Molecular Weight Distribution Index Research Articles

Comparison of Eco-friendly Ti-M Bimetallic Coordination Catalysts and Commercial Monometallic Sb- or Ti-Based Catalysts for the Synthesis of Poly(ethylene-co-isosorbide terephthalate).

Sustainable development greatly benefits from the effective synthesis of bio-based copolymers that are environmentally friendly. To enhance the polymerization reactivity for the production of poly(ethylene-co-isosorbide terephthalate) (PEIT), five highly active Ti-M (M = Mg, Zn, Al, Fe, and Cu) bimetallic coordination catalysts were designed. The catalytic activity of Ti-M bimetallic coordination catalysts and single Sb- or Ti-based catalysts was compared, and the effects of catalysts with a different type of coordination metal (Mg, Zn, Al, Fe, and Cu) on the thermodynamic and crystallization properties of copolyesters were explored. In polymerization, it was found that Ti-M bimetallic catalysts with 5 ppm (Ti) had higher catalytic activity than traditional antimony-based catalysts or Ti-based catalysts with 200 ppm (Sb) or 5 ppm (Ti). The Ti-Al coordination catalyst showed the best-improved reaction rate of isosorbide among the five transition metals used. Utilizing Ti-M bimetallic catalysts, a high-quality PEIT was successfully synthesized with the highest number-average molecular weight of 2.82 × 104 g/mol and the narrowest molecular weight distribution index of 1.43. The glass-transition temperature of PEIT reached 88.3 °C, allowing the copolyesters to be used in applications requiring a higher Tg, like hot filling. The crystallization kinetics of copolyesters prepared by some Ti-M catalysts was faster than that of copolyesters prepared by conventional titanium catalysts.

High efficiency synthesis of temperature resistant polyamideimide resin with branched structure using microreactor

Polyamideimide (PAI) resins have a wide range of applications. It is significant to explore novel and efficient synthesis methods. This paper describes a method for the rapid synthesis of branched PAIs in a microreactor using 4,4-methylenediphenyl diisocyanate (MDI) and 1,2,4-benzoic acid anhydride (TMA) as substrates. The isocyanate group reacts with the amide bond to build the branched structure. A high molar ratio of substrate helps to form more branched structures. High molar ratios also lead to high molecular weight products with narrow distribution, where the number average molecular weight of PAI-1.35 is as high as 1828.14 kg/mol and the molecular weight distribution index is only 1.09. Some oligomers are present in the products obtained at low molar ratios, which affect the mechanical and thermal properties of the products. Curing with epoxy resin can form a bulk structure and eliminate the effect of oligomers. The PAI films obtained after curing have excellent mechanical and thermal properties.

Effect of solvent on the microstructure of polyvinyl alcohol

AbstractThe method for producing polyvinyl alcohol (PVA) by the solution polymerization of vinyl acetate first and then alcoholysis strategy is industrial. Where solvent plays a vital role in control over stereoregularity, molecular weight and its distribution, crystallinity and so on. In this report, when methyl acetate was used as a solvent in the polymerization of vinyl acetate instead of methanol, prepared PVA was characterized by Fourier‐transform infrared spectroscopy (FT‐IR), nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that PVA obtained in methyl acetate has a higher content of syndiotactic structure, crystallinity melting temperature and enhanced thermal stability compared with PVA obtained in methanol due to the formation of Π ‐ Π complex between methyl acetate and vinyl acetate and the enhanced steric hindrance effect during polymerization. Additionally, methyl acetate has a smaller chain transfer constant (1.31 × 10−4), which benefits to decrease the branching degree and molecular weight distribution index of PVA. This research provides more ideas for the choice of solvents in the industrial production of polyvinyl alcohol.

Fine-tune of lignin properties by its fractionation with a sequential organic solvent extraction

