Toughening of isothermally polymerized cyclic butylene terephthalate for use in composites

Interest in thermoplastic composites is growing because of their advantages over thermosets in recyclability and in toughness. The melt viscosity of thermoplastic polymers is very high, which makes fibre impregnation difficult. This can be solved by using in-situ polymerization with cyclic butylene terephthalate (CBT). However this leads to a brittle PBT. To solve this problem physical and chemical modification of the polymerized CBT (pCBT) was performed, to disturb the crystallization. Chemical modification with PC and with PTHF has an embrittling effect because of a bad chemical interaction. When polycaprolactone is added to the CBT a copolymer is formed which leads to a lower crystallinity, resulting in a higher toughness of the pCBT. This tougher matrix material was used in composites and a two times tougher composite is produced when only 7 wt% PCL is added to the CBT. The physical modification evaluated was the addition of carbon nanotubes (CNT). Although an increase in stiffness and strength of the pCBT is seen when CNTs are added up to 0.1 wt%, the failure strain decreases.     

Crystallization and morphology of polymerized cyclic butylene terephthalate

The crystallization behavior and morphology of polymerized cyclic butylene terephthalate (pCBT) were investigated by thermal differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The spherulite growth rate was analyzed based on the Hoffman and Lauritzen theory to better understand the crystallization behavior. We found four typical morphologic features of pCBT corresponding to the crystallization temperature spectrum: usual negative spherulite, unusual spherulite, mixed birefringence spherulite coexisting with boundary crystals, and highly disordered spherulitic crystallites. The Avrami crystallization kinetics confirmed the occurrence of combined heterogeneous nucleation accompanied by a change in the spherulitic shape of pCBT, which also agreed with the PLM results. The equilibrium melting temperature and glass transition temperature of pCBT were 257.8 °C and 41.1 °C, respectively. A regime II–III transition occurred at 200.9 °C, which was 10 °C lower than that reported for poly(butylene terephthalate) (PBT). Coinciding with and attributed to the regime transition, the boundary crystal disappeared at temperatures above 200 °C and the morphology changed from the mixed type to highly disordered spherulitic crystallites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1127–1134, 2010     

Poly(butylene terephthalate)‐functionalized MWNTs by in situ ring‐opening polymerization of cyclic butylene terephthalate oligomers

Poly(butylene terephthalate) (PBT) had been covalently attached onto the surface of multiwalled carbon nanotubes (MWNTs) by a “grafting from” method based on in situ ring‐opening polymerization (ROP) of cyclic butylene terephthalate oligomers (CBT) using MWNT‐supported initiator (MWNT‐g‐Sn). The Sn? O bond grafted on the surface of MWNTs, which was confirmed by X‐ray photoelectron spectroscopy, provided the initiating sites for ROP of CBT. Fourier transformed infrared spectroscopy and nuclear magnetic resonance were used to confirm the chemical structure of MWNT‐graft‐PBT copolymer and emission transmission electron microscope was utilized to observe the nanostructure of the PBT functionalized MWNTs. A distinct core–shell structure with PBT layer as the shell could be observed after functionalization of PBT despite it was not uniform. The results of thermogravimetric analysis indicated that the grafting ratio of PBT was about 59.3%. Furthermore, the solubility of the PBT functionalized MWNTs in phenol/tetrachloroethane had also been investigated. Copyright © 2010 John Wiley & Sons, Ltd.     

Correlation between polymerization of cyclic butylene terephthalate (CBT) and crystallization of polymerized CBT

The correlation between ring-opening polymerization(ROP) of cyclic butylene terephthalate(CBT) and crystallization of polymerized CBT(p CBT) strongly affected the final properties of p CBT and its composites.The major objective of this contribution is to pinpoint the threshold temperature between them and the interrelation is successfully disclosed.That is,crystallization during polymerization occurs below 204 °C and the crystallization properties of p CBT are determined by this isothermal ROP stage; polymerization and crystallization are gradually separated with the increase of temperature of ROP(TP) from 204 °C,and the crystallization properties of p CBT are dominated by cooling stage; only polymerization is performed above 212 °C.Moreover,quantitative analysis suggests that uniform crystal size distributions and thicker lamellar crystals derive from the stage of crystallization during polymerization.On the contrary,the crystal size distributions become wider above 204 °C of TP and lead to obvious double melting peaks during heating scan.These efforts provide a very useful guide for the related investigation and application of CBT.     

