Hydroxyl-terminated liquid polymers

Characterization of Hydroxyl-Terminated Liquid Polymers of Epichlorohydrin... 

Hydroxyl-terminated liquid polybutadienes are prepared for reactions with diisocyanates to form elastomeric polyurethanes (see Chap. 6). Such materials can be prepared by anionic polymerizations as living polymers and then quenched at the appropriate molecular weight. These polybutadienes can also be formed by free-radical mechanism. The microstructures of the two products differ, however, and this may affect the properties of the finished products. To form hydroxyl-terminated polymers by free-radical mechanism, the polymerization reactions may be initiated by hydroxyl radicals from hydrogen peroxide. 

The cationic ring-opening polymerization of epichlorohydrin in conjunction with a glycol or water as a modifier produced hydroxyl-terminated epichlorohydrin (HTE) liquid polymers (1-2). Hydroxyl-terminated polyethers of other alkylene oxides (3 4), oxetane and its derivatives (5 6), and copolymers of tetrahydrofuran (7-15) have also been reported. These hydroxyl-terminated polyethers are theoretically difunctional and used as reactive prepolymers. 

Table 1. Functionality of Hydroxyl-Terminated Epichlorohydrin Liquid Polymers 3)...

Examples of commercially available polymers are the Poly bd R45-HTLO Resin of Sartomer (hydroxyl-terminated homopolymer of polybutadiene) or Kraton Liquid L-2203 (hydroxyl-terminated ethylene/butylene polymer) of Kraton Polymers. 

The radical containing an hydroxyethyl group which is formed (9.5), initiates the formation of polymeric chains which, by recombination, give hydroxy-telechelic polymers (reactions 9.6 and 9.7). Based on the principles mentioned various hydroxy-telechelic polymers were obtained by radical polymerisation of styrene [9], acrylonitrile [10], butyl acrylate or butadiene [10-14]. Of course, the oligo-polyols derived from styrene and acrylonitrile are solid and difficult to use in PU, but butyl acrylate and butadiene lead to liquid polymers with terminal hydroxyl groups, which are useful in polyurethane manufacture. 

Hydroxyl-terminated polybutadiene (HTPB) can be produced by such reactions. Such elastomers of low molecular weight (3000-10,000) are used as binders and liquid rubbers. Telechejicpolymers (that is, polymers with reactive end groups), containing one or more end groups with the capacity to react with other molecules, can be prepared in this way. 

Hydroxyl Terminated Poly BD Resins, Functional Liquid Polymers, Electrical applications brochure, Atochem North America, Inc., Oct. 1990. 

Polyurethane (PU) PV membranes were reported by Schauer et al. (1999). PU membranes were prepared by the reaction of toluene-2,4-diisocyanate with hydroxyl-terminated oligomers. Oligomers were either liquid polybutadiene (PB) (MW 3000) or propylene oxide-based PEs (MW 420 and 4800). The prepared membranes were used in PV of binary mixtures of water-EtOH, water-dioxane, and EtOH-toluene, respectively. Membranes obtained from the polymer quatemized poly[3-(N, N -dimethyl)aminopropylamide-co-acrylonitriles] showed selective separation of water from aqueous EtOH solution by PV (Yoshikawa et al. 1991). The separation factor toward water reached over 15,000. Membrane performance showed a good correlation to membrane polarity. DSC melting endotherms of the water-swoUen membranes were studied to clarify the state of water in the membrane. The resnlts suggested that there were two states of water in the membrane bound and free. The higher the fraction of bound water in the membrane, clearly, the more preferentially was water permeated. 

Villa [32—34] has modified Uquid polysulfide polymers by reacting them with either vinyl cyclohexane diepoxide or abietic acid. The modified products were used as an effective additive. While the reaction between liquid polysulfide polymer and abietic acid is not fully known. Villa has theorized that the reaction proceeds with inversion of a mercaptan terminal to hydroxyl terminal followed by esterification [32]. The following reaction takes place ... 

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. 

Because the ketene acetal-terminated prepolymer is a viscous Liquid at room temperature, therapeutic agents and the triol can be mixed into the prepolymer at room temperature and the mixture crosslink id at temperatures as low as 40°C. This allows incorporation of heat-sensitive therapeutic agents into a solid polymer under very mild conditions of thermal stress. However, because the prepolymer con-tedns reactive ketene acetal groups, any hydroxyl groups present in the therapeutic agent will result in the covalent attachment of the therapeutic agent to the matrix via ortho ester bonds (16). 

---