Cyclic Butylene Terephthalate Oligomers Research Articles

Isocyanate toughened pCBT: Reactive blending and tensile properties

Cyclic butylene terephthalate oligomers (CBT) were reacted in a ring-opening polymerization with three types of isocyanates: a bifunctional aromatic type, a bifunctional aliphatic type and a polymeric aromatic isocyanate. All reactions took place in a batch mixer. The use of 0.5 to 1 wt% isocyanate led to a dramatic increase in elongation at break of polymer- ized cyclic butylene terephthalate (pCBT), from 8 to above 100%. The stiffness and strength of the modified pCBT, however, were found to slightly decrease. Proton nuclear magnetic resonance (NMR) analysis shows that the formation of thermally stable amide groups is the dominant chain extension reaction mechanism. Gel content measurements suggest a linear struc- ture for samples containing bifunctional isocyanates while pCBT modified with polyfunctional isocyanate exhibited some gel formation at higher isocyanate content. Melting and crystallization temperatures as well as degree of crystallinity were found to decrease with increasing isocyanate content. No phase separation was detected by scanning electron microscopy (SEM) analysis. Moreover, a high degree of polymerization is deduced due to the absence of CBT oligomer crystals.

Living lamellar crystal initiating polymerization and brittleness mechanism investigations based on crystallization during the ring-opening of cyclic butylene terephthalate oligomers

The brittleness of polymerized cyclic butylene terephthalate (pCBT) is generally ascribed to its high crystallization degree and perfect crystal structure. Herein, a simple and effective method for improving the brittleness of pCBT is presented. Unlike other published toughening methods, this method did not decrease or destroy any of the natural advantages of cyclic butylene terephthalate oligomers (CBT) and its ring-opening polymerization (ROP). The melting behaviour and crystallization of CBT demonstrated that some CBT crystals were unable to melt completely during ROP. These un-melted crystals served as self-compatible nucleators and reduced the crystallization induction time of pCBT during ROP, they also plant many stress concentration points which result in the brittleness of pCBT, according to mechanical tests and crystallization kinetics. Finally, the “living lamellar crystal” initiating ROP and new brittleness mechanisms were proposed.

Improved Electrical Conductivity of a Carbon Nanotube Mat Composite Prepared by In-Situ Polymerization and Compression Molding with Compression Pressure

A fabrication method to improve the processability of thermoplastic carbon nanotube (CNT) mat composites was investigated by using in-situ polymerizable and low viscous cyclic butylene terephthalate oligomers. The electrical conductivity of the CNT mat composites strongly depended on the compression pressure, and the trend can be explained in terms of two cases, low and high compression pressure, respectively. High CNT mat content in the CNT mat composites and the surface of the CNT mat composites with fully contacted CNTs was achieved under high compression pressure, and direct contact between four probes and the surface of the CNT mat composites with fully contacted CNTs gave resistance of <TEX>$2.1{\Omega}$</TEX>. In this study the maximum electrical conductivity of the CNT mat composites, obtained under a maximum applied compression pressure of 27 MPa, was 11 904 S <TEX>$m^{-1}$</TEX>, where the weight fraction of the CNT mat was 36.5%.

Polyvinylidene fluoride/poly(ethylene terephthalate) conductive composites for proton exchange membrane fuel cell bipolar plates: Crystallization, structure, and through‐plane electrical resistivity

AbstractPolyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET)‐based composites for proton exchange membrane fuel cell bipolar plates (BPs) were prepared at different crystallization temperatures and characterized by X‐ray diffraction, differential scanning calorimetry, and resistivity setup. Composite conductivity was made possible by using a mixture of carbon black (CB) and graphite (GR). To improve composite processability, its viscosity was reduced by adding a small amount of cyclic butylene terephthalate (c‐BT) oligomer and thermoplastic polyolefin elastomer. In the PVDF/PET‐based composite, it was found that PVDF phase could crystallize easily but PET crystallization was difficult. Because of the CB/GR additives, the formed crystals in PVDF/PET phases had a poor perfection degree and showed a lower melting temperature when compared with pure PVDF and PET. It was observed that PET nucleation was accelerated but not that of PVDF. According to through‐plane resistivity results, composite crystallization temperature range was divided into two parts (below/above 170°C), in which a different variation behavior of through‐plane resistivity was observed. It has been proved that the resistivity was mainly governed by the network of CB/GR developed inside the PET phase, and decreasing the crystallinity of PET led to a decrease of through‐plane resistivity, which is desirable for BPs. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Miscibility in cyclic poly(butylene terephthalate) and styrene maleimide blends prepared by solid‐dispersion and in situ polymerization of cyclic butylene terephthalate oligomers within styrene maleimide

