Formation of the New Trigonal Polymorph in iPP−1-Hexene Copolymers. Competition with the Mesomorphic Phase

Abstract

The polymorphic structure and the thermal transitions of several iPP-1-hexene copolymers have been analyzed by performing DSC and variable-temperature X-ray diffraction experiments. Special attention has been paid to the range of "intermediate" comonomer contents, between around 8 and 12 mol %, where the new trigonal form of iPP starts to be observed. It was found that the mesomorphic modification is also easily obtained in that comonomer range, so that the possibility of such mesomorphic phase acting as a transient structure of the trigonal form was entertained. However, the results have clearly shown that the mesomorphic modification is not acting as such transient structure, and rather it is a competitor (as well as the R crystals) for the formation of the trigonal phase.

Fourier Transform Infrared Spectroscopy study of polymorphism in propylene-co-1-pentene copolymers: Trigonal form identification

“…In addition to those four crystalline modifications, a new trigonal form, also named as d, has been recently reported in the case of metallocene copolymers of propylene with high contents of 1-hexene or 1-pentene as comonomers [20][21][22][23][24][25][26][27], as well as in metallocene terpolymers of propene with both 1-hexene and 1-pentene as comonomeric units at analogous compositions [28,29]. The new trigonal modification is the only one obtained for comonomer contents above around 14 mol%, while variable percentages of it were found in the comonomer range from around 8 to 13 mol% 1-hexene and 1-pentene.…”

“…The new trigonal modification is the only one obtained for comonomer contents above around 14 mol%, while variable percentages of it were found in the comonomer range from around 8 to 13 mol% 1-hexene and 1-pentene. At these intermediate contents, it has been established [26] that the mesomorphic modification, as well as the a crystals, are coexisting in the formation of the new trigonal modification. One of the most interesting characteristics of those copolymers exhibiting the d form is the unexpectedly high degrees of crystallinity obtained, which are around 25% to 40% at comonomer contents ranging from 15 to 30 mol% [22,30].…”

Synthesis, molecular characterization, evaluation of polymorphic behavior and indentation response in isotactic poly(propylene-co-1-heptene) copolymers

“…The interest on those copolymers allowed finding a new polymorphic form [17] in 2005 for metallocene isotactic copolymers of propylene with high contents of 1-hexene (cPHe) or 1-pentene (cPPe) as comonomers [18][19][20][21][22][23]. This structure shows a trigonal cell and indicates that the packing of polymer molecules is mainly driven by density http://dx.doi.org/10.1016/j.eurpolymj.2014.12.035 0014-3057/Ó 2015 Elsevier Ltd. All rights reserved.…”

“…Furthermore, the new trigonal polymorph is the only one able to crystallize at compositions higher than 14 mol% (up to a limit for 1-hexene copolymers of around 30% of hexene units [17b]), although there are kinetic differences between using 1-hexene or 1-pentene as comonomers [20,30].…”

Influence of structure on the properties of polypropylene copolymers and terpolymers

“…In addition, a new trigonal form has been described in the case of copolymers of iPP with high contents of 1-hexene or 1-pentene as comonomers. [5][6][7][8][9][10] Moreover, a kind of mesomorphic form has been found to appear not only in homopolymer but also in different random copolymers, with comonomers such as ethylene, 1-butene, 1-pentene and other -olefin copolymers. [11][12][13][14] Among the different paths for modifying the ability to crystallize the iPP and the type of polymorph desired, this paper focuses on the introduction of comonomer units.…”