Polyphenylene Ether Macromonomers

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1 Polyphenylene Ether Macromonomers Edward N. Peters, Alvaro Carrillo, Scott M. Fisher SABIC Innovative Plastics, Selkirk, NY USA Abstract The continuous progression of electronics toward high speed digital, wireless, and the transfer of large data files have placed increased demands on the performance of dielectric materials used in Printed Wiring Boards (PWBs). Polyphenylene ether (PPE) has been used for over 20 years to enhance the performance of epoxy based PWBs. However, its use and performance were limited by process complications, limited solubility in solvents and high viscosities. An understanding of market needs, the customer s infrastructure and processes, and the ability to manufacture macromonomers in our current assets has led to the successful commercialization of PPE engineering macromonomers. The PPE family of macromonomers offer high solubility in solvents, broad performance enhancements such as lower dielectric properties, lower moisture uptake, higher heat, and improved flame resistance. Indeed, these macromers have been heralded as a breakthrough in the search for materials that broadly enhance the performance of dielectric materials. Introduction Complex microelectronics devices place high demands on dielectric materials. The electronics industry is propelled by constant technological changes, which have brought improved, innovative products to the marketplace. [1,2] Dielectric materials play a critical role in the advancement of the microelectronics industry. The continuous progression toward portable, high frequency microelectronic systems places high desideratum on material performance, notably low dielectric constants (Dk), low loss tangent (Df), low coefficient of thermal expansion, low moisture uptake, and good thermal stability. Fortunately, these emerging trends play right into the strengths of PPE. The use of PPE and other engineering thermoplastics has been investigated as a means to enhance performance of thermoset resins. However, in the solvent-based process typically used to make laminates for PWBs, high molecular weight polymers have limited solubility, increased the solution viscosity, and the cured material can have a variety of morphologies. There were several stages of incremental improvements in PPE which had limited success in PWBs. Broad customer acceptance was not achieved until the development and commercialization of telechelic PPE macromonomers. Polyphenylene ether Poly(2,6-dimethylphenylene ethers) or PPE was first prepared by Allan S. Hay via oxidative coupling polymerization. [3, 4] The chemical structure is depicted in Figure 1. The

2 principal repeat unit is 2,6-dimethyl-1,4-phenylene. [5-10] In general, there is a 2,6- dimethylphenoxy tail end-group and a 3,5-dimethyl-4-hydroxyphenyl head end-group present at opposite ends of the polymer chain. [7, 11] Figure 1. Chemical structure of PPE PPE is a highly aromatic polymer with a fairly stiff backbone and contains no hydrolysable bonds and no polarizable groups. These structural details result in a polymer with outstanding hydrolytic stability, very low moisture absorption, extremely high Tg, outstanding dielectric properties, and ease of flame retarding without the use of halogenated materials. [8, 11-12] This unique performance profile would suggest that PPE would be an ideal material for enhancing the performance of epoxy resins for electronic applications. However, the complexities related to the high molecular weight (MW) hindered their successful application in electronic materials. [13-15] There is a long history on the use of PPE with epoxy resins. The first reported use of PPE in epoxy resins was 45 years ago by Daniel Fox. [16] In 1991 GE Electromaterials commercialized GETEK* Low Dk/Df Laminate and Prepregs. Redistributed PPE was used in the epoxy formulation to make laminates for higher performance printed wiring boards. [8] (GETEK is now the trademark of Isola Group SARL) A unique feature of PPE is that it can co-redistribute with phenols and quinones to form a mixture of lower MW PPEs. Thus, facile methods have been developed to redistribute or depolymerize PPE to lower MW oligomers or telechelics. [17-22] In general, redistribution of PPE with a bisphenol is an elegant method for obtaining low MW PPE with increased phenolic end groups. [22] An example of the preparation of redistributed PPE (r-ppr) involves adding bisphenol A (BPA) and benzoyl peroxide (BPO) to a PPE/toluene solution. The temperature is raised to C. Under these conditions the peroxide decomposes and generates radicals. The BPO radical react with BPA to form a BPA radical which initiates the redistribution reactions. [20] The BPA radical can react with a PPE molecule to form a ketal. The unstable ketal then dissociates (with hydrogen transfer) to a BPA terminated PPE oligomer and a lower MW PPE oligomer. Typically the reaction is over in about 3 hours. The redistribution reaction is depicted in Figure 2. The effect of the amount of BPA and BPO (equal wt%) on the number average MW of r-ppe appears in Figure 3. Mn decreases with increasing levels of BPA and BPO. After redistribution, the toluene solution of r-ppe can be mixed with epoxy resins, up-staged, and used in treaters for making PWBs or other processes.

