Cyclic Butylene Terephthalate Research Articles

Organocatalyzed ring‐opening polymerization of cyclic butylene terephthalate oligomers

ABSTRACTIn 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 Mn 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

Morphology and properties evolution upon ring-opening polymerization during extrusion of cyclic butylene terephthalate and graphene-related-materials into thermally conductive nanocomposites

In this work, the study of thermal conductivity before and after in-situ ring-opening polymerization of cyclic butylene terephthalate into poly (butylene terephthalate) in presence of graphene-related materials (GRM) is addressed, to gain insight in the modification of nanocomposites morphology upon polymerization. Five types of GRM were used: one type of graphite nanoplatelets, two different grades of reduced graphene oxide (rGO) and the same rGO grades after thermal annealing for 1h at 1700°C under vacuum to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and nanoparticle organization were investigated by means of differential scanning calorimetry, electron microscopy and rheology. Electrical and thermal properties were investigated by means of volumetric resistivity and bulk thermal conductivity measurement. In particular, the reduction of nanoflake aspect ratio during ring-opening polymerization was found to have a detrimental effect on both electrical and thermal conductivities in nanocomposites.

Effect of processing conditions on the thermal and electrical conductivity of poly (butylene terephthalate) nanocomposites prepared via ring-opening polymerization

Successful preparation of polymer nanocomposites, exploiting graphene-related materials, via melt mixing technology requires precise design, optimization and control of processing. In the present work, the effect of different processing parameters during the preparation of poly (butylene terephthalate) nanocomposites, through ring-opening polymerization of cyclic butylene terephthalate in presence of graphite nanoplatelets (GNP), was thoroughly addressed. Processing temperature (240°C or 260°C), extrusion time (5 or 10min) and shear rate (50 or 100rpm) were varied by means of a full factorial design of experiment approach, leading to the preparation of polybutylene terephthalate/GNP nanocomposite in 8 different processing conditions. Morphology and quality of GNP were investigated by means of electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry and Raman spectroscopy. Molecular weight of the polymer matrix in nanocomposites and nanoflake dispersion were experimentally determined as a function of the different processing conditions. The effect of transformation parameters on electrical and thermal properties was studied by means of electrical and thermal conductivity measurement. Heat and charge transport performance evidenced a clear correlation with the dispersion and fragmentation of the GNP nanoflakes; in particular, gentle processing conditions (low shear rate, short mixing time) turned out to be the most favourable condition to obtain high conductivity values.

Influence of high temperature on the flexural properties of GF/pCBT laminates and their fusion-bonded joints

Abstract The glass fiber reinforced poly cyclic butylene terephthalate (GF/pCBT) composite laminates and their fusion-bonded joints were prepared at appropriate polymerization temperature. The connection types of joints were designed and optimized. A series of bending tests were conducted to research their mechanical behaviors at different temperatures. Experimental results showed that flexural properties of laminates and joints decreased as temperature increased. The temperature sensitivity of specimens changes in the temperature range from 50 °C to 75 °C due to the glass transition of the pCBT matrix. Furthermore, the failure modes of GF/pCBT composite joints were investigated at room and high temperature. In addition, the specimens suffered by different high temperatures ranging from 25 °C to 200 °C were cooled and then tested at room temperature. The results indicated the flexural strength of laminates was nearly constant after experience of high temperature, and increased slightly when the temperature is above 175 °C. The flexural strength of fusion-bonded joints was not affected by high temperature.

Effect of morphology and defectiveness of graphene-related materials on the electrical and thermal conductivity of their polymer nanocomposites

In this work, electrically and thermally conductive poly (butylene terephthalate) nanocomposites were prepared by in-situ ring-opening polymerization of cyclic butylene terephthalate (CBT) in presence of a tin-based catalyst. One type of graphite nanoplatelets (GNP) and two different grades of reduced graphene oxide (rGO) were used. Furthermore, high temperature annealing treatment under vacuum at 1700{\deg}C was carried out on both RGO to reduce their defectiveness and study the correlation between the electrical/thermal properties of the nanocomposites and the nanoflakes structure/defectiveness. The morphology and quality of the nanomaterials were investigated by means of electron microscopy, x-ray photoelectron spectroscopy, thermogravimetry and Raman spectroscopy. Thermal, mechanical and electrical properties of the nanocomposites were investigated by means of rheology, dynamic mechanical thermal analysis, volumetric resistivity and thermal conductivity measurements. Physical properties of nanocomposites were correlated with the structure and defectiveness of nanoflakes, evidencing a strong dependence of properties on nanoflakes structure and defectiveness. In particular, a significant enhancement of both thermal and electrical conductivities was demonstrated upon the reduction of nanoflakes defectiveness.

