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Di Lorenzo M.L.,CNR Institute of Chemistry and Technology of Polymers
Journal of Applied Polymer Science | Year: 2010

The isothermal and nonisothermal crystallization kinetics of cis-1,4-polybutadiene has been investigated with respect to the content of cis units and the linearity of the main chain. The rate of spherulite growth increases with chain regularity as the presence of branches as well as segments with different configurations slows the crystallization rate. The major parameter that determines the crystallization rate is the presence in the formulation of heterogeneities that favor the formation of primary nuclei and determine an anticipated onset of crystallization. As the activity of the heterogeneous nuclei depends more on the type and number of foreign particle than on any chain parameter, no straightforward information on the influence of the chain structure on the crystallization rate can be derived by mere calorimetric analysis, at least for analyzed samples. It is only with combined analysis by optical microscopy that comprehensive information on the crystallization kinetics of cis-1,4-polybuta-diene can be derived. The results reported in this contribution point out the importance, in polymer science, of preferring complementary instrumentation and not limiting experimental investigations to a single technique of analysis. © 2010 Wiley Periodicals, Inc.

Della Vecchia N.F.,University of Naples Federico II | Avolio R.,CNR Institute of Chemistry and Technology of Polymers | Alfe M.,National Research Council Italy | Errico M.E.,CNR Institute of Chemistry and Technology of Polymers | And 2 more authors.
Advanced Functional Materials | Year: 2013

Rational approaches to engineering polydopamine films with tailored properties for surface coating and functionalization are currently challenged by the lack of detailed information about the polymer structure and the mechanism of buildup. Using an integrated chemical and spectroscopic approach enables the demonstration of: a) a three-component structure of polydopamine, comprising uncyclized (catecholamine) and cyclized (indole) units, as well as novel pyrrolecarboxylic acid moieties; b) remarkable variations in the relative proportions of the cyclized and uncyclized units with starting dopamine concentration; c) the occurrence of oligomer components up to the tetramer level; d) the covalent incorporation of Tris buffer; and e) the role of dopamine quinone as a crucial control point for directing the buildup pathways and tuning the properties. The importance of the uncyclized amine-containing units in polydopamine adhesion is also highlighted. The proper selection of substrate concentration and buffer is thus proposed as a practical means of tailoring polydopamine functionality via control of competing pathways downstream of dopamine quinone. Polydopamine is shown to consist of diverse oligomer components (up to tetramers) including uncyclized catecholamine motifs, 5,6-dihydroxyindole units, and hitherto unrecognized pyrrolecarboxylic acid moieties. Uncyclized amine units prevail with 10 × 10-3 M dopamine, and indoles/pyrroles with a 0.5 × 10-3 M concentration. Covalent incorporation of 50 × 10-3 M Tris is demonstrated. The polydopamine functionality can be tailored via o-quinone as a control point. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Di Lorenzo M.L.,CNR Institute of Chemistry and Technology of Polymers | Righetti M.C.,CNR Institute for Chemical and Physical Processes
European Polymer Journal | Year: 2013

The manuscript details an investigation on the kinetics of vitrification of the rigid amorphous fraction in poly[(R)-3-hydroxybutyrate] (PHB) in dependence of thermal history. PHB was cooled from the melt at various rates, then the combined evolution of crystal and amorphous fractions was monitored during storage at 25 °C. The permanence at room temperature induces progressive growth of PHB crystals and concurrent vitrification of rigid amorphous fraction. During the initial stages of the crystal growth, the amount of rigid amorphous fraction that vitrifies depends on the previous thermal history. After prolonged storage at 25 °C, the increase of the crystal fraction corresponds to a reduction of both mobile amorphous and rigid amorphous content. The decreased coupling between the amorphous and crystal segments, reported in the literature for a few other semicrystalline polymers upon annealing at high temperatures, is shown to occur also in PHB, but during crystallization at low temperature. This finding provides one step forward a thorough understanding of the relation between crystal formation and reduced mobility of the coupled amorphous portions. © 2012 Elsevier Ltd. All rights reserved.

