Polymers, linear, synthetic catalysts

Molecular catalysts, often in the form of metal ions complexed to a suitable ligand, can also be attached to dendrimer surfaces [3,9,10,93,94,96,148,149]. Such materials are generally structurally better defined than catalysts bounded to linear polymers, but like random-polymer catalysts they can be easily separated from reaction products. Note, however, that this approach results in a synthetic dead-end as far as further manipulation of the terminal groups is concerned, and thus some of the advantages of using dendrimers, such as solubility modulation, are lost. 

Phenol - formaldehyde polymers are the oldest synthetic polymers. These are obtained by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst. The reaction starts with the initial formation of o-and/or p-hydroxymethylphenol derivatives, which further react with phenol to form compounds having rings joined to each other through -CH2 groups. The initial product could be a linear product - Novolac used in paints. 

Phillips catalysts for linear polyethylene and polypropylene and the graft copolymerizations for impact polystyrene and ABS are even younger and have not yet spread into the less industrialized countries of world. The production of polyolefins, poly (vinyl chloride), and styrene resins on a worldwide basis as well as of all synthetic polymers is shown in Figure 3. A comparison of the U.S. production in Figure 1 and in Figure 3 demonstrates the effect of age and dissemination of technology. It shows that relatively more poly (vinyl chloride) but less polyolefins and styrene resins are produced worldwide than in this country. 

In contrast with synthetic polymers, proteins are characterized by very high levels of structural order. Unlike synthetic polymers, proteins are characterized by absolutely uniform chain lengths and well-defined monomer sequences (primary structure) [3]. These features are two of the requirements that enable folding of linear polypeptide chains into structurally well-defined and functional proteins. Proteins play an important role in numerous processes in biology, e.g. as carriers for small molecules and ions (examples are presented in Chapter 2.2), as catalysts, or as muscle fibers, and their exquisite properties are closely related to their well-defined three-dimensional structure [3]. 

In aqueous solution the catalytic esterolyses with polymeric catalysts is accelerated by hydrophobic bonding . The catalytic effect of synthetic polymers on hydrolysis has been reviewed by Kunitake and Okahata (57). Linear polyvinylimid-azole (Scheme 5) increases the rate of hydrolyses of 3-nitro-4-acyloxybenzoic acid by a factor of 103 with respect to monomeric imidazole 58-62). The primary reaction is the acylation of polyvinylimidazole. The effect is dependent on chain length of the acid and the solvent. The hydrophobic interaction causes an autocatalytic course of reaction rate. The acylated polyvinylimidazole is more hydrophobic than the starting polymer. At a 75% conversion the rate is five times higher than the initial rate. 

Polyacetylene (PA), the simplest linear conjugated polymer, has been actively studied for two main reasons. First, the discovery of the direct synthesis method of PA films on the surface of a Ziegler-Natta catalyst solution [1]. Second, the discovery of a large increase in electronic conductivity, due to a synthetic metal by doping with small quantities of electron-attracting species such as iodine, AsFs, etc., or with an electron donor such as sodium. However, because of its high reactivity and poor solubility, it is difficult to obtain the experimental structural data of PA. 

Chain-growth polymerization exhibits a preference for head-to-tail addition. Branching affects the physical properties of the polymer because linear unbranched chains can pack together more closely than branched chains can. The substituents are on the same side of the carbon chain in an isotactic polymer, alternate on both sides of the chain in a syndiotactic polymer, and are randomly oriented in an atactic polymer. The structure of a polymer can be controlled with Ziegler-Natta catalysts. Natural rubber is a polymer of 2-methyl-l,3-butadiene. Synthetic rubbers have been made by polymerizing dienes other than isoprene. Heating mbber with sulfur to cross-link the chains is called vulcanization. 

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