Model development for semicontinuous production of ethylene and norbornene copolymers having uniform composition

Terminal and penultimate models for controlling copolymer composition distribution (CCD) in ethylene and norbornene (NB) copolymerization were developed by taking into account the variation of active site concentration with the initial comonomer ratio. The models were validated by batch polymerization experimental data. The terminal model gave better correlation with the composition data whereas the penultimate model had a better fit to the rate data. The terminal model was then used to design NB feeding policies in semicontinuous processes for targeted CCD profiles. Based on the model results, a series of ethylene‐NB copolymers with various NB contents were prepared. With the same NB content, the semicontinuous process produced a uniform composition, whereas the batch process yielded broad CCD. The batch samples had lower T_g values and broader transition ranges, even yielded crystalline materials. In contrast, the semicontinuous samples overcame the disadvantages. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

不同乙烯含量丙烯无规共聚物结构表征

采用聚丙烯Ziegler-Natta催化剂及淤浆聚合法考察了乙烯-丙烯共聚行为,获得了不同乙烯含量丙烯无规共聚物,分别通过傅里叶红外光谱（FT-IR）、差示扫描量热（DSC）、凝胶渗透色谱（GPC）和13C NMR核磁谱进行了结构和性能表征。结果表明,随着原料中乙烯含量的增加,催化剂的共聚合活性增大,丙烯无规共聚物中乙烯含量增加,共聚物由以丙烯链段为主逐渐过渡到以乙烯链段为主;当反应原料中乙烯质量分数介于15%～30%时,共聚物的DSC测试结果达到较低值;共聚物的数均分子量和重均分子量均达到最低值,同时,共聚物中乙烯和丙烯在聚合物链段中的分布更均匀。     

Conditions of homogeneous deformation of poly(ethylene terephthalate) films during uniaxially drawing

Amorphous poly(ethylene terephthalate) film was uniaxially drawn over a wide range of temperatures from below to above the T_g at a constant strain rate. The geometry of the deformation in macroscopic dimensions of the sample demonstrates that homogeneous deformation can be obtained when the drawing temperature (T_def) is not lower than 69°C. The change of the cold crystallization peak temperature (T_cc) and crystallinity determined by differential scanning calorimetry and density measurement, respectively, were studied in terms of the T_def and the draw ratio (λ). The orientation, relaxation, and crystallization during drawing were investigated as a function of T_def as well as of λ. The results suggest that 69°C is the critical temperature at which the sample with the highest orientation and the least slippage of the molecular chain and without obvious crystallization can be obtained. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2044–2048, 2000     

Influence of the longest ethylene and isotactic propylene sequences on crystallization elution fractionation of ethylene/propylene copolymers

Crystallization elution fractionation (CEF) is the newest crystallization-based technique for estimating the chemical composition distribution of ethylene/1-olefin copolymers. Understanding the separation mechanism of CEF for ethylene/propylene copolymers over their full compositional range is challenging because the crystallizabilities of the copolymer chains depend on the longest ethylene sequence and on longest isotactic propylene sequence. We developed a mathematical model to describe the CEF mechanism for ethylene/propylene copolymers over the entire compositional range using population balances for the crystallization and dissolution stages. The joint distribution of longest ethylene and isotactic propylene sequences determines how the copolymer populations crystallize and dissolve. The model was validated with experimental CEF profiles of ethylene/propylene copolymers varying from pure ethylene to propylene homopolymers.     

Phase behaviour in poly(ethylene oxide-b-t-butyl methacrylate) block copolymers

The lamellar thickness of the poly(ethylene oxide)-poly(t-butyl methacrylate) (PEO-PTBMA) diblock copolymer system, obtained by differential scanning calorimetry and small angle X-ray scattering investigations, is correlated with the degree of polymerization of the amorphous (PTBMA) and crystallizable (PEO) sequences. The non-equilibrium exponents obtained immediately after bulk crystallization are different to those from extrapolated equilibrium results. Within the experimental standard deviations, the theoretical predictions of DiMarzio et al. and of Whitmore and Noolandi could be confirmed. The molecular weights of PEO and PTBMA ranged from 250 to 21000 g mol⁻¹ and from 1500 to 17000 g mol⁻¹, respectively. Both the equilibrium lamellar thickness l and the PEO domain size d_PEO increase with increasing PEO and decreasing PTBMA degrees of polymerization Z according to d_PEO l Z^0.97±0.08_EOZ^{−(0.53±0.19)}_TBMA.     

