@article { ISI:000355985200027, title = {Role of the molecular structure of carboxylate-alumoxanes in the enhanced nucleation of polypropylene}, journal = {Chemical Communications}, volume = {51}, number = {49}, year = {2015}, month = {MAY}, pages = {10026-10029}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

We have reported the use of carboxylate-alumoxanes as efficient nucleating agents for isotactic polypropylene (iPP) with a possible structural correlation to the nucleation efficiency. The unique, butterfly-like structure of carboxylate-alumoxanes correlates well with the nucleation characteristics of iPP and, for the first time, the impact of a thermally induced, crystalline transition of carboxylate-alumoxanes, which alters neither the structural conformation nor the nucleation efficiency of the transformed material, is demonstrated.

}, issn = {1359-7345}, doi = {10.1039/c5cc01327e}, author = {Mani, Mohan Raj and Chellaswamy, Ramesh and Marathe, Yogesh N. and Pillai, Vijayamohanan K.} } @article { ISI:000368191100026, title = {Enhanced nucleation of polypropylene by metal-organic frameworks (MOFs) based on aluminium dicarboxylates: influence of structural features}, journal = {RSC Advances}, volume = {6}, number = {3}, year = {2016}, month = {DEC}, pages = {1907-1912}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Metal-organic frameworks (MOFs) based on aluminium dicarboxylates provide a new platform for the enhanced nucleation of isotactic polypropylene (iPP). For instance, aluminium dicarboxylates exhibit a unique butterfly-like structure similar to that of carboxylate-alumoxanes and correlates well with the nucleation characteristics of iPP. A subtle change in the structure of the ligand backbone (fumarate/succinate) does not alter the framework structure despite changing the hydrophilic/hydrophobic character and its subsequent nucleation characteristics. This suggests that the nucleating agent should facilitate favourable interaction with hydrophobic iPP for efficient nucleation. Further, a systematic variation of the alkyl chain length in the Al-dicarboxylate does not change the nucleation efficiency considerably, even though it increases the distance between the octahedral alumina chains in the metal-organic framework, suggesting that the butterfly-like structure present in the framework is a key aspect for nucleation. Finally, the significance of the orientational conformation of the dicarboxylate around the metal centre for the nucleation is confirmed by the poor nucleation efficiency of chromium and zirconium suberate MOFs where the orientation of suberate would be different from that of aluminium suberate due to the difference in the ligation of the carboxylate group. The present work thus provides valuable pathways for developing new nucleating agents based on MOFs with appropriate selection and orientation of the organic linkers around the metal centre.

}, issn = {2046-2069}, doi = {10.1039/c5ra22764j}, author = {Mani, Mohan Raj and Chellaswamy, Ramesh and Marathe, Yogesh N. and Pillai, Vijayamohanan K.} } @article { ISI:000372856300024, title = {New understanding on regulating the crystallization and morphology of the beta-polymorph of isotactic polypropylene based on carboxylate-alumoxane nucleating agents}, journal = {Macromolecules}, volume = {49}, number = {6}, year = {2016}, month = {MAR}, pages = {2197-2205}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Carboxylate alumoxane derived from p-n-alkylbenzoic acids, where n-alkyl group changes from 2 to 8 carbon atoms, exhibits dual nucleating ability and nucleates isotactic polypropylene (iPP) into predominantly in the beta-phase under specific conditions. The selectivity of the beta-phase nucleation depends on the concentration of the nucleating agent, end melting temperature and cooling rate. The beta-phase obtained from p-n-alkylbenzoate-alumoxanes is compared with the beta-phase obtained from calcium pimelate (CaP), an efficient beta-phase selective, nucleating agent, using the results from DSC, WAXS, and SAXS analysis. The lamellar morphology of iPP nucleated with different nucleating agents crystallized at different crystallization temperatures (T-C) under controlled nonisothermal conditions are evaluated using SAXS analysis. The long period increases with increasing crystallization temperature and the long period of the beta-phase is always larger than that of the alpha-phase for a given crystallization temperature. Furthermore, the variation of long period with crystallization temperature clearly brings out two crystallization temperature ranges; the low temperature range and the high temperature range. However, the beta-phase shows a lower changeover temperature compared to that of the alpha-phase. The one-dimensional correlation analysis of the beta-phase shows that the thickness of the crystal lamellae (lc) increases with T-C and exhibits the low and high crystallization temperature ranges, while the thickness, of the amorphous layer (la) more or less remains constant. In-situ high temperature WAXS studies capture the beta-phase to the a-phase transition and the transformed material con-elates well with the lamellar thickness of the beta-phase. The morphological difference between the alpha- and the beta-phases are discussed and attributed to the differences in the impact properties and the melting temperature. This study clearly demonstrates that the lamellar morphology mainly depends on the T-C and not on the nature of the nucleating agents.

}, issn = {0024-9297}, doi = {10.1021/acs.macromol.5b02466}, author = {Mani, Mohan Raj and Chellaswamy, Ramesh and Marathe, Yogesh N. and Pillai, Vijayamohanan K.} }