The present invention describes a process for the synthesis of spherical particles of polyvinyl alcohol—PVA and/or polyvinyl acetate—PVAc with shell nucleus structure from total or partial hydrolysis in a caustic aqueous medium with obtaining particulates of PVA/PVAc with controlled spherical morphology, to be used in vascular embolization.

The present invention describes a process for the synthesis of spherical particles of polyvinyl alcohol—PVA and/or polyvinyl acetate—PVAc with shell nucleus structure from total or partial hydrolysis in a caustic aqueous medium with obtaining particulates of PVA/PVAc with controlled spherical morphology, to be used in vascular embolization.

Provided is a dispersion stabilizer for suspension polymerization, the dispersion stabilizer making it possible to obtain, through suspension polymerization of a vinyl compound such as vinyl chloride, resin particles having uniform particle diameters and few large particles, and also having a high porosity and a large plasticizer absorption. A modified vinyl alcohol polymer has a hydrodynamic radius (Rh) (unit: nm) that satisfies equation (1) where x is the viscosity average polymerization degree. (1): 0.186x.sup.0.542×1.30≥Rh≥0.186x.sup.0.542×1.06

Provided is a dispersion stabilizer for suspension polymerization, the dispersion stabilizer making it possible to obtain, through suspension polymerization of a vinyl compound such as vinyl chloride, resin particles having uniform particle diameters and few large particles, and also having a high porosity and a large plasticizer absorption. A modified vinyl alcohol polymer has a hydrodynamic radius (Rh) (unit: nm) that satisfies equation (1) where x is the viscosity average polymerization degree. (1): 0.186x.sup.0.542×1.30≥Rh≥0.186x.sup.0.542×1.06

Provided is a dispersion stabilizer for suspension polymerization, the dispersion stabilizer making it possible to obtain, through suspension polymerization of a vinyl compound such as vinyl chloride, resin particles having uniform particle diameters and few large particles, and also having a high porosity and a large plasticizer absorption. A modified vinyl alcohol polymer has a hydrodynamic radius (Rh) (unit: nm) that satisfies equation (1) where x is the viscosity average polymerization degree. (1): 0.186x.sup.0.542×1.30≥Rh≥0.186x.sup.0.542×1.06

An iodine-containing (meth)acrylate compound represented by formula (1):

##STR00001##

wherein R.sup.1 represents a hydrogen atom, methyl, or halogen; each R.sup.2 independently represents a hydrogen atom, a linear organic group having 1 to 20 carbon atoms, a branched organic group having 3 to 20 carbon atoms, or a cyclic organic group having 3 to 20 carbon atoms; A represents an organic group having 1 to 30 carbon atoms; A contains at least one acyl group; n.sup.1 represents 0 or 1; and n.sup.2 represents an integer of 1 to 20.

An iodine-containing (meth)acrylate compound represented by formula (1):

##STR00001##

wherein R.sup.1 represents a hydrogen atom, methyl, or halogen; each R.sup.2 independently represents a hydrogen atom, a linear organic group having 1 to 20 carbon atoms, a branched organic group having 3 to 20 carbon atoms, or a cyclic organic group having 3 to 20 carbon atoms; A represents an organic group having 1 to 30 carbon atoms; A contains at least one acyl group; n.sup.1 represents 0 or 1; and n.sup.2 represents an integer of 1 to 20.

Compositions comprising phosphonate-functionalized polyene copolymers and a reinforcing filler, in particular rubber compositions, and to their uses is provided.

This phosphonate-functionalized polyene copolymer comprises, in its main linear chain, unsaturated units resulting from at least one conjugated polyene monomer and units substituted by a —C(O)O-A-P(O)OR.sub.1OR.sub.2 functional group, in which R.sub.1 and R.sub.2, which are identical or different, each represent H or a C.sub.1-C.sub.6 alkyl and A represents a (C.sub.1-C.sub.6)alkylene radical or a (C.sub.1-C.sub.5)alkylene radical containing at least one heteroatom.

The use of this copolymer in a tire composition additionally comprising a diene elastomer and a reinforcing filler, for improving the interactions between the filler and the diene elastomer included in the said tire composition is also provided.

Compositions comprising phosphonate-functionalized polyene copolymers and a reinforcing filler, in particular rubber compositions, and to their uses is provided.

This phosphonate-functionalized polyene copolymer comprises, in its main linear chain, unsaturated units resulting from at least one conjugated polyene monomer and units substituted by a —C(O)O-A-P(O)OR.sub.1OR.sub.2 functional group, in which R.sub.1 and R.sub.2, which are identical or different, each represent H or a C.sub.1-C.sub.6 alkyl and A represents a (C.sub.1-C.sub.6)alkylene radical or a (C.sub.1-C.sub.5)alkylene radical containing at least one heteroatom.

The use of this copolymer in a tire composition additionally comprising a diene elastomer and a reinforcing filler, for improving the interactions between the filler and the diene elastomer included in the said tire composition is also provided.

A dispersion stabilizer for suspension polymerization is provided that includes a vinyl alcohol-based polymer (A), wherein a 0.1 mass % concentration aqueous solution of the polymer (A) has an absorbance (a1) of less than 0.25 at a wavelength of 280 nm, the aqueous solution has an absorbance (a2) of less than 0.030 at a wavelength of 320 nm, the polymer (A) has a degree of saponification of not less than 68 mol % and not more than 98 mol %, the polymer (A) has a viscosity-average degree of polymerization of more than 1500 and less than 4500, and the polymer (A) in powder form has a YI value of not less than 5. The dispersion stabilizer is capable of producing a vinyl-based resin that is excellent in polymerization stability, has a small particle size, and has an improved bulk density.