Isotactic polypropylene oxide

Stabilizing Activity of Pyrocatechols in Thermal Oxidation and in y-Irradiation of Polypropylene. It is interesting to compare the relationships found on stabilizing isotactic polypropylene oxidized over the melting temperature with the results of our previous study (22, 23) of the stabilizing properties of some derivatives of pyrocatechol in y-irradiated polypropylene. 

C 0 chain. The four planar isotactic structures of polypropylene oxide may be designated for convenience as d (up), d (down), l (up) and l (down) isotactic structure 12). The d (up) and d (down) structures are superimpos-able by turning the polymer chain end-over-end so are the l (up) and l (down) structures. In crystallization of isotactic polypropylene oxide obtained from polymerization of racemic monomer, all the four chain structures may be able to fit together in the crystal without a serious packing difficulty because the oxygen and methylene groups are isoelectronic and are of similar size 12). 

The isolated polyether matrix was modeled using polypropylene glycol (2000 MW) and isotactic polypropylene oxide. The polypropylene glycol was degassed and placed over molecular sieves to remove residual water present in the polyol. The isotactic polypropylene oxide was isolated by repeated crystallization from acetone (9). Inherent viscosity was 1.85 in benzene (0.5% concentration) at 25°C. Films of the isotactic polypropylene oxide were cast onto glass plates (cleaned as described previously) from a 6% solution of the polymer in N,N-dimethylformamide, dried in a forced air draft oven for 1 h at 75°C, and then placed in a vacuum desiccator (0.1 mm mercury) for 24 h to insure complete removal of residual solvent. 

The introduction of oxygen into the hydrocarbon chain of polymers rednces their thermal stability. This trend is illustrated by the examples of polyformaldehyde (T g = 170 "C), polyethylene oxide (PEO Tjg= 345 °C), isotactic polypropylene oxide (iPPO Tjg = 195 °C) and atactic polypropylene oxide (T = 295 "C) here thermal resistances are lower than those in the corresponding hydrocarbon polymers, namely polyethylene (T g = 406 "C) and polypropylene (T g = 390 °C). 

Elame ionisation detection/detector Eourier-transform infrared spectroscopy Gas chromatography/gas chromatogram Gas chromatography-mass spectrometry Gel permeation chromatography High-density polyethylene Hexamethyl cyclotrisilazone Isotactic polypropylene Isotactic polypropylene oxide... 

Due to the large size of the calixarene molecules, they were also used for the synthesis of stereoregular polymers. Thus, neodymium complex containing the calixarene 32 was active in the formation of isotactic polypropylene oxide (Scheme 4.20) [80]. 

The isolated polyether matrix was modeled through the use of polypropylene glycol (2000 MW) and isotactic polypropylene oxide. 

A HEWLETT-PACKARD 5950B ESCA spectrometer was utilized in the ESCA studies of solvent cast block copolyether-urethane-urea, copolyurethane-urea, polyurea and isotactic polypropylene oxide films. The samples were allowed to come to equilibrium at 10" Torr at 300°K prior to data collection. The X-rays from the Al(K j 2) line at 1487 eV were used. Samples were scanned 10 times witft a scan width of 20 eV centered around elemental spectra of interest C(ls) 290-270 eV N(ls) 405-385 eV 0(ls) 540-520 eV. Radiation damage was evaluated by overlaying the carbon spectrum obtained first for each sample and one obtained after all other elements of interest were scanned. Differences in spectra were within experimental error, therefore radiation damage was considered to be negligible for the qualitative studies. All bands were referenced to the 285 eV band of the C(ls) spectrum for each sample. Peak areas were determined digitally and by planimeter. 

Additive-free film samples of isotactic polypropylene (iPP, 30pm Himont Profax resin) and polyethylenes (LLDPE, 120ym, linear low density DuPont Sclair resin, and UHMW-PE, 120wm, ultra high molecular weight, high density Himont LSR 5641-1B resin) were oxidized by exposure in air to y-radiation (AECL Gamma Cell 220, 1.0... 

Oxidative degradation of polypropylene chemically incorporates oxygen to the polymeric chains. Why would an isotactic polypropylene be less susceptible to this type of degradation than one that is atactic ... 

The oxidation rate of 0.5 gram atactic polypropylene with 0.02M cobalt acetate in 10 ml. of a 1/1 mixture by volume of chlorobenzene and acetic acid increases from 2.7 X 10"4 to 2.76 X 10"8 mole kg. 1 sec."1 in the presence of 0.04M sodium bromide. The rate of powdered isotactic polypropylene under the same conditions increases only from 2.05 X 10"8 to 2.45 X 10"3 mole kg. 1 sec. 1 in the presence of sodium bromide. 

A very important field of polymerization, stereospecific polymerization, was opened in 1955. In this year, Natta and his coworkers (1—3) polymerized a-olefins to crystalline isotactic poly-a-olefins with the Ziegler catalyst, and Pruitt and Baggett (4,5) polymerized dl-propylene oxide to crystalline polypropylene oxide, which was later identified as an isotactic polymer by Price and his coworkers (6,7). Since then, a large number of compounds including both unsaturated and cyclic compounds were polymerized stereospecifically and asymmetrically. Development of the stereospecific polymerization stimulated... 

