Thermal and mechanical properties of block copolymers of poly(hexamethylene terephthalate) and poly(oxyethylene) units

Block copolyetheresters of poly(hexamethylene terephthalate) (6GT) with poly(oxyethylene) terephthalate (POET) units have been prepared by polycondensation and certain of their thermal, morphological and mechanical properties have been determined. The copolymers rich in 6GT or POET units show the crystalline characteristics of the single respective homopolymers, whereas in the middle of the composition range crystalline phases of both types coexist. Increase in the proportion of POET units causes a decrease in the melting and glass transition temperatures and in the crystallisation rates whilst concomitantly the mechanical properties change from fibrous to elastomer in type. The results are interpreted in terms of a polycrystallite model in which the compostion-dependent nature of the crystallites and tie bars determines the overall mechanical properties of the copolymers.     

Crystallization, and morphology of poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) segmented block copolymers

A new type of poly(ether-ester) based on poly(trimethylene terephthalate) as rigid segments and poly(ethylene oxide terephthalate) as soft segments was synthesized and its crystallization behavior and morphology were investigated. Differential Scanning Calorimetry revealed that the copolymer containing 57 wt% soft segments presented a low glass transition temperature (−46.4 °C) and a high melting temperature (201.8 °C), suggesting that it had the typical characteristic of thermoplastic elastomer. With increasing soft segment content from 35 to 57 wt%, the crystallization morphology transformed from banded spherulites to compact seaweed morphology at a certain film thickness, which was due to the change of surface tension and diffusivity caused by increasing the soft segment content. Moreover, with the decrease of film thickness from 15 to 2 μm, the crystallization morphology of the copolymer (57 wt% soft segment) changed from wheatear-like, compact seaweed to dendritic. Scanning Electron Microscopy revealed that some flower-like crystals presenting in the bulk, which had been surprisingly found in the poly(ether-ester) segmented block copolymers for the first time. Possible mechanism was discussed in the text.     

Thermal analysis, X-ray and electron diffraction studies on crystalline phase transitions in solvent-treated poly(hexamethylene terephthalate)

The crystal polymorphism, transformation, and morphologies in chloroform solvent-cast poly(hexamethylene terephthalate) (PHT) were examined by using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and temperature in situ transmission electron microscopy (TEM). Solvent-induced crystallization of PHT at room temperature yielded an initial crystal of γ-form, as confirmed by WAXD. Upon DSC scanning, the original γ-form in PHT exhibited three endothermic peaks, whose origins and association were carefully analyzed. The first peak, much smaller than the other two, is in the temperature range of ca. 100-120 °C. It was found that the solvent-induced γ-form was transformed to β-form at 125 °C via a solid-to-solid transformation mechanism. In addition, WAXD showed that γ- and β-forms co-existed in the temperature range of 100-125 °C. These mixed crystal forms were further identified using TEM, and the selected-area electron diffraction (ED) patterns revealed that both γ- and β-form crystals co-existed and were packed within the same spherulite. Solid-solid transformation from the solvent-induced γ-form to β-form in PHT upon heat scanning was presented with evidence and discussed.     

Polyester-Polyether Block Copolymers II. Thermal and Mechanical Properties of Poly(hexamethylene terephthalate)/Poly(oxytetramethylene) Block Copolymers

The melting and crystallisation behaviour of crystalline phases in poly (hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been investigated in relation to copolymer composition and polyether block molecular weight (m.w.). In contrast to that in corresponding homopolymer blends, the polyester crystallinity in the block polymers is greatly reduced by incorporation of polyether units, though some persists even at low polyester contents. Concomitant changes in the glass transition temperatures show part of the polyester component to form a homogeneous component of the amorphous phase. The mechanical properties change with composition in parallel with the changes in copolymer crystallinity and T_g. Copolymers with 20-60 w % of poly(oxytetramethylene) units of m.w. 2000 are highly extensible elastomers. Those with higher m. w. polyether blocks have higher modulus and strength but suffer a serious loss of properties at 60d?C. The observations are interpreted in terms of a model in which polyester crystallites (and polyether crystallites also, for the higher m. w. polyether blocks) are supported within an amorphous matrix by tie-molecules whose nature changes with the copolymer compositions. The results are compared with those for analogous polyester-polyethers having different structural components.     

