Prepolymer containing terminal

A hydrocarbon prepolymer containing terminal carboxyl groups (28) is available to the propellant chemist. These polymers were synthesized to eliminate some of the variables found in the copolymers. The carboxyl groups can be made of the same types with like reactivity. These linear non-branched polymers impart greater extensibility to elastomeric formulations. The chemistry in propellants is similar to the random functionality polymer. As 20 years of the chemistry of crosslinked propellant binders is reviewed, one familiar with the art cannot fail to predict solid propellant formulations using these polymers tailored to the specific requirements of the solid rocket design with the confidence that any discipline of science can be practiced. 

Recent commercial development of isocyanatoethyl methacrylate (18 lEM) by Dow has made it possible to prepare PU polymers or prepolymers containing terminal or pendant methacrylic groups that can be cured either by means of free-radical initiators or by radiation using UV or electron-beam radiation. 

A tertiary amine such as triethylamine is then added to the isocyanate-terminated prepolymer (containing carboxylic acid groups). The tertiary amine reacts with the pendant carboxylic acid groups, forming a carboxylic acid salt. The presence of this salt, together with adequate stirring, allows the dispersion of the prepolymer in water by the so-called melt dispersion process [57]. 

An oligomeric polysiloxane photoinitiator (PSDAP) containing dialkoxy acetophenone moieties, prepared by reacting diallyloxy-acetophenone with penta-methyl-disiloxane and H-terminated dimethyl-silicone in the presence of chloro-platinic acid, has been claimed [87] to be compatible with silicone prepolymers containing methylvinyl siloxane co-units and active in their UV curing. 

The reaction between TDI and polyols has been simulated in a computer study [154], The objective was to prepare NCO-terminated prepolymers containing a minimum of monomeric TDI. Twelve simultaneous and/or consecutive reactions were treated mathematically. The calculated predictions were in good agreement with experimental results. 

Preparation of Cast Pads. One hundred parts Adlprene LlOO (an Isocyanate terminated prepolymer containing polyoxytetra-methylene chain segments and having an equivalent weight of about 1025, manufactured by duPont) Is heated to 87-88 C while 12.5 parts MOCA, 4,4 -methylenebls(2-chloroanlllne), Is brought to 124-126. Degassing of the Adlprene LlOO and MOCA at a pressure of 1-2 Torr for about 5 and 1 minutes, respectively, follows. 

The prepolymers can be different types of materials. They must, however, contain residual unsaturation in order to react and crosslink with the monomers. Examples of such materials may be polyurethane acrylates that are prepared from urethane prepolymers. The excess isocyanate groups are treated with hydroxyethyl or hydroxypropyl acrylates. Other prepolymers with terminal and/or pendant hydroxy groups are also often esterified with acrylic acid. The oligomers might also be bisphenol A diglycidyl ethers prereacted with acrylic acid to form terminal acrylate groups. An example of these would be ... 

In the melt-dispersion process (95), an NCO-terminated prepolymer is prepared next from a polyester or polyether diol, a diisocyanate, and a glycol containing a potential ionic group. The NCO/OH is between 1.2 and 1.8. Then, the prepolymer is terminated with urea to form biurets, which are further alkylated to give an ionomer as shown in Fig. 17. The bis-biuret can be considered to be somewhat hydrophilic to be methylolated with formaldehyde. Upon dilution with water, a stable dispersion is formed. 

Polyethylene glycol (PEG) is another well-known molecule used to reduce protein adsorption and/or platelet adhesion. Surface enrichment of a triblock oligomeric PEG containing additive from a polyurethane matrix was reported [54,55]. The authors used PEG as the active groups to suppress protein and platelet adhesion. The authors first synthesized a methylene diphenyl diisocyanate (MDI)-poly (tetramethylene oxide) (PTMO) 1000 prepolymer with a MW of approximately 4750 (PU4750), and then this prepolymer was terminally functionalized with mono amino-polyethylene oxide (PEG) with different MW (PEO550, 2000, or 5000, Table 2.3). This triblock copolymer was mixed with a polyurethane (MDI/ PTMO 1000/ethylene diamine (ED)) at different ratios in dimethylformamide (DMF) and cast into polymer films. The surface compositions of these films were evaluated by XPS. 

One-component urethane coatings are usually based on MDI, TDI or HDI terminated prepolymers containing free isocyanate groups. Pigmenting such systems is delicate due to moisture in the pigment, which can cause premature gelation. Therefore, these systems must contain additives for moisture removal such as zeolites (alumosilicates). Since the chain extension in such systems is carried out with water from air, one of the products of the reaction is CO2, which diffuses from the film without foaming. 

Urethane bond-hastd polymers, called polyurethane (PU), include a wide family of polymers obtained from the reaction of starting monomers and/or prepolymers containing alcoholic and isocyanate functional groups typically, polyesters-polyols (polyesters with alcoholic termination) and diisocyanates are reacted to obtain PU. Final products often consist of reticulated polymers rather than linear ones, depending on the final use and desired properties. 

