Number-average Molecular Weight Research Articles

Aromatic (Co)polycarbonates bearing pendant norbornenyl groups: Synthesis, characterization and post-polymerization modification

A homo- and three co-polycarbonates (PC-NBs) bearing pendant norbornenyl groups were synthesized via solution polycondensation of triphosgene with 4, 4'-(bicyclo (2.2.1) hept-5-en-2 yl methylene) bis (2-methoxyphenol) (BPA-NB) or various mol % compositions of BPA-NB and bisphenol-A, respectively. 1H-NMR spectroscopy confirmed the chemical structure and composition of PC-NBs. Inherent viscosity and number-average molecular weight (Mn) values of PC-NBs were in the range 0.44 – 0.64 dL g−1 and 21,800 – 34,100 g mol−1, respectively, indicating the formation of polymers of medium to reasonably high molecular weights. Tough, transparent, and flexible films of PC-NBs could be cast from chloroform solution. X-Ray diffraction studies indicated the amorphous nature of PC-NBs. Glass transition temperature (Tg) values, determined by DSC analysis, of PC-NBs were in the range 154 – 175°C and Tg values increased with the increase in mol % of BPA-NB. The post-polymerization modification of a representative PC-NB was demonstrated using 3,6-diphenyl-1,2,4,5-tetrazine via tetrazine-ene reaction.

The Hydrogen Bonding in the Hard Domains of the Siloxane Polyurea Copolymer Elastomers

For probing the structure–property relationships of the polyurea elastomers, we synthesize the siloxane polyurea copolymer elastomer by using two aminopropyl-terminated polysiloxane monomers with low and high number-average molecular weight (Mn), i.e., L-30D and H-130D. To study the influence of the copolymer structures on the film properties, these films are analyzed to obtain the tensile performance, UV-vis spectra, cross-sectional topographies, and glass transition temperature (Tg). The two synthetic thermoplastic elastomer films are characterized by transparency, ductility, and the Tg of the hard domains, depending on the reacting compositions. Furthermore, the film elasticity behavior is studied by the strain recovery and cyclic tensile test, and then, the linear fitting of the tensile data is used to describe the film elasticity based on the Mooney–Rivlin model. Moreover, the temperature-dependent infrared (IR) spectra during heating and cooling are conducted to study the strength and recovery rate of the hydrogen bonding, respectively, and their influence on the film performance is further analyzed; the calculated Mn of the hard segment chains is correlated to the macroscopic recovery rate of the hydrogen bonding. These results can add deep insight to the structure–property relationships of the siloxane polyurea copolymer.

Bromine-containing copolymer polycarbonate for simultaneous thermal stability, transparency, and thin-wall flame-retardant polycarbonate

The incorporation of traditional low molecule bromine flame retardants can enhance the flame retardancy of polycarbonate (PC), yet their poor compatibility with PC impairs its transparency and mechanical properties. Here, brominated polycarbonate (B50PC) was synthesized by interfacial polycondensation method using bisphenol A, tetrabromobisphenol A, and triphosgene. The number average molecular weight (Mn) of B50PC reached 14,600, and compared to the low molecule bromine flame retardant tetrabromobisphenol A (TBBPA), its initial decomposition temperature increased by 38.7 % under air atmosphere. The PC composites containing 5 wt% B50PC achieved the V-0 rating in the UL-94 test, with LOI increased by 10.3 %. At the same time, the peak heat release rate (PHRR) was decreased by 28.6 % and the ignition time (TTI) was delayed by 21.3 %. Compared with that of samples with TBBPA, the composite with the same amount of B50PC maintained the original elongation at break of PC and the transmittance remained at 84.9 %. In summary, the composites with B50PC maintains outstanding transparency and mechanical properties while enhancing the flame retardancy. This work has developed a high molecular bromine flame retardant that combines flame retardancy and transparency, offering a strategy for expanding the application of PC in the electronics, construction, and aerospace sectors.

