Polypropylene copolymers-Appearance

Swing reactor operation, where the operating conditions are changed to make different polymers, have been considered theoretically but do not appear to have been used in practice. Dual reactors in series have been used for impact polypropylene copolymer production (Burdett, 1992). 

The dithiocarbamates have the pentacoordinate binuclear structure (44). The diamyl- and diethyl-dithiocarbamate complexes have been found to inhibit the hardening of asphalt, but the effect appears too weak to be useful.127 The latter complex is an effective antioxidant for polyethylene,128 polypropylene,129 polystyrene,130 poly(methyl methacrylate)130 and an isoprene-styrene copolymer.131 The di-n-butyldithiocarbamate complex is important in the vulcanization and injection moulding of rubber,132 as a stabilizer against photolytic and thermal degradation. 

Catalysts derived from reaction systems such as triethylaluminium-water and triethylaluminium-water-acetylacetone [225], triethylaluminium-triphe-nylphosphine [226], triethylaluminium-pyrogallol [209] and rare-earth metal phosphonate- triisobutylaluminium-glycerol [227] appeared to be effective in the copolymerisation of propylene oxide and carbon dioxide, yielding high molecular weight polypropylene ether-carbonate)s (Table 9.4) but not the respective alternating copolymer which is polypropylene carbonate). 

In addition to the AFR block polymer, there is also some copolymer of methylvinylpyridine and acrylonitrile. The amount of this copolymer varies with both the free radical temperature and the amount of benzoyl peroxide used. At room temperature, the AFR polymerization appears to be the main reaction. Both comonomers in the polymer made with inert polypropylene powder at room temperature are found at much lower levels than in the AFR polymer. Furthermore, the polar polymer made with active polypropylene at room temperature is essentially non-extractable. At 50°C. under the condition used the product isolated seemed to be a 50-50% mixture of block polymer and free copolymer. 

A number of block copolymers prepared with Ziegler-Natta catalysts have been reported however, in most cases the compositions may include significant amounts of homopolymer. The Ziegler-Natta method appears to be inferior to anionic polymerization for synthesizing carefully tailored block copolymers. Nevertheless, bock copolymers of ethylene and propylene (Eastman Kodak s Pofyallomers) have been commercialized. Unlike the elastomeric random copolymers of ethylene and propylene, these are high-impact plastics exhibiting crystallinity characteristics of both isotactic polypropylene and linear polyethylene. They also contain homopolymers in addition to block copolymers. 

The photo-oxidative degradation of polypropylene and stabilization by hindered amines has been reviewed. A study has appeared of the effect of P-carotene on the photoreactivity of anthracene in hexane solution and a kinetic scheme has been proposed to account for the photochemical and photophysical processes that occur on irradiation at 365 nm. Quenching rate constants have been determined between /S-carotene and singlet oxygen. Some characteristics have been communicated of the sensitized photo-oxidation of abietic acid contained in a vinyl butyl ether-butyl methacrylate-methacrylic acid copolymer. At 400 nm... 

Since rapid collection of erstwhile single cells can be brought about by the use of dielectrophoresis, and the shape of the mass of cells so formed is controlled by the shape of the electrodes, by the frequency of the field, and by the shape of the cells, it appeared worthwhile to see if the shapes so formed could be made more permanent, so as to prepare desired structures of the cellular aggregates. To this end, the gel-forming properties of a relatively nontoxic block copolymer solution in water were used. A concentrated aqueous solution of the block copolymer of polyethylene oxide and polypropylene oxide (PEO-PPO) is quite fluid at 0°C to about 5°C, but sets reversibly to a rather stiff gel at about 30-40°C. The PEO-PPO polymer solutions are reported to be relatively nontoxic to most organisms (Pluronic resin F-127), Wyandotte Chemicals Corp.). 

The phase transition between micellar phases of polyethylene oxide-polypropylene oxide-polyethylene oxide) (PEO-PPO-PEO) triblock copolymer in aqueous solution was investigated as a function of temperature using FTIR spectroscopy. As the temperature increases, PO blocks appear to be stretched conformers with strong interchain interactions, and the formation of a hydrophobic core in the micellar phase. The EO chains are found to change to a more disordered structure with low-chain packing density. Both the EO and PO blocks exhibit dehydration during the phase ttansition (78). 

The scratch resistance of polypropylene was improved by blending 20 wt% PPE/HIPS blend (Noryl PX0844) as a modifier and 5 % styrene-ethylene/ propylene diblock copolymer (Kraton G) as a compatibilizer (Sue 2001, 2002). It appears that the fracture energy dissipation in the PP matrix occurs by craze promotion around the dispersed particles of PPE/HIPS blend and thus preventing crack formation, while the compatibilizer promoted the PP/PPE interfacial adhesion. 

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