A modulated dsc study on the in situ polymerization of cyclic butylene terephthalate oligomers

The polymerization of a cyclic butylene terephthalate (CBT) oligomer was studied as a function of temperature (T=200 and 260°C, respectively) by modulated DSC (MDSC). The first heating was followed by cooling after various holding times (5, 15 and 30 min) prior to the second heating which ended always at T=260°C. This allowed us to study the crystallization and melting behavior of the resulting polybutylene terephthalate (PBT), as well. In contrary to the usual belief, the CBT polymerization is exothermic and the related process is superimposed to that of the CBT melting. The melting behavior of the PBT was affected by the polymerization mode (performed below or above the melting temperature of the PBT product) of the CBT. Annealing above the melting temperature of PBT yielded a product featuring double melting. This was attributed to the presence of crystallites with different degrees of perfection. The crystals perfection which occurred via recrystallization/remelting was manifested by a pronounced exothermic peak in the non-reversing trace.     

Characterization of PBT/POSS nanocomposites prepared by in situ polymerization of cyclic poly(butylene terephthalate) initiated by functionalized POSS

Novel poly(butylene terephthalate) (PBT)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized by ring‐opening polymerization of cyclic poly(butylene terephthalate) initiated by functionalized POSS with various feed ratios. The impact of POSS incorporation on melting and crystallization behaviors of PBT/POSS nanocomposites was investigated by means of X‐ray diffraction and differential scanning calorimetry. It was found that the novel organic–inorganic association result in the significant alterations in the melting and crystallization behavior of PBT. Thermal studies confirmed that the incorporation of POSS can enhance the thermal stability of the polymers, and the copolymer glass transition temperature increased with the increasing of POSS macromonomer content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1853–1859, 2010     

Hybrids from HNBR and in situ polymerizable cyclic butylene terephthalate (CBT): Structure and rolling wear properties

Hybrids composed of peroxide-curable hydrogenated acrylonitrile-butadiene rubber (HNBR) and cyclic butylene terephthalate oligomers (CBT) were produced. CBT was expected to polymerize in situ when curing the HNBR. Extraction, differential scanning calorimetry (DSC), dynamic-mechanical thermal analysis (DMTA), wide-angle X-ray scattering (WAXS) and atomic force microscopy (AFM) were adopted to investigate the CBT conversion and the phase structure of the hybrids before (T = 190 °C; HNBR-(p)CBT) and after annealing (T = 250 °C; HNBR-pCBT). Unlubricated rolling wear properties of the related compounds with different CBT contents were assessed in orbital rolling ball (steel)-on-plate (rubber) test rig (Orbital-RBOP). The dynamic coefficient of friction and the specific wear rate were determined. Both (p)CBT and pCBT improved the rolling wear resistance of the hybrids compared to plain HNBR. However, the polymerized CBT (pCBT) improved the wear properties more than the unpolymerized CBT ((p)CBT). The wear mechanisms were identified by inspecting the worn surfaces in scanning electron microscope (SEM) and are discussed as a function of (p)CBT/pCBT modification. Changes in the structure and properties of the hybrids caused by the annealing-induced polymerization of CBT were analyzed.     

Organocatalyzed ring‐opening polymerization of cyclic butylene terephthalate oligomers

In this study, various organic compounds, with different activation modes, have been tested as catalysts for the ring‐opening polymerization (ROP) of cyclic butylene terephthalate oligomers (CBT) in bulk at 210 °C, using tert‐butylbenzyl alcohol (tBnOH) as initiator. Among them, 1,3,5‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) appeared to be the most efficient, achieving high monomer conversions in short reaction times (within minutes). Analysis by size‐exclusion chromatography (SEC) of the poly(butylene terephthalate) (PBT) synthesized using this catalyst also showed that the polymerization follows the expected theoretical M _n trend for molecular weights up to 50 kg·mol^?1. Chain‐end fidelity relatively to the alcohol initiator has been confirmed by MALDI‐TOF mass spectroscopy, which showed that all polymer chains possess the tert‐butylbenzyl moiety as chain‐end. Finally, to demonstrate the potential of this system for the synthesis of PBT‐based block copolymers, a monomethyl ether poly(ethylene glycol) (PEG) of 5000 g·mol^?1 has been employed as initiator for the ROP of CBT. A PEO‐b‐PBT block copolymer of 15,000 g·mol^?1 could thus been obtained, as confirmed by the shift of the SEC traces towards higher molecular weights and the same diffusion coefficient determined for ¹H NMR signals of the PEO block and the PBT block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1611–1619     

Toughening of a highly cross-linked epoxy resin by reactive blending with bisphenol A polycarbonate. I. FTIR spectroscopy

A highly cross-linked thermosetting epoxy resin was modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate (PC). Prior to the curing process the PC component was dissolved at high temperature in the uncured epoxy matrix. FTIR investigation of this reactive mixture demonstrated the occurrence of physical and chemical interactions among the blend components. Isothermal kinetic measurements performed by FTIR spectroscopy showed that the presence of PC does not affect the overall curing mechanism but decreases both the initial reaction rate and the final conversion of reactants. © 1994 John Wiley & Sons, Inc.     