Controllable synthesis, characterization, and evaluation of poly (lauryl methacrylate-soybean oil) as a lubricant additive

Traditional free radical polymerization has poor controllability, and traditional petroleum-based lubricant additives have adverse effects on the environment. Poly (lauryl methacrylate (LMA)-soybean oil (SBO)) (P(LMA-SBO) was synthesized using Salen-Cu(II) complex as a catalyst and azodiisobutyronitrile (AIBN) as an initiator by the Schlenk techniques. The structure of P(LMA-SBO) was characterized by infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC) followed by evaluating the solidification point depression performance by the Chinese standard method GB/T 510-2018, and the wax crystal morphology was studied by optical microscopy. The results show the catalytic activity could be 22.88 × 104 g·mol−1·h−1 and the number average molecular weight (M n) of the copolymer is 8.71 × 104 with a low dispersity (Ɖ) of 1.37 under the optimal conditions, which indicates good controllability of the polymerization. Adding 1.0%(w) P(LMA-SBO) to the lubricating oil fraction (350–500 °C) could reduce the solidification point by 15 °C. Therefore, the Salen-Cu (II) catalyst was successfully applied to the controlled polymerization of LMA and SBO. The vegetable oil-based solidification point depressant of P(LMA-SBO) could be used as a potential alternative to replace the traditional solidification point depressant in the future.

Synthesis, Structures, Thermal stability and optical spectroscopy of Pt(II) di‑yne and poly‑yne incorporating 2,2′-Bipyridine-4,4′-diyl spacer

In platinum(II) di-ynes and poly-ynes the optical properties are influenced by the pattern of conjugation in the functionalised acetylide linker groups. We report the synthesis and characterisation of new Pt(II) di‑yne trans-[(Ph)(Et₃P)₂Pt–CC–Ar–CC–Pt(PEt₃)₂(Ph)] (Pt-M) and Pt(II) poly‑yne trans-[Pt(nBu3P)2Pt–CC–Ar–CC–]n (Pt-P) (Ar = 2,2′-bipyridine-4,4′-diyl) materials using analytical and spectroscopic techniques. The solid-state structure of the protected ligand precursor 4,4′-bis(trimethylsilylethynyl)-2,2′-bipyridine (LP1) and the dinuclear Pt(II) di‑yne (Pt-M) have been determined by the single-crystal X-ray diffraction (SC-XRD) while the number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index (PDI) of the Pt(II) poly‑yne (Pt-P) have been determined by the gel permeation chromatography/light-scattering (GPC/LS) methods (Mn/Mw/PDI = 55,210/88,560/1.6). The thermal stability of the protected and di-terminal alkynyl ligands, Pt(II) di‑yne (Pt-M) and Pt(II) poly‑yne (Pt-P) have been evaluated and are discussed. To delineate the impact of incorporating the heavy Pt(II) ion along the polymer backbone, optical absorption studies have been performed and are discussed in detail. The results of optical absorption studies, especially (Pt-M) have been compared to their 5,5′- and 6,6′-bis(ethynyl) substituted analogues to better understand the effect of ligand topology on the effective conjugation.

Solvent-based synthesis, structural elucidation and thermal characterisation of free radical grafted PHBV

This study investigates the solvent-based free-radical graft copolymerization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with C11 (undecenoic acid, UDA), C12 (dodecene, DD), and C18 (octadecene, OD) alkene substrates using dicumyl peroxide as an initiator. Comprehensive Nuclear Magnetic Resonance (NMR) spectroscopy was employed to confirm and quantify grafting, which was achieved at up to 5.8 mol% of monomer units. Thermal analysis revealed a significant reduction in melting temperature for all modified PHBVs, ranging from 10-20°C decrease in comparison to virgin PHBV. A decrease in crystallisation temperature and a reduction in glass transition temperature was measured for the UDA and DD grafted PHBV. Additionally, molecular weight analysis showed a marked decrease in weight average molecular weight (M¯w) and number average molecular weight (M¯n) for PHBV grafted with UDA, which was attributed to the presence of carboxylic acid functionality, which accelerates chain scission. The molecular weight profiles of the dodecene and octadecene grafted PHBV were only marginally reduced (32% and 18% reductions in M¯w, respectively), which is a much less severe reduction than has been previously observed for similar chemistries. Overall, this work demonstrates that solvent-based free-radical graft copolymerization can reduce the melting temperature and disrupt the crystallinity of PHBV, hence improving its processability and progressing the field of PHA modification and application.

