Crystallization and melting behaviors of isotactic polypropylene nucleated with compound nucleating agents

Crystallization and melting behaviors of isotactic polypropylene (iPP) nucleated with compound nucleating agents of sodium 2,2′‐methylene‐bis (4,6‐di‐tert‐butylphenyl) phosphate (hereinafter called as NA40)/dicyclohexylterephthalamide (hereinafter called as NABW) (weight ratio of NA40 to NABW is 1:1) were studied by differential scanning calorimetry and wide‐angle X‐ray diffraction (WAXD), the relative β‐amount of iPP nucleated with these compound nucleating agents was also calculated in Turner‐Jones equation by using wide‐angle X‐ray diffraction data. Under isothermal crystallization, there exists a temperature range favorable for formation of β‐iPP. When the concentration of compound nucleating agents is 0.2 wt %, the temperature range is from 100 to 140 °C. While in nonisothermal crystallization, lower cooling rate is favorable for form of β‐iPP and the relative β‐amount of iPP increases with the decreasing of cooling rate in crystallization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 911–916, 2008     

Nucleation characteristics of the α/β compounded nucleating agents and their influences on crystallization behavior and mechanical properties of isotactic polypropylene

Nucleation characteristics of isotactic polypropylene (iPP) nucleated by the α/β compounded nucleating agents (NAs) were investigated by wide‐angle X‐ray scattering, differential scanning calorimetry and mechanical testing. The results showed that the nucleation effect of the α/β compounded NAs depends on not only nucleation efficiency (NE) of individual β and α NAs and their ratios but also the processing conditions, especially the cooling rates. The nucleating characteristics of the α/β compounded NAs can be illustrated by competitive nucleation. The NA with high NE played a leading role during iPP crystallization even at a low weight ratio and at different cooling rates. The stiffness and toughness of iPP can be simultaneously improved by using suitable compositions at the appropriate ratios. Finally, the nonisothermal crystallization kinetics of iPP nucleated with the α/β compounded NAs was described by Caze method and the crystallization activation energy of nucleated iPP was calculated by Kissinger equation. The result indicated that the crystal growth pattern of nucleated iPP was heterogeneous nucleation followed by three‐dimension spherical growth. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 653–665, 2010     

Investigation on the dynamic crystallization and melting behavior of β‐nucleated isotactic polypropylene with different stereo‐defect distribution—the role of dual‐selective β‐nucleation agent

The selectivities of different β‐nucleating agents might be quite different from each other, which is important in determining the crystallization and properties of the obtained β‐isotactic polypropylene (β‐iPP). However, the relationship between molecular structure and dynamic crystallization behavior of β‐iPP nucleated by dual‐selective β‐nucleating agent (DS‐β‐NA) is still not clear. In this study, the dynamic crystallization and melting behavior of two β‐iPP with nearly same average isotacticity but different stereo‐defect distribution, nucleated by a DS‐β‐NA (N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide; trade name TMB‐5), were studied by differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electronic microscopy. The results indicated that in the presence of TMB‐5, the dynamic crystallization and melting behavior of the samples are quite different because the joint effects of the dual selectivity of TMB‐5 and stereo‐defect distribution of the iPP under different cooling rates. Two important roles were observed: (i) slow cooling rate favors the formation of high β‐fraction; and (ii) high crystallization temperature favors the crystallization of α‐phase accelerated by TMB‐5. Generally, the dual selectivity of the DS‐β‐NA, the stereo‐defect distribution of iPP, and the cooling rate were important factors in determining the formation of β‐crystal. Copyright © 2013 John Wiley & Sons, Ltd.     

