Thermosetting resin composition of semi-IPN composite, and varnish, prepreg and metal clad laminated board using the same

1. A thermosetting resin composition comprising a polyphenylene ether-modified butadiene prepolymer which includes a polyphenylene ether (A) and a butadiene polymer, characterized in that the thermosetting resin composition is obtained by a process for manufacture of the thermosetting resin composition wherein:

the butadiene polymer has a crosslinked structure;

the process has a step (1) in which a butadiene polymer (B) crosslinks with a crosslinking agent (C) (excluding the butadiene polymer (B)) in the presence of the polyphenylene ether (A) in a medium to obtain the polyphenylene ether-modified butadiene prepolymer;

a number average molecular weight of the polyphenylene ether (A) is in a range of 7,000 to 30,000;

the butadiene polymer (B) molecule contains 40% or more of a 1,2-butadiene unit having a 1,2-vinyl group in a side chain; and

the butadiene polymer (B) is not a modified polybutadiene in which the 1,2-vinyl group in the side chain, or one or both of the terminals in the molecule, is chemically modified to be converted to epoxy, glycol, phenol, maleic acid, (meth)acryl, or urethane, and

with the proviso that excluded from the polyphenylene ether (A) is a polyphenylene ether which is a modified phenol product so obtained by redistribution reaction of a polyphenylene ether resin having a number average molecular weight of 10,000-30,000 with a phenolic compound in the presence of a reaction initiator that the number average molecular weight of the product becomes 5 to 70% of that of the polyphenylene ether resin.

2. The thermosetting resin composition according to claim 1 , wherein:

the butadiene polymer (B) comprises:

(j) a —[CH 2 —CH═CH—CH 2 ]— unit and

(k) a —[CH 2 —CH(CH═CH 2 )]— unit,

with a ratio of j:k being 60 to 5:40 to 95; and

the crosslinking agent (C) is a compound having one or more ethylenically unsaturated double bonds in a molecule.

3. The thermosetting resin composition according to claim 1 , wherein:

the crosslinking agent (C) contains at least one maleimide compound represented by the formula (1):

wherein R 1 is an aliphatic or aromatic organic group having a valence of m; Xa and Xb, which may be identical or different from each other, each is a monovalent atom or organic group selected from a hydrogen atom, a halogen atom and an aliphatic organic group; and m represents an integer of 1 or greater.

4. The thermosetting resin composition according to claim 1 , wherein:

the crosslinking agent (C) is at least one maleimide compound selected from the group consisting of N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(4-methylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-diethylphenyl)maleimide, N-(2-methoxyphenyl)maleimide, N-benzylmaleimide, N-dodecylmaleimide, N-isopropylmaleimide and N-cyclohexylmaleimide.

5. The thermosetting resin composition according to claim 1 , wherein:

the crosslinking agent (C) is at least one vinyl compound including divinylbiphenyl.

6. The thermosetting resin composition according to claim 1 , wherein:

a mixing proportion of the polyphenylene ether (A) is in a range of 2 to 200 parts by weight based on 100 parts by weight of the total amount of the butadiene polymer (B) and the crosslinking agent (C), and a mixing proportion of the crosslinking agent (C) is in a range of 2 to 200 parts by weight based on 100 parts by weight of the butadiene polymer (B).

7. The thermosetting resin composition according to claim 1 , wherein:

a conversion rate of the crosslinking agent (C) falls in the range of 5 to 100% in the step (1).

8. The thermosetting resin composition according to claim 1 , wherein:

a radical reaction initiator (D) is further incorporated in the step (1) and then the butadiene polymer (B) crosslinks with the crosslinking agent (C).

9. The thermosetting resin composition according to claim 1 , wherein:

the process further comprises a step (2) in which the polyphenylene ether-modified butadiene prepolymer obtained in the step (1) is incorporated with a radical reaction initiator (D).

10. The thermosetting resin composition according to claim 1 , wherein:

the process further comprises a step (2) in which the polyphenylene ether-modified butadiene prepolymer obtained in the step (1) is incorporated with a compound (E) of a crosslinkable monomer or crosslinkable polymer which contains one or more groups having an ethylenically unsaturated double bond in a molecule.

11. The thermosetting resin composition according to claim 1 , wherein:

the process further comprises a step (2) in which the polyphenylene ether-modified butadiene prepolymer obtained in the step (1) is incorporated with a compound (E) of a crosslinkable monomer or crosslinkable polymer which is at least one selected from the group consisting of a butadiene polymer (B-1), maleimide compounds and styrene-butadiene copolymers; and

the butadiene polymer (B-1) is not a modified polybutadiene in which the 1,2-vinyl group in the side chain, or one or both of the terminals in the molecule, is chemically modified to be converted to epoxy, glycol, phenol, maleic acid, (meth)acryl, or urethane.

12. The thermosetting resin composition according to claim 1 , wherein:

the process further comprises a step (2) in which the polyphenylene ether-modified butadiene prepolymer obtained in the step (1) is incorporated with a compound (F) of at least one of a bromine-based flame retardant and a phosphorus-based flame retardant.

13. The thermosetting resin composition according to claim 1 , wherein:

the process further comprises a step (2) in which the polyphenylene ether-modified butadiene prepolymer obtained in the step (1) is incorporated with inorganic filler (G).

14. A resin varnish for printed circuit boards, obtained by dissolving or dispersing the thermosetting resin composition according to claim 1 in a solvent.

15. A prepreg obtained by impregnating the resin varnish for printed circuit boards according to claim 14 into a substrate, and then drying the impregnated substrate.

16. A metal clad laminated board obtained by stacking one or more sheets of the prepreg for printed circuit boards according to claim 15 , disposing metal foil on one side or both sides of the stacked prepreg, and pressing them together while heating.

17. The thermosetting resin composition according to claim 1 , wherein said step (1) is a preliminary reaction step in which the butadiene polymer (B) reacts with the crosslinking agent (C) so as to obtain said polyphenylene ether-modified butadiene prepolymer, in an uncured state before complete curing, having mutual entanglement of molecular chains of the polyphenylene ether (A) and crosslinking product between the butadiene polymer (B) and the crosslinking agent (C).