Structure-property behaviour of poly(ether ether ketone)-polydimethylsiloxane block copolymers and their ketamine precursors (original) (raw)
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POLYMER CRYSTALLIZATION, 2018
This work reports the crystallization behavior of a series of poly(ether-mb-amide) multiblock copolymer (PEAc) samples, composed of long-chain carbon polyamide 1012 (PA1012) as hard segments and poly(tetramethylene oxide) (PTMO) as soft segments. Rheological and dynamic mechanical results showed that PA1012-mb-PTMO multiblock copolymers are microphase segregated in the both melt and solid states, forming two partially miscible phases with distinct crystallization and glass-transition temperatures that depend on composition. The copolymers are probably in the weak segregation limit, as the PA1012-rich phase can break out and form spherulitic templates during cooling from the melt.
Crystallization in Block Copolymers with More than One Crystallizable Block
Progress in Understanding of Polymer Crystallization
Recent results on the crystallization of block copolymers with more than one crystallizable block are reviewed. The effect that each block has on the nucleation, crystallization kinetics and location of thermal transitions of the other blocks has been considered in detail. Depending on the thermodynamic repulsion between the blocks, the initial melt morphology in weakly segregated double crystalline diblock copolymers can be sequentially transformed by the crystallization of the different blocks. The crystallization kinetics of each block can be dramatically affected by the presence of the other, and by the crystallization temperature; the magnitude of the effect is a function of thermodynamic repulsion. Also the morphology has been investigated and peculiar double crystalline spherulites with intercalated semi-crystalline lamellae of each component have been observed in weakly segregated diblock copolymers. In the case of ABC triblock copolymers with more than one crystallizable block, many interesting effects have been found; among them, self-nucleation, sequential or coincident crystallization, and fractionated crystallization can be mentioned. Additionally, the effect of the topological constrains due to the number of free ends has been studied. Factors like chemical structure, molecular weight, molecular architecture and number of crystallizable blocks provide a very large number of possibilities to tailor the morphology and properties of these interesting novel materials.
Polymer, 2001
Well-de®ned diblock copolymers of polystyrene and smectic side-chain liquid crystalline siloxanes have been prepared with a wide range of molecular weights (M n total from 20,000 to 165,000) and liquid crystalline siloxane weight fractions (0.4±0.91). Two different types of block copolymers were examined, each series having a different mesogen attached to the siloxane block. Increasing the rigidity of the mesogen led to stronger microphase segregation between the PS and LCP blocks, and to a higher T g and LC clearing point for the LCP block. Samples with large LCP weight fractions (.0.8) and low T g (, 2 258C) LCP blocks were elastomeric at room temperature, presumably because of the high molecular weight of the siloxane block (80±130 K). As the mesogen choice and the block lengths were varied, four general types of morphologies were observed using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS): hexagonally packed LC cylinders, alternating PS±LCP lamellae, weakly ordered PS cylinders, and hexagonally packed PS cylinders. The PS cylinder morphology persisted to unusually high LCP weight fractions. q
Polymer International, 2014
The melting and crystallization behaviours of a polyethylene-block-poly(methyl methacrylate) (PE-b-PMMA) diblock copolymer and a PE homopolymer were investigated using multiple heating and cooling rate differential scanning calorimetry (DSC) experiments, and modelling of the crystallization kinetics and lamellar thickness distribution. This new model was first validated applying literature and experimental data. The model-predicted morphology (n = 3.2) closely matched the spherulitic morphology (n = 3), which was determined using polarized optical microscopy. For each experimental cooling rate, the model predicted diblock copolymer crystallinity that well matched the entire DSC crystallinity curve, notably for an Avrami-Erofeev index of n = 2; and apparent crystallization activation energy that hardly varied with the cooling rates used, relative crystallinity (), and crystallization temperature or time. This disfavours the concept of variable activation energy. The use of the right crystallization model and parameter estimation algorithm is important for addressing the mathematical artefact. Under non-isothermal cooling, the PE-b-PMMA diblock copolymer, as per the model prediction, crystallized without confinement (n ≠ 1), preserving the cylindrical structure. From the characteristic shapes of the crystallization function f((T)) versus 1/T and crystallization rate versus plots, the resulting T cmax and narrow max range can guide the search for an appropriate crystallization model. The overall treatment illustrated in this study is not restricted to a PE homopolymer and a PE-b-isotactic PMMA block copolymer. It can be generally applied to crystalline homopolymers and copolymers (alternating, random and block), as well as their blends. The block copolymers and blends can be crystalline-amorphous as well as crystalline-crystalline.