The influences of α/β compound nucleating agents based on octamethylenedicarboxylic dibenzoylhydrazide on crystallization and melting behavior of isotactic polypropylene

The influences of α/β compound nucleating agents based on octamethylenedicarboxylic dibenzoylhydrazide on crystallization and melting behavior of isotactic polypropylene (iPP) were analyzed. It is found that the crystallization temperatures of nucleated iPP were increased by above 11.0°C and the relative contents of β‐crystals (K_β ) in iPP reached above 0.40 after addition of compound nucleating agents. The K_β values depend on cooling rate, crystallization temperature in isothermal crystallization, and the difference between the crystallization temperatures of iPP nucleated by two individual nucleating agents. The nonisothermal crystallization kinetics were studied by Caze method and Mo method, respectively. The effective activation energy was calculated by the Friedman's method. The results illustrate that the half crystallization time was shortened and the crystallization rate was increased obviously after addition of nucleating agents, and the effective activation energy was increased with the relative crystallinity.     

Effects of β‐nucleating agent and crystallization conditions on the crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes composites

In this study, the effects of crystallization conditions (cooling rate and end temperature of cooling) on crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes (iPP/MWCNTs) composites nucleated with different concentrations of β‐nucleating agent (tradename TMB‐5) were investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and scanning electronic microscopy (SEM). The results of DSC, WAXD and SEM revealed that the addition of MWCNTs and TMB‐5 evidently elevates crystallization temperatures and significantly decreases the crystal sizes of iPP. Because of the competition between α‐nucleation (provided by MWCNTs) and β‐nucleation (induced by TMB‐5), the β‐phase crystallization takes place only when 0.15 wt% and higher concentration of TMB‐5 is added. Non‐isothermal crystallization kinetics study showed that the crystallization activation energy ΔE of β‐nucleated iPP/MWCNTs composites is obviously higher than that of pure iPP, which slightly increases with the increase of TMB‐5 concentration, accompanying with the transition of its polymorphic crystallization behavior. The results of non‐isothermal crystallization and melting behavior suggested that the cooling rate and end temperature of cooling (T_end) are important factors in determining the proportion and thermal stability of β‐phase: Lower cooling rate favors the formation of less amount of β‐phase with higher thermal stability, while higher cooling rate encourages the formation of higher proportion of β‐phase with lower thermal stability. The T_end = 100°C can eliminate the β–α recrystallization during the subsequent heating and therefore enhance the thermal stability of the β‐phase. By properly selecting TMB‐5 concentration, cooling rate and T_end, high β‐phase proportion of 88.9% of the sample was obtained. Copyright © 2014 John Wiley & Sons, Ltd.     

Probing into the epitaxial crystallization of β form isotactic polypropylene: From experimental observations to molecular mechanics computation

Compared with the most stable crystalline form of isotactic polypropylene (α‐iPP), β‐iPP shows superior impact strength and high temperature performance, though the mechanism of how the frustrated structure of β‐iPP is formed still remains unclear. In present work, the single crystal structure of a traditional β‐iPP nucleating agent, N,N′‐dicyclohexylterephthalamide (DCHT), was obtained for the first time and correlated with the epitaxial crystallization of β‐iPP on the surface of DCHT crystal. The combination of synchrotron radiation X‐ray microdiffraction and molecular chain packing model confirmed that a two dimensional match of chain‐axis and inter‐chain direction coexists between β‐iPP (110) plane and DCHT (001) plane. It was further found that an epitaxial model is helpful to understand the formation of the frustrated structure of 3₁ helices packing in β‐iPP. The molecular mechanics computation showed that as the (001) plane of DCHT is fixed, the packing mode of β‐iPP (110) plane on the substrate surface is more stable than that of α‐iPP (010) plane. This work clarifies the epitaxial crystallization mechanism of β‐iPP on DCHT by employing both experimental and computational evidences. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 418–424     

Specificity and versatility of nucleating agents toward isotactic polypropylene crystal phases

