氯化聚丙烯甲苯溶液的特性黏数及其黏均分子量

分别用乌氏黏度计和旋转黏度计测定了氯化聚丙烯甲苯溶液的特性黏数和黏度,把特性黏数和黏度进行关联,发现ηsp/C与浓度C(ml/g)的关系用多项式ηsp/C=[η]+k1[η]2C+k2[η]2C2拟合,可以得到很好的结果。并且用特性黏数和Mark-Houwink方程求出了不同氯化聚丙烯(CPP)的黏均分子量。     

Lower critical solution temperatures of thermo‐responsive poly(N‐isopropylacrylamide) copolymers with racemate or single enantiomer groups

BACKGROUND: Thermo‐responsive copolymers with racemate or single enantiomer groups are attracting increasing attention due to their fascinating functional properties and potential applications. However, there is a lack of systematic information about the lower critical solution temperature (LCST) of poly(N‐isopropylacrylamide)‐based thermo‐responsive chiral recognition systems. In this study, a series of thermo‐responsive chiral recognition copolymers, poly[(N‐isopropylacrylamide)‐co‐(N‐(S)‐sec‐butylacrylamide)] (PN‐S‐B) and poly[(N‐isopropylacrylamide)‐co‐(N‐(R,S)‐sec‐butylacrylamide)] (PN‐R,S‐B), with different molar compositions, were prepared. The effects of heating and cooling processes, optical activity and amount of chiral recognition groups in the copolymers on the LCSTs of the prepared copolymers were systematically studied. RESULTS: LCST hysteresis phenomena are found in the phase transition processes of PN‐S‐B and PN‐R,S‐B copolymers in a heating and cooling cycle. The LCSTs of PN‐S‐B and PN‐R,S‐B during the heating process are higher than those during the cooling process. With similar molar ratios of N‐isopropylacrylamide groups in the copolymers, the LCST of the copolymer containing a single enantiomer (PN‐S‐B) is lower than that of the copolymer containing racemate (PN‐R,S‐B) due to the steric structural difference. The LCSTs of PN‐R,S‐B copolymers are in inverse proportion to the molar contents of the hydrophobic R,S‐B moieties in these copolymers. CONCLUSION: The results provide valuable guidance for designing and fabricating thermo‐responsive chiral recognition systems with desired LCSTs. Copyright © 2008 Society of Chemical Industry     

Surface‐initiated atom transfer radical polymerization of regenerated cellulose membranes with thermo‐responsive properties

Using atom transfer radical polymerization (ATRP), thermo‐responsive regenerated cellulose membranes were synthesized. Regenerated cellulose membranes were firstly modified by reacting the hydroxyl groups on the surface with 2‐bromoisobutyryl bromide, followed by grafting with poly(N‐isopropylacrylamide). The membranes had obvious thermally modulated permeability properties. Analysis was carried out by means of X‐ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The results showed that N‐isopropylacrylamide had been grafted successfully on the surface of the regenerated cellulose membranes. The thermally modulated permeability properties of the grafted membranes were studied using water flux measurements. It was found that the thermally modulated permeability properties of a cellulose surface can be tailored by the use of the ATRP method. Copyright © 2010 Society of Chemical Industry     

Preparation of copolymer of L‐aspartic acid and L‐glutamic acid

In this article, a new copolymer of L ‐aspartic acid and L ‐glutamic acid, which may be a biodegradable high molecular polymer and can be used more widely in many areas, was synthesized. The conditions of preparation, such as catalyst, reaction time, reaction temperature, the amount of catalyst, the times of adding catalyst, and the molar ratio of L ‐aspartic acid to L ‐glutamic acid, were optimized. The copolymer was characterized by ¹³C NMR, infrared spectroscopy, and X‐ray diffractometer. The molecular weight was determined by GPC. The result indicated that production yield, purity of product, and molecular weight of product increased with amount of catalyst and molar ratio of L ‐aspartic acid to L ‐glutamic acid increasing. The best condition of preparation was the following: reacting 2–4 h at the temperature of 180–200°C. The product yield with the molecular weight 13,000.00 reached 63.2% and the purity of product was 96.33% when the copolymerization was carried out at the temperature of 200°C under vacuum for 2 h. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3626–3633, 2006     

Broadening of molecular‐weight distribution in solid‐state polymerization resulting from condensate diffusion

