Effects of Branches on the Crystallization Kinetics of Polypropylene-g- Polystyrene and Polypropylene-g-Poly（n-butyl acrylate） Graft Copolymers with Well-defined Molecular Structures

Effects of branches on the crystallization kinetics of polypropylene-g-polystyrene(PP-g-PS) and polypropylene-gpoly(n-butyl acrylate)(PP-g-PnBA) graft copolymers with well-defined molecular structures were systematically investigated by DSC.The Avrami equation was used to analyze the isothermal crystallization process,while the analysis of nonisothermal crystallization process was based on the Jeziorny-modified Avrami model and Mo model.The kinetics results of isothermal and nonisothermal crystallization verified the peculiar effects of branches on the crystallization process of PP backbones in PP-g-PS and PP-g-PnBA graft copolymers:on one hand,the interaction between branches(π-π interaction between PS branches,or dipole-dipole interaction between PnBA branches) restrained the mobility and reptation ability of the PP backbones,which hindered the crystallization process;on the other hand,the heterogeneous nucleation effect resulting from the branched structure and fluctuation-assisted nucleation mechanism(caused by microphase separation between the PS or PnBA rich phase and the PP rich phase) became more pronounced with increasing branch length,which facilitated the crystallization process.     

Effect of functionalization on non-isothermal crystallization behavior of polypropylene

The non-isothermal crystallization kinetics of three functionalized polypropylenes (PPs; polypropylenes-g-acrylic acid [PP-g-AA], polypropylenes-g-glycidyl methacrylate [PP-g-GMA], polypropylenes-g-maleic anhydride [PP-g-MAH]) at different cooling rates were investigated by differential scanning calorimetry, using the Jeziorny method, Ozawa method, and Mo method. The result showed that Mo method can adequately describe the non-isothermal crystallization kinetics of pure PP and functionalized PPs, and at a given relative crystallinity, the crystallization rate obtained using Mo method followed an order of PP-g-AA > PP-g-GMA > PP > PP-g-MAH. The crystallization activation energy for these samples was calculated using Kissinger's method, which indicated that the introduction of monomers had a confinement effect on the motion of PP chains.     

Isothermal and nonisothermal crystallization kinetics of novel biobased poly(ethylene succinate-<Emphasis Type="Italic">co</Emphasis>-ethylene sebacate) copolymers from the amorphous state

In this work, the isothermal and nonisothermal crystallization kinetics of three novel biobased poly(ethylene succinate-co-ethylene sebacate) (PESSe) copolymers was systematically investigated with differential scanning calorimetry under different crystallization conditions from the amorphous state. For the isothermal cold crystallization kinetics study, the Avrami equation could well describe the crystallization process of PESSe at various crystallization temperatures. All three PESSe copolymers crystallized through the same crystallization mechanism; moreover, the overall isothermal cold crystallization rate of PESSe decreased with increasing ethylene sebacate (ESe) comonomer content. The nonisothermal cold crystallization kinetics of PESSe was also studied at different heating rates. With increasing ESe content or heating rate, the nonisothermal cold crystallization exotherm of PESSe copolymers shifted to high temperature range. Both the crystallization rate parameter and crystallization rate coefficient of PESSe copolymers decreased with increasing ESe content, indicating that PESSe copolymer with higher ESe content crystallized more slowly than that with lower ESe content. The Ozawa equation was used to analyze the nonisothermal cold crystallization kinetics of PESSe copolymers, which was found to fit the crystallization process very well.     