Rizzarelli P.,CNR Institute of Chemistry and Technology of Polymers | Carroccio S.,CNR Institute of Chemistry and Technology of Polymers
Analytica Chimica Acta | Year: 2014

In the last decades, the solid-waste management related to the extensively growing production of plastic materials, in concert with their durability, have stimulated increasing interest in biodegradable polymers. At present, a variety of biodegradable polymers has already been introduced onto the market and can now be competitive with non biodegradable thermoplastics in different fields (packaging, biomedical, textile, etc.). However, a significant economical effort is still directed in tailoring structural properties in order to further broaden the range of applications without impairing biodegradation. Improving the performance of biodegradable materials requires a good characterization of both physico-chemical and mechanical parameters. Polymer analysis can involve many different features including detailed characterization of chemical structures and compositions as well as average molecular mass determination. It is of outstanding importance in troubleshooting of a polymer manufacturing process and for quality control, especially in biomedical applications. This review describes recent trends in the structural characterization of biodegradable materials by modern mass spectrometry (MS). It provides an overview of the analytical tools used to evaluate their degradation. Several successful applications of MALDI-TOF MS (matrix assisted laser desorption ionization time of flight) and ESI MS (electrospray mass spectrometry) for the determination of the structural architecture of biodegradable macromolecules, including their topology, composition, chemical structure of the end groups have been reported. However, MS methodologies have been recently applied to evaluate the biodegradation of polymeric materials. ESI MS represents the most useful technique for characterizing water-soluble polymers possessing different end group structures, with the advantage of being easily interfaced with solution-based separation techniques such as high-performance liquid chromatography (HPLC). © 2013 Elsevier B.V.

Rizzarelli P.,CNR Institute of Chemistry and Technology of Polymers
Rapid Communications in Mass Spectrometry | Year: 2013

RATIONALE Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight/Time- Of-Flight Tandem Mass Spectrometry (MALDI-TOF MS/MS) was employed to analyze five poly(butylene succinate) (PBSu) oligomers and to investigate their fragmentation pathways. METHODS MALDI-TOF MS/MS analysis was performed on cyclic and linear oligomers terminated by dicarboxyl groups, carboxyl and hydroxyl groups, hydroxyl and olefin groups, and dihydroxyl groups. The sodium adduct ions of these oligomers were selected as precursor ions. Experiments were carried out with and without argon as the collision gas. RESULTS A β-hydrogen transfer rearrangement, leading to the selective cleavage of the -O-CH2- bonds, and cleavage of the -CH2-CO- bonds, the ester bonds, and the -CH2-CH2- bonds in the diol moiety were observed. Two fragmentation mechanisms, correlated to the end-group structure of the precursor ions, were also proposed. The detection of cyclic anhydrides was related to the presence of succinic acid terminal groups. The formation of microcyclic oligoesters probably occurred via an intramolecular transesterification mechanism involving a hydroxyl end group. CONCLUSIONS A β-hydrogen transfer rearrangement has been proposed as the main fragmentation mechanism occurring in PBSu without using the collision gas. Cleavages of almost all types of bonds take place in the MALDI CID experiments. According to the structures of the most abundant product ions, six fragmentation pathways have been proposed when using argon as the collision gas. Two fragmentation mechanisms were suggested as being correlated to the end-group structure of the precursor ions. Copyright © 2013 John Wiley & Sons, Ltd.

Righetti M.C.,CNR Institute for Chemical and Physical Processes | Di Lorenzo M.L.,CNR Institute of Chemistry and Technology of Polymers
Thermochimica Acta | Year: 2011

In the present study the correlation between the melting behaviour of poly(3-hydroxybutyrate) (PHB) original, non-reorganized crystals and the crystallinity increase during isothermal crystallization is presented and discussed. Since the reorganization processes modify the melting curve of original crystals, it is necessary to prevent and hinder all the processes that influence and increase the lamellar thickness. PHB exhibits melting/ recrystallization on heating, the occurring of lamellar thickening in the solid state being excluded. The first step of the study was the identification of the scanning rate which inhibits PHB recrystallization at sufficiently high T c. For the extrapolated onset and peak temperatures of the main melting endotherm, which is connected to fusion of dominant lamellae, a double dependence on the crystallization time was found. The crystallization time at which Tonset and Tpeak change their trends was found to correspond to the spherulite impingement time, so that the two different dependencies were put in relation with primary and secondary crystallizations respectively. The increase of both Tonset and Tpeak at high crystallization times after spherulite impingement was considered an effect due to crystal superheating and an indication of a stabilization process of the crystalline phase. Such stabilization, which produces an increase of the melting temperature, is probably connected with the volume filling that occurs after spherulite impingement. © 2010 Elsevier B.V. All rights reserved.

