Multiblock poly(ether-ester-amide)s based on polyamide-6 and poly(ethylene glycol), 2 Effect of composition and soft-segment length on the structure of poly(ether-ester-amide)s as revealed by X-ray scattering

Isotropic unannealed and annealed melt-pressed and quenched samples of segmented multiblock poly(ether-ester-amide)s based on polyamide-6 and poly(ethylene glycol)s (PEGs) of molecular weights 400 and 1000 with various hard/soft segment weight ratios were investigated. The effect of composition, segment length and annealing temperature on the crystal structure was studied by differential scanning calorimetry, wide-angle and small-angle X-ray scattering. In addition to the γ-phase, one of the unannealed samples having relatively long hard and soft segments exhibits a high amount of α-phase. This is assumed to be due to the high flexibility of the PEG segments, linking the polyamide blocks thus enhancing their mobility. The lack of hydrogen bonds between the PEG segments facilitates crystallization of the polyamide segments in the more perfect α-modification, which is the most pronounced in the above mentioned sample. Part of the α-phase transforms into the α-phase upon annealing in all copolymer samples studied, similarly to polyamide-6.     

Sequential reordering in condensation copolymers, 2. Melting- and crystallization-induced sequential reordering in miscible poly(butylene terephthalate)/polyarylate blends

A 50/50 (weight ratio (38/62 mole ratio referred to repeating units)) blend of poly(butylene terephthalate) (PBT) and polyarylate (PAr), was studied by means of thermal, solubility, X-ray and nuclear magnetic resonance techniques after annealing procedures that enable transesterification. Prolonged thermal treatment at 290°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples at the relatively low temperature of 140°C results in the reappearance of melting endotherms in the differential scanning calorimetry curves. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions. In that way a PBT/PAr blend was shown to be another polymer system, along with poly(ethylene terephthalate) (PET)/polycarbonate (PC) and PET/PAr blends, in which the entire cycle is realized, from two homopolymers via a block- and random copolymer to a block copolymer. The unusually low temperature at which the crystallization-induced sequential reordering to block polymers takes place is explained by the miscibility of PBT and PAr which enables transreactions to take place in the bulk.     

Poly(ether/ester)s based on poly(tetramethylene terephthalate) and poly(ethylene glycol), 4. Modification with 2-butyne-1,4-diol

A series of poly(ether/ester)s derived from dimethyl terephthalate, 1,4-butanediol, 2-butyne-1,4-diol (2-BD-1,4) and α-hydro-ω-hydroxypoly(oxyethylene) (molecular weight 1000) is synthesized. The mole ratio of the starting components is selected to result in copolymers with constant hard : soft segment weight ratio (59:41). The amount of 2-BD-1,4 is varied from 0 to 20 wt.-% referred to the total amount of the short-chain diols used. The incorporation of 2-BD-1,4 in the macrochains is proved by ¹H NMR measurements. A small increase of the oxygen index is found with increasing the amount of 2-BD-1,4. It is established that the poly(ether/ester) containing 10 wt.-% of 2-BD-1,4 behaves as known poly(ether/ester)s. Data from differential scanning calorimetry suggest a three-phase structure, two amorphous and one crystalline one. Small-angle X-ray studies of the annealed samples reveal a strong tendency to phase separation with increasing the annealing temperature. The latter is in agreement with density measurements.     

Poly(Ether/Ester)s based on poly(tetramethylene terephthalate) and poly(ethylene glycol), 3. Effect of thermal treatment and drawing on the structure of the poly(ether/ester)s

Annealed drawn and undrawn bristles of poly(ether/ester)s based on poly(tetramethylene terephthalate) (PTMT) and poly(ethylene glycol) PEG 1000 (in various ratios) are studied by means of small-angle X-ray scatering and differential scanning calorimetry (DSC). The samples with the lowest PTMT content (49 wt.-% PTMT) show on abrupt increase of the scattering intensity and the long spacing with increasing annealing temperature T_a, this increase becoming less pronounced with increasing fraction of hard segment (PTMT). The DSC heating scans are characterized by a low-temperature glass transition due to the soft polyether segments and a multiple melting behaviour at about 200°C due to the crystalline hard PTMT segments. The data suggest a dependence of the thermal behaviour on the chemical composition, annealing temperature, and orientation. The characteristics of the undrawn samples are similar to those of the homopolyester PTMT and the copolymers based on PTMT and poly(tetramethylene oxide). Evidence is found for an increase of phase separation with an increase of the annealing temperature. The formation of larger amorphous regions of PEG with increasing T_a determines the thermal and scattering behaviour observed.     

Microhardness under strain, 4. Reversible microhardness in polyblock thermoplastic elastomers with poly(butylene terephthalate) as hard segments

The microhardness (H) technique was recently applied to poly(butylene terephthalate) (PBT) and its multiblock copolymers for examination of the stress-induced polymorphic transition. Following these investigations the present study attempts to observe the reversible variation of microhardness under strain. For this purpose bristles of drawn and annealed (at 160°C in vacuum) poly(ether ester) (PEE) were characterized with respect to their microhardness at various stages of tensile deformation. H was measured under and after loading (σ) in deformation steps of 5% each. In accordance with previous results on PBT and PEE, H values at σ ≠ 0 show a sharp drop (by 40%) in a relatively narrow deformation interval (ε = 10–15%), owing to the stress-induced α ⇔︁ β polymorphic transition. The hardness measurements at σ = 0 show a continuous decrease of H with a remaining strain. H values at σ = 0, corresponding to plastic deformation up to 5%, are much higher than the corresponding ones taken under stress at an overall deformation between 10 and 25%. The higher H values are explained by the regeneration of the starting α modification. Results reveal that in materials characterized by high and reversible deformability it is possible to observe a reversible microhardness behaviour, provided the strain–induced structural changes are reversible.     