聚丙烯-g-聚氨酯共聚物的非等温结晶动力学研究

用DSC法研究了聚丙烯 (PP)和聚丙烯接枝聚氨酯的共聚物 (PP g PU)在不同冷却速率下的非等温结晶动力学 .用Avrami方程和莫志深改进法对DSC测定结果进行了处理 ,结果表明 ,PP g PU的动力学参数能很好的符合Avrami方程和莫志深改进方程 .PP接枝了聚氨酯支链后 ,结晶速率增大 ,球晶的生长和成核机制也相应发生改变 ,而其变化规律与接枝物的组成和结构密切相关     

Grafting polypropylene and treatment of calcium carbonate to improve structure and properties of polypropylene composites

In this paper, calcium carbonate was chemically treated with two kinds of dicarboxylic acids before compounding with polypropylene in the presence of dicumyl peroxide (DCP). It was observed that the mixture of dicarboxylic acids could improve the crystallization and impact strength properties of calcium carbonate/polypropylene composite. With further addition of DCP, more PP-g-MA was produced in the blend, resulting in PP composites with larger β-phase content and improved mechanical properties. In the experiments, the maximum K _β value of 52.0 % was obtained. The elongation at break of composite increased from 252 % for PP composite with untreated calcium carbonate to 444 % for PP composite with chemically treated calcium carbonate.     

Crystallization of polypropylene,nylon-66 and poly(ethylene terephthalate) at pressures to 200 MPa: Kinetics and characterization of products

The crystallization kinetics of polypropylene (PP), polyamide (PA66), and poly(ethylene terephthalate) (PET) were studied, using a pressure dilatometer (to 200 MPa) to follow the volume changes associated with the crystallization process. The commonly used Avrami equation fitted the isothermal/isobaric crystallization data of PP and PA66 well. The Avrami exponent n was between 1.3 and 1.7, independent of crystallization pressure and temperature. Lines of constant Avrami rate parameter Z in the P-T plane were essentially parallel to the pressure dependence of the melting points and crystallization temperatures. However, the Avrami equation was not suitable for PET. The Malkin, Dietz, and Kim equations provided better fits. The crystallization half-time of PET increased with pressure at constant supercooling, in contrast to PP and PA66, for which it remained essentially unchanged. X-ray diffraction, differential scanning calorimetry, and pressure dilatometry were used to study the effect of formation pressure on the crystal structure, the melting point, and the density of products which were crystallized for short times (minutes) at various temperatures and pressures. No new crystal structures were found for PA66 and PET, but a mixture of monoclinic and triclinic crystals existed in PP above a formation pressure of 50 MPa. The melting points increased with formation pressure for PET, but remained unchanged for PP and PA66. Density at ambient conditions decreased with formation pressure for PP, but increased for PET and PA66. © 1994 John Wiley & Sons, Inc.     

Melting and crystallization of tetrafluoroethylene-ethylene copolymers

The melting and crystallization of copolymers of tetrafluoroethylene with ethylene, synthesized in bulk and in suspension by semi-flow method, were studied by DSC. X-ray diffractions and infrared spectra of the copolymers were measured and new crystalline reflections different from those of the homopolymers were observed. The melting temperature of the copolymers synthesized in bulk depends strongly on the composition and exhibits several maxima. A certain small decrease in the melting temperature within the range of the alternating composition is observed. For alternating copolymers synthesized in suspension, the peaks are monomodal indicating a higher structural and chemical homogeneity of the copolymer. The nonisothermal crystallization kinetics in the temperature interval from 260 to 255°C of the alternating copolymer prepared in suspension can be described by a modified Avrami equation. The mechanism of nucleation and nuclei growth during the nonisothermal crystallization of the tetrafluoroethylene-ethylene copolymer is close to that of polyethylene.     

Crystallization and melting behaviors of polystyrene-b-poly(ethylene-co-butene) block copolymers

Non-isothermal and isothermal crystallization behaviors of polystyrene-b-poly(ethylene-co-butene) (PSt-b-PEB) block copolymers with different compositions and chain lengths were investigated by differential scanning calorimetry (DSC). The results show that crystallization of PEB block is strongly dependent on the composition. Crystallization temperature (T_c), melting temperature (T_m) and fusion enthalpy (ΔH_f) increase rapidly with PEB volume fraction (V_E) for block copolymers with V_E below 50%, but there is little change when PEB block becomes the major component. Glass transition temperature (T_g) of the PSt block and order-disorder transition temperature (T_ODT) of block copolymers also have a weak effect. The isothermal crystallization kinetics results show that Avrami exponent (n) was strongly dependent on the composition and crystallization temperature. For the block copolymers with V_E below 38.7 vol%, the values of n vary between 0.9 and 1.3, indicating that crystallization is confined. For the PSt-b-PEB block copolymers with V_E higher than 50%, fractionated crystallization behavior is usually observed. A two-step isothermal crystallization procedure is applied to these block copolymers. It is found that breakout crystallization occurs at higher T_c, but confined at lower T_c. Two overlapped melting peaks are observed for the block copolymers with fractionated crystallization behavior after two-step crystallization, and only the higher melting peak corresponding to breakout crystallization can be used to derive equilibrium melting temperature.     

