Carboxyl groups, prepolymer

Prepolymer produced via the terephthalic acid (TPA) monomer route shows an increased reactivity in comparison with that produced by the dimethanol tereph-thalate (DMT) monomer process [49], This behavior is possibly caused by the enhanced CEG content, which is usually higher in products from the TPA process as a result of insufficient conversion of the acid monomer in the esterification reaction (Figure 5.23). The increased reactivity may be caused by an autocatalytic influence of the carboxylic groups which seems to be disturbed by an unbalanced content of OH groups in the case of degradation. 

Since these polymers vary in average functionability, primary and secondary carboxyl groups, 1-2 and 1-4 addition product, and chainbranching products, it is not surprising that excellent control must be exercised during manufacture of the prepolymers and during propellant production. 

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. 

CTPB. Ultimately, prepolymers were developed with carboxyl groups in the terminal positions to take full advantage of the entire length of the polymer chain. These butadiene prepolymers were synthesized by a free radical- or lithium-initiation technique to an average molecular weight of 3500-5000 and a nearly bifunctional structure. These attributes provided for substantially improved mechanical behavior of highly loaded solid propellants, particularly at low temperatures. Pro-... 

Reactivity of Functional Groups. The reactivity of the functional groups of liquid prepolymers significantly affects the processing, cure behavior, and the ultimate mechanical properties of the cured binder and propellant. The reactivity of carboxyl groups of CTPB can be determined by the rate of reaction with n-butyl alcohol. The rate of esterification is measured from the rate of water evolution from the alcohol—carboxylic acid reaction, and a plot of water evolved vs. time then permits the calculation of the corresponding rate constants. 

Successive addition of monomers to the end of macromolecular initiator is the usual technique for the synthesis of tailored blockcopolymers. Anionic polymerization of pivalolactone, a-pyrrolidone— and the NCA of T-methyl-D-glutamate -2 was started from the end group of a prepolymer consisting carboxylate group or acyl lactam group or amino group. Living polymer of C-capro-lactone was expected to be formed by the initiated polymerization from polymer carbanion under kinetic controlled condition. 

The structural formula reveals that this polymer contains two different types of carboxyl group which have different dissociation constants. While the first dissociation step is characterized by a pK value of 3.4, the pK value of the second step is about 7.4. Both pK values were determined via titration of the prepolymer with sodium hydroxide solution. The exchange capacity of the finished stationary phase is directly proportional to its polymer content. It may be calculated in advance, since, owing to the chemical composition, the concentration of the exchange groups in the prepolymer is known. 

Table 5.5 lists the best performance data obtained for some piperazine oligomer membranes interfacially reacted with isophthaloyl chloride. The objective of these tests was to achieve single-pass seawater desalination membranes. As such, the presence of free carboxylate groups was avoided. Use was made of the tri-mesoyl chloride or alternate triacyl halides in the oligomer formation step, and diacyl chlorides in the interfacial reaction step. A few examples of seawater desalination membranes were obtained. Best results were seen for piperazine-cyanurate prepolymers interfacially crosslinked by isophthaloyl chloride, but fluxes were low in view of the operating test pressure of 1,500 psi. 

The prepolymer approach which worked well for piperazineamide interfacial membranes was not useful in the case of FT-30 and its analogs. Poor solubility of aromatic amide precursors in aqueous media was the main obstacle. A patent application has appeared on the use of prepolymer formed from 1,3-benzenediamine and trimellitic anhydride acid chloride.66 This prepolymer contains a free carboxylate group and is soluble in water as the sodium salt. A membrane is obtained by reaction of this intermediate with trimesoyl chloride, followed by a curing step at 110° to 130°C. Salt rejections of 98.5 to 99.1% on 2,000 ppm sodium chloride solution at 200 psi were obtained fluxes were 4 to 11 gfd. 

Problem 4.4 A sample (2.0 g) of polyether polyol prepolymer (M = 2048) dissolved in chlorohydrocarbon solvent was treated with excess succinic anhydride to convert each hydroxyl group in the polyol to a carboxyl group by formation of succinic half-ester. A sample (1.0 g) of this treated polymer recovered from the solution by precipitation (in excess of ethanol) required 12.8 mL of N/10 KOH fof carboxyl titration. Deteimine the hydroxyl functionality of the polyol. 

Acrylate Copolymer (AC) A copolymer of eight parts of n-butyl methacrylate, one part of ethyl methacrylate and one part of styrene was prepared. 800 g of n-butyl methacrylate, 100 g of ethyl methacrylate and 100 g of styrene were heated with stirring in a 2000 cc three-necked flask, equipped with a reflux condenser and nitrogen inlet. The reaction was carried out at 80°C until a prepolymer of syrupy consistency was obtained. The polymer was very similar in nature to the polyacrylate used in a previous study (7,8), except that it contained no pendant hydroxyl or carboxyl groups needed for the melamine-formaldehyde cure. 

The primary paints used in the electrodeposition process are anionic type resins with a carboxyl group (RCOOH) polybutadiene resin) and cationic type resin (R—NH2, epoxy resin). Hydrophilic groups and neutralizing agents are added to the water insoluble or undispersed prepolymers to convert them to soluble or dispersed materials. 

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