Synthesis of azelaic acid copolyester plasticizers and their application in PVC.

A series of 2-methyl-1,3-propanediol (MPO) modified azelaic acid and hexylene glycol copolyester (PHMAZ) plasticizers with varying contents were synthesized using a direct esterification melt polycondensation method, and their structures were characterized systematically. Analysis using infrared spectroscopy and nuclear magnetic resonance spectroscopy confirmed the synthesis of the designed copolyester structure. Gel permeation chromatography (GPC) tests indicated that the number average molecular weight of each copolyester sample ranged between 2000 and 3000. These copolyesters were used to plasticize polyvinyl chloride (PVC) resin, and the glass transition temperature of the plasticized PVC samples was tested using a differential scanning calorimeter (DSC). Further characterization of the plasticizing effects was conducted using an electronic universal testing machine. The research results showed that as the content of MPO increased, the plasticizing effect of the copolyester initially increased and then decreased. Specifically, the copolyester containing 45% MPO, PHMAZ-45, demonstrated the best plasticizing effect on PVC, with the glass transition temperature of the plasticized PVC system around -35 °C, elongation at break at 908.4%, and a plasticizing efficiency of 254.5%. Additionally, this new type of copolyester plasticizer uses bio-based raw materials, exhibits excellent plasticizing effects, and the preparation process is stable and controllable. It holds promising potential to replace traditional volatile and toxic phthalate esters, presenting significant industrial application value.

Rheological and microscopic characterization and correlation analysis of asphalt under high-intensity ultraviolet radiation

The lower radiation intensity (2–20 W/m2) was widely used for asphalt ultraviolet (UV) aging. The effect of high-intensity radiation on asphalt properties and microscopic morphology is unknown. This study investigated the rheological behavior, microscopic characterization, and correlation analysis of SBS modified asphalt under high-intensity UV radiation. Rheological properties tests encompassed temperature sweep (TS), multiple stress creep recovery (MSCR), and frequency sweep (FS). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Gel Permeation Chromatography (GPC) tests were performed to reveal the microscopic characterization. In the early stages of UV aging, the rutting factor of asphalt was increased. The increment decreased as the UV aging time increased. The UV aging process did not alter the temperature sensitivity of asphalt. The complex shear modulus was influenced by UV radiation duration and loading frequency. Extended exposure to high-intensity UV radiation resulted in the formation of microcracks on the surface of the asphalt. The maximum molecular weight of the UV-aged asphalt was higher than that of the original asphalt. The degraded SBS modifier deteriorated the homogeneity of asphalt. The sulfoxide aging index, carbonyl aging index, number-average molecular weight (Mn), weight average molecular weight (Mw), and polymer dispersity index (PDI) presented a better correlation with rheological behavior indexes. The correlation between small molecule size (SMS), medium molecule size (MMS), and large molecule size (LMS) with rutting factor and complex shear modulus was poor. It was worth mentioning that the correlation between the MSCR test results and microscopic performance indicators was the best. Especially for the recovery rate and Jnr at 3.2 kPa, the mean absolute value of the correlation coefficient was 0.953.

Surface pre-treatment of aluminum alloy for mechanical improvement of adhesive bonding by maple-assisted pulsed laser evaporation technique.