X-ray and neutron scattering studies of poly(ester carbonate)/poly(ethylene terephthalate) alloys

Quenched blends of poly(ester carbonate) (PEC) and poly(ethylene terephthalate) (PET) have a single T_g and behave as single-phase amorphous alloys up to 67% PET. However, small-angle neutron scattering (SANS) data show that the PET molecules are not statistically distributed as classical Gaussian coils in the PEC matrix. In quenched amorphous PEC-rich films (a single phase), PET-rich domains of varying PET concentration appear to be randomly distributed in the PEC matrix, and the excess SANS intensity is attributable to fluctuations in PET concentrations. Wide- and small-angle X-ray scattering data and SANS results show incomplete phase separation of PET and PEC molecules upon annealing. A possible model for annealed blends (two phases) might be domains of folded-chain, crystalline PET with interlamellar amorphous regions composed of a mixture of PET and PEC molecules. These domains are dispersed in the amorphous PEC matrix.     

Synthesis, characterization, and properties of poly(ethylene terephthalate)/poly(1,4-butylene succinate) block copolymers

Reactive blending at 290 °C of a series of mixtures of poly(ethylene terephthalate) (PET) and poly(1,4-butylene succinate) (PBS) led to the formation of block PET/PBS copolyesters. The block lengths of the resulting copolymers decreased with the severity of the treatment. Copolyesters with PET/PBS molar compositions of 90/10, 80/20, 70/30, and 50/50 were prepared by this method and their composition and microstructure were characterized by ¹H and ¹³C NMR, respectively. The T_g, T_m, and crystallinity of the copolymers decreased as the content in PBS and the degree of randomness increased. The elastic modulus and tensile strength of the copolymers decreased with the content of PBS, whereas, on the contrary, the elongation at break increased. The PET/PBS copolymers exhibited a pronounced hydrolytic degradability, which increased with the content in 1,4-butylene succinic units. Hydrolysis mainly occurred on the aliphatic ester groups.     

Polyester-Polyether Block Copolymers III. Supramolecular Texture in Poly(hexamethylene terephthalate)/Poly(oxytetramethylene) Block Copolymers and Related Homopolymers and Blends

Optical and electron microscopy and small-angle X-ray scattering have been used to investigate the texture of poly(hexamethylene terephthalate)/poly(oxtetramethylene) multi-block copolymers. The findings are consistent with a substantial separation of the combined sub-species into separate phases, and with the aggregation of the alkylene terephthalate ‘hard’ segment blocks into crystalline forms analogous to those of the homopolymer alone and connected by microfibrillar units. The observations are correlated with the mechanical properties of the copolymers in terms of a ‘string of beads’ model, and compared with existing knowledge of phase-separation morphology in other families of block copolymers. Some investigation has also been made into the morphology of poly(hexamethylene terephthalate) and poly(oxytetramethylene) homopolymers and their blends crystallised from the melt. The results are considered in relation to the properties of the corresponding copolymers.     

Crystallization behavior and morphology of double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers

Double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers (PTT/PEOT), with PTT content ranging from 16.5 to 65.5 wt%, were synthesized by melt copolycondensation. The morphological transformation of samples from microphase separation to macrophase separation was investigated by gel permeation chromatography and transmission electron microscopy. Differential scanning calorimetry and in situ wide‐angle X‐ray diffraction suggested that all copolycondensation samples displayed double crystalline behavior. The melt‐crystallization peak temperatures (T_{m, c} values) of PTT chains monotonously increased with increasing PTT content and were higher than that of homo‐PTT when the content of PTT was above 30.6 wt%. Interestingly, T_{m, c} values of PEOT chains were also increased with increasing PTT content. Polarized optical microscopy revealed that all copolycondensation samples studied could form ring‐banded spherulites and band spacing increased with increasing T_c values. In addition, band spacing decreased with increasing PTT content at a given T_c. Strangely, although PEOT was the main component in all copolycondensation samples, spherulitic morphology formed by the advance crystallization of PTT did not change after PEOT crystallization. Only a subtle change of quadrant tones was detected. © 2012 Society of Chemical Industry     

Synthesis and characterisation of copolyesters from poly(ethylene terephthalate) and poly(hexamethylene terephthalate)

Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (T_g). melting points (T_m) and crystallisation temperatures (T_c) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in T_g, T_m and T_c. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation.     

Thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate)/poly(hexamethylene isophthalamide) blends

This work examines the thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate) (PTT)/poly(hexamethylene isophthalamide) (PA 6I) blends. Two temperatures, i.e., 250 and 260°C, are used to prepare the blends, respectively. Differential scanning calorimetry results indicate the immiscible feature of the blends. It is thus concluded that the ester‐amide interchange reaction hardly occurred in the PTT/PA 6I blends. Depending on the composition and mixing temperature, the crystallization ability of PTT in the blends is either enhanced or hindered. Basically, a lower PA 6I content shifts the PTT melt crystallization to a higher temperature, whereas a higher PA 6I content causes an opposing outcome. The original complex melting behavior of neat PTT becomes more regular after the incorporation of 60 wt % or 80 wt % of PA 6I. Thermogravimetry analyses (TGA) show that the thermal stability of the blends improves as the PA 6I content increases. The two‐phased morphology of the blends is examined by scanning electron microscopy (SEM). Polarized light microscopy (PLM) results reveal that the PTT spherulites become coarser with the inclusion of PA 6I; only smaller/dispersed crystallites are observed in the blend with 20 wt % of PTT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

X-ray diffraction studies of ABA propylene–ethylene block copolymers

ABA triblock copolymers of propylene and ethylene, where the central block is a random copolymer of ethylene and propylene and the A blocks are either isotactic polypropylene or polyethylene, are described. Structural changes induced by stretching at room and elevated temperatures are reported. WAXS was used to monitor these changes. The results indicate theat block copolymers were synthesized and that different combinations of mechanical properties may be obtained by varying the type and length of the A blocks and adjusting the monomer ratio in the random B block.     

Crystallization behaviour of random block copolymers of poly(butylene terephthalate) and poly(tetramethylene ether glycol)

The morphology and crystallization behaviour of random block copolymers of poly(butylene terephthalate) and poly(tetramethylene ether glycol) have been investigated. Single crystals have been grown in thin films crystallized from the melt. Well defined lamellae, exhibiting (hkO) single crystal electron diffraction patterns have been observed in copolymers containing down to 49 wt% (0.83 mole fraction) poly(butylene terephthalate). WAXS and electron diffraction support a model of a relatively pure poly(butylene terephthalate) crystal core with the poly(tetramethylene ether glycol) (soft segment) sequences and short hard segments being rejected to the lamellar surface and the soft segment rich matrix. The lateral dimensions of the lamellae are determined by the number of hard segment sequences long enough to traverse the stable crystal size at the crystallization temperature. This leads to an initial population of crystals formed at T_c and a second set of smaller crystals that grow from the short hard segment sequences upon cooling to room temperature. The result is fractionation by sequence length due to a coupling of the sequence distribution with the stable crystal size at the crystallization temperature.     

Confined crystallization of nanolayered poly(ethylene terephthalate) using X-ray diffraction methods

The development of crystalline lamellae in ultra-thin layers of poly(ethylene terephthalate) PET confined between polycarbonate (PC) layers in an alternating assembly is investigated as a function of layer thickness by means of X-ray diffraction methods. Isothermal crystallization from the glassy state is in-situ followed by means of small-angle X-ray diffraction. It is found that the reduced size of the PET layers influences the lamellar nanostructure and induces a preferential lamellar orientation. Two lamellar populations, flat-on and edge-on, are found to coexist in a wide range of crystallization temperatures (T_c = 117–150 °C) and within layer thicknesses down to 35 nm. Flat-on lamellae appear at a reduced crystallization rate with respect to bulk PET giving rise to crystals of similar dimensions separated by larger amorphous regions. In addition, a narrower distribution of lamellar orientations develops when the layer thickness is reduced or the crystallization temperature is raised. In case of edge-on lamellae, crystallization conditions also influence the development of lamellar orientation; however, the latter is little affected by the reduced size of the layers. Results suggest that flat-on lamellae arise as a consequence of spatial confinement and edge-on lamellae could be generated due to the interactions with the PC interface.     

