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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. Source


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. Source


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. Source


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. Source


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. Source

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