SUMMARY: Vinylcyclopropanes are important synthetic intermediates in organic chemistry and are mostly synthesized by the simultaneous introduction of the cyclopropane and the vinyl unit, e. g., by the reaction of trans-1,4-dihalobutenes with b -dicarbonyl compounds or the addition of carbenes to dienes. The polymerization of vinylcyclopropane itself results in vinyl polymers with predominantly 1,2-structural units. The radical polymerization of substituted vinylcyclopropanes results in polymers with mainly 1,5-ring-opened units, whereby radical stabilizing substituents or electron-withdrawing groups increase the radical polymerizability and the ring-opening ability. The vinylcyclopropanes undergo a radical copolymerization with other vinyl monomers, such as methacrylates, and, in comparison to the polymerization of these linear vinyl monomers, the vinylcyclopropanes show a significantly lower volume shrinkage during ring-opening polymerization. Hybrid vinylcyclopropanes are polymerized step-by-step under formation of reactive polymers or polymer networks. Multifunctional cross-linking vinylcyclopropanes can be used as new low-shrinking matrix monomers for photopolymerizable materials. In addition, the sol-gel process of trialkoxysilyl-functionalized vinylcyclopropanes affords low shrinking organic-inorganic nanocomposites.
The controlled in situ generation of water in transition-metal alkoxide/carboxylic acid mixtures allows the preparation of carboxylate-substituted metal oxide clusters in very high yields. This approach can also be extended to carboxylic acids with functional groups, such as acrylic and methacrylic acid. 1 Examples of methacrylate-substituted clusters prepared by this method include Zr 6 (OH) 4 O 4 (OMc) 12 (OMc ) methacrylate), 2 Zr 4 O 2 (OMc) 12 , 2,3 Ti 6 O 4 (OEt) 8 (OMc) 8 , 4 Nb 4 O 4 (O iPr) 8 (OMc) 4 , 5 and several Ti/Zr mixed-metal clusters. 6 We have recently shown that polymerization of 0.5-2 mol % of Zr 6 (OH) 4 O 4 (OMc) 12 or Zr 4 O 2 (OMc) 12 with functionalized olefins (methyl methacrylate, methacrylic acid) as comonomers results in an interesting new class of inorganic-organic hybrid polymers in which the clusters as the inorganic building blocks cross-link the polymer chains very efficiently. 1,3,7 This results in an improvement of the thermal stability of the polymers, and the swelling in organic solvents can be controlled by the kind and proportion of the incorporated clusters. In this communication we report that the mechanical properties of an inorganic-organic hybrid polymer are also greatly improved upon copolymerization with the cluster Zr 4 O 2 (OMc) 12 .The synthesis of the alkoxysilane derivatives bis-[(methacryloyloxy)propoxycarbonylethyl)](3-triethoxysilyl)propylamine (1) and (1,3(2)-bismethacryloyloxypropyl)-(3-triethoxysilylpropylaminocarbonyl)butyrate (2) and their sol-gel processing was previously described. 8 Solgel processing of the silanes, followed by evaporation of all volatile compounds, resulted in the formation of an oil with a low viscosity for 1 and a viscous resin for 2 (samples 1c and 2c). 8 In the latter case, unreacted Si-OH groups were removed by silylation with Me 3 SiCl in the presence of 2,4,6-trimethylpyridine. A polysiloxane network is formed during the hydrolytic polycondensation of both compounds, while the methacrylate substituents remain unreacted. Upon irradiation with visible light, the methacrylate groups of the polycondensates were cross-linked, and glassy polymers were obtained. For the determination of the mechanical properties of reference samples, the polycondensates were cast in 25 × 2 × 2 mm dies and photochemically Trimmel, G.; Moraru, B.; Tesch, W.; Fratzl, P.; Gross, S.; Kickelbick, G.; Hü sing, N. Mater. Res. Soc. Symp. Proc. 2001, 628, CC2.3.1. Trimmel, G.; Moraru, B.; Gross, S.; Di Noto, V.; Schubert, U. Macromol. Symp., in press. Gross, S.; Trimmel, G.; Schubert, U.; Di Noto, V. J. Polym. Adv. Technol., in press. (8) Moszner, N.; Völkel, T.; Cramer von Clausbruch, S.; Geiter, E.; Batliner, N.; Rheinberger, V. Chem. Mater.hardened (samples 1p and 2p). 9 The flexural strength and flexural moduli of the test specimens (Table 1) was determined according to ISO 4049. Inspection of Table 1 shows that both the flexural strength and the flexural modulus of the hybrid polymers slightly decrease after storage in water for 1 day.Photochemical ...
Dendritic methacrylic crosslinking agents were synthesized by modification of amino functional poly(propy1eneimine) dendrimers. On the basis of model reactions, several experimental methods for the introduction of methacrylate end groups were evaluated. In case of the Michael reaction of 2-(acryloy1oxy)ethyl methacrylate (1) the amino-end groups of the dendrimers of the second, the fourth or the fifth generation add exclusively onto the acrylic double bonds of 1 forming methacrylic end groups in the modified dendrimers. The quantitative and uniform conversion could be proved by NMR spectroscopy. Analogous dendrimer modifications were carried out with mixtures of 1 and other acrylates. The dendrimeric methacrylates of different generations were polymerized in solution and bulk at 80 "C with 2,2'-azoisobutyronitrile as initiator. The polymerization enthalpy of the dendrimeric methacrylates was determined by differential scanning calorimetry and shows that the polymerization of approximately every double bond takes place. The polymerization of methacrylic dendrimers yields crosslinked polymers with glass transition temperatures near or below room temperature.
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