Group IV complexes as initiators for the ring opening polymerization studies: Ligand and metal screening

International Conference and Exhibition on Biopolymers & Bioplastics

August 10-12, 2015 San Francisco, USA

Sreenath Pappuru1, Vijaya Sundar3, Vinodh Subramanian3, Dillip Kumar Chand1, Chakraborty Debashis2 and Ramkumar Venkatachalam1

Scientific Tracks Abstracts: J Material Sci Eng

Abstract :

The complexation of salicylbenzoxazole ligand 2-(5-X-benzoxazol-2-yl)-6-R1-4-R2-phenol, L with titanium, zirconium and
hafnium alkoxides selectively formed either mononuclear L2M(OR)2, 1-9 or oxo-bridging dinuclear complexes [(μ-O)L2M(OR)]2,
10-12 depending on the substituents on salicylbenzoxazole ligands. The ligands which have R1=R2=H or Br on the phenol moiety
afforded mononuclear complexes 1-9. Notably the ligand which has R1=R2=Cl substituent on the phenol ring afforded oxo bridged
dinuclear complexes 10-12. The substituents on benzoxazole ring (X=H or Cl) does not influence the nuclearity of complexes. All these
complexes were fully characterized by various spectroscopic techniques including elemental analysis and X-ray crystallography. In
ring-opening polymerization (ROP) ofrac-Lactide (rac-LA), all these complexes produced isotactic rich (Pm upto 0.78) and alkoxide
terminated polymers with narrow molecular weight distributions (MWDs) with predictable molecular weights (Mn). Ring-opening
copolymerization (ROC) of L-lactide (L-LA) and ε-caprolactone(ε-CL) to yield block copolymers was also studied. In particular,
dinuclearZr complex (11) was found to exhibit extremely high activity in homo polymerisation of rac-LA and ROC of L-LA and
ε-CL which is comparable with the previously reported active group IV complexes. Additionally, homo polymerisation of epoxides
[rac-cyclohexene oxide (CHO), rac-propylene oxide (PO) and rac-styrene oxide (SO)] were also investigated. The reactivity of these
monomers in homopolymerization promoted by these complexes varied in the order of CHO>PO>SO. The yield and molecular
weight of the polymers increase with the prolonged reaction time. The complexes which have electronegative substituents on the
phenol ring and oxazoline ring (5, 6, 8, 9, 11 and 12) improved the catalytic ability sharply. DFT studies have been carried out on ROP
of LAs initiated by both the Ti and Zr complexes. The results indicate that the activation barrier height for the ring opening transition
state of lactide monomer for Zr(IV) complex is low and hence facile compared to Ti(IV) complex. From density functional theory
(DFT) calculations we explained the mechanistic pathways for ROP of lactide promoted by Ti and Zr complexes in detail.

Biography :

Sreenath Pappuru is a highly motivated and enthusiastic Organometallic and Polymer Chemist with a Masters degree in Organic Chemistry (2008-2010) from
Sri Venkateswara University, Tirupathi, Andhra Pradesh and currently pursuing PhD in IIT Madras (from 2010) in Sustainable Polymer Chemistry/Organometallic
Chemistry. He has achieved best poster award during PhD in International Symposium on “Nature Inspired initiatives in Chemical Trends” (NIICT-2014), March
2-5, 2014.