Prepolymer molten

Reaction Injection Molding. RIM uses the anionic polymeri2ation of nylon-6 to carry out polymeri2ation in the mold. A commercial process involves the production of block copolymers of nylon-6 and a polyether by mixing molten caprolactam, catalyst, and polyether prepolymer, and reacting in a mold (27,28). 

For the solubility of TPA in prepolymer, no data are available and the polymer-solvent interaction parameter X of the Flory-Huggins relationship is not accurately known. No experimental data are available for the vapour pressures of dimer or trimer. The published values for the diffusion coefficient of EG in solid and molten PET vary by orders of magnitude. For the diffusion of water, acetaldehyde and DEG in polymer, no reliable data are available. It is not even agreed upon if the mutual diffusion coefficients depend on the polymer molecular weight or on the melt viscosity, and if they are linear or exponential functions of temperature. Molecular modelling, accompanied by the rapid growth of computer performance, will hopefully help to solve this problem in the near future. The mass-transfer mechanisms for by-products in solid PET are not established, and the dependency of the solid-state polycondensation rate on crystallinity is still a matter of assumptions. 

When handling heated prepolymers or molten prepolymers, impervious gloves must be worn. These materials can cause severe burns, as they are poor conductors of heat. In this condition, they can readily be absorbed into the body. If MOCA is overheated to above 140°C, dangerous fumes will be given off. 

Adhesives wet, flow, and set to a solid during bond formation. The transformation from liquid adhesive to solid bond can be achieved in a number of ways. Where the adhesive is a polymer, the initial starting material is a liquid monomer or prepolymer that, under the conditions of bonding with heat, pressure, and/or catalyst, polymerizes to the solid polymer in the glue line. It is also usual to apply solutions of preformed polymers in suitable solvents to the faces of adherends, and allow bond formation to take place with evaporation of solvent. Alternatively, polymers that can be melted or softened to flow at elevated temperatures can be applied as hot melt adhesives to form the bond on cooling. With porous adherends like wood, penetration of the pores by liquid or molten adhesives is an important factor in bond formation. 

A reactive extruder may be considered to be a horizontal reactor with one or two internal screws for conveying reactant polymer or monomer in the form of a solid or slurry, melt, or liquid. The most common reactants are polymer or prepolymer melts and gaseous, liquid, or molten low molecular weight compounds. 

BD. The final NCO/OH ratio was kept at 1.05/1. The prepolymers were heated to 80-100°C to give a workable viscosity and the liquid or molten chain extender was then added to the prepolymer. The respective catalysts were used in CHDI-prepolymers in order to accelerate the cure. The mixture was then press-molded in a Carver press at 100°C for from 1/2 to 1 hour and post-cured for 16 hours at the same temperature. 

Liquid State. The liquid state in most thermoplastics is produced by heating until molten in vinyls it is generally obtained by dispersing resin particles in plasticizer to produce a plastisol and in rubber it is obtained by use of latex. In thermosetting plastics, the monomers are reacted only up to low molecular weight reactive prepolymers, which are still liquid or at least readily fusible at low temperature. 

More recently Dieterich and Reiff (166) have described the formation of aqueous urethane dispersions by the dispersion of ionomer melts with subsequent polycondensation in two-phase systems. The principle of this procedure consists of reacting molten ionic modified polyester or polyether prepolymers containing NCO groups with urea to yield bis(biuret), followed by methylolation by means of aqueous formaldehyde in a homogeneous phase, and the resulting plasticized melt of methylolated ionic urethane bis(biurets) dispersed in water at 50-130 °C. These steps can be represented schematically as follows ... 

As an alternate intermediate, adiponitrile is employed to react with hexamethylene diamine and steam in a multistage distillation column to prepare nylon-6,6 [194]. The process is carried out in the presence of an oxygen-containing phosphorous catalyst at an elevated temperature and pressure. Nylon-6,6 of high molecular weight can be produced by the postpolymerization of lower molecular weight polymer in the molten state in the presence of a phosphonic acid catalyst [195] or in the solid state [196]. In a different approach, a prepolymer is formed in a reactor system. 

The first commercial product was introduced in 1975 as Thermid 600 by Gulf Oil Chemicals and is now sold by National Starch and Chemical Corporation. The fully imidized prepolymer has to be processed in NMP, with all its attendant problems. However, the molecular weight can be adjusted to provide a resin which melts at about 200° C and immediately starts to polymerize when molten and so, has a narrow processing window. 

Chemistry. Their chemistry is a fairly complex two-stage process. Typically, in the first stage, propylene glycol is mixed with maleic anhydride and phthalic anhydride (Table 3.17), and cooked 8 to 28 hr at 204 to 232°C to produce a molten prepolymer of Mn = 800 to 3000 (Fig. 3.15). This is mixed with st5trene monomer to pro-... 

The concept of low-molecular-weight imide prepolymers can be viewed as an alternative route to enhanced processability. The development of such systems has been conducted on the basis of three fundamental requirements. First, the prepolymers should be of low molecular weight, allowing for the possibility of a low melting point and low viscosity. Second, imide groups should be present in the prepolymer so as to remove the particularly troublesome polyamic acid to imide conversion process mentioned previously. Third, the prepolymers should have reactive terminal groups capable of reaction by an addition mechanism so as to convert the molten prepolymer to a cross-linked polymer without the harmful evolution of volatiles. 

