Mechanical relaxation in polypropylene as a function of polymorphism and degree of lamella orientation

Mechanical relaxation data as a function of temperature (ca. 1 Hz) have been obtained for several samples of isotactic polypropylene crystallized from the melt, which exhibit both α and β forms as well as varying degrees of lamella orientation. The samples ranged in morphology from an unoriented sample showing only the α form to one highly oriented having approximately 90 per cent the β form. Results for the logarithmic decrement Δ and loss modulus G″ are that the low temperature (ca. ?75°C) and glass temperature (ca. 0°C) relaxations show little or no sensitivity to orientation in the α form, but that the intensity of the two processes is different in the α form than in the β form for samples of nearly equal overall per cent crystallinity. In both Δ and G″, the low-temperature peak decreased and the glass temperature peak increased in intensity as the fraction of β form crystallinity present increased. Data for the high-temperature relaxation (ca. 80°C) indicate a dependence upon orientation and/or crystal form in addition to a dependence upon per cent crystallinity.     

茂金属催化聚合的聚1-丁烯的结构表征

以 η5 五甲基茂基三苄氧基钛 (Cp Ti(OBz) 3 和改性甲基铝氧烷 (mMAO)为催化剂 ,合成立体嵌段聚 1 丁烯 ,分子量高 ,分子量分布窄 ( Mw/ Mn=1 1～ 1 2 ) .聚合产物经沸乙醚、沸庚烷连续抽提分离 ,聚合物在两种溶剂中都能部分溶解 .各级份经13C NMR ,WAXD ,DSC和GPC等手段分析 ,结果表明乙醚可溶级份是无规聚 1 丁烯 ,庚烷可溶级份是立体嵌段聚 1 丁烯 ,庚烷不溶级份是等规聚 1 丁烯 .聚合温度较低 (0℃和30℃ )时 ,聚合物有结晶性 ,结晶度达 30 %以上 ,DSC分析有两个吸热峰 ;聚合温度较高 (4 0℃ )时 ,聚合物无结晶尖锐X射线衍射峰 ,也无熔融吸热峰 .     

聚氯乙烯/纳米水滑石复合材料的形态与力学性能

对由原位悬浮聚合制备的聚氯乙烯(PVC)纳米水滑石复合树脂加工得到的纳米复合材料的形态和力学性能进行了研究,并与直接熔融加工得到的PVC纳米水滑石复合材料进行比较.发现由前一方法得到的PVC纳米水滑石复合材料中纳米水滑石的分散性明显优于由后一方法得到的PVC纳米水滑石复合材料,水滑石以初级粒子形式存在,分散良好,无明显团聚体;与之对应,由前一方法得到的PVC纳米水滑石复合材料的力学性能也明显优于由后一方法得到的PVC纳米水滑石复合材料,当纳米水滑石含量小于5wt%时,复合材料的杨氏摸量、拉伸强度和缺口冲击强度均随水滑石含量增加而增大;纳米水滑石的引入可显著提高复合树脂的热稳定性;PVC纳米水滑石复合材料的储能和损耗模量略大于纯PVC材料,而损耗因子和玻璃化温度变化不大.     

Relationship of deformation behavior to thermal transitions of ethylene/styrene and ethylene/octene copolymers

The stress‐strain response of low‐crystallinity ethylene‐octene (EO) and ethylene‐styrene (ES) copolymers with 7–20 mol % comonomer was compared over a temperature range that spanned the glass‐transition and crystal melting regions. Above the onset temperature of the glass transition, the copolymers exhibited elastomeric behavior with low initial modulus, uniform deformation to high strains, and high recovery after the stress was released. In the glass‐transition range, an initial low‐stress elastomeric response was followed by a distinct “bump” in the stress‐strain curve. On the basis of the temperature and rate dependence of the stress‐strain curve, local strain‐rate measurements, local temperature changes, and recovery characteristics, the “bump” was identified as high strain yielding. Hence, the stress‐strain curve sequentially exhibited the features of elastomeric and plastic deformation. Following high strain yielding, strain hardening dramatically increased the fracture strength. This behavior was defined as elastomeric‐plastic. Elastomeric‐plastic behavior in the broad glass‐transition range constituted a gradual transition from elastomeric behavior at higher temperatures to low‐temperature plastic behavior with high modulus and macroscopic necking. Because of the lower glass‐transition temperature of EO, ?40 °C as compared with ?10 °C for ES, the onset of elastomeric‐plastic behavior occurred at a significantly lower temperature. The concept of a network of flexible chains with fringed micellar crystals serving as the multifunctional junctions that provides the structural basis for elastomeric behavior of low‐crystallinity ethylene copolymers was extended to elastomeric‐plastic behavior by considering a network with a fraction of rigid, glassy chains. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 142–152, 2002     

