Prepolymer chemical structure

Prepolymer An intermediate chemical structure between that of a monomer and the final resin. 

The idea of synthesizing imide oligomers which carry acetylenic terminations appeared attractive because homopolymerization through acetylenic endgroups occurs without any volatile evolution and provides materials with good properties. Landis et. al (8,9) published the synthesis of such acetylene terminated imide oligomers from benzophenone tetracarboxylic anhydride, aromatic diamine and 3-ethynylaniline via the classical route. As usual, the amide acid is formed as an intermediate which, after chemical cyclodehydration, provides the polymide. Since ethynyl-terminated polyimide is used as a matrix resin for fiber composites, processing is possible via the amide acid, which is soluble in acetone, or via the fully imidized prepolymer, which is soluble in NMP. The chemical structure of the fully imidized ethynyl-terminated polyimide is provided in Fig. 44. 

As in all thermosetting polyimides, the diamine and the tetracarboxylic dianhydride employed to build the backbone can be varied. Alteration of the diamine, tetraacid or both, allow the modification of the polyimide s melting point and solubility. Of interest to the end user is the influence of chemical structure on the melting transition of the prepolymer and the Tg of the fully cured product. Lowering the uncured Tg means increasing flow and, in most... 

The key to acetylene terminated polyimides is the availability of the end-capper which carries the acetylene group. Hergenrother (130) published a series of ATI resins based on 4-ethynylphthalic anhydride as endcapping agent. This approach first requires the synthesis of an amine-terminated amide acid prepolymer, by reacting 1 mole of tetracarboxylic dianhydride with 2 moles of diamine, which subsequently is endcapped with 4-ethynylphthalic anhydride. The imide oligomer is finally obtained via chemical cyclodehydration. The properties of the ATI resin prepared via this route are not too different from those prepared from 3-ethynylaniline as an endcapper. When l,3-bis(3-aminophenox)benzene was used as diamine, the prepolymer is completely soluble in DMAc or NMP at room temperature, whereas 4,4 -methylene dianiline and 4,4 -oxydianiline based ATIs were only partially soluble. The chemical structure of ATIs based on 4-ethynylphthalic anhydride endcapper is shown in Fig. 45. 

Most polyurethanes are different from other elastomers in that they are cast. Two components are mixed together. One component is a prepolymer which consists of two major chemical structures. One... 

The chemical structure of the epoxy matrix constituent as well as processing are reported to strongly influence 11 -I3> the thermoset network and hence the properties and durability of the crosslinked polymer 11 ,4-16). The cure of a reactive prepolymer involves the transformation of low-molecular-weight reactive substances from liquid to rubber and solid states as a result of the formation of a polymeric network by chemical reaction of some groups in the system. Gelation and vitrification are the two macroscopic phenomena encountered during this process which strongly alter the viscoelastic behavior of the material. 

Another type of film investigated recently has been aromatic cyanate esters prepared from the Ciba-Geigy products AroCy L-10 (l,l-bis(4-cyanatophenyl) ethane) and AroCy B-30 (the prepolymer form of 2,2/-bis(4-cyanatophenyl) isopropylidene, AroCy B-10) [89], The chemical structures of these molecules are shown in 4. Spectral measurements from these aromatic cyanate ester ma-... 

The chemical structure of the prepolymer influences its chemical resistance. As a result of their structure, polyesters have inherently better oil resistance but lower hydrolytic stability. The ether groups in the polyether urethanes... 

Figure 7.7. Chemical structures of iminodiacetic acid—glycerol prepolymers (A), and diacid—glycerol prepolymers (B). Note n = 2 for succinic acid, n = 3 for glutaric acid, and n = 7 for azelaic acid.

An Isocyanate terminated prepolymer such as Adlprene LlOO has a chemical structure (R represents isomeric forms of the tolylene radical) of the type ... 

Many commercial thermosets are quite often used as complex mixtures of several co-reacting monomers and prepolymers, specifically formulated to suit a given end-use application. For example, in coating and adhesive applications, often mixtures of different epoxies, differing in chemical structure and/or molecular weights, are used as required. Even two different thermoset-... 

