Crystallization/Melting Kinetics and Morphological Analysis of Polyphenylene Sulfide

Crystallization and melting kinetics of polyphenylene sulfide (PPS) are determined using fast scanning calorimetry. The temperature dependence of half‐time crystallization of isothermally melt‐crystallized PPS shows a downward convex curve with a minimum at 160 °C. The minimum crystallization half‐time is about 3 s. The analysis of heating rate dependence of the melting temperature reveals a zero‐entropy‐production melting temperature of the sample. The microstructure of the sample, which is prepared by fast scanning calorimetry, is investigated by small‐angle X‐ray scattering and polarizing optical microscopy. The crystallinity and lamellar thickness of the sample annealed for 400 s decrease with decreasing crystallization temperature. The size of spherulites becomes small as the isothermal temperature is decreased. Transcrystalline morphology is observed near the surface between the sample and nitrogen gas at a crystallization temperature of 120 °C. The thickness of the transcrystalline layer disappears as the isothermal temperature is increased.     

Trapping Dynamic Disulfide Bonds in the Hard Segments of Thermoplastic Polyurethane Elastomers

Dynamic covalent bonds placed within a polymer chain result in stimulus‐responsive materials where the breaking/making and/or exchange of the dynamic bonds controls the response. A key attribute to access such properties is the molecular mobility of the dynamic bonds. The focus of this work is to understand how incorporating a dynamic bond, in the form of disulfide bonds, into the hard phase of a polyurethane will impact the properties of the materials. Thus, uncross‐linked polyurethanes with aliphatic disulfide‐containing hard segments are synthesized via a two‐step protocol, using 2,2′‐dithiodiethanol and/or 1,4‐butanediol in the second step as the chain extenders. Thermomechanical studies show that, if the dynamic bonds are selectively placed in the hard phase of the polyurethane, the dynamic nature of the disulfide bond can be effectively “switched‐off” below the melting temperature of the hard phase. As such the dynamic and mechanical properties of the materials can be controlled by tailoring the nature of the hard phase.

     

Chain Microstructure,Crystallization, and Morphology of Olefinic Blocky Copolymers

The chain microstructure, crystallization, and morphology of three olefinic blocky copolymers (OBCs) are compared. The weight percentage of the hard block and the octene content in it are calculated from the ¹³C NMR spectra with a two‐site first‐order Markovian model. The lengths of the hard blocks are compared from the melting and crystallization behaviors. The remarkable difference between the crystallinity measured by DSC, and wide‐angle X‐ray diffraction (WAXD) indicates the presence of partially ordered phases. Small angle X‐ray scattering (SAXS) shows that the partially ordered phases in OBC‐A are mainly located at the interface between the crystalline and amorphous phases, but exist as separated microdomains in OBC‐B. As the hard block becomes shorter, there are also more, separated partially ordered phases in OBC‐C. Spherulites are observed in all OBCs by POM and the size of the spherulites decreases in the order: OBC‐A > OBC‐B > OBC‐C. TEM shows that spherulites are poorly developed in a thin film of OBC‐B.     

Crystallization and Melting Behaviors of PPC‐BS/PVA Blends

The isothermal crystallization and melting behaviors of poly(propylene carbonate) end‐capped with benzenesulfonyl/poly(vinyl alcohol) (PPC‐BS/PVA) blends over rich PVA composition range were first investigated by differential scanning calorimetry (DSC). PPC‐BS/PVA interaction parameter, χ₁₂, calculated from equilibrium melting temperature depression was ?0.44, revealing miscibility of PPC‐BS with PVA in the melt and favorable interactions. The temperature dependence of crystallization rate constant at initial crystallization stage was analyzed using the modified Lauritzen‐Hoffman expression. The chain width, a₀, the thickness of a monomolecular layer, b₀, the fold and lateral surface free energies, σ_e and σ, and the work of chain folding, q, for neat PVA were first reckoned to be 4.50 Å, 4.78 Å, 76.0 erg · cm^?2, 8.81 erg · cm^?2, and 4.70 kcal · mol^?1, respectively. The values of σ_e and q for PVA in PPC‐BS/PVA blends exhibited a maximum in the neighborhood of 10/90 PPC‐BS/PVA, respectively.

Kinetic analysis of the temperature dependence of crystallization rate constant at initial crystallization stage for neat PVA and PPC‐BS/PVA blends.     