Photo-induced graft copolymerization of methyl methacrylate on cellulose

Graft copolymerization initiated by ultraviolet light irradiation at 40°C in a hard glass vessel under nitrogen was examined. The graft copolymerization was observed to occur easily after some induction period without any use of photosensitizer, though it was found the per cent grafting and the grafting efficiency were markedly affected by the quantities of cellulose and monomer. In the system without cellulose, homopolymerization of methyl methacrylate hardly took place, but the use of cellulose caused the formation of homopolymer too, and a grafting efficiency in the range of 60–80% generally resulted. Ferric chloride or sodium anthraquinone-2,7-disulfonate (AQ) acted on the polymerization reaction as photosensitizers to reduce its induction period. Though ferric chloride acted to develop both the per cent grafting and the number of grafts, not the same effects were observed with AQ. Oxalic acid, which was employed with the object of eliminating very small amount of metals contained in cellulose, was found to act favorably in the formation of grafts, much like ferric chloride.     

Amorphous fraction controlled mechanical and optical properties of polylactic acid below glass transition temperature

A negative relation between strength and crystallinity is observed in polylactic acid below glass transition temperature. Study indicates that entangled molecules in amorphous regions act as load bearing structures and are responsible for stress induced crazing. A three-phase model is proposed to explain how amorphous fraction changes with heat treatments and contributes to polymer modulus below glass transition temperature. Incorporation of carbon quantum dots into amorphous fraction dominated PLA creates a new type of luminescent composites that can be used for food labelling, tracking, packaging and production of origin.     

尼龙6与半芳香性非晶尼龙原位共混物的结构与性能

一种半芳香的非晶尼龙共聚物溶解于熔融的己内酰胺中,引发后者负离子开环聚合原位制备尼龙6与非晶尼龙的共混物.与纯尼龙6相比较,此原位共混物的强度与模量显著提高.非晶区呈现单一的玻璃化转变,表明共混物为均相体系,其组分的相容性源于负离子聚合过程中链交换反应引起的共聚.与纯尼龙6相比较,此共混物的熔点与结晶度显著降低.此外,与纯尼龙6只存在α晶不同,共混物中伴生有大量的γ晶.当非晶尼龙含量为20 wt%时,绝大部分晶体为γ晶.然而,共混物中球晶仅有一定程度细化.共混物强度和模量的提高被认为主要源于非晶区分子活动能力降低以及γ晶相对含量的提高.     

Triblock copolymers of lactide with poly(ethylene glycol) and influence of stereochemical composition

Polymerization of L-lactide (LLA) and poly(ethylene glycol) (PEG) at 120°C using stannous 2-ethyl hexanoate results in ABA triblock copolymers in good yields. The glass transition temperature of the copolymers shows strong dependence on the composition. One- and two-phase triblock copolymers can be prepared by controlling the molecular weight of the PEG soft block, as well as the initial LLA/PEG charge ratio. Incorporation of racemic lactide during polymerization drastically affects the crystallinity of the block copolymers obtained. ¹H and ¹³C (solid state) NMR are powerful tools for characterization of the polymer materials.     