Adhesive joints are widely used for structural bonding in various industrial sectors. The performance of bonded joints is commonly attributed to the cleanliness of the substrate and the pre-treatment of the surfaces to be bonded. In this study, the Matrix Assisted Pulsed Laser Evaporation (MAPLE) deposition technique was used for surface modification of aluminum (Al) plates by the deposition of poly(propylene glycol) bis(2-aminopropyl ether) (PPG-NH2) of different number average molecular weights (Mn) of 400 g mol-1, 2000 g mol-1, and 4000 g mol-1, respectively. Fourier-transformed infrared spectroscopy (FT-IR) analysis indicated the characteristic peaks for the deposited layers of PPG-NH2 of different molecular weights in all cases while scanning electron microscopy (SEM) revealed continuous layers on the surface of Al plates. In order to demonstrate alterations in the wettability of Al substrates, a crucial aspect in surface treatment and adhesive bonding, measurements of contact angles, surface free energies (SFE), and adhesion work (W a) were conducted. The tensile strength measurements were performed using the lap-joint test after applying the commercial silyl-based polymer adhesive Bison Max Repair Extreme Adhesive®. It was evidenced that at higher values of the SFE and W a, the tensile strength was almost 3 times higher for PPG-NH2 with Mn = 4000 g mol-1 compared with the untreated Al sample. This study provides valuable insights into the successful application of the MAPLE technique as a pre-treatment method for reinforcing adhesive bonding of Al plates, which can lead to improved mechanical performance in various industrial applications.

Temperature-sensitive fragrance-releasing polymeric microcapsules

This research aimed to control release of fragrance using thermally-actuated microcapsules so that the release rate shows a considerable change at a certain temperature. Accordingly, four different polymers, namely, two grades of poly(methyl methacrylate) having different molecular weight as well as two poly[(methyl methacrylate)–co-(2-ethylhexyl acrylate)] copolymers, which were synthesized in this work, were designated as capsules’ shell. Number-average molecular weight of the copolymers and one of the two used PMMA grades was in the range of 47 to 56 kDa while that of the other PMMA grade was 344 kDa. Furthermore, Tg of the lower molecular weight grade PMMA and the two copolymers was determined as 119.3, 72.2 and 66.3 °C, respectively, using DSC experiments. Subsequently, R-Limonene as a model fragrance, was encapsulated by either of the polymers using solvent evaporation method. Effect of various parameters, including molecular weight and Tg of the shell polymer and concentration of emulsifier, on morphological characteristics of the microcapsules were investigated. Using two microscopic techniques, it was observed that increment of molecular weight of shell polymer enhances microcapsules’ size, shell thickness and porosity. Moreover, elevation of emulsifier concentration to a certain value of 1.5 wt% was shown to lessen size and porosity of microcapsules. The fragrance release profiles were determined and fitted to several mathematical models, proving that at least one more mechanism, in addition to diffusion, is involved in the release, which was attributed to capillary effects in the shell pores. Moreover, a pronounced increase in release rate upon elevation of temperature from 5 to 15 °C was observed for either of the copolymer shells. The effect was ascribed to remarkable strengthening of segmental mobility of the copolymers due to elevation of temperature and can be regarded as a promising way for the fabrication of smart microcapsules capable of thermal controlling fragrance release.

Isolation and characterization of a hepatoprotective polysaccharide from Lonicera caerulea L. var. edulis Turcz. ex Herd. fruit against APAP-induced acute liver injury mice

The structure and bioactivities of a novel polysaccharide from Lonicera caerulea L. var. edulis Turcz. ex Herd. fruit (THP-3) were investigated. The crude polysaccharides of Turcz. ex Herd. (THP) were extracted by hot water extraction. After purification, the chemical structure of polysaccharides was identified. Then, a mouse model of acute drug-induced liver injury was constructed using 4-acetamidophenol (APAP) and pretreated with THP. The number-average molecular weight of THP-3 was 48.89 kDa and the mass average molar mass was 97.87 kDa. THP-3 was mainly composed of arabinose (42.54 %), glucose (27.62 %), galacturonic acid and galactose (29.84 %). The main linkage types of THP-3 were 1-linked Araf, 1,4-linked Glcp, and 1,3,6-linked Galp. In addition, after THP treatment, serum Alanine aminotransferase (ALT), Aspartate aminotransferase (AST) and γ-glutamyl transpeptidase (γGT) in AILI mice were successfully down-regulated. The results showed that THP could prevent the characteristic morphological changes of hepatic lobular injury and lipid depletion caused by APAP, reduced the level of oxidative damage in mice, increased the expression of APAP-induced hypolipidemia and related inflammatory indicators, and improved the detoxification function of liver. In general, the newly extracted THP polysaccharide has a good liver protection effect and is an ideal natural medicine for the treatment of liver diseases.

