Prepolymer equipment

Urethanes are processed as mbber-like elastomers, cast systems, or thermoplastic elastomers. The elastomer form is mixed and processed on conventional mbber mills and internal mixers, and can be compression, transfer, or injection molded. The Hquid prepolymers are cast using automatic metered casting machines, and the thermoplastic peUets are processed like aU thermoplastic materials on traditional plastic equipment. The unique property of the urethanes is ultrahigh abrasion resistance in moderately high Shore A (75—95) durometers. In addition, tear, tensUe, and resistance to many oUs is very high. The main deficiencies of the urethanes are their resistance to heat over 100°C and that shear and sliding abrasion tend to make the polymers soft and gummy. 

A wide range of polyurethane-type products has become available in recent years for coating applications. These include simple solutions of linear polyurethanes, two-pot alkyd-isocyanate and polyether-isocyanate systems and a variety of prepolymer and adduct systems. The coatings can vary considerably in hardness and flexibility and find use mainly because of their toughness, abrasion resistance and flexibility. Uses include metal finishes in chemical plant, wood finishes for boats and sports equipment, finishes for rubber goods and rain-erosion-resistant coatings for aircraft. One type of coating is potentially competitive with PVC leathercloth. Both alkyd-di-isocyanate and adduct-diisocyanate compositions may be coated on to fabrics from solutions of controlled viscosity and solids content. Such coated fabrics are soft, flexible and, unlike PVC leathercloth, free from plasticisers. 

The full-prepolymer, quasi-prepolymer, and one-shot techniques may appear to be quite similar, but they each have important bearing on equipment requirements and physical properties. The full-prepolymer method, for example, is die process of choice for making high-performance cast elastomers with superb dynamic properties, such as industrial bumpers and bushings. Quasi-prepolymers are used in less demanding applications like shoe soles, adhesives, and spray elastomers. One-shots make up the rest, including most foams and elastomers. 

A prepolymer is made first by charging Pluracol E2000 [1000.0 g, 1.0 eq., poly(ethylene oxide), 56 OH, BASF] to a suitable container equipped with a mechanical stirrer and a nitrogen gas inlet. Flush the container with dry nitrogen and add Desmodur W (264.0 g, 2.0 eq., 4,4 -methylene-bis(cyclohexyl isocyanate), 31.8% NCO, Bayer). While maintaining a positive N2 pressure on the reaction mixture, stir and heat at 80°C for 2 h. Cool the product to room temperature and check the NCO content (theory = 3.32 %). It might be necessary to warm the highly viscous prepolymer to take samples for titration. To a portion of this prepolymer (250.0 g, 0.2 eq.), add Dabco T-12 (0.25 g, dibutyltin dilaurate,... 

The monomers TPA and EG are mixed upstream to the esterification reactor in a jacketed slurry preparation unit equipped with a stirrer for highly viscous fluids (e.g. Intermig ). The typical molar ratio of EG to TPA lies between 1.1 and 1.3. The esterification temperature and the molar ratio of monomers are the main controlling factors for the average degree of polycondensation of the esterification product (prepolymer), as well as for its content of carboxyl end groups and DEG. The latter mainly occurs as randomly distributed units of the polymer molecules. 

Oil-Based SINs. The SINs produced were based on a castor oil polyester-urethane and styrene crosslinked with 1 mole percent of technical grade (55%) divinyl benzene (DVB) (7). This structure may be written poly[(castor oil, sebacic acid, TDI)-SIN-(Styfene, DVB)], poly[(CO,SA,TDI)-SIN-(S,DVB)]. Benzoyl peroxide (BP) (0.48%) was used as the free radical initiator for the styrene and 1,4-tolylene-diisocyanate (TDI) was used as the crosslinker for the polyester prepolymer. A 500 ml resin kettle equipped with a N inlet, condenser, thermometer, and high torque stirrer was used as the polymerization reactor. 

Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. 

First-generation solventless polyurethane adhesives are one-component isocyanate terminated prepolymers formed by the reaction of MDI (4,4 methylene bis (phenyl isocyanate)), or other isocyanates with polyether and/ or polyester polyols. One-component 100% solids adhesives rely on moisture from the air or substrates or from induced moisture misting during the converting process, to cure the adhesive via an isocyanate/water reaction and subsequent polyurea-polyurethane polymer formation. Typically the high viscosity of the adhesive is such as to require adhesive delivery equipment and application rollers heated from 65-80 °C for use. They have a high level... 

This area is expected to see further growth for RIM, part of which will come at the expense of cast systems (4). Many new formulations with inproved properties will become possible through the use of "HOT RIM" equipment which will allow low melting solid isocyanate MDI prepolymers to be used along with low melting solid polyols in the "B" side. 

Preparation of the polymers was carried out by a two step method. First, MDI prepolymers were prepared in a 5 liter round bottom flask equipped with a stirrer, thermometer, addition funnel, and nitroggn inlet. The dried polyols were added dropwise tg MDI at 75°C and the reaction temperature was maintained at 85°C. The mole ratios of MDI to polyol listed in Table II gave prepolymers containing 18.67% free NCO groups by weight or an isocyanate equivalent weight of 225. In the case of prepolymers 2 and 4, the DPG was added first and then the 2000 molecular weight polyol was added. 

Prepolymer-MDI Polycocyclotrimers. The NCO terminated prepolymers were prepared by reacting MDI with poly(oxytetramethy-lenediol) (MW=1000, 2000) in the reaction kettle, equipped with the nitrogen inlet and outlet, mechanical stirrer, heating mantle and a thermometer. The reaction was carried out at 70°C without any catalyst and was terminated when the NCO content reached the theoretical values. (11)... 

Isocyanate prepolymers were prepared in glass reaction vessels in a laboratory fume hood. The reaction vessel was equipped with a stirrer, temperature controller and nitrogen inlet. The reaction was carried out under a dry-nitrogen atmosphere to minimise exposnre to atmospheric moisture and polyol oxidation. 

Acrylate Copolymer (AC) A copolymer of eight parts of n-butyl methacrylate, one part of ethyl methacrylate and one part of styrene was prepared. 800 g of n-butyl methacrylate, 100 g of ethyl methacrylate and 100 g of styrene were heated with stirring in a 2000 cc three-necked flask, equipped with a reflux condenser and nitrogen inlet. The reaction was carried out at 80°C until a prepolymer of syrupy consistency was obtained. The polymer was very similar in nature to the polyacrylate used in a previous study (7,8), except that it contained no pendant hydroxyl or carboxyl groups needed for the melamine-formaldehyde cure. 

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