A kinetic model for the solid‐state polymerization of poly(bisphenol A carbonate) in a single particle has been developed and used to investigate the broadening of molecular‐weight distribution as a result of slow condensate diffusion. The model is based on melt‐phase transesterification kinetics and Fickian diffusion of phenol, the condensate, in the amorphous regions of the semicrystalline particle. Model predictions compare favorably to experimental data. When diffusion is slow compared to reaction, a condensate concentration gradient is established. This gradient induces a molecular‐weight gradient, which results in a broadened overall molecular‐weight distribution with an overall polydispersity above the theoretical limit for homogenous step‐growth polymerization. As the mass transfer resistance inside the particle is decreased, the average molecular weight increases faster with time, and the overall polydispersity decreases. A stoichiometric imbalance of end groups decreases the obtainable molecular weight but mitigates the deleterious effects of slow condensate diffusion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 928–943, 2001     

Effects of molecular weight on dual light‐ and thermo‐responsive behaviors of homopolymers with azobenzene units and terminal oligo(ethylene glycol) units

A series of water‐soluble dual light‐ and thermo‐responsive homopolymers bearing azobenzene units and terminal oligo(ethylene glycol) units with well‐defined molecular weight (M _n = 0.69 × 10⁴ to 4.60 × 10⁴ g mol^?1) were synthesized via reversible addition–fragmentation chain transfer polymerization. All the homopolymers exhibited reversible photoisomerization and their lower critical solution temperatures showed an unusual increase with increasing molecular weight. Interestingly, by increasing the molecular weight, the aggregate morphology of these polymers was found to evolve from a spherical to a cylindrical shape. © 2017 Society of Chemical Industry     

Dispersion of carbon nanotubes in ultrahigh‐molecular‐weight polyethylene by melt mixing dominated by elongation stress

A novel melt‐mixing method and corresponding mixer for polymer materials are reported. The effects of carbon nanotube (CNT) loading, rotation rate and mixing time on the morphology and properties of CNTs/ultrahigh‐molecular‐weight polyethylene (UHMWPE) nanocomposites were experimentally investigated in detail using the mixer. Homogeneous dispersion of CNTs in intractable UHMWPE is successfully realized without the aid of any additives or solvents. Differential scanning calorimetry results showed that the crystallinity increases 13.8% when 1 wt% of CNTs is added into the composites. The maximum crystallinity increased 13.5% and then decreased slightly with increasing rotation rate. The mixing time had little effect on crystallinity. Rheological tests reveal that the effect of CNT loading on the storage modulus/complex viscosity is a result of competition between the viscosity decrease due to the selective adsorption of UHMWPE onto CNT surfaces and the viscosity increase caused by the formation of an interconnected polymer–nanotube network. The storage modulus/complex viscosity decreased with increasing rotation rate/mixing time. This is a synergic result of the selective adsorption of the long molecular chains onto the CNT surface and their thermomechanical degradation. The results showed that the mixing process dominated by elongation stress is a simple, efficient green way to prepare CNTs/UHMWPE nanocomposites via melt mixing. © 2018 Society of Chemical Industry     

Efficient Estimation of Seasonal Long‐Range‐Dependent Processes

Abstract. This paper studies asymptotic properties of the exact maximum likelihood estimates (MLE) for a general class of Gaussian seasonal long‐range‐dependent processes. This class includes the commonly used Gegenbauer and seasonal autoregressive fractionally integrated moving average processes. By means of an approximation of the spectral density, the exact MLE of this class are shown to be consistent, asymptotically normal and efficient. Finite sample performance of these estimates is examined by Monte Carlo simulations and it is shown that the estimates behave very well even for moderate sample sizes. The estimation methodology is illustrated by a real‐life Internet traffic example.     

Effect of sequence distribution on short‐range ordering in poly(ether sulfone) copolymers

Three kinds of poly(ether sulfone) copolymer samples, R50, B50, and A50, showing marked differences in tensile behavior because of different sequence distributions were investigated by radial distribution function (RDF) methods. The RDF patterns were not virtually identical and showed that the short‐range order (0–14 Å) in the samples had been essentially affected by the sequence distribution. Most of the intramolecular distances in the copolymer were successfully resolved in the RDF pattern. However, there were only suggestions of broad peaks at r = 5.5 Å and r = 11 Å, attributable to intermolecular ordering, which indicated that little intermolecular ordering had occurred in either sample. The appearance of two peaks at about 5 Å periodic suggested the existence of more or less parallel chain segments in the copolymers. Therefore, substantial structural differences between the three copolymers were shown. The structural information revealed by these RDF results was in agreement with the tensile property changes caused by the sequence distribution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 534–537, 2007     

Probe dependency of polymer‐plasticizer and polymer‐polymer interaction parameters in inverse gas chromatography