AbstractBlends of cyclic butylene terephthalate oligomers (CBT) and styrene maleimide (SMI) were prepared by a solid dispersion technique in various compositions ranging from 90 to 10 wt % of CBT. In situ polymerization of the oligomers in the blend at 190°C produced a blend of cyclic poly(butylene terephthalate) (c‐PBT) and SMI. The blends were characterized by a variety of techniques including differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that the presence of 30 wt % and above of SMI impeded the crystallization of c‐PBT to such an extent that crystallization could not be detected under the conditions of the DSC experiment. The blend system exhibited a single composition‐dependent glass transition temperature (Tg), which indicated the presence of miscibility. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and characterization of poly (butylene terephthalate)/graphene composites by in-situ polymerization of cyclic butylene terephthalate

The ultra-low viscosity of cyclic butylene terephthalate oligomers has been exploited to perform their in-situ ring-opening polymerization in the presence of graphene, to obtain homogeneously dispersed poly(butylene terephthalate)/graphene (PBT/G) composites containing 0.5 to 1.0 %wt of graphene. The results of gel permeation chromatography show that increasing amounts of graphene causes a decrease in the average molecular weight of PBT if the time of polymerization is kept constant, and morphological investigations performed by electron microscopy and x-rays diffraction show that high levels of dispersion of the G sheets are easily obtained by this method of composites processing. Thermal properties of the composites were studied by differential scanning calorimetry and thermogravimetric analysis; results indicate that increasing amounts of G do not strongly influence the degree of crystallinity and the crystallization temperature of PBT, while its thermal stability is significantly increased by the presence of G. All the PBT/G composites demonstrated to be electrically conductive; we found that the electric field assisted thermal annealing of the PBT/G composites induces an increase in conductivity.

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 &amp; Sons, Ltd.

Entropically-driven ring-opening polymerization of cyclic butylene terephthalate: Rheology and kinetics

Cyclic butylene terephthalate oligomers (CBT) with ultra-low melt viscosity can be polymerized into poly (butylene terephthalate) (pCBT) via entropically-driven ring-opening polymerization (ED-ROP) in a short time (ranging from several seconds to 10 min) with no chemical emission and no heat generation during the polymerization process. Due to no heat generation, dynamic rheological measurements were used to monitor the polymerization of CBT from 220 to 250°C. The polymerization was accompanied by a steep increase of the melt viscosity and modulus in isothermal rheological tests, and much faster at higher temperature. With rheological results, reptation theory and Double reptation model were adopted to determine the variation of the molecular weight and concentration with time for pCBT. According to the ED-ROP mechanism of CBT, kinetics equations were also established to simulate the polymerization process. Furthermore, using the results of variation of molecular weight with time for pCBT and kinetics equations, the polymerization rate constants for initiation and propagation steps were evaluated, and the activation energy was also obtained. It was proved that rheological method is a convenient and reliable way to investigate the kinetics of ED-ROP of CBT. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Synthesis and properties of poly(butylene terephthalate)/multiwalled carbon nanotube nanocomposites prepared by in situ polymerization and in situ compatibilization

AbstractA novel cyclic initiator was synthesized from dibutyl tin(IV) oxide and hydroxyl‐functionalized multiwalled carbon nanotubes (MWNTs) and was used to initiate the ring‐opening polymerization of cyclic butylene terephthalate oligomers to prepare poly(butylene terephthalate) (PBT)/MWNT nanocomposites. The results of Fourier transform infrared and NMR spectroscopy confirmed that a graft structure of PBT on the MWNTs was formed during the in situ polymerization; this structure acted as an in situ compatibilizer in the nanocomposites. The PBT covalently attached to the MWNT surface enhanced the interface adhesion between the MWNTs and PBT matrix and, thus, improved the compatibility. The morphologies of the nanocomposites were observed by field emission scanning electron microscopy and transmission electron microscopy, which showed that the nanotubes were homogeneously dispersed in the PBT matrix when the MWNT content was lower than 0.75 wt %. Differential scanning calorimetry and thermogravimetric analysis were used to investigate the thermal properties of the nanocomposites. The results indicate that the MWNTs acted as nucleation sites in the matrix, and the efficiency of nucleation was closely related to the dispersion of the MWNTs in the matrix. Additionally, the thermal stability of PBT was improved by the addition of the MWNTs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Rolling and sliding wear properties of hybrid systems composed of uncured/cured HNBR and partly polymerized cyclic butylene terephthalate (CBT)

