Enhanced Phase Transition in Poly(ethylene glycol) Grafted Butene-1 Copolymers

In the present work, a series of poly(ethylene glycol) grafted polybutene-1 copolymers (PB-g-PEG) were designed and successfully synthesized with reaction intermediate method, of which the branch densities and length could be tuned independently. The branch density varied from 0.39 mol% to 1.23 mol% and the branch length was tuned by employing PEG number-averaged molecular weight (M-n) from 350 Da to 750 Da and 1000 Da. The non-isothermal crystallization and phase transition behaviors of these butene-1 copolymers with varying branches were systematically explored by differential scanning calorimeter. The results first showed that compared with the linear polybutene-1 homopolymer, presence of steric 4-[4-(trimethylsilylalkynyl)-phenyl]-1-butene (TMS) groups suppressed crystallization and phase transition of copolymers. Interestingly, the introduction of long poly(ethylene glycol) (PEG) branches with M-n = 350-1000 Da not only elevated the peak temperature of the non-isothermal crystallization but also enhanced the II-I phase transition, with respect to copolymers with TMS groups. Furthermore, the quantitative correlations between phase transition kinetics with the branch parameters (density and length) were explored. It was found that the phase transition presents a non-monotonic trend with increasing branch density and branch length. In this case, the optimal branch density and length obtained were 0.77 mol% and 750 Da, respectively. Employing the small angle X-ray scattering and transmission electron microscopy, a direct correlation between the phase transition kinetics and the long periodicity of separated phase was obtained, which may be due to the increased internal stress and facilitated stress transport.