Androsch R.,Martin Luther University of Halle Wittenberg | Di Lorenzo M.L.,CNR Institute of Chemistry and Technology of Polymers
Macromolecules | Year: 2013

Aging of glassy poly(l-lactic acid) (PLLA) allows formation of crystal nuclei which enhances/accelerates subsequent crystallization at temperatures above the glass transition. The effects of the time and temperature of aging on nuclei formation have quantitatively been probed by analysis of isothermal crystallization at 393 K, using fast scanning chip calorimetry and polarizing optical microscopy. Crystal nuclei begin to form on aging the glass of PLLA at 343 K after about 101 s. The time of nuclei formation increases exponentially with decreasing temperature, so that aging at 323 K requires a minimum time of 104 s, and the extrapolated time for generation of nuclei at 295 K is about 108 s. The aging-controlled increase of the nuclei density in glassy PLLA leads to a distinct decrease of the half-time of crystallization. The half-time of crystallization of nonaged PLLA at 393 K is about 600 s and decreases to less than half of this value due to aging at 343 K for a period of only 103 s. Nuclei formation on aging the glass of PLLA is connected with a tremendous decrease of the size of spherulites which develop upon subsequent cold-crystallization. The detection of formation of crystal nuclei in glassy PLLA is discussed in the framework of prior analyses of the effect of the crystallization pathway on structure and properties of crystallizable polymers. © 2013 American Chemical Society.

Di Lorenzo M.L.,CNR Institute of Chemistry and Technology of Polymers | Gazzano M.,CNR Institute for Organic Syntheses and Photoreactivity | Righetti M.C.,CNR Institute for Chemical and Physical Processes
Macromolecules | Year: 2012

The influence of mobility of the amorphous chains on crystallization of poly(3-hydroxybutyrate) (PHB) is detailed in this contribution. Thermal analysis of initially amorphous PHB reveals the occurrence of two distinct exotherms, indicating that cold crystallization proceeds via a two-stage process. The experimental data were rationalized taking into account the role of vitrification/devitrification of the rigid amorphous fraction (RAF) on crystallization kinetics of PHB. The rigid amorphous structure, which is established simultaneously with crystals growth during the first stage of cold crystallization, slows down crystallization before completion. The coupling between the crystalline and amorphous segments hinders further crystallization by the creation of an immobilized amorphous layer that surrounds the crystals. Further increase of the temperature results in mobilization of the RAF. Once the amorphous layer coupled with the crystals has gained sufficient mobility, chain rearrangements needed to accommodate the PHB segments into ordered structures can take place, and crystallization can proceed further. This study demonstrates that the physical state of the rigid amorphous fraction affects the crystallization kinetics of poly(3-hydroxybutyrate). © 2012 American Chemical Society.

Raimo M.,CNR Institute of Chemistry and Technology of Polymers
Polymer Journal | Year: 2011

Isothermal crystallization of a polyoxymethylene copolymer in the temperature range of 423-429 K (150-156 °C) was performed using a differential scanning calorimeter (DSC) and data of crystalline development processed within the framework of a nucleation and growth model. Morphological investigations on DSC crystallized specimens were performed by scanning electron microscopy (SEM) and correlated to DSC data to obtain good estimations of spherulite growth rates in the explored temperature range. The accuracy of the growth rate has been enhanced by Hoffman regime analysis using reliable values of input parameters. Moreover, the function describing the number of growing spherulites as a function of time at constant temperature has been obtained. © The Society of Polymer Science, Japan (SPSJ). All rights reserved.

Raimo M.,CNR Institute of Chemistry and Technology of Polymers
Progress in Crystal Growth and Characterization of Materials | Year: 2011

This work reviews criteria for the successful application of regime analysis to polymers and also discusses the influence of accuracy of input variables on the results. Despite that it has often been stated that the uncertainty in the input parameters remarkably affects the trustworthiness of the outcomes of the regime analysis, the literature offers on the subject only a fragmentary information and there is no paper looking over all the effects of accuracy of the input parameters. Here the influence of errors in input parameters has been investigated and methods to test the reliability of thermodynamic outcomes have been discussed. Mathematical ways to ascertain the accuracy of the input parameters consist in comparisons between the growth rates expressed by the Hoffman-Lauritzen equation and their derivatives generated by means of the output of the regime analysis. These comparisons, under the hypothesis of validity of the secondary nucleation theory, allow excluding the presence of remarkable errors in input values and variables. © 2011 Elsevier Ltd. All rights reserved.

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