The crystallization characteristics of polypropylene and low ethylene content polypropylene copolymer with copolyesters

The crystallization characteristics of polypropylene (PP) and low ethylene content PP copolymers with and without nucleating agents were studied by differential scanning calorimetry (DSC). PP and PP copolymers was blended with three different kinds of co[poly(butylene terephthalate-p-oxybenzoate)] copolyesters, designated B28, B46, and B64, with the copolyester level varying from 5 to 15 wt.%. All samples were prepared by solution blending in hot xylene solvent at 50 °C. The crystallization behavior of samples was then studied by DSC. The results indicate that these three copolyesters accelerate the crystallization rate of PP and PP copolymers in a manner similar to that of a nucleating agent. The acceleration of crystallization rate was most pronounced in these blend systems with a maximum level at 5 wt.% of B28. The observed changes in crystallization behavior are explained by the effect of the composition and the amount of copolyester in the blends.     

Synthesis and flocculation performance of graft and random copolymer microgels of acrylamide and diallyldimethylammonium chloride

Graft (from linear homopolymers) and random (from a linear random copolymer) copolymer microgels of diallyldimethylammonium chloride (DADMAC) and acrylamide were synthesized via a free-radical mechanism using a γ-radiation technique. These copolymer microgels were evaluated as flocculants on a model dilute TiO₂ colloid suspension using a turbidimeter and a disc centrifuge photosedimentometer, and their performances were compared with the linear homopolymers and their blends. It was found that microgels produced after an appropriate irradiation time showed improved flocculation behavior over their nonirradiated linear counterparts. The graft microgels performed better than the corresponding random microgels. For a γ-radiation dosage of 100 krad/h, the graft microgels obtained by irradiating a 30% DADMAC (by weight) homopolymer blend for 3 h showed the maximum reduction in the relative turbidity of the TiO₂ suspension as well as the largest fraction of larger particles flocculated. Received: 18 May 1999 Accepted in revised form: 1 June 1999     

Miscibility as a function of copolymer composition in blends of a random copolymer and a homopolymer

Random copolymers of n-butyl acrylate (BA) and cyclohexyl acrylate (CHA) were synthesized by solution polymerization in cyclohexane. Blends of polystyrene with the poly(CHA-stat-BA) copolymers were prepared by solvent casting and coprecipitation. The miscibility of the blends was characterized by means of differential scanning calorimetry. While blends with a low content of CHA in the copolymer showed two characteristic glass-transition temperatures of the corresponding blend components, those with a CHA content higher than 70% presented good compatibility. Phase separation of the miscible blends took place after annealing at 200 °C for 1 h, which implies an upper miscibility gap (lower critical solution temperature).     

Cocrystallization of ethylene/1‐octene copolymer blends during crystallization analysis fractionation and crystallization elution fractionation

Blending of ethylene/1‐octene copolymers can be used to achieve a well‐controlled broad chemical composition distribution (CCD) required in several polyolefin applications. The CCD of copolymer blends can be estimated using crystallization analysis fractionation (CRYSTAF) or crystallization elution fractionation (CEF). Unfortunately, both techniques may be affected by the cocrystallization of chains with different compositions, leading to profiles that do not truly reflect the actual CCD of the polymer. Therefore, understanding how the polymer microstructure and the analytical conditions influence copolymer cocrystallization is critical for the proper interpretation of CRYSTAF and CEF curves. In this investigation, we studied the effect of chain crystallizabilities, blend compositions, and cooling rates on cocrystallization during CEF and CRYSTAF analysis. Cocrystallization is more prevalent when the copolymer blend has components with similar crystallizabilities, one of the components is present in much higher amount, and fast cooling rates are used. CEF was found to provide better CCD estimates than CRYSTAF in a much shorter analysis time. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Higher order Morita approximations for random copolymer localization

The Morita approximation is a constrained annealing procedure which yields upper bounds on the quenched average free energy for models of quenched randomness. In this article we consider a bilateral Dyck path model, first introduced by S.G. Whittington and collaborators, of the localization of a random copolymer at the interface between two immiscible solvents. The distribution of comonomers along the polymer chain is initially determined by a random process and once chosen it remains fixed. Morita approximations in which we control correlations to various orders between neighbouring monomers along the polymer chain are applied to this model. Although at low orders the Morita approximation does not yield the correct path properties in the localized region of the phase diagram, we show that this problem can be overcome by including sufficiently high-order correlations in the Morita approximation. In addition by comparison with an appropriate lower bound, we show that well-within the localized phase the Morita approximation provides a relatively tight upper bound on the limiting quenched average free energy for bilateral Dyck path localization.     

