This work focuses on the synthesis of polyrotaxanes with high molecular weight template poly(ethylene glycol) PEG (20 kg mol⁻¹) having various and well-defined amounts of α-cyclodextrins (α-CD) per chain N from 3 up to 125. N is the complexation degree of the polyrotaxane defined to be the average number of cyclodextrin molecules per template chain. The usual route has been used for high values of N, while sparsely complexed polyrotaxanes have been synthesized with an original one pot synthesis in water. Furthermore, a systematic study was carried out to understand and control the complexation degree N of the polyrotaxane as a function of the complexation time, the temperature and the initial ratio of α-CD to template polymer. It has been shown that a high temperature thermal plateau leads to the formation of very sparsely complexed (low N) pseudo-polyrotaxanes for which, the threaded α-CD act like nuclei and generate a favourable driving force for the final complexation at lower temperature.