Effect Of Molecular Weight On The Quality Of Poly(alpha-methylstyrene) Mandrel And The Process Of Thermal Degradation

Hollow poly(alpha-methylstyrene)(PAMS) showed application in inertial confinement fusion(ICF) experiments as the degradable mandrels of hollow plastic microspheres. Fabrication of target capsules can meet the design specification such as uniformity, regular morphology. Generally, glow discharge polymer (GDP), high density carbonate (HDC) and polyimide (PI) microspheres, et al. have been fabricated for the candidate targets of the ignition experiments. Although the diameter and wall thickness of final capsules can meet ICF requirements, but the spherical symmetry and surface finish are still short of ignition standards. Preparation and application of high-quality final ignition depends mainly on the precision forming and high efficient degradating of PAMS mandrels, so research the balling performance and thermal degradation of PAMS microspheres is particularly important.The molecular weight is also an important factor which dominant the processe of PAMS hollow shells formation and degradation. Based on emulsion encapsulated technology, an investigation of the properties of PAMS mandrels, especially about size distribution, emulsion stability, sphericity, thickness uniformity and surface finish has been performed. According to the results, perfect sphericity and good wall thickness uniformity can be obtained when the molecular weight of PAMS was in the range of 300 kg·mol-1 to 500 kg·mol-1, which compared to the 800 kg·mol-1 one. Moreover, the relevant mechanisms of how the molecular weight affecting the wall uniformity and the sphericity of the PAMS shells by influencing the diffusion rates of FB were also explained. Therefore,the curing time could be prolonged by reducing the molecular weight of PAMS and the diffusion rates of FB could be accordingly decreased. Our experiments are prevailing in simplify PAMS synthesis route consistent with optimizing degradation mandrel fabricationtechniques.This paper studied the influence of molecular weight on the PAMS thermal degradation temperature by using thermal analysis techniques. Further, the diversification of molecular weight and distribution was monitored during the PAMS degradation process.The results indicated that the pyrolysis temperature of PAMS with high molecular weight was below the lower one. Moreover, this work proposed a kinetic equation to study solid polymer thermal decomposition in which the influence of molecular weight to the decomposition is included based on an independent identical particle (ⅡP) model. Applications of this equation to the thermal decomposition of solid PAMS show that the higher the molecular weight is, the faster the PAMS decomposes in the main decomposition temperature range. Focus on improving the thermal degradation PAMS, the influence of initiator on the PAMS thermal degradation process was investigated. By adding DTBP, the PAMS degradation temperature can be greatly reduced without changing the main degradation product of PAMS. Moreover, the thermal pyrolysis behaviour of PAMS was not affected by the content of DTBP. To reduce the uncertainty of target fabrication, the content of DTBP is as little as possible.