Jeng-Yueh Shieh

Synthesis of novel flame retardant epoxy hardeners and properties of cured products

Abstract Novel flame-retardant curing agents for epoxy resins, [ODOPM–PN] and [ODOPM–MPN], were prepared from phenol formaldehyde novolac (PN), melamine-phenol formaldehyde novolac (MPN) and a reactive 2-(6-oxid-6H-dibenz〈c,e〉 〈1,2〉oxaphosphorin-6-yl)-methanol (ODOPM) while ODOPM was synthesized through the reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and formaldehyde. The compounds (ODOPM–PN and ODOPM–MPN) were used as flame-retardant hardener for o -cresol formaldehyde novolac epoxy (CNE) resin in electronic application. The thermal stability and flame retardancy were determined by thermal gravimetric analysis and UL 94 vertical test. The glass transition temperatures were measured by dynamic mechanical analysis. The phosphorus–nitrogen synergistic effect on flame retardancy combined with the rigid structure of ODOPM have resulted in better flame retardancy, higher glass transition temperature and thermal stability for the phosphorus–nitrogen containing epoxy resin system than the regular phosphorus-containing flame retardant epoxy resin system. UL 94-VO rating could be achieved with a lower phosphorus content of as low as 0.81% with 2.36% nitrogen for the ODOPM–MPN cured epoxy resin system and no fume and toxic gas emission were observed.

Synthesis and properties of epoxy resins containing 2-(6-oxid-6H-dibenz(c,e)(1,2) oxaphosphorin-6-yl) 1,4-benzenediol (II)

2-(6-Oxid-6H-dibenz〈c,e〉 〈1,2〉oxa-phosphorin-6-yl)1,4-benzenediol (ODOPB) was prepared by the addition reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and p-benzoquinone while DOPO was synthesized through multistep reaction from o-phenylphenol and phosphorus trichloride. The compound (ODOPB) was used as a reactive flame-retardant in o-cresol formaldehyde novolac epoxy resin (CNE) for electronic application. Owing to the rigid structure of ODOPB and pendant P group, the resultant phosphorus-containing epoxy resin exhibited better flame retardance, higher glass transition temperature and thermal stability than the regular bromine-containing flame-retardant epoxy resin. UL 94-VO rating could be achieved with a phosphorus content of as low as 1.1% (comparable to a bromine content of 6%) in the cured resin and no fume and toxic gas emission were observed.

Phosphorus-containing epoxy resin for an electronic application

A phosphorus-containing epoxy resin, 6-H-dibenz[c,e][1,2] oxaphosphorin-6-[2,5-bis(oxiranylmethoxy)phenyl]-6-oxide (DOPO epoxy resin), was synthesized and cured with phenolic novolac (Ph Nov), 4,4′-diaminodiphenylsulfone (DDS), or dicyandiamide (DICY). The reactivity of these three curing agents toward DOPO epoxy resin was found in the order of DICY > DDS > Ph Nov. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorus-containing epoxy resin showed lower weight loss temperature and higher char yield than that of bisphenol-A based epoxy resin. The high char yields and limiting oxygen index (LOI) values as well as excellent UL-94 vertical burn test results of DOPO epoxy resin indicated the flame-retardant effectiveness of phosphorus-containing epoxy resins. The DOPO epoxy resin was investigated as a reactive flame-retardant additive in an electronic encapsulation application. Owing to the rigid structure of DOPO and the pendant P group, the resulting phosphorus-containing encapsulant exhibited better flame retardancy, higher glass transition temperature, and thermal stability than the regular encapsulant containing a brominated epoxy resin. High LOI value and UL-94 V-0 rating could be achieved with a phosphorus content of as low as 1.03% (comparable to bromine content of 7.24%) in the cured epoxy, and no fume and toxic gas emission were observed.

Synthesis and properties of epoxy resins containing bis(3-hydroxyphenyl) phenyl phosphate

A reactive phosphorus-containing diol compound, bis(3-hydroxyphenyl) phenyl phosphate (BHPP), was synthesized. The compound (BHPP) was used as a reactive flame-retardant for diglycidyl ether of bisphenol-A (DGEBA). Thermal stability and the weight loss behavior of the cured polymers were studied by thermogravimetric analysis. The phosphorous-containing epoxy resin showed lower weight loss temperature and higher char yield than that of DGEBA. The high char yields and limiting oxygen index values as well as excellent UL-94 vertical burn test results of BHPP/DGEBA indicated the flame retardancy of the phosphorous-containing epoxy resins. The resulting phosphorous-containing epoxy resin exhibited better flame retardancy and higher thermal stability than the regular bromine containing flame retardant epoxy resin in encapsulation application. UL 94-VO rating could be achieved with a phosphorus content of as low as 1.5% (comparable to bromine content of 10%) in the cured resin, and no fume and toxic gas emission were observed.

PHOSPHORUS CONTAINING PET AND PEN BY DIRECT ESTERIFICATION

Abstract A series of various flame retardant copolyesters containing various amounts of phosphorus were synthesized by direct esterification process using the compound of [(6-oxido-6H-dibenz 〈c,e〉〈1,2〉 oxaphosphorin-6-yl)methyl]-butanedioic acid (ODOP-BDA) and bis (hydroxyethyl) terephthalate (BHET) or bis (hydroxyethyl) naphthalate (BHEN). The copolyesters having inherent viscosity of 0.517–0.617 dl/g were obtained in quantitative yield. These phosphorus-containing copolyesters have good thermal and flame retardant properties. These copolyesters were investigated by the differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Owing to the incorporation of the rigid structure of DOPO and pendant P group, the resulting phosphorus containing copolyesters exhibited better flame retardancy, higher char yield and thermal stability than homopolymers of PET and PEN. UL 94-VO rating could be achieved with a phosphorus content of as low as 0.75% for PET, 0.5% for PEN and no fume and toxic gas emission were observed.

Synthesis and properties of novel phosphorus-containing hardener for epoxy resins

A novel phosphorus-containing curing agent, 2-(6-oxid-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl) phenol formaldehyde novolac [OD-PN], was prepared from phenol formaldehyde novolac resin (PN) and a reactive 2-(6-oxid-6H-dibenz(c,e)(1,2)oxa-phosphorin-6-yl)chloride (ODC) while ODC was synthesized through reaction between o-phenylphenol and phosphoryl trichloride. The compound (OD-PN) was used as a reactive flame-retardant in o-cresol formaldehyde novolac epoxy resin (CNE) for electronic application. Owing to the rigid structure of ODC and pendant P group, the resulted phosphorus containing epoxy resin exhibited better flame retardancy, higher glass transition temperature, and thermal stability than the noncyclic P-containing curing agent or the bromine containing flame-retardant epoxy resin. UL 94-VO rating could be achieved with a phosphorus content of as low as 1.21% (comparable to bromine content of 6%) in the cured resin, and no fumes and toxic gas emission were observed. The relationship between the structure and flammability for both phosphorus containing curing agents OD-PN and TP-PN (triphenyl phosphate-phenol formaldehyde novolac reaction product ) are also examined.