Inverse gas chromatography has been widely used to determine the Flory–Huggins parameter, χ, between a plasticizer and a polymer, or between two polymers. Many studies showed that interaction parameters may be probe dependent. In a recent study it was proposed that, when a specific interaction occurred between two polymers, the probes had less interaction with the polymers, leading to a lower solubility parameter for polymer blends than the volume average of the components. An equation was derived to relate the probe dependency to the deviation of solubility parameter of polymer mixtures. Here this approach is applied to plasticized poly(vinyl chloride) (PVC) and a copolymer, and to poly(vinylidene fluoride)–poly(ethyl methacrylate) blends. For a PVC and epoxidized oil system the relative deviation of specific retention volume showed two trends, with saturated hydrocarbons as one group, and polar and aromatic probes as another group. For the poly(vinylidene fluoride)/poly(ethyl methacrylate) system the plot of retention volume deviation versus solubility parameter of probes also showed separate trends for n‐alkanes, esters, and alcohols. But the plot of ?₂?₃RT(χ₂₃/V₂) versus solubility parameter had better linearity for the systems studied. The slope of this plot was used as an indicator for miscibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Modelling of biaxial ratcheting behaviour of ultrahigh‐molecular‐weight polyethylene with viscoplasticity theory based on overstress for polymers

Biaxial ratcheting behaviour of ultrahigh‐molecular‐weight polyethylene (UHMWPE) has been modelled using the viscoplasticity theory based on overstress for polymers (VBOP) with the modified Chaboche kinematic hardening rule. Investigated loading condition is: axial strain‐controlled cyclic loading of thin‐walled tubular specimen in the presence of constant pressure. To improve the circumferential strain ratcheting response of UHMWPE, changes designed to account for kinematic hardening and tangent modulus effects are proposed. Numerical results are compared with previously obtained experimental data. It is shown that modified tangent modulus improves the model responses. The biaxial ratcheting behaviour of UHMWPE is modelled quantitatively with VBOP. © 2015 Society of Chemical Industry     

Molecular characteristics of room‐temperature soluble fractions of low‐density polyethylene film resins

The molecular characteristics of the room‐temperature soluble fractions (RT solubles) of three low‐density polyethylene film resins were characterized by size‐exclusion chromatography (SEC), SEC combined with FTIR (SEC–FTIR), and nuclear magnetic resonance spectroscopy (NMR). The high‐molecular‐weight components of the RT solubles were found to be highly branched components with uniform short‐chain branching (SCB) profiles. For the low‐molecular‐weight components, however, SCB content was a function of molecular weight (MW), increasing with an increase in MW. When the chain ends were considered as SCB equivalents, the distribution of the sum of SCB and chain ends across the molecular weight distribution was practically flat, suggesting that the driving force for polymer chains remaining in solution at RT was the length of the undisrupted methylene sequence in the backbone, or methylene run length, which was too short to form crystal lamellae with a melting temperature above RT, regardless of the molecular weight of the polymer. Moreover, the NMR results revealed that the polymer components of the RT solubles had “superrandom” SCB distributions, that is, the fraction of comonomer clusters in the polymer chains of the RT solubles was lower than that predicted by Bernoullian statistical analysis, indicating that the probability of adding a comonomer to a comonomer‐ended propagating chain was lower than that of adding a comonomer to an ethylene‐ended one, presumably because of an unfavorable steric effect. Furthermore, contrary to the common belief that RT solubles are mainly low‐molecular‐weight polymers, high‐molecular‐weight components were found in high concentrations in the RT solubles, with a cutoff MW as high as 1,000,000 g/mol. The proportion of RT solubles in the film resins was found to depend on the type of resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4992–5006, 2006     

Short‐time fabrication of well‐mixed high‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blends under elongational flow: morphology,mechanical properties and mechanism

As linear polyethylenes, ultrahigh‐molecular‐weight polyethylene (UHMWPE) and high‐density polyethylene (HDPE) have the same molecular structure, but the large difference in viscosity between them makes it difficult to obtain well‐mixed blends. An innovative eccentric rotor extruder (ERE) generating an elongational flow was used to prepare HDPE/UHMWPE blends within short processing times. Compared with the obvious two‐phase morphology of a sample from a twin‐screw extruder observed with a scanning electron microscope, few small UHMWPE particles were observed in the HDPE matrix for a sample from the ERE, indicating the good mixing on a molecular level of HDPE/UHMWPE blends achieved by the ERE during short processing times. The morphological changes of blends prepared using the ERE evidenced the good integration of HDPE and UHMWPE even though the UHMWPE content is up to 50 wt% in the blends. Moreover, all blends retained most of the intrinsic molecular weight. The good mixing was further confirmed from the thermal, crystallization and rheological behaviors determined using differential scanning calorimetry and dynamic rheological measurements. Importantly, the 50/50 blend presented improved mechanical properties, especially super‐impact strength of 151.9 kJ m^?2 with incomplete‐break fracture state. The strengthening and great toughening effects of UHMWPE on the blends were attributed to the addition of unwrapped UHMWPE long molecular chains. The effective disentanglement mechanism of UHMWPE chains under elongational flow was explained schematically by a non‐parallel three‐plate model. © 2019 Society of Chemical Industry     