Crystallization and thermoreversible gelation of poly(butylene terephthalate)–epoxy mixtures

The thermoreversible gelation of solutions of poly(butylene terephthalate) (PBT) and a liquid diglycidyl ether of bisphenol-A epoxy has been investigated. The morphology of the gels and the conditions under which they form have been characterized by optical microscopy, thermal analysis, and x-ray scattering. Gels were found to form under two different conditions and with different morphologies. Gels formed after a considerable delay when homogenous PBT-epoxy solutions were cooled to slightly below the dissolution temperature of crystalline PBT. These gels contained large, irregular PBT spherulites and smaller birefringent interspherulitic matter. The melting of these gels and the onset of macroscopic flow coincided with the melting of the interspherulitic matter, and occurred before the melting of the large spherulites. Thermoreversible gels formed very quickly when PBT-epoxy solutions were self-nucleated by heating a dispersion of crystalline PBT in epoxy slightly and briefly above the dissolution temperature and then cooling. These gels displayed only a weak background birefringence and were molten when the weak birefringence disappeared. In both cases, gelation occurred by the formation of a three-dimensional PBT network in the epoxy liquid, and the nodes of the network were crystalline PBT particles. $ 1994 John Wiley & Sons, Inc.     

Kinetic relationships of metal filling of epoxy resin by in situ reduction of silver nitrate

The kinetics of metal filling of ED-20 epoxy oligomer by its action on AgNO₃ in the temperature interval 50–90°C was studied.     

Chemical shrinkage and thermomechanical characterization of an epoxy resin during cure by a novel in situ measurement method

In this study, a novel technique is presented to enable the characterization of the dimensional changes and evolution of mechanical properties of a resin during cure. This is achieved using an innovative in situ device called thermal flux cell combined with a Dynamical Mechanical thermal Analyser (DMA). With this system, it is now possible to eliminate the sources of error induced while combining two or more instruments. This device consists into a mold containing the resin where the upper and lower surfaces acting as heat flux sensors. Changes in temperature and thermal flux are directly monitored as well as the dynamical displacement and the stiffness during the curing process. In this work, an epoxy DGEBA resin was used to demonstrate the innovative approach. The tested resin was characterized using different vibration frequencies and amplitudes of the DMA. The results were then processed in order to provide accurate data on gel time and cure kinetics behavior. The volume and mechanical changes were also derived from experimental data and linked to the degree of cure. Chemo and thermo-mechanical models were created to predict the changes in chemical shrinkage and stiffness during cure.     

The effect of stoichiometry on chain segment and ion mobility in partially polymerized epoxy systems

The temperature dependence of steady-shear viscosity and ionic conductivity were measured for a series of unreacted mixtures and partially cured, ungelled samples of diglycidyl ether of bisphenol-A (DGEBA) and an amine cross-linking agent, diamino diphenyl sulfone (DDS). Six stoichiometric ratios of epoxide groups to amine hydrogens were examined. Free volume expressions were used to model the temperature dependence of the conductivity and viscosity for the unreacted DGEBA-DDS mixtures. In addition, these expressions were combined to successfully correlate changes in viscosity and conductivity during the DGEBA-DDS polymerization prior to gelation. It also was demonstrated that the change in weight average molecular weight during polymerization could be interpreted from the dielectric data. Through studying variations in the stoichiometry, it was possible to examine the effects of changes in chemical structure and ion concentration on the fitted parameters in the free volume models. The inherent ion transport factor (ζ₀) was found to be inversely proportional to the concentration of ions in the test samples. The fractional free volume for segmental motion (B) was found to increase with an increase in the glass transition temperature and to be a function of the rigidity of the polymer. ©1995 John Wiley & Sons, Inc.     

