No abstract

Monoalkyl-and dialkyl-imidazolium surfactants were used to prepare organically modified montmorillonites with markedly improved thermal stability in comparison with their alkyl-ammonium equivalents (the decomposition temperatures increased by ca. 100°C). Such an increase in the thermal stability affords the opportunity to form syndiotactic polystyrene (s-PS)/imidazolium-montmorillonite nanocomposites even under static melt-intercalation conditions in the absence of high shear rates or solvents. Upon nanocomposite formation, s-PS exhibited an improvement in the thermal stability in comparison with neat s-PS, and the ␤-crystal form of s-PS became dominant. This crystallization response agrees with previous studies of s-PS/pyridinium-montmorillonite hybrids and is tentatively attributed to a heterogeneous nucleation action by the inorganic fillers.

This paper discusses a direct (one-pot) polymerization process to prepare isotactic polypropylene (i-PP) having a terminal functional group including Cl, OH, and NH2. The chemistry involves metallocene-mediated propylene polymerization using rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2/MAO complex in the presence of styrene derivatives (St-f), carrying a Cl (St-Cl) or a silane-protected OH (St-OSi) or a silane-protected NH2 (St-NSi2), followed by hydrogenation. Apparently, the propylene propagating chain end engages in a facile consecutive chain transfer reaction, reacting with St-f and then hydrogen, with high catalyst reactivity under the proper St-f and hydrogen concentrations. The polymer molecular weight was inversely proportional to the molar ratio of [St-f]/[propylene] with a chain transfer constant (ktr/kp) of 1/21 for St-Cl, 1/34 for St-NSi2, and 1/48 for St-OSi, respectively. Both silane protecting groups were hydrolyzed in acidic aqueous solution during the sample workup step to obtain the desirable i-PP polymers with a terminal OH and NH 2 group (i.e., PP-t-St-OH and PP-t-St-NH2). The terminal functional group was confirmed by end group analysis and chain extension reaction. Despite the high molecular weight, the terminal functional group in PP engages a coupling reaction with polycapolactone (PCL) in solution and melt to form PP-b-PCL diblock copolymers that are very effective compatibilizers in PP/ PCL polymer blends.

No abstract

This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s-PS), and elastomers, such as poly(ethylene-co-1-octene) and poly(ethylene-co-styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ϳ270°C to low glass-transition temperature ϳϪ60°C. The chemistry involves two reaction steps, including the preparation of a borane group-terminated polyolefin by the combination of a metallocene catalyst and a borane chain-transfer agent as well as the interconversion of a borane terminal group to an anionic (OO Ϫ K ϩ) terminal group for the subsequent ring-opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of ␣-olefins to the ring-opening polymerization of ethylene oxide. The well-defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (M w /M n Ͻ 2.5), and absence of homopolymer.