Synthesis,characterization, and evaluation of novel polyhydantoins as gas separation membranes

Novel polyhydantoins ( PHYs ) were synthesized from original aromatic diisocyanates and bisiminoacetates by a two‐step polycondensation procedure, which involved the cyclization of polyurea intermediates promoted by acid catalysis. The physical properties of the novel PHYs were evaluated by comparing them with a classical PHY derived from 4,4′‐methylenediphenyl diisocyanate. All PHYs were soluble and could be processed into dense films, which showed good mechanical properties (tensile strength up to 110 MPa) and thermal stability of >400 °C. High glass transition temperatures (T_gs), ranging from 260 to 410 °C, were observed. Fractional free volume (FFV) was strongly dependent on the chemical structure, and a linear correlation between gas permeability and FFV of PHYs could be found. The gas separation properties were comparable to those of the commercial polyimide Matrimid^®, with the exception of one of the PHYs which exhibited very promising properties as its gas productivity was comparable to the gas separation performance of well‐established experimental polyimides. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4052–4060     

Grafting of polyethylene glycols onto nanometer silica surface by 1,4‐phenylene diisocyanate

In this paper, polyethylene glycol (PEG) molecules have been grafted onto the surface of nanometer silica in toluene by using 1,4‐phenylene diisocyanate (PPDI) as a coupling agent, and dibutyltion dilaurate (DBTDL) as a catalyst. This process was executed by using a one‐step procedure involving a first reaction of PPDI with silica and a subsequent reaction of isocyanate‐bound silica with PEG. The PEG‐grafted silica has been characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and SEM analyses. The effects of reaction time, temperature and molar ratio of reactant on the effectiveness of the surface grafting were also investigated. Optimum grafting conditions of PEG were obtained at the temperature of 80 °C for 8 h. Maximum grafting of PEG molecules ratio was 22.6%, and maximum overall grafting ratio was 35%, as determined by TGA. Copyright © 2010 John Wiley & Sons, Ltd.     

Artifact Formation In The Soxhlet Extraction Of Environmental Samples With Acetone

Abstract

A study was performed to confirm suspected artifactual formation of acetone derivatives during the Soxhlet extraction of soil samples with acetone. The conditions employed simulated very closely those normally employed for the extraction of soils for neutral and moderately polar organic compounds such as pesticides. A series of acidic, neutral, and basic organic-free soils were extracted with hexane/acetone solvent mixture and the extracts concentrated in a Kuderna-Danish apparatus. The extracts were analyzed by capillary column gas chromatographic mass spectrometry. In nearly all cases, simple dimeric products such as diacetonecohol and mesityl oxide were formed in varying amounts. The acidified and basic soils yielded complex mixtures of dimers, trimers, tetramers and other complex homologs. Some of the more common substances found include phorone, mesitylene and isophorone. The latter substance is listed as an EPA priority pollutant.     

Preparation and Characterization of Poly(L-lactic acid)/Polybutadiene Block Copolymers

A two-step process to prepare poly(L-lactic acid) (PLLA)/polybutadiene (PB) block copolymers was studied. Melt polymerization was used to prepare poly(L-lactic acid) terminated with hydroxy groups, at the same time hydroxy-terminated polybutadiene and 1,6-hexamethylene diisocyanate were employed to synthesize isocyanate-terminated polybutadiene (ITPB). Then PLLA and ITPB were reacted with different PB/PLLA weight ratios. Consequently, a series of PLLA/PB copolymers with linear or crosslinked chains was obtained. Viscosity of the linear copolymer was measured by an Ubbelohde viscometer. Swelling characteristics and crosslink density of the crosslink copolymer were investigated. Fourier transform infrared and proton nuclear magnetic resonance were used to characterize the structure of the copolymer, and dynamic mechanical analysis (DMA) was applied to characterize its thermal properties. Mechanical property measurements showed that a toughened PLLA polymer was synthesized. Atomic force microscope was utilized to characterize its micro-morphology.     

CURE CHARACTERISTICS OF HYDROXYL TERMINATED POLYBUTADIENE PREPOLYMER WITH BLOCKED TOLUENE DIISOCYANATE-Ⅰ

Controlled release of TDI and hence the cure characteristics of several blocked TDI with HTPB are reported. The reactions were followed through viscosity measurements as a function of time and temperature under the catalytic influence of triethylamine. The effect of nature of substituents present on the end capping substrate, temperature, solvent, basicity of catalyst and kinetics thereon have been studied.     

