Polypropylene production schemes

The triblock terpolymer polypropylene oxide)-h-poly[2-(dimethylami-no)ethyl methacrylate]-b-poly[oligo(ethylene glycol) methacrylate], PPO-fc-PDMAEMA-fc-POEGMA, was prepared using the PPO macroinitiator followed by the addition of CuCl, HMTETA, and DMAEMA for the polymerization of the second block and finally OEGMA for the synthesis of the final product (Scheme 54) [128]. 

A flow scheme of polypropylene production involving the slurry process with the removal of catalyst residues from the polymer is presented in Figure 3.52 [51],... 

Figure 3.53 Flow scheme of polypropylene production using the slurry polymerisation process...

Starting from the degradation studied on labeled polypropylene the scheme presented in Fig. 13 could be conceived [69]. The studies on the UV exposure of polypropylene confirm this mechanism [70]. However, the differences in the oxidation product abundances was noticed [70] because of the unlike energetic conditions and the specific contributions of degrading factors that act in weathering investigations (Fig. 14). 

In the case of the polyolefins, random chain scission is initially the dominant process. This is shown typically for polypropylene in Scheme 2. However some low molar mass oxidation products are formed via vicinal hydroperoxides in both PP and PE [20]. The alkoxyl radicals formed by decomposition of the hydroperoxides contain weak carbon-carbon bonds in the a positions to the hydroperoxide groups, which lead to the formation of low molecular weight aldehydes and alcohols that rapidly oxidise further to carboxylic acids. These are biodegradable species, similar to products formed by hydrolysis of aliphatic polyesters and, as in the case of cis-PI, they are rapidly bioassimilated to give cell biomass (see below). 

Microwave-assisted reactions allow rapid product generation in high yield under uniform conditions. Therefore, they should be ideally suited for parallel synthesis applications. The first example of parallel reactions carried out under microwave irradiation conditions involved the nucleophilic substitution of an alkyl iodide with 60 diverse piperidine or piperazine derivatives (Scheme 4.22) [76]. Reactions were carried out in a multimode microwave reactor in individual sealed polypropylene vials using acetonitrile as solvent. Screening of the resulting 2-aminothiazole library in a herpes simplex virus-1 (HSV-1) assay led to three confirmed hits, demonstrating the potential of this method for rapid lead optimization. 

In 1993 we have published a method which met most of these requirements and for the first time allowed for the large-scale synthesis of dendrimers [2], Since that time, each of the steps have been optimized in the reaction scheme. In this chapter, we present state-of-the-art procedures for the large-scale production of the polypropylene imine) dendrimers. 

The resolution of racemic FTC butyrate (34) was required for the synthesis of the antiviral drug emtricitabine (Emtriva) (Scheme 7.15) a nucleoside reverse transcriptase inhibitor targeted for treatment of human immunodeficiency virus (HIV) and hepatitis infections [35]. The racemic FTC butyrate ester (34) was treated with immobilized cholesterol esterase, which cleaved the required isomer to the corresponding alcohol (-) 35 with 91% and 52% conversion [36]. The product was isolated as the hydrochloride salt to give 31% yield (98% ) from the 8 kg demonstration. The esterase was immobilized by precipitation onto an accurel polypropylene support using acetone followed by cross linking with glutaralde-... 

A conceptual question is whether simple octahedral or even tetrahedral complexes that have a dynamic Lewis-basic pendant group, donating a pair of electrons to the metal center, are suitable for the production of an elastomeric polypropylene. As shown in Scheme 7, a dynamic equilibrium may take place between a tetrahedral and an octahedral configuration (X=halide, E=donor group with a lone electron pair, R=C, N, P, or other anionic bridging group). (A plausible frans-octahedral complex, which can be formed in this type of dynamic process, is unable to perform the olefin insertion and has no catalytic activity [5,20,80,81].)... 

A miktoarm star copolymer carrying one PS arm and two polypropylene oxide) arms126 was prepared by the method given in Scheme 56. Living PS chains were end-capped with one unit of DPE, to reduce the reactivity of the chain end, followed by the addition of epichlorohydrin to produce the epoxide functionalized polymer. It was shown by SEC analysis and chemical titration that the epoxide content of the final product was 95 wt %. The desired functionalized... 

The fundamental reaction mechanism for the free-radical oxidation of hydrocarbons has been used to relate the consumption of oxygen to the formation of oxidation products in polypropylene. A kinetic interpretation is based on the steady-state approximation equating the rates of the initiation and termination reactions. With this approach it is possible to derive mathematical equations describing the consumption of oxygen or the formation of specific oxidation products. To solve the equations it is necessary to determine the most likely route for initiation of oxidation. The initiation mechanism chosen is the bimolecular reaction of hydroperoxides, reaction (1 ) of Scheme 1.55, with a rate coefficient k. ... 