Phase Morphology and Mechanical Properties of Cyclic Butylene Terephthalate Oligomer-Containing Rubbers: Effect of Mixing Temperature.

In this work, the effect of mixing temperature (Tmix) on the mechanical, rheological, and morphological properties of rubber/cyclic butylene terephthalate (CBT) oligomer compounds was studied. Apolar (styrene butadiene rubber, SBR) and polar (acrylonitrile butadiene rubber, NBR) rubbers were modified by CBT (20 phr) for reinforcement and viscosity reduction. The mechanical properties were determined in tensile, tear, and dynamical mechanical analysis (DMTA) tests. The CBT-caused viscosity changes were assessed by parallel-plate rheometry. The morphology was studied by scanning electron microscopy (SEM). CBT became better dispersed in the rubber matrices with elevated mixing temperatures (at which CBT was in partially molten state), which resulted in improved tensile properties. With increasing mixing temperature the size of the CBT particles in the compounds decreased significantly, from few hundred microns to 5–10 microns. Compounding at temperatures above 120 °C and 140 °C for NBR and SBR, respectively, yielded reduced tensile mechanical properties most likely due to the degradation of the base rubber. The viscosity reduction by CBT was more pronounced in mixes with coarser CBT dispersions prepared at lower mixing temperatures.

Synergistic enhancement of thermal conductivity in composites filled with expanded graphite and multi-walled carbon nanotube fillers via melt-compounding based on polymerizable low-viscosity oligomer matrix

We found that the thermal conductivity of the polycarbonate (PC) composite filled with both 9.9 wt% expanded graphite (EG) and 0.1 wt% multi-walled carbon nanotube (MWCNT) fillers was synergistically improved by 49% compared to that of the PC composite filled with 10 wt% EG alone. In order to induce the optimal internal structure favorable for thermal conduction by enhancing the dispersion of the second MWCNT fillers, we applied a two-step melt-compounding to fabricate composites using a MWCNT masterbatch based on a polymerizable oligomer resin, cyclic butylene terephthalate (CBT), which is characterized by ultra-low viscosity and excellent impregnability during initial melting. Three-dimensional (3D) non-destructive characterization using X-ray micro computed tomography (micro-CT) was utilized to demonstrate the synergistic enhancement and to verify dispersion and 3D thermal network of the fillers in the composites accurately. The synergistic enhancement was significantly affected by the formation of the efficient thermally conductive pathways and dispersion of the second MWCNT fillers.

Investigating the Thermal and Thermophysical Properties of Composite Materials Based on Polyethylene Terephthalate and Superconcentrates of Layered Silicate Nanoparticles in Cyclic Butylene Terephthalate

New composite materials based on polyethylene terephthalate and superconcentrates of layered silicate nanoparticles in cyclic butylene terephthalate were developed and investigated. It was shown that the obtained concentrates of nanoparticles are sufficiently thermally stable for the modification of heat-resistant polymer matrices and increase the thermal and processing properties of the polyethylene terephthalate without lowering the molecular weight. By differential scanning calorimetry it was shown that the concentrates of layered silicate nanoparticles act as nucleators for the crystallising PET.

Catalytic Ring-Opening (Co)polymerization of Semiaromatic and Aliphatic (Macro)lactones

The ring-opening polymerization (ROP) of cyclic butylene terephthalate oligomers (cBT) using an aluminum salen catalyst was investigated. The kinetic analysis of the ROP of cBT in tetrachloroethane (TCE) revealed a first-order dependence of the rate constant in catalyst as well as monomer concentration. Comparison with the ROP in other solvents showed that TCE significantly retards the reaction by short-term reversible catalyst deactivation and by long-term permanent deactivation. The apparent activation energy for the ROP of cBT and e-caprolactone (CL) were determined independently, and the difference in reactivity was used to investigate the possibility to synthesize blocky copolymers. Sequence distribution analysis of the copolymers obtained over a period of time from a single feed copolymerization revealed that over the full reaction range the degree of randomness was high. A sequential feed approach, in which CL was added after the polymerization of cBT was completed, showed that the propagation reac...

Preparation and Characterization of Multiwalled Carbon Nanotubes-Reinforced pCBT by Ring-Opening Polymerization of Cyclic Butylene Terephthalate

Multiwalled carbon nanotubes (MWCNT)-reinforced polymerized cyclic butylene terephthalate (pCBT) nanocomposites were prepared by in situ ring opening polymerization of cyclic butylene terephthalate oligomers (CBT). The results of differential scanning calorimetry (DSC) indicated that the melting peak located at the low temperature (Tm1) increased and that at higher temperature (Tm2) decreased with the increasing of content of the MWCNT. During the cooling the MWCNT served as nucleation points from where crystallization can start. The more the MWCNT in the system the earlier the crystallization starts. The Morphological investigations performed by scanning electron microscopy (SEM) shown that the MWCNT were embedded in the matrix and held tightly by the matrix. The modulus and strength increased with MWCNT concentration in the nanocomposites, however, the elongation at break, absorbed energy at break and impact strength were decreased with the increasing of MWCNT content.