A molecular thermodynamic model for random copolymer solutions

A new Helmholtz energy model of mixing for random copolymer solutions based on a close-packed lattice has been developed. The model contains three terms: the contribution of the athermal mixing of polymer chain and solvent, the Helmoltz energy of mixing in a multi-component Ising lattice where the interactions between segments is accounted for, and the contribution of the dissociation of the polymer and the association of monomers. The Guggenheim model, Yang et al.'s model and the sticky-point model of Cummings, Zhou and Stell are used respectively, for the above three contributions. Comparisons between Monte Carlo simulated coexistence curves with those predicted by various theories for random copolymer solutions with various chain lengths, chain compositions and inter-segment interaction parameters show that the agreement between simulations and the predictions of this work is nearly perfect. The model can be used satisfactorily to correlate the liquid–liquid equilibria of practical random copolymer solutions.     

Stretching‐induced phase transition of the butene‐1/ethylene random copolymer: Orientation and kinetics

The stretching‐induced phase transition from tetragonal Form II to hexagonal Form I and the evolution of corresponding crystallite orientation were studied for the butene‐1/ethylene random copolymer with 1.5 mol % ethylene by using a combination of tensile test and in situ wide‐angle X‐ray diffraction. Three orientation pathways were distinguished for II‐I phase transition, including phase transition accomplishing within off‐axis oriented crystallites (Orientation Pathway 1), phase transition with simultaneous formation of highly oriented crystallites (Orientation Pathway 2), and phase transition occurring within the highly oriented crystallites already formed (Orientation Pathway 3). The kinetics of II‐I transition was correlated with the macroscopic mechanical response, which exhibits a strong dependence on orientation. In Orientation Pathway 1, the triggering of phase transition corresponds to the mechanical yielding. More interestingly, the kinetics of transition exhibits the identical dependence on stress. However, in Orientation Pathways 2 and 3, appearance of the highly oriented crystallites substantially alters transition kinetics, which is tentatively associated with the stress bearing by interstack tie chains. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 116–126     

Flow-induced crystallization of propylene/ethylene random copolymers

The influence of the co-monomer content and processing conditions on the crystallization kinetics of propylene/ethylene (P/E) random copolymers is studied using DSC and rheometry. The presence of ethylene lowers the melting and crystallization temperature compared to pure polypropylene, and the quiescent crystallization rate, [(X)\dot], \dot{X}, increases at equal nominal undercooling, because both the crystal growth rate, G, and number of nuclei, N, increases. The effect of flow on the kinetics of crystallization decreases with the ethylene content. Still, different regimes of flow-induced crystallization are observed, but their size and the position of the transitions between them depend on the ethylene content, and can be expressed in terms of the level of molecular orientation, molecular stretch, and crystallization capacity of the system.     

Effects of toughening propylene/ethylene graft copolymer on the crystallization behavior and mechanical properties of polypropylene random-copolymerized with a small amount of ethylene

Linear low-density polyethylene (LLDPE) was grafted onto the backbone chains of isotactic polypropylene (iPP) during reactive melt-extrusion to produce a novel toughening modifier, propylene/ethylene graft copolymer (PEGC), to improve the properties of iPP random(-copolymerized with a small amount of ethylene) (PPR). The crystallization behavior as well as the non-isothermal crystallization kinetics of the PEGC modified PPRs were investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). The fractured surface topography was characterized using scanning electron microscopy (SEM), and the mechanical properties through notched impact and tensile testing as well as dynamic mechanical thermal analysis (DMTA). The results show that, at a PEGC content of 8 wt%, notched impact strength of the PEGC modified PPR increased by 30.6% at low temperature (−25 °C). As regards crystalline morphology, the PEGC, as an effective heterogeneous nucleating agent, fostered nucleation of the PPR to elevate its crystallization temperature as well as rate of crystallization, thus refining the PPR (iPP) spherulites and improving the interfacial structure between iPP spherulites. The Jeziorny approach was unsatisfactory for simulation of the non-isothermal crystallization process of the PEGC modified PPRs; however, the Mo method described consistently the crystallization kinetics over the entire isothermal process.     