A new polymerization technology for manufacturing polycarbonate has been established without using phosgene and methylene chloride (11,12). The new process, called Solid-state Polymerization Process , consists of three steps, namely, prepolymerization, crystallization, and solid-state polymerization (Figure 3). In die prepolymerization step, the amoiphous prepolymer is obtained by molten-state prepolymerization of bisphenol-A and diphenyl carbonate. The amorphous prepolymer is converted to the crystallized prepolymer in the crystallization step, and finally, in the solid-state polymerization step, the polycarbonate of Ae desired molecular weight is obtained. 

Although solid-state polymerizations of polyamides and polyesters (which are crystalline polymers), have been known since 1939 and 1962 (13,14), until now, it has been considered impossible to produce polycarbonate by solid-state polymerization, because polycarbonates are amorphous polymers and become molten at the temperatures necessary to effect polymerization. The key technology in solid-state polymerization of polycarbonate is the crystallization of the amorphous piepolymer. It has been found that the low molecular weight amorphous prepolymer is easily crystallized, and the obtained crystallized prepolymer retains its solid-state when it is heated to the temperatures necessary for polymerization. 

Prepolymerization Step. A clear amorphous prepolymer is obtained by performing a molten-state prepolymerization between bisphenol-A and diphenyl carbonate, while eliminating phenol (Figure 4). In this step, obtaining a low molecular weight (Mw 2,0CKF-20,000) prepolymer with low melt viscosity is sufficient, therefore, the prepolymeiization can be easily carried out at a relative low temperature (< 250 C). Discoloration of the piepolymer does not occur because of low temperature and short residence time compart to the melt process which must be performed at a temperature as high as 280 C to 310 C. 

The materials used are listed in Table 3.26. Polyol and chain extenders were dried and degassed at 100°C under vacuum for at least 1 h before use. Dry CHDI flakes are added to the previously dried and degassed molten CAPA 225, the reactants being held in a round-bottomed polymerization reaction vessel equipped with a stirrer and located in an oil bath at 100°C with a steady flow of dry nitrogen passing continuously over the mixture and forming a blanket of gas. The CHDI flakes dissolve slowly in the polyol and and after solution is complete the clear solution resulting is held at 100°C for 30 min to form the prepolymer. 

Injection Molding. Both thermosetting and thermoplastic polymers can be used in the injectionmolding process, though the practical requirements are very different for the two types of polymers. In injection molding, a cavity in the shape of the desired object is filled with molten thermoplastic or a thermosetting prepolymer resin. When the sohd polymer has formed, the object is removed from the mold and... 

Recent patent literature from Asahi describes novel polymerization processes that involve equipment with no moving parts, where the molten prepolymer is allowed to fall through holes and descend either freely or along a wire as a molten strand (70). The molten polymer from the bottom of the reactor is recycled to the top to reach the desired molecular weights. The setup provides a method to overcome mass transfer resistances and allows for removal of phenol from the system. Another process which has been an area of patent activity from GE and Asahi is in the area of solid-state polymerization of polycarbonate, wherein the prepolymer is converted to flakes/powder/particles and crystallized. The solids are then polymerized at a lower temperature than in conventional melt pol5unerization. Both methods seem to be in the development stage. 

Another procedure for synthesis of polsrmer blends is by formation of interpenetrating polymer networks. A network of one polymer is swollen with the other monomer or prepol5mier after that, the monomer or prepolymer is crosslinked (63). In contrast to the preceding methods used for thermoplastics and uncrosslinked elastomers, blends of reactoplastics are prepared by this method. Phase Structure Development in Molten State. 

The distinction between them is made by the technique used for solidification. Melt spinning consists of extruding a molten polymer and into an appropriate medium (gas or liquid), where it is solidified by the transfer of heat. Dry spinning involves the extrusion of a polymer solution into a heated gas, where the solvent is removed and the fiber solidified. Wet spinning represents the extrusion of a polymer solution into a liquid chemical bath. The subsequent solidification takes place by mass transfer. In reaction spinning, a prepolymer (partially reacted material) is extruded into a heated fluid medium, where solidification takes place by chemical reaction. 

Molten polymer injected into metal mold solidifles by cooling Molten polymer with volatile blowing agent that expands the polymer as it evaporates or degrades, producing a gas Starting prepolymers (usually condensation-type) are injected into a heated mold, where they react... 

A series of TPU-CNF and TPU-CNFOX composites were synthesized following a two-step polymerization procedure. Stoichiometric amounts of MDI and PCL were reacted at 80°C under nitrogen gas atmosphere for 150 min to produce a prepolymer. In a second step, 80 g of molten prepolymer were hand-mixed with a proper amount of CNF or CNFOX, 6.5 g of BDO, and the catalyst. Mole ratio of 6 1 5 of MDI PCL BDO was used producing 33 wt. % of hard segments. The mixtme was pomed in a chaotic mixer preheated at 110 °C, and mixed for 5 minutes. TPU composite materials were collected, and compression molded at 220 °C. Neat TPU and composite systems were then kept at room temperature for further analysis. 

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