Abstract
Copolymerization is an effective strategy to regulate the molecular structure and tune crystalline structures. In this work, novel butene-1 copolymers with different polyethylene glycol (PEG) grafts (number-average molecular weight Mn = 750, 2000, and 4000 g/mol) were synthesized, for the first time introducing long-chain grafts to the polybutene-1 main chain. For these PEG-grafted copolymers, crystallization, melting, and phase transition behaviors were explored using differential scanning calorimetry. With respect to the linear homopolymer, the incorporation of a trimethylsilyl group decreases the cooling crystallization temperature (Tc), whereas the presence of the long PEG grafts unexpectedly elevates Tc. For isothermal crystallization, a critical temperature was found at 70 °C, below which all polyethylene glycol-grafted butene-1 (PB-PEG) copolymers have faster crystallization kinetics than polybutene-1 (PB). The subsequent melting process shows that for the identical crystallization temperature, generated PB-PEG crystallites always have lower melting temperatures than that of PB. Moreover, the II-I phase transition behavior of copolymers is also dependent on the length of PEG grafts. When form II, obtained from isothermal crystallization at 60 °C, was annealed at 25 °C, PB-PEG-750, with the shortest PEG grafts of Mn = 750 g/mol, could have the faster transition rate than PB. However, PB-PEG-750 exhibits a negative correlation between transition rate and crystallization temperature. Differently, in PB-PEG copolymers with PEG grafts Mn = 2000 and 4000 g/mol, transition rates rise with elevating crystallization temperature, which is similar with homopolymer PB. Therefore, the grafting of the PEG side chain provides the available method to tune phase transition without sacrificing crystallization capability in butene-1 copolymers.
Highlights
Polybutene-1 (PB-1) is one class of polymeric material which has outstanding mechanical properties, such as excellent creep resistance, good crack resistance, good heat resistance, and high hardness [1,2,3,4,5,6,7,8].There are three possible crystal modifications in PB-1, which are the hexagonal form I/I’, tetragonal form II, and orthorhombic form III [9,10,11]
The effects of TMS branch and polyethylene glycol (PEG) graft on copolymer crystallization were investigated with the Differential Scanning Calorimetry (DSC) dynamic cooling protocol, illustrated by Figure S3a
PEG elevated grafts, Tsignificantly, c was elevated significantly, the PB-TMS and PB-PEG copolymers have the the PB-TMS and PB-PEG copolymers have the same branch density
Summary
Polybutene-1 (PB-1) is one class of polymeric material which has outstanding mechanical properties, such as excellent creep resistance, good crack resistance, good heat resistance, and high hardness [1,2,3,4,5,6,7,8].There are three possible crystal modifications in PB-1, which are the hexagonal form I/I’, tetragonal form II, and orthorhombic form III [9,10,11]. From the thermodynamic point of view, the hexagonal phase is most stable, of which form I’ is obtained directly by melt or solution crystallization, and form I is converted from the metastable tetragonal form II through solid-solid phase transformation [12,13,14]. Tetragonal form II is metastable, it is the crystal modification that is usually generated from melt crystallization due to the kinetic advantage [15,16]. After II-I phase transition, the melting temperature is elevated and the mechanical strength of hardness is improved. On the other hand, when transformation is completely suppressed, form II exhibits a very high fracture strain of over
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