Synthesis of biodegradable polyesteramides with pendant functional groups

Morpholine-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 ring-opening copolymerization of either ε-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, 0,10 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 · 104. The ring-opening homopolymerization of morpho-line-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 the p-methoxybenzyl group but also in severe degradation of the copolymers, due to acidolysis of main-chain ester bonds

Analysis of irradiation processes for laser-induced periodic surface structures

The influence of errors on the irradiation process for laser-induced periodic surface structures (LIPSS) was studied theoretically with energy density simulations. Therefore an irradiation model has been extended by a selection of technical variations. The influence of errors has been found in a deviation from optimal conditions, by a shift or spread of accumulated fluence and a variation of local fluence, related to variations of the peak fluence and relative pulse intersection. The analysis of the irradiation process by energy density simulations, gives the possibility to perform realistic irradiation simulations and derive optimization strategies for the determination of irradiation parameters. This analysis is required for the application of LIPSS for surface functionalization. © 2013 The Authors

Towards Friction Control using laser-induced periodic Surface Structures

This paper aims at contributing to the study of laser-induced periodic surface structures (LIPSS) and the description of their tribological properties in order to facilitate the knowledge for contact mechanical applications. To obtain laser parameters for LIPSS formation, we propose to execute two D2-Experiments. For the transfer of results from static experiments to areas of LIPSS we propose the discrete accumulation of fluences. Areas covered by homogeneously distributed LIPSS were machined. Friction force of these areas was measured using a tribometer in a ball on flat configuration. The friction force was found to be higher on the structured area than on the initial surface

Diskussie — Kiesrechthervorming zonder grondwetswijziging?

In a reaction to ’The Implications of Proportional Representation with Eighteen Districts’ by R. Verboom {Acta Politica III: 2 Jan. 1968, p. 118-131), the author defends his proposal to divide the country into rather large districts, with a system of proportional representation and the possibility of combined party lists. This would facilitate the formation of two large political groups, which could offer real alternatives to the voters at the polls. The winning group would form the new cabinet, which would represent the will of the majority of the voters. Thus there would be no need for a directly elected prime minister as proposed by ’Democrats ’66’

Copolymerization of ε-caprolactone and morpholine-2,5-dione derivatives

Novel biodegradable poly(ester-amide)s were prepared by ring-opening copolymerization of -caprolactone and 3- and/or 6-alkyl-substituted morpholine-2,5-dione derivatives. The copolymerizations were carried out in the bulk using stannous octoate as an initiator. Molecular weights of the copolymers ranged from 1,0 · 104 to 8,3 · 104 and decreased with increasing mole fractions of morpholine-2,5-dione derivatives in the feed. 13C NMR sequence analysis indicated that the copolymers had a random distribution of -oxycaproyl and depsipeptide units, which resulted from the occurrence of transesterification reactions during copolymerization. The results of the DSC measurements and 13C NMR sequence analysis showed a close relationship between the crystallinity and average length of ε-oxycaproyl blocks. Copolymers with a mole fraction of depsipeptide units smaller than 0,20 were semi-crystalline, whereas incorporation of larger amounts of depsipeptide units resulted in amorphous copolymers. The melting point depression as a function of the molar composition of the semi-crystalline copolymers was in good agreement with the melting point depression predicted by the Baur equation, which indicated the rejection of depsipeptide units from crystals consisting of ε-oxycaproyl units

Glycine/Glycolic acid based copolymers

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 ([] = 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