In this work, different lignins were obtained from two different extraction methods (kraft and organosolv) but from the same raw material (Eucalyptus globulus sp.). They were subsequently fractionated to determine the differences of each extraction method and their corresponding physicochemical properties found in fractionation sequence and obtained fractions. The goal of the fractionation was to obtain lignin fractions with narrower molecular weight distribution and lower polydispersity index (PI). The solvent sequence was designed based on the environmental friendly properties, health and safety assessments of the selected organic solvents: (methanol (MeOH), ethanol (EtOH), propan-2-one (DMK), ethyl acetate (EtOAc), propan-1-ol (nPrOH), propan-2-ol (iPrOH), butan-2-one (MEK), and butan-1-ol (tBuOH)). The different fractions obtained were characterised to determine their chemical structure by several analytical techniques, such as Fourier Transformed Infrared Spectroscopy (FTIR), Ultraviolet (UV), Phosphorus-31 Nuclear Magnetic Resonance (31P NMR), Pyrolysis–Gas Chromatography/Mass Spectrometry (Py-GC/MS), Thermogravimetric analysis (TGA), and Differential scanning calorimetry (DSC). In addition, Gel Permeation Chromatography (GPC) was used to obtain the molecular weight distribution. This study showed an effective method for obtaining homogeneous lignins with specific structures and properties depending on the solvent and molecular weight attained. Moreover, the method designed was found to be effective regardless of the lignin extraction process employed; besides, various lignin fractions were obtained which were different from each other, having specific target applications depending on their structure and chemical properties, ranging from small molecules with abundant reactive sites to act as active materials or copolymer reagents for many applications, to larger and more inactive molecules with higher thermal resistivity.

Structural changes in corn starch granules treated at different temperatures

The four structural levels of corn starch granules are as follows: particle structure, growth ring, crystalline region and chain structure. In this study, corn starch granules treated at different temperatures (50, 60, 70, 80, and 90 °C), then freeze-dried were evaluated. The corn starch granules remained largely intact in the control and at 50 °C and 60 °C, but with increasing temperature, the starch granules were broken. The growth ring structure and crystallization zone gradually broke up and disappeared with increasing temperature. Moreover, with increasing temperature, the degree of order (DO) and degree of the double helix (DD) of the crystalline region decreased gradually, indicating that the double helix structure of amylopectin in corn starch dissociated during heating. The molecular weight distribution index of corn starch was analyzed by gel permeation chromatography (GPC) and found that it increased with increasing temperature, indicating that the molecular chains of corn starch were broken during heating. In sum, the structural levels of corn starch granules, including the particle structure, growth ring, and crystalline region were damaged to varying degrees, whereas chain structure has been changed, after being processed at different temperatures. This study provides a model for theory of gelatinization in corn starch system.

Flow regime identification in horizontal pneumatic conveying by nonintrusive acoustic emission detection

AbstractThis work investigated flow regimes identification in horizontal pneumatic conveying from the scope of particle motions based on acoustic emission detection. Results showed that the variation of acoustic energy and acoustic energy fraction could be used to identify the transition between suspension flow and stratified flow. Near the transition point, the acoustic energy was maximum, and the energy fraction of particle‐wall collision mutated at high mass fluxes. Furthermore, the fluctuation distribution index (FI) was constructed learning from the concept of polymer molecular weight distribution index, and the “circumferential fluctuation difference (D)” was defined. Based on this, new identification criteria and flow regime diagram were established. In suspension flow, D >0. In stratified flow, D <0. While in slug flow, D ≈ 0. According to these criteria, flow regimes can be identified independently of changing trends of measurement parameters. The universality of above criteria was further verified under different operating conditions.

Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization of Poly(ethylmethacrylate) with Pendant Carbazole Groups

Carbazole containing polymers have captured the interest of researchers for use in optoelectronics. For an important material to exhibit its optoelectronic properties intrinsic uniformity in the molecular level is required. Thus, a monomer of ethyl methacrylate with pendant carbazole group was synthesized and polymerized via Reversible Addition-Fragmentation Chain Transfer (RAFT) to produce polymers with controlled molecular weight distribution and narrow polydispersity index (PDI). This method of polymerization was compared with that of free radical polymerization by gel permeation chromatography (GPC). The RAFT’s polymerization kinetics was observed to follow a plot of number average molecular weight (Mn) versus % conversion, characteristic of living polymerization. It was also shown to possess polymer chain extension capability. The structure of the monomer and the polymers were characterized by Fourier-Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance (NMR).

Cost-Effective Sustainable Synthesis of High-Performance High-Molecular-Weight Poly(trimethylene terephthalate) by Eco-Friendly and Highly Active Ti/Mg Catalysts

Efficient sustainable synthesis of high-performance poly(trimethylene terephthalate) (PTT) with simultaneously high molecular weight, narrow molecular weight distribution, and tiny cyclic dimer suitable for high end applications at low cost still faces challenges. Novel nontoxic and 1,3-propanediol-soluble Ti/Mg bimetal catalyst mainly based on biobased 1,3-propanodiol and food grade materials has been productively synthesized and also carefully characterized. The Ti/Mg catalyst was found to be exceptionally active catalysts for the polycondensation of terephthalic acid and 1,3-propanediol from a renewable resource capable of producing high-molecular-weight PTT as an environmentally friendly and recyclable material in both laboratory reactor and continuous pilot plant. The high-quality PTT samples with the highest number-average molecular weight up to 68 870 g/mol ever reported so far, the narrowest molecular weight distribution index down to 1.92, and the second lowest cyclic dimer content down to 2.21% ...