Effect of Functionalized Carbon Nanotubes on Molecular Interaction and Properties of Polyurethane Composites

Summary: Functionalized MWNTs were incorporated into PU by solution mixing to improve the mechanical and thermal properties of composites. A homogeneous dispersion of MWNTs was successfully achieved in PU matrix as evidenced by scanning electron microscopy. It may be attributed to the hydrogen bonds existing between C?O groups of hard segments of PU chains and COOH groups of the MWNT‐COOH. The incorporation of the MWNTs effectively enhanced the crystallization of the PU matrix through heterogeneous nucleation, and the nucleation effect was more evident at 10 wt.‐% functionalized MWNTs as compared to other composite systems. Mechanical properties of the PU‐MWNTs composites were assessed as a function of MWNT concentration and dispersion of MWNT in PU matrix. The most significant improvement in mechanical properties was obtained, e.g., 740% increase in modulus and 180% increase in tensile strength over pure PU with 20% MWNT content. The thermal stability of composites due to thermal gravimetric measurements was significantly improved.

A possible interaction of H‐bonding existed between PU chain and MWNT‐COOH.     

Synthesis and Properties of Segmented Polyurethanes with Triptycene Units in the Soft Segment

Segmented polyurethanes based on poly(tetramethylene glycol) soft segments (SS) containing aromatic units are synthesized. Hydroquinone bis(2‐hydroxyethyl) ether and 4,4′‐methylenebis(phenyl isocyanate) are used as the chain extender and the diisocyanate, respectively. Effects of incorporation of hydroquinone (HQ) and triptycene hydroquinone into the soft segments on the morphology and properties of the undeformed segmented polyurethanes are investigated. Differential scanning calorimetry and dynamic mechanical analysis indicate that the incorporation of triptycene units leads to an increased glass transition temperature (T_g) and an elimination of the crystallization of soft segments. The tensile analysis shows there is no strain hardening for the polymer films with triptycene‐containing soft segments. Wide‐angle x‐ray diffraction demonstrates that the absence of strain hardening in triptycene‐containing segmented polyurethane likely arises from the suppressed strain induced crystallization. In contrast, the less bulky HQ units show little effect on either thermally or strain induced crystallization of the soft segments. Morphology studies, including small angle x‐ray scattering on the compression molded films and atomic force microscopy on the solvent cast film, reveal that polyurethanes with HQ and triptycene containing soft segments maintain distinct microphase separated morphology.

     

Structure and Mechanical Properties of an Injection‐Molded Thermoplastic Polyurethane as a Function of Melt Temperature

Thermoplastic polyurethanes (TPUs) molded at 205, 215, and 235 °C are monitored by SAXS and WAXS during straining. A non‐affine nanostructure deformation and related evolution mechanisms are found. DSC and microscopy are applied. DSC shows two melting endotherms. The results indicate that melts kept below the second peak stay phase‐separated. The orientation parameter f(?) and df/d? from WAXS are related to chain orientation mechanisms (strain ?). SAXS shows hard domains that are only correlated to a next neighbor (“sandwich”). Thick sandwiches lengthen more than thin ones. Thin‐layer sandwiches feature a strain limit. Some are converted into thick‐layer sandwiches. Two materials have tough hard domains. Material processed at 235 °C is soft and contains weak hard domains that fail for ? > 0.75.     