Significantly enhanced surface electrical conduction of poly(butylene terephthalate) insulators by direct fluorination

Commercialization of cyclic butylene terephthalate oligomers has opened the door to bulky poly(butylene terephthalate) (PBT) matrix composite parts. In view of the potential applications of PBT in high voltage insulation or other sectors, where surface charge can play an unwanted role, PBT sheets were surface fluorinated in a laboratory vessel using a F2/N2 mixture with 12.5% F2 by volume at the different temperatures of 25, 55, and 85 ° C for the same time of 30 min, to enhance surface electrical conduction and to investigate the effect of fluorination temperature. Conductivity measurements reveal that the fluorinated samples have a much higher surface conductivity than the unfluorinated sample, and surface conductivity significantly increases with fluorination temperature. In accordance with the conductivity measurements, surface potential measurements after corona charging show that the fluorinated samples have a lower or much lower initial surface potential or even no surface potential, strongly depending on fluorination temperature and ambient humidity, compared with a high surface potential of the unfluorinated sample. ATR-IR analyses indicate that fluorination led to substantial changes in surface composition and structure, depending on fluorination temperature. SEM cross section and surface images show an increase of the fluorinated layer thickness with fluorination temperature and a modification of the surface morphology. Contact angle measurements of water show that fluorination also led to a significant increase in surface hydrophilicity, especially at higher fluorination temperatures. The intrinsic increase in surface electrical conduction is considered to be a result of competition between surface compositional changes and surface structural changes or the chemical traps and the physical traps.

Synchronous architecture of ring-banded and non-ring-banded morphology within one spherulite based on in situ ring-opening polymerization of cyclic butylene terephthalate oligomers

Ring-banded morphology of pCBT accompanied by the synchronous evolution of non-ring-banded patterns was investigated through the crystallization of pCBT prepared by ROP of CBT.

Effect of aging on the mechanical performance of GF/pCBT composites

In this paper, we studied the mechanical performance of the thermoplastic composites serviced in aging environment. A serious of specimens was exposed in various conditions for up to 28 days, and then the hygroscopicity and mechanisation of the material were investigated. It is found that water absorb rate first increases and then decreases with increasing of the duration in corrosion tests. Chloride ion concentration and corrosion time have influence on the moisture absorption kinetics of the materials. Results also show that mechanical properties such as modulus and strength of poly cyclic butylene terephthalate and its glass fibre-reinforced composites various with moisture absorption curves.

Effect of hard segment length on the properties of poly(ether ester) elastomer prepared by one pot copolymerization of poly(ethylene glycol) and cyclic butylene terephthalate

A series of poly(ether ester) thermoplastic elastomer were synthesized by a novel single step of cyclic butylene terephthalate (CBT) and poly(ethylene glycol) (PEG) in the presence of stannoxane catalyst at an elevated temperature. The resultant copolymers (pCBT–PEG) based on polymerized cyclic butylene terephthalate (pCBT) as the hard segment and PEG as the soft segment were characterized by means of fourier transform infrared spectrometer (FI-IR), proton nuclear magnetic resonance (1H NMR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) testing. The influence of hard segment length on the properties of the copolymer was investigated in the case of the soft segment length remaining constant. It is found that the pCBT segment length calculated from 1H NMR spectra was decreased with the increase of PEG content. The glass transition, melting and crystallization temperatures and the degree of crystallinity of hard segments were increased with the increase of the pCBT segment length. Thermogravimetry (TG) and derivative TG (DTG) results revealed that the thermal degradation of copolymers was slower than that of the pCBT homopolymer. Mechanical properties of polymers were also reported and the stiffness of the copolymer was improved with the increase of hard segment length.

Effect of modification of cyclic butylene terephthalate on crystallinity and properties after ring-opening polymerisation

Ring-opening polymerisation of the macro-cyclic oligomer of butylene terephthalate at elevated temperatures was found to produce high molecular weight polybutylene terephthalate that was both highly crystalline and brittle. The impact of reactive and non-reactive additives on the polymerisation, crystallisation and final crystal structure was extensively studied using differential scanning calorimetry and rheological methods and correlated with observed improvements in fracture toughness and tensile properties for both the neat resin and mode I and II fracture toughness of the fibre-reinforced composites. The reactive modifiers used were bi-functional epoxy resins, namely diglycidyl ether of bis phenol A, butanediol diglycidyl ether and bis[(glycidyl ether)phenyl)]-m-xylene, while the non-reactive modifiers were selected β nucleants and the ductile thermoplastic, polyethylene glycidyl methacrylate.