One of the obvious features of the oxidation of polypropylene is the formation of hydroperoxides (reaction (3) in Scheme 1.55) as a product. The initiation of the oxidation sequence is usually considered to be thermolysis of hydroperoxides formed during synthesis and processing (shown as the bimolecular reaction (1 ) in Scheme 1.55). The kinetics of oxidation in the melt then become those of a branched chain reaction as the number of free radicals in the system continually increases with time (ie the product of the oxidation is also an initiator). Because of the different stabilities of the hydroperoxides (e.g. p-, s- and t- isolated or associated) under the conditions of the oxidation, only a fraction of those formed will be measured in any hydroperoxide analysis of the oxidizing polymer. The kinetic character of the oxidation will change from a linear chain reaction, in which the steady-state approximation applies, to a branched-chain reaction, for which the approximation might not be valid since the rate of formation of free radicals is not... 

Scheme 3.1. Formation of oxidation products in the degradation of polypropylene through the tertiary hydroperoxide intermediate that may he identified by MIR spectroscopy (often combined with derivatization). After Blakey (2001).

Amorphous and semi-crystalline polypropylene samples were pyrolyzed in He from 388°-438°C and in air from 240°-289°C. A novel interfaced pyrolysis gas chromatographic peak identification system was used to analyze the products on-the-fly the chemical structures of the products were determined also by mass spectrometry. Pyrolysis of polypropylene in He has activation energies of 5-1-56 kcal mol 1 and a first-order rate constant of JO 3 sec 1 at 414°C. The olefinic products observed can be rationalized by a mechanism involving intramolecular chain transfer processes of primary and secondary alkyl radicals, the latter being of greater importance. Oxidative pyrolysis of polypropylene has an activation energy of about 16 kcal mol 1 the first-order rate constant is about 5 X JO 3 sec 1 at 264°C. The main products aside from C02, H20, acetaldehyde, and hydrocarbons are ketones. A simple mechanistic scheme has been proposed involving C-C scissions of tertiary alkoxy radical accompanied by H transfer, which can account for most of the observed products. Similar processes for secondary alkoxy radicals seem to lead mainly to formaldehyde. Differences in pyrolysis product distributions reported here and by other workers may be attributed to the rapid removal of the products by the carrier gas in our experiments. 

Pseudomonas cepacia (Amano PS-30) lipase immobilized on polypropylene beads was the key enzyme in a Bristol-Meyers Squibb process for the production of a HMG-CoA reductase inhibitor (Scheme 9) [68]. Racemic lactone rac-... 

Another Bristol-Meyers Squibb process represents an enzymatic route for the production of side-chain precursors of Paclitaxel (33, Scheme 10) [69]. Racemic czs-azetidinone acetate (rac-31) is subjected to the hydrolytic treatment of Pseudomonas cepacia lipase (PCL), which is used in its immobilized form on polypropylene beads. Thus, (3R,4S)-acetate 31 can be obtained in high ee as well as the remaining alcohol 32. The process takes place in 150 1 reactors where 1.2 kg mc-31/batch can be resolved with a hydrolysis rate of 0.12 g/lh. Lowering the reaction temperature to 5 °C after full conversion causes (3R,4S)-31 subsequently to crystallize. Due to the immobilization, the enzyme can be reused for at least ten cycles without any loss of activity, productivity, or optical purity of the product. Paclitaxel is finally accessible by further chemical steps. 

Low molecular weight dicarboxylic acids, keto acids and hydroxy acids have been shown to form as photooxidation products of polyethylene and polypropylene. These are almost certainly formed by intramolecular reactions of alkylperoxyl and peracyl radicals shown typically in Scheme 3.7. Back-biting along the aliphatic chain gives rise to unstable hydroperoxides and the elimination of small molecular fragments. It will be seen in Chapter 5 that these low molar mass oxidation products, which are already present in the environment from natural sources, are the first point of microbial attack in the surface of environmentally degraded polymers, leading to oxidation initiated bioerosion (Chapter 5). 

A general scheme for the production of such functionalized polymers can be presented as follows The polymer support (polyethylene (PE), polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (FIFE), ethylene-propylene copolymers (CEP), etc.) are subjected to mechanical, chemical, radiation-chemical ( -irradiation or with accelerated electrons) or high-frequency (HF), UV-irradiation treatment with a subsequent grafting of the appropriate monomers ... 

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