Nucleating agents with an ≈6.5 Å lattice parameter induced the α phase of isotactic polypropylene (iPP, α‐iPP). A 6.5 Å periodicity is also involved in the nucleating agents for the β phase of iPP (β‐iPP). The similarity in substrate periodicities suggests that some nucleating agents may induce either the α or β phase under different crystallization conditions. 4‐Fluorobenzoic acid, dicyclohexylterephthalamide, and γ‐quinacridone (the latter two are known as β‐iPP nucleators) were tested over a wide range of crystallization temperatures [up to crystallization temperature (T_c) > 145 °C]. The two former nucleating agents induce exclusively α‐iPP and β‐iPP, respectively. γ‐Quinacridone on the contrary is a versatile agent with respect to the crystal phase generated. More specifically, the same crystal face of γ‐quinacridone induces either β‐iPP or α‐iPP when T_c is below or above ≈140 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2504–2515, 2002     

Non-isothermal crystallization behavior of polypropylene with nucleating agents and nano-calcium carbonate

The non-isothermal crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP was investigated by DSC. The crystalline morphology of iPP was observed by polarized light microscopy. It was found that the crystallization rate increased with the addition of nanometer-scale calcium carbonate (nm-CaCO₃) particles. The addition of dibenzylidene sorbitol (DBS) could greatly reduce the spherulite size of iPP. The crystallization temperature for the iPP with DBS was higher than for non-nucleated iPP. DBS was an effective nucleating agent for iPP. The results of measurements suggested that there was a coordinated action to the crystallization of iPP when the organic nucleating agents (DBS) and nm-CaCO₃ were added to iPP together. Comparison to the modified Avrami equation and Ozawa equation, another method—Mo’s method can describe the non-isothermal crystallization behavior of iPP and nucleated iPP more satisfactorily.     

Comparison of different nucleating agents on crystallization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerates)

In this study, thymine and melamine were introduced as nucleating agents for poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerates) (PHBVs) and poly(3‐hydroxybutyrate) (PHB), and their effects were compared with that of boron nitride (BN). Because the overall crystallization rate of PHBVs decreases significantly with the increase in the 3‐hydroxyvalerate comonomer content, the study focused on the crystallization of PHBVs. Isothermal crystallization kinetics of the neat PHBVs and the nucleated PHBVs were studied by differential scanning calorimetry (DSC). The Avrami equation was derived and the parameters were assessed for the nucleation and crystal growth mechanism. The nucleation and crystal growth were examined using polarized optical microscopy. All nucleating agents had similar particle sizes and showed good dispersion in the polymer matrix, as revealed by scanning electron microscopy. The results indicated that BN and thymine significantly increased the overall crystallization rate for all PHBVs studied and demonstrated very similar nucleating effects. Melamine reacted with PHBVs and accelerated the thermal degradation, and hence was less effective in nucleating PHBVs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1564–1577, 2007     

Molecular weight dependency of crystallization and melting behavior of β‐nucleated isotactic polypropylene

Compounds of isotactic polypropylene (iPP) and β‐nucleating agent were used to investigate the relationship between the development of β phase and molecular weight in iPP under quiescent crystallization conditions by using wide angle X‐ray diffraction and differential scanning calorimetry techniques. In all cases, the dependency of the formation of β phase in iPP on molecular weight of iPP at a defined crystallization temperature range was found. The iPP with high molecular weight possessed a wide range of crystallization temperature in inducing rich β phase. However, poor or even no β phase was obtained for the samples with low molecular weight in the same range. In addition, an upper critical crystallization temperature of producing dominant β phase was found at 125 °C. Beyond this temperature, a phenomenon of prevailing α phase became obvious. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1301–1308     

Nonisothermal crystallization behaviors of polypropylene with α/β nucleating agents

