Prepolymer characterization

Tor [7] developed a new method for the preparation of thin, uniform, self-mounted enzyme membrane, directly coating the surface of glass pH electrodes. The enzyme was dissolved in a solution containing synthetic prepolymers. The electrode was dipped in the solution, dried, and drained carefully. The backbone polymer was then cross-linked under controlled conditions to generate a thin enzyme membrane. The method was demonstrated and characterized by the determination of acetylcholine by an acetylcholine esterase electrode, urea by a urease electrode, and penicillin G by a penicillinase electrode. Linear response in a wide range of substrate concentrations and high storage and operational stability were recorded for all the enzymes tested. 

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. 

GPC is extremely valuable for both analytic and preparative work with a wide variety of systems ranging from low to very high molecular weights [2], The method can be applied to a wide variety of solvents and polymers, depending on the type of gel used. GPC has been used for routine polymer characterization and quality control, particularly in determinations of MWD and for characterizing low polymers and small molecules, e.g., for prepolymers in resins and for polymer additives [7,8]. 

Prepolymer and Propellant Quality Control. Prepolymer Control. The characterization of the functionally terminated prepolymers was an important factor in the control of these materials required to assure satisfactory reproducibility of solid propellant properties. To characterize these materials adequately, it was necessary to develop new analytical methods or to improve existing methods to provide the desired level of control. It was ultimately demonstrated that (1) propellant mechanical... 

Polyurethanes offer a convenient method by which iimnobilization of enzymes can be affected. Prepolymers are polymers with active end groups. While the primary purpose of the isocyanate end groups is serving as chain-extending agents, they also react with the amines that characterize an enzyme backbone. Thus, as many of the studies cited will show, the reaction sequence is (1) preparation of an aqueous solution of the enzyme and (2) emulsification of the solution with the prepolymer. The reaction time is on the order of 0.5 hours compared to the 24 hours required by some methods. 

In this work both the prepolymers and the block copolymers were prepared in bulk and, therefore, it is not surprising that a large amount of homopolymer was obtained74,75. The subsequent characterization of the products was carried out, after a selective solvent extraction process, using NMR, IR, osmometry, viscosimetry and GPC. 

In Chaps. 2 to 6, a case study is developed in order to apply and test the methods developed along the whole book. To this purpose, the reaction between phenol and formaldehyde for the production of a prepolymer of phenolic resins has been chosen for several reasons. In fact, this reactive system is widely used in different forms for the production of different polymers moreover, it is characterized by a noticeable production of heat and by a complex kinetic behavior. Such features represent strong challenges for controlling and monitoring tasks. 

The characterization results of the product are summarized in Table 10. The number of branches per backbone chain was calculated from Eq. (29) assuming the M of one branch to be equal to the M of the starting prepolymer. This assumption is supported by the result described in Table 11, where the intrinsic viscosity [ij] of... 

Materials. This paper is mainly concerned with two Hycar 2100R polymers, Hycar 2103 and Hycar 2106. These are characterized in Table I. Isocyanate Prepolymer C is used as the curative. Its typical properties are summarized in Table II. 

Both series of polyurethanes were prepared using a prepolymer technique in which reactants were mixed at 70 °C/1 hour, cast into molds at 105 °C/2 hours, and cured at 80 °C/14 hours. The BD/MDI hard segment contents ranged from 0% (transparent, colorless homopolyurethanes) to 30% w/w (opaque, white copolyurethanes). All elastomers were characterized using DSC, dynamic mechanical, and tensile stress-strain measurements. 

The DAP prepolymer was prepared by bulk polymerization of DAP, in whieh conversion was about 10%, and characterized as Rus = 0.275, P = 65.8, and Pw/Pn = 3.71. That is, the polymer carries, on average, 36 pendant allyl groups and one crosslinkage per prepolymer molecule. It should be noted that under the same polymerization conditions for the preparation of DAP prepolymer the theoretical gel point was estimated to be 3.4%, being quite low eompared with 10% conversion. 

Polymers and copolymers were laboratory-prepared samples. Samples W4 and W7 of the diblock copolymer AB poly(styrene-fo-tetramethylene oxide) (PS—PT) were synthesized by producing a polystyrene prepolymer whose terminal group was transformed to a macroinitiator for the polymerization of THF. Samples B13 and B16 of the diblock copolymer AB poly[styrene-h-(dimethyl siloxane)] (PS-PDMS) were prepared by sequential anionic polymerization. Samples of statistical copolymers of styrene and n-butyl methacrylate (PSBMA) were produced by radical copolymerization. Details of synthetic and characterization methods have been reported elsewhere (15, 17-19). 

Chemical gels, and perhaps physical gels also, show power-law frequency-dependences of the linear viscoelastic moduli G and G at the transition from sol to gel, and thus the spectrum can be characterized completely by a power law exponent n and a relaxation strength S, The constants n and S vary systematically with molecular weight of the prepolymer and with the ratio of prepolymer to cross-linker. 

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. 

In any case, the prepolymer synthesis results in somewhat better defined domains, characterized by the relative translucency of the prepolymer route material relative to the one-shot route, and as illustrated in the transition behavior. Figure 3. Better defined domains mean a purer rubber phase, which in turn may yield greater toughness to this form of the material. Important questions as to the development of intermediate Tg s with extensive interfacial boundary material (48) or on complete thermodynamic miscibility (49) remain for the future. 

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