Thermal Decomposition Kinetics of Functionalized Polynorbornene
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The mechanism and kinetic parameters for the thermal decomposition of four functionalized addition-polymerized polynorbornenes were studied by dynamic and isothermal thermogravimetric analyses and by mass spectrometry. The dynamic and isothermal thermogravimetric analyses showed a first-order degradation reaction mechanism with an activation energy of 229.6 ± 12.5 kJ/mol. Based on the polymer structure, reference mass spectra for related molecules, and a cross-comparison of the mass spectra, the backbone, free-radical scission mechanism was found to occur by cleavage of the linkages between bicyclic rings and the production of volatile monomer and oligomers. The degradation of polynorbornene occurred via a depropagation and transfer reaction process. Initially, the depropagation pathway was preferred, but with increasing conversion, intra- and intermolecular hydrogen transfer reactions dominated. I. INTRODUCTION
The synthesis of polynorbornene or poly(bicyclo[2.2.1]-hepte-2-ene) (PNB) was first described by Anderson et al.1 Two types of polymers were formed: a brittle, saturated, low molecular weight, addition polymer and a ring opening metathesis polymerization (ROMP) material. The former material possesses a saturated backbone consisting of linked, fully intact norbornanetype molecules. It has excellent thermal stability. The synthesis method was later refined by McKeon using reaction conditions that would enable the selective production of either the ROMP or addition polymerization.2 Kaminsky reported that addition-polymerized PNB can be produced in the amorphous and highly crystalline forms.3,4 Due to low solubility and lack of a suitable melting point, the crystalline material is difficult to process, and the focus shifted to the amorphous material. A facile addition polymerization route using an organo (nickel or palladium) complex was found for synthesizing amorphous PNB.5 There are numerous publications on the subject.6–13 The addition-polymerization route allows considerable freedom to tailor the two critical aspects: tight control of the molecular weight and flexibility in choice of sidegroups on the norbornene repeat unit. This has allowed synthesis of a wide variety of functionalized polynorbornenes with a variety of mechanical, thermal, and electrical properties. Several functionalized polynorbornenes have been described by Grove.14 Some of the attributes that make PNB attractive include excellent thermalperformance a)
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J. Mater. Res., Vol. 17, No. 3, Mar 2002 Downloaded: 14 Mar 2015
(glass transition temperature Tg exceeding 350 °C), excellent adhesion to a wide variety of materials, low moisture absorption ( 0.999). The average activation energy for BuTESPNB was 236.8 kJ/mol with a standard deviation of 4.7 kJ/mol. Once the activation energy was determined, the two other kinetic parameters could be determined by manipulating Eq. (2) to give Eq. (4):
dW dT = n ln W + ln A ln −Ea exp RT −
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