Reactions with co-monomers

The properties of PET can be modified by the incorporation of co-monomers. Typical examples of these are isophthalic acid (IPA) (influences stress cracking resistance and melting temperature), 2,6-naphthalene dicarboxylic acid (NDC) (improves mechanical properties and reduces gas permeability), cyclohexane 

Year Author(s) Reference Reactions Catalysis constant K constant K TCC) a (kJmol ) 

Like the monomers, the co-monomers are diols or diacids, and according to their functional groups, their reactions with TPA and EG follow the principal mechanisms outlined above. Very few data have been published on reactions with co-monomers, and it may be assumed that the same mechanisms and catalysis concepts should hold. Nevertheless, it has been observed that co-monomers influence the overall reaction rates significantly. In a typical batch process, the polycondensation time needed to prepare a polymer with an IV of 0.64 dL/g increases by about one third with co-monomer IPA and by about two thirds with co-monomer CHDM, in comparison to homo-PET. This may in part be due to the differing correlations between Pn and IV, but additionally a reduced reactivity due to steric and electronic effects or the influence of co-monomers on the mobility of functional groups seems probable. 

Yoda [28] investigated the activity of 20 catalysts in the transesterification reaction of PET and poly(ethylene isophthalate) (PEI) and found the same order of reactivity as for the transesterification of DMT with EG. The most effective catalysts were the acetates of Zn, Pb(n) and Hg(n), together with Co(m) acety-lacetonate and Sb203. Titanium catalysts were not included in Yoda s study, but are known to be effective catalysts in PET blending [46], 

PET contains about 2-3 % of short chain oligomers, which cause problems in fire processing of fire polymer. Oligomers can occur as linear or cyclic molecules and can be extracted by suitable solvents. Different compounds have been identified depending on fire solvent and file analysis technique used [49-52]. After tlieir extraction from fire polymer, oligomers will reform by thermal treatment of fire extracted sample [49], and a dynamic equilibrium between polymer and oligomers has been proposed. 

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The use of metal-complex initiating systems proved to be especially promising in carrying out the reactions with acrylic monomers which can be easily polymerized, when the common initiators of radical reactions are excepted. The use of Fe(CO)s -I- DMFA system allows us to perform homolytical addition of bromoform to acrylic monomers selectively at C-Br bond with no essential polymerization (ref. 10). 

The half-life times of the polymerization reaction can be adjusted from a few seconds to several days. Typical for such catalysts is the metalcarbene bond, as shown in Figure 1.5. In varieties of the catalytic principle of the metalcarbene bond, this bond is not initially present, but may be formed by a co-catalyst or by some reactions with the monomer itself. 

Frechet and coworkers have reported the development of a functionalized polymer monolith for use in parallel solution phase synthesis in continuous flow applications [10]. In this report, the authors outline the preparation of an azalac-tone-functionalized monolith for scavenging nucleophiles. This method involves the preparation of a macroporous polyfchloromethylstyrene co-divinylbenzene) monolith via the polymerization of the relevant mixture of monomer, initiator and porogen. These are allowed to react with a free radical initiator (4-cyanovaleric acid), followed by reaction with the monomer of choice, to synthesize the functionalized monolith. The authors have thus prepared monoliths functionalized with VAZ to provide an azalactone-functionalized monolith. These monoliths were then demonstrated to completely remove amines after flowing a solution of amine in THF through the monolith for 30 min. They have also reported the reaction of these monoliths with alcohols as well. A small demonstration library of ureas was prepared and after 8 min of residence time up to 76% of the alkyl amines were found to be scavenged (Scheme 8.6). 

Two types of compounds are employed as photoinitiators of free radical polymerizations, which differ in their mode of action of generating reactive free radicals. Type I initiators undergo a very rapid bond cleavage after absorption of a photon. On the other hand, type II initiators form relatively long-Hved excited triplet states capable of undergoing hydrogen-abstraction or electron-transfer reactions with co-initiator molecules that are deliberately added to the monomer-containing system. 

As far as Tl-based catalyst Is concerned, an Increase of 1-butene from 0 to 10 g/1 causes a slight Increase In S.A. MFI, Instead, goes from 1.7 to 9.1 g/10 reflecting a certain sensitivity of the Titanium toward chain-transfer ractlon with co-monomer. A different behaviour Is showed by Hf-based catalyst addition of 1-butene from 0 to 25 g/1 to the reaction mixture Is accompanied by a substantial decrease In the specific activity while Intrinsic viscosity remains almost unchanged. 

Thianthrene-di-, tri-, and tetracarboxylic acids, and a variety of their derivatives, were prepared and polymerized with co-monomers to obtain thianthiene-containing polyimides, aramids and polybenzoxazoles. The multiply substituted thianthrene derivatives were prepared starting with dichloro-substituted benzamide or phthalimide via chlorine displacement by sulfur nucleophiles. The protected carboxyl groups enhanced the displacement reaction to give thianthrene bisamides and imides in good yields. Deprotection with base gave carboxylic acid derivatives. 

The structure of the UQ-cyt c reductase, also known as the cytochrome bc complex, has been determined by Johann Deisenhofer and his colleagues. (Deisenhofer was a co-recipient of the Nobel Prize in Chemistry for his work on the structure of a photosynthetic reaction center [see Chapter 22]). The complex is a dimer, with each monomer consisting of 11 protein subunits and 2165 amino acid residues (monomer mass, 248 kD). The dimeric structure is pear-shaped and consists of a large domain that extends 75 A into the mito-... 

Photooxidation of Co2(CO)8 is a complex reaction, with major products being the simple monomers Co(02)(CO) (n = 1, 2) with the dioxygen bound side-on (rj2).89 The same products arise from reaction of Co atoms with CO and 02 at 10-12 K. 

A third type of reaction, namely CO insertion, is also described. The rate of CO insertion into the Pd-Me bond in several classical diphosphine monomers has been found to be very dependent on the nature of the ligand. Full car-bonylation of, for example, dendrimer 56-[GJ occurs when this compound is pressurized to 1 bar of CO. Experiments with 13CO corroborate the formation of the acetyl complex while insertion of norbornene into the Pd-acetyl bond can be easily performed. Dendrimers of generations 2 and 3 react similarly (Scheme 27). 

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