Biodegradable polymers for use in surgery — poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers: 2. In vitro degradation

The degradation mechanism of a series of poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers, synthesized as described in Part 1¹, has been studied in vitro. The need for the development of in vitro test methods for candidate biomaterials is set down. The effect of time, temperature, pH and selected enzymes on the rate and mechanism of degradation is elucidated. The degradation products are identified. The degree of degradation was monitored molecularly by gel permeation chromatography (g.p.c.) and end-group titration techniques. The composition of the copolymers was obtained using infra-red (i.r.) and nuclear magnetic resonance (n.m.r.) spectroscopy. Mass loss and water uptake data are also given. The mechanism of degradation is shown to be by hydrolysis. The effect of ethylene oxide (EO) and ⁶⁰Co γ-irradiation sterilization on the copolymers was investigated.     

The crystal structure of poly(trimethylene terephthalate) by X-ray and electron diffraction

The crystal structure of poly(trimethylene terephthalate), [C₆H₄COO(CH₂)₃OCO]_n has been determined by a combination of electron diffraction, X-ray diffraction and packing analyses.Single crystals having a parallelogram shape were grown from a nitrobenzene solution. Seen in the electron microscope they consist of platelets about 80 Å thick. Single crystal electron diffraction and X-ray fibre diffraction patterns show that the chain molecules are normal to the base plane of the single crystal. For both single crystal and fibre the unit cell of poly(trimethylene terephthalate) is triclinic with parameters: $\text{a = 4.637}\text{A}\text{?}$, $\text{b = 6.266}\text{A}\text{?}$, $\text{c = 18.64}\text{A}\text{?}$ (fibre axis), α = 98.4°, β = 93.0°, γ = = 111.1°. The space group is P1, and the calculated crystalline density: 1.387 g/cm³. Conformational energies were calculated for the monomeric repeating unit using semi-empirical methods. The starting geometry of the residue was derived from previous studies on relevant model compounds. The several plausible molecular models thus obtained were examined by packing and X-ray analyses. The structure consists of rigid planar terephthaloyl residues alternating with a more flexible trimethylene sequence. This OCH₂CH₂CH₂O segment of the chain has a trans-gauche-gauche-trans conformation.     

Reactively formed ENPT copolymers as compatibilizers in ternary blends of poly(ethylene naphthalate)/poly(pentamethylene terephthalate)/poly(ether imide)

The compatibility of ternary blends of poly(ethylene naphthalate)/poly(pentamethylene terephthalate)/poly(ether imide) (PEN/PPT/PEI) was studied by examining the transesterification of PEN and PPT. ENPT copolymers were formed in situ as compatibilizers between PPT and PEI components in ternary blends. Differential scanning calorimetric (DSC) results for ternary blends showed the immiscibility of PEN/PPT/PEI, but ternary blends of all compositions were phase‐homogeneous after heat treatment at 300°C for more than 60 min. Annealing samples at 300°C yielded amorphous blends with a clear, single glass transition temperature (T_g), as the final state. Additionally, ENPT copolymer improved the compatibility of ENPT/PPT/PEI blends, yielding a homogeneous phase in the ENPT‐rich compositions. The morphology of the ENPT/PPT/PEI blends was altered from heterogeneous to homogeneous by controlling the concentration of PPT in the ENPT copolymers as well as the concentration of the ENPT copolymers. Moreover, a homogeneous phase with a clear T_g was observed when the concentration of PPT in the ENPT copolymer fell to 70 wt% in the ENPT/PEI = 50/50 blends. Experimental results indicate how the concentration of PPT in the ENPT copolymer affects miscibility in the ENPT/PEI blends. POLYM. ENG. SCI. 46:337–343, 2006. © 2006 Society of Plastics Engineers     

Poly(dimethylsiloxane)/poly(hexamethylene oxide) mixed macrodiol based polyurethane elastomers. I. Synthesis and properties

