Tuning the properties of segmented polyurea by regulating soft‐segment length

Polyurea is being widely advocated as a “retrofit” coating on structures, which mandate protection against blast. The physical properties of polyurea can be tuned by judicious choice of reactants, and the processing methodology employed for its preparation. The purpose of this study is to establish the dependence of material properties on the soft segment length in polyurea. Polyurea formulations were prepared by reaction of commercially available isocyanate prepolymer with poly(propylene oxide) based amines of varying molecular weights (230–2000 g/mol). The effect of increasing the soft segment length on the mechanical properties of polyurea under both quasi‐static as well as dynamic conditions was determined. Ductility was found to increase proportionally with increasing soft segment length, with a concomitant decrease in the tensile strength. All the compositions exhibited sub‐ambient glass transition temperature, which was found to reduce with increasing soft‐segment length. Time–temperature superposition principle was used to arrive at master curves for all compositions. The frequency essential to initiate the process of dynamic “rubber to glass” transition was found to be directly proportional to the soft segment length. All the formulations were found to be capable of exhibiting an elastomeric response even under high frequencies typical of blast loadings. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46284.     

Emergence of time‐dependent material properties in chain extended polyureas

In this article, we report the emergence of material properties of polyurea over a finite time frame. Due to the rapid isocyanate–amine reaction, polyurea formation occurs practically instantaneously. Despite being an “instant‐curing” system, the material properties of polyurea evolve substantially with time: phenomenon, which warrants a methodical study. The curing process of polyurea formulations, containing both aliphatic and aromatic chain extender, has been studied systematically with an aim to gain insight into the time frame associated with its curing and subsequent stress relaxation. Formulations containing aromatic chain extender mandated relatively lesser time to “gel,” but the complete disappearance of NCO absorbance mandated much longer periods ～7 h. Interestingly, in all the formulations, mechanical properties improved with time and reached their optimal properties over a period of 15 days. This improvement has been attributed to several processes simultaneously occurring within the matrix; the foremost being the relaxation of internal stresses which tend to buildup in the polymer during the spray coating process. In addition, significant changes occur in the internal morphology of segmented polymers, which in turn is a result of H‐bond rearrangement.     

Factors that enable the formation of porous strut morphology in “Swiss Cheese” viscoelastic polyurethane foam technology

Several factors were investigated that affect porous strut morphology in the Highly Porous Supersoft Viscoelastic Foam. Porous strut morphology and high air permeability of the Swiss‐Cheese TDI VE technology were found to be enabled by the combination of immiscible polyether polyols mixed with a third, highly hydrophobic polyol of high equivalent weight that is immiscible with either of the first two polyether polyols. Completely “punctured through” pores in struts were observed more frequently in foam samples where an isocyanate index of 90 versus 100 was employed. When isocyanate index is fixed to 90, it was found that a poly(1,2‐butylene oxide) (“PBO”) monol level of ≥3.0 parts per hundred polyol (pphp) was needed to see the first signs of a “punctured” pore strut morphology. Studies show that a “high‐Eq.Wt.‐hydrophobic‐polyol‐leaving‐voids” model is consistent with observed results. Hydrophobic polyols that allowed the formation of porous strut morphology included BO‐4000 monol (Eq.Wt. ～ 4000) and PBD‐10000 diol (Eq.Wt. ～ 5000). The use of these hydrophobic polyols also yielded air flows that were significantly higher than those obtained with the “standard” viscoelastic foam formulations that were prepared at the same isocyanate index. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44449.     

Effects of shell crosslinking on polyurea microcapsules containing a free‐radical initiator

Microencapsulation of a material is often used when a controlled release of a substance is desired. This study examines the effects of crosslinking in polyurea microcapsule shells on stability of microcapsules containing the free‐radical initiator cumene hydroperoxide (CHP). Crosslinking of polyurea shells was varied by using amine monomers containing different amine functionalities, and/or changing the isocyanate/primary amine ratio. Thermogravimetric analysis was performed to determine thermal properties of these microcapsules, and the pot lives of monomer systems containing these microcapsules were measured. Thermal stability is greater with a moderate degree of crosslinking from a trifunctional amine, and decreases when crosslinking is increased through use of higher amine functionality. Stability in monomer media generally increases with increased crosslinking through higher amine functionality, but is less predictable due to crosslinks formed between capsules. Generally, increasing crosslinking through altering the isocyanate to primary amine ratio decreases capsule stability in both dry and monomer storage. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42408.     