A correlation between microstructure and rheological properties of broad MWD high-density polyethylene

A correlation between molecular structure parameters and rheological behavior was determined for three different grades of high-density polyethylene (HDPE). The molecular structure parameters including number-average molecular weight (M n ), weight-average molecular weight (M w ), molecular weight distribution (MWD) and branching index were characterized by gel permeation chromatography (GPC). Moreover, a fast and easy method for investigating side chain branching using Fourier transform infrared (FTIR) spectroscopy was discussed. The rheological characterizations of both linear and non-linear viscoelastic regions were performed by a modular compact rheometer (MCR) in the dynamic mode. Zero shear viscosity (η 0), relaxation time, relaxation time distribution, stress relaxation modulus and damping function were obtained from the rheological characterization. Moreover, molecular weight distribution was calculated for each sample and compared with the GPC results. The GPC results confirmed broad molecular weight distribution for all three HDPE samples. The relationship between zero shear viscosity and molecular weight at 180 °C was found as \(\eta_{0} = 2.5 \times 10^{ - 14} M_{w}^{3.6}\) and for zero shear viscosity and MWD at 180 °C was found as \(\eta_{0} = 1.6 \times 10^{ - 15} M_{w}^{3.6} \left( {\frac{{M_{w} }}{{M_{n} }}} \right)\). By choosing the mixing parameter (β) value of 0.73, the values of molecular parameters obtained from the rheology and GPC tests were significantly accommodated. Furthermore, it was found that the damping function of type C was an appropriate type for the polyethylenes of selected broad MWD.

Diluting ferric carboxymaltose in sodium chloride infusion solution (0.9% w/v) in polypropylene bottles and bags: effects on chemical stability

ObjectivesThis study was designed to assess the physicochemical stability of colloidal ferric carboxymaltose solution (Ferinject) when diluted and stored in polypropylene (PP) bottles and bags for infusion.MethodsTwo batches of ferric...

Effect of Catalyst on Preparation and Properties of PBT / PTMG Poly(ether ester)

Taking dimethyl terephthalate(DMT), 1, 4-butylene glycol(BG) and polytetrahydrofuran(PTMG) as main raw materials, a series of PBT/PTMG poly(ether ester) thermoplastic elastomers were prepared with catalysts of tetrabutyl titanate, tetrabutyl titanate/magnesium acetat, tetrapropyl-zirconium and zinc acetate/antimony trioxide respectively. The effect of catalysts on the transesterification rate of the synthesis process, the molecular weight distribution, crystallinity, mechanical properties and heat resistance of the synthesized materials were mainly concerned. The synthesized thermoplastic elastomers were characterized by means of SEM, GPC, DSC, TG and mechanical testing. The results show that:while taking tetrabutyl titanate/magnesium acetate as catalyst, with the increasing amount of the catalyst,the transesterification rate increased, and the molecular weight and crystallinity increased, the molecular weight distribution index decreased, the toughness enhanced and the thermal decomposition temperature was above 390℃ for the synthesized thermoplastic elastomer.

Optimal Operating Strategies for Emulsion Polymerization with Chain Transfer Agent

Batch and semibatch emulsion polymerization was investigated with a chain transfer agent (CTA) to optimize key process attributes such as monomer conversion and product properties such as molecular weight and particle size. The test monomer, styrene was polymerized in the presence of the chain transfer agent, n-dodecyl mercaptan, to control the final molecular weight. The process model used for conducting optimization incorporated the nucleation, reaction kinetics, and phase heterogeneity involving the aqueous, monomer droplet and polymer particle phases during the various stages of the reaction. The model developed was able to predict the behavior of emulsion polymerization, while describing the significant effect of CTA on molecular weight distribution (MWD) and polydispersity index (PDI) for both batch and semibatch processes. The optimal operating strategies for the process were developed using reaction temperature and monomer feed rate as process variables to obtain desired process trajectories and p...

