Improved process for the continuous production of slow crystallizing polyester resin comprising esterification of at least one dicarboxylic acid or mono-esters thereof or di-esters thereof with at least one polyol, melt polymerizing the esterified mixture, preparing uniform crystalline hemispherical prepolymer by particle former process, adding at least one diol having tertiary or quaternary carbon atoms with pendant groups such as neopentyl glycol or 2-methyl-1,3- propanediol or any suitable diol at any stage during esterification or melt polymerization but before the particle former process; and solid state polymerizing the prepolymer to obtain high molecular weight slow crystallizing polyester. Slow crystallizing low molecular weight crystalline hemispherical prepolymer having IV of about 0.1 dl/g to about 0.45 and uniform hemispherical shape, uniform particle size, uniform crystallinity prepared by the above process and is used as precursor to prepare high molecular weight resin. Slow crystallizing high molecular weight polyester resin with an IV from about 0.5dl/g to about 1.2 dl/g having reduced melting point prepared by the above process and is used for the production of thick walled transparent preforms, large containers, films or sheets with accepted clarity.