Polypropylene oxidation mechanism

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

Meluch et al.10 reported that high-pressure steam hydrolyzes flexible polyurethane foams rapidly at temperatures of 232-316°C. The diamines are distilled and extracted from the steam and the polyols are isolated from the hydrolysis residue. Good results were obtained by using reclaimed polyol in flexible-foam recipes at file 5% level. Mahoney et al.53 reported the reaction of polyurethane foams with superheated water at 200°C for 15 min to form toluene diamines and polypropylene oxide. Gerlock et al.54 studied the mechanism and kinetics of the reaction... 

The biodegradation of poly(alkylene glycols) is hindered by their lack of water solubility, and only the low oligomers of polypropylene glycol) are biodegradable with any certainty (179—181), as are those of poly(tetramethylene glycol) (182). A similar exo-oxidation mechanism to that reported for poly(ethylene glycol) has been proposed. 

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. 

Reaction-induced phase separation is certainly also the reason for which an inhomogeneous structure is observed for photocured polyurethane acrylate networks based on polypropylene oxide (Barbeau et al., 1999). TEM analysis demonstrates the presence of inhomogeneities on the length scale of 10-200 nm, mostly constituted by clusters of small hard units (the diacrylated diisocyanate) connected by polyacrylate chains. In addition, a suborganization of the reacted diisocyanate hard segments inside the polyurethane acrylate matrix is revealed by SAXS measurements. Post-reaction increases the crosslink density inside the hard domains. The bimodal shape of the dynamic mechanical relaxation spectra corroborates the presence of a two-phase structure. 

Synergism with hindered amines has been less investigated. To all appearances, the first example of the synergistic mechanism of this type in the case of inhibited polypropylene oxidation was pointed out by one of the authors of the present paper as far back as 1964 (61). ... 

The photostabilization of polymers continues to be a rapidly advancing area of scientific and technological interest. Carlsson and Wileshave written several reviews on photostabilizing mechanisms in polymers, while Swasey has given an updated guide to stabilization, and Reid has discussed the effects of stabilizers in vinyl polymers. Nemzek and Mayo have predicted the service life of polypropylene, and Bredereck has reviewed the photostabilization of PVC. Several comprehensive review articles have appeared. Pospisil has reviewed in considerable depth the photo-oxidation mechanisms of phenolic anti-oxidants, Shlyapintokh has reviewed the kinetics of stabilizer distribution, Vink has... 

Polyester PUs have good material properties, but they are susceptible to hydrolytic cleavage of the ester linkage while polyether based urethanes have relatively high resistance to hydrolytic chain scission. Polyethylene oxide (PEO) based materials exhibit poor water resistance due to the hydrophilic nature of the ethylene oxide. Although the PUs mechanical properties obtained with polypropylene oxide (PPO) are not as good as those made from PTMO, PPO has also been widely used because of its low cost and reasonable hydrolytic stability [2]. 

The applications of these techniques is illustrated by data on a variety of polymers, although the bulk of the discussion concerns a typical amorphous polymer, atactic polystyrene and a crystalline polymer, polyethylene oxide. A number of results are quoted which seem to indicate that phenyl group rotations or oscillations are not an important mechanism in the relaxation of polystyrene. Other materials mentioned are polypropylene oxide, starch and ionized copoly-... 

An example of the commonly used polymer in pharmaceutical systems is the A-B-A block copolymer of polyethylene oxide-polypropylene oxide-polyethylene oxide, PEO-PPO-PEO, commercially available as Poloxamers, Pluronics (BASF). On hydrophobic drug particles or oil droplets, the polymer adsorbs with the B hydrophobic chain (PPO) close to the surface, leaving the two hydrophilic A chains dangling in solution. These nonionic polymers provide stabilization against flocculation and/or coalescence by a mechanism usually referred to as steric stabilization [9]. In order to understand the principles of steric stabilization, one must first consider the adsorption and conformation of the polymer at the solid/liquid or liquid/liquid interface. The PPO chain adsorbs on the surface with many attachment points forming small loops , whereas the A chains (sometimes referred to as tails ) extend to some distance (few nm) from the surface [10]. 

Huang and colleagues (Huang et al, 2005 Pan et al, 2008 Yang et al, 2006) studied the moisture sensitivity of types of SMPU fibers that were prepared by MHI, which was synthesized from MDI, EDO, adipic acid, ethylene glycol, ethylene oxide, polypropylene oxide (PPO) andbisphenol A. MHI did not disclose the exact SMPU formula, but it is assumed to be of PPO/MDI/BDO compositiom This chapter therefore aims to reveal the effects of heat and moisture conditions on the mechanical and thermal properties of wet-spun SMPU fibers. 

The optical activity is a very helpful tool in the study of mechanism of polymerization. The first optically active polypropylene oxide was prepared by Price (34) starting from the pure enantiomer. The preparation of optically active polymers is also possible when using the racemic monomer and proceeding in a ste-reocontrolled reaction. The pioneering work in this field was done by Inoue, Tsuruta and Furukawa (35) who demonstrated the possibility to obtain optically active polypropylene oxide from the racemic monomer using diethylzinc-d-bomeol initiator. 

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