SAXS/WAXS/DSC studies on crystallization of a polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymer with lamellar morphology and low glass transition temperature

Crystallization of a polystyrene-b-poly(ethylene oxide)-b-polystyrene (S-EO-S) triblock copolymer, S₄₀EO₁₃₆S₄₀, with lamellar morphology in the melt and low glass transition temperature (T_g=47 °C) of the S block was studied. The triblock copolymer was cooled from ordered melt and isothermal crystallization was conducted at crystallization temperatures (T_c) near the T_g of the S block. It is found that crystallization behavior of S₄₀EO₁₃₆S₄₀ strongly depends on T_c. When T_c is far below T_g, an Avrami exponent n=0.5 is observed, which is attributed to diffusion-controlled confined crystallization. As T_c slightly increases, the Avrami exponent is 1.0, indicating that crystallization is confined and crystallization rate is determined by the rate of homogeneous nucleation. When T_c is just below the T_g of the S block, crystallization tends to become breakout and accordingly Avrami exponent changes from 1.0 to 3.2. Crystallinity and melting temperature of the EO block in breakout crystallization are slightly higher than those in confined crystallization. Time-resolved small and wide angle X-ray scattering (SAXS/WAXS) were used to monitor isothermal crystallization of S₄₀EO₁₃₆S₄₀. It shows that the long period is constant in confined crystallization, but it gradually increases during breakout crystallization. WAXS result reveals that confined or breakout crystallization has no effect on the crystal structure of the EO block.     

The influence of soft segment length on the properties of poly(butylene terephthalate-co-succinate)-b-poly(ethylene glycol) segmented random copolymers

Three series of poly(butylene terephthalate-co-succinate)-b-poly(ethylene glycol) segmented random copolymers with starting PEG number-average molecular weight (M_n(PEG)) at 600, 1000 and 2000, respectively, as well as hard segment poly(butylene succinate) (PBS) molar fraction (M_PBS) increasing from 10% to 30% were synthesized through a transesterification/polycondensation process and characterized by means of GPC, NMR, DSC, WAXD and mechanical testing etc. The investigations were mainly focused on the influence of M_n(PEG) on the properties of resulting copolymers bearing two sorts of hard segments. It is revealed that all the samples show a relatively symmetrical GPC curves with the number-average molecular weight more than 4 × 10⁴, while the polydispersity decreases from 1.9 to 1.4 as the increasing M_n(PEG) because of the prolonged time for polycondensation and the faster exclusion of small molecules by-product with the decreased molten viscosity. The sequence distribution analysis shows that the average sequence length of hard segment PBT decreases while that of PBS increases with the increasing M_PBS and are independent of the soft segment length. The approximate unit degree of randomness as well as the soft segment length turns out that the segments take a statistically random distribution along the backbone. Micro-phase separation structure is verified for the appearance of two glass transition temperatures and two melting points, respectively, in DSC thermograms of most samples. The depression of melting points and the reduction of crystallinity of hard segments with increasing M_PBS are related to the crystal lattice transition from α-PBT to PBS and discussed in the viewpoint of cohensive energy. Mechanical testing results demonstrate that the increase of amorphous domains the increase of M_PBS as well as M_n(PEG) will provide high elongation and good flexibility of copolymer chain. The in vitro degradation experiments show that the partial substitution of aromatic segment PBT with aliphatic PBS will substantially accelerate the degradation rate with enhanced safety of degradation by-products and while changing M_n(PEG) broaden the spectrum to tailor the properties.     