In this work, the nonisothermal crystallization and subsequent melting behaviors of polypropylene (PP) nucleated with different nucleating agents (NAs) have been studied. α‐phase NA 1,3:2,4‐bis (3,4‐dimethylbenzylidene) sorbitol (DMDBS, Millad 3988), β‐phase NA aryl amides compound (TMB‐5), and their compounds were introduced into PP matrix, respectively. The results show that the nonisothermal crystallization behaviors and crystalline structures of PP with compounded NAs are dependent on the composition of NAs. In the sample of PP with 0.1 wt % DMDBS and 0.1 wt % TMB‐5, the nucleation efficiency (NE) of TMB‐5 is much higher than that of DMDBS and PP crystallizes mainly nucleated by TMB‐5, and in this condition, β‐phase PP is the main crystallization structure. For the sample of PP with 0.2 wt % DMDBS and 0.2 wt % TMB‐5, 0.2 wt % DMDBS has higher NE than 0.2 wt % TMB5, and α‐phase is the main crystalline structure. The cooling rate is proved to be very important in controlling the nonisothermal crystallization behavior and the final crystalline structure of nucleated PP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1853–1867, 2008     

Nucleation,Crystallization, and Thermal Fractionation of Poly (ε‐Caprolactone)‐Grafted‐Lignin: Effects of Grafted Chains Length and Lignin Content

Poly(ε‐caprolactone)‐grafted‐lignin (PCL‐g‐lignin) copolymers with 2 to 37 wt % lignin are employed to study the effect of lignin on the morphology, nucleation, and crystallization kinetics of PCL. Lignin displays a nucleating action on PCL chains originating an intersecting lamellar morphology. Lignin is an excellent nucleating agent for PCL at low contents (2–5 wt %) with nucleation efficiency values that are close to or >100%. This nucleating effect increases the crystallization and melting temperature of PCL under nonisothermal conditions and accelerates the overall isothermal crystallization rate of PCL. At lignin contents >18 wt %, antinucleation effects appear, that decrease crystallization and melting temperatures, reduce crystallinity degree, hinder annealing during thermal fractionation and significantly retard isothermal crystallization kinetics. The results can be explained by a competition between nucleating effects and intermolecular interactions caused by hydrogen bonding between PCL and lignin building blocks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1736–1750     

Correlations between microstructure of α‐row nuclei and polymorphism of shear‐induced iPP/carbon fiber cylindrite

Herein, we reported the formation mechanism of hybrid crystalline (cylindrite) in isotactic polypropylene (iPP)/carbon fiber (CF) via pulling a CF within the iPP melt. The α‐row nuclei layer closely attached to the surface of CF acts as a self‐nucleation site, rather than a heterogeneous nucleation one, to grow cylindrites. As a result, the polymorphic feature of iPP/CF cylindrite is significantly influenced by the microstructure of α‐row nuclei. With decreasing crystallization temperature (T_c), the polymorphic cylindrite changes from pure α‐form to mixed α‐/β‐form and to β‐rich form. The main characteristics of this change include: (a) the outlines of α‐row nuclei layer correspond to wave‐like, saw‐like, and straight lines; (b) the orientation level of iPP molecules in the α‐row nuclei layer become higher; (c) the α‐lamellae rearrange from loose to compact; and (d) the distance between the growth sites of β‐sectors and the surface of CF is evidently longer than in the case of α‐sectors. Moreover, this study provides a guideline for developing the interfacial enhanced iPP/CF composites through manipulation of polymorphic structure in cylindrites. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 368–377     

Study of the crystallization behaviors of isotactic polypropylene with sodium benzoate as a specific versatile nucleating agent

