Most of animal and plant tissues can be regarded as natural composites made of rigid and soft components. Some of them, such as nacre, bone, or enamel, correspond to mineral-polymer composites, and others, such as the plant cell wall or tendon, correspond to polymer-polymer composites. It has been believed for a long time that the outstanding mechanical properties of these natural composites are due to well-organized geometric and chemical interactions between the rigid and soft components. Recent studies [1][2][3][4][5][6][7][8][9][10][11] have reported that many natural composites with high mechanical strength can be characterized by the following structural features: (i) consisting of an alignment of elongated stiff particles or stiff fibers (often on the scale of micrometers to nanometers), embodied in a flexible matrix of soft component, and (ii) existence of the tight interface between the stiff element and the soft matrix; these features conform with the design principle of industrial composites, such as fiberglass reinforced plastics. In addition, some researchers 9,10 propose that high viscoelasticity and well-developed hierarchy of structure, which are inherent in the animal and plant tissues, also enhance their bulk and adhesive strength.Recently, novel hydrogels, which seem to be analogous to the cartilage and other natural composites, have been developed. 12 The gels were named as "double-network (DN) gel"
Upon irradiation of 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TM DPO) with U.V. light in 0,-free benzene solution a doublet indicative of phosphorus-centred radical? was observed. By this technique x-scission of TM DPO yielding the diphenylphosphinoyl radical (Ph,P=O) was directly evidenced. This radical was found to add to the carbonyl group? of intact TMDPO with k = 1.6 x 1 O7 M-I s-' forming a radical of the general structure A[Ph,P(O)]COP(O)Ph, (A: 2,4,6-trimethylbenzoyl). In the timeresolved measurements CI DEP due to the radical-pair mechanism was observed.
Eighteen binary metal oxides consisting of TiO2–MmOn, ZnO–MmOn and Al2O3–MmOn (MmOn: metal oxide) were prepared by the usual co-precipitation method, their acid amounts and strengths being determined by n-butylamine titration using various acid-base indicators. The acid strengths of fourteen of the tested binary oxides of molar ratio 1 : 1 were found to be remarkably higher than those of the component single oxides. High acid strengths were as follows: H0≤−8.2 for TiO2–SiO2, H0≤−5.6 for TiO2–Al2O3 and Al2O3–ZrO2 and H0≤−3 for TiO2–CdO, TiO2–SnO2 and ZnO–SiO2. The acid amounts of sixteen binary oxides were larger than those of the component oxides. The effect of the composition of binary oxides on acidity was examined for TiO2–Al2O3, ZnO–Al2O3 and Al2O3–ZrO2. The acidity maxima appearing for TiO2–Al2O3 and ZnO–Al2O3 were found to be of molar ratio\simeq9:1 and for Al2O3–ZrO2\simeq3:2. A fairly good correlation has been demonstrated between the observed highest acid strengths and the average electronegativities of metal ions of binary oxides.
Phosphonyl radicals of the structure O=$R1 (R2) with R1 and Rz: C6&(l); C$&, OCH(CH3 )2 (2); CH,, OCH, (3); OCH, (4) and O q & (5) were generated by UV-photolysis of appropriate acylphosphine oxides or acylphosphonates which are effective initiators of the free radical polymerization of o l e f i c compounds. All five radicals are very reactive towards monomers such as methacrylonitrile, styrene and methyl methacrylate (kR'+M = 5 . lo7 to 2.10s 1. mol-' . s -l ) , as was found by employing laser flash photolysis techniques. In the cases of acrylonitrile, methyl acrylate, butyl vinyl ether, and vinyl acetate kR'+M ranged from 106 -lo7 1 * mol-ls-l. The high reactivity of the radicals 1-5 is due to their tetrahedral structure. The Q-e scheme of Alfrey and Price proved useful to recognize trends in the dependence of kR'+M on the chemical nature of both phosphonyl radicals and monomers.
0025-1 16X/85/%03.001. mol-' . cm-l at 425 nm and @(T) = l,O. The maximum laser output at 1 = 347 Actinometry was performed with solutions of benzophenone (1,15
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