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(Mn) 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.

Effect of Linear and Ring-like Co-units on the Temperature Dependence of Nucleation and Growth in Ⅱ-Ⅰ Phase Transition of Butene-1 Copolymers

The phase transition from tetragonal form II to hexagonal form I was studied for the butene-1/ethylene and butene-1/1,5- hexadiene random copolymers, which have comparable molecular weight but distinct linear ethylene and ringlike methylene-1,3- cyclopentane （MCP） structural co-units, respectively. It is known that this solid phase transition follows the nucleation-growth mechanism, so the stepwise annealing protocol was utilized to investigate the influences of co-units on the optimal nucleation and growth temperatures. Compared with optimal nucleation and growth temperatures of-10 and 3 5 ℃, respectively, in polybutene-1 homopolymer, two butene-1/ethylene copolymers with 1.5 mol% and 4.3 mol% co-units have the slightly lower optimal nucleation temperature of-15 ℃ but much higher optimal growth temperature of 50 ℃. Clearly, the effect of ethylene co-unit is more significant on varying optimal temperature for growth than for nucleation. Furthermore, when the incorporated co-unit is ringlike MCP, the optimal nucleation temperature is -15 ℃ for 2.15 mol% co-units, the same with above BE copolymers, but -13 ℃ for a very low concentration of 0.65 mol%. Interestingly, the optimal growth temperature of butene-1/1,5-hexadiene copolymers with 0.65 mo1%-2.15 mol% MCP co- units increases to 55 ℃, which is also independent on co-unit concentration. These obtained values of optimal temperatures provide crucial parameters for rapid II-I phase transition.