Sodium benzoate (SB), a conventional nucleating agent of α‐phase isotactic polypropylene (iPP) was discovered to induce the creation of β‐phase iPP under certain crystalline conditions. Polarized optical microscopy (POM) and wide angle X‐ray diffraction (WAXD) were carried out to verify the versatile nucleating activity of SB and investigate the influences of SB's content, isothermal crystallization temperature, and crystallization time on the formation of β‐phase iPP. The current experimental results indicated that, under isothermal crystallization conditions, SB showed peculiar nucleating characteristics on inducing iPP crystallization which were different from those of the commercial β form nucleating agent (TMB‐5). The content of β crystal form of iPP nucleated with SB (PP/SB) increased initially with the increase of crystallization temperature, nucleating agent (SB) percentage or crystallization time, reached a maximum value, and then decreased as the crystallization temperature, nucleating agent percentage or crystallization time further increased. While the content of β crystal form of iPP nucleated with TMB‐5 (PP/TMB‐5) showed a completely different changing pattern with the crystallization conditions. The obvious difference of the two kinds of nucleating agents on inducing iPP crystallization can be explained by the versatile nucleating ability of SB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1183–1192, 2008     

Isothermal crystallization kinetics of polypropylene latex–based nanocomposites with organo‐modified clay

The effect of organo‐modified clay (Cloisite 93A) on the crystal structure and isothermal crystallization behavior of isotactic polypropylene (iPP) in iPP/clay nanocomposites prepared by latex technology was investigated by wide angle X‐ray diffraction, differential scanning calorimetry and polarized optical microscopy. The X‐ray diffraction results indicated that the higher clay loading promotes the formation of the β‐phase crystallites, as evidenced by the appearance of a new peak corresponding to the (300) reflection of β‐iPP. Analysis of the isothermal crystallization showed that the PP nanocomposite (1% C93A) exhibited higher crystallization rates than the neat PP. The unfilled iPP matrix and nanocomposites clearly shows double melting behavior; the shape of the melting transition progressively changes toward single melting with increasing crystallization temperature. The fold surface free energy (σ_e) of polymer chains in the nanocomposites was lower than that in the PP latex (PPL). It should be reasonable to treat C93A as a good nucleating agent for the crystallization of PPL, which plays a determinant effect on the reduction in σ_e during the isothermal crystallization of the nanocomposites. The activation energy, ΔE_a, decreased with the incorporation of clay nanoparticles into the matrix, which in turn indicates that the nucleation process is facilitated by the presence of clay. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1927–1938, 2010     

Crystallization and melting behavior of isotactic polypropylene nucleated with individual and compound nucleating agents

In this study, α-phase nucleating agent (NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), β-phase rare earth NA (WBG), and their compound NAs were introduced into isotactic polypropylene (iPP) matrix, respectively. Crystallization kinetics and subsequent melting behavior of the nucleated iPPs were comparatively studied by differential scanning calorimetry (DSC) under both isothermal and nonisothermal conditions. For the isothermal crystallization process, it is found that the Avrami model successfully described the crystallization kinetics. The active energy of nonisothermal crystallization of iPP was determined by the Kissinger method and showed that the addition of nucleating agents increased the activation energy. Melting behavior and crystalline structure of the nucleated iPPs are dependent on the nature of NAs and crystallization conditions. Higher proportion of β-phase can be obtained at higher content of β-nucleating agent and lower crystallization temperature or lower cooling rate.     

Miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and methoxy poly(ethylene glycol) blends

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHB‐HHx) and methoxy poly(ethylene glycol) (MPEG) blends were prepared using melt blending. The single glass transition temperature, T_g, between the T_gs of the two components and the negative χ value indicated that PHB‐HHx and MPEG formed miscible blends over the range of compositions studied. The Gordon–Taylor equation proved that there was an interaction between PHB‐HHx and MPEG in their blends. FTIR supported the presence of hydrogen bonding between the hydroxyl group of MPEG and the carbonyl group of PHB‐HHx. The spherulitic morphology and isothermal crystallization behavior of the miscible PHB‐HHx/MPEG blends were investigated at two crystallization temperatures (70 and 40 °C). At 70 °C, melting MPEG acted as a noncrystalline diluent that reduced the crystallization rate of the blends, while insoluble MPEG particles acted as a nucleating agent at 40 °C, enhancing the crystallization rate of the blends. However, no interspherulitic phase separation was observed at the two crystallization temperatures. The constant value of the Avrami exponent demonstrated that MPEG did not affect the three‐dimensional spherulitic growth mechanism of PHB‐HHx crystals in the blends, although the MPEG phase, such as the melting state or insoluble state, influenced the crystallization rate of the blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2852–2863, 2006     