Influence of the network chain orientation on the fracture toughness of a mesogenic epoxy resin modified with CTBN

A biphenol‐type epoxy resin, which had a mesogenic group in the backbone moiety, was modified with carboxy‐terminated butadiene acrylonitrile copolymer (CTBN) as a reactive elastomer, and its fracture toughness was measured. With the addition of CTBN, the fracture toughness of the biphenol‐type epoxy resin significantly increased and became significantly higher than that of a bisphenol A‐type epoxy resin modified with CTBN. The network chain orientation in the cured biphenol‐type epoxy resin system was clearly observed during the fracture process with polarized microscopy Fourier transform infrared measurements, although such a phenomenon was not observed in the bisphenol A‐type epoxy resin system. The high toughness of the cured biphenol‐type system was clearly due to the consumption of the mechanical energy by a large deformation of the matrix resin due to the orientation of the network chains during the fracture process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1198–1209, 2003     

Elastomer reinforcement from a glassy polymer polymerized in situ

Cross-linked networks of poly(dimethylsiloxane) were swelled with styrene containing benzoyl peroxide. Polymerization of the styrene in situ, by increasing the temperature, gave novel elastomeric composites. Scanning electron micrographs suggest that low concentrations of styrene (～ 14 wt.%) gave primarily low-molecular-weight polystyrene (PS), which acted merely as a diluent in the networks. Larger amounts gave PS which phase separated into glassy particles having diameters in the approximate range 0.05–1.5 μm. In these cases, an increase in wt.% PS gave networks showing large increases in ultimate strength, which was to be expected. Surprisingly, there were also increases in maximum extensibility, which usually decreases in response to modifications which increase the ultimate strength.     

Thermal behaviour of a polyhedral oligomeric silsesquioxane with epoxy resin cured by diamines

A new material belongs to the family of polyhedral oligomeric silsesquioxanes, the 1-(3-glycidyl) propoxy-3,5,7,9,11,13,15-isobutylpentacyclo-[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxane (glycidylisobutyl-POSS) is characterized by differential scanning calorimetry, thermogravimetric analysis and atomic force microscopy. Epoxy systems based on diglycidyl ether of bisphenol A (DGEBA) cured with the diamines, 4,4'-diamine-diphenylmethane (DDM) and 1,4-phenylenediamine (pPDA), were kinetically studied by differential scanning calorimetry in isothermal and dynamic modes. The thermal behaviour of these systems as the glycidylisobutyl-POSS was added, is discussed later. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of hydroxyl end groups in poly(ethyiene terephthalate) and poly(butylene terephthalate) by reaction with dichloroacetic anhydride

Summary A chemical method is described which provides a reproducible quantitative determination of hydroxyl end groups in poly(ethylene terephthalate) and poly (butylene terephthalate). It is based on esterification at 60° C of the hydroxyl end group with dichloroacetic anhydride as an acetylating reagent in dichloroacetic acid as a solvent. After removal of the excess of esterification reagent and solvent by precipitation techniques, the chlorine content of the modified polymer, which is a measure of the hydroxyl group content, is determined by X-ray fluorescence. The standard deviation of the method is 0.7 mmol OH/kg in the region of 10–200 mmol/kg.

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Bestimmung von Hydroxyl-endgruppen in Polyäthylenterephthalat und Polybutylenterephthalat durch Reaktion mit Dichloressigsäureanhydrid

Zusammenfassung Die Methode basiert auf der Veresterung der Hydroxyl-Endgruppe mit Dichloressigsäureanhydrid als Acetylierungsreagens in Dichloressigsäure als Lösungsmittel bei 60° C. Nach Entfernung des Überschusses an Veresterungsreagens und Lösungsmittel durch Fälltechniken wird der Chlorgehalt des Derivats, der ein Maß für den Hydroxylgruppengehalt ist, mit Hilfe der Röntgenfluorescenz bestimmt. Die Standardabweichung der Methode beträgt 0,7 mmol OH/kg im Bereich von 10–200 mmol/kg.

     

Reactive compatibilization of polyamide‐6 (PA 6)/polybutylene terephthalate (PBT) blends by a multifunctional epoxy resin

A multifunctional epoxy resin has been demonstrated to be an efficient reactive compatibilizer for the incompatible and immiscible blends of polyamide‐6 (PA 6) and polybutylene terephthalate (PBT). The torque measurements give indirect evidence that the reaction between PA and PBT with epoxy has an opportunity to produce an in situ formed copolymer, which can be as an effective compatibilizer to reduce and suppress the size of the disperse phase, and to greatly enhance mechanical properties of PA/PBT blends. The mechanical property improvement is more pronounced in the PA‐rich blends than that in the PBT‐rich blends. The fracture behavior of the blend with less than 0.3 phr compatibilizer is governed by a particle pullout mechanism, whereas shear yielding is dominant in the fracture behavior of the blend with more than 0.3 phr compatibilizer. As the melt and crystallization temperatures of the base polymers are so close, either PA or PBT can be regarded as a mutual nucleating agent to enhance the crystallization on the other component. The presence of compatibilizer and in situ formed copolymer in the compatibilized blends tends to interfere with the crystallization of the base polymers in various blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 23–33, 2000