Effect of surface modification of graphite oxide on the morphological,thermal, and mechanical properties of polyurea/graphite oxide composites

Three surface modifiers, namely, aminopolyether (D2000), phenyl isocyanate, and poly(ethylene glycol) (PEG800), which have different affinities to the hard and soft segments in polyurea, were used to synthesize functionalized graphite oxides (GO). The PEG800‐modified (PEG800‐GO) and phenyl isocyanate‐modified (i‐GO) GOs were highly exfoliated and dispersed in DMF, whereas the D2000‐modified GO (D2000‐GO) produced some precipitates. Polyurea/GO composites were prepared using a solution‐blending method, in which functionalized GO platelet suspensions in dimethyl formamide were used. Results show that PEG800‐GO and i‐GO are uniformly dispersed throughout the polymer matrix on a nanoscale, whereas D2000‐GO forms visible aggregates. The well‐dispersed GO platelets improved the thermal stability and mechanical properties of polyurea. PEG800‐GO, which has a strong affinity for the soft segments, shows a more significant reinforcing effect. At 2.0 wt % GO loading, the tensile strength of polyurea was enhanced by ～75%. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39775.     

The chain extension of anionic prepolymers in the preparation of aqueous poly(urethane–urea) dispersions

Anionic polyurethane prepolymers end‐capped with isocyanate groups were dispersed and chain‐extended in aqueous media using three different extension agents: hydrazine, 1,2‐ethylene diamine (EDA) and 1,2‐propylene diamine (PDA). Two types of prepolymer were used. The first was prepared from isophorone diisocyanate (IPDI), α,α‐dimethylol propionic acid (DMPA) and poly(propylene oxide) diol (PPO) and the second from α,α,α′,α′‐tetramethyl‐1,3‐xylylene diisocyanate (m‐TMXDI), poly(caprolactone) diol (PCL) and DMPA. The colloidal particles which formed in the dispersion process and the constituent poly(urethane–urea) chains were characterised by a combination of dynamic and static light scattering, gel permeation chromatography and FTIR spectroscopy. Using EDA as the extender, a study was made of how the degree of extension depended on the molar ratio of amine to isocyanate groups, [NH₂]/[NCO] (= R_{A, I}). It was found that using a stoichiometric balance of isocyanate and amine groups did not lead to high degree of extension, and better chain extension was obtained at lower R_{A, I} values. In a comparative study using stoichiometric balances of isocyanate and amine groups, the degrees of extension obtained using PDA and EDA were approximately the same, while hydrazine was the least effective. Force–extension studies were carried out on samples prepared from films cast from the aqueous poly(urethane–urea) dispersions in order to assess the influence of chain‐extender type and stoichiometry on bulk properties; values of Young's modulus, tensile strength and maximum extension are reported. Copyright © 2003 Society of Chemical Industry     

Kinetics of isocyanate amine reactions

Development of polyurea-urethane and polyurea reaction injection molding (RIM) systems has created a need for kinetics of polyurea formation. Adiabatic batch reactions in solution were used to determine heats of reaction and relative reactivity of several aromatic amines and n-butanol with phenyl isocyanate (PI). In addition to comparing times required to reach 25, 50 and 75% conversion for both catalyzed and uncatalyzed reactions, n-th order models with Arrhenius rate constants were used to fit some of the exotherms. The reaction of 3,5-diethyl toluene (2,4 and 2,6)-diamine and PI could not be modeled due to unequal reactivity of the two amine groups. This unequal reactivity was studied using high performance liquid chromatography (HPLC) separation of the reaction products. The reactions of primary aliphatic amines and aromatic isocyanates were too rapid to be monitored in the batch apparatus. With a flow apparatus the reaction half time was estimated to be ～ 0.002 s.     

