This review covers new experimental and theoretical physical research related to the formation of polymeric membranes by phase separation of a polymer solution, and to the morphology of these membranes. Two main phase separation processes for polymeric membrane formation are discussed: thermally induced phase separation and immersion precipitation. Special attention is paid to phase transitions like liquid-liquid demixing, crystallization, gelation, and vitrification, and their relation to membrane morphology. In addition, the mass transfer processes involved in immersion precipitation, and their influence on membrane morphology are discussed.

AB block copolymers of ϵ‐caprolactone and (L)‐lactide could be prepared by ring‐opening polymerization in the melt at 110°C using stannous octoate as a catalyst and ethanol as an initiator provided ϵ‐caprolactone was polymerized first. Ethanol initiated the polymerization of ϵ‐caprolactone producing a polymer with ϵ‐caprolactone derived hydroxyl end groups which after addition of L‐lactide in the second step of the polymerization initiated the ring‐opening copolymerization of L‐lactide. The number‐average molecular weights of the poly(ϵ‐caprolactone) blocks varied from 1.5 to 5.2 × 103, while those of the poly(L‐lactide) blocks ranged from 17.4 to 49.7 × 103. The polydispersities of the block copolymers varied from 1.16 to 1.27. The number‐average molecular weights of the polymers were controlled by the monomer/hydroxyl group ratio, and were independent on the monomer/stannous octoate ratio within the range of experimental conditions studied. When L‐lactide was polymerized first, followed by copolymerization of ϵ‐caprolactone, random copolymers were obtained. The formation of random copolymers was attributed to the occurrence of transesterification reactions. These side reactions were caused by the ϵ‐caprolactone derived hydroxyl end groups generated during the copolymerization of ϵ‐caprolactone with pre‐polymers of L‐lactide. The polymerization proceeds through an ester alcoholysis reaction mechanism, in which the stannous octoate activated ester groups of the monomers react with hydroxyl groups. © 1997 John Wiley & Sons, Inc.

Five new indenyl zirconium metallocenes with 2-alkyl and 2-aryl substituents were synthesized and characterized. For the synthesis of the ligand the di-Grignard reagent 1,2-bis(magnesiomethyl)benzene dichloride was explored as a synthon to 2-substituted indenes. This procedure provides access to a variety of functionalized 2-indenylmetallocenes such as bis(2-ferrocenylindene)zirconium dichloride and bis(2-adamantylindenyl)zirconium dichloride. Crystallographic characterization of bis[2-(4-(dimethylamino)phenyl)indenyl] zirconium dichloride revealed an anti conformation with a coplanar orientation of the dimethylamino substituent to the aryl ring in the solid state. The polymerization behavior of all five zirconocene dichlorides in liquid propylene was studied in the presence of MAO at various temperatures, and the results were compared to those for the known catalyst system bis(2-phenylindenyl)zirconium dichloride/MAO (M1/MAO). The productivity of the 2-arylindene metallocenes in propylene polymerization was on the order of 100−7000 kg of PP/((mol of Zr) h). In contrast, the (2-adamantylindenyl)metallocenes exhibited very low productivities of 6 kg PP/((mol of Zr) h) in propylene polymerization.

Isothermal phase diagrams for the semicrystalline poly‐L‐lactide (PLLA) and the amorphous poly‐DL‐lactide (PDLLA) in combination with several solvent–nonsolvent combinations (dioxane/water, dioxane/methanol, chloroform/methanol, and NMP/water) have been determined. The locations of the liquid–liquid miscibility gap, the solid–liquid miscibility gap and the vitrification boundary in the isothermal phase diagrams at 25°C were identified. The liquid–liquid miscibility gap for the systems with PLLA was located in the same composition range as the corresponding systems with PDLLA. For the systems containing PLLA solid–liquid demixing was thermodynamically preferred over liquid–liquid demixing. Attempts were made to correlate the experimental findings with predictions on the basis of the Flory‐Huggins theory for ternary solutions using interaction parameters derived from independent experiments. Qualitative agreement was found between the theoretical predictions and the experimentally obtained liquid–liquid miscibility gap. No good agreement was found for the solid–liquid miscibility gap. © 1996 John Wiley & Sons, Inc.

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