Non-isothermal crystallization and melting behavior of compatibilized polypropylene/recycled poly(ethylene terephthalate) blends

Binary blends of polypropylene (PP)/recycled poly(ethylene terephthalate) (r-PET), r-PET/maleic anhydride grafted PP (PP-g-MA), r-PET/glycidyl methacrylate grafted PP (PP-g-GMA), and ternary blends of PP/r-PET (80/20 w/w) compatibilized with various amounts (2-10 wt%) of PP-g-MA or PP-g-GMA were prepared on a twin-screw extruder. The non-isothermal crystallization and melting behavior, and the crystallization morphology were investigated by DSC and POM. The chemical reactions of r-PET with PP-g-MA and PP-g-GMA were characterized by FT-IR. DSC results show that the crystallization peak temperatures of r-PET and PP increased when blending them together, due to the heterogeneous nucleation effect on each other. The of r-PET increased with increasing the content of PP-g-MA while slightly influenced by the content of PP-g-GMA in the binary blends of r-PET with grafted PP, implying different reactivity of r-PET with PP-g-MA and PP-g-GMA. The of PP in the ternary blends retained or slightly decreased, dependent on the compatibilizers and their contents. The melting peak temperature of r-PET in PP/r-PET blends compatibilized by PP-g-MA was lower than that of compatibilized by PP-g-GMA, indicating that PP-g-MA had stronger reactivity towards r-PET compared to PP-g-GMA. The crystallization and melting behavior of blends was influenced by the pre-melting temperature, especially the melting behavior of r-PET in the blends. The crystallization behavior of PP in the blends was also evaluated by Mo’s method. POM confirmed the heterogeneous nucleation effect of r-PET on PP.     

Effect of long chain branching on the rheological behavior,crystallization and mechanical properties of polypropylene random copolymer

Long chain branched polypropylene random copolymers (LCB-PPRs) were prepared via reactive extrusion with the addition of dicumyl peroxide (DCP) and various amounts of 1,6-hexanediol diacrylate (HDDA) into PPR. Fourier transform infrared spectrometer (FTIR) was applied to confirm the existence of branching and investigate the grafting degree for the modified PPRs. Melt flow index (MFI) and oscillatory shear rheological properties including complex viscosity, storage modulus, loss tangent and the Cole-Cole plots were studied to differentiate the LCB-PPRs from linear PPR. Differential scanning calorimetry (DSC) and polarized light microscopy (PLM) were used to study the melting and crystallization behavior and the spherulite morphology, respectively. Qualitative and quantitative analyses of rheological curves demonstrated the existence of LCB. The effect of the LCB on crystalline morphology, crystallization behavior and molecular mobility, and, thereby, the mechanical properties were studied and analyzed. Due to the entanglements between molecular chains and the nucleating effect of LCB, LCB-PPRs showed higher crystallization temperature and crystallinity, higher crystallization rate, more uniformly dispersed and much smaller crystallite compared with virgin PPR, thus giving rise to significantly improve impact strength. Moreover, the LCB-PPRs exhibited the improved yield strength. The mobility of the molecular chain segments, as demonstrated by dynamic mechanical analysis (DMA), was improved for the modified PPRs, which also contributed to the improvement of their mechanical properties.     

Miscibility diagrams of random copolymer blend systems

The miscibility of copolymers A_xB_1?x and A_yB_1?y, derived from the same monomer pair (A, B) but differing in composition, was studied. The systems (A, B) were (S, MMA), (BMA, MMA), (S, BMA), and (CIS, BMA) (S: styrene, CIS: p-chlorostyrene, MMA: methylmethacrylate, BMA: n-butylmethacrylate). Miscibility diagrams were recorded, at low and high temperatures, using cast films and dry films. All blend systems feature hightemperature miscibility gaps. Unusual effects of the compositions x and y on miscibility in blends A_xB_1?x/A_yB_1?y were observed. The classical prediction that miscibility should depend only on the composition difference |x – y| usually is too simple. It appears necessary to consider dyad interactions.     

