer backbones in which the structure of the polymer is known or reasonably ascertained to consist of repeating units instead of being random, and where there is a reported average number of SRU, a variable range of SRU, or an unknown number of SRU. Polymers identified with SRU names on the Inventory include certain polyethylene glycols and derivatives, certain polypropylene glycols and their derivatives, and siloxanes and silicones. 

I LEARNING CHECK 2.8 Draw the structural formula of a portion of polypropylene containing four repeating units of the monomer propylene,... 

Draw the structural formula of the repeating unit for the following addition polymers (a) polypropylene, (b) poly(vinyl acetate), and (c) poly(vinyl alcohol). 

Isotactic A stereoregular structure where the sites of steric isomerism in each repeating unit of the polymer has the same configuration. In other words in an isotactic polypropylene all the methyl groups will be located on one side of the plane of the polymer chain (Fig. 2.14). 

The regularity of the polymer backbone is the key factor isotactic polypropylene crystallizes forming a rigid stable solid, whereas atactic polypropylene does not and forms a rubbery elastic solid. For flexible polymers, the structure of the solid is dictated by the symmetry of the polymer backbone. For the formation of a semi-crystalline solid it is necessary for there to be either an element of symmetry in the repeat unit chemical structure or strong interactions to aid the packing of the molecule and initiate the alignment that is required for the crystal growth process. 

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