Crystallization and Melting Behavior of Poly(3‐hydroxybutyrate)‐Based Blends

Summary: Blends of high molecular weight poly(R‐3‐hydroxybutyrate) (PHB) ( = 352 000 g · mol^?1), comprising of either low molecular weight poly(R‐3‐hydroxybutyrate) (D‐PHB) ( = 3 900 g · mol^?1) or poly[(R‐3‐hydroxybutyrate)‐co‐(R‐3‐hydroxyvalerate)] (PHBV) ( = 238 000 g · mol^?1) with 12 mol‐% hydroxyvalerate (HV) content as a second constituent, were investigated along with the thermal properties and morphologies. After isothermal crystallization, a lowering of the melting temperature of PHB can be observed with increasing content of the second component in the blends. This behavior points towards miscibility of the constituents both in the liquid and the solid state. Crystallization kinetics was studied under isothermal and non‐isothermal conditions. The overall kinetics of isothermal crystallization was analyzed in terms of the Avrami equation. Only one crystallization peak is observed in all cases for the PHB/D‐PHB and PHB/PHBV blends under the conditions studied. This demonstrates co‐crystallization of the constituents. The addition of D‐PHB or PHBV to PHB reduces the rate of crystallization of the blends compared to that of neat PHB. The corresponding activation energies of crystallization also decrease with an increasing concentration of the second constituent. Non‐isothermal crystallization, carried out with different cooling rates held constant, is discussed in terms of a quasi‐isothermal approach. The corresponding rate constants as functions of reciprocal undercooling show Arrhenius‐like behavior in a certain range of temperatures. At sufficiently high undercooling, the rate constants of crystallization for the isothermal process exceed those reflecting non‐isothermal conditions, whereas in the limit of low undercoolings, the rate constants become similar. Ring‐banded morphologies are observed when PHB is in excess. When the respective second component is the major component, fibrous textures of the spherulites develop.

Polarized micrograph of PHB/PHBV 90/10.     

Crystallization,Melting and Morphology of Syndiotactic/Atactic Polystyrene Blends: Molecular Weight Effects of Atactic Polystyrene

Summary: Molecular weight (MW) effects of atactic polystyrene (aPS) on the morphologies and crystallization kinetics of syndiotactic polystyrene (sPS) blends have been investigated, and miscibility was confirmed for all the sPS/aPS blends. Addition of aPS(M) or aPS(L) leads to a significant increase in the entropy of mixing and gives rise to a pronounced decrease in the equilibrium melting temperature of the blends. On heating from the glassy state, the crystallization peak temperature of the sPS/aPS(H) blend increased with increasing aPS content due to a dilution effect, whereas those of sPS/aPS(M) and sPS/aPS(L) decreased mainly due to enhanced chain mobility. On cooling from the melt state, the crystallization peak temperature decreased with increasing aPS content regardless of the aPS MW. A higher activation energy is required for the sPS component transport from the miscible melt to the growth front in the sPS/aPS(L), suggesting that extra energy is required for the demixing process. Interspherulitic segregation of aPS diluents was evident in the sPS/aPS(L) blends, while interfibrillar segregation morphology was obtained in the sPS/aPS(H) as well as the sPS/aPS(U) blends.

SEM images of sPS/aPS blends 50/50(L) at 230 °C (C) and 70/30(L) at 250 °C (D).     

新型聚氨酯材料的血液相容性及毒理学研究

目的 通过对新型聚氨酯材料的血液相容性及毒理性研究，评价新型聚氨酯作为人工心脏辅助泵体材料的可行性。方法 实验包括溶血实验、刺激试验及全身急性毒性试验，观察72h组织及动物反应情况。结果新型聚氨酯材料溶血指数小于5％，血液相容性良好，无明显毒性。结论此种新型聚氨酯符合人工心脏辅助泵体材料的要求。     

One‐Step Synthesis of Biodegradable Polyurethane Prepolymer and Its Rapid Gelation Behavior at High Water Content

In this study, a very simple, scalable, and low‐cost one‐step recipe is presented for preparing a biodegradable polyurethane prepolymer composed of isocyanate terminated linear polyethylene glycol and isocyanate terminated four‐armed polycaprolactone. Then, the corresponding hydrogels are easily formed by mixing the prepolymer with water in few minutes. The resulting hydrogel shows excellent mechanical properties with high tensile strength (up to 233.6 KPa) and recorded elongation rate (5000%), while maintaining high water content (up to 91% mass ratio). Meanwhile, the maximum water retaining capacity of the hydrogel can be up to 40 times of polyurethane prepolymer (in mass), which is equal to 97.6% water content. In addition, the degradation properties of the obtained hydrogel are studied in detail. This study demonstrates a facile approach to prepare the hydrogel with both excellent mechanical properties and high water content, which marks it as a potential candidate for applications in agrological field, such as sand fixing in desertification control.

