Vladimir Divjaković

Structure and physical properties of segmented polyurethane elastomers containing chemical crosslinks in the hard segment

Two series of segmented polyurethanes, one containing 50% soft segments and the other with 70% soft segments were synthesized. Chemical crosslinks were introduced through the hard segment in a controlled way. Chemical polyurethane networks were characterized by swelling. The effect of the degree of crosslinking on properties was examined. It was found that chemical crosslinks in the hard segment reduce the mobility of the soft phase and destroy the crystallinity of the hard phase, but they improve heat stability of the hard domains.

Effect of Nano-and Micro-Silica Fillers on Polyurethane Foam Properties:

Two series of rigid and flexible polyurethane foams were prepared with two types of silica fillers. The density of the flexible foams was 60 kg/m 3 and that of rigid 30 kg/m3. The fillers were micro-silica of the average particle size of 1.5 mm and nano-silica of the average particle size of 12 nm. The concentration of fillers varied from 0–20%. The micro-silica filler did not show any significant effect on density of either rigid or flexible foams. Nano-silica increased the density of both types of foams only at concentration above 20%. Nano-silica lowered the compression strength of both types of foams at all concentrations while micro-silica exhibited the same effect at concentrations above 10%. The hardness and compression strength in flexible polyurethane foams with nano-silica was increased and the rebound resilience decreased. Reduced density of foams was not changed by nano-silica concentrations up to 20%. It is assumed that the nano-filler, as an additional physical crosslinker, increased modulus of the flexible segment in the polyurethane matrix, resulting in increased hardness and compression strength. The micro-filler in flexible foams lowered hardness and compression strength, but increased rebound resilience. Wide angle X-ray scattering (WAXS) showed amorphous morphology of both flexible and rigid foams filled with nano-silica. WAXS of the micro-silica filled foams showed the presence of randomly oriented crystalline quartz particles and the amorphous structure of the polymeric matrix.

Crystallization and melting behaviour of PHB and PHB/HV copolymer

Abstract The crystallization and melting behaviour of bacterially produced poly(3-hydroxybutyrate) homopolymer and poly(3-hydroxybutyrate/3-hydroxyvalerate) copolymer were investigated by means of optical microscopy, wide-angle X-ray scattering and calorimetric measurements. The spherulitic growth rate and X-ray diffraction patterns were measured at various temperatures, in order to understand the temperature dependence of crystallization kinetics and the changes in the degree of crystallinity which take place on heating. Structural reorganization during heating was investigated further by means of differential thermal analysis measurements at various heating rates.

Temperature influence on changes of parameters of the unit cell of biopolymer PHB

Abstract The changes of parameters of the unit cell of biopolymer poly(β-hydroxybutyrate) (PHB) during heating from room temperature to the melting temperature are measured and results are presented here. The considerable increase of value of parameter a with increase of temperature is noticed with coefficient of thermal expansion of (≈ 1.4 ± 0.3) × 10−4°C−1. In the same time the changes of parameters b and c are negligible. On the basis of wide-angle X-ray scattering diffractograms the coefficient k is determined to be 1.06 ± 0.08 (Hermans—Weidinger method).

Effect of addition of polyethylene on properties of polypropylene/ethylene–propylene rubber blends

Toughening of polypropylene was carried out by adding two types of ethylene-propylene rubber (EPR) having different ethylene content, and three commercial types of EPR containing high density polyethylene (PE). The concentration of EPR was varied from 0–30%. Globular morphology of the dispersed phase was observed at all concentrations. Average particle size of the dispersed phase (EPR) was about 2–4 μm with about 10% within the 0.5–1 μm range. Although most of the properties were not affected by the presence of polyethylene, high notched Izod impact strength was achieved only with samples containing PE. Melt flow rate, yield strength and modulus were found to decrease almost linearly with increasing elastomer concentration in the blend. Elongation at break was enhanced by the addition of EPR, particularly those containing PE. The contribution of PE to the properties was explained by the specific EPR/PE particle morphology (core-shell or interpenetrating) but the exact mechanism of toughening of PP with EPR in the presence of PE is not clear.

Transition metal complexes with the thiosemicarbazide-based ligands—I. Nickel(II) complexes with the quadridentate ligands based on S-methylisothiosemicarbazide; X-ray crystal structure of (acetyl-acetone N(1)-salicylidene-S-methylizothiosemicarbazonato) nickel(II)

Abstract The reaction of a warm ethanolic solution of [Ni(SALSMeTSC-H)Py]Cl·0.5Py (SALSMeTSC = salicylaldehyde S-methylisothiosemicarbazone) with salicylaldehyde and acetylacetone (HACAC), yielded the corresponding square-planar complexes [Ni(SAL 2 SMeTSC-2H)] ( A ) and [Ni(SALACACSMeTSC-2H)] ( B ) (SAL 2 SMeTSC, and SALACACSMeTSC = quadridentate 2O2N ligand: N(1),N(3)- bis (salicylidene)-S-methylisothiosemicarbazide, and acetylacetone N(1)-salicylidene-S-methylisothiosemicarbazone, respectively). An X-ray analysis of complex B showed that in the reaction of the starting complex with HACAC a rearrangement of the salicylaldehyde moiety takes place (while the CN(3) bond of the azomethine group is ruptured) and its binding to the N(1) nitrogen. At the same time, HACAC is simultaneously bonded to the liberated N(3)-nitrogen of the hydrazine fragment. Crystal data for the complex B (NiC 14 H 15 N 3 O 2 S) are: M r = 348.0, orthorhombic, space group Pna2 1 , a = 7.484(3), b = 21.995(8), c = 8.866(3) A; V = 1459.44 A 3 , Z = 4, F (000) = 720, Dc = 1.58 g cm −1 , Do = 1.56 g cm −1 , μ(MoKα) = 14.45 cm −1 . The structure was solved by the heavy-atom method and refined anisotropically to an R value of 0.078 for 1174 non-zero reflections. The complex molecules are planar, the NiNi distance of nearest molecules being about 3.76 A. The compounds have been characterized by elemental analysis as well as by IR and electronic spectra.

