Synthesis and Characterization of Polynorbornenes Prepared by Vinyl-addition and ROMP Methods, and Poly(p-xylylene) Derivatives

Abstract

Part I. Synthesis and Characterization of Substituted Polynorbornene Derivatives via Vinyl-addition Polymerization

Vinyl polynorbornene (PNB) is an attractive polymeric material for micro-electronic applications. It has high thermal stability, high glass transition temperature (Tg), low dielectric constant, low moisture absorption, high transparency and low birefringence. However, poor processability and mechanical brittleness limit the application of PNB. To improve the processability, mechanical property of PNB, This paper describes palladium (II) catalyst based synthesis and detailed characterization of vinyl-type polynorbornenes (PNBs) with bulky phenyl, adamantane, or norbornane substituents linked by ester and ether bridges. The structure-property relationships of the substituted PNBs were investigated concerning the thermal stability, glass transition temperature, wide-angle X-ray scattering (WAXS) patterns, mechanical properties, and dielectric characteristics. PNBs with phenyl substituted pendant groups improved the solubility and film forming properties due to aromatic-aromatic interactions. The substituted PNBs exhibited good thermal and thermo-mechanical properties with thermal decomposition temperature (Td,5%) above 300 °C and glass transition temperature in the range of 134-325 °C. WAXS studies revealed the presence of local nano-scale order in the noncrystalline state, especially in ester bridged adamantane and norbornane substituted polymers, probably due to the steric packing requirements of bulky side groups coupled with dipolar interactions. Nanoindentation results showed high modulus (6.5-7.9 GPa) and hardness (0.11-0.38 GPa) for PNBs with diester adamantane and norbornane substituted polymers. Excellent dielectric properties with a dielectric constant (ε) of 2.45 and a dielectric loss tangent (tan δ) of 0.005 were measured for poly Poly [cis-norbornene-exo-2,3-dicarboxylic acid diadamantylmethyl ester] at 1 GHz, rendering it very attractive for interconnect dielectric films in high-frequency electronic devices.

Keywords: vinyl polymerization; polynorbornene derivatives; Pd catalyst; interconnect dielectric polymer; low dielectric constant; low dielectric loss; glass transition temperature

Part II. Synthesis and Characterization of Ring- opening Metathesis Polynorbornene Derivatives Bearing Adamantane and Norbornane Side Groups

Polar functionalized norbornenes contacting bulky adamantane and norbornane side groups were polymerized by ring-opening metathesis polymerization (ROMP) with Grubbs 3rd generation catalyst. The thermal, optical and structural property of the adamantane substituted polymer was compared with its hydrogenated derivative. The obtained polymers were thermally stable over 350 oC. In particular, adamantane substituted polymer showed high thermal stability of 400 oC having the glass transition temperature (Tg) of 140 oC. While, the fully hydrogenated polymer (hROMP-1-ad) showed a slight enhancement in thermal stability by 10 oC. A little decrease of Tg and increase of refractive index was observed for hydrogenated adamantane substituted polymer. Therefore, the rigid and bulky adamantane side groups increased the thermal stability and maintained reasonable Tg . Wide angle X-ray scattering (WAXS) analysis revealed that the hROMP-1-ad showed a densely packed ordered structure. Keywords: adamantane, ROMP, glass transition temperature, polar functionalized norbornenes.

Part III. Thermally Cross-linkable Poly(p-xylylene)s for Advanced Low-Dielectric Applications

Low dielectric constant insulating polymers have recently attracted a great deal of research interest owing to the critical need to decrease the RC delay time, cross-talk and power dissipation in the new generation of high frequency integrated circuits. Such applications require new class of polymers with a combination of properties: high thermal stability (degradation temperature (Td) > 400 °C), low water uptake (<1%), high glass transition temperature (Tg) >180 °C, dielectric constant less than 2.8, dielectric loss tan δ < 0.002, and thermosetting properties. These stringent requirements could not be satisfied by existing polymers. In order to meet such requirements, we prepared a thermally crosslinkable p-xylylene copolymer through Gilch type polymerization. A novel series of poly(p-xylylene) (PPX) homopolymer and copolymers containing thermally cross-¬¬linkable cyclohexenyl moiety are successfully prepared via base-catalyzed Gilch route to yield high molecular-weight polymers. The resulting polymers are highly soluble in a wide range of organic solvents and could be solution cast into flexible and transparent films. The polymers are thermally stable up to 350 °C and the glass transition temperature (Tg) is in the range of 136 ~ 250 °C. These polymers undergo thermal cross-linking via the cyclohexenyl moiety, as indicated by an exothermic peak in the first-heating DSC thermograms of copolymers and subsequent solubility study. The cross-linked polymer exhibits a high Tg of 294 °C, a low coefficient of thermal expansion (CTE) of 45 ppm/K. Moreover, a low dielectric constant of 2.5 and a very low dielectric loss tan  of 0.0003 at 1 GHz are obtained, which are superior to conventional interconnect dielectric polymers. Keywords: thermal cross-linking; low-dielectric properties; poly(p-xylylene)