Relative strength of H‐bonding groups on biodegradable polymer‐based blends in solution

The intermolecular hydrogen bonding interactions between poly(3‐hydroxybutyrate) and poly(styrene‐co‐vinyl phenol) copolymers with mutual solvent epichlorohydrin were thoroughly investigated by steady‐state fluorescence and viscosity techniques. Fluorescence spectroscopy along with viscosity technique was used to asses the intermolecular hydrogen bonding between poly‐(3‐hydroxybutyrate) and its blends with five copolymer samples of styrene–vinyl phenol, containing different proportions of vinyl phenol but similar average molecular weight and polydispersity index. In the case of very low OH contents (2–4 mol %), as expected, both components of poly(3‐hydroxybutyrate) and poly(styrene‐co‐4‐vinylphenol) chains are well separated and remain so independently of the mixed polymer ratio and overall polymer concentration as well. Conversely, when the OH content reaches 5.8 mol % or more, a significant decrease of the intrinsic fluorescence intensity emitted by the copolymer is detected upon addition of aliquots of poly(3‐hydroxybutyrate). In these cases, an average value for the interassociation equilibrium constant, K_A = 8.7, was obtained using a binding model formalism. A good agreement of these results with those obtained from complementary viscosity measurements, through the interaction parameter, Δb, was found. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 900–910, 2006     

Effects of 1,2‐butadiene on the anionic copolymerization of styrene and 1,3‐butadiene in the presence of polar additives

1,2‐Butadiene is shown to be a chain terminating/transferring agent in butyllithium‐initiated diene polymerization. The influence of 1,2‐butadiene on the anionic copolymerization of 1,3‐butadiene and styrene is investigated using n‐butyllithium as initiator and tetrahydrofuran or N,N,N′,N′‐tetramethylethylenediamine as polar additive. A decrease of copolymerization rate is observed on the addition of 1,2‐butadiene. On introducing 1,2‐butadiene, the number average molecular weight (M_n ) decreases and the molecular weight distribution broadens. The vinyl content of copolymer increases slightly with an increase of 1,2‐butadiene. During the copolymerization, 1,2‐butadiene in the presence of a high ratio of polar additives to n‐butyllithium greatly decreases the copolymerization rate, resulting in a lower value of M_n and a narrower molecular weight distribution than that found for a low ratio of polar additives to n‐butyllithium. This evolution can be explained by the base‐catalyzed isomerization of 1,2‐butadiene to form 1‐butylene in the presence of polar additives. With an increasing amount of 1,2‐butadiene, the vulcanized rubber exhibits an increased rolling resistance and a reduced wet skid resistance owing to the decrease of coupling efficiency. These results further indicate the activity of alkynyllithium derivatives produced by the reaction of alkyllithium and 1‐butyne is less than that of the alkyllithium. Copyright © 2007 Society of Chemical Industry     

Improvement of the tribological behavior of ultra‐high‐molecular‐weight polyethylene by incorporation of poly (phenyl p‐hydroxyzoate)

Ultra‐high‐molecular‐weight polyethylene/poly (phenyl p‐hydroxyzoate) composites (coded as UHMWPE/PPHZ) were prepared by compression molding. The effects of the poly (phenyl p‐hydroxyzoate) on the tribological properties of the UHMWPE/PPHZ composites were investigated, based on the evaluations of the tribological properties of the composites with various compositions and the examinations of the worn steel surfaces and composites structures by means of scanning electron microscopy and transmission electron microscopy. It was found that the incorporation of the PPHZ led to a significant decrease in the wear rate of the composites. The composites with the volume fraction of the PPHZ particulates within 45% ～ 75% showed the best wear resistance. The friction coefficient of the UHMWPE/PPHZ composites decreased with increasing load and sliding velocity, while the wear rates increased with increasing load. This was attributed to the enhanced softening and plastic deformation of the composites at elevated load or sliding velocity. The UHMWPE/PPHZ composites of different compositions had differences in the microstructures and the transfer film characteristics on the counterpart steel surface as well. This accounted for their different friction and wear behaviors. The transfer film of the UHMWPE/PPHZ composites appeared to be thinner and more coherent, which was largely responsible for their better wear resistance of t composite than the UHMWPE matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2336–2343, 2005     