The compatibilizing effect of poly(hexamethylene oxide) (PHMO) on the synthesis of polyurethanes based on α,ω‐bis(6‐hydroxyethoxypropyl) poly(dimethylsiloxane) (PDMS) was investigated. The hard segments of the polyurethanes were based on 4,4′‐methylenediphenyl diisocyanate (MDI) and 1,4‐butanediol. The effects of the PDMS/PHMO composition, method of polyurethane synthesis, hard segment weight percentage, catalyst, and molecular weight of the PDMS on polyurethane synthesis, properties, and morphology were investigated using size exclusion chromatography, tensile testing, and differential scanning calorimetry (DSC). The large difference in the solubility parameters between PDMS and conventional reagents used in polyurethane synthesis was found to be the main problem associated with preparing PDMS‐based polyurethanes with good mechanical properties. Incorporation of a polyether macrodiol such as PHMO improved the compatibility and yielded polyurethanes with significantly improved mechanical properties and processability. The optimum PDMS/PHMO composition was 80 : 20 (w/w), which yielded a polyurethane with properties comparable to those of the commercial material Pellethane™ 2363‐80A. The one‐step polymerization was sensitive to the hard segment weight percentage of the polyurethane and was limited to materials with about a 40 wt % hard segment; higher concentrations yielded materials with poor mechanical properties. A catalyst was essential for the one‐step process and tetracoordinated tin catalysts (e.g., dibutyltin dilaurate) were the most effective. Two‐step bulk polymerization overcame most of the problems associated with reactant immiscibility by the end capping of the macrodiol and required no catalysts. The DSC results demonstrated that in cases where poor properties were observed, the corresponding polyurethanes were highly phase separated and the hard segments formed were generally longer than the average expected length based on the reactant stoichiometry. Based on these results, we postulated that at low levels (∼ 20 wt %) the soft segment component derived from PHMO macrodiol was concentrated mainly in the interfacial regions, strengthening the adhesion between hard and soft domains of PDMS‐based polyurethanes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2026–2040, 2000     

Morphology studies of poly(ethylene terephthalate)/silica nanocomposites

Poly(ethylene terephthalate)/silica nanocomposites have been prepared through in situ polymerization. The morphology was investigated by atomic force microscopy in the tapping mode and scanning electron microscope. The interface morphological structure of the poly(ethylene terephthalate)/silica nanocomposites strongly depends on the ratio of silica in the matrix. When silica weight fraction is lower than 3 wt%, the system consists of aggregated silica particles dispersed in the organic matrix; beyond this concentration, the structure is co-continuous with that of the organic matrix. Surface of poly(ethylene terephthalate) was smooth; while nanocomposites were rough, there are good interfacial adhesion and compatibility between the polymer matrix and the nanofillers.     

Paclitaxel-incorporated nanoparticles using block copolymers composed of poly(ethylene glycol)/poly(3-hydroxyoctanoate)

Block copolymers composed of poly(3-hydroxyoctanoate) (PHO) and methoxy poly(ethylene glycol) (PEG) were synthesized to prepare paclitaxel-incorporated nanoparticle for antitumor drug delivery. In a ¹H-NMR study, chemical structures of PHO/PEG block copolymers were confirmed and their molecular weight (M.W.) was analyzed with gel permeation chromatography (GPC). Paclitaxel as a model anticancer drug was incorporated into the nanoparticles of PHO/PEG block copolymer. They have spherical shapes and their particle sizes were less than 100 nm. In a ¹H-NMR study in D₂O, specific peaks of PEG solely appeared while peaks of PHO disappeared, indicating that nanoparticles have core-shell structures. The higher M.W. of PEG decreased loading efficiency and particle size. The higher drug feeding increased drug contents and average size of nanoparticles. In the drug release study, the higher M.W. of PEG block induced the acceleration of drug release rate. The increase in drug contents induced the slow release rate of drug. In an antitumor activity study in vitro, paclitaxel nanoparticles have practically similar anti-proliferation activity against HCT116 human colon carcinoma cells. In an in vivo animal study using HCT116 colon carcinoma cell-bearing mice, paclitaxel nanoparticles have enhanced antitumor activity compared to paclitaxel itself. Therefore, paclitaxel-incorporated nanoparticles of PHO/PEG block copolymer are a promising vehicle for antitumor drug delivery.