3 + + Figure 2. Redistribution reaction M n, g/mol Bisphenol, Peroxide, wt% Figure 3. Change in Mn after redistribution The preparation and use of r-ppe requires the use of hot toluene. In addition, the solubility of r-ppe in toluene at ambient temperatures was around 15-18%. Hence, higher temperatures were required for higher levels of r-ppe. Widespread use of this technology was limited because most laminators did not have the capability for the redistribution chemistry and the ability to use of hot toluene. In 2003, a low MW PPE oligomer for use in thermoset resins was announced at the NPE show by GE Plastics as Noryl* ETX resin. [23] This mono-functional oligomer eliminated the need to use redistribution chemistry to obtain low MW PPE oligomers. However, the solubility in toluene at ambient temperature was not significantly improved over r-ppe. A better understanding of the material and process needs were obtained from the Voice of the customer. Most laminating companies had similar requirements. The biggest need was good solubility in MEK, the preferred solvent used to make their varnish. Performance needs included higher Tg, lower Dk and Df, lower moisture absorption, and generally good toughness and stability for secondary operations and end use.

4 Manufacturing and selling a unique, lower MW building block for use in thermoset resins presented new challenges such as reproducibly controlling the MW of the oligomers. The benefits of using any new oligomer would have to be quantified in order to drive market development, guide potential customers, and edify the commercial team. Preparation of telechelic macromonomers Stopping the polymerization after low conversion can give low MW PPE. However, this also results in unreacted 2,6-dimethylphenol, and a broad MW distribution. In addition, the stopping point can be difficult to reproduce. A standard method of controlling the MW of condensation polymerization of bifunctional monomers is by the addition of a small amount of mono-functional monomer. [24] However, the PPE monomer, 2,6-dimethylphenol, is monofunctional. Hence, a procedure was developed using a bi-functional comonomer to control MW. The polymerization reaction propagates from both ends of the bisphenol. There can only be one bisphenol per polymer chain. The average MW of the oligomer decreases with increasing amount of bisphenol. This is exemplified in the diagram in Figure 4 for conversion of mono (M) and bifunctional (B) monomers into polymer chains. As the amount of B is increased the MW is decreased. Thus, the bisphenol is acting as a chain terminator, but instead of being at the end of the polymer chain it is internal. Monomer Ratio: 10:1 10 M + 1 B M M B Monomer Ratio: 10:2 10 M + 2 B M B M B M-M-M-M-M- B-M-M-M-M-M 2 M-M-M- B-M-M Figure 4. Conceptual rendering of making macromonomers The use of a bisphenol results in a reproducible synthesis for preparing very low MW material. In addition, the functionality (OH end groups) is increased to approximately 2, which gives increased reactivity with thermoset resins. The structure of PPE telechelic macromonomers is depicted in Figure 5. Figure 5. PPE Macromonomer