     

A Robust Proton NMR Method to Investigate Hard/Soft Ratios,Crystallinity, and Component Mobility in Polymers

Summary: An improved proton NMR method for the real‐time measurement of the hard/soft ratio or the crystallinity, and the mobile‐fraction dynamics, in phase‐separated or semicrystalline polymers is presented. It avoids some difficulties associated with earlier approaches and can be applied on high‐ as well as inexpensive low‐field instrumentation. A pulsed mixed magic‐sandwich echo is shown to provide near‐quantitative refocusing of the rigid contribution to the initial part of the free induction decay. This essentially removes the need to account for signal loss during the receiver dead time, and the method should thus be useful for a variety of applications where the magnetization distribution over differently mobile fractions is to be determined. The overall decay of the mobile signal of a semicrystalline polymer was found to exhibit a significant field dependence, such that the apparent transverse relaxation function of the amorphous part is in a real‐time experiment best characterized by a subsequent Carr–Purcell–Meiboom–Gill pulse train. It is demonstrated to be mainly influenced by mobility, while instrumental effects play a minor role. The mobility of the amorphous fraction depends not only on the overall crystallinity, but also on the crystallization conditions, thus on the nanometer‐scale morphology.

Isothermal crystallization of sPP monitored on a 20 MHz low‐field proton NMR spectrometer using the MSE‐CPMG experiment.     

Crystallization Kinetics and Melting Behaviour of the Novel Biodegradable Polyesters Poly(propylene azelate) and Poly(propylene sebacate)

Novel biodegradable poly(propylene sebacate) (PPSeb) and poly(propylene azelate) (PPAz) polyesters were synthesized and fully characterized using WAXD, standard DSC, high‐rate DSC, and modulated‐temperature DSC. Multiple‐melting behaviour, observed for samples isothermally crystallized from the melt, was attributed to sequential melting–recrystallization–remelting. Study of isothermal and nonisothermal crystallization kinetics revealed a higher crystallization rate for PPSeb compared to PPAz. The Avrami and the Lauritzen‐Hoffman models were successfully applied to DSC measurements, using also data obtained after self‐nucleation, in order to diminish the effect of primary nucleation. Finally, the effective activation energy was estimated using the differential isoconversional method of Friedman.

     

Effect of Level of Crystallinity on Melt Memory Above the Equilibrium Melting Temperature in a Random Ethylene 1‐Butene Copolymer

A strong memory effect of crystallization has been observed in melts of random ethylene copolymers even above the equilibrium melting temperature. Melt memory is correlated with self‐seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and are unable to diffuse quickly to the randomized melt state. Fast diffusion is restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. The effect of topological constraints on melt memory, or on number of remaining self‐seeds in the melt, is analyzed studying the melting and subsequent crystallization of a model ethylene 1‐butene copolymer with 2.2 mol% ethyl branches prepared with different levels of crystallinity. There is a critical threshold level of crystallinity of 6–12% to observe the effect of melt memory on the subsequent crystallization rate of this copolymer. A faster development of the initial crystallinity may more efficiently trap knots and loops around the crystallites, leading to a lower crystallinity threshold than for slow or isothermally crystallized copolymers.

     

A Transparent,High Refractive,Shape‐Memory,Healable, and Recyclable Phenolic Polyurethane Thermoset: Unexpected Roles of Bromine Substituents and Tertiary Amine Catalysts

The applications of polyurethane (PU) thermosets are limited by the lack of plasticity after curing due to permanent crosslinks. Besides, the low refractive index is insufficient for optical devices. Here, a transparent, high refractive, recyclable, and healable PU thermoset is developed based on dynamic bromined phenyl‐carbamate bonds (BPCB). It exhibits tensile strength of ≈52 MPa, good shape‐memory ability, and can be reprocessed or healed nearly completely at 110 °C in 30 min. Tertiary amine catalysts and bromine substituents jointly play unexpected roles to promote the forward and reverse reactions significantly, leading to high bond‐exchange efficiency of BPCB. Furthermore, the introducing of BPCB can endow the material with higher refractive index (n_D = 1.5850) simultaneously. In summary, this material is of potential as dynamic PU thermoset in various fields, especially in advanced optical devices.     

