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41.
Maurizio Carotenuto Liberata Guadagno Vittoria Vittoria Giancarlo Galli Emo Chiellini 《Macromolecular rapid communications》1996,17(7):447-454
Quenched nematic films of a liquid crystalline polyester were crystallized either thermally or by solvent induced crystallization, and their structural organization was analyzed. All techniques show that the thermal crystallization transforms part of the nematic phase into a crystalline one, the remaining part leaving unchanged. By contrast, the solvent induced crystallization does transform a part of the nematic phase into a crystalline phase, leaving the residual part in a much more disordered state resembling the amorphous state. 相似文献
42.
Giancarlo Galli Emo Chiellini Yusuf Yagci Ersin I. Serhatli Michele Laus Annino Sante Angeloni 《Macromolecular Symposia》1996,107(1):85-97
The scope for the study of the synthesis and properties of liquid crystalline (LC) block copolymers is briefly outlined. While there are many approaches to the synthesis of LC block copolymers, the use of azo macroinitiators is very versatile and allows one to produce diverse block copolymer architectures. Azo macroinitiators are prepared by cationic or promoted cationic polymerization of tetrahydrofuran (1) or cyclohexene oxide (2), and are then used to initiate the free-radical polymerization of various methacrylates 3,4 or acrylates 5–9 containing mesogenic azobenzene or biphenyl units thereby yielding block copolymers. The AB or ABA block copolymers are microphase-separated and form smectic and/or nematic mesophases similar to the respective LC homopolymers. 相似文献
43.
Federica Chiellini Ranieri Bizzarri Christopher K. Ober Dirk Schmaljiohann Tianyue Yu W. Mark Saltzman Roberto Solaro Emo Chiellini 《Macromolecular Symposia》2003,197(1):369-380
Semi-interpenetrating hydrogel networks were prepared by radical polimerization of monomer HEMA, co-monomer EGDMA as cross-linking agent and in the presence of 1 wt % of poly(alkyl β-malolactonate)s. Biological evaluation in terms of cell adhesion and proliferation of the prepared materials showed the ability of HEMA-based hydrogels to sustain a good cell adhesion and proliferation. Moreover, a method based on soft-lithography to obtained surface microstructured semi-interpenetrating hydrogel networks was developed, thus allowing for further investigation of the influence of surface topography on cell behavior. 相似文献
44.
Emo Chiellini Roberto Nocci 《Journal of polymer science. Part A, Polymer chemistry》1973,11(2):493-505
Mixtures of methyl methacrylate (MMA) and 4-methyl-1-pentene (4MP)(molar ratio MMA/4MP = 3–0.1) have been subjected to polymerization by VOCl3/Al(C2H5)3. The amorphous polymeric products, extractable with boiling methanol up to 75%, consist mainly of MMA monomeric units (~80%). The composition of the product was almost independent of the starting MMA/4MP ratio. Comparison of these results with thoseof homopolymerization experiments shows that the presence of MMA drastically reduces the polymerization rate of 4MP. Moreover, 4MP is polymerized with rather low stereospecificity in the presence of MMA. Fractionation by solvent extraction of the unchanged polymeric products as well as of hydrolyzed samples seems to exclude the formation of random copolymers, suggesting to us that the polymerization of the two monomers takes place by different mechanisms. On taking into account these data and analogous data obtained with 4MP and alkyl acrylates or tert-butyl methacrylate, is it suggested that, contrary to what has previously been proposed, the MMA polymerization by Ziegler-Natta catalysts does not take place at the same centers which polymerize 4MP; moreover a coordinated anionic mechanism for MMA polymerization does not seem to be very probable. 相似文献
45.
Ogoshi T Fujiwara T Bertolucci M Galli G Chiellini E Chujo Y Wynne KJ 《Journal of the American Chemical Society》2004,126(39):12284-12285
A new surface phenomenon is reported for hybrid nanocomposites comprising (1) a low Tg poly(dimethylsiloxane) (PDMS) phase cross-linked by (2) a siliceous phase (SP) generated by in situ hydrolysis/condensation of poly(diethoxysiloxane) (PDES), and (3) fumed silica nanoparticles (FSN). After ambient temperature cure, tapping mode atomic force microscopy (TM-AFM) easily reveals near-surface FSN. For nanocomposites with higher PDES content, FSN surprisingly "disappear" after a further cure at 100 degrees C. The observation is explained by further condensation of extant siliceous fragments creating an amorphous reticular phase, which acts as a mechanical barrier between the FSN and the AFM tip. 相似文献
46.