Mechanical properties of solvolysis lignin-derived polyurethanes

In order to study the tensile properties of solvolysis lignin polyurethanes, polyurethane (PU) films were prepared from the solvolysis lignin (SL)–polyethylene glycol (PEG)–diphenylmethane diisocyanate (MDI) system, and in addition to this further PU films were also prepared from the SL–MDI system. In the SL–PEG-MDI system, the SL content, the molecular weight of PEG and the NCO:OH ratio were varied in order to control the physical properties. The tensile stress and Young's modulus of the PUs of the SL–PEG–MDI type increased with increasing SL content and NCO:OH ratio. The tensile properties of the PUs from the SL–MDI system showed no NCO:OH ratio dependency; i.e. the mechanical properties of PUs are not influenced by the change in crosslinking. It is possible to control the tensile properties of PUs of the SL–PEG–MDI type by changing the content of PEG and SL at a constant NCO:OH ratio.     

Chitosan Cross-Linked Films for Drug Delivery Application

This work evaluated such a cross-linked chitosan based controlled release device to be later used for sustained drug release. Cross linking was required to control chitosan swelling/deswelling rate. Hexamethylene 1,6-Bis (aminocarboxysulfonate), a bisulfite blocked diisocyanate obtained by the reaction of 1,6 Hexamethylene Diisocyanate and Sodium bisulfite, was used as cross linking agent. Two films formulations were tested: 30 and 50% cross-linked, and they were prepared by solvent evaporation technique. Chitosan cross-linked films were characterized for cross linkage by FTIR, for hydrophilicity by Contact Angle and for swelling behavior by Gravimetric method. Cross linking reaction was confirmed by FTIR. Moreover, cross linking increased the hydrophilic character of cross-linked films and suppressed swelling. However, 30% cross-linked film swollen less than the 50% one, while 50% cross-linked film swollen less than chitosan film itself. This behavior was attributed to the hydrophilic character of the cross linking agent and to the polymeric network formation by cross linking.     

二苯甲烷二异氰酸酯(MDI)聚合反应动力学研究

采用TG-DSC-DTG技术研究了二苯甲烷二异氰酸酯(MDI)在流动高纯氮气中的聚合反应动力学. 利用Flynn-Wall-Ozawa法进行了非等温动力学计算, 得到了MDI聚合反应的动力学参数, 通过Satava-Sestak法、Coats-Redfern法对不同机理模型进行选取, 确定了MDI聚合反应的机理为随机成核和随后生长模型, 机理函数为 . 由以上三种方法计算结果表明: MDI聚合反应的表观活化能E＝58.42 kJ•mol^－1, 指前因子A＝ 5006 min^－1, 动力学方程为: [－ln(1－α)]^1/2＝5006exp(-58.42*1000/8.314T)t.     

Controlled Release of Model Drug from Biodegradable Segmented Polyurethane Ureas: Morphological and Structural Features

Segmented polyurethane ureas (SPUUs), which are being used in implant devices, were evaluated as drug delivery matrices using theophylline as a model drug without much sacrificing the mechanical properties of films after drug doping. SPUUs were synthesized from aliphatic diisocyanate (lysine methyl ester diisocyante (LDI)), poly(caprolactone) diol with molecular weights 530, 1250 and 2000 and 1,4-butanediamine. Three series of segmented SPUUs were prepared with various soft segment lengths and were characterized by Fourier transform infrared spectroscopy, dynamic viscoelastic measurements and tensile testing. A single tanδ peak was observed in dynamic viscoelastic measurements, which revealed phase mixing of hard and soft segments. Low elongation at break was observed in case of PCL 2000 based SPUUs, may be due to partial cystallization of PCL segment. The degradation of SPUUs in alkaline solution and in vitro drug release of theophylline in pH 7.4 buffer were also investigated. The drug release behavior from these films were analyzed by the exponent relation M_t/M_∞ = ktⁿ, where k and n are constants and M_t/M_∞ is the fraction of drug released until time, t. The constant n was found to be close to 0.5 in all samples, which suggests the release of drug from these polymers can be explained by the Fickian diffusion model.     

Preparation of Aqueous Polyurethane Dispersions Using Aromatic Diisocyanate

Aqueous polyurethane dispersions were prepared by the reaction of hydroxyl-terminated poly(ethylene adipate), ethylene glycol, dimethylol propionic acid and aromaic diisocyante, 4,4′-diphenylmethane diisocyanate. The influence of molecular weight of oligoester and molar ratio between isocyanate and hydroxyl groups (NCO/OH) in the prepolymerization step were investigated. Molecular weight, particle size and particle size distribution were measured and compared. It was verified that the molecular weight increases with increasing in NCO/OH molar ratio. The results suggest that the hard segment content plays an important role in particle size and particle size distribution of the dispersions.