Enantiodivergent synthesis of cytotoxic styryl lactones from d-xylose. The first total synthesis of (+)- and (−)-crassalactone C

Abstract Enantiodivergent total syntheses of both (+)- and (−)-enantiomers of goniofufurone, 7- epi -goniofufurone and crassalactone C have been accomplished starting from d -xylose. The key steps of the synthesis of 7- epi -(+)-goniofufurone were a stereo-selective addition of phenyl magnesium bromide to a protected dialdose, and a stereospecific furano–lactone ring formation by reaction of a related hemiacetal derivative with Meldrums acid. Synthesis of both (+)-goniofufurone and (+)-crassalactone C required a configurational inversion at C-5 in the common intermediate that was efficiently achieved under the standard Mitsunobu conditions, or alternatively through a sequential oxidation of the benzylic hydroxyl group followed by a stereo-selective reduction with borohydride. A similar approach was then applied to the synthesis of the unnatural (−)-enantiomers of goniofufurone, 7- epi -goniofufurone and crassalactone C, as well as two novel, conformationally constrained analogues of both (+)- and (−)-goniofufurone. Their in vitro antiproliferative activities against a number of human tumour cell lines were recorded and compared with those observed for the parent natural products.

Analysis of N—H ··· O hydrogen bonds in new C(O)—NH—P(O)-based phosphoric triamides and analogous structures deposited in the Cambridge Structural Database

Five new compounds belonging to the phosphoric triamide family have been synthesized: two of them with the formula XC(O)NHP(O)Y [X = CF3 (1) and CClF2 (2), Y = NHCH2C(CH3)2CH2NH] involving a 1,3-diazaphosphorinane ring part, and three 2,6-Cl2C6H3C(O)NHP(O)Z2 phosphoric triamides [Z = NHC(CH3)3 (3), N(CH3)(C6H11) (4) and N(CH3)(CH2C6H5) (5)]. The characterization was performed by (31)P{(1)H}, (1)H, (13)C NMR, IR spectroscopy besides (19)F NMR for fluorine containing compounds (1) and (2), and X-ray single-crystal structure analysis for (1), (3), (4) and (5). In each molecule the P atom has a distorted tetrahedral environment. The N atoms bonded to P atom have mainly sp(2) character with a very slight tendency to a pyramidal coordination for some amido groups. Different types of N-H···O hydrogen bonds have been analyzed for (1), (3), (4) and (5) and 118 other structures (including 194 hydrogen bonds) deposited in the Cambridge Structural Database, containing either C(O)-NH-P(O)[N(C)(C)]2 or C(O)-NH-P(O)[NH(C)]2. The participation of N(CP)-H···O=P [N(CP) = the nitrogen atom of the C(O)-NH-P(O) fragment], N-H···O=P, N-H···O=C and N(CP)-H···O=C hydrogen bonds in different hydrogen-bonded motifs are discussed. Moreover, the involvement of the O atoms of C=O or P=O in the [N(CP)-H][N-H]···O=P, [N-H]2···O=P, [N-H]2···O=C and [N-H]3···O=C groups are considered. A histogram of N···O distances, the distribution of N-H···O angles and the scatterplot of N-H···O angles versus N···O distances are studied.

Conformationally constrained goniofufurone mimics as inhibitors of tumour cells growth: Design, synthesis and SAR study.

Synthesis of conformationally restricted (+)-goniofufurone (1) and 7-epi-(+)-goniofufurone (2) analogues, with embedded O-isopropylidene, O-methylidene or cyclic carbonate functions is disclosed starting from d-glucose. A number of potential bioisosteres of 1 and 2 bearing both 5,7-O-methylidene and 4-substituted cinnamoyloxy functions at the C-7 position have also been synthesized. In vitro cytotoxicity of target molecules against a number of human tumour cell lines were recorded and compared with those observed for the parent molecules 1 and 2. Some of the analogues displayed powerful antiproliferative effects on selected human tumour cell lines, but all of them were devoid of any cytotoxicity towards the normal foetal lung fibroblasts (MRC-5). A SAR study reveals the structural features of these lactones that may increase their antiproliferative activity.

N,N′-Dicyclo­hexyl-N′′-(4-nitro­benzo­yl)phospho­ric triamide

The P atom in the title compound, C19H29N4O4P, exhibits a tetrahedral coordination and the phosphoryl and carbonyl groups are anti to each other. Adjacent molecules are linked by N—H⋯O hydrogen bonds to form a layer motif.