Preparation and Characterization of UV-Curable Cyclohexanone-Formaldehyde Resin and Its Cured Film Properties

UV-curable cyclohexanone-formaldehyde (UVCF) resin was prepared with cyclohexanone-formaldehyde (CF) resin, isophorone diisocyanate (IPDI), and pentaerythritol triacrylate (PETA) as base substance, bridging agent, and functional monomer, respectively. The structure of UVCF was characterized by Fourier transform infrared spectroscopy (FT-IR),1H-nuclear magnetic resonance spectroscopy (1H-NMR), and gel permeation chromatography (GPC). The viscosity and photopolymerization behavior of the UV-curable formulations were studied. The thermal stability and mechanical properties of the cured films were also investigated. The results showed that UVCF resin was successfully prepared, the number of average molecular weight was about 2010, and its molecular weight distribution index was 2.8. With the increase of UVCF resin content, the viscosity of the UV-curable formulations increased. After exposure to UV irradiation for 230 s, the photopolymerization conversion of the UV-curable formulations was above 80%. Moreover, when the UVCF content was 60%, the formulations had high photopolymerization rate, and the cured UVCF films showed good thermal stability and mechanical properties.

Controlled synthesis of chiral polymers for the kinetic resolution of racemic amino acids

A novel lysine bearing vinyl monomer, (S)-2-(tert-butoxycarbonylamino)-6-(4′-vinylbenzamido)hexanoic acid, was designed and synthesized. It underwent reversible addition–fragmentation chain transfer polymerization induced by azobisisobutyronitrile in the presence of 2-cyano-2-propyl dodecyl trithiocarbonate in dioxane at 65 °C. The number-average molecular weights of the resultant polymers increased linearly with the monomer conversion and the molecular weight distribution indices kept relatively low, indicating a well-controlled chain growth process. After deprotection of N-Boc groups, the monomer and the polymers were used as stereospecific inhibitors in the fractional crystallization of racemic glutamic acid monohydrochloride (rac-Glu·HCl). The polymers showed much better performance than the monomer. At a polymer concentration above 0.5 wt%, the R-enantiomer was obtained with an enantiomeric excess (ee%) over 97%, independent of the molecular weights of the polymer additives. In contrast, 10 wt% of the monomer was required to achieve the same result under identical conditions. However, with an addition of 0.1 wt% polymeric inhibitors, the ee% of the resolved R-Glu·HCl crystals increased initially and then decreased with an increased molecular weight of polymer additives, and for the polymer with a moderate Mn of 5800 Dalton, R-Glu·HCl with ee% over 97% was yielded. Because of the large absorption difference in the UV-Vis range between the polymer inhibitor and the resolved molecules, the residual fraction of additives in the resolved crystals was evaluated by means of UV-Vis spectrophotometry, and all results showed that there were very low fractions of polymer residues (<0.1%). Moreover, the polymers were also efficient for the kinetic resolution of rac-threonine and rac-asparagine monohydrate conglomerates at concentrations of 0.5 and 1.0 wt%, respectively, yielding preferentially R-enantiomers with ee% ∼98%.

Photocatalytic Degradation of Polyethylene Glycol by Nano-Titanium Dioxide Modified With Ferric Acetylacetonate

The surface of anatase TiO2 nanoparticles was modified by ferric acetylacetonate complex Fe(acac)3. This modification improved the dispersion of TiO2 in polymer and also the photocatalytic activity. The photodegradation of polyethylene glycol (PEG) catalyzed by modified TiO2 (Fe-TiO2) was extensively studied. The degradation character was evident. For example, the polymer lost its weight gradually, and the molecular weight decreased. Meantime the molecular weight distribution index increased. The molecular weight of PEG has a great influence upon the degradation. In all cases Fe-TiO2 displayed much higher catalytic activity than the neat TiO2.

Synthesis of Substituted Phosphotungstic Acids and their Catalytic Performance on Cationic Polymerization of β-Pinene

Substituted phosphotungstic acids containing manganese, chromium, molybdenum and vanadium were prepared, and their catalytic performance on cationic polymerization of β-pinene was also investigated. The experimental results show that the substituted phosphotungstic acids are mono-substituted and keep Keggin structure. The substituted phosphotungstic acids containing Mn or Cr exhibit similar catalytic performance as phosphotungstic acid, instead show bad properties if containing Mo or V. The yield of polymer is up to 44.3 %, and the average number molecular weight is about 1200, and molecular weight distribution index is 1.4.