An asymmetric polymerized small molecular acceptor with temperature-dependent aggregation and superior batch-to-batch reproducibility for efficient all-polymer solar cells

Polymerized small molecular acceptors (PSMAs) have been instrumental in driving the advancements in power conversion efficiencies (PCEs) of all-polymer solar cells (all-PSCs). However, PSMAs commonly face challenges such as low molecular weights and notable batch-to-batch variation, posing significant obstacles to the transition of all-PSCs from lab to fab. Herein, a novel PSMA, which we refer to PAY-IT with an asymmetric conjugated skeleton is reported. The A–D1A'D2–A-type asymmetric monomer endows PAY-IT a random conjugated backbone, thus offering a desired temperature dependent aggregation behavior, which is hardly observed in conventional PSMAs. This characteristic facilitates chain growth during polymerization, thus yielding high molecular weights and low batch-to-batch sensitivity for the polymer. Moreover, the “S-shape” configuration of the asymmetric monomer endows PAY-IT good planarity and excellent charge transport property. As a result, the all-PSC consisted of PAY-IT and PM6 showcased a remarkable PCE of 14.9 %. More importantly, three batches of PAY-IT with number-average molecular weights ranging from 18.3 to 26.2 kDa exhibited nearly identical PCE (14.4–14.9 %), demonstrating superior batch-to-batch reproducibility of this polymer acceptor. This work explored PSMAs with asymmetric skeleton for the first time, and the results demonstrated a new design concept for the development of state-of-the-art PSMAs with minimal batch-to-batch variation.

Biodegradable composites fabricated using recycled poly(lactic acid)-based single-use coffee cup and regenerated cellulose fiber

ABSTRACT A series of biodegradable composites, including maleic acid-grafted recycled poly(lactic acid) (g-rPLA) and chemically modified lyocell (m-lyocell), were successfully synthesized. The rPLA was obtained from waste PLA-based single-use coffee cups. The storage modulus at −20°C of g-rPLA was increased from 1920 MPa for pure PLA to 3370 MPa for 5 wt% g-rPLA/m-lyocell composites, which is more than 75% enhancement. The number-average molecular weight after photodegradation for 60 days of g-rPLA and 5 wt% g-rPLA/m-lyocell composites was decreased by about 67.12% and 26.17% as compared to the samples before photodegradation, respectively. The results of photodegradations for composites indicate that the change of number-average molecular weight after photodegradation decreased by increasing the loading of m-lyocell. This result suggests that the existence of m-lyocell improved the UV protection ability of the g-rPLA. With the enhancement of mechanical properties and UV protection ability, this work provides an appropriate approach for the applications to reuse the waste PLA-based single-use coffee cups.

Efficient production of polyhydroxybutyrate using lignocellulosic biomass derived from oil palm trunks by the inhibitor-tolerant strain Burkholderia ambifaria E5-3.