In all of the above discussions we have treated only the monomers with carbon-carbon double-bonds. It is probable that polymers of non-oleftnic monomers such as polypropylene oxide (103, 104, 105) poly-ethylidene (106, 107, 108, 109) and polyaldehydes (110, 111) polymerize to isotactic structures by the same mechanism. The same correlation of ionicity of the catalysts with the isotactic structures and syndiotactic structures should also be possible. 

In this section we will discuss the molecular structure of this polymer based on our results mainly from the solid-state 13C NMR, paying particular attention to the phase structure [24]. This polymer has somewhat different character when compared to the crystalline polymers such as polyethylene and poly(tetrameth-ylene) oxide discussed previously. Isotactic polypropylene has a helical molecular chain conformation as the most stable conformation and its amorphous component is in a glassy state at room temperature, while the most stable molecular chain conformation of the polymers examined in the previous sections is planar zig-zag form and their amorphous phase is in the rubbery state at room temperature. This difference will reflect on their phase structure. 

The crystalline fraction was found to be formed via a cleavage of the C1g-0(CH2—O) bond in the monomer molecule and proved many years ago to be an isotactic polymer (with regular head-to-tail linkages) (Figure 9.1) [42]. The structure of the amorphous fraction, on the other hand, varies depending on the kind of catalyst. Some amorphous polypropylene oxide)s prepared with catalysts such as diethylzinc-methanol [43] or aluminium isopropoxide-zinc chloride [44] consist of regular head-to-tail linked units, but they are atactic (the mole fraction of isotactic diads is less than 0.6) [43]. Some other amorphous polypropylene oxide)s obtained with catalysts derived from reactions in the diethylzinc-water [44,45], and triethylaluminium-water [46] systems, and with aluminium isopropoxide [44], have been found to be irregular, i.e. to contain head-to-head and tail-to-tail enchained monomer units. 

For most polymers, the yield of hydroperoxides is relatively low even in the presence of oxygen excess. The relatively high values were, e.g., obtained during oxidation of atactic polypropylene [79], In the initial phases of oxidation, the yield of hydroperoxide related to 1 mol of oxygen absorbed is 0.6 at 130 °C when passing the maximum concentration it decreases considerably. In isotactic polypropylene, the maximum yield of hydroperoxides attains the value 0.2, only [80]. This may be probably related with a local accumulation of hydroperoxides in domains of defects in the crystalline structure which leads to an increased ratio of participation of hydroperoxide groups in the chain reaction of an oxidation process (induced decomposition of hydroperoxides) and finally to a lower yield of hydroperoxides... 

This paper describes the theory which permits us to characterize adequately the stereosequence length in stereoregular polymers from the equilibrium percent crystallinity at room temperature and from the melting points of the polymers. Results based on this theory are given on the characterization of the isotactic stereosequence length in the crystalline fractions of polypropylene oxide polymers made from the following catalyst systems (a) ferric chloride (17, 19) (b) diethyl zinc-water (10) (c) diethyl zinc-water-isopropylamine (d) diethyl zinc-water-cyclohexylamine (14). 

About 45% of the propylene produced is used for the production of isotactic polypropylene. About 10% fractions of the total are consumed for each of acrylonitrile production, the preparation of the oxo-alcohols, for propylene oxide, and for cumene (isopropylbenzene) production. 

In the example we elaborate here, we focus on oxyfluorinated iPP (e.g. oxy-fluorinated isotactic polypropylene films, SOLVAY ELTEX P KL 177 obtained from SOLVAY ALKOR-DRAKA Snc.). In principle, corona treated iPP films can be utilized similarly well. The freshly oxidized films are cut into small lxl cm2 sized samples and are inserted quickly after mounting to the metallic sample puck (using a minute amount of a fast curing epoxy). 

In macromolecular chemistry helically wound carbon chains are well known. In isotactic polypropylene (Fig. 6) the methyl groups are arranged on a helix. Some other chiral polymers form helices, like polymethylmethacrylate, polytriphenylmethyl-methacrylate poly-l,2-butadiene and poly-tert-butylethylene oxide... 

U.V. Makedonov, A.Z. Margolin, H.la. Rapoport, LS. Shibriaeva About the reasons of the change of effective constants of the rate of reactions of continuation and chains breaks in the period of oxidation induction of isotropic and oriented isotactic polypropylene////zg/zzzzo/eczz/z7r compounds (1986), 28 (A), No 7, 1380-1386 (in Russian). 

Alternative sources of acidic species during the oxidation of isotactic polypropylene have been suggested from mass-spectrometric analysis of thermal-decomposition products from polymer hydroperoxides (Commerce et al, 1997). Acetone, acetic acid and methanol comprised 70% of the decomposition products, suggesting either a high extent of oxidation involving secondary hydroperoxides or direct reactions of hydroxyl radicals with ketones (derived through reactions discussed in the next section). 

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