Photoinitiated polymerization of methacrylates comprising phenyl moieties

Investigation of photopolymerization kinetics of 4-(4-methacryloyloxyphenyl)-butan-2-one (1) in comparison with 2-phenoxyethyl methacrylate (2) and phenyl methacrylate (3) using a UV-LED emitting at 395 nm shows significantly faster polymerization of 1 compared to both 2 and 3 at 40°C. Vitrification affects photopolymerization kinetics of all methacrylates under investigation. Interestingly, quantitative final conversion is observed during photoinitiated polymerization of 1 and 2 whereas 3 shows limited conversion at about 80%. Furthermore, higher degree of polymerization is obtained by photoinitiated polymerization of 1 compared to 2 and 3. This shows that the 3-oxobutyl substituent at the phenyl ring of 1 significantly affects both polymerization kinetics and final conversion of the photoinitiated polymerization. Moreover, an additional higher molecular weight fraction is observed in case of polymerization of 1 at 85°C that is above the glass transition temperature of the polymer formed during photoinitiated polymerization. As a thermal polymerization at 85°C in the absence of light results in a high molecular weight polymer as well, an additional thermal process may be discussed as reason for the higher molecular weight polymer fraction in case of the photopolymer made at 85°C.     

Effect of temperature and solvents on stereospecific polymerization of vinyl alkyl ethers catalyzed by aluminum sulfate–sulfuric acid complex

The effect of polymerization temperature and solvents was determined on the crystallinity of polymers of vinyl isobutyl ether and of vinyl n-butyl ether prepared with aluminum sulfate–sulfuric acid complex catalyst. Principally, the methyl ethyl ketone (MEK)-insoluble fractions of these polymers were used for characterization. Density, per cent crystallinity by x-ray diffraction, infrared ratio, and dilatometric volume contraction of these polymer fractions were used as criteria of crystallinity. The MEK-insoluble fractions of poly(vinyl n-butyl ethers) prepared in carbon disulfide in the temperature range of ?30 to +25°C did not show any significant difference in the values of the above crystallinity parameters. The polymer obtained at 50°C. was less crystalline than the rest of the polymers. The MEK-insoluble fractions of poly(vinyl isobutyl ethers) prepared at 0–50°C. in carbon disulfide and n-heptane solvents also did not significantly differ in their degree of crystallinity. They were, however, decidedly less crystalline than the MEK-insoluble fractions of the corresponding polymers obtained at ?20°C. These data a indicate that on increasing the temperature of polymerization the crystallinity of the polymers was either unchanged or decreased slightly. The polymerizations of vinyl n-butyl ether and vinyl isobutyl ethers were also carried out in binary mixtures of carbon disulfide with n-heptane, chlorobenzene, and MEK. Generally, increasing the concentration of carbon disulfide increased the inherent viscosities of polymers as well as the weight percentage of their MEK-insoluble fractions. The MEK-insoluble fraction of poly(vinyl isobutyl ether) prepared in carbon disulfide-MEK mixture (volume ratio 2:1) was isotactic and highly crystalline. Likewise, the MEK-insoluble fractions of two polymers of vinyl n-butyl ether prepared in MEK itself were also isotactic and highly crystalline. Compared to poly(tetramethylene oxide), these latter fractions exhibited less dependence of rate of crystallization upon temperature. Consequently, at low degrees of supercooling they crystallize much more rapidly than does poly(tetramethylene oxide).     

Study of a plasticized‐unoriented P(VF2/VF3) (73/27 mol%) copolymer. I. The effects of crystallization conditions on morphology,physical, and thermal properties

The results of a study on the effects of a plasticizer, tricresyl phosphate, on the mechanical and thermal properties of unoriented films of poly(vinylidene fluoride–trifluoroethylene) (VF₂/VF₃) copolymer (73/27 mol%) are presented. Films were prepared by both quenching and slow‐cooling from the melt with plasticizer concentrations of 0, 5, and 10% by weight. For the slow‐cooled films, a reduction in crystallinity by 25% was observed for the heavily plasticized films, together with a reduced dynamic mechanical modulus (≈ 58%) and an increased dielectric constant (≈ 200%). For the quenched films, a small increase in crystallinity was observed together with a reduced modulus and an increased dielectric constant. Measurements of the temperature dependence of the modulus and dielectric constant at 10 Hz. were also carried out from −100°C to 100°C. This data showed that for slow‐cooled films the glass transition temperature decreased from −28°C to ‐52°C at the highest doping level. DSC thermal analysis shows a decrease in the Curie transition (≈ 4°C) and melting temperatures (≈ 9°C) for the quenched films, while the slow‐cooled films only showed a decrease in melting temperature (≈ 10°C), while the Curie transition temperature was unaffected. In addition, evidence of a two‐phase system or a nonferroelectric crystal phase is noted by the presence of two Curie transition temperature peaks. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 19–28, 1999     