Detection of low levels of long‐chain branching in polydisperse polyethylene materials

Creep experiments have been applied to probe the zero‐shear viscosity, η₀, of polyethylene chains directly and precisely in a constant‐stress rheometer at 190°C. Such experiments, when combined with precise measurements of the weight‐average molecular weight, M_w, calibrated relative to linear chains of high‐density polyethylene, are shown to provide a very sensitive approach to detect low levels (0.005 branches per 1000 carbons) of long‐chain branching (LCB). This detection limit is shown to be insensitive to whether the molecular weight distribution (MWD) breadth, M_w/M_n, rises from about two to ten. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and biological activity of medium molecular weight polymers containing 3,6‐endo‐methylene‐1,2,3,6‐tetrahydrophthalimidobutanoyl‐5‐fluorouracil

A new monomer, 3,6‐endo‐methylene‐1,2,3,6‐tetrahydrophthalimidobutanoyl‐5‐fluorouracil (ETBFU), was synthesized by reaction of 3,6‐endo‐methylene‐1,2,3,6‐tetrahydrophthalimidobutanoyl chloride and 5‐fluorouracil. The homopolymer of ETBFU and its copolymers with acrylic acid (AA) or vinyl acetate (VAc) were prepared by photopolymerization using 2,2‐dimethoxy‐2‐phenylacetophenone as an initiator at 25 °C. The synthesized ETBFU and its polymers were identified by FTIR, ¹H NMR and ¹³C NMR spectroscopies. The ETBFU content in poly(ETBFU‐co‐AA) and poly(ETBFU‐co‐VAc) was 43 and 14 mol%, respectively. The apparent number‐average molecular weight (M_n) of the polymers determined by GPC ranged from 8400 to 11 300. The in vitro cytotoxicity of the samples against mouse mammary carcinoma (FM3A), mouse leukaemia (P388), and human histiocytic lymphoma (U937) cancer cell lines decreased in the order 5‐FU ≥ ETBFU > poly(ETBFU) > poly(ETBFU‐co‐AA) > poly(ETBFU‐co‐VAc). The in vivo antitumour activity of the polymers against Balb/C mice bearing sarcoma 180 tumour cells was greater than that of 5‐fluorouracil at all doses tested. © 2000 Society of Chemical Industry     

Influence of viscosity ratio on processing and morphology of thermotropic liquid crystal polymer‐reinforced poly(ethylene 2,6‐naphthalate) blends

Thermotropic liquid crystal polymer (TLCP) microfibril‐reinforced poly(ethylene 2,6‐naphthalate) (PEN) composites with various intrinsic viscosities were prepared by a melt compounding method. Polymer composites consisting of bulk cheap polyester with a small amount of expensive TLCP are of interest from a commercial perspective. The TLCP acts as a nucleating agent in the TLCP/PEN composites, enhancing the crystallization of the PEN matrix through heterogeneous nucleation. The structural viscosity index of the TLCP/PEN composites was lower than that of PEN and TLCP, which was attributed to the formation of TLCP fibrillar structures with elongated fibrils in the PEN matrix. The TLCP/PEN composites with higher intrinsic viscosity than the polymer matrix contained these elongated fibrils, and had a TLCP component with a smaller average diameter, and a narrower diameter distribution than TLCP/PEN composites with lower intrinsic viscosity. The higher intrinsic viscosity of the polymer matrix, the higher shear rate and the lower viscosity ratio of TLCP to PEN can all favour TLCP fibrillation in the polymer composites. Copyright © 2006 Society of Chemical Industry     

Numerical and experimental investigation on surface air entrainment mechanisms of a novel long‐short blades agitator

We investigate numerically and experimentally the mechanisms of surface air entrainment in the vessels equipped with the long‐short blades agitator. VOF method coupled with LES model is used to visualize the surface air entrainment process. In the case of partial submergence of the long blades (LBs), the interaction of the LBs with the liquid free surface creates a depression behind the LBs. Backfilling of the liquid into the depression leads to gas separation and entrapping into the liquid. The critical tip velocity of the LBs, u_tip,c, for the onset of gas entrainment is measured in vessels with diameters, T = 200～600 mm. It is found that when H/T ≥ 1.0, u_tip,c is determined by the LBs, independent of the liquid level. u_tip,c is also affected by the size of the vessel through the diameter of the sweeping circle of the LBs, but for substantially large vessels, it approaches a constant value. © 2017 American Institute of Chemical Engineers AIChE J, 63: 316–325, 2018