Reactive polyurethane adhesives polyurethane prepolymers with terminal hydroxyl groups or terminal isocyanate groups. Uses plastics, metals, silicate-containing materials. 

There are many different formulations for two component polyurethane sealants dependent of the sealant properties required. The usual NCO/OH equivalent ratio is 1.05 to 1.10. One component is a liquid isocyanate-terminated prepolymer containing pigments, fillers such as calcimn carbonate or talc, and an antisag agent such as fimied silica. The second component is a hydroxyl terminated polymer, pigment, and a catalyst such as methylene dianiline. The individual components are mixed at elevated temperatures under dry conditions so that premature crosslinking does not occur. Prior to use, the two components are mixed well and have a pot life of about 1 to 4 hours. Cure time to develop full sealant properties is 1 to 2 days. 

High molar mass epoxy prepolymers containing rabber dispersions based on carboxyl-terminated butadiene-acrylonitrile copolymer were prepared from initially miscible solution of low molar mass epoxy prepolymers, bisphenol A and carboxyl-terminated NBR. During chain extension inside a twin screw extruder due to epoxy-phenoxy and epoxy-carboxy reactions, a phase separation process occurs. Epoxy-phenoxy and epoxy-carboxy reactions were catalysed by triphenylphosphine. The effect of reaction parameters (temperature, catalyst, reactant stoichiometry) on the reactive extrasion process were analysed. The structure of the prepolymers showed low branching reactions (2-5%). Low molar mass prepolymers had a Newtonian rheological behaviour. Cloud-point temperatures of different reactive liquid butadiene aciylonitrile random copolymer/epoxy resin blends were measured for different rubber concentrations. Rubber... 

Blocked isocyanate, for our purposes, will refer to the reaction product of a diisocyanate or isocyanate-terminated prepolymer in which the isocyanate functionality has been reacted with a blocking agent . Once blocked , the diisocyanate can be added to polyols or certain chain extenders, and these materials will not react at room temperature. The concept is shown in the sixth item of Fig. 1. An adhesive formulated with a blocked isocyanate is basically a two-component adhesive that does not react until heated to the activation temperature. When an adhesive is made with a blocked isocyanate together with hydroxyl-containing curatives, the adhesive has a good long shelf life at room temperature. However, once heated... 

Polyaddition reactions based on isocyanate-terminated poly(ethylene glycol)s and subsequent block copolymerization with styrene monomer were utilized for the impregnation of wood [54]. Hazer [55] prepared block copolymers containing poly(ethylene adipate) and po-ly(peroxy carbamate) by an addition of the respective isocyanate-terminated prepolymers to polyazoesters. By both bulk and solution polymerization and subsequent thermal polymerization in the presence of a vinyl monomer, multiblock copolymers could be formed. 

Furthermore, photochemically induced homolytical bond cleavage can also be applied when the prepolymer itself does not contain suitable chromophoric groups [113-115]. Upon thermolysis of ACPA in the presence of styrene, a carboxyl-terminated polystyrene is formed. This styrene-based prepolymer was reacted with lead tetraacetate and irradiated with UV light yielding free radicals capable of initiating the polymerization of a second monomer (Scheme 33) [113]. 

Hydroxy-terminated polyester (HTPS) is made from diethylene glycol and adipic acid, and hydroxy-terminated polyether (HTPE) is made from propylene glycol. Hydroxy-terminated polyacetylene (HTPA) is synthesized from butynediol and paraformaldehyde and is characterized by acetylenic triple bonds. The terminal OH groups of these polymers are cured with isophorone diisocyanate. Table 4.3 shows the chemical properties of typical polymers and prepolymers used in composite propellants and explosives.E4 All of these polymers are inert, but, with the exception of HTPB, contain relatively high oxygen contents in their molecular structures. 

This paper discusses the three butadiene prepolymers which have been used most extensively in solid rocket propellants—i.e., the copolymer of butadiene and acrylic acid (PBAA), the terpolymer of butadiene, acrylic acid, and acrylonitrile (PBAN), and the carboxyl-terminated polybutadiene (CTPB). Since the chemistry of all of these carboxyl-containing prepolymers is essentially the same, the discussion of butadiene propellants in this paper is concerned mainly with those based on CTPB. 

The polycyclotrimerization of difunctional isocyanates (or NCO-terminated prepolymers) produces polymer networks containing heterocyclic, thermostable per-hydro-1,3,5-triazine-2,4,6-trione (isocyanurate) rings as crosslinks ... 

BMIs and maleimide-terminated prepolymers have been considered for systems with improved Fire, Smoke and Toxicity properties. Of particular interest are phosphorous-containing bismaleimides because they provide high Limiting Oxigen Index (LOI) values (30). 3,3 -bis(maleimidophenyl) methyl phosphine oxide is such a compound (Fig. 7). 

Urethanes. The basis for urethane chemistry is the reaction of an isocyanate group with a component containing an active hydrogen. The first step in formulating a urethane sealant is to prepare what is commonly called (lie prepolymer, typically by reaction of a hydroxy-terminated polyether with a stoichiometric amount of a diisocyanate. 

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