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.

SUMMARYMorpholine-2,5-dione derivatives having substituents with benzyl-protected carboxylic acid, benzyloxycarbonyl-protected amine and p-methoxy-protected thiol groups, respectively, were prepared in 29-58% yield by cyclization of the corresponding N-[(2RS)-bromopropionyl]-L-amino acids. Polyesteramides with protected pendant functional groups were obtained by ringopening copolymerization of either &-caprolactone or DL-lactide with morpholine-2,5-dione derivatives having protected functional substituents. The copolymerizations were carried out in the bulk at 130°C using stannous octoate as an initiator and using low mole fractions (0,05, 0,lO and 0,20) of morpholine-2,5-dione derivatives in the feed. The molecular weight of the resulting copolymers ranged from 1,4 to 8,3 . lo4. The ring-opening homopolymerization of morpholine-2,5-dione derivatives with protected functional substituents was not successful. Polyesteramides with either pendant carboxylic acid groups or pendant amine groups were prepared by catalytic hydrogenation of the corresponding protected copolymers. Treatment of copolymers having pendant p-methoxybenzyl-protected thiol groups with trifluoromethanesulfonic acid resulted not only in the removal of thep-methoxybenzyl group but also in severe degradation of the copolymers, due to acidolysis of main-chain ester bonds.

In this communication we describe the synthesis of a novel class of highly preorganized host molecules in which the structural features of the calix[4]arenes and spherands are combined (calixspherand a), together with the complexation with alkali cations. The hexa-anisyl spherand 1 represents a macrocyclic host with an enforced cavity in which Li+ or Na+ cations are complexed with a very high thermodynamic stability.' Cram and co-workers have shown that these complexes of 1 with Li+ and Na+ are also kinetically very stable. However, the scope of complexation is Organic Chemistry,

Glycine/glycolic acid based biodegradable copolymers have been prepared by ring‐opening homopolymerization of morpholine‐2,5‐dione, and ring‐opening copolymerization of morpholine‐2,5‐dione and glycolide. The homopolymerization of morpholine‐2,5‐dione was carried out in the melt at 200°C for 3 min using stannous octoate as an initiator, and continued at lower reaction temperatures (100–160°C) for 2–48 h. The highest yields (60%) and intrinsic viscosities ([η] = 0.50 dL/g; DMSO, 25°C) were obtained after 3 min reaction at 200°C and 17 h at 130°C using a molar ratio of monomer and initiator of 1000. The polymer prepared by homopolymerization of morpholine‐2,5‐dione was composed of alternating glycine and glycolic acid residues, and had a glass transition temperature of 67°C and a melting temperature of 199°C. Random copolymers of glycine and glycolic acid were synthesized by copolymerization of morpholine‐2,5‐dione and glycolide in the melt at 200°C, followed by 17 h reaction at 130°C using stannous octoate as an initiator. The morphology of the copolymers varied from semi‐crystalline to amorphous, depending on the mole fraction of glycolic acid residues incorporated. © 1994 John Wiley & Sons, Inc.

Polydepsipeptides with alternatiii .a-hydroxy acid and a-amino acid residues were synthesized by ring-opening polymerization 3 I morpholine-2,5-dione derivatives. The polymerizations were performed in the melt using stannous octoate as an initiator. Molecular weights of the polydepsipeptides obtained ranged from 0,9 . lo4 to 1,4 * lo4. Morpholine-2,5-dione derivatives unsubstituted at the &position gave polymers with the highest molecular weights. Poly((S)-alaninealt-glycolic acid) was semi-crystalline,. whereas all other polydepsipeptides synthesized were amorphous. Morphoiine-2,5-dione derivatives were synthesized by N-acylation of glycine, (S)alanine or (5')-valine with chloroacetyl chloride or (R,S)-2-bromopropionyl bromide, followed by ring-closure of N-(2-halogenacyl)-amino acid sodium salts in the melt in 4 to 83% yield. Low yields in the cyclization reaction of N-(2-halogenacyl)-(S)-valine were accompanied by the formation of the corresponding polydepsipeptides in 13 to 46% yield, with molecular weights ranging from 3,3 . 104 to 4,9 -lo4. 0 1990, HUthig & Wepf Verlag, Base1CCC 0025-1 16X/90/$03.00