Formation Of Prepolymer Research Articles

Unravelling the Phases of Melamine Formaldehyde Resin Cure by Infrared Spectroscopy (FTIR) and Multivariate Curve Resolution (MCR).

Here, we study resin cure and network formation of solid melamine formaldehyde pre-polymer over a large temperature range via dynamic temperature curing profiles. Real-time infrared spectroscopy is used to analyze the chemical changes during network formation and network hardening. By applying chemometrics (multivariate curve resolution, MCR), the essential chemical functionalities that constitute the network at a given stage of curing are mathematically extracted and tracked over time. The three spectral components identified by MCR were methylol-rich, ether linkages-rich and methylene linkages-rich resin entities. Based on dynamic changes of their characteristic spectral patterns in dependence of temperature, curing is divided into five phases: (I) stationary phase with free methylols as main chemical feature, (II) formation of flexible network cross-linked by ether linkages, (III) formation of rigid, ether-cross-linked network, (IV) further hardening via transformation of methylols and ethers into methylene-cross-linkages, and (V) network consolidation via transformation of ether into methylene bridges. The presented spectroscopic/chemometric approach can be used as methodological basis for the functionality design of MF-based surface films at the stage of laminate pressing, i.e., for tailoring the technological property profile of cured MF films using a causal understanding of the underlying chemistry based on molecular markers and spectroscopic fingerprints.

Preparation and characterization of 2,4–D butyl ester capsule suspension for mitigation of its drift risk

ABSTRACTA novel capsule suspension (CS) formulation was prepared by in situ polymerization of melamine formaldehyde (MF) resin which was the first time to be used to encapsulate 2,4–D butyl ester. The prepared 2,4–D butyl ester capsule suspensions were studied by ultraviolet spectrophotometer (UV), laser particle size analyzer, Optical microscopy (OM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Results showed that the encapsulation efficiency reached 93.23%, and the mean particle size (D50) could be reduced to 13.80 µm by adding 4% Tween80. OM and SEM images illustrated that the core-shell structure related largely to the stability of emulsion. The spherical microcapsules possessed with rougher outer surface and the shell was about 1.5-2.0 µm thick with good methanol tolerance. Then, the formation of pre-polymer, shell material and microcapsules were revealed by FT-IR. Finally, experiments showed that the 2,4–D butyl ester CS exhibited a sustained releasing behavior in water, which could reach to 14 days.

EFFECT OF INCREASING NCO/OH MOLAR RATIO ON THE CHEMICAL AND MECHANICAL PROPERTIES OF ISOCYANATE TERMINATED POLYURETHANE PREPOLYMER DERIVED FROM BIO-MASS

The study deals the effect of increasing NCO/OH molar ratio on the physico-mechanical properties of isocyanate terminated polyurethane prepolymer. The prepolymer was prepared using castor oil and toluene-2,4-diisocyanate. The NCO/OH molar ratio has been varied from 1.6 to 2.0. The formation of the prepolymer was confirmed by UV and FTIR spectroscopy. The results reveal that the curing time of the prepolymer decreased with increase in NCO/OH molar ratio. When NCO/OH molar ratio increased, the tensile strength of the polyurethane film increased, while percent elongation decreased due to increase in hard segment content.

Synthesis and characterization of castor oil-segmented thermoplastic polyurethane with controlled mechanical properties

Novel castor oil-segmented thermoplastic polyurethane series (PUs) have been prepared and extensively characterized in this study. The castor oil, poly(tetrahydrofuran) polyol, and poly(dimethylsiloxane) have been employed as soft segments in the polymer synthesis with a maximum bio-based content up to 14.1wt%. We demonstrate here that it is possible to prepare thermoplastic polyurethane containing castor oil via polyaddition approach in which the formation of prepolymer needs to be carried out with the addition of reasonably small amount of castor oil together with excess amount of the diisocyanate in the very first step. This is followed by the addition of the other polyols and finally a low molecular weight chain extender. The developed synthesis resulted in the formation of branched thermoplastic polyurethane with an elongation at break of about 1200%, which is considerably high compared to reported values for polyurethanes containing castor oil as soft segments. We have demonstrated that mechanical properties and flexibility of polyurethane can be significantly altered by both incorporated castor oil and controllable poly(dimethylsiloxane)/poly(tetrahydrofuran) polyol ratio during the synthesis. Especially the synthesized polyurethanes exhibited good biocompatibility and high transparency, which are useful properties for polymers as potential biomaterials. In addition, thermal stability and thermal transition of polyurethanes have been investigated.

Effect of different catalysts on urea–formaldehyde resin synthesis

ABSTRACTFour catalysts (H2SO4, HCl, H3PO4, and NaOH/NH4OH) were studied in the preparation of melamine modified urea–formaldehyde (UFM) resins. 13C‐nuclear magnetic resonance spectroscopic analysis of the UFM resins at different synthesis stages revealed the polymer structure and detailed reaction mechanism. Three acidic catalysts (H2SO4, HCl, and H3PO4) enhanced the resin polymerization through the formation of various contents of methylene, ether linkages, and urons. H3PO4 yielded the most terminal ether linkages at the first stage and enhanced polycondensation by depleting all free urea and glycols to form the most linear methylene linkages NHCH2NH in the end. However, at the initial synthesis stage, NaOH/NH4OH catalyzed the formation of UFM prepolymer to a limited extent with a large amount of free urea left, and therefore produced the final polymer with relatively more substituted methylolureas and linear ether linkages. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40644.

Synthesis and characterization of starch-modified polyurethane

Corn starch was reacted with urethane prepolymer in order to modifying starch and preparing new hydrophobic copolymers. These copolymers were prepared by two-step reactions. The polycaprolactone terminated hexamethylene diisocyanate (HDI) (as prepolymer) was prepared by introducing diisocyanate on both ends of PCL at a molar ratio of 1:2 (PCL:HDI). The grafting was performed by addition of polycaprolactone based prepolymer to starch solution of DMSO with different weight ratio of starch and prepolymer. The samples were characterized and examined by FTIR and 1H NMR spectroscopy, DSC analysis, and scanning electron microscopy (SEM). By introducing NCO groups onto the PCL terminals, the FTIR spectrum shows a new sharp peak, representing the NCO groups and formation of prepolymer. By grafting this prepolymer onto starch a NH and urethane band were appeared. The effect of prepolymer percentage on hydrophobicity was measured through contact angle and it was found that increases with increasing amount of prepolymer. Glass transition temperature ( T g) is also affected with increasing amount of urethane linkages. Surface morphology of modified starch was studied by SEM. It was observed that the surfaces of modified starch are rougher and disordered than the surface of unmodified starch particles. This confirms the grafting and modification of starch. This modified starch can be used as filler in biodegradable starch based polymers.