A methacrylic resin having a cyclic structure in a main chain thereof, a shaped article, and an optical component or automotive part, in which the glass transition temperature is higher than 120° C. and 160° C. or lower, and the sign of the orientational birefringence when being oriented so as to have a degree of orientation of 0.03 is different from the sign of the orientational birefringence when being oriented so as to have a degree of orientation of 0.08.

[Problem] To provide a radiation curable resin composition that is suitable as a primary material of an optical fiber and has a fast curing rate by irradiation with radiation.

[Solution] A radiation polymerizable composition for forming a primary coating layer of an optical fiber, the radiation polymerizable composition comprising: (A) a urethane oligomer comprising a structure represented by formula (I) below:

##STR00001## wherein R is a vinyl group and * is a bond; (B) one or more compounds of: (i) maleic anhydride, (ii) a compound represented by formula (II):

##STR00002## wherein R.sup.1 is a single bond or an alkanediyl group comprising 1 to 6 carbon atoms, and R.sup.2 is a hydrogen atom, a hydroxy group, or a group represented by predetermined formula (II-1) or formula (II-2), or (iii) a compound represented by formula (III):

##STR00003## wherein R.sup.5 is an alkanediyl group comprising 1 to 6 carbon atoms; and (C) a radiation polymerization initiator.

[Problem] To provide a radiation curable resin composition that is suitable as a primary material of an optical fiber and has a fast curing rate by irradiation with radiation.

[Solution] A radiation polymerizable composition for forming a primary coating layer of an optical fiber, the radiation polymerizable composition comprising: (A) a urethane oligomer comprising a structure represented by formula (I) below:

##STR00001## wherein R is a vinyl group and * is a bond; (B) one or more compounds of: (i) maleic anhydride, (ii) a compound represented by formula (II):

##STR00002## wherein R.sup.1 is a single bond or an alkanediyl group comprising 1 to 6 carbon atoms, and R.sup.2 is a hydrogen atom, a hydroxy group, or a group represented by predetermined formula (II-1) or formula (II-2), or (iii) a compound represented by formula (III):

##STR00003## wherein R.sup.5 is an alkanediyl group comprising 1 to 6 carbon atoms; and (C) a radiation polymerization initiator.

[Problem] To provide a radiation curable resin composition that is suitable as a primary material of an optical fiber and has a fast curing rate by irradiation with radiation.

[Solution] A radiation polymerizable composition for forming a primary coating layer of an optical fiber, the radiation polymerizable composition comprising: (A) a urethane oligomer comprising a structure represented by formula (I) below:

##STR00001## wherein R is a vinyl group and * is a bond; (B) one or more compounds of: (i) maleic anhydride, (ii) a compound represented by formula (II):

##STR00002## wherein R.sup.1 is a single bond or an alkanediyl group comprising 1 to 6 carbon atoms, and R.sup.2 is a hydrogen atom, a hydroxy group, or a group represented by predetermined formula (II-1) or formula (II-2), or (iii) a compound represented by formula (III):

##STR00003## wherein R.sup.5 is an alkanediyl group comprising 1 to 6 carbon atoms; and (C) a radiation polymerization initiator.

An optical polymer material includes an alternating copolymer made of a monomer of a styrene derivative and a monomer of a maleimide derivative, and has a nonlinear property in which the photoelastic coefficient of the optical polymer material decreases to a predetermined value with increase in composition ratio of the styrene derivative, and rises above the predetermined value with further increase in composition ratio of the styrene derivative. A composition ratio of the styrene derivative is within a predetermined range. An absolute value of the photoelastic coefficient is equal to or smaller than a first absolute value within the predetermined range of the composition ratio, and an absolute value of the intrinsic birefringence is equal to or smaller than a second absolute value of the optical polymer material within the predetermined range of the composition ratio.

An optical polymer material includes an alternating copolymer made of a monomer of a styrene derivative and a monomer of a maleimide derivative, and has a nonlinear property in which the photoelastic coefficient of the optical polymer material decreases to a predetermined value with increase in composition ratio of the styrene derivative, and rises above the predetermined value with further increase in composition ratio of the styrene derivative. A composition ratio of the styrene derivative is within a predetermined range. An absolute value of the photoelastic coefficient is equal to or smaller than a first absolute value within the predetermined range of the composition ratio, and an absolute value of the intrinsic birefringence is equal to or smaller than a second absolute value of the optical polymer material within the predetermined range of the composition ratio.

An optical polymer material includes an alternating copolymer made of a monomer of a styrene derivative and a monomer of a maleimide derivative, and has a nonlinear property in which the photoelastic coefficient of the optical polymer material decreases to a predetermined value with increase in composition ratio of the styrene derivative, and rises above the predetermined value with further increase in composition ratio of the styrene derivative. A composition ratio of the styrene derivative is within a predetermined range. An absolute value of the photoelastic coefficient is equal to or smaller than a first absolute value within the predetermined range of the composition ratio, and an absolute value of the intrinsic birefringence is equal to or smaller than a second absolute value of the optical polymer material within the predetermined range of the composition ratio.

The compound (A) is represented by formula (1).

R.sub.1O—R.sub.2—OR.sub.1   (1)

(In formula (1), each R.sub.1 independently represents a group represented by formula (2), or a hydrogen atom, and R.sub.2 represents a linear or branched alkylene group having 1 to 16 carbon atoms, or a linear or branched alkenylene group having 2 to 16 carbon atoms, provided that at least one R.sub.1 is a group represented by formula (2).)

##STR00001##

(In formula (2), -* represents a bonding hand.)

The compound (A) is represented by formula (1).

R.sub.1O—R.sub.2—OR.sub.1   (1)

(In formula (1), each R.sub.1 independently represents a group represented by formula (2), or a hydrogen atom, and R.sub.2 represents a linear or branched alkylene group having 1 to 16 carbon atoms, or a linear or branched alkenylene group having 2 to 16 carbon atoms, provided that at least one R.sub.1 is a group represented by formula (2).)

##STR00001##

(In formula (2), -* represents a bonding hand.)

Provided herein according to some embodiments is a dual cure stereolithography resin that includes thermoplastic particles, which thermoplastic particles are insoluble in the resin and insoluble during a first, light, cure in which an intermediate object is produced, but then dissolve or swell in the intermediate object during the second, heat, cure.