Domenico Lupinacci

Mesophase Formation in Polymers With Anisometric Side – Groups in Relation to Their Chemical and Stereochemical Structure

Abstract The influence of the flexibility of the polymer main chain on the smectic ordering has been investigated, by means of optical, diffractometric and calorimetric techniques, in several polymers carrying rigid anisometric side-groups. The effect of the chemical structure of the sidegroups has been examined throughout: atactic polymers with biphenylyl side-groups may be amorphous or mesomorphous depending on the nature of the groups linking the biphenylyl moiety to the backbone chain. Correlations between the molecular weight and the stereochemical structure of the macromolecules and the occurrence of a thermotropic smectic phase in a series of polyacrylates and polymethacrylates, have been reported.

Physico-chemical and mechanical characterization of hydrogels of poly (vinyl alcohol) and hyaluronic acid

Hydrogels are three-dimensional polymeric networks very similar to biological tissues and potentially useful as soft tissue substitutes and drug delivery systems. Many synthetic polymers can be used to make hydrogels: poly (vinyl alcohol) is widely employed to make hydrogels for biomedical applications. Improvements in the biocompatibility characteristics of synthetic materials could be achieved by the addition of biological macromolecules. The resulting materials named “bioartificial polymeric materials” could possess the good mechanical properties of the synthetic component and adequate biocompatibility due to the biological component. We have used poly (vinyl alcohol) to make hydrogels containing various amounts of hyaluronic acid. These bioartificial materials were studied to investigate the effect of the presence of the hyaluronic acid on the structural properties of the hydrogels. Thermal, mechanical, morphological and X-ray analyses were performed. A close correspondence between the network consistency and the degree of crystallinity developed in the matrix suggested that the hyaluronic acid, when its content is about 20%, could provide heterogeneous crystallization nuclei for poly (vinyl alcohol) thus increasing the crystallization degree, and consequently, the storage modulus.

Enzyme-based bioartificial polymeric materials : The α-amylase-poly(vinyl alcohol) system

The possibility of realizing bioartificial polymeric materials from blends of the enzyme α-amylase (EC 3.2.1.1) and poly(vinyl alcohol), in the form of film and hydrogel, was investigated. The interactions at molecular level between the enzyme and the synthetic polymer have been studied by calorimetry, X-ray diffractometry and morphological analysis. A certain degree of interaction through which the α-amylase molecules influence the crystallinity of the poly(vinyl alcohol) was observed. The thermal stability of the enzyme in the blends was enhanced, while its biological activity did not vary significantly. In addition, hydrogels prepared by a freeze–thawing method can be considered suitable for manufacturing delivery systems capable of releasing enzymes which maintain their full biological activity. ©1997 SCI

Studies on comb-like polymers: 5 A d.s.c. investigation of samples of poly(octadecylethylene) with different history☆

Abstract The crude product of the stereospecific polymerization of octadecylethylene shows, on d.s.c. analysis, two enthalpy changes associated with the melting or the crystallization of two immiscible crystalline phases. It is shown that the crystallization of the crude polymer from dilute heptane solutions leads to a satisfactory separation of supposedly isotactic from atactic material. Contrary to previous statements, it is demonstrated that both these materials display single melting and crystallization phenomena. It is also shown that appropriate annealing treatments lead to a narrow distribution of the crystallite sizes for all the crystalline structured formed by poly(octadecylethylene).

Synthesis and characterization of copolymers containing biphenylyl rings linked to the main chain through spacers of various lengths

Abstract Copolymers between 1-(4-biphenylyloxy carbonyl)ethylene (I), 1-[2-(4-biphenylyloxy)ethyloxy carbonyl]ethylene (II) and 1-[6-(4-biphenylyloxy carbonyl)]ethylene (III) were synthesized by radical polymerization. They were characterized by DSC, TOA, RX and viscosity techniques. The smectic order of poly(I) and the crystalline order of poly(III) depend on the amounts of comonomers incorporated. The obtained data demonstrate that the presence of quantities of comonomers exceeding 10% leads to complete destruction of smectic and crystalline order in poly(I) and poly(III) respectively.

Investigation by X-ray diffraction of phase transitions of the mesomorphic polymer poly(p-biphenylyl acrylate)

Abstract An Investigation was performed on the glassy state — smectic A and on the smectic A — Isotropie l i quid transitions of the mesomorphic polymer poly(p-biphenylyl acrylate) by x-ray diffraction. An hysteresis effect and strong pretransitional effects were observed in the integrated x-ray diffracted intensity. Moreover an abrupt change of the lateral distance between the biphenylyl groups was observed in a narrow temperature range at the melting. This fact was attributed to a change in the organization of the long rigid side groups around the main chain.

Polymer Mesophases. Studies on the Smectic-isotropic Transition of Poly(p-Biphenylyl Acrylate)

Poly(p-biphenylyl acrylate) (PPBA) displays a thermodynamically stable smectic mesophase at temperatures below ca 270°. The X-ray diffraction diagram of this polymer shows a sharp reflection, with higher orders, corresponding to a spacing of 23,2 a. Optical observation and X-ray photographs of fibres of PPBA indicated good preferred orientation along the fibre axes. The structure is not influenced by the stereochemical configuration of the macromolecules, whereas the temperature of the smectic-isotropic transition of PPBA has been found to increase with decreasing degree of isotacticity. The smectic-isotropic transition of PPBA has been studied with different techniques, and the effect of the copolymerization, of the addition of a diluent and of the polymer molecular weight has been investigated. All the data indicate that the smectic-isotropic transition of PPBA resembles closely the fusion of semicrystalline polymers.