Sequential reordering in condensation copolymers, 4. Crystallization-induced sequential reordering in poly(ethylene terephthalate)/polycarbonate copolymers as revealed by the behavior of the amorphous phases

An equimolar blend of poly(ethylene terephthalate) (PET) 3

1 Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).

and bisphenol-A-polycarbonate (PC) 4

2 Systematic structure-based IUPAC nomenclature: poly(oxycarbonyloxy-1,4-phenylene-1-methylethylidene-1,4-phenylene).

is studied by dynamic-mechanical thermal analysis (DMTA) and X-ray scattering after thermal treatment that enables transesterification. As demonstrated by wide-angle X-ray scattering (WAXS) measurements, prolonged thermal treatment at 280°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples below the melting temperature of PET results in restoration of the crystallization ability. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions which closes the cycle of transformations from two homopolymers via block- and random copolymer back to a block copolymer. The behavior of the amorphous phases is studied by means of DMTA demonstrating that their glass transition temperatures T_g's vary in accordance with the crystallinity changes. The random copolymer is characterized by a more or less homogeneous amorphous phase. In contrast to this, the mechanical mixture and the two block copolymers (the initial and that with the restored blocky structure) show DMTA peaks of two amorphous phases, clearly separated and with distinct individual T_g's. Viscosity measurements also demonstrate that the random copolymer significantly differs in its viscosity as compared to all other samples. These results represent a further evidence for the effect of block restoration via crystallization-induced sequential reordering.     

Sequential reordering in condensation copolymers, 1. Melting- and crystallization-induced sequential reordering in immiscible blends of poly(ethylene terephthalate) with polycarbonate or polyarylate

Unlike previous attempts, the entire cycle of melting- and crystallization-induced reordering is realized in binary polymer blends in the following order: two homopolymers → block copolymer → random copolymer → block copolymer. Blends of poly(ethylene terephthalate)

1 Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).

(PET) and bisphenol-A/polycarbonate (PC) as well as PET/polyarylate (PAr) blends, are annealed directly in a differential scanning calorimeter at 280°C for various times. Scanning the samples in the heating mode reveals the complete disappearance of crystallization or melting in the blends where the ratio of PET/PC repeating units is less than 5.7/1.0. Such an amorphization is attributed to the formation of random copolymers. This statement is confirmed by NMR measurements, by the observation of one glass transition temperature T_g in the range between the initial two T_gs, and by solubility tests. Once randomized, annealing the samples at 235°C and 245°C, i. e., below melting of PET, results in a T_g shift toward the T_g of PET as well as in reappearance of melting. This effect is accompanied by an eight-fold crystallinity increase in the equimolar blend, as compared to the randomized sample. The regenerated crystallization ability is explained by restoration of the blocks. According to previous findings, it is concluded that the considerable enthropy increase is the main driving force of randomization. The rival trend to the formation of a block copolymer by sequential reordering is driven by the crystallization of PET blocks formed. The conclusion that the observed changes in the crystallization ability and T_g-values are based on sequential reordering is supported by experiments with samples containing increased amounts of transesterification catalyst leading to a much faster appearance of these changes. No randomization is observed with the blend composition ratio of repeating units PET/PC > 5.7/1.0. When the annealing is performed for 300 min at 165°C, where no significant exchange reactions are expected to occur, no restoration of the crystallization ability is observed.     

Über die Strukturbildung aus Salzlösungen der ataktischen Polymethacrylsäure mit n-Alkylaminen

The influence of chain length of the n-aliphatic amines on the morphology and the internal arrangement of supermolecular structures formed from aqueous and n-butanolic solutions of their salts with atactic polymethacrylic acid has been investigated. All structures observed by means of light and electron microscop have rather perfect morphology. Higher n-amine (C₄, C₆ C₁₂, and C₁₇) salts are optically anisotrop. n-Butylamine salt shows an electron diffraction pattern similar a crystal. Higher amine salts have sharp melting points. It is supposed that the observed supermolecular structures of lower (up to C₄) n-amine salts with polymethacrylic acid are built up from the main chains while the anisotropic structures with crystalline-like internal arrangement of higher n-amine (more than C₄) salts are due to the side n-aliphatic chains.     

Sequential Reordering in Condensation Copolymers, 6. Average Block Lengths in Poly(ethylene terephthalate) – Polyamide 6 Copolymers As Revealed by NMR Spectroscopy

An equimolar physical blend comprising poly(ethylene terephthalate) (PET), polyamide 6 (PA6) and catalytic amounts of p‐toluene sulfonic acid (pTSA) was studied by differential scanning calorimetry (DSC) and ¹³C NMR spectroscopy before and after reactive blending for various times at 280°C that enables interchange reactions. With the extension of the reaction time, DSC traces showed an abrupt decrease in ability to crystallize, and after two hours of blending the system did not reveal any crystallization or melting behavior. By means of ¹³C NMR spectroscopy, a clear distinction was made between the PET/PA6 physical blend and the copolymers with different degrees of interchange reactions. The ¹³C NMR sequence length determination in various PET–PA6 based copolyesteramides showed PET block lengths of 4–10 repeat units which was in good agreement with the crystallizability of these systems. A combination of selective degradation of the PET blocks and ¹H NMR allowed, for the first time, the characterization of both PET and PA6 sequence lengths. This method was shown to be more sensitive, as compared to ¹³C NMR spectroscopy without selective degradation, for sequence analysis in copolymers with close to random distributions of PET and PA6 sequence lengths.