The polydispersity of ethylene sequence in metallocene ethylene/α-olefin copolymers III: crystallization and melting behavior of short ethylene sequence

Crystallization and melting behavior of short ethylene sequence of metallocene ethylene/α-olefin copolymer with high comonomer content have been studied by standard DSC and modulated-temperature differential scanning calorimetry (M-TDSC) technique. In addition to high temperature endotherm around 120°C, a low temperature endotherm is observed at lower temperatures (40-80°C), depending on time and temperature of isothermal crystallization. The peak position of the low temperature endotherm T_m^low varies linearly with the logarithm of crystallization time and the slope, D, decreases with increasing crystallization temperature T_c. The T_m^low also depends on the thermal history before the crystallization at T_c, and an extrapolation of T_m^low (30.6°C) to a few seconds has been obtained after two step isothermal crystallization before the crystallization at 30°C. The T_m^low is nearly equal to T_c, and it indicates that the initial crystallization at low temperature is nearly reversible. Direct evidence of conformational entropy change of secondary crystallization has been obtained by using M-TDSC technique. Both the M-TDSC result and the activation energy analysis of temperature dependence suggest that crystal perfection process and conformational entropy decreasing in residual amorphous co-exist during secondary crystallization.     

Crystallinity and amorphous segmental properties in random propylene–ethylene copolymers: NMR correlation

We present a characterization of the state of semi-crystallization of random propylene–ethylene copolymers, observing the transverse relaxation of protons attached to the chains. The degree of crystallinity was determined step by step, from NMR, during the progressive annealing of the copolymers, quenched at room temperature from the melt. The ethylene content varied over the range 0–4.7 (w/w). It is shown that the empirical temperature dependence of the degree of crystallinity, as detected by NMR, obeys a single curve; this curve is translated along the temperature axis in accordance with the melting point depression when the ethylene content varies. The degree of crystallinity is primarily a function of the undercooling, whatever the ethylene content. Considering any state of semi-crystallization, a strong correlation between the degree of crystallinity and the relaxation rate of the protons attached to amorphous segments is established; the NMR sensitivity to crystallinity is considerably enhanced when detected by amorphous properties. © 1999 Society of Chemical Industry     

丙烯/1-丁烯无规共聚物与丙烯/乙烯抗冲共聚物的对比研究

对丙烯/1-丁烯无规共聚物(PPB)与丙烯/乙烯抗冲共聚物(PPE)的结晶行为进行对比,在等温结晶时,通过相对结晶度随时间的变化关系、等温结晶曲线等研究,表明丙烯/1-丁烯无规共聚物结晶速率明显低于丙烯/乙烯抗冲共聚物,同时丙烯/乙烯抗冲共聚物的等温结晶速率随乙烯单元含量增加没有明显降低。根据Avrami方程计算了共聚物的结晶活化能,证明丙烯/1-丁烯无规共聚物的结晶能力较丙烯/乙烯抗冲共聚物低。扫描电镜分析丙烯/1-丁烯无规共聚物在丁烯单元摩尔分数2.39%时没有韧性拉伸,而丙烯/乙烯抗冲共聚物在乙烯单元摩尔分数3%时出现韧性拉伸。     

Multiple melting behaviour of poly(ethylene terephthalate)

Differential scanning calorimetry (DSC) and temperature modulated DSC (MTDSC) have been used to investigate the melting behaviour of poly(ethylene terephthalate) (PET). Multiple melting endotherms were observed even at high heating rates, e.g. 160 K min⁻¹ and these have been attributed to the presence of two different distributions of lamella thickness and re-crystallisation (reorganisation) on heating. This has been confirmed by MTDSC—the presence of endotherms and an exotherm in the reversing component of the heat flow during heating. Examination of the endotherms of samples heating stepwise indicated that further crystallisation took place above the isothermal crystallisation temperature (T_c). Some part of this was associated with lamella thickening and crystal perfecting. The multiple melting endotherms observed are a consequence of the balance between the melting and re-crystallisation and the lamella thickness distribution existing within the sample, prior to heating. The triple melting endotherms observed are attributed to the melting of secondary and primary lamellae produced on crystallisation and to thickened lamellae produced during heating to the melting point.     

Microstructure of Ethylene/Propylene Random Copolymers Prepared by a Fluorinated Bis(phenoxy-imine)Ti Catalyst

Summary Living copolymerization of ethylene and propylene was catalyzed by a fluorine-containing bis(phenoxy-imine) titanium catalyst. A series of ethylene-propylene copolymers with different propylene contents were prepared and the copolymers were characterized by ¹³C-NMR, GPC and DSC. The copolymers were found to have the following characteristics: (1) Molecular weight distribution of the copolymer is rather narrow; (2) There exist only isolated propylene units distributed along the polymer chains even at propylene content as high as 14.9 mol%; (3) The distribution of ethylene sequence are not homogeneous. Insertion of propylene changes from 2,1-insertion in homopolymerization into 1,2-insertion when the preceding unit is ethylene.     

