Influence of branching on melting behavior and isothermal crystallization of poly(butylene terephthalate)

et al. 2011

Polym J

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The melting behavior and crystallization kinetics of PBN-PDEN and PBN-PTDEN copolymers were investigated using differential scanning calorimetry. Multiple endotherms were observed in all of the copolymers under investigation, originating from melting and recrystallization processes. By applying the Hoffman-Weeks method, the T m 1 of the a and b¢-PBN phases were derived. The T m 1 value of the b¢-form, which has not been determined before, is significantly higher, as expected, because the b¢-phase is thermodynamically favored and more tightly packed. The isothermal crystallization kinetics were analyzed according to the Avrami treatment. The presence of either oxygen or sulfur atoms in the PBN polymeric chain was found to reduce its crystallizability. In particular, the crystallization rate regularly decreased as the co-unit content was increased. Lastly, the a-PBN phase was found to crystallize faster than b¢-one, which is expected, as it the more kinetically favored phase. Polymer Journal (2012) 44, 174-180; doi:10.1038/pj.2011.112; published online 9 November 2011Keywords: equilibrium melting temperature; melt isothermal crystallization; random copolymers of poly(butylene naphthalate) INTRODUCTION Naphthalene-containing thermoplastic polyesters have attracted an increasing degree of interest in recent years. Poly(ethylene naphthalate), poly(butylene naphthalate) and poly(propylene naphthalate) are the best known members of this family of thermoplastics. These newly developed high-performance polymers that contain a rigid naphthalene ring and a flexible alkylene group in the repeat unit exhibit physical and mechanical properties superior to the widely used corresponding phthalate-based polyesters. In particular, poly(butylene 2,6-naphthalate) (PBN) is characterized by very good gas barrier properties, high UV resistance, high solvent-resistance, long-term electrical properties and thermostability. To date, two crystalline structures for PBN, denoted as a-and b-forms, have been acknowledged. The transition between these two forms can take place reversibly by mechanical deformation. 1 Ju et al. investigated the crystalline forms of PBN samples obtained by different thermal treatments in bulk. The a-form was produced by annealing a quenched sample in the solid state or by crystallizing PBN from the static melt at temperatures lower than 225 1C. An exclusive b¢-form was generated by performing non-isothermal crystallization from the melt at an extremely low cooling rate (0.1 1C per min). This thermally prepared b¢-form is characterized by a WAXD profile similar to that of the b-form obtained by mechanical deformation, except for the substantial d-spacing deviation in the (0-11) and (010) planes. 2 Nevertheless, if PBN is melt crystallized at high T c , both the a and b¢-forms are obtained simultaneously, and their relative ratio is dependent on the adopted crystallization temperature. Additionally, changes in the crystalline form never occur in the solid state. Lastly,

Section: Calorimetric Measurementsmentioning

confidence: 99%

Equilibrium melting temperature and crystallization kinetics of α- and β′-PBN crystal forms

Soccio

et al. 2011

Polym J

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“…10,[15][16][17] There has been much discussion in the literature as to the possible origin of the phenomenon: multiple endotherms can be attributed to the presence of two or more groups of crystals with different morphologies or lamellar thickness 15 or they can be ascribed to a recrystallization process occurring during the DSC scan. 10,16 In addition, both processes could operate at different undercooling degrees. 17 The multiple endotherm behavior is typical of many polyesters, for the beststudied of which the phenomenon has often been ascribed to a reorganization process taking place during the DSC scan.…”

Section: Resultsmentioning

confidence: 98%

“…Analogous results were found in some investigations of the effect of long branches on PBT. 10 A partially crystalline material is expected to exhibit different glass-transition behavior than that of completely amorphous material. Although some conflicting results are reported in the literature, 14 crystallinity usually acts like crosslinking and raises T g through its restrictive effect on segmental motion of amorphous polymer chains.…”

Section: Resultsmentioning

confidence: 99%

“…For a better definition of the starting time, for each isothermal scan, blank runs were also performed with the same sample, at a temperature above the melting point where no phase change occurred. 10 The blank runs were subtracted from the isothermal crystallization scan and the start of the process was taken as the intersection of the extrapolated baseline and the resulting exothermal curve. The isothermally crystallized samples were then heated directly from T c to melting at 10°C/min.…”

Section: Calorimetric Measurementsmentioning

confidence: 99%

“…[7][8][9] Subsequently, given that it is well known that the presence of branches markedly changes the crystallization kinetics and melting behavior of linear polymers, the crystallization behavior of branched PBT was also investigated. 10 To our knowledge, to date no studies have appeared on the thermal behavior of branched poly-(butylene isophthalate); the only data available in the literature concern linear PBI. 11,12 Herein we report the results of a detailed investigation about the influence of long branches on the thermal behavior and isothermal crystallization kinetics of PBI, carried out to obtain information on the kinetic and thermodynamic parameters that control the crystalline growth of the polymer.…”

Section: Introductionmentioning

confidence: 98%

See 2 more Smart Citations

Influence of branching on the thermal behavior of poly(butylene isophthalate)

J of Applied Polymer Sci

Munari

2002

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ABSTRACT:The thermal behavior of linear and randomly branched poly(butylene isophthalate) samples was investigated by thermogravimetric analysis and differential scanning calorimetry. As to the thermal stability, it was found to be good and similar for all the samples. The thermal analysis carried out using DSC technique showed that the melting temperature of the polymers decreased with increasing branching unit content, although the glass-transition temperature was practically not affected by ramifications. The multiple endotherms typical of linear PBI were also observed in branched samples and were found to be influenced both by temperature and degree of branching. By applying the Hoffman-Weeks' method, the equilibrium melting temperatures of the polymers were obtained. The presence of a crystal-amorphous interphase was evidenced only for the branched samples and the interphase amount was found to increase as the branching unit content was increased. Isothermal melt crystallization kinetics was analyzed according to Avrami's treatment. The introduction of branching points was found to decrease the overall crystallization rate of poly(butylene isophthalate). Values of Avrami's exponent n close to 3 were obtained for all the samples, in agreement with a crystallization process originating from predetermined nuclei and characterized by three dimensional spherulitic growth.

Preparation and thermal behavior of random poly(butylene terephthalate/azelate) copolyesters

Munari

et al. 1999

J. Appl. Polym. Sci.

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Poly(butylene terephthalate), poly(butylene azelate), and poly(butylene terephthalate/butylene azelate) random copolymers of various compositions were synthesized in bulk using the well-known two-stage polycondensation procedure, and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. As far as the thermal stability is concerned, it was found to be rather similar for all copolymers and homopolymers investigated. All the copolymers were found to be partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. Flory's equation was found to describe the T m -composition data and permitted to calculate the melting temperatures (T°m ) and the heats of fusion (⌬H u ) of both the completely crystalline homopolymers. Owing to the high crystallization rate, the glass transition was observable only for the copolymers containing from 30 to 70 mol % of the terephthalate units; even though the samples cannot be frozen in a completely amorphous state, the data obtained confirmed that the introduction of the aromatic units gave rise to an increase of T g , due to a chain stiffening.