Lignocellulosic biomass is a valuable, renewable substrate for the synthesis of polyhydroxybutyrate (PHB), an ecofriendly biopolymer. In this study, bacterial strain E5-3 was isolated from soil in Japan; it was identified as Burkholderia ambifaria strain E5-3 by 16S rRNA gene sequencing. The strain showed optimal growth at 37°C with an initial pH of 9. It demonstrated diverse metabolic ability, processing a broad range of carbon substrates, including xylose, glucose, sucrose, glycerol, cellobiose, and, notably, palm oil. Palm oil induced the highest cellular growth, with a PHB content of 65% wt. The strain exhibited inherent tolerance to potential fermentation inhibitors derived from lignocellulosic hydrolysate, withstanding 3g/L 5-hydroxymethylfurfural and 1.25g/L acetic acid. Employing a fed-batch fermentation strategy with a combination of glucose, xylose, and cellobiose resulted in PHB production 2.7-times that in traditional batch fermentation. The use of oil palm trunk hydrolysate, without inhibitor pretreatment, in a fed-batch fermentation setup led to significant cell growth with a PHB content of 45% wt, equivalent to 10g/L. The physicochemical attributes of xylose-derived PHB produced by strain E5-3 included a molecular weight of 722kDa, a number-average molecular weight of 191kDa, and a polydispersity index of 3.78. The amorphous structure of this PHB displayed a glass transition temperature of 4.59°C, while its crystalline counterpart had a melting point of 171.03°C. This research highlights the potential of lignocellulosic feedstocks, especially oil palm trunk hydrolysate, for PHB production through fed-batch fermentation by B. ambifaria strain E5-3, which has high inhibitor tolerance.

From Facile One-Pot Synthesis of Semi-Degradable Amphiphilic Miktoarm Polymers to Unique Degradation Properties.

We report a one-pot synthesis of well-defined A5B and A8B miktoarm star-shaped polymers where N,N-dimethylaminoethyl methacrylate (DMAEMA) and various cyclic esters such as ε-caprolactone (ε-CL), lactide (LA) and glycolide (GA) were used for the synthesis. Miktopolymers were obtained by simultaneously carrying out atom transfer radical polymerization (ATRP) of DMAEMA, ring-opening polymerization (ROP) of cyclic esters, and click reaction between the azide group in gluconamide-based (GLBr5-Az) or lactonamide-based (GLBr8-Az) ATRP initiators and 4-pentyn-1-ol. The relatively low dispersity indices of the obtained miktoarm stars (Đ = 1.2-1.6) indicate that control over the polymerization processes was sustained despite almost complete monomers conversions (83-99%). The presence of salts from phosphate-buffered saline (PBS) in polymer solutions affects the phase transition, increasing cloud point temperatures (TCP) values. The critical aggregation concentration (CAC) values increased with a decreasing number of average molecular weights of the hydrophobic fraction. Hydrolytic degradation studies revealed that the highest reduction of molecular weight was observed for polymers with PCL and PLGCL arm. The influence of the composition on the miktopolymers hydrophilicity was investigated via water contact angle (WCA) measurement. Thermogravimetric analysis (TGA) disclosed that the number of arms and their composition in the miktopolymer affects its weight loss under the influence of temperature.

Structural characteristics, immune-activating mechanisms in vitro, and immunomodulatory effects in vivo of the exopolysaccharide EPS53 from Streptococcus thermophilus XJ53

Our previous investigations have successfully identified the repeating structural units of EPS53, an exopolysaccharide derived from Streptococcus thermophilus XJ53 fermented milk, and substantiated its potential immunomodulatory properties. The present study further elucidated the structural characteristics of EPS53 and investigated the underlying mechanisms governing its in vitro immunoreactivity as well as its in vivo immunoreactivity. The results obtained from multi-detector high performance gel filtration chromatography revealed that EPS53 adopted a rigid rod conformation in aqueous solution, with the weight-average molecular weight of 1464 kDa, the number-average molecular weight of 694 kDa, and the polydispersity index of 2.11. Congo red experiment confirmed the absence of a triple helix conformation. Scanning electron microscopy showed that EPS53 displayed a three-dimensional fibrous structure covered with flakes. The in vitro findings indicated that EPS53 enhanced phagocytosis ability, reactive oxygen species (ROS) production, and cytokine levels of macrophages via the TLR4-mediated NF-κB/MAPK signaling pathways as confirmed by immunofluorescence staining experiments, inhibition blocking experiments, and Western blot assay. Additionally, the in vivo experiments demonstrated that EPS53 significantly increased macrophage and neutrophil number while enhancing NO and ROS levels in zebrafish larvae; thus, providing further evidence for the immunomodulatory efficacy of EPS53.

