Giovanna Costa

Functionalization of isotactic polypropylene with maleic anhydride by reactive extrusion: mechanism of melt grafting

Abstract In this work, chemical structures and molecular parameters of grafted materials of PP- g -MAH prepared by melt reactive extrusion were studied by using electrospray ionization-mass spectrometer and gel permeation chromatography. It was found that the initial radicals, due to homolitic scission of dicumyl peroxide could be combined with maleic anhydride (MAH) monomers as well as polypropylene (PP) molecular chains. The homopolymerization of MAH cannot occur and the MAH radicals undergo a dismutational reaction under the processing condition (180–190°C). A modified mechanism of melt grafting MAH onto PP has been proposed tentatively on the basis of our experimental results and other experimental findings published in the literature.

Reactive blending of polyamide 6,6 and Vectra A

In this paper, blends of Nylon 6,6 with the liquid crystal polymer Vectra A950 are considered; specifically we focused our attention on Nylon 6,6 modifications by interchange reactions that can occur in the melt, as a function of mixing conditions and blend compositions. Two matrix samples have been used, characterised by a slightly different relative amount of amine and carboxylic end groups, being the latter predominant in both cases. The dried polymers Nylon 6,6/Vectra, combined in weight ratios between 95/5 and 50/50, were subjected to reactive blending with different methods (single-screw extruder, Brabender, pyrex reactor). Pure Nylon samples have been also investigated as reference materials. The soluble Nylon 6,6-rich fraction of each blend was separated from the insoluble Vectra-rich one and used for molecular and spectroscopic characterisations. Thermal and morphological analyses, as well as testing of tensile properties, were carried out on the blends. Evidences of the occurrence of interchange reactions are given and the most probable ones are suggested.

Polyacetylenes Bearing Mesogenic Side Groups: Synthesis and Properties, 1. Mesogenic Substituents with a Short Flexible Spacer

We report on the synthesis and polymerization of novel acetylenic monomers derived from 3-butyn-1-ol and bearing different potentially mesogenic substitutuents. Polymerization is carried out in solution with typical metathesis catalysts based on Mo and W and yields polyacetylenes with fairly high molecular weight and soluble in common organic solvents. Polymers are fully characterized by the point of view of the molecular structure, by GPC, FT-IR, NMR and UV/VIS techniques, and of the thermal and morphological behavior, by TGA, DSC, POM and X-ray diffraction experiments. Polymers with different amounts of cis and trans units are obtained, depending upon polymerization conditions. Although the monomers do not show any liquid crystalline behavior, polymers P2 and P3, containing in the side-chain respectively biphenyl and benzoyloxy benzoate as mesogenic cores, exhibit an enantiotropic smectic phase.

Molecular weight distribution of polycaprolactam, anionically synthesized in presence of lithium chloride

Abstract Samples of polycaprolactam, obtained by anionic polymerization of caprolactam in bulk under adiabatic conditions and in presence of different amounts of lithium chloride, have been fractionated using a method based on summative fractionation of the polyamide in the amorphous state. By increasing the amount of lithium chloride in the system, the limiting viscosity number of the as-polymerized material decreases; at the same time the integral distribution curves reveal a bimodal molecular weight distribution as a consequence of the complex pattern of main and side reactions. The high molecular weight peak is very narrow, both with and without lithium chloride in the polymerizing system. Lithium chloride considerably reduces the polydispersity of the low molecular weight portion, which is very broad for the non-salt treated polycaprolactam. The relative importance of the two peaks, which is almost even for polycaprolactam synthesized without salt, is shifted in favour of the lower molecular weight peak by increasing the salt content. This effect is also accompanied by a higher production of water-soluble oligomers.

Polyacetylenes bearing mesogenic side groups: synthesis and properties. Part 3. Influence of flexible spacer length and tail functionality

Abstract We report on the synthesis of some novel liquid crystalline polyacetylenes derived from monosubstituted acetylenic monomers where the acetylenic moiety is linked through a short spacer (one or three methylene units and an ether bridge) to a biphenyl mesogenic core. The influence of length and functionality of the terminal groups on the thermal behaviour and on the nature of the mesophases is discussed. All the monomers show liquid crystalline behaviour. Polymerisations are carried out in solution with typical metathesis catalysts based on Mo and W and yield polyacetylenes with fairly high MW soluble in common organic solvents. Polymers are fully characterised by GPC, FT-IR, and 1 H NMR techniques; their thermal and morphological behaviour has been studied by TGA, DSC, POM and X-ray diffraction experiments.

