Equilibrium and non-equilibrium polycondensation process of segmented poly-perfluoro(oxymethylene-ran-oxyethylene0-carbonates

摘要

The melt transesterification polyreaction between diphenyl carbonate and p9oly-perfluoro(oxymethylene-ran-oxethylene)dimethylol terminated olgomers (briefly perfluoropolyethers or PFPE diols) to give linear,highly fluorinated polycarbonates was investigated.The PFPE-polycarbonate were characterised by GPC and ~19F NMR spectroscopy.RThe polycondensation was catalysed by Zn(Ac)_2 at temperatures comprised between +120 and +200 deg C.The polymerisations carried out in closed systems (no by-product distillation) gave information on some aspects of the equilibrium thermodynamics of the process.The effects of temperature and stoichiometric ratio were particularly studied.it resulted that the equilibrium degree of polymerisation (X_n)_eq is invesely proportional on a semi-log scale to the temperature of polymerisation as typical of exothermal processes.The standard enthalpy of polymerisation was calculated (DELTAH_0=-31(+-)3 kJ/mol).It was found,in apparent disagreement with theory,that maximum molecular weights were acheved when an excss of di9phenyl carbonate monomer is used.In equilibrium conditions low molecular weights (M_n<= 10~4) were generally obtained.The non-equilibrium conditions focused to the obgtainment of high molecular weight poycarbonates were also investigated,using temperature ramps and pressure steps to get the phenol off the reaction medium.A comparison between two different functionality PFPE oligomers was finally done in non-equilibrium conditions,showing that M_n as high as 10~5 can be obtained starting from a PFPE macromonomer with a OH functionality as high as 2.