Copolymerization of ethylene and 1-octene by homogeneous and different supported metallocenic catalysts

In this work, the performance of the homogeneous catalyst system based on Et(Flu)₂ZrCl₂/MAO was evaluated on the copolymerization of ethylene and 1-octene. Characteristics of some of the produced polymers were also investigated. A study was performed to compare this system with that of Cp₂ZrCl₂/MAO. The influence of different support materials for the Cp₂ZrCl₂ was also evaluated, using silica, MgCl₂, and the zeolite sodic mordenite NaM. An increase in activity was observed in relation to the comonomer addition for the two homogeneous catalysts. The copolymers produced by the Et(Flu)₂ZrCl₂/MAO system showed higher molecular weight and narrower molecular weight distribution. We verified that the catalyst supported on SiO₂ was the most active one, although the copolymers produced with the catalyst supported on NaM showed higher molecular weight and lower molecular weight distribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 724–730, 2001     

Crystallization of the γ form in random propylene‐ethylene copolymers

Wide‐angle X‐ray scattering and differential scanning calorimetry measurements have been conducted on seven random copolymers of propylene with ethylene in order to study the γ phase formation as a function of the comonomer content. The lamellar morphology of the samples was also investigated by small‐angle X‐ray scattering. The content of the γ phase was found to go through a maximum with crystallization temperature and to increase with comonomer concentration, up to a point (ethylene ≥6.5 wt%) where the latter parameter became less influential. The multiple melting endotherms behaviour of the samples was studied by DSC and temperature‐controlled diffractometric techniques. The attribution of the DSC peaks to the different isotactic polypropylene polymorphs that form in these conditions was confirmed. The results obtained permitted us to ascertain that, in the experimental conditions chosen, some further formation of crystallites takes place during the quenching to room temperature after the crystallization isotherm. In this phase, the chains organize themselves in stacks with thin lamellae, forming a distinct population with respect to those formed on isothermal crystallization. The melting of the thinner lamellae determines a convergence of the two populations into just one, still retaining an organization in stacks, that gradually disappears until complete melting of the material. Copyright © 2004 Society of Chemical Industry     

Effect of irradiation on mechanical and structural properties of ethylene vinyl acetate copolymers hollow fibers

Effect of irradiation on mechanical and structural properties of ethylene vinyl acetate copolymers (EVA) hollow fibers was studied by the tests such as determination of gel content, density, tensile, FTIR, SEM, and DMA. These effects were discussed based on dose and irradiation environment. The results of gel content depicted that irradiated EVA in ambient conditions had tendency to chain scission while the crosslinking overcame in irradiated samples under nitrogen. Density insignificantly enhanced with irradiation dose. In tensile test, irradiation induced increase in tensile strength and decrease in elongation at break (especially in samples irradiated in nitrogen). Also, changing in layer orientation could be observed by SEM images. In addition, irradiation caused altering peak intensity in FTIR spectrum. DMA results demonstrated that irradiation broaden the elastic zone. Totally, irradiation enhances features especially in irradiated EVA18 in nitrogen. Since, according to stabilization of induced deformation and improvement of mechanical properties (that created by radiation), the irradiated samples can be used in different applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structural evaluation of copolymers of ethylene and 1‐octadecene by using the temperature rising elution fractionation technique

Three samples of ethylene‐octadecene copolymers having different quantitative composition were analyzed structurally and in terms of their thermal behavior. The samples were fractionated by temperature rising elution fractionation, presenting different chemical composition distributions (CCD) that are essentially the result of the proportion of incorporated octadecene. The CCD profiles were relatively wide for samples generated by metallocene catalysts. The analyses of the fractions showed that the melting and crystallization temperatures decrease with increasing comonomer incorporation, but this relation is affected by the average molecular weight of the chains. The melting thermograms of those fractions having higher proportions of octadecene may be divided into two characteristic regions: the first one, at a higher temperature, originates from the melting of the least modified chains, which crystallize more perfectly. The second one is formed by the melting of chains having a high degree of comonomer incorporation, which melt in a diffuse manner over a wide range of temperatures. It is probable that the morphology of the crystals formed in this region does not follow the folded chain model, and are better represented by a model involving the alignment of chain segments (bundling). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 221–227, 2001     

Antimicrobial‐releasing films and coatings for food packaging based on carvacrol and ethylene copolymers