CO2‐delayed crystallization of isotactic polypropylene: A kinetic study

The effect of CO₂ on the nonisothermal crystallization of isotactic polypropylene (iPP) was studied with high‐pressure differential scanning calorimetry at cooling rates of 0.2–5 °C/min. CO₂ significantly delayed the melt crystallization of iPP, and both the crystallization temperature and the heat of crystallization decreased with increasing CO₂ pressure. The crystallization rate of iPP, as characterized by the half‐time, was also prolonged by the presence of CO₂. With a modified Ozawa model developed by Seo, the Avrami crystallization exponent n of iPP was calculated. This value was depressed by the addition of CO₂ and was strongly dependent on the CO₂ pressure at low cooling rates. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1518–1525, 2003     

Effect of the Metal Phenylphosphonates on the Nonisothermal Crystallization and Performance of Isotactic Polypropylene

The use of metal phenylphosphonates as efficient nucleating agents (NAs) for isotactic polypropylene (iPP) is reported and a possible structural correlation to the nucleation efficiency is studied. First, three kinds of metal phenylphosphonates are synthesized via reflux method: Ca(C₆H₅PO₃)?2H₂O (CaPPA), Ca(C₆H₅PO₃H)₂ (CaPPA2), and Al(HO₃PC₆H₅)(O₃PC₆H₅)?H₂O (AlPPA2). Then, the nonisothermal crystallization behaviors, mechanical, and optical properties of iPP composites are investigated. Compared to CaPPA2 and AlPPA2, CaPPA exhibits more effective heterogeneous nucleation effect during iPP crystallization. Furthermore, the nucleation efficiency of CaPPA is similar to industrial standard NAs NA‐21 and NA‐11. With the addition of 0.1 wt % CaPPA, the crystallization temperature is enhanced and the parameter F(T) of Mo method is decreased appreciably. Moreover, the flexural modulus, impact strength, and haze values of iPP composites are improved remarkably by introducing CaPPA. The CH/π interaction between polymer and aromatic cleft of CaPPA is considered to facilitate the attachment of iPP chains and subsequent nucleation and crystallization, which is verified by the viscoelastic properties of pure iPP and composites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 161–173     

Isotope Effects on the Crystallization Kinetics of Selectively Deuterated Poly(ε‐Caprolactone)

Deuterium labeling of semi‐crystalline polymers can dramatically affect their crystallization behaviors. However, the influence of different labeled positions in a partially deuterated polymer on its crystallization is still far from understood. Here, we synthesized a series of selectively deuterated poly(ε‐caprolactones) (PCLs) through ring‐opening polymerization of ε‐caprolactone with controlled deuteration sites, including fully protiated (D0), fully deuterated (D10), tetra deuteration at the 3‐ and 7‐ caprolactone ring positions (D4) and hexa deuteration at the 4‐, 5‐, and 6‐ caprolactone ring positions (D6). All the PCLs showed a similar lamellar structure and parameters. Differential scanning calorimetry (DSC) analysis revealed that the equilibrium melting temperature $T_m^0$, melting temperature T_m , crystallization temperature T_c , and crystallization kinetics changed systemically with the deuterium content except for D4, which indicates that the presence of ? CD₂? moieties on either side of ester group in the polymer chain combined with isotopic inhomogeneity could influence the chain packing. The nonmonotonic trend of T_m as a function of deuterium content could be attributed to the difference in a hydrogen‐bond like intermolecular interaction between different PCLs. Partially deuterated PCLs (D4 and D6) showed an Avrami index near 2. After analyzing the parameters at the same supercooling temperature ΔT_c , the existence of two crystallization regimes of PCLs were detected. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 771–779