Polymer backbones with spacer groups

Another approach is to attempt to chemically modify the toxicants to yield nontoxic products which are returned to their active state by digestive or metabolic processes. The pesticide trichlotfon, which is toxic to fire ants, is not effective as an agent for control of the species due to its rapid action. Polymeric insecticides of the ester of trichlorfon with PAA have been prepared with hydrolytically unstable covalent linkages [225]. The preparation of polymeric esters of trichlorfon with spacer groups between the insecticide and the polymer backbone 2 have been prepared to eliminate the limited toxicity of the polymeric insecticide 1, which is a reflection of the limited loading and slow hydrolysis of the insecticide due to the steric hindrance of the polymer backbone (Scheme 3.18). 

Polyphosphazenes bearing crown ethers (12-crown-4,15-crown-5 and 18-crown-6) as single or as mixed substituents with trifluoroethoxy or methoxy-ethoxyethoxy groups were synthesized by Cowie [601,602] and Allcock [484] and their conductivity studied because it was shown that the incorporation of crown ether molecules into a polymer electrolyte could increase their ionic conductivity. In these macromolecules, the crown ether units were linked to the backbone through oxymethylene spacer groups. 

The synthesis of the first polymer-supported chiral Mn-salen derivatives was reported independently by Sivaram171 and Minutolo.171-173 Different monomeric Jacobsen-type units, containing two polymerizable vinyl groups, were copolymerized with styrene and divinylbenzene to yield the corresponding cross-linked polymers as a monolithic compact block.174-176 The less mobile system (Figure 19) with no spacer between the aromatic ring and the polymer backbone is less enantioselective. 

Whether chelation (as opposed to covalent bonding) of an active moiety to an excipient qualifies the entire construct as a new chemical entity (NCE) is a moot point. A case in point is polymer platinate. This compound consists of a polymer backbone, hydroxypropylmethacrylamide, linked to a polypeptide spacer. The peptide is in turn linked with an aminomalonate chelating group, which chelates the platinum compound (Fig. 2). 

Investigations in the past years have proved that applying the concept of flexible spacer, polymers can be synthesized systematically, which exhibit the l.c. state. Owing to the flexible linkage of the mesogenic molecules to the polymer main chain, very similar relations can be expected with respect to 1-l.c., like chemical constitution and phase behavior, or dielectric properties and field effects for the l.c. side chain polymers. This will be in contrast to main chain polymers, where the entire macromolecule, or in case of semiflexible polymers parts of the macromolecules, form the l.c. structure. The introduction of a flexible spacer between backbone and mesogenic group can be performed in a broad variety of chemical reactions. Some arbitrarily... 

The spacer units in 3.60 are assembled from polyphosphazenes that bear p-bromophc-noxy side groups via a lithiation reaction, and treatment with a diorganochlorophosphine to give 3.62. The chemistry is summarized in reaction sequence (45).107 Polymer 3.62 coordinates to a variety of metallo species,108 including osmium cluster compounds and cobalt carbonyl hydroformylation catalysts. When used as a polymeric hydroformylation catalyst, this latter species proved how stable the polyphosphazene backbone is under the drastic conditions often needed for these types of reactions. The weakest bonds in the molecule proved to be those between the phosphine phosphorus atoms and the aromatic spacer groups. 

Materials and Film Preparation. The molecular structure of the polymerized lipid referred to as CO-1.5 is shown in Figure 1. The material is a co-polymer of a double 18-carbon alkyl chain lipid with a side-group spacer and five main-chain spacer groups. The purpose of the spacer chains is to allow more free volume for the lipid chains to orientationally order normal to the polymer backbone. The lipid chain contains an amide, and the main-chain spacer groups contain tertiary amines. The polymer was synthesized following the general procedures given by Laschewsky et al. (10). 

Gangadhara et al. have linked the cyanobiphenyl mesogen via a dicarbox-imide-group to an oxanorbornene ring system Vl-n, n=2-8 (see Fig. 4). Polymerization was carried out with Schrock type initiator 4. The dicarboximide linkage probably hindered the formation of LC phases even the introduction of relatively long spacers between the polymer backbone and the mesogen did not lead to liquid crystalline monomers or polymers [41]. 

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