Blends of poly(methyl methacrylate) (PMMA) with PMMA ionomers: Mechanical properties

Rigid–rigid blends made of ionomer and ionomer precursor polymer, based on poly(methyl methacrylate) (PMMA), have been investigated. Two series of blends have been prepared for studying mechanical properties. In one series, dynamic mechanical properties were determined over a wide range of temperatures. As the weight fraction of the ionomer was increased, there was a modest increase of modulus at ambient temperature and a very large increase in the rubbery modulus at elevated temperatures above the glass transition temperature of PMMA. In a second series of tests, tensile stress–strain measurements, made at an ambient temperature, were carried out over a wide range of blend compositions. For all blends tested, the mechanical properties exhibited a synergistic enhancement, i.e., average values of modulus, strength and fracture energy were all higher than expected based on the rule of mixtures. Measurements of fracture toughness also exhibited synergy, with a maximum value, higher than the value of either blend component, being attained in blends containing about 30 wt % of the PMMA ionomer. These results are interpreted in terms of a higher resistance to fracture of the more chain-entangled ionomer phase and good interfacial adhesion between the two components of the blend. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1235–1245, 1998     

Structure of polymers formed by anionic polymerization of adipimide

Products obtained by anionic polymerization of adipimide contain foreign structures derived from 6-oxo-1,11-undecanedioic acid, as a result of base catalysed condensation. The decrease in adipimide units, however, is much greater than corresponds to the number of oxodicarboxylic acid units so that there must be additional reactions consuming adipimide units. At short polymerization periods, the polymers are mostly crosslinked; the fraction of insoluble polymer decreases with increasing temperature and time of polymerization. Even at low polymerization temperatures, the content of adipimide monomer units in the polymers is below 90 per cent. Therefore, the polymerization products have to be considered as copolymers rather than as homopolymers.     

聚合温度对聚氯乙烯树脂结构和性能的影响

采用凝胶渗透色谱法、¹³H NMR和DSC法测定了悬浮聚合PVC树脂的平均分子量、间规度、结晶度和玻璃化温度.结果表明:聚合温度下降,PVC的平均分子量上升,分子量的对数值与聚合温度的倒数成正比;PVC的间规度和结晶度均增大,在形成结晶的间规链段的最短长度(ξ_min)为6时,由间规度计算的结晶度理论值与测定值接近;分子量和结晶度增加的共同作用,使PVC的玻璃化转变温度上升.     

Investigation of the Evolution Behavior of Light Tar During Bituminous Coal Pyrolysis in a Fluidized Bed Reactor

The evolution behavior of the light tar fraction of tar during large bituminous coal particle pyrolysis in a fluidized bed reactor at 500-900℃ was investigated to optimize the industrial process. The coal residence time was varied from 30 s to 150 s. The crude tar obtained was distilled and separated into the light fraction and the heavy fraction through an evaporator under conditions of 280℃ and 10⁴ Pa. The light tar was subjected to GC-MS analysis, and the 300 main species in each spectrum were determined and analyzed. The experimental results showed that the evolution behavior of the light tar fraction and the heavy tar fraction presented spectacularly different variation trends with pyrolysis temperature and coal residence time. The molecular weight and number of rings per aromatic compound molecule contained in the light tar fraction increased with increasing pyrolysis temperature because of polymerization. It was also observed that the amount of methyl substituents decreased with an increasing number of rings per molecule of poly-aromatic ring compounds. The chain aliphatic compound evolution was suppressed and underwent heterocyclization with increasing temperature.     