5 IV, dl/g Solubility of macromonomer Solubility of Homo-oligomer Solubility in MEK, wt% Bisphenol, wt% Figure 6. Effect of Bisphenol on IV and Solubility The effect of bisphenol levels on controlling the intrinsic viscosity (IV) and solubility in MEK (methyl ethyl ketone) of the macromonomers is shown in Figure 6. The intrinsic viscosity decrease with increasing levels of bisphenol. In addition, a quantum jump in MEK solubility occurs with bisphenol levels greater than 16-17wt%. For comparison, mono-functional PPE homo-oligomers over the same IV range showed essentially little or no solubility in MEK. The combination of lower MW and increase hydroxyl groups which are available for hydrogen bonding to solvent results in increased solubility of the macromonomer in MEK. From the results shown in Figure 6, the target bisphenol level and IV were chosen for SA90. Evaluation in epoxy resin SA90 is not a compounded thermoplastic. It is a building block that various customers would use to formulate their products. This was a new area for our commercial team and a new material for our validation customers. Therefore, usage, handling, performance data of SA90 in thermoset resins was needed for market development, product brochures, and customer edification. Hence, evaluations were undertaken to generate a basic understanding of structure-property relationships. Castings were prepared with epoxy resin (Bisphenol A epoxy) and varying levels of SA90. The examination of the performance of neat resins was chosen because it would provide a unique window to observe the quantifiable effects of PPE telechelic oligomers incorporated into the epoxy network, unfettered by confounding factors such as fillers or reinforcement materials. Over the compositional range studied, all cured resins had a single Tg as determined by differential scanning calorimetry (DSC). The Tgs increased with increasing levels of SA90 as shown in Figure 7. The effect of SA90 on the fracture toughness (K 1C ) of epoxy castings is shown in Figure 8. There are substantial increases of fracture toughness with increasing content of SA90.

Figure 7. Effect of SA90 on Tg Figure 8. Effect of SA90 on K 1c Low dielectric properties are important criteria of dielectric materials.

A low Dk can translate to faster signal, reduce crosstalk and allows for thinner print circuit boards. The Df controls signal losses.

PPE has excellent dielectric properties and the addition of SA90 to epoxy resins results in significant lowering of Dk and Df as shown in Figures 9 and 10. Figure 9. Effect of SA90 on Dk Figure 10.

Indeed, the insulating properties of dielectric materials are reduced by water because water molecules have a dipole moment and are polarizable.

6 Figure 7. Effect of SA90 on Tg Figure 8. Effect of SA90 on K 1c Low dielectric properties are important criteria of dielectric materials. The two key dielectric properties are dielectric constant (Dk, relative permittivity) and loss tangent (Df, dissipation factor). The dielectric constant affects signal propagation speed. A low Dk can translate to faster signal, reduce crosstalk and allows for thinner print circuit boards. The Df controls signal losses. A low Df can minimize signal loss and reduces energy absorption into the dielectric material. This can allow for longer battery life, etc. PPE has excellent dielectric properties and the addition of SA90 to epoxy resins results in significant lowering of Dk and Df as shown in Figures 9 and 10. Figure 9. Effect of SA90 on Dk Figure 10. Effect of SA90 on Df The dielectric properties of materials are a function of several variables including water absorption. Indeed, the insulating properties of dielectric materials are reduced by water because water molecules have a dipole moment and are polarizable. [25] Resins containing polar moieties are more susceptible to moisture absorption because water molecules via hydrogen bonding between water molecules and polar moieties. [26, 27] PPE does not contain polar groups, and therefore, has very low water absorption. The effect of SA90 on moisture uptake and the corresponding effect on dielectric properties were examined by immersion of test specimens in water at 80 C. The higher temperature was chosen to accelerate the water absorption and shorten the test time. The results appear graphically in Figure 11. For all materials, moisture uptake, Dk, and Df

7 increased with increasing immersion times. Compared to epoxy resin, as the amount of SA90 increased, the moisture uptake decreases. In addition, the amount of change in dielectric properties was significantly reduced with increased SA90 levels. Figure 11. Effect of Moisture and SA90 on Dk and Df of Epoxy Resin Clearly, the use of SA90 in epoxy resins increased Tgs, lowered dielectric properties, lowered moisture absorption, and improved the retention of dielectric properties under moist conditions. These unique combinations of features suggest that SA90 offers a viable option for broadly enhancing the performance of epoxy based dielectric materials. Conclusions The PPE telechelic macromonomer, NORYL SA90 Resin, was successfully commercialized. The performance enhancing attributes of SA90 indicate that it is an important material for use in dielectric materials has resulted in wide market acceptance. [30, 31] Indeed, SA90 has been heralded as a breakthrough in the search for materials that broadly enhanced performance of epoxy resins. It is the first material in a family of telechelic macromonomers design for use in thermoset resins. Success can be attributed to several factors which include: Understanding and addressing customer needs Development of PPE telechelic macromonomers High solubility allows SA90 to fit into laminator s infrastructure and process Linking structure property relationships to market needs The use of PPE in electronics has good industry recognition. Global cross-functional team References 1. D. S. Soane, Z. Martynenko, Polymers in Microelectronics Elsevier: New York, 1989