For photocured polymer materials, the Persoz hardness was shown to depend mainly on the chemical structure of the prepolymer chain, on the functionality of the reactive diluent, on the photoinitiator system and on the duration of the UV exposure. The hardness of tack-free coatings thus continues to increase with further irradiation, as shown by Figure 6 for polyurethane-acrylates. This slow hardening process is likely to result from some further polymerization of the unreacted acrylic functions since their concentration was found to decrease concomittantly. 

This full IPN combines the network of an NLO active epoxy-based polymer and the network of an NLO active phenoxy-silicon polymer. l The epoxy-based NLO network is prepared from the epoxy prepolymer (BPAZO) based on the diglycidyl ether of bisphenol A and 4-(4 -nitrophenylazo)aniline functionalized with crosslinkable acryloyl groups. The second NLO network of a phenoxy-silicon polymer is based on an alkoxysilane dye (ASD) of (3-glycidoxypropyl)trimethoxysilane and 4(4 -nitrophenylazo)aniline, and the multifunctional phenoxyl molecule 1,1,1- tris(4-hydroxyphenyl)ethane (THPE).22 Figure 4 shows the chemical structures of BPAZO, ASD, and THPE. Each network can be formed... 

Fig. 3. General chemical structure of polyurethane prepolymer (modified from Hepburn, 1982).

Figure 19. Basic chemical structure of polyurethane prepolymers [8].

The basic chemical structure of polyurethane prepolymers is illustrated in Fig. 19. A good overview on polyurethane adhesive chemistry is given by Habenicht [8]. 

As can be seen from Table 6.18, the chemical structure of the polyurethane-urea part of the hybrid does not affect the properties of hybrid dispersions, obviously not counting the MFFT which is much higher if polyesterdiol has been used as a starting material for the prepolymer-ionomer synthesis (compare MDPUR-ASD 300 and MDPUR-ASD 24). 

Here, the effect of chemical structure of the polyurethane-urea part of the hybrid is, of course, substantial (see Table 6.19). For hybrid dispersion synthesised without coalescent using polyesterdiol as a starting material for the prepolymer-ionomer, the Tg is so high that films cannot he obtained. On the other hand, if polyetherdiol is applied as a starting material in the synthesis of the same dispersion, films of very good mechanical properties are obtained. This was the reason for using polyetherdiol rather than polyesterdiol as the starting material for synthesis of dispersions in this study. 

A phenolic resin was synthesized fiom phenol, 4-(l,l-dimethylethyl)phenol and methanal. How can the chemical structure ofthis soluble phenolic prepolymer be analyzed ... 

The double bonds in bismalemide are highly electron-deficient due to two flanking carbonyl groups, and are reactive towards a bimolecular addition reaction. Hence the maleimide groups of a bismaleimide monomer or chain-extended prepolymer can undergo homopolymerisation to produce 3D network structures. To manipulate the structure and properties, different types of maleimide monomer or prepolymer can be used. The reactivity of such resins depends on their chemical structure and UPE. 

These eompounds are formed into a prepolymer, which in turn is converted into a series of high-moleeular-weight eompounds when reacted with a suitable euring agent. Polymers featuring the epoxide group as a part the chemieal struetures will reaet with other chemical species to form a three-dimensional cross-linked network. One of the most popular forms of epoxide resin is derived from bisphenol A, and the associated epoxide resin has the following chemical structure ... 

In -this paper, we will shortly discuss our approach to prepare hydroxy-terminated MDl/BDO-based urethane oligomers and their 4-diphenylmethane carbamates, 18 and describe in more detail the synthesis of monodisperse hydroxy-terminated oligo(oxy-tetramethylenes), their use for the investigation of the prepolymer formation, and the synthesis of linear PU-elastomers with narrow (monodisperse) soft and/or hard segment length distribution by using the hydroxy-terminated segment precursors. The chemical structures of the model systems studied in this... 

The addition of antihydrolysis agents is required in many engineering applications. Particularly useful are diarylcarbodiimides with alkyl substituents in an ortho-position to the -N=C=N group. Although polyethers, such as polytetrahydrofuran, are not hydrolytically degraded because of their chemical structure, in Europe considerably more polyester is used than polyether. This can be explained by the positive effect of carbodiimides as hydrolysis stabilizers that are tailored to specific applications. The additive load ranges from 0.5 to 2%. Its protective effect is not influenced by whether carbodiimide is added directly to the polyester or to the prepolymers. In... 

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