Oligomers and prepolymers

Brearley et al" at DuPont (Wilmington, DE, USA) used in-line transmission NIR to monitor carboxyl end groups and degree of polymerization (DP) in PET oligomer and prepolymer melt streams in a new polyester process. The business value was derived from several sources. 

When the mixture of monomers is cast in an open mold, the air bubbles formed at the jet nozzle in the mold usually have enough time to leave the material due to the low viscosity of the reactive liquid. When more viscous oligomers and prepolymers are used, particularly in the case of low-lifetime reactive mixtures, it may be necessary to use some simple procedures, for example, filling through a pipe immersed into the mold, to prevent the formation of air bubbles in the product. 

Chem. Descrip. 1,6-Hexamethylene diisocyanate CAS 822-06-0 EINECS/ELINCS 212-485-8 Uses Monomer to produce light-stable, weather-resist, oligomers and prepolymers for coatings, elastomers, and foams Features Difunctional resist, to abrasion and moisture superior hardness, flexibility, color retention... 

The polyisocyanates used for preparing carbodiimide foams include TDl, TDl-based prepolymers, liquid-MDl oligomers and polymeric isocyanates. Many catalysts for producing carbodiimide foams have been disclosed in the patent literature. Some of these are shown in Table 13. 

In the same way, Oishi et al. [256] used IEM to functionalize oligomers carrying an acid function obtained by polymerization of chiral acrylamides. Chiral polyacrylamide macromonomers were synthesized from 2-methacryloyloxyethyl isocyanate and prepolymers, i.e., poly[(S)-methyl-benzyl acrylamide] or poly(L-phenylalanine ethylester acrylamide) with a terminal carboxylic acid or hydroxyl group. Radical homopolymerizations of polyacrylamide macromonomers were carried out under different conditions to obtain the corresponding optically active polymers, as shown in Scheme 52. 

Synthesis of piperazine-terminated oligomers as prepolymers for interfacial membrane formation was also examined.46 48 Excess piperazine was reacted with di- and triacyl chlorides in an inert solvent such as 1,2-dichloroethane. The resulting amine-terminated polyamide oligomers had low solubility in the solvent system and precipitated. This served to limit the degree of polymerization of the oligomer. Even so, a portion of the product was insoluble in water and was filtered out during preparation of the aqueous oligomeric amine solution for the interfacial reaction step. 

Choice from a wide range of radiation curable formulations to achieve the desired target properties of the coatings is of foremost importance (Defoort et al. 2001, Kumar et al. 2006, 2008). Radiation curable formulations typically consist of the oligomer (or prepolymer), reactive diluents, additives, and photoinitiators (in case of UV curing). Therefore, the understanding of the structure-property relationship of the different components of the coating formulation recipe is a must (Ruiz et al. 2002). 

Chem. Descrip. Benzophenone (50%), 4-methylbenzophenone (50%) Uses Photoinitiator for systems based on acrylic oligomers and monomers, overprint varnishes, clear lacquers for wood, plastic, paper, metal, and optical fiber substrates, flooring coatings, printing inl , adhesives Features High sol. and compat. with various curable systems Properties Colorless to It. yel. clear vise, liq. faint char, odor sol. in most common org. soivs., monomers, prepolymers insol. in water Use Level 0.2-8%... 

The structures of the oligomers or prepolymers are just as important in determining the final properties of the coatings that are cured by cationic mechanisms as are those that are cured free-radical mechanism. As a result, considerable effort has gone into preparations and studies of prepolymers and oligomers. 

Isocyanates (Figure 3.3). Toluene diisocyanate (TDI) is a mixture of mostly 2,4- plus some 2,6-isomer. Two commercial ratios are 80/20 and 65/35. The 4- position is more reactive the 2- and 6- positions are sterically hindered. This gives the processor the ability to make prepolymers (oligomers) and run two-stage reactions. 

There are three principal methods of fabricating PDLC (to disperse liquid crystals in polymer matrix) phase separation, encapsulation and permeation. In the phase separation method, liquid crystal materials, prepoljnner (monomer or oligomer) and photoinitiator (curing agent) are mixed, and then polymerization is brought about by heating [2] or UV irradiation [3]. During the polymerization, the liquid crystal material phase separates from the solution, and liquid crystal droplets and a polymer matrix are formed. By measurement of the nematic-isotropic transition temperature, the purity of the liquid crystal in the droplets can be checked. In the case that the polymerization-induced phase separation is not complete and unreacted prepolymer is dissolved in the liquid crystal droplets, the... 

Polyurethanes are condensation polymers formed by step-growth polymerization in which the chain length of the polymer increases steadily as the reaction progresses. Two major routes of polymerization of polyurethanes are one-step and two-step synthesis methods. In one-step synthesis, the diisocyanate, polyol, and a chain extender are mixed together and allowed to react. In the two-step route, an oligomer or prepolymer synthesized from diisocyanate and polyol and the chain extender are allowed to react. The two-step route offers some advantages over the one-step route, such as a reduced polydispersity index and a higher extent of phase separation. 

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... 

Another approach is based on multi-component systems [97-101]. It has been pursued, in particular, by the group of Professor Dalton. In many cases they have used a two components system formed by a polyurethane NLO oligomer with isocyanate end groups that is reacted with a cross-linking agent, triethanolamine, as example [102, 103]. In this approach, the oligomer (or prepolymer) is prepared first then a solution of the oligomer and of the cross-linker is spin-coated on the substrate (Fig. 2.25). 

Presence and type of photoreactive prepolymers, oligomers, and diluents Type of additionable photoinitiators or unsaturated Presence and type of thermal crosslinking agents and other additives Presence and type of conventional crosslinkers. 

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