Enhancing the stability of UV‐curable thiol/vinyl carbonate resins

In this study, the effect of various stabilizer systems on low‐cytotoxic thiol/vinyl carbonate formulations was evaluated with the aim to inhibit premature dark polymerization reactions. The addition of hydroxybenzene‐based radical scavengers such as pyrogallol (PyG), hydroquinone monomethyl ether (MEHQ), or butylated hydroxytoluene (BHT) resulted in a significantly decelerated increase in viscosity compared to formulations without stabilizers during a defined storage period at 50 °C. The usage of bicomponent stabilization systems in appropriate concentrations further reduced the viscosity increase for nonpigmented formulations. The most effective heterosynergistic stabilization system based on PyG and diisoctyl phosphonic acid (9 mM/90 mM) exerts only a minor influence on the polymerization performance, which was shown by photo‐DSC measurements. The herein presented stabilization of vinyl carbonate/thiol resins exhibits a significant contribution to bringing these low‐toxic building blocks into industrial applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44934.     

Synthesis and characterization of poly(propylene glycol) polytrioxamide and poly(urea oxamide) segmented copolymers

This report describes the synthesis and characterization of unprecedented poly(propylene glycol) (PPG) polytrioxamide and poly(urea oxamide) (UOx) segmented copolymers containing monodisperse hard segments. Synthesis of the segmented copolymers relied on an efficient two‐step end‐capping sequence, which resulted in novel difunctional oxamic hydrazide‐terminated polyether oligomers. Polymerization with oxalyl chloride or 4,4′‐methylenebis(cyclohexyl isocyanate) provided the desired segmented copolymers displaying thermoplastic elastomeric behavior. Variable‐temperature Fourier transform infrared and ¹H NMR spectroscopies confirmed the presence of hard segment structures and revealed ordered hydrogen bonding interactions with thermal dissociation profiles similar to those of polyurea and polyoxamide copolymer analogs. Dynamic mechanical analysis of PPG‐UOx exhibited a longer, rubbery plateau with increased moduli compared to PPG polyurea, and tensile analysis revealed a dramatic increase in copolymer toughness due to enhanced hydrogen bonding. A new step‐growth polymerization strategy is described that is capable of producing tunable hydrogen bonding segmented copolymer architectures. © 2013 Society of Chemical Industry     

Preparation of soluble copolyurethaneimide containing oxyethylene and oxypropylene units

Soluble copolyurethaneimides were synthesized by the isocyanate method in a solution of N‐methyl‐2‐pyrrolidone (NMP). The isocyanate‐terminated prepolyurethane prepared from low molecular weight poly(ethylene glycol) (PEG) or poly(propylene glycol) (PPG) and methylene diisocyanate was reacted with pyromellitic dianhydride at high temperature. The resulting copolyurethaneimides were soluble in polar solvents like N‐methyl‐2‐pyrrolidone and N,N'‐dimethylformamide. The film‐forming properties were investigated by changing the molecular weights of PEG and PPG. With PPG, the film‐forming property was enhanced. The inherent viscosity, solubility, thermal property, molecular weight distribution, and mechanical property were compared with the aromatic polyimide. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3502–3507, 2002     

高固含量聚脲多元醇的合成研究

通过选择合适的基础聚醚、多元胺、异氰酸酯、分散剂,在实验室以间歇法合成了聚脲多元醇,考察了基础聚醚、多元胺、异氰酸酯、分散剂对聚脲多元醇黏度和固含量的影响,制得的聚脲多元醇不挥发物质量分数15%²0%,贮存稳定。     

Evaluation of thermo‐viscosity parameters of dextran in polar and nonpolar solvent

Some thermo‐viscosity parameters like Viscosity‐molecular weight constant (K), the short‐range parameter, (A) and long‐range parameter (B) have been evaluated for the polymer “Dextran” of three different molecular weights (M?_w = 19,500, 75,000, and 250,000) in three different solvents like 6 (M) aqueous urea, 2 (M) aqueous glycine, and 50% aqueous glucose at temperatures ranging from 25 to 50°C. The study reveals that the viscosity‐molecular weight constant (K) decreases with increase in temperature for polar solvents like aqueous urea and aqueous glycine. The value of “K” increases with the rise in temperature within the range of 25 to 35°C in case of a nonpolar solvent aqueous glucose and then “K” decreases with the increase in temperature within the range of 40 to 50°C for the nonpolar solvent aqueous glucose. The short‐range parameter (A) shows the same trend as shown by “K” and the long‐range parameter “B” exhibits no definite trend with the variation of temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 440–452, 2001     