The phase structure, rolling and sliding wear properties of the hybrids composed of uncured/cured hydrogenated acrylonitrile/butadiene rubber (HNBR) and partly polymerized cyclic butylene terephthalate oligomers (CBT) were investigated. The ratio between HNBR and CBT was varied in the hybrids between 1:0.5 and 1:2. The CBT conversion and phase structure were studied by extraction, differential scanning calorimetry, and dynamic-mechanical thermal analysis.The rolling and sliding wear behaviors of the hybrids under unlubricated condition were determined by using various wear test rigs. It was found that the partly polymerized CBT worked as reinforcement in the HNBR matrix. The specific wear rate of the compounds usually decreased with increasing amount of CBT in both rolling and sliding wear tests. The coefficient of friction (COF) of the hybrids strongly depended on the type and configuration of the wear tests. Dynamic vulcanization of the HNBR in the HNBR/CBT mixes mostly improved the tribological performance. The wear mechanisms were studied as a function of CBT content and discussed.

Novel conductive polymer composites based on poly(butylene terephtalate) filled with carbon fibers

AbstractPoly(butylene terephthalate) (cPBT) synthesized from cyclic Butylene Terephthalate oligomers (CBT) was used as a matrix for carbon fibre (CF) conducting polymer composites (CPC). DSC, rheological studies and measurements of torque of CBT/CF were performed in order to optimise the processing conditions of CPC. DC and AC measurements were carried out for these composites and have shown a low percolation threshold for cPBT/CF.

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.

Surface Characteristics of Polyhedral Oligomeric Silsesquioxane Modified Clay and Its Application in Polymerization of Macrocyclic Polyester Oligomers

Novel porous aminopropyllsooctyl polyhedral oligomeric silsesquioxane (POSS) modified montmorillonite clay complexes (POSS-Mts) with large interlayer distance and specific surface area have been successfully prepared via ion-exchange reaction and followed by freeze-drying treatment. The morphology of the POSS-Mts is highly influenced by the POSS concentration, pH of the suspension and drying procedure, but the interlayer distance of the POSS-Mts does not change much when the POSS concentration is above 0.4 CEC. The POSS-Mts were used as Sn-catalyst supporters to initiate the ring-opening polymerization of cyclic butylene terephthalate oligomers (CBT) for the first time. No diffraction peak was detected by wide-angle X-ray diffraction for the polymerized composites (pCBT/POSS-Mt), even at 10 wt % loading of POSS-Mt. A clay network rather than exfoliation structure was observed unexpectedly in the composites by transmission electron microscopy. The pCBT/POSS-Mt composite with 10 wt % POSS-Mt was further melt-compounded with commercial PBT resin as a master batch. The tensile properties of the resultant PBT/POSS-Mt composites were highly improved as compared to the pristine PBT due to the homogeneous dispersion of POSS-Mt in the PBT matrix.

Crystallization‐induced shrinkage, crystalline, and thermomechanical properties of in situ polymerized cyclic butylene terephthalate

AbstractThe polymerization and crystallization of cyclic butylene terephthalate oligomers (CBT) were followed by fiber Bragg grating (FBG) and normal force measurements under isothermal conditions at T = 170 and 190°C, respectively. It was found that the FBG and normal force sense only the crystallization‐induced shrinkage. The course of the FBG signal and the normal force as a function of time suggested that crystallization of the polymerized CBT (pCBT) occurs in two steps. The primary crystallization‐induced shrinkage is several hundreds by contrast to the secondary one showing several tens in ppm/min unit according to the FBG results. The two‐step crystallization was confirmed by normal force measurements. The crystallinity and crystalline structure of the pCBTs were studied by differential scanning calorimetry and wide‐angle X‐ray scattering. It was found that the crystallinity and the crystalline parameters slightly differ for the pCBTs formed at T = 170 and 190°C, respectively. The pCBT produced at T = 190°C had slightly higher crystallinity and more perfect crystals than the pCBT formed at T = 170°C. The reliability of the FBG sensing was checked by thermomechanical analysis (TMA). A fair agreement was established between the thermal contraction and thermal expansion measured by FBG and TMA, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Hybrids of HNBR and in situ polymerizable cyclic butylene terephthalate (CBT) oligomers: properties and dry sliding behavior