Interpenetrating polymer networks of polyurethane and polytriazole: Effect of the composition and number average molecular weight of glycidyl azide polymer on the mechanical properties and morphology

AbstractOn account of some special advantages of interpenetrating polymer networks (IPNs), the preparation of IPNs with excellent properties may be a promising way to strengthen the polyurethanes (PUs) and toughen the glycidyl azide polymer (GAP) based polytriazoles (PTAs). This work provides the effect of composition and number average molecular weight (Mn) of GAP on the mechanical properties and morphology of full‐IPNs. A series of IPNs based on the crosslinked Ace‐terminated GAP (Ace‐GAP) as polytriazole phase and crosslinked hydroxy‐terminated liquid fluorinated polymer (HTLF‐1500) as polyurethane phase (namely, GAP‐HTLF‐X full‐IPNs) were successfully fabricated via in situ polymerization without any catalysts at 80°C by azide–alkynyl click chemistry and hydroxyl‐isocyanate urethane reaction. These IPNs were characterized using attenuated total reflectance/Fourier‐transform infrared spectroscopy (ATR/FTIR), uniaxial tensile testing, swelling measurement, and scanning electron microscopy (SEM). The tensile strength of GAP‐HTLF full‐IPNs gradually increased by increasing the weight ratio of Ace‐GAP, but the breaking elongation dramatically decreased compared with elongation at break of HTLF polyurethane. In addition, a small Mn of GAP is beneficial in enhancing the tensile strength, elongation at break and toughness of the IPNs. However, a small Mn of GAP corresponds to increased difficulty of preparing GAP‐HTLF full‐IPNs. GAP1k‐HTLF full‐IPN was not successfully prepared. When the Mn of GAP was 2000 g/mol, the GAP2k‐HTLF‐80 full‐IPN exhibited prominent mechanical performance with a tensile strength of 83.1 MPa, elongation at break of 28.5% and fracture energy of 99.1 kJ/m3. Swelling measurement showed that when the weight ratio of GAP with larger Mn (5, 3, and 2 k) increased to more than 70%, the molecular interpenetration existed in the IPNs, demonstrating the presence of additional physical crosslinks and entanglement for full‐IPNs. SEM studies revealed that highly formed interpenetration and few microphase separations can be observed on the fracture surface of the IPNs with optimal mechanical properties. Combined with the results of mechanical properties, swelling measurement, and SEM studies, the degree of molecular interpenetration and microphase separation were beneficial to improve the mechanical properties of elastomers. This work can provide a certain guiding significance for the preparation of IPN with excellent properties.

Synthesis of propellant grade HHTPB by hydrogenation of HTPB using Pd-activated charcoal as catalyst

To derive more performance from the conventional composite propellant based on hydroxyl-terminated polybutadiene (HTPB) and ammonium perchlorate (AP), it is envisaged to hydrogenate HTPB, which increases the H/C (hydrogen to carbon ratio) of the base polymer. This paper attempts to describe the partial hydrogenation of HTPB using a catalytic method that uses palladium supported by activated charcoal as a catalyst and HTPB polymer as a precursor. HTPB has a hydroxyl value of 41.0 mg KOH/g with a number-average molecular weight (Mn) of 6150, polydispersity (PD) of 2.25 was used as a precursor. Iso-propyl alcohol (IPA) and toluene were used as a solvent media to disperse the HTPB polymer during hydrogenation. The estimate revealed an increase in specific impulse (ISP) up to 1.2 s with ∼37 % hydrogenated HTPB (HHTPB) as binder in composite solid propellants. Partial hydrogenation is only attempted to retain other process capabilities essential for realizing a defect-free solid propellant grain with good structural integrity. In contrast, others attempted to reach near saturation. A reactor capacity of 100 ml, operating at 60 bar pressure, was used to synthesize HHTPB, and the extent of hydrogenation was controlled based on the numerous experiments varying the reactor parameters like operating temperature, operating pressure, and solvent-to-polymer ratio for a given catalyst concentration. Detailed characterization of the end product by FTIR, 1H NMR and 13C NMR to reveal the degree of hydrogenation along with generic polymer characteristics. The measured hydroxyl value of HHTPB is comparable with HTPB; however, a marginal increase in molecular weight and polydispersity was noticed at 37 % conversion, wherein other researchers found a loss in -OH value. Thermogravimetry analysis revealed that no significant change in the gasification rate. A slight increase in the H/C ratio and calorific value was observed for HHTPB compared to HTPB. Despite the increase in viscosity of HHTPB, the increase in the vinyl-type functional distribution of HHTPB aids for better process-ability during propellant processing. However, the propellant formulation should be optimized with the help of plasticizers, solid loading, etc., to achieve the required properties.

