SYNOPSISAn alternating copolymer of N-methylmaleimide and isobutene was produced by a radical precipitation polymerization method. The copolymer thus produced is a new class of transparent polymeric material that shows a unique balance of optical, thermal, and mechanical properties. The visible light transmittance was more than 90% and the stress optical coefficient was smaller than that of polycarbonate, leading to moldings with lower birefringence. The heat deflection temperature of the copolymer was as high as 157"C, and the thermal expansion coefficient was about 30% smaller than those of poly(methy1 methacrylate) and polycarbonate. The copolymer showed excellent mechanical properties, specifically, the flexural modulus was the highest among the typical amorphous polymers. 0 1996
SUMMARY: Ethylene homo-and copolymerization with 1-hexene were performed in the presence of diphenylmethylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Cp)(Flu)ZrCl 2 ) derivatives activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH N B(C 6 F 5 ) 4 )/triisobutylaluminium (iBu 3 Al) or methylaluminoxane (MAO) to study the role of the substituent on activity, comonomer incorporation and molecular weight. C 1 symmetric metallocenes which have several substituents in b-position of the cyclopentadienyl ligand produce lower molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst at 200 8C, whereas the copolymerization reactivity is significantly influenced by the volume of the substituent: the trimethylsilyl substituted derivative produces ethylene/1-hexene copolymers with a broad chemical composition distribution. Polyethylene obtained with the diphenylmethylidene(cyclopentadienyl)(indenyl)zirconium dichloride (Ph 2 C(Cp)(Ind)ZrCl 2 ) based catalyst is branched, and the molecular weight distribution and the chemical composition distribution are significantly affected by the cocatalyst. C s symmetric metallocenes which have alkyl substituents in 2,7 position of the fluorenyl ligand produce higher molecular weight copolymers than the Ph 2 C(Cp)(Flu)ZrCl 2 catalyst with equal copolymerization reactivity.
SynopsisAnion exchange membranes with excellent durability were prepared by chemical modification of Nafion. The modification was achieved by transformation of the sulfonic acid group into quaternary ammonium group. Namely, Nafion membrane was first converted into an amide-type membrane. Reduction of the carbonxyl group to methylene followed by quaternarization with alkyl iodide resulted in the formation of an anion exchange membrane. The electric resistance of the resulting membranes depends on the equivalent weight of the starting membranes (4.4-6.0 12 cm2 in 0.5N NaCl). The characteristics of the membranes are the excellent stability toward chemical substances such as organic solvents, oxidizing agents, acids, etc. For example, the membranes are stable in aqueous saturated chlorine solution a t 60°C for 1000 hr.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.