A peroxide curable hydrogenated nitrile rubber (HNBR) was modified by cyclic butylene terephthalate oligomer (CBT), added in 100 parts per hundred rubber (phr). CBT polymerization was expected to occur simultaneously with that of the curing of the HNBR rubber (T = 190°C, t =2 5 min). Differential scanning calorimetry (DSC) indicated that only a minor part of CBT has been polymerized (pCBT) in the hybrid. Dynamic mechanical thermal analysis (DMTA) revealed that HNBR formed the continuous whereas (p)CBT the dispersed phase. Mechanical properties (hardness, tensile modulus, ultimate tensile strength and strain, tear strength) of the HNBR and HNBR/CBT were determined and collated. Tribological properties were investigated with pin(steel)-on- plate(rubber) (POP), with roller(steel)-on-plate (rubber) (ROP), with oscillating steel cylinder on rubber plate (Fretting) test configurations. Coefficient of friction (COF) and specific wear rate of the HNBR-based systems were determined. It was found that the resistance to wear increases with CBT hybridization. On the other hand, COF did not change much with CBT content. The friction and wear characteristics strongly depended on the test configurations. The worn surface of the HNBR systems was inspected in scanning electron microscope (SEM) to conclude the typical wear mechanisms. SEM investiga- tion showed that the CBT was predominantly recrystallized from its molten state under the curing conditions set. The well developed prism- and platy-like, micron-scaled CBT crystals were made responsible for the reinforcing effect observed.

Melting and crystallization of in-situ polymerized cyclic butylene terephthalates with and without organoclay: a modulated DSC study

The polymerization of cyclic butylene terephthalate oligomers (CBT) were studied in presence (in 5 wt.%) and absence of an organoclay (Cloisite ® 30B) by modulated DSC (MDSC). The organoclay containing samples were produced by dry and melt blending, respectively. The first heating, causing the polymerization of the CBT catalyzed by an organotin compound, was followed by cooling prior to the second heating. The MDSC scans covered the temperature interval between 0 and 260°C. The aim of this protocol was to study the crystallization and melting behavior of the resulting poly- butylene terephthalate (pCBT) and its organoclay modified nanocomposites. It was found that the thermal behaviors of the polymerizing and polymerized CBT (pCBT) were strongly affected by the sample preparation. The organoclay suppressed the crystallization of the pCBT produced during the first heating. However, results from the second heating suggest that more perfect crystallites were formed in the organoclay modified pCBT variants. The organoclay also affected the conver- sion and mean molecular mass of the resulting pCBT which were slightly lower than those of the plain pCBT polymerized under identical conditions.

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.

On the in‐situ polymerization of cyclic butylene terephthalate oligomers: DSC and rheological studies

AbstractThe thermal and rheological behaviors of cyclic butylene terephthalate (CBT) were studied with differential scanning calorimetry (DSC) and plate–plate rheometry, respectively. DSC scans were taken at different heating rates. The related first‐heat thermograms indicated crystallization and melting of the resulting poly (butylene terephthalate) (PBT) only at very low heating rate (0.5°C/min). As the crystallization and melting enthalpies were closely matched, one could conclude that the polymerization is essentially athermic. The polymerization was accompanied by a steep increase of the melt viscosity in isothermal rheological tests performed in the temperature range T = 145–210°C. Changes in the viscoelasticity of the polymerizing CBT and crystallizing PBT could be best followed by considering the changes in the phase angle. Viscosity increased with the conversion exponentially in the first approximation. POLYM. ENG. SCI., 46:743–750, 2006. © 2006 Society of Plastics Engineers

Thermal analysis of novel underfill materials with optimum processing characteristics

AbstractThis work encompasses the development of low‐viscosity cyclic oligomer underfill formulations that cure without heat evolution. Boron nitride, silica‐coated aluminum nitride, and alumina ceramic powders were used as fillers in cyclic butylene terephthalate oligomer melts. The melts were heated with a suitable catalyst to induce polymerization. The effects of the filler type and composition on the thermal and mechanical properties of the poly(butylene terephthalate)/filler composites were examined with differential scanning calorimetry, temperature‐modulated differential scanning calorimetry, thermogravimetric analysis, thermomechanical analysis, and dynamic mechanical analysis. Scanning electron microscopy was employed to elucidate the morphology of these composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1300–1307, 2005