Polyetheric chains

The polymerisation reaction of PO, initiated by a bifunctional starter such as 1,2 propyleneglycol, leads to the formation of polyether diols, each hydroxyl group generating a polyetheric chain, terminated by a hydroxyl group [1-13] ... 

The pseudoliving character of PO anionic polymerisation produces a large variety of block copolymers, by simply changing the nature of the oxirane monomer because the catalytic species (potassium alcoholate) remains active during and after the polymerisation reaction. Thus, if a polyether is synthesised first by anionic polymerisation of PO and the polymerisation continues with another monomer, such as EO, a block copolyether PO-EO with a terminal poly[EO] block is obtained. Another synthetic variant is to obtain a polyethoxylated polyether first by the anionic polymerisation of EO initiated by glycerol [108], followed by the addition of PO to the resulting polyethoxylated triol. A block copolyether PO-EO is obtained with internal poly[EO] block linked to the starter. Another possibility is to add the monomers in three steps first PO is added to glycerol, followed by EO addition and finally by the addition of PO. A copolyether triol block copolymer PO-EO with the internal poly[EO] block situated inside the polyetheric chain between two poly[PO] blocks is obtained [4, 100, 101]. 

Polyethers being simple aliphatic ethers are very susceptible to auto-oxidation (self-oxidation), even by simple storage in air at room temperature. This behaviour is explained by the lability of the hydrogen atoms situated in the alpha position (attached to the carbon atoms linked to the etheric oxygen atoms of polyetheric chains) ... 

A radical R abstracts a hydrogen atom from the polyetheric chain generating a polymeric radical ... 

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]. 

The hydrogen atoms situated in the a position against the etheric oxygen atoms of the polyetheric chain are very susceptible to radical attack (hydrogen abstraction by radical mechanism), giving transfer reactions [1, 12, 18]. 

By the attack of the radical I on a polyetheric chain, radical species situated at a carbon atoms of the polyetheric chains are generated by transfer reactions ... 

Both radicals, I and the radical generated on the polyetheric chains, initiate the radical polymerisation of vinylic monomers. The radical I leads to the formation of ungrafted carbocatenary vinylic polymer. The polyetheric radical generates the formation of graft species ... 

For an improved stabilisation efficiency, the NAD which have longer polyetheric chains than the polyetheric chains of the polyether polyols are preferred for use as continuous phase [4, 6]. 

The most important way to synthesise macromers having polyetheric chains is to attach to the one terminal hydroxyl group a double bond (by various reactions of hydroxyl groups) or to introduce a double bond as a lateral group in the polyetheric chain [4, 8, 9, 11, 12, 40-56]. 

The best way to obtain macromers with polyetheric chains is to use the reactions of polyether terminal hydroxyl groups with reagents containing double bonds. 

When using a macromer as a NAD, a high macromer content copolymer, called a comb polymer , is formed first. After the consumption of 1-3% of the total quantity of vinylic monomers, the resulting high macromer content copolymer is self-organised in the similar spherical proto-particles, which turn the reaction mass from transparent to opaque, with the carbocatenary polymeric part situated inside the spheres and the polyetheric chain situated outside the sphere, in the continuous liquid polyether phase. The next steps are identical to those of nonreactive NAD. The particles formed remain constant in number but increase in particle diameter size, the final diameter being around 10-20 times higher than the initial proto-particle diameter, of around 0.3-1 pm. 

Obviously, the extension of the polyetheric chain using KOH as catalyst needs a purification step. The advantage of using tertiary amines or the catalytic effect of the amino polyol is very important from the technological point of view because the purification step is eliminated, the production cycle is short and the yield in polyether polyol is very high. 

The effect on the viscosity decrease by the introduction of EO units in the polyetheric chains is more significant in the case of aromatic diamine alkoxylation, such as the alkoxylation of o-TDA [4]. 

The resulting amino polyols (structure 13.2) do not have a polyetheric structure, but if the addition of alkylene oxide continues by extension of the chains derived from hydroxyl groups, real structures of polyether polyols are formed (reaction 13.3). 

It is already well known that the PUs are obtained by reacting a diisocyanate (I) with a macrodiol (MD) of a polyesteric or polyetheric type, and with a glycol as a chain extender (CE). The simplest approach seems to be the simultaneous mixing of the three components on approaching the one shot synthesis route ... 

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