Stereocomplexes from Biosourced Lactide/Butylene Succinate‐Based Copolymers and Their Role as Crystallization Accelerating Agent

Biosourced co(polyester urethane)s containing different ratios of enantiomeric oligo(L ‐ or D ‐ lactide) (OLLA/ODLA) sequences and oligo(butylene succinate) (OBS) blocks (P(OD(L)LA‐b‐OBS)) are synthesized. Their stereocomplexation is confirmed by differential scanning calorimetry and X‐ray diffraction. The process is efficient independently on the OLA/OBS ratio and for OLLA/ODLA ratios from 2:3 to 3:2. The preformed stereocomplexes show remarkable crystallization accelerating efficiency when melt‐blended with a commercial PLLA in amounts from 2.5 to 10 wt%. Spectacular increase in the polyester matrix crystallinity (from 2 up to 42%) and crystallization rate (half‐time of ca. 3 min compared to ca. 30 min for the neat PLLA) is observed.     

Melt Crystallization and Morphology of Poly(p‐phenylene sulfide) under High Pressure

The high‐pressure melt‐crystallization behaviors of poly(p‐phenylene sulfide) (PPS) were investigated using WAXD, DSC, TEM and SEM. PPS extended‐chain crystals with c‐axis thickness exceeding 4.5 µm were formed at high pressure. The DSC results showed that the melting temperature and melting enthalpy of high‐pressure crystallized PPS samples were up to 327.53 °C and 94.96 J · g^?1, respectively, which were higher than the values of ideal PPS perfect crystals used by some researchers, and the melting enthalpy of the samples fluctuated regularly during the thickening growth of the PPS crystals. Other characteristic morphologies obtained at high pressure, i.e. spherulites and rod‐like crystals, were also presented with the SEM measurements.

     

Enhanced Mechanical and Shape Memory Properties of Poly(propylene glycol)‐Based Star‐Shaped Polyurethane

A poly(propylene glycol)‐based star‐shaped thermoplastic shape memory polyurethane elastomer (STPU) is synthesized by bulk polymerization with the addition of trifunctional poly‐propylene glycerol (PPG‐3) to improve the mechanical and shape memory properties. The mechanical properties are enhanced significantly with the addition of PPG‐3. The tensile strength of STPU is up to 36.0 MPa, which is almost two times higher than that of linear polyurethane (18.4 MPa). The star‐shaped structure, reduction in microphase separation, and good phase compatibility of STPU are the reasons for the enhancement of mechanical properties. The branching degree of STPU (up to 1.83) is much higher than that of linear polyurethane (0.5). STPU shows higher shape memory fixity ratio (97.2%) at ?10 °C and recovery ratio (96.7%) at 40 °C than TPU. Therefore, the design and synthesis of star‐shaped polyurethane is an effective approach for improving the mechanical and shape memory properties of polyurethane elastomer.     

Enhanced Crystallization Rate of Poly(l‐lactide) Mediated by a Hydrazide Compound: Nucleating Mechanism Study

A low molecular weight hydrazide compound, tetramethylenedicarboxylic di (2‐hydroxybenzohydrazide) (TMBH), greatly improves the crystallization rate and crystallinity of poly(l ‐lactide) (PLLA). The nucleating efficiency of TMBH on the crystallization of PLLA exhibits obvious concentration dependence, which increases first and then decreases slightly with the increase of TMBH loading, reaching a maximum at 0.3 wt%. Time‐resolved Fourier transform infrared spectroscopy spectra indicate that the formation of skeletal conformational ordering structure of PLLA has been accelerated in the presence of TMBH, which can act as efficient precursors speeding up both the nucleation of PLLA on TMBH surface and the formation of intrachain 10₃ helix structure. The possible hydrogen bonding interaction between the ? OH or ? NH groups in TMBH and the ? C?O groups in PLLA backbones is supposed to be an important factor, which promotes the migration of PLLA chains to TMBH crystallites and the emergence of interchain interactions as well as the conformational ordering.

     

Morphology and Melt Crystallization of PCL‐PEG Diblock Copolymers

ROP of PCL was realized in the presence of mPEG with = 5 000, using Zn(La)₂ as a catalyst. The resulting diblock copolymers with molar ratios of the CL/EO repeat units from 0.2–5.0 were characterized by DSC, WAXD, SEC, and ¹H NMR. Melt crystallization was studied and analyzed with the Avrami equation. The spherulite growth rate G was determined at different crystallization temperatures. The G values were found to range between those of mPEG and PCL homopolymers. The morphology of an isothermally crystallized sample with CL/EO = 0.5 was examined. Spherulites with PCL embedded in PEG were observed, in contrast to concentric spherulites reported in the literature.