Reactive compatibilization of blends of PET and PP modified by GMA grafting

The melt radical grafting of glycidyl methacrylate (GMA) onto isotactic polypropylene (PP) was carried out in Brabender internal mixer and the influence of reaction procedure, radical initiator concentration and addition of co-monomer (styrene) on the grafting efficiency was examined. The viscosity, the thermal behaviour and melt rheology of PP-g-GMA samples was then analysed as a function of grafted GMA content. Blends of poly(ethylene terephthalate) (PET) with PP and PP-g-GMA (5.2 wt% GMA), prepared in internal mixer, were characterised by SEM, DSC and melt viscosimetry. The morphological analysis of PET/PP-g-GMA blends (80/20, 50/50 w/w) pointed out a marked improvement of phase dispersion (with particle size of about 0.6 μm for 80/20 blend) and interfacial adhesion, as compared to non-compatibilized PET/PP blend. The results of mixing torque and thermal analysis supported the occurrence of in-situ compatibilization reaction between epoxy groups of GMA modified PP and carboxyl end-groups of PET in the melt.     

Effect of sequence distribution on the isothermal crystallization kinetics and successive self-nucleation and annealing (SSA) behavior of poly(ε-caprolactone-co-ε-caprolactam) copolymers

Two types of miscible poly(ε-caprolactone-co-ε-caprolactam) copolymers were studied. In both cases catalyzed hydrolytic ring-opening polymerization was employed. For the first type, the comonomers were added simultaneously to obtain random copolymers. For the second type, the comonomers were added sequentially to obtain block copolymers. Successive self-nucleation and annealing (SSA) and isothermal crystallization studies were performed to both types of copolymers. The SSA results reflect the differences in molecular microstructure: block versus random copolymers. In a wide composition range only the polycaprolactam sequences were capable of crystallization in the random copolymers. Avrami indexes of approximately 3-4 were obtained corresponding to the spherulitic crystallization of these units within the copolymers. The block copolymer samples experienced a relatively small reduction of crystallization kinetics with composition, and this was attributed to the dilution effect caused by the miscible non-crystalline polycaprolactone units. On the other hand, for the random copolymers, the rate of crystallization strongly increased with polycaprolactam content while the energy barrier for secondary nucleation decreased exponentially. The comparison between miscible block and random copolymers provides a unique opportunity to distinguish the dilution effect of the polycaprolactone units (a moderate effect) on the isothermal crystallization and melting of the polyamide phase from the molecular microstructural effect in the random copolymers case (a dramatically strong effect), where the polycaprolactam sequences are interrupted statistically by polycaprolactone sequences.     

Influence of amorphous block on the thermal behavior of well-defined block copolymers based on ε-caprolactone

In this work, we studied the thermal characterization of block copolymers based on ε-caprolactone. The copolymers were obtained by anionic polymerization techniques, using different co-monomers such as styrene (S) and dimethylsiloxane (DMS). Synthesized copolymers were characterized by H-nuclear magnetic resonance, size exclusion chromatography, and Fourier transform infrared spectroscopy. Isothermal crystallization was performed by differential scanning calorimetry (DSC), and Avrami’s theory was employed in order to obtain kinetics parameters of interest, such as the half-life for the crystallization process (t _1/2), the bulk crystallization constant (k), and the Avrami’s exponent (n). The spherulitic growth was measured by polarized optical microscopy in order to determine the crystallization behavior. Poly(ε-caprolactone) block (PCL) crystallization was analyzed by considering the physico-chemical characteristics of the neighboring block, PS or PDMS. The chemical nature of the neighbor block in the PCL-based copolymer affects the kinetics parameters of Avrami’s equation, as can be deduced by comparing the values obtained for pure PCL and the studied block copolymers. On the other hand, the apparent thermal degradation activation energies E _ad for PCL and block copolymers were determined by Ozawa’s method. The incorporation of PDMS instead of PS improves the stability of the resulting copolymer, as it was observed by thermogravimetric analysis.     