Efficiency in antimicrobial packages based on the release of active agents depends on their retention into the packaging materials and on the extent and rate of their release to the package headspace. In this work, the effects of polymer chemical composition and matrix morphology on the release of carvacrol were explored. Films and coatings containing carvacrol, and manufactured from four polyolefin latexes of a range of polarities (ethylene–octene (LLDPE) < ethylene–vinyl acetate (EVA) < < ethylene–methacrylic acid (EMA) ≈ ethylene–alkaline methacrylate (ION)), were characterized in terms of their active and functional properties. Scanning electron microscopy images evidenced that films presented heterogeneous structures caused by an incomplete coalescence of their polymeric particles. Consequently, different film structures of decreasing heterogeneity, porosity and roughness (LLDPE > EVA > > ION > EMA) were obtained, exhibiting morphologies generally correlated with the melting temperatures and active behaviours of the polymers. LLDPE and EVA, the most heterogeneous polymers, were generally more permeable, less resistant, more deformable, less transparent and more wettable than EMA and ION, of coalesced structure. For carvacrol, LLDPE and EVA yielded higher values of the diffusion coefficient, in agreement with their permeability results, whereas EMA and ION showed higher solubilities, according to their greater affinity for the active molecule, as derived from their ionic nature. The evolution of the release of carvacrol from the studied films was experimentally measured and theoretically predicted through determination of its solubility and diffusivity parameters. Excellent agreement between both experimental and predicted data was finally observed. © 2015 Society of Chemical Industry     

Biodegradability of poly(ethylene terephthalate) copolymers with poly(ethylene glycol)s and poly(tetramethylene glycol)

Poly(ethylene terephthalate) copolymers were prepared by melt polycondensation of dimethyl terephthalate and excess ethylene glycol with 10–40mol% (in feed) of poly(ethylene glycol) (E) and poly(tetramethylene glycol) (B), with molecular weight (MW) of E and B 200–7500 and 1000, respectively. The reduced specific viscosity of copolymers increased with increasing MW and content of polyglycol comonomer. The temperature of melting (T_m), cold crystallization and glass transition (T_g) decreased with the copolymerization. T_m depression of copolymers suggested that the E series copolymers are the block type at higher content of the comonomer. T_g was decreased below room temperature by the copolymerization, which affected the crystallinity and the density of copolymer films. Water absorption increased with increasing content of comonomer, and the increase was much higher for E1000 series films than B1000 series films. The biodegradability was estimated by weight loss of copolymer films in buffer solution with and without a lipase at 37°C. The weight loss was enhanced a little by the presence of a lipase, and increased abruptly at higher comonomer content, which was correlated to the water absorption and the concentration of ester linkages between PET and PEG segments. The weight loss of B series films was much lower than that of E series films. The abrupt increase of the weight loss by alkaline hydrolysis is almost consistent with that by biodegradation.     

Effect of dialcohols on properties of poly(ethylene 2,6‐naphthalate) copolymers

Properties of poly(ethylene 2,6‐naphthalate) (PEN) and its copolymers containing diethylene glycol (DEG), propanediol (PD), butanediol (BD), and bisphenol A ethoxylate (BSA) were investigated. The copolymer composition was determined by ¹H‐NMR spectroscopy. It has a higher value than the feed composition due to the high volatility of ethylene glycol (EG). The melting temperature of the copolymers was gradually depressed with the increase of dialcohol in the composition. The complex viscosity of the copolymers did not depend on the molecular weight, but on the chemical structure. The complex viscosity of the copolymers containing 3 mol % of DEG, BD, and 5 mol % of BD was lower than that of PEN, and the mechanical properties were similar with the value of PEN. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2900–2905, 1999     

傅立叶变换红外光谱法快速测定乙丙共聚物中的乙烯含量

研究了用傅立叶变换红外光谱法测定乙丙共聚物中乙烯含量的方法。建立了傅立叶红外光谱法快速测定乙丙共聚物中乙烯含量的标准工作曲线,对其准确性和精密度进行了评价。结果表明,测定样品的最大相对误差为2.82%,重复测定同一样片的相对标准偏差为0.48%,方法的准确性和精密度良好。该方法适用于乙烯质量分数为0%~33%的乙丙无规共聚物和嵌段共聚物的测定,并且已在生产中得到很好的应用。     

金属茂均相催化剂用于乙烯聚合的研究

研究金属茂均相催化剂中过渡金属的性质对乙烯聚合的影响。以丁烯基取代的二茂二氯化锆（ＣｐＢｕ）２ＺｒＣｌ２和丁烯基取代的二茂二氯化锆（ＣｐＢｕ）２ＨｆＣｌ２与甲基铝氧烷组成的均相催化剂体系，对乙烯聚合进行了较详细的比较研究。