•CO2 adducts from polyethylenimines grafted with C4 to C16 alkyls were synthesised.•These CO2 adducts can release CO2 to blow castor oil-based PUs.•The CO2 adduct with C8 alkyl chain is the best blowing agent.•The blowing agents are climate-friendly and the PU foams are more renewable.Alternatives to climate changing blowing agents (e.g. chlorofluorocarbons) and petroleum sourced raw materials (e.g. polyether polyols) are very attractive in the polyurethane (PU) foam industry. We explore a series of CO2 adducts from a branched polyethylenimine (bPEI) alkylated with C4 to C16 alkyl glycidyl ethers. These adducts can serve as CO2 releasing blowing agents during the exothermic polymerisation of PUs. A 13% alkylation of the bPEI amine groups enhances the dispersibility of the resultant CO2 adducts into the PU foaming mixtures containing a castor oil-derived polyol. In particular, the CO2 adduct with a C8 alkyl (2-ethylhexyl) side chain possesses the best dispersibility and is among the most effective in decreasing the foam density. It generates PU foams whose density and compressive strength are almost suitable for thermal insulation of underground steel pipes. This is the first report showing that PU foams from biomass polyols can be blown by CO2 adducts that are environmentally neutral.Download high-res image (255KB)Download full-size image

•Transesterification synthesis of APCs from Cn diols (n = 2–6) and diethyl carbonate are investigated.•Formation pathways towards all the detected by-products and the APC ether linkages are delineated.•Cyclic carbonates and cyclic ethers are formed via growing chain backbiting.•THF and allyl alcohol are generated from the decarboxylation of corresponding cyclic carbonates.An overall picture of the reaction pathways towards the side products and final polymers during the transesterification synthesis of biodegradable aliphatic carbonates (APCs) were delineated for the first time. Catalysed by sodium ethoxide, the normal reaction between α,ω-diols (carbon number n = 2–6) and diethyl carbonate generates APC oligomers with propagating terminal alkoxide anions. These anions can backbite at the nearest carbonate carbons or the nearest carbonate α-CH2 carbons in the same APC chains, eliminating corresponding cyclic carbonates or cyclic ethers. Also, each alkoxide anion can randomly attack a carbonate α-CH2 carbon in another APC chain, generating ether linkages in the final polymers whose percentages are about 100%, 1.35%, 0.08% and 0% for n = 2, 3, 4 and 5, respectively. The content of cyclic carbonates shows a similar decreasing trend; ethylene carbonate (n = 2) even predominates over the final polymer while trimethylene carbonate (n = 3) and 1,4-butylene carbonate (n = 4) are only minor by-products. Moreover, the latter two cyclic carbonates are not stable enough and can further decarboxylate, forming relatively high amount of allyl alcohol and tetrahydrofuran, respectively. However, trimethylene oxide (n = 3) and tetrahydropyran (n = 5) are minor cyclic ethers. The thorough understanding of the chemical process is essential to improve the APC synthesis.Download high-res image (166KB)Download full-size image

The polyurethane foam community has encountered increasing pressure to replace the ozone depleting and/or global warming blowing agents, such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). In this study, a series of polypropylene glycol-grafted polyethyleneimines (PPG-PEIs) were synthesised with the grafting rate ranging from 9% to 19%. Their CO2 adducts (PPG-PEI–CO2s) are thermally instable and can release CO2 to blow polyurethanes, whose polymerisation is exothermic. A PPG grafting rate of about 11% (found in sample 1:9-PPG-PEI–CO2) is enough to homogenously disperse the blowing agent into polyurethane raw materials. The CO2 adducts with a PPG grafting rate of about 11–14% are particularly effective to decrease the foam density. The foams blown by 1:9-PPG-PEI–CO2 possess a thermal conductivity higher than those of traditional polyurethane foams (0.040 vs. 0.020–0.027 W m−1 K−1), hindering their application in thermal insulation. However, these new blowing agents are advantageous in zero emission of volatile organic compounds (VOCs), as well as their climate friendliness. We believe these blowing agents can be used in thermally insulating foams in cars and aircraft where VOCs are strictly regulated.