乙烯含量对抗冲丙烯共聚物等温结晶行为的影响

利用DSC研究了乙烯含量不同的4种抗冲丙烯共聚物的等温结晶动力学.结果表明4种样品在考察的温度范围内(126~130℃)的等温结晶动力学完全符合Avrami方程,并得到了不同结晶温度下Avrami方程的结晶动力学参数k,n和t1/2,随着样品中乙烯含量的增加,Avrami指数(n)随温度变化不大,样品的结晶过程可能属于三维扩散控制的成核增长,4种样品的结晶活化能ΔE在279.5~343.1 kJ/mol范围内,且随乙烯含量增加,结晶活化能增大,充分说明样品中的乙烯含量是影响其结晶活化能的主要因素.结晶分级分析测试结果显示,随着乙烯含量的增加,聚丙烯均聚物部分链结构规整性提高,结构规整、可结晶的长序列含量在减少,可见乙烯含量的变化规律直接决定上述参数的变化规律.     

Isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone)

The isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone) are investigated by differential scanning calorimetry over two temperature regions. The Avrami equation describes the primary stage of isothermal crystallization kinetics with the exponent n ≈ 2 for both melt and cold crystallization. With the Hoffman–Weeks method, the equilibrium melting point is estimated to be 406 °C. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter (K_g) of the isothermal melt and cold crystallization is estimated. In addition, the K_g value of the isothermal melt crystallization is compared to those of the other poly(aryl ether ketone)s. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1992–1997, 2000     

Bulk and solution crystallization kinetics of isotactic polybutene-1

The crystallization kinetics of an unfractionated sample of isotactic polybutene-1 have been studied from the melt and from dilute solutions in amyl acetate by the dilatometric method. The kinetics of bulk crystallization followed the Avrami equation for most of the transformation with a deviation towards the end of the crystallization process. The Avrami exponent is found to be temperature dependent with the value of n ≈ 3 at high undercooling (indicating a homogeneous nucleation process) and n ≈ 4 at lower undercooling (indicating a heterogeneous nucleation process). The temperature coefficients of the rate constants indicate a nucleation controlled process of crystallization.     

Effect of nanoscale fully vulcanized acrylic rubber powders on crystallization of poly(butylene terephthalate): Isothermal crystallization

Poly(butylene terephthalate) (PBT) was blended with nanoscale fully vulcanized acrylic rubber (FVAR) powders in a twin extruder, and the FVAR powders were dispersed well in PBT from scanning electron microscopy (SEM) and transmission electron microscope (TEM) investigation. The isothermal crystallization kinetics of PBT/FVAR blends were investigated by differential scanning calorimeter (DSC) and simulated by Avrami model. Equilibrium melting temperature was estimated by the nonlinear Hoffman-Weeks relation. The active energy (ΔE) and nucleation parameters (K_g) increased with the addition of FVAR, suggesting that FVAR particles hindered the crystallization; however more content FVAR had a lower ΔE and K_g because FVAR powders acted as heterogeneous nuclei in the nucleation of crystallization and facilitated the crystallization of PBT. The crystallization ability followed the order: PBT > PBT/FVAR6 > PBT/FVAR3 > PBT/FVAR1 when undercooling was considered.     

