Polymer-polyol

Installation of an external circuit in the system of a tubular turbulent divergent-convergent device causes changes in the conditions of the reaction mass motion. Firstly, in addition to the transporting pump, a turbulent flow is formed and persists 

Rapid and intensive mixing, and a combination of turbulent and laminar flows, enables the acceleration of monomer polymerisation, an increase in its depth, and exclusion of large particle formation in the polyester. This defines the dispersing stability not only for polymer-polyol but for other compositions of polyol dispersions, and results in highly flexible polyurethane foam processability and a high quality of moulded articles. Some properties of polymer-polyol and flexible polyurethane foam are given in Tables 5.6 and 5.7 [27]. 

Conditions Synthesis period, h Viscosity, Pa s Solid residual, % Average size of polymer particle, pm Gravitational stability of dispersion, 24 h(T = 45 °C) Monomer odour (acryl- nitrile) 

2 Mixing devices equipped with a tubular turbulent divergent-convergent device (8 sections) in an external circuit. 

Analysis of the properties of polymer-polyol and flexible polynrethane foam shows that the process flow turbulisation in polymer-polyol production enables the manufacturing of products with high-quality properties and reduces process time considerably. 

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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. 

One unusual but nevertheless important application of SAN has been in the manufacture of polymer polyols used in the manufacture of flexible polyurethane foams. Proportions of up to 40% of the polyol may be used to increase stiffness as foam bulk densities are lowered (see Section 27.5.4). 

There is an increasing market for higher resilience foams using the so-called polymer polyols. Amongst the earliest to become established were suspensions of styrene-aerylonitrile copolymer in the polyol. A variation involved some grafting of SAN, either instead of or in addition to the use of a suspension. 

In the 1990s this approach became more common in order to ensure sufficient compressive strength with the trend to lower bulk densities. Furthermore the proportion of SAN to polyol has been increased to about 40%. This may lead to serious stability problems and care must be taken to control the size and distribution of the particles and prevent agglomeration. Polymer polyols using polystyrene as the polymer component have recently become available (Postech-Shell) and are claimed to exhibit good stability, low viscosity and less discolouration as well as providing price advantages. 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

With amine initiators the so-called self-catalyzed polyols are obtained, which are used in the formulation of rigid spray foam systems. The rigidity or stiffness of a foam is increased by aromatic initiators, such as Mannich bases derived from phenol, phenolic resins, toluenediamine, or methylenedianiline (MDA). In the manufacture of highly resilient flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. 

ACRN is used to make acrylic fibers, acrylonitrile-butadiene-styrene (ABS), and styrene-acrylonitrile (SAN). Worldwide acrylic fiber accounts for over half of total demand while ABS and SAN consume about 30% of output. Smaller applications include nitrile rubber copolymers (4%), adiponitrile (ADN) and acrylamide. Acrylic fibers are used in carpets and clothing while ABS and SAN resins are used in pipes and fittings, automobiles, furniture, and packaging276. In the United States the ACRN uses are distributed differently 38% is used in ADN, 22% in ABS and SAN, 17% in acrylic fibers, 11% in acrylamide, 3% in nitrile elastomers, and 9% in miscellaneous, which includes polymers, polyols, barrier resins and carbon fibers277. 

Modified polyether polyols have appeared in recent years, i.e., graft polyether polyols (polymer polyols, copolymer polyols) which were first developed by Union Carbide Corp. in the mid-1960 s. 

Graft Polyol Technology. Graft polyols (or polymer polyols) are prepared by grafting both acrylonitrile and styrene monomer or acrylonitrile alone to conventional polyether polyols. Graft polyols provide increased load-bearing ability as well as cell-opening, which prevent or minimize the formation of closed-cell foams, because closed-cell flexible foams readily shrink. 

Normally a 70/30 to 50/50 blend of a 4500-6500 EO-capped polyether triol with a polymer polyol is used, together with an 80 20 blend of TDI (80/20 isomer ratio) and polymeric MDI. Recently, higher-solids-content graft polyols, e.g., 30-50% solid polyols, have become available in the market. 

Polymer Polyol, 20% Solids, with a Hydroxyl Number of 28. 

Polymer polyols (filled polyols) 2. Aminic polyols... 

The utilisation of the high MW aminic polyether polyols in the synthesis of polymer polyols [graft polyether polyols and polyisocyanate polyaddition (PIPA) polyols] is presented in Chapter 6 [148, 151]. 

Polymer polyols are defined as very fine and stable dispersions of solid polymers (vinylic polymers and copolymers, polyurea, polyurethanes) in liquid polyethers. Currently polymer polyols represent one of the most important group of polyolic intermediates for elastic polyurethanes [1-10]. 

These kind of polyether polyols containing polymeric fillers are called polymer polyols and are produced on a large industrial scale, because they are one of the most important group of polyols used for high performance flexible polyurethane (PU) foams and PU elastomers [8-12]. 

Polymer polyols are divided, by the nature of the polymer finely dispersed in the polyether matrix, into the following categories [8-10] ... 

The third component, the graft species, acts as a nonaqueous dispersant (NAD), a compound having, in the same structure, polyetheric chains and vinylic polymer chains. This compound assures the stability of the resulting polymer dispersion and prevents sedimentation and coalescence of the vinylic polymer particles [1-5]. The mechanism of this dispersion stabilisation will be discussed later. The median diameter of solid particles for a performance polymer polyol is generally less than 1 [am, usually 0.2-0.5 im [30]. 

Shell developed a special line of polymer polyols based exclusively on styrene [11], the stabilisation of the resulting dispersion of polystyrene in liquid polyether being given by special NAD [8, 9, 32, 33] and of course not to the graft species, which in the case of polystyrene are practically absent. 

The structure (6.8) is another type of NAD formed in situ by transfer reaction with the tertiary amine type polyethers. Addition of a high molecular weight polyether initiated by an alkanolamine, ethylene diamine, N-methyl substituted propylene diamine, or N,N dimethyl dipropylene diamines in the polyether polyol used for grafting leads to the formation of very stable polymeric dispersions [37]. The solid fraction has particles of low median diameter (<1.5 pm). The resulting polymer polyols have low viscosities which give good stabilisation of the polymeric dispersion. 

The dispersions obtained by copolymerisation of styrene with ACN, with low ACN content (ACN being around 25-30% in the monomer mixture), are more difficult to stabilise. For such low ACN content polymer polyols, or for polymer polyols based exclusively on styrene, more efficient NAD are necessary. These are discussed in the next chapters, i.e., macromers (reactive NAD) and nonreactive NAD. 

Stabilisation of Polymer Dispersions in Polymer Polyols with Macromers (Reactive NAD)... 

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