聚ε-己内酯的微米硅球固定化猪胰脂肪酶促合成

本文采用微米硅球固定化猪胰脂肪酶为催化剂合成聚ε-己内酯, 以期获得具有较高分子量、 良好生物相容性和使用安全性的生物可降解医用高分子材料.     

Optical activity in CE6 A new metastable blue phase?

The optical rotation of a mixture of 60 per cent of chiral and 40 per cent of racemic CE6 as an 18 μm thick sample placed between glass plates treated with PI has been measured. This mixture exhibits one blue phase (BP1) on heating over a temperature range of about 0·1°C. On cooling the sample on the other hand, the BP region is expanded to 0·6°C and is divided into two regions. One region (BP1) (of range about 0·38°C below the isotropic-blue phase transition) shows two Bragg wavelengths which increase with decreasing temperature. For the second region (BPS) (of range about 0·22°C above the cholesteric-blue phase transition), one Bragg wavelength decreases with decreasing temperature, and a third Bragg wavelength appears. At constant temperature both phases remained stable for a period of several days.     

PC/PET/EPDM共混体系的结晶与熔融行为

本文用解偏振光法与DSC法分别测定并研究了PC/PET/EPDM共混体系的结晶速度、结晶度、Avrami指数(n)和熔融温度及其影响因素,共混物中PET的结晶速度、结晶度均随PC含量增加而下降;EPDM用量不超过10%时,可提高PET的结晶速度,但不影响结晶度和成核与增长方式,n值不变。当EPDM为5%时,结晶速度呈现极大值。经退火处理的共混物呈现熔融双峰,PC量增加,高温熔融峰略移向高温方向;热处理温度升高或时间延长,则低温熔融峰移向高温方向。     

新型光、 热双响应形状记忆聚合物的制备与性能

通过多巴胺表面原位聚合反应修饰玻璃微珠, 利用X光电子能谱仪(XPS)和傅里叶变换红外光谱仪 (FTIR)对修饰前后玻璃微珠表面的化学组成进行了表征, 用热失重分析仪(TGA)对其热稳定性进行了测试, 并利用透射电子显微镜(TEM)和扫描电子显微镜(SEM)对其形貌进行了观察; 研究了改性玻璃微珠对形状记忆共混物聚己内酯和聚氨酯(PCL/TPU)的热性能、 力学性能和形状记忆性能的影响. 结果表明, 成功制备了表面包覆聚多巴胺的玻璃微珠(PHGM), 改性玻璃微珠的加入不仅增强了复合材料的力学性能(当改性玻璃微珠含量为3%时, 材料的拉伸强度提高到53.3 MPa, 杨氏模量提高到178.4 MPa), 还赋予了复合材料优异的光热效应. 所制备的形状记忆复合材料在808 nm近红外光的照射下, 可以在短时间内(7 s)升高到材料的开关温度并回复到初始形状.     

Stereochemistry of photoinitiated emulsion polymerization

The tacticity of poly(methyl methacrylate) (PMMA) samples made by emulsion polymerization (EP) has been determined by NMR spectroscopy at higher resolution than any previous study. When photoinitiation is employed at room temperature, the polymer obtained is highly syndiotactic and more stereoregular than that obtained in homogeneous radical polymerization under the same conditions. The percentage of racemic dyads and the length of racemic sequences vary significantly with the degree of conversion and the temperature, but not with variation of the hydrophobic or the hydrophilic part of the detergent molecules. A magnetic field of 5 kG or less accelerates the polymerization reaction and increases the polymer molecular weight when dibenzyl ketone is employed as oil-soluble photoinitiator, and has an indirect influence on the polymer tacticity. From measurements of the temperature dependence of the polymer steric composition, the difference of activation enthalphy and entropy of the meso and racemic additions have been calculated. The values do not follow the correlations from precedent literature for radical polymerization in solution if the reaction is considered a first-order Markov process. The persistence ratio p depends on the detergent and the temperature of the EP; in some cases its difference from unity exceeds the experimental error. These results are interpreted as a conformational effect of the locus of the polymerization in the first stage of the EP (when micelles are present) that favors the racemic addition more than is expected in a homologous solvent such as an alkane, e.g., at the same temperature.