Polymerization, urethane

Examples of high polydispersity ratios and bimodal distributions have been previously rationalized by heterogeneous reaction conditions. Tirrell et al.(19) found Mw/Mn values well over 2.0 and low molecular weight shoulders in slow, low temperature RIM polymerized urethanes based on polycaprolactone diols. Xu et al. 

Malofsky and Baccei, from the Loctite Corporation, report on the significant mechanical property improvements obtained with maleimide and nadic capped monomers and prepolymers as additives in anaerobic methacrylate/ acrylate adhesive systems. Significant improvement in thermal resistance was noted in a PEGMA (polyethyleneglycol diroethacrylate) system in which a polymerizable maleimide addition was incorporated. A "neat" polymerized urethane methacrylate failed catastrophically within 1000 hrs. at... 

Figure 10 demonstrates, once again, the outstanding resistance in thermal aging with the use of the meta-phenylene-dimaleimide (m-PDM) additive as a comonomer with a urethane methacrylate monomer. The "neat" polymerized urethane methacrylate failed catastrophically within 1000... 

The facile synthesis of aliphatic [ ]polyurethanes by using di-tert-butyl tricarbonate to prepare the appropriate monomers has yielded a general class of polymers. These structures are especially interesting in the context of biodegradable polymers, since the synthetic procedure is applicable to all amino alcohols with a spacer of at least four carbon atoms between the two functionalities. The reagent is the key element for the selective formation of the a,a>-isocyanato alcohol 355 intermediates for polymeric urethanes. 

Extensive use of mixed anhydrides of carbonic acids has been made in peptide synthesis. Polymer-based mixed carbonic anhydrides prepared by Shambhu and Digenis (1974) and Martin et al. (1978a) gave exclusively the amide of benzoic acid with aliphatic amines [Eq. (4)], but with aniline, some polymeric urethane was also formed. 

Figure8.10 (a)Shiftofthe2090cm Raman band with strain for the cross-polymerized urethane-diacetylene copolymer (after [68]) (b) dependence of the peak position of the 2090cm Raman band upon strain , t loading unloading, o, reloading (after [68])...

Hydroxy isocyanates have never been isolated because of the interaction of the hydroxyl and isocyanate groups with the formation of cyclic or polymeric urethans. The products are usually readily hydro-... 

The kinetic features were exposed for two cases of IPN formation via reaction injection molding (RIM) and via usual molding. Kinetic measurements were performed at isothermal conditions using the DSC method and have shown that due to a different reaction mechanism (polyaddition and polymerization), urethane formation always begins after the mixing of all components. The reaction proceeds under conditions when the polyester component is not yet reacted and urethane formation proceeds in a solution of polyester network components. Polyester network begins to form when PU is either fully or partially formed, i.e., in the medium of the other network. Again, in this work the question about phase separation had not been considered. 

A large number of polymeric compounds have been investigated, but most modem propellants utilize prepolymers that ate hydroxy-functional polybutadienes (HTPB), carboxy-functional polybutadienes (CTPB), or a family of polyethylene oxides (PEGs) to form urethanes. Typical cure reactions... 

Uses. Neopentyl glycol is used extensively as a chemical intermediate in the manufacture of polyester resins (see Alkyd resins), polyurethane polyols (see Urethane polymers), synthetic lubricants, polymeric plasticizers (qv), and other polymers. It imparts a combination of desirable properties to properly formulated esterification products, including low color, good weathering and chemical resistance, and improved thermal and hydrolytic stabiUty. 

Propylene oxide and other epoxides undergo homopolymerization to form polyethers. In industry the polymerization is started with multihinctional compounds to give a polyether stmcture having hydroxyl end groups. The hydroxyl end groups are utilized in a polyurethane forming reaction. This article is mainly concerned with propylene oxide (PO) and its various homopolymers that are used in the urethane industry. 

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

The addition polymerization of diisocyanates with macroglycols to produce urethane polymers was pioneered in 1937 (1). The rapid formation of high molecular weight urethane polymers from Hquid monomers, which occurs even at ambient temperature, is a unique feature of the polyaddition process, yielding products that range from cross-linked networks to linear fibers and elastomers. The enormous versatility of the polyaddition process allowed the manufacture of a myriad of products for a wide variety of appHcations. 

Isocyanates. The commodity isocyanates TDI and PMDI ate most widely used in the manufacture of urethane polymers (see also Isocyanates, organic). The former is an 80 20 mixture of 2,4- and 2,6-isomers, respectively the latter a polymeric isocyanate obtained by phosgenation of aniline—formaldehyde-derived polyamines. A coproduct in the manufacture of PMDI is 4,4 -methylenebis(phenyHsocyanate) (MDI). A 65 35 mixture of 2,4- and 2,6-TDI, pure 2,4-TDI and MDI enriched in the 2,4 -isomer are also available. The manufacture of TDI involves the dinitration of toluene, catalytic hydrogenation to the diamines, and phosgenation. Separation of the undesired 2,3-isomer is necessary because its presence interferes with polymerization (13). 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Low viscosity urethane polymers have been prepared from castor od and polymeric isocyanates (82). These low mix viscosity systems are extremely usehd for potting electrical components where fast penetration without air voids, and fast dispensing cycles are desirable. Very low viscosity urethane systems containing castor polyols have been prepared for use in reclaiming water-logged buried telephone cable and for encapsulating telephone cable sphces (83—86). 

Polymerization of castor od, chemical or oxidative, results in higher viscosity or bodied ods that are more usehd in urethane coatings than the untreated castor od (87). Other castor derivatives used to prepare urethanes are amides prepared by reaction of castor od and alkanolamines, amides of ricinoleic acid with long-chain di- and triamines, and butanediol diricinoleate (88,89). 

The addition—reaction product of bisphenol A [80-05-07] and glycidyl methacrylate [106-91-2] is a compromise between epoxy and methacrylate resins (245). This BSI—GMA resin polymerizes through a free-radical induced covalent bonding of methacrylate rather than the epoxide reaction of epoxy resins (246). Mineral fillers coated with a silane coupling agent, which bond the powdered inorganic fillers chemically to the resin matrix, are incorporated into BSI—GMA monomer diluted with other methacrylate monomers to make it less viscous (245). A second monomer commonly used to make composites is urethane dimethacrylate [69766-88-7]. 

Blocked isocyanates are particularly helpful in dual cure mechanisms. In one instance, UV light first polymerizes an acrylate polymer containing hydroxyl groups. The system also contains a malonate ester-blocked isocyanate. The one-component system is heated, which starts the polymerization of the acrylate. Higher temperatures unblock the isocyanate, permitting the cure of the urethane to proceed [15]. 

The most commonly used isocyanate in urethane adhesives is MDI. The pure material methylene diphenyl-isocyanate is a solid that melts around 37°C. Many variations of MDI are commercially available, and these variations fall into three major classes monomeric MDI, modified MDI s, and polymeric MDI s. 

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