Series Of Prepolymers Research Articles

A facile method to fabricate thermally stable methacrylate‐terminated oligo(2,6‐dimethyl‐1,4‐phenylene oxide)/benzoxazine thermosetting resins with low dielectric constants and losses at 10 GHz

AbstractPoly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as a kind of low dielectric polymer has been applied in telecommunications. However, developing PPO based thermosetting resins with good comprehensive properties is highly challenging. Herein, an interpenetrating polymer network (IPN) design strategy for the preparation of methacrylate‐terminated oligo(2,6‐dimethyl‐1,4‐phenylene oxide) (SA9000) based thermosetting resins is presented. Two series of prepolymers are prepared by blending bisphenol A/furfurylamine benzoxazine (B‐f) or bisphenol A/aniline benzoxazine (B‐a) with SA9000. Then the IPN films are fabricated by the programmed temperature rising method with simultaneous polymerization reactions of both SA9000 and benzoxazines. Owing to the intermolecular interactions between SA9000 and benzoxazines, the polymerization peak temperatures of all prepolymers are lower than those of SA9000 and benzoxazines. In comparison with B‐a based films, B‐f/SA9000 films display better miscibility and higher thermal resistances over the entire composition range, due to the strengthened hydrogen bonding and higher cross‐linking density resulting from the presence of furan ring of B‐f. Specifically, B‐f/SA9000 films possess the advantages of low dielectric constants (2.296–2.475) and low‐loss grade dielectric losses (0.00550–0.00683) at 10 GHz. The current work provides a simple and effective path for the fabrication of high‐performance thermosetting PPO resins based on benzoxazine chemistry and IPN structure design.

Effect of polymer architecture and hard/soft segment ratio on the surface morphology and mechanical properties of polyurethane films for potential orthodontic treatment

AbstractIn this study, polyurethane (PU) films are prepared by using 1,4‐butanediol and trimethylolpropane as chain extender and crosslinking agent, respectively. A series of prepolymers are synthesized by varying the feeding molar ratios of methylene diisocyanate to polytetramethylene ether glycol, which are hard and soft segments, respectively. The influence of polymer architecture, chemical composition, and artificial saliva treatment on the surface morphology and mechanical strength of PU films are studied. The crosslinking polymer architecture and higher content of hard segment correlates with enhanced tensile strength and less decrease of tensile strength in the condition of artificial saliva, but reduced elongation at break. The in vitro cytotoxicity study demonstrates that PU films have excellent cytocompatibility.

Synthesis and characterization of fully bio-based unsaturated polyester resins

The sustainable tomorrow for future generations lies with the present industrial development toward the proper utilization of various bio-based products. For a transition to a higher level of sustainability, it is necessary to form a new platform for advanced technology products. This paper reports the development of new fully bio-based unsaturated polyesters resins (UPRs). A series of prepolymers were synthesized by varying saturated diacids (oxalic, succinic and adipic acid), itaconic acid and 1,2-propandiol. Dimethyl itaconate was used as a reactive diluent (RD) in amounts of 30, 35 and 40 wt%. Rheological measurements showed that the obtained resins possessed viscosities (234–2226 mPa s) amenable to a variety of liquid molding techniques. The impact of composition variables—prepolymer structure and amount of RD—on the chemical, mechanical and thermal properties of the thermosets was examined by DMA, TA and tensile measurements and was discussed in detail. The tensile properties (37–52 MPa), glass transition temperature (60–97 °C) and coefficient of thermal expansion (71–168 10−6 °C−1) of the cured resins were in the desired range for UPRs. This investigation showed that UPRs based on itaconic acid can be tailored during synthesis of the prepolymer to meet the needs of different property profiles.

High-Glass-Transition-Temperature Hydrocarbon Polymers Produced through Cationic Cyclization of Diene Polymers with Various Microstructures

A series of prepolymers were treated with CF3SO3H to cationically cyclize adjacent diene–styrene/diene–diene units into main-chain cyclic units. Diene–diphenylethylene alternating copolymers synthesized using anionic copolymerization were first cyclized completely without intermolecular linking reactions. The cyclization produced much higher Tg values (approximately 200 °C) than those of cyclized random diene–styrene copolymers (approximately 130 °C). To eliminate the number of spacer carbons between cyclic repeating units, poly(1-phenyl-1,3-butadiene) (PPB) was used as a prepolymer in cationic cyclization. The Tg increased substantially from 200 to 271 °C as the 3,4-structure content increased from 8% to 80%. The cyclized PPB with high 3,4-structure content is the highest Tg hydrocarbon polymer yet reported. All results indicated that the backbone rigidity of the cyclic hydrocarbon polymer can be drastically increased by reducing the number of spacer carbons and increasing carbon sharing between cyclic repeating units.

