Crystallization in Block Copolymers

Crystallization in Block Copolymers - Crystallization in...

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Crystallization in Block Copolymers I.W. Hamley School of Chemistry, University of Leeds, Leeds LS2 9JT, UK E-mail: I.W.Hamley@chem.leeds.ac.uk Crystallization in block copolymers has a profound effect on their structure. This review ar- ticle focusses on the morphology of semicrystalline block copolymers, and those contain- ing two crystallizable blocks. The effect of crystallization on mechanical properties is brief- ly considered. The extent of chain folding upon crystallization is discussed, as is the orien- tation of crystal stems with respect to the microstructure. The effect of selective solvent on solution crystallization is also highlighted. Recent work on crystallization kinetics is sum- marized and Fnally the theories for crystallization in block copolymers are outlined. Keywords: Block copolymers, Crystallization, Chain folding List of Symbol and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 114 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 2 Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 115 3M o r p h o l o g y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4 Domain Spacing Scaling . . . . . . . . . . . . . . . . . . . . . . . . . 121 5 Chain Folding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 6 Orientation of Folded Chains . . . . . . . . . . . . . . . . . . . . . . 126 7 Block Copolymers with Two Crystallizable Blocks . . . . . . . . . . 130 8 Solution Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . 131 9 Crystallization Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . 133 10 Theories for Crystallization . . . . . . . . . . . . . . . . . . . . . . . 135 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Advances in Polymer Science, Vol.148 © Springer-Verlag Berlin Heidelberg 1999
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114 I.W. Hamley List of Abbreviations SANS small-angle neutron scattering SAXS small-angle X-ray scattering WAXS wide-angle X-ray scattering DSC differential scanning calorimetry TEM transmission electron microscopy LFRS low frequency Raman spectroscopy PE poly(ethylene) PEO poly(ethylene oxide) [poly(oxyethylene)] PCL poly( I -caprolactone) PS poly(styrene) PEP poly(ethylenpropylene) PEE poly(ethyl ethylene) PB poly(butadiene) PVCH poly(vinylcyclohexane) PBO poly(butylene oxide) [poly(oxybutylene)] PPO poly(propylene oxide) [poly(oxypropylene)] 1 Introduction Crystallization of polymers is of great technological importance due to the me- chanical properties imparted, which ultimately result from the change in molec- ular conformation. In semicrystalline block copolymers, the presence of a non- crystalline block enables modi±cation of the mechanical and structural proper- ties compared to a crystalline homopolymer, through introduction of a rubbery or glassy component. Crystallization in homopolymers leads to an extended conformation, or to kinetically controlled chain folding. In block copolymers, on the other hand, equilibrium chain folding can occur, the equilibrium number of folds being controlled by the size of the second, noncrystallizable block. The most important crystallizable block copolymers are those containing po- ly(ethylene) or poly(ethylene oxide) (PEO) [systematic name poly(oxyethyl- ene)]. Poly(ethylene) (PE) in block copolymers is prepared by anionic polymer- ization of poly(1,4-butadiene) (1,4-PB) followed by hydrogenation and has a melting point in the range 100–110 °C. This synthetic method leads to ethyl branches in the copolymer, with on average 2–3 branches per 100 repeats. These branches induce lengths for folded chains which are set by the branch density and not by the thermodynamics of crystallization. The melting temperature of
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Crystallization in Block Copolymers - Crystallization in...

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