Provided is a polymethallyl alcohol copolymer having a structural unit (A) represented by the following formula (A) and a structural unit (B) represented by the following formula (B), a molar ratio (A)/(B) of the structural unit (A) to the structural unit (B) being greater than or equal to 0.5; a method of producing the copolymer; and a molding containing the copolymer. In the formula (B), X represents at least one selected from the group consisting of a hydrogen atom, an alkoxy group, a hydroxy group, and an alkyl group having 1 to 3 carbon atoms.

##STR00001##

A process for preparing a composition by free-radical polymerization of a monomer composition comprising: a) at least one ethylenically unsaturated carboxylic acid containing monomer or anhydride thereof; b) optionally at least one ethylenically unsaturated monomer different from a) but copolymerizable therewith; and c) at least one crosslinking monomer containing at least two ethylenically unsaturated groups. The monomer composition is polymerized in an organic medium having a solubilizing effect on one or more of the monomeric ingredients, but substantially none on the resulting polymer. The polymerization is conducted in the presence of a free radical forming catalyst and at least one steric stabilizing polymer polymerized from a vinyl lactam and a copolymerizable monomer selected from a short chain alkyl ester of (meth)acrylic acid, a long chain alkyl ester of (meth)acrylic acid, and combinations thereof.

Provided are: a water-absorbent resin which, when used as an absorbent material, retains a high water-absorption performance, increases the diffusivity of a to-be-absorbed liquid and makes it possible to effectively decrease the amount of re-wet; and an absorbent article formed using an absorbent material including the water-absorbent resin. The water-absorbent resin according to the present invention is a water-absorbent resin obtained by polymerizing a water-soluble ethylenically monomer in the presence of an internal-crosslinking agent and thereafter post-crosslinking the polymer with a post-crosslinking agent, characterized in that when subjected to a liquid flow test, the water-absorbent resin has an effective absorbent material index (K) indicated by equation (I) of 250 or greater.

Effective absorbent material index (K)=[(the amount of liquid flow) (g)]×[(artificial-urine absorption ratio) (g/g)]  (I)

Provided are: a water-absorbent resin which, when used as an absorbent material, retains a high water-absorption performance, increases the diffusivity of a to-be-absorbed liquid and makes it possible to effectively decrease the amount of re-wet; and an absorbent article formed using an absorbent material including the water-absorbent resin. The water-absorbent resin according to the present invention is a water-absorbent resin obtained by polymerizing a water-soluble ethylenically monomer in the presence of an internal-crosslinking agent and thereafter post-crosslinking the polymer with a post-crosslinking agent, characterized in that when subjected to a liquid flow test, the water-absorbent resin has an effective absorbent material index (K) indicated by equation (I) of 250 or greater.

Effective absorbent material index (K)=[(the amount of liquid flow) (g)]×[(artificial-urine absorption ratio) (g/g)]  (I)

Disclosed is a resin comprising a structural unit derived from a compound represented by formula (I) and a structural unit having an acid-labile group: ##STR00001## ##STR00002##
wherein R.sup.1 represents a hydrocarbon group which may have a substituent, R.sup.2 each independently represent an alkyl group which may have a halogen atom, a hydrogen atom or a halogen atom, Ar represents an aromatic hydrocarbon group which may have a substituent, L.sup.1 represents a group represented by formula (L.sup.1-1), etc., L.sup.11, L.sup.13, L.sup.15 and L.sup.17 each independently represent an alkanediyl group, L.sup.12, L.sup.14, L.sup.16 and L.sup.18 each independently represent —O—, —CO—, —CO—O—, etc., * and ** are bonds, and ** represents a bond to an iodine atom.

Disclosed is a resin comprising a structural unit derived from a compound represented by formula (I) and a structural unit having an acid-labile group: ##STR00001## ##STR00002##
wherein R.sup.1 represents a hydrocarbon group which may have a substituent, R.sup.2 each independently represent an alkyl group which may have a halogen atom, a hydrogen atom or a halogen atom, Ar represents an aromatic hydrocarbon group which may have a substituent, L.sup.1 represents a group represented by formula (L.sup.1-1), etc., L.sup.11, L.sup.13, L.sup.15 and L.sup.17 each independently represent an alkanediyl group, L.sup.12, L.sup.14, L.sup.16 and L.sup.18 each independently represent —O—, —CO—, —CO—O—, etc., * and ** are bonds, and ** represents a bond to an iodine atom.

The problem to be solved by the invention is to provide an ionomer having excellent transparency, maintaining a high elastic modulus at high temperatures, being less coloration, and having a reduced odor during molding processing. The means for solving the problem is an ionomer comprising 0.05 to 1.0 mol % of (meth)acrylic acid ester units, 4.5 to 9.0 mol % of carboxylic acid units, 0.65 to 3.0 mol % of carboxylic acid neutralized product units, and ethylene units, based on the total monomer units which constitute the resin, with the total content of the (meth)acrylic acid ester units, the carboxylic acid units, and the carboxylic acid neutralized product units being 7.0 to 10 mol %.

The problem to be solved by the invention is to provide an ionomer having excellent transparency, maintaining a high elastic modulus at high temperatures, being less coloration, and having a reduced odor during molding processing. The means for solving the problem is an ionomer comprising 0.05 to 1.0 mol % of (meth)acrylic acid ester units, 4.5 to 9.0 mol % of carboxylic acid units, 0.65 to 3.0 mol % of carboxylic acid neutralized product units, and ethylene units, based on the total monomer units which constitute the resin, with the total content of the (meth)acrylic acid ester units, the carboxylic acid units, and the carboxylic acid neutralized product units being 7.0 to 10 mol %.

Disclosed is an absorbent article 100 including an absorber 10 containing water-absorbent resin particles 10a, in which the water-absorbent resin particles 10a have a maximum gel resistance measured by procedures (1) to (3) of 0.3 to 1.5 N, and a water absorption amount for physiological saline under a load of 4.14 kPa of 12 mL/g or more.

Disclosed is an absorbent article 100 including an absorber 10 containing water-absorbent resin particles 10a, in which the water-absorbent resin particles 10a have a maximum gel resistance measured by procedures (1) to (3) of 0.3 to 1.5 N, and a water absorption amount for physiological saline under a load of 4.14 kPa of 12 mL/g or more.