PHD polyols

Polyurea dispersion polyols (PHD polyols, Polyhamstoff Dispersion polyols) were developed by Mobay Corp. (151). PHD polyols are usually... 

In automotive applications, e.g., automotive seats, molded HR foam is the major process used. HR foam is produced by using four kinds of technologies (a) crosslinker technology, b) graft-polyol technology, (c) PHD polyol technology, and (d) specialty isocyanate technology. 

TECHNIQUE HOT-CURE COLD-CURE GRAFT PHD POLYOL SPECIALTY... 

Many of the same basic raw materials shown in Table II for RIM fascia systems are also used in high modulus systems. Additionally, however, polyether polyols "filled" with dispersions of polyureas are used( 2) These are the so-called PHD polyols developed by Bayer AG, the PHD being an abbreviation for Polyharnstoff-Dispersion. These polyols provide the same "filler" effect as the graft polyols (Table II) for increasing the modulus of the polymer without increasing the amount of extender. 

Phillips, B. A. Taylor, R. P. PHD Polyols for RIM Applications, paper presented at Rubber Division, American Chemical Society Meeting, Atlanta, Georgia, Mar. 27-30, 1979. 

PHD polymer polyols are a special class of filled polyols developed successfully by Bayer, PHD being the abbreviation of the German name polyharnstoff dispersion or polyurea dispersions [67-69]. PHD polyols contain organic urea, oligomeric or polymeric polyurea, finely dispersed in liquid polyether polyols [67-73]. The difference between PHD polyols and graft polyether polyols is the different nature of the solid polymer dispersed (it is a heterocatenary polymer - polyurea - instead of carbocatenary polymer) which is obtained by another synthetic procedure (polyaddition reaction between a diisocyanate and a diamine instead of radical polymerisation). The reaction between the diisocyanate and the diamine, takes place in situ (reaction 6.19), in liquid poly ether. The resultant polyurea being insoluble in polyether, precipitates in the form of very fine particles ... 

Usually the viscosity of PHD polymer polyols is higher than the viscosity of graft polyether polyols, at the same solids content. For example a graft polyether polyol, with a 20% solid fraction (copoly[ACN - styrene]), has a viscosity of 2000-3000 MPa-s at 25 °C, but a PHD polyol, with the same solids concentration has a viscosity of 3000-3500 MPa-s at 25 °C [10, 67-69]. This high viscosity is direct evidence of the intensive interaction, by secondary forces, between the polyurea filler and the continuous liquid polyether phase. 

Very interesting PHD polyols are obtained by the reaction in polyether media of TDI with primary amines and, instead of polymeric polyurea, organic diurea compounds are generated, insoluble in polyethers, in the form of a very fine dispersion. Example of amines used include ammonia, anilines and substituted anilines, and fatty amines (reactions 6.22 and 6.23). 

Usually an equimolecular mixture diamine, TDI is used (a very small excess of TDI is frequently used to compensate for the consumption of TDI in reaction with hydroxyl groups), which normally leads to maximum molecular weight in the resultant polyurea. As a general observation, the molecular weight of solid polyurea from PHD polyols has a lower molecular weight than the copoly [ACN - styrene] obtained as filler in graft polyether polyols. 

Figure 6.11 Technological scheme for PHD polyols synthesis (variant). 1) Static mixer for polyether with hydrazine 2) Static mixer for polyether with TDI 3) Static mixer for TDI-hydrazine reaction 4) Loop reactor with total recirculation 5) Recirculation...

Generally, PHD polyols are obtained with 5-20% solid content (maximum 28%) and have a similar aspect with graft polyether polyols, i.e., white opaque dispersions, the median diameter of particles being < 1 im. 

PHD polyols are successfully used for high resilience flexible PU foams (made by the cold cure process), for continuous slabstock flexible PU foams and for elastomers obtained especially by reaction injection moulding (RIM) technology. 

The synthesis of polyisocyanate polyaddition (PIPA) polymer polyols is very similar to the synthesis of PHD polyols, with the difference that, instead of polyurea, a PU finely... 

In a similar way with PHD polyols, PIPA polyols can be produced in very high efficiency stirred reactors or using the static mixers in series. A technological variant for PIPA polyol fabrication, by reaction of TEOA with TDI, is presented in Figure 6.12. 

In the manufacture of highly resilient flexible foams and some 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 polyharnstoff dispersion (PHD) polyols, which are marketed by Bayer (53). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion (54). The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM applications where elastomers of high modulus, low thermal coefficient of expansion, and improved paintability are needed. 

As was the case for graft and PHD polymer polyols, by using PIPA polyols, an increase in hardness, tensile strength and tear strength of the resultant flexible PU foams was observed, as compared to the PU foams made with unfilled polyether polyols. 

In the practice, the most important polymer polyols are graft polyether polyols, PHD and PIPA polyols, but other good quality polymer dispersions in liquid polyethers have been created, which at this moment are not industrially important, such as ... 

In Chapter 3, the chemistry and technology of the most important oligo-polyols used for elastic polyurethanes fabrication, in fact high MW oligomers (2000-12000 daltons) with terminal hydroxyl groups and low functionality (2-4 hydroxyl groups/mol) were discussed. Polyalkylene oxide polyols (homopolymers of PO or copolymers PO - EO, random or block copolymers), polytetrahydrofuran polyols, filled polyols (graft poly ether polyols, poly Harnstoff dispersion - polyurea dispersions (PHD) and polyisocyanate poly addition (PIPA) polyols), polybutadiene polyols and polysiloxane polyols were all discussed. The elastic polyurethanes represent around 72% of the total polyurethanes produced worldwide. 

PHD (polyharnstoff dispersion) or PUD (polyurea dispersion) polyols have been introduced by Bayer-Mobay as an alternative to... 

Janssen A (1993) Enzymatic synthesis of polyol esters in aqueous-organic two-phase systems. PhD thesis, Agricultural University of Wageningen, NL... 

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