Chun-Shan Wang

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.

Novel phosphorus-containing epoxy resins Part I. Synthesis and properties

Two series of novel multifunctional phosphorus-containing epoxy resins (phosphorus content 2 and 4%) were synthesized from the addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and the glycidyl ether of cresol formaldehyde novolac (functionalitya 12, C12 and then cured with 4,4 0 -diaminodiphenyl sulfone (DDS), phenol novolac (PN) or dicyandiamide (DICY). The addition reaction was monitored by high performance liquid chromatography (HPLC) and epoxide equivalent weight (EEW) titration. The proposed structure was confirmed by FTIR and NMR spectra. Thermal properties of cured epoxy resins were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA). The flame-retardancy of cured epoxy resins was tested by UL-94 vertical test and limiting oxygen index (LOI). These cured epoxy resins exhibited high glass transition and high thermal stability and achieved UL-94 vertical tests of V-0 grade (nonflammable). q 2000 Elsevier Science Ltd. All rights reserved.

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 of novel trifunctional epoxy resins and their modification with polydimethylsiloxane for electronic application

The modification of novel trifunctional epoxy resins with silicon rubber to reduce stress while maintaining a high glass transition temperature is described. Trifunctional epoxy resins were synthesized from the condensation of 4-hydroxybenzaldehyde, chloroacetaldehyde or crotonaldehyde with phenol, followed by epoxidation with a halohydrin. The structure of the synthesized triphenols was characterized by infra-red, mass, and nuclear magnetic resonance spectrometry. Toughening of trifunctional epoxy resins was achieved by hydrosilation with side chain methyl hydrogen siloxanes. The dynamic viscoelastic properties and morphologies of neat silicon rubber-modified epoxy networks were investigated. The mechanical properties of encapsulants formulated from the synthesized silicone rubber-modified epoxy resins were also studied. The dispersed silicon rubbers effectively reduced the internal stress of cured epoxy resins by reducing Youngs modulus and the coefficient of thermal expansion, while the glass transition temperature was slightly depressed.

Modification of epoxy resins with polysiloxane thermoplastic polyurethane for electronic encapsulation: 1

A stable dispersion of polysiloxane thermoplastic polyurethane (TPU) particles in an epoxy resin matrix was achieved via epoxy ring opening with the isocyanate groups of urethane prepolymer to form an oxazolidone. The effects of the structure and molecular weight of the polysiloxane TPU in reducing the stress of electronic encapsulants were investigated. The mechanical and dynamic viscoelastic properties of polysiloxane TPU-modified epoxy networks were also studied. A phase-separated structure was observed via scanning electron microscopy. The dispersed polysiloxane TPU rubbers effectively reduce the stress of cured epoxy resins by reducing the flexural modulus and the coefficient of thermal expansion, while the glass transition temperature is increased because of the formation of the rigid oxazolidone structure. Electronic devices encapsulated with the polysiloxane TPU-modified epoxy moulding compounds have exhibited an excellent resistance in the thermal shock cycling test and have resulted in an extended device used life.

Modification of epoxy resin with siloxane containing phenol aralkyl epoxy resin for electronic encapsulation application

Abstract A process was developed to incorporate stable dispersed polysiloxane particles into a phenol aralkyl novolac epoxy resin, which was used as an ingredient in the encapsulant formulation to withstand the thermal stress. The mechanical and dynamic viscoelastic properties and morphologies of rubber-modified epoxy networks were studied. A “sea-island” structure (“islands” of silicone rubber dispersed in the “sea” of an epoxy resin) was observed in cured rubber-modified epoxy networks via SEM. The dispersed silicone rubber-modified aralkyl novolac epoxy resin effectively reduces the stress of cured epoxy molding compounds by reducing flexural modulus and the coefficient of thermal expansion (CTE), while the glass-transition temperature (Tg) was hardly depressed. Electronic devices encapsulated with the dispersed silicone rubber-modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and have resulted in an extended use life for the devices.

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.

Novel bismaleimide with naphthalene side group. 1. From 1-naphthaldehyde and 2,6-dimethylaniline

Abstract Novel bismaleimide (BMI) and epoxy resin with naphthalene side group were synthesized from the intermediates bis(4-amino-3,5-dimethylphenyl)naphthylmethane (BADN) and bis(4-hydroxy-3,5-dimethylphenyl)naphthylmethane (BHDN) which were obtained from the reactions between 1-naphthaldehyde and 2,6-dimethylaniline or 2,6-dimethylphenol, respectively. The monomers were characterized by Fourier transform infrared spectroscopy, elemental analysis, mass spectrometry and potentiometery. Their corresponding bismaleimide bis(4-maleimido-3,5-dimethylphenyl)naphthylmethane (BMDN) and the diglycidyl ether of BHDN (DGEBN) were cured with 4,4′-diaminodiphenylmethane (DDM) at various mole ratio and their curing behaviors investigated by differential scanning calorimetry (d.s.c.) and (FTi.r.). Thermogravimetric analyses indicated that the cured systems of BMI and epoxy resins were stable up to 416–424 and 377–395°C, respectively, in nitrogen atmosphere, and the former afforded a relatively higher char yield than the latter. In addition, the cured bismaleimide possessed better Tg, moisture resistance, lower coefficient of thermal expansion (α) and dielectric constant (ϵ) than that of the epoxy system.

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.