Kinetic study of in situ normal and AGET atom transfer radical copolymerization of n–butyl acrylate and styrene: Effect of nanoclay loading and catalyst concentration

AbstractThe effect of clay nanolayers and catalyst concentration on the kinetics of atom transfer radical copolymerization of styrene and butyl acrylate initiated by activators generated by electron transfer (AGET initiation system) or an alkyl halide (normal initiation system) was studied. Monomer conversion was studied by attenuated total reflection–Fourier transform infrared spectroscopy, and also proton nuclear magnetic resonance (1H NMR) spectroscopy was utilized to evaluate the heterogeneity in the composition of poly(styrene‐co‐butyl acrylate) chains. A decrease in the copolymerization rate of styrene and butyl acrylate in the presence of clay platelets was observed since clay layers confine the accessibility of monomer and growing radical chains. Considering the linear first‐order kinetics of the polymerization, successful AGET and normal atom transfer radical polymerization (ATRP) in the presence of clay nanolayers were carried out. Consequently, poly(styrene‐co‐butyl acrylate) chains with narrow molecular weight distribution and low polydispersity indices (1.13–1.15) were obtained. The linearity of ln([M]0/[M]) versus time and molecular weight distribution against conversion plots indicates that the proportion of propagating radicals is almost constant during the polymerization, which is the result of insignificant contribution of termination and transfer reactions. Controlled synthesis of poly(styrene‐co‐butyl acrylate)/clay is implemented with the diminishing catalyst concentration of copper(I) bromide/N,N,N′,N′′,N′′‐pentamethyl diethylene triamine without affecting the copolymerization rate of normal ATRP. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 789–799, 2012

Synthesis and photophysical properties of porphyrin-containing polymers

A series of porphyrin-containing polymers with triazole rings as linkers have been successfully synthesized by click polymerization. The polycycloadditions of porphyrin-containing dialkyne 1 and 1,4-diazidobenzene 2 were initiated either by simple heating or by Cu(I)-catalyst, affording polymers P1-P8 with relatively high molecular weight. The polymerization process was monitored by gel permeation chromatography analysis. The polymer prepared by thermally initiated click polymerization has unimodal molecular weight distribution and moderate polydispersity index after prolonging reaction time to 170 h. Compared with the metal-free click polymerization, the rate of molecular weight growth in Cu(I)-catalyzed click polymerization declined, leading to relatively low molecular weight of the resulting polymer. The as-synthesized polymers are soluble in common organic solvents and stable at a temperature up to 350 °C. The photophysical properties of the porphyrin monomer and the polymer were investigated by UV–vis and fluorescence spectroscopy. This approach offers practical advantages over other synthetic methods used to prepare main-chain porphyrin-containing polymers with regard to the absence of byproducts generated during the polymerization reaction.

Preparation of mid-to-high molecular weight konjac glucomannan (MHKGM) using controllable enzyme-catalyzed degradation and investigation of MHKGM properties

Mid-to-high molecular weight konjac glucomannan (MHKGM) powders with different molecular weights were prepared and purified from their enzymatic hydrolysis solutions. MHKGM powder yield was optimized with respect to substrate concentration, urea concentration, the number of alcohol washings, and drying temperature. Properties of MHKGM powder were characterized by SEC, FTIR, UV, XRD, rheological, and thermal analysis techniques. The results showed that under the correct conditions a high productive yield of MHKGM can be obtained. MHKGMs have the same chemical structure as that of native KGM, but their weight average molecular weight (Mw), molecular weight distribution index (Mw/Mn), radius of gyration (Rg), solution optical clarity, rheological properties, and other physical properties such as water solubility are very different from those of native KGM. This study provides useful a reference for making MHKGM powder with varying molecular weight and the potential applications of KGM such as healthy food additives.

The effect of the spacer length on binitroxide mediated radical polymerization of styrene

Series of binitroxides, (N,N′-bis(4-(2,2,6,6-tetramethylpiperidin-1-yloxyl)diaminoalkane), ·Cn· (n=0, 2, 3, 4 methylene groups), was used as mediators in the radical polymerization of styrene initiated with benzoyl peroxide (BPO). The length of the methylene spacer linking two 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radicals affected the polymerization process. For the mediators, ·C0·, ·C2· and ·C3·, elongation of the spacer decreases the conversion rate as well as the number average molecular weight (Mn), molecular weight distribution (MWD) and polydispersity index (PDI). For all these mediators, a bimodal MWD was confirmed. The use of N,N′-bis(4-(2,2,6,6-tetramethylpiperidin-1-yloxyl))diaminobutane, ·C4·, results in trimodal MWD with an additional polymer fraction with a high molecular weight originating from an uncontrolled process. In the initial stages of polymerization, electron spin resonance spectroscopy (ESR) showed that the combination reaction between ·C4· and growing polymer chain (P·) is much slower than that for the ·C0· controlling agent, thereby promoting the synthesis of long polymer chains. With the exception of the ·C0· mediator, the remaining biradicals did not exhibit spin-spin interactions between the TEMPO groups in the propagation of polymerization. Therefore, the spin-spin coupling between binitroxide ends does not appear to have a remarkable influence on the polymerization process. Open image in new window