Compatibilizing efficiency of copolymer precursors for immiscible polymer blends

An anhydride‐terminated polystyrene (PS‐b‐Anh) as a block copolymer precursor and a copolymer (PS‐co‐TMI) of styrene (St) and 3‐isopropenyl‐α,α‐dimethylbenzene isocyanate (TMI) as a graft copolymer precursor are chosen to investigate the effect of the type of the copolymer precursor on its compatibilizing and stabilizing efficiency for polymer blends. Results show that during the melt blending of the PS and PA6, the addition of PS‐b‐Anh dramatically decreases the size of the dispersed phase domains, irrespective of its molecular weight. This indicates that a diblock copolymer PS‐block‐PA6 (PS‐b‐PA6) is formed by a reaction between the terminal anhydride moiety of the PS‐b‐Anh and the terminal amine group of the PA6. When PS/PA6 (30/70) blends are annealed at 230°C for 15 min, their morphologies are much more stable in the presence of the PS‐b‐Anh block copolymer precursor than in the presence of the PS‐co‐TMI graft copolymer precursor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Template-Free Preparation of a Mesopore-Rich Hierarchically Porous Carbon Monolith from a Thermally Rearrangeable Polyurea Network

A mesopore-rich, hierarchically porous carbon monolith was prepared by carbonizing a polyisocyanurate network derived by thermal rearrangement of a polyurea network. The initial polyurea network was synthesized by the cross-linking polymerization of tetrakis(4-aminophenyl)methane (TAPM) and hexamethylene diisocyanate (HDI) in the sol-forming condition, followed by precipitation into nanoparticulate solids in a nonsolvent. The powder was molded into a shape and then heated at 200–400 °C to obtain the porous carbon precursor composed of the rearranged network. The thermolysis of urea bonds to amine and isocyanate groups, the subsequent cyclization of isocyanates to isocyanurates, and the vaporization of volatiles caused sintering of the nanoparticles into a monolithic network with micro-, meso-, and macropores. The rearranged network was carbonized to obtain a carbon monolith. It was found that the rearranged network, with a high isocyanurate ratio, led to a porous carbon with a high mesopore ratio. The electrical conductivity of the resulting carbon monoliths exhibited a rapid response to carbon dioxide adsorption, indicating efficient gas transport through the hierarchical pore structure.     

聚脲交联改性丙烯酸酯弹性乳液的制备与性能研究

为了在性能上对聚脲交联改性后的丙烯酸酯乳液(PUA)和纯丙乳液(以)进行比较,文章以丙酮为溶剂,通过端氨基聚醚和甲苯二异氰酸酯的缩合反应合成了端异氰酸酯基聚脲预聚物,由于丙酮与胺基的可逆缩合反应,降低了胺基与异氰酸酯基反应的活性,从而可以更好地控制反应速度,降低副反应的发生几率.聚脲预聚体经丙烯酸羟乙基酯双键封端制备了含有2个双键的聚氨酯脲大单体,以其为外交联剂,通过与甲基丙烯酸甲酯、丙烯酸丁酯的乳液共聚反应制备了聚氨酯脲改性的纯丙弹性乳液,对乳液涂膜进行了FT-IR,DSC和TGA的表征.研究表明:PUA涂膜比PA涂膜具有更好的热稳定性、机械性能、耐低温性以及耐溶剂性.     

Hybrid thermosets from polyisocyanate/water glass/emulsifier systems: Effects of melamine‐formaldehyde resin

Melamine‐formaldehyde resin (MF) was selected as potential reactive emulsifier for polyurea‐based thermoset resins produced from polyisocyanate/water glass (WG)/emulsifier systems. As emulsifier tricresylphosphate and/or MF served for the initial water‐in‐oil type (“water” = WG; “oil” = polyisocyanate + emulsifier) emulsions. The MF content of the systems has been varied (≤15 wt %) and its effect on the structure, mechanical, thermal and flammability properties of the final polyurea‐based thermosets studied. It was found that MF is a suitable emulsifier, which can fully replace the phosphate without negatively affecting the properties of the resulting hybrid thermosets. Moreover, hybridization with MF was often accompanied with pronounced improvements in fracture mechanical and static flexural properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Propylene/1‐Hexene Copolymer as a Tailor‐Made Poly(propylene) for Membrane Preparation via the Thermally Induced Phase Separation (TIPS) Process

Summary: Poly[propylene‐co‐(1‐hexene)], one example of a “tailor‐made poly(propylene)”, was synthesized using an iso‐specific metallocene catalyst in order to study the influence of copolymer composition on the pore size of isotactic poly(propylene) (iPP) membranes prepared by the TIPS process. The structure of the copolymers and their properties in solution were analyzed and discussed in relation to the polymer‐diluent phase diagram, the droplet growth kinetics during the TIPS process, the viscosity of the system and the final pore size of the membranes. The crystallization curve in the phase diagram was found to shift significantly as comonomer content increased and thus the droplet growth period was drastically increased. The resulting increase of the characteristic pore size in the membranes demonstrated that it is possible to use tailor‐made poly(propylene)s to control the pore size in porous membranes prepared via the TIPS process (under otherwise constant conditions).