E. Welzl 《Discrete and Computational Geometry》2001,25(3):351-364
Let S be a set of n points in d -space, no i+1 points on a common (i-1) -flat for 1 ≤ i ≤ d . An oriented (d-1) -simplex spanned by d points in S is called a j-facet of S if there are exactly j points from S on the positive side of its affine hull. We show: (*) {\em For j ≤ n/2 - 2 , the total number of (≤ j) -facets (i.e. the number of i -facets with 0 ≤ i ≤ j ) in 3-space is maximized in convex position (where these numbers are known).} A large part of this presentation is a preparatory
review of some basic properties of the collection of j -facets—some with their proofs—and of relations to well-established concepts and results from the theory of convex polytopes
(h -vector, Dehn—Sommerville relations, Upper Bound Theorem, Generalized Lower Bound Theorem). The relations are established
via a duality closely related to the Gale transform—similar to previous works by Lee, by Clarkson, and by Mulmuley.
A central definition is as follows. Given a directed line ℓ and a j -facet F of S , we say that {\it ℓ enters F } if ℓ intersects the relative interior of F in a single point, and if ℓ is directed from the positive to the negative side of F . One of the results reviewed is a tight upper bound of j+d-1 \choose d-1 on the maximum number of j -facets entered by a directed line.
Based on these considerations, we also introduce a vector for a point relative to a point set, which—intuitively speaking—expresses
``how interior' the point is relative to the point set. This concept allows us to show that statement (*) above is equivalent
to the Generalized Lower Bound Theorem for d -polytopes with at most d+4 vertices.
Received May 21, 1999, and in revised form July 6, 2000. Online publication January 17, 2001. 相似文献
47.
Random sampling is an efficient method to deal with constrained optimization problems in computational geometry. In a first
step, one finds the optimal solution subject to a random subset of the constraints; in many cases, the expected number of
constraints still violated by that solution is then significantly smaller than the overall number of constraints that remain.
This phenomenon can be exploited in several ways, and typically results in simple and asymptotically fast algorithms.
Very often the analysis of random sampling in this context boils down to a simple identity (the sampling lemma ) which holds in a general framework, yet has not been stated explicitly in the literature.
In the more restricted but still general setting of LP-type problems , we prove tail estimates for the sampling lemma, giving Chernoff-type bounds for the number of constraints violated by the
solution of a random subset. As an application, we provide the first theoretical analysis of multiple pricing , a heuristic used in the simplex method for linear programming in order to reduce a large problem to few small ones. This
follows from our analysis of a reduction scheme for general LP-type problems, which can be considered as a simplification
of an algorithm due to Clarkson. The simplified version needs less random resources and allows a Chernoff-type tail estimate.
Received June 8, 2000, and in revised form September 10, 2000. Online publication March 26, 2001. 相似文献
48.
49.
Michele Laus Annino Sante Angeloni Oriano Francescangeli Giancarlo Galli Emo Chiellini 《Macromolecular Symposia》1997,117(1):275-280
The peculiar liquid crystalline behavior of two poly(urethane-ester)s TDI-C6C4 and TDI-C6C8 is reported. Evidence is provided of the formation of two nematic mesophases, a cybotactic nematic and a conventional nematic mesophase, in TDI-C6C8 and of one cybotactic nematic mesophase in TDI-C6C4. IR spectroscopy indicates that different hydrogen bonded and non-bonded structures occur with varying temperature. The transition from the nematic cybotactic mesophase to the nematic mesophase, or to the isotropic phase, is accompanied by a substantial decrease of the strength of the hydrogen bonds. This is also reflected in the dynamic-mechanical behavior of these poly(urethane-ester)s which is similar to the one of slightly crosslinked thermoreversible networks. 相似文献
50.
Roberto Solaro Elisabetta E. Chiellini Donatella Giannasi Fabrizio Morganti Emo Chiellini 《Macromolecular Symposia》1997,118(1):603-617
The work performed by our research group during the last few years in the area of bioerodible-biodegradable polymers as designed to the formulation of systems for the controlled delivery of drugs and as specific sorbents of uraemic toxins is broadly reviewed. In particular, attention has been focused on the strategies adopted in the preparation of functional polymers containing hydroxyl or carboxyl groups, suitable to establish specific bonding and non-bonding interactions with conventional and proteic drugs. 相似文献