Isothermal crystallization of propylene-1-decene copolymers

The isothermal crystallization and subsequent melting behavior of one propylene homopolymer and three propylene-1-decene copolymers with different comonomer contents prepared by metallocene catalyst were studied using differential scanning calorimetry (DSC). It is found that the Avrami exponent of the propylene copolymers decreases gradually with the increase of comonomer content, from 3.0 for the propylene homopolymer to 1.4 for the copolymer with 7.83 mol% 1-decene units. Higher comonomer content also weakens the dependence of crystallization rate constant and crystallization halftime on temperature. Double melting peaks, which correspond to α and γ crystal phases, respectively, are observed for all copolymers under isothermal crystallization. The result shows that higher crystallization temperature is favorable to the segregation of α and γ crystal phases, resulting in higher proportion of γ crystal phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Side chain crystallization in microphase-separated poly(styrene-block-octadecylmethacrylate) copolymers

The crystallization behavior of two microphase-separated poly(styrene-b-octadecylmethacrylate) block copolymers with lamellar and cylindrical morphology is studied by DSC. The findings are compared with results for a polyoctadecylmetharcylate (PODMA) homopolymer. The situation in the block copolymers is characterized by the occurrence of a confined side chain crystallization in small PODMA domains surrounded by a glassy polystyrene phase. The strength of confinement effects depends significantly on the block copolymer morphology. The crystallization behavior of PODMA lamellae with a thickness of about 10 nm is only slightly affected and similar to the situation in the homopolymer. In cylindrical PODMA domains with a diameter of about 10 nm strong confinement effects are observed: the degree of crystallinity is 50% reduced and the crystallization kinetics slows down. The Avrami coefficients change from n≈3 for the homopolymer and PODMA lamellae to n≈1 for PODMA cylinders. This observation indicates one-dimensional growth in small cylinders or a change from heterogeneous to homogeneous nucleation. Pros and cons of both approaches are discussed. A speculative picture explaining qualitatively the differences in the crystallization behavior of PODMA lamellae and cylinders in a glassy polystyrene matrix is presented.     

Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

The crystallization behavior of isotactic propylene‐1‐hexene (PH) random copolymer having 5.7% mole fraction of hexene content was investigated using simultaneous time‐resolved small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques. For this copolymer, the hexene component cannot be incorporated into the unit cell structure of isotactic polypropylene (iPP). Only α‐phase crystal form of iPP was observed when samples were melt crystallized at temperatures of 40 °C, 60 °C, 80 °C, and 100 °C. Comprehensive analysis of SAXS and WAXD profiles indicated that the crystalline morphology is correlated with crystallization temperature. At high temperatures (e.g., 100 °C) the dominant morphology is the lamellar structure; while at low temperatures (e.g., 40 °C) only highly disordered small crystal blocks can be formed. These morphologies are kinetically controlled. Under a small degree of supercooling (the corresponding iPP crystallization rate is slow), a segmental segregation between iPP and hexene components probably takes place, leading to the formation of iPP lamellar crystals with a higher degree of order. In contrast, under a large degree of supercooling (the corresponding iPP crystallization rate is fast), defective small crystal blocks are favored due to the large thermodynamic driving force and low chain mobility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 26–32, 2010     

Spherulite growth rate and fold surface free energy of the form II mesophase in isotactic polybutene-1 and random butene-1/ethylene copolymers

The spherulite growth rate of isotactic polybutene-1 and random butene-1/ethylene copolymers has been measured in a wide range of temperatures between the glass transition and the melting temperature. The presence of ethylene co-units in the butene-1 chain leads to a distinct decrease of both the maximum spherulite growth rate and the temperature of fastest growth. The data were analyzed within the frame of the Hoffman–Lauritzen theory of crystallization to obtain form II mesophase surface free energies. The robust performed analysis revealed that the form II mesophase fold surface free energy in random copolymers of butene-1 with less than 5 mol% ethylene is 50–100 % higher than in the homopolymer. It is suggested that the increase of the fold surface free energy is related to the exclusion of ethylene chain defects from crystallization and their accumulation at the basal planes of the form II mesophase.     

环氧乙烷与苯乙烯两亲性聚合物的合成

Graft eopolymer eontaining poly(ethylene oxide)side chains on a polystyrene backbone were acrylamided. The amide groups in the copolymers were ionized by using potassium naphthalene, and grafting was achieved by utilizing the amide anions as initiator sites for the polymerization of ethylene oxide at 70℃. The graft copolymers was characterized with respect to molecule weight and composition using NMR, IR, GPC, and DSC. GPC result from the graft copolymer sample suggested a narrow size distribution.