Analytical data of Acacia nilotica var. Nilotica gum

This study aimed to characterize the exudate gum from Acacia nilotica var. nilotica in Sudan and compare its physicochemical properties to Acacia seyal var. seyal and Acacia senegal var. senegal (gum Arabic). Samples were collected from six different states in Sudan over three seasons. The gum had a moisture content of 10.50%, ash content of 1.86%, pH value of 5.19, specific optical rotation of +94.70, intrinsic viscosity of 10.44 cm3 g-1, nitrogen content of 0.024%, protein content of 0.16%, acid equivalent weight of 1907.82, and total uronic acid content of 10.18%. Sugar content analysis revealed arabinose (41.20%), galactose (17.43%), and rhamnose (10.68%). Potassium was the predominant cation, followed by calcium, magnesium, sodium, lead, and iron. Acacia nilotica was classified as part of the Gummeferae series and exhibited a positive specific optical rotation. The Number average molecular weight (Mn) was estimated using osmometric measurements and gel permeation chromatography. The gum had a higher molecular weight and lower intrinsic viscosity compared to gum Arabic, suggesting a spheroidal shape of molecule. Amino acid analysis showed similarities with gum Arabic, with hydroxyproline and serine as principal amino acids. Variations in cationic composition were attributed to differences in soil type among collection locations. KEY WORDS: Physicochemical characterization, Acacia senegal var. senegal gum, Acacia seyal var. seyal gum, Acacia nilotica var. nilotica gum, gammiferae Bull. Chem. Soc. Ethiop. 2024, 38(4), 839-852. DOI: https://dx.doi.org/10.4314/bcse.v38i4.2

Biobased high barrier copolyesters derived from furandicarboxylic acid and citric acid

Biobased feedstocks developed from renewable resources play a crucial role in polymers. Dimethyl octahydro-2,5-pentalenediol (MeOPD) with excellent thermal stability and rigidity is a biobased bicyclic diol derived from citric acid. In this work, MeOPD was first reacted with dimethyl carbonate (DMC) to form oligo (dimethyl octahydro-2,5-pentalenediol carbonate) (OMC). Subsequently, a series of poly(butylene-co-dimethyl octahydro-2,5-pentalenediol furanoate-co-carbonate) (PBMFC) polyesters with MeOPD units ranging from 5 to 31 mol% were synthesized via melt polycondensation from OMC, dimethyl furan-2,5-dicarboxylate (DMFD) and 1,4-butanediol (BDO). Due to the low reactivity of MeOPD, its actual content in copolymer is much lower than that in the feed, and as the MeOPD content rises, the number-average molecular weight of PBMFCs drops from 25,200 g/mol of PBMFC5 to 12,800 g/mol of PBMFC31. Despite the presence of MC units weakens thermal stability, PBMFCs still maintain good thermal stability, evidenced by Td,5% ranging from 294-325 °C in N2 and from 295-339 °C in air. The mechanical properties are also satisfactory, exhibiting tensile modulus ≥ 500 MPa, tensile strength ≥ 23 MPa, and elongation at break ≥ 150 %. Compared to PET, PBMFCs demonstrate commendable gas barrier properties, with CO2 and O2 barrier capability being 4.7–11.0 times and 2.0–3.6 times that of PET, respectively. All results indicate that PBMFCs can serve as a renewable potential material for packaging application.