The effect of free isocyanate content on properties of one component urethane adhesive

One-component polyurethane adhesives were prepared from difunctional linear polyether polyol and two types of isocyanates in order to achieve excellent adhesion to various substrates. The structure of the prepolymer was varied by using different stoichiometric excesses of isocyanate in the range between 5 and 24wt%. The simulation of synthesis between polyol and two isocyanates with 15wt% of the NCO groups was performed on a rheometer in order to determine the optimal reaction time. The average molecular weight, determined by GPC, and Brookfield viscosity of the prepolymers decreased with increasing amounts of free isocyanate (NCO) concentration. The structure of the prepolymers as well as the type and amount of side reactions as a function of the free NCO was determined by NMR analysis. The cross-linking, arising from allophanate linkages, was more pronounced at higher amounts of free NCO. Thermal properties of synthesized urethane prepolymers were investigated by DSC and TGA techniques. The glass transition temperatures (Tg) of the prepolymers depend on the type of isocyanate used for the synthesis. Adhesion strength was also tested. Maximum tensile strength was observed at 15wt% of NCO for both series of prepolymers.

Synthesis and characterization of excellent transparency poly(urethane-methacrylate)

A series of novel crosslinked poly(urethane–methacrylate) (PUA) was synthesized. PUA was polymerized in a three-step process: The low number average molecular weight unsaturated polyester (UPE) containing hydroxyl groups was synthesized by 1,2-propanediol (PG), 2-butyl-2-ethyl-1,3-propanediol (BEPD) and maleic anhydride (MA). A series of prepolymers, which had double bonds at the end of the chain, was prepared from isophorone diisocyanate (IPDI), UPE, and β-hydroxyethyl methacrylate (HEMA) in the presence of dibutytin dilaurate (DBTL) as catalyst. The novel functional prepolymer was initiated by 2,2-azobis-isobutyronitrile(AIBN) to form thermosetting materials. The structure of the thermosetting materials was characterized by Fourier Transform Infrared (FTIR). Mechanical, thermal, and optical properties were tested. The results showed that the advanced PUA had good thermal and mechanical properties and high transparence. The throughput of PUA was above 90%, thus the PUA was possible to be used as excellent optical material. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Polyurethane ionomer dispersions from a blocked aromatic‐diisocyanate prepolymer

AbstractAqueous anionic blocked aromatic polyurethane prepolymers were synthesized by a prepolymer mixing process and their dispersions were obtained by adding water to the blocked prepolymer solutions. A series of prepolymers were prepared by using toluene 2,4‐diisocyanate, 4,4′‐diphenylmethane diisocyanate, polytetramethylene glycol, dimethylol propionic acid, methyl ethyl ketoxime and ε‐caprolactam. The aqueous dispersions were characterized by Fourier‐transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. The particle sizes, viscosities, pH and storage stabilities of the dispersions were studied and compared. Some mechanical properties of the cast films obtained from the aqueous dispersions and the adhesive properties of the dispersions were also evaluated. Copyright © 2004 Society of Chemical Industry

Blocked isocyanate‐terminated prepolymers in a delayed‐cure durable‐press finish for wool. Influence of isocyanate and blocking group structure on reactivity

AbstractA series of prepolymers containing terminal blocked isocyanate groups was prepared by reaction of isocyanate‐terminated prepolymers [derived from a poly(propylene oxide) diol (MW = 2000) or a triol (MW = 3000) and different diisocyanates] with various blocking agents. Their curing rates with a polyepoxide crosslinking agent were measured to assess their suitability for a delayed‐cure durable‐press treatment for wool. The curing rates varied over a wide range, but commonly used blocking groups such as phenols, caprolactam, β‐diketones, and alcohols were not sufficiently reactive for the intended application, although others, e.g., oximes and certain blocking agents containing a basic center such as N,N‐diethylhydroxylamine, hydroxypyridines, and hydroxyquinolines, had the required reactivity. Blocking by 1,3‐dipolar cycloaddition of nitrones was examined, but the reactivities were too low. Prepolymers containing blocked aromatic isocyanates were more reactive than those containing blocked aliphatic isocyanates. Difunctional butanone oxime‐blocked pre‐polymers cured slightly more slowly than analogous trifunctional prepolymers.

Thermal degradation of polymers. Part XIX. The thermal cyclization and characterization of quinazolone pre‐polymers

AbstractA series of pre‐polymers prepared from 4,4′‐diaminodiphenyl‐3,3′dicarboxylic acid and aromatic diacetamido compounds have been thermally cyclized and their structures have been investigated using infrared spectroscopy, combustion analysis, and weight loss techniques. The structures obtained on cyclization are discussed in terms of concurrent cyclization and decarboxylation reactions resulting in incomplete cyclization. Specific structural features due to the lability of main chain bonds at the cyclization temperatures are also discussed. Dynamic thermogravimetry and isothermal weight loss studies have been used to evaluate thermal stability and kinetic parameters. The results are discussed in terms of the overall complexity of the polymer structure and the complexity of the degradation process. It is concluded that in such systems, where the structural variations are large, it is not possible to define a meaningful stability sequence because like systems are not under comparison.