Morphologies, crystallinity and dynamic mechanical characterizations of polypropylene/polystyrene blends compatibilized with PP-g-PS copolymer: Effect of the side chain length

PP-g-PS copolymers were synthesized with the same polypropylene (PP) backbones and various side chain lengths of PS sequences via reactive comonomer p-allyltoluene (p-AT) by Ziegler–Natta copolymerization and the subsequent living anionic graft-polymerization. ¹H NMR characterized that the PP-g-PS copolymer had grafted 3.15 side chains per 1000 carbons in the PP backbones and the length of PS sequences varied in the range of 25.8–309.9 units. PP/PS blends with the PP-g-PS copolymer as compatibilizer (wt. 75/25/5) were prepared and characterized by SEM, WAXD and DMA to investigate the morphologies, crystallinity and glass transition temperatures of the PP/PS blends. All the results pointed out that the average side chain length (GL) of the graft copolymer (GL is from 25.8 to 309.9) made great effects of the PP/PS blends, such as the PS dispersed phase, the crystallinity of the PP component and the two glass transition temperatures of the blends, which showed the same trend with the increase of the GL. Overall, only with a suitable average side chain length, the PP-g-PS copolymer could achieve optimal compatibilizing efficiency of the PP/PS blends.     

Isothermal crystallization kinetics and melting behaviour of PET/ATO nanocomposites prepared by in situ polymerization

Neat poly(ethylene terephthalate) (PET) and PET/antimony doped tin oxide (ATO) nanocomposites were prepared by in situ polymerization. The study of the isothermal crystallization behaviors of neat PET and PET/ATO nanocomposites was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. For neat PET and PET/ATO nanocomposites, the Avrami exponent n both decreased with increasing crystallization temperature. In addition, for the same crystallization temperature, the value of n increased with increasing ATO content. These suggested that the crystallization types related to the values of n in the Avrami theory could not be suitable for the crystallization of PET and its nanocomposites. The change of the n values indicated that the addition of ATO resulted in the increase of the crystallizing growth points. That is a heterogeneous nucleating effect of ATO on crystallization of PET. In the DSC scan after isothermal crystallization process, multiple melting behavior was found. And the multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae produced during different crystallization processes. The equilibrium melting temperature of PET in the nanocomposites increased with increasing the ATO content. Surface free energy of PET chain folding for crystallization of PET/ATO nanocomposites was lower than that of neat PET, confirming the heterogeneous nucleation effect of ATO.     

Thermal and structural investigation of random ethylene/1-hexene copolymers with high 1-hexene content

Random ethylene/1-hexene copolymers with the 1-hexene content in the range from 2 to 28 mol% were produced with a novel post-metallocene catalyst and analyzed by three techniques, FTIR, ¹³C NMR, and DSC. The 1-hexene content and the sequence distribution in the copolymers were determined by means of FTIR-M and ¹³C NMR. The crystallization behavior of the copolymers was studied by DSC under dynamic and isothermal conditions; the Avrami model was used to analyze the crystallization kinetics. It was found that both the 1-hexene content and the crystallization temperature affect the relative crystallinity. The bulk crystallization rate decreases with the 1-hexene content and reduces exponentially with an increase of T _c. The melting behavior of isothermally crystallized samples was also investigated and it was found that the melting temperatures of the copolymers under equilibrium conditions were related to the composition.     

聚丙烯/纳米蒙脱土复合材料的结晶动力学研究

采用热分析方法，研究了聚丙烯／纳米蒙脱土复合材料（PP／CLAY）的等温结晶行为，并分别用Avrami方程和赵志英方法对所得数据进行了分析，研究结果表明，纳米蒙脱土微粒对聚丙烯等温和非等温结晶行为均有不同程度的影响，可提高聚丙烯的结晶速率并改善结晶结构。     

A novel route to the synthesis of PP-g-PMMA copolymer via ATRP reaction initiated by Si-Cl bond

The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler-Natta catalyst supported on MgCl₂. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP-co-ADMS was chlorinated to PP-Si-Cl by refluxing the copolymer with SOCl₂ in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst to produce graft copolymer PP-g-PMMA, which was characterized with ¹H NMR, ¹³C NMR, GPC and DSC. Polymer blend of iPP/PP-g-PMMA/PMMA was prepared and the results shown that PP-g-PMMA was an effective compatilizer.