Condensation prepolymers

The PMR range of resin materials utilize a two-step reaction, in which a norbornene-terminated prepolymer is formed in situ by the condensation reaction of low molecule weight diamines with norbornene-capped imides or acid esters [37]. The PMR-15 designation refers to polymerization of monomeric reactants, with a mixture of diaminodiphenylmethane and a dimethyl ester and a norbornene-containing monomethyl ester, to form a condensation prepolymer having molecular weight approximately equal to 1500. PMR resins are used as matrix materials in high performance composites in the aerospace industry. 

Historically, the adhesives based on reactive condensation prepolymers were the first materials to be extensively studied, developed and introduced to the market. 

FM36 Condensation prepolymer Glass fibre tape Adhesive paste... 

Historically, the adhesives based on reactive condensation prepolymers were the first materials to he extensively studied, developed, and introduced to the market. One of the best performing polyimides in this category is Nolimid 380, produced by Rhone-Poulenc after an extensive series of tests. The resin binder is the mixture of monomers 30a and 30b, as well as the low-molecular-weight (oligoimide) poiyimide 31 of Fig. 9.15. Typical compositions are prepared as previously reported by mixing the two monomers and 4,4 -oxybisbenzeneamine in NMP and methanol.To this solution, introduced into a roll-mill, are added aluminum powder (400 mesh)... 

The prepolymer is separated from the water by spray drying and then formed into cylindrical pellets of uniform size (159). At this point additives can be added to the porous pellets from solution or suspension. These pellets are then placed in a soHd-phase condensation reactor where they are heated to 260°C for up to 4 h under nitrogen, with a small amount of water added. The pressure is maintained close to atmospheric pressure. At the end, x > n. 

Another significant use of 3-methylphenol is in the production of herbicides and insecticides. 2-/ f2 -Butyl-5-methylphenol is converted to the dinitro acetate derivative, 2-/ f2 -butyl-5-methyl-4,6-dinitrophenyl acetate [2487-01 -6] which is used as both a pre- and postemergent herbicide to control broad leaf weeds (42). Carbamate derivatives of 3-methylphenol based compounds are used as insecticides. The condensation of 3-methylphenol with formaldehyde yields a curable phenoHc resin. Since 3-methylphenol is trifunctional with respect to its reaction with formaldehyde, it is possible to form a thermosetting resin by the reaction of a prepolymer with paraformaldehyde or other suitable formaldehyde sources. 3-Methylphenol is also used in the production of fragrances and flavors. It is reduced with hydrogen under nickel catalysis and the corresponding esters are used as synthetic musk (see Table 3). 

Step-Growth Gopolymerization. A sample of a block copolymer prepared by condensation polymerisation is shown in equation 30 (37). In this process, a prepolymer diol (HO—Z—OH) is capped with isocyanate end groups and chain extended with a low molecular-weight diol (HO—E—OH) to give a so-called segmented block copolymer, containing polyurethane hard blocks and O—Z—O soft blocks. 

At moderately high molecular weights, the reaction mass becomes highly viscous, which limits heat transfer and evaporation of the condensation water. This high viscosity limits further melt polymerization in the bulk. In the literature, the melt polymerization stage is sometimes omitted and the prepolymers are condensed to high molecular weights in the solid state.6,28 41 The polymerizations can easily be carried out without a catalyst. 

The prepolymer is subjected to further condensation by heating for 4 hat 260° C while passing superheated steam at a pressure of 1 bar through the solid bed. The white PA-4,6 obtained has a ijrt,i of 4.6 as measured in 96% sulfuric acid. 

Compounds XIV - XVII have potential for use in subsequent phosphazane ollgomer/polymer syntheses because of their available functionality. In fact, treatment of XVI with two equivalents of Ph2PCl in the presence of Et3N yields the P(III)-P(V)-P(III) triphosphazane XVIII quantitatively. Compounds XV and XVII are especially interesting because they are A-B type 1,4- stabilized reactive monomers (prepolymers) (14). Because A-B monomers contain both elements of functionality necessary for condensation, precise control of the reactant ratio can be maintained and products with the highest possible molecular weights can be expected (14). 

The properties of a polymer network depend not only on the molar masses, functionalities, chain structures, and proportions of reactants used to prepare the network but also on the conditions (concentration and temperature) of preparation. In the Gaussian sense, the perfect network can never be obtained in practice, but, through random or condensation polymerisations(T) of polyfunctional monomers and prepolymers, networks with imperfections which are to some extent quantifiable can be prepared, and the importance of such imperfections on network properties can be ascertained. In this context, the use of well-characterised random polymerisations for network preparation may be contrasted with the more traditional method of cross-linking polymer chains. With the latter, uncertainties can exist with regard to the... 

Scheme 2. Polyanhydride synthesis via melt polycondensation involves first the formation of oligomeric acetylated prepolymers, followed by condensation under vacuum. Acetic acid is formed as a byproduct of the second reaction.

In the case of PBT, the CEG content of the prepolymer should not exceed 40meq/kg, or otherwise the poly condensation reaction is inhibited due to an increased formation of tetrahydrofuran (THF). The effect of the CEG content in a PBT prepolymer on the final IV is shown in Figure 5.20. 

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. 

Baekeland found that a relatively stable resole prepolymer could be obtained by the controlled condensation of phenol and formaldehyde under alkaline conditions. These linear polymers of phenol-formaldehyde (PF) may be converted to infusible cross-linked polymers called resites by heating or by the addition of mineral acids. As shown in structure 4.80, the initial products obtained when formaldehyde is condensed with phenol are hydroxybenzyl alcohols. The linear resole polymer is called an A-stage resin, and the cross-linked resite is called a C-stage resin. 

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