Effect of fiber surface modification on water absorption and hydrothermal aging behaviors of GF/pCBT composites

Water absorption and aging behaviors of fiber reinforced polymerized poly (cyclic butylene terephthalate) (GF/pCBT) composites are investigated. We coated nano-silica on glass fiber surface by physical vapor deposition (PVD) method. Subsequently, we immersed pCBT composites reinforced with nano-treated/untreated fibers in 25 °C and 60 °C distilled water until their saturated moisture. We also exposed some specimens in various hydrothermal aging environments. We tested the mechanical performance of these test specimens and found that the mechanical performance of both pCBT cast and GF/pCBT composites reduces obviously after water absorption and hydrothermal aging. However, nano-silica modified fiber reinforced composites have higher remaining strength than GF/pCBT. Scanning electron microscope (SEM) is used to study the microscopic phase and nanoparticle modified mechanism, and better interface characteristic between fibers and matrix is observed.

Effect of fiber surface modification on the lifetime of glass fiber reinforced polymerized cyclic butylene terephthalate composites in hygrothermal conditions

Abstract Mechanical performances of polymerized cyclic butylene terephthalate (pCBT) matrix, glass fiber reinforced pCBT (GF/pCBT), and nano-silica modified glass fiber/pCBT composites (nano-GF/pCBT) in hygrothermal condition were investigated. All the materials were aged in hygrothermal environments for up to three months, and then their mechanical strength degeneration ratio (SDR) was calculated. To study the aging effect of temperature, specimens with and without nano-silica modification were tested in temperatures ranging from 298 to 500 K. Differential scanning calorimeter (DSC) test, dynamic mechanical analysis (DMA), and fiber pull-out test were adopted to complement the experimental results. It is found that all the SDR-time curves follow the linear relationship in hygrothermal environment, while SDR-temperature curves follow a bilinear relationship due to the effect of glass transition temperature (Tg) of the matrix. Fibers modified by coating nano-silica on the surface could decrease SDR of the composites. This is due to the fact that the fillers on the fiber surface could resist the movement of pCBT molecular chain and diffusion of water molecules in aging conditions. The fiber pull-out test verifies that the interface strength between fiber and matrix is enhanced by the modification.

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 (pCBT) strongly affected the final properties of pCBT 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 pCBT are determined by this isothermal ROP stage; polymerization and crystallization are gradually separated with the increase of temperature of ROP (T P) from 204 °C, and the crystallization properties of pCBT 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 T P 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.

New Bismaleimide Resin Toughened by In Situ Ring-Opening Polymer of Cyclic Butylene Terephthalate Oligomer with Unique Organotin Initiator

A new organotin initiator with amino-terminated hyperbranched polysiloxane (HSiSn) for the ring-opening polymerization of cyclic butylene terephthalate (CBT) oligomer was synthesized. Compared with a traditional initiator, butyltin chloride dihydroxide (BCD), HSiSn has a moderate initiate speed, lower toxicity, and good reactivity. Poly(butylene terephthalate) (PBT) is the ring-opening polymer of CBT, of which the crystalline and molecular weight are almost independent of the initiator used, but the PBT initiated by HSiSn has better thermal stability than that by BCD. On this basis, a series of new toughened bismaleimide (BD) resins (HSiSn/CBT-BD) were prepared through the in situ formation of PBT during the prepolymerization of BD resin with HSiSn. Compared with BCD/CBT-BD and BD resins, HSiSn/CBT-BD resins with small loadings of CBT (≤5 wt %) have remarkably improved integrated performances, including higher impact strengths, improved flexural, and tensile properties, better dielectric properties, and e...

Preparation and Characterization of <i>In Situ</i> Polymerized Cyclic Butylene Terephthalate and its Composites

A fatal disadvantage of continuously reinforced thermoplastic composites is the high melt viscosity of the matrix which hampers impregnation. However, the melt viscosity of low molecular weight CBT resin can reach extremely low value, which simplifies impregnation and enables the use of thermoset production methods. The thermal analysis, rheological analysis and mechanical property on the polymerization and crystallization of CBT into poly (cyclic butylene terephthalate) (PCBT) at different ratios of catalyst were investigated in this paper. The continuous glass fiber (GF) reinforced PCBT composite with over 70% fiber volume content was prepared via in situ polymerization, and the mechanical property of the PCBT was studied. The best impregnation time was decreased and the degree of crystallinity was increased respectively with catalyst fraction increasing. The tensile/flexural strength and modulus of PCBT resin and GF/PCBT composites were enhanced when the catalyst fraction increased from 0.3% to 0.6%.