We synthesised a series of ω-aminoalkyl sodium hydrogen phosphates (AAP-n-Na, n = 3, 4, 5, 6, purity > 99%), which have potential applications as bioactive cosmetic ingredients and surface modifiers of bone minerals (i.e. hydroxyapatites). Results from Fourier transformed infrared (FTIR), nuclear magnetic resonance (NMR) and high resolution mass spectroscopy, and elemental analysis all matched their chemical structures. The acid dissociation constants (pKa's) of each AAP-n (acid form of AAP-n-Na, n = 2–6) were measured by potentiometric titration, showing a general increasing trend with an increase in the chain length of AAP-n. However, the pKa3 constant, which corresponds to the deprotonation of the ammonium group in AAP-n-Na, displayed an unusual decrease when n = even. This odd–even effect can be explained by the pairwise self-association of AAP-n-Na molecules in water where intermolecular hydrogen bonding in case of n = even is weaker than that in case of n = odd. All AAP-n-Na at concentrations up to 0.1% (w/v) were non-toxic to L929 fibroblasts and MG 63 osteoblast-like cells in terms of cell growth and morphology. These basic data were important for applications of AAP-n and their salts in biomedical engineering.A series of ω-aminoalkyl sodium phosphates (AAP-n-Na) were synthesised and characterised in terms of chemical structure, pKa constant and cytotoxicity.

In this study, nanohydroxyapatite/polyurethane (nHA/PU) composites with various contents of methoxypoly(ethylene glycol) modified nHA (0 wt%, 10 wt%, 20 wt% and 30 wt%) were prepared by solution blending process. The physicochemical properties of the composite membranes were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electronic microscopy (TEM), Differential scanning calorimetry (DSC), Thermo gravimetric analysis (TGA) and tensile tests. TEM photos of the nanocomposites showed that the nHA was uniformly dispersed in the polymer matrix. The membrane with 10 wt% nHA showed the highest tensile strength which was about 75% higher than that of the pure PU membrane. However, the tensile strength decreased when high content (above 20 wt%) fillers were added, which was still higher than that of pure PU. TGA measurements suggested that the thermal stability of the membranes was improved owing to nHA fillers. XRD and DSC results illustrated that the crystallinity of PU soft segments decreased with the increasing content of nanoparticles in the composites.

•Amorphous calcium phosphate (ACP) nanoparticles were synthesized in methanol/water mixtures.•The ACP colloidal particles were stabilized by polyethylene glycol chains around each particle.•The ACP powders remained amorphous for over 1 year.Amorphous calcium phosphates (ACPs) usually exhibit superior bioactivity and bioresorbability over crystalline calcium phosphates. However, due to the tendency of transforming into more stable hydroxyapatites (HAs) during storage, the commercialization of ACPs is still restricted. In this work, a monophosphate-terminated methoxy-poly(ethylene glycol) (mPEG-OPO3H2) was used as an in-situ chemical stabilizer and surface modifier to ACPs’ nanoparticles which were synthesized in methanol/water mixtures. The results indicate that the high content of methanol (50% and 75%, v/v) favors the formation of ACPs and the low content (0% and 25%) of methanol results in HA crystals. All the calcium phosphates (CaPs) displayed a colloidal appearance in the corresponding mother solution. In addition, the centrifuged precipitates can be redispersed in some organic solvents. For example, the methanol colloids still showed narrow particle size distributions (20 and 120 nm) without any sedimentation after 3 months. The ACP powders can maintain their amorphous structure up to 1 year. Such long-term storage stability and unique organic redispersibility are attributed to the formation of polyethylene glycol (PEG) brushes onto the individual ACP nanoparticles.Amorphous calcium phosphate colloidal particles were prepared in methanol/water mixtures, stabilized by polyethylene glycol chains around individual core particles.

Traditional poly(ethylene glycol) (PEG)-modified polyurethanes usually exhibit high biocompatibility, but still lack reactivity with biological molecules to induce appropriate cell and tissue responses. In this study, PEG diglycidyl ether (Mn = 526 Da) and PEG bis(amine) (Mn = 1000 Da) were respectively grafted onto carboxyl-group-containing poly(carbonate urethane) backbones that chain-extended with lysine, to generate reactivity while maintaining biocompatibility. The PEG chains disordered and plasticized the hard segments where they attached, reducing H-bonded urea groups and lowering glass transition temperatures. The Mn ranged from 33,000 to 70,000 Da for the precursor polyurethanes, which largely decreased by 24–75% following PEG grafting. Hemocompatibility was enhanced due to the flexibility and hydrophilicity of the PEG chains. Solutions of the PEG-grafted polyurethanes were transformed into hydrocolloids when dropped into water. Reactivity was proved by immobilization of albumin onto the colloidal particles. These new functional PEG-grafted polyurethanes can potentially form multifunctional bioconjugates for applications as biomaterials and in pharmaceutics.