Macromolecular Chemistry and Physics, 1994
A novel type of block copolymers comprising both side-chain and main-chain liquid-crystalline (LC) blocks in the same macromolecular structure was synthesized and studied. The former block was either one of two LC polymethacrylates containing an azobenzene mesogen with different substituents (block A), and the latter was a semiflexible LC polyester block (block B). Thermal, dynamic-mechanical, and X-ray diffraction data indicated that the two structurally different blocks were at least partly phase-separated within the glassy and LC states. The thermodynamic phase transition parameters of block A were not affected by copolymer composition. However, significant deviations of the thermodynamic parameters of block B were observed relative to those of the corresponding homopolymers. In particular, the normalized transition enthalpies of block B were much lower, suggesting the occurrence of a more or less diffuse interphase. An increase in the nematic-isotropic temperature was found at variance with previous results on most of the LC block copolymers, in which only one block was an LC component. a) Systematic IUPAC nomenclature: 6-[4-(4-hexyloxyphenylazo)phenoxy]hexyl methacrylate (6a) and 6-[4-(4-decyloxyphenylazo)phenoxy]hexyl methacrylate (6 b).
European Polymer Journal, 2004
In this work, the behavior of the crystallizable blocks within polystyrene-b-poly(ethylene oxide)-b-poly(e-caprolactone) linear triblock copolymers is studied. The apparent crystallization and melting temperatures of PEO and PCL can be coincident as a result of their close values, their dependence on the molecular weight of the blocks and on the relative amount of each component within the copolymers. When the content of both PEO and PCL is low, typically 20% or less, both blocks crystallized coincidentally upon cooling from the melt at very large supercoolings (T c ¼ À40°C), suggesting that homogeneous nucleation has taken place. A S 63 EO 16 C 20 copolymer (where subscripts denote the weight fraction of the components) exhibited a small angle X-ray scattering (SAXS) pattern at room temperature that suggests a cylindrical morphology for the minor components, where the crystallization of PEO and PCL blocks can take place subsequently near)40°C in a hard confinement fashion within the vitreous PS matrix. We have employed differential scanning calorimetry (DSC) to study the self-nucleation process and the results indicate that the difficulty in generating enough self-seeds to nucleate every isolated microdomain causes the disappearance of Domain II (or exclusive self-nucleation Domain) and therefore a direct transition from complete melting (Domain I) to self-nucleation and annealing (Domain III) is observed. When the content of both PEO and PCL blocks is larger than 35%, a coincident crystallization can be observed as well as coincident melting. For a S 15 EO 37 C 48 triblock copolymer, PS is a minor phase and mixed spherulites composed of both PCL and PEO blocks were observed by Polarized Optical Microscope (POM) at appropriate supercoolings. In this case, the self-nucleation behavior is standard, and through its use the crystallization and melting process of both blocks can be separated. Wide angle X-ray scattering (WAXS) at different temperatures was used to corroborate the sequential melting of both semicrystalline blocks deduced by self-nucleation. Isothermal crystallizations were also followed by WAXS as a function of time and the results showed that depending on the crystallization temperature (T c), only the PCL block crystallizes (at high T c), or the PCL block crystallizes first followed by the PEO at later times (at lower T c).