Porous size is controlled by the polymer and the TIPS process.     

Electrospinning of plant oil‐based,non‐isocyanate polyurethanes for biomedical applications

Non‐isocyanate polyurethanes (NIPU) have rapidly emerged as a sustainable, less toxic, and environmentally friendly alternative to traditional isocyanate‐based thermoplastic polyurethane (TPU) synthesis. TPU is widely used in the medical industry due to its excellent mechanical properties and elasticity. However, little work has been done to synthesize and electrospin NIPU into fibrous mats for biomedical applications. In this work, melt polymerization of a plant oil‐based cyclic carbonate monomer with polyether soft segments and various diamines yielded isocyanate‐free, segmented poly(amide hydroxyurethane)s (PAHUs). Electrospinning of segmented PAHUs afforded ductile, free‐standing fibrous mats with Young's modulus values between 7 and 8 MPa, suitable for tissue scaffold applications. PAHU fiber mats exhibited 3–4 times greater water uptake than the electrospun TPU control, demonstrating potential utility in drug delivery. Fibroblasts adhered to electrospun PAHU fibrous mats with viability values over 90% after 72‐h, validating its biocompatibility. The results highlight the high performance and potential of electrospun isocyanate‐free polyurethanes mats for biomedical application. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46464.     

Synthesis and characterization of multi‐hollow opaque polymer pigments

A new generation multihollow opaque polymer pigment was synthesized by suspension polymerization of “water‐in‐oil‐in‐water” emulsion method, where methyl methacrylate and ethylene glycol dimethacrylate monomer mixture was used as oil phase. The effects of surfactant and cosurfactant composition in terms of “hydrophilic/lipophilic balance” on the stability of the “water‐in‐oil” emulsion and the size of water droplets were studied. Low droplet sizes and the optimum stability were obtained with “Span 80&Tween 80” surfactant mixture at an HLB value of 8. The desired size distribution was obtained at “monomer/surfactant/water” ratio of 75.5/9.4/15.1 at an ultrasonic mixing power of 80 W lasting for 30 s. The surface morphology and hollow structure of polymer pigments were analyzed by scanning and transmission electron microscopy techniques. L*a*b color and gloss properties of polymer pigments were examined. The opacity values were assessed by contrast ratio measurements, and the pigments provided up to 97.3% opacity with 50% v/v solid content in resin. In addition, the pigments exhibited low gloss values and yielded matte films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43696.     

Biodegradable high oxygen barrier membrane for chilled meat packaging

“Chilled” meat is more nutritional, healthy and hygienic than the meat kept at ambient temperature. “Poly(propylene carbonate) (PPC) and poly(vinly alcohol) (PVA) were used to prepare biodegradable three‐layer PPC/PVA/PPC films with high barrier and tensile properties. The potential benefits of the developed films were also evaluated on the shelf life of chilled meat products. Compared to PPC film, using 20 wt % PVA as an intermediate layer in PPC/PVA/PPC film remarkably enhanced oxygen barrier performance at 0 and 50 RH % by about 500 times, tensile strength by about 8 times, and Young's modulus by nine times, but no beneficial effect on water vapor barrier performance has been observed. A new “sandwich” type of completely biodegradable material with high barrier was obtained. The application of PPC/PVA20/PPC film as the packaging material of chilled meat was effectively kept the total viable count (TVC) and total volatile basic nitrogen (TVB‐N) to acceptable levels in chilled meats until 19th day of storage at 4°C, however, the spoilage occurred within 11th and 14th days of refrigerated storage in term of TVC and TVB‐N, respectively, in the chilled meats packed with only PPC. Herein, we report that PPC/PVA/PPC three‐layer film can be a promising well‐defined biodegradable material with excellent potential in chilled meat packaging. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41871.