8 2. 2. W. T. Shugg, Handbook of Electrical and Electronic Insulating Materials, Van Nostrand Reinhold, New York, A. S. Hay, J. Polym. Sci., 58, 581 (1962) 4. A. S. Hay, Adv. Polym. Sci. 4, 496 (1967) 5. D. M. White, Polym. Prep. Am. Chem. Soc. Div. Polym. Chem., 13, 373 (1972) 6. F. Laupetre, L. Monnerie, Eur. Polym. J., 11, 845 (1975) 7. J. Bialy, I. Penczek, J. Mlodecka, Polimery, 19, 412 (1974). 8. E. N. Peters, Engineering Plastics Handbook Thermoplastics, Properties, and Applications, J. Margolis ed., McGraw-Hill, New York (2006) Chapter 9, pp D. M. White, Polym. Prep. Am. Chem. Soc. Div. Polym. Chem., 13, 373 (1972) 10. F. Laupetre, L. Monnerie, Eur. Polym. J., 11, 845 (1975) 11. E. N. Peters, Polymer Data Handbook, 2 nd ed., J. E. Mark ed., Oxford University Press: New York, 2009, pp E. N. Peters, A. Kruglov, E. Delsman, H. Guo, A. Carrillo, G. Rocha, SPE ANTEC 2007., pp E. N. Peters, Eshbach s Handbook of Engineers Fundamentals, 5th ed., M Kutz, ed., Wiley-Interscience, New York (2009) Chapter 5, pp E. N. Peters, R. K. Arisman, Engineering Thermoplastics in Applied Polymer Science - 21 st Century. Craver, C. D., Carraher, C. E., eds. Elsevier: New York, E. N. Peters, Plastics: Thermoplastics, Thermosets, and Elastomers Handbook of Materials Selection, M. Kutz, ed., Chapter 11, Wiley-Interscience: New York, D. W. Fox US Patent 3,375,298 March D. M. White, J. Org. Chem., 34, D. M. White J. Polym. Sci., Polym. Chem. Ed., J. Krijgsman, J. Feijen, R. Gaymans, J. Polym, 44, H.-J. Hwang, S.-W. Hsu, C.-S. Wang, J. Appl. Polym. Sci., 110, H. A. M. van Aert, M. H. P. van Genderen, G. J. M. L. van Steenpaal, L. Nelissen, E. W. Meijer, Macromolecules 30, D. M. White J. Polym. Sci. Part A-1, Reinforced Plastics Volume 47, Issue 8, September 2003, Page 21; Advanced Materials & Processes, September 1, 2003; and Mikell Knights in Plastics Technology, July G. Odian Principals of Polymerization 3 rd edition, John Wiley New York W. T. Shugg, Handbook of Electrical and Electronic Insulating Materials, Van Nostrand Reingold, New York, L. E. Nielsen, Mechanical Properties of Polymers (1962) Reinhold, New York p E. Baer, Engineering Design for Plastics, (1964) Reinhold, New York p Chemistry and Technology of Cyanate Ester Resins, I. Hamerton ed., Blackie Academic & Professional: London, E. N. Peters, S. Fisher, H. Guo, SPE ANTEC 2009, pp E. N. Peters, S. Fisher, H. Guo, IPC/APEX 2009 Conference Proceedings 31. E.N. Peters, S. M. Fisher, H. Guo OnBoard Technology May page E. N. Peters, S. M. Fisher, H. Guo, C. Degonzague IPC/APEX 2011 Conference Proceedings

TECHNICAL UPDATE. Ricon Resins Peroxide Curing Data and Use as a Reactive Plasticizer in Polyphenylene Ether Based CCL and PWB

TECHNICAL UPDATE. Ricon Resins Peroxide Curing Data and Use as a Reactive Plasticizer in Polyphenylene Ether Based CCL and PWB TARGET MARKETS/ APPLICATIONS Copper clad laminate (CCL) and printed wiring [Circuit] boards (PWB) Structural composites Radomes Aerospace applications ADDITIONAL INFO SDS /TDS: Ricon 100, 154, 157, 184,