Investigation on elastomer–silica interactions by inverse gas chromatography and image analysis aided transmission electron microscopy

A study on the interactions between silica and elastomers typically used in tire tread production has been carried out by inverse gas chromatography (IGC) and image analysis aided transmission electron microscopy (TEM/AIA). At infinite dilution, IGC has been performed using precipitated silica as the stationary phase to determine its surface properties and to calculate the adsorption free energy and enthalpy of low molecular weight analogues of elastomers, used as the eluates. Vulcanized samples based on different matrices employed in tire formulations, i.e., natural rubber, butadiene rubber, and styrene-butadiene rubber, have been investigated by TEM/AIA to determine the dispersion of the filler within the matrix as well as to achieve quantitative information on aggregate size and shape distribution of silica and, consequently, on the polymer-filler interactions. A comparison between thermodynamic predictions deduced by IGC and the results from morphological analysis concerning filled compounds shows a very satisfactory agreement.

Gel permeation chromatographic analysis of N-trifluoroacetylated poly(ε-caprolactam): Calibration procedures

Abstract A calibration procedure for the gel permeation chromatography (g.p.c.) of N -trifluoroacetylated poly(e-caprolactam) ( N -TFA PCL) is proposed. The method requires only that M n and M w be determined independently without any preliminary condition on the distribution broadness. Four samples covering a range of molecular masses typical of commercial PCL materials are analysed and very good agreement between the measured average molar masses and the g.p.c. computed ones is found. The Mark-Houwink relationship in methylene chloride is derived from the molar mass distribution data and the intrinsic viscosity measurements on the unfractionated samples. The universal calibration curve based on polystyrene hydrodynamic volume is found to be inapplicable to N -TFA PCL, which shows a very peculiar retention behaviour.

Reactive blending of polyamide 6,6 and vectra A, 2. Role of a bifunctional epoxy coupler

In a previous paper Nylon 6,6/Vectra A blends have been prepared and investigated; in particular, our attention has been focused on Nylon 6,6 modifications due to interchange reactions that occur in the melt, as a function of mixing conditions and blend compositions, and improve the compatibility of the blend. The results indicated that only a small amount of copolymeric species form because of the low reaction kinetics and unfavorable physical and rheological aspects. In order to overcome these limits, a further research on Nylon 6,6/Vectra A blends has been carried out to test the role of modified processing conditions in the presence of a reactive additive able to improve the extent of reactions between blend components and the melt viscosity of the polyamide matrix. The potential of a Nylon 6,6 sample with predominant -NH 2 end-groups on its reactive blending with Vectra with or without the reactive third component has been investigated. Nylon and Vectra, combined in weight ratios between 90/10 and 50/50, were subjected to reactive blending with different methods (a laboratory Pyrex reactor, a singlescrew extruder, and a Brabender mixer). Neat Nylon samples have been also investigated as reference materials. Thermal and morphological analyses were carried out on the blends. The soluble Nylon 6,6-rich fraction of each blend was sepa- rated from the insoluble Vectra-rich one, and both were used for spectroscopic characterizations; mixed Nylon-Vectra copolymers have been recognized in both the soluble and insoluble fractions of the blends.

Reinforcement of diene elastomers by organically modified layered silicates

Abstract Nanocomposites were prepared based on diene rubbers and layered clays modified with an alkyl quaternary ammonium cation (organoclay). A diene rubber, either polybutadiene, or synthetic or naturally occurring polyisoprene or styrene-butadiene copolymer, was melt blended with either a preformed organoclay or with a mixture of pristine clay and ammonium cation. Besides isolated lamellae, nanocomposites showed the presence of crystalline organoclays with intercalated organic layers made only by low molecular mass substances, essentially the ammonium cation, and no evidences for the intercalation of polymer chains were observed. Dynamic-mechanical properties of sulphur cured compounds with carbon black as the main filler and a minor amount of organoclay were investigated. The organoclay was found to bring about a reduction of Mooney viscosity, an increase of storage modulus at low temperature as well as an increase of thermoplasticity.

Styrene–diene block copolymers as embedding matrices for polymer-dispersed liquid crystal films

Abstract Composite films made of the nematic mixture E7 or the nematic single component K15 embedded in styrene–diene triblock copolymers have been prepared by the solvent cast method from homogeneous solutions; their phase separation behaviour has been investigated by calorimetric and morphological analyses as a function of mixture and matrix compositions, diene nature, casting solvent and evaporation time. Three copolymeric samples of comparable molecular weight have been used; two of them, based on polybutadiene, differ in their styrene content (30 and 55% by weight), in the third the major fraction of soft segments (75%) is made of polyisoprene. Films based on homopolymeric polystyrene and polybutadiene have been also prepared and tested as reference materials. The results reveal a substantially different solubility of the liquid crystal (LC) in the two phases of the copolymer micro-heterogeneous structures. The droplet size, shape and distribution that characterise the film morphology change considerably upon increasing the LC concentration in the blends, varying the casting solvent or lowering the evaporation rate; moreover a significant role is played by the nature of the elastomeric fraction. The dependence of morphological features on the various parameters is tentatively discussed in terms of both the affinity between the casting solvent and the matrix blocks and the critical surface tensions of LC and copolymer components.