The scientific and technical advances in the field of polymer science has been abundant in recent years. Amongst the various polymeric materials available in market, synthesis of polyolefins has been in the forefront since decades. A major challenge in this domain remains in attaining stereoregular polyolefins especially polypropylene (PP) and significant efforts were carried out by synthesizing various internal donors (ID) aiding the catalysts involved in producing them. This short review gives an overview of i) various generations of Ziegler–Natta (ZN) catalyst systems ii) general classes of ID that has been demonstrated by the researchers over the past decades iii) their influence on PP isotacticity and polymer properties. The coordination modes of different donor classes on supported ZN system and comparative study especially between phthalate and diether ID classes were also addressed here. This review also presents the studies carried out on phthalate catalyst structure analysis, detailed comparison study on phthalate and diether IDs in terms of PP isotacticity, regioselectivity, hydrogen response, and also their cross combination study and competitive behavior. Further a brief description on other structurally varied IDs like malonates, maleates, silyl diol esters, bifunctional donors, multi ether donors demonstrated for isotactic PP were also presented. Studies conducted on compatibility of incorporation of two different classes of IDs on a single supported ZN system for the fundamental understanding of the catalyst behavior; and also on how mixed donor approach enables in tuning the catalyst for polymer properties were also presented. This review also provides an opportunity to the young minds and the basic researchers from academic point of view by and large to create new polymeric materials with useful properties or modify the existing materials for new applications by incorporating new IDs for further improvisation of the stereo regularity in obtaining the polymers. Graphic Abstract

Various classes of molecules like diethers, succinates, diesters, amido esters are currently being used as internal donors on MgCl2 supported titanium catalysts for isotactic polypropylene as an alternative to phthalate donors owing to their potential health risk laid down by REACH legislation. In the present paper, design and synthesis of a few novel amido ester internal donors with single chiral center (7–11) by mimicking the model amido ester 3 having two chiral centers; and their catalyst preparation method were described. Further preliminary polymerization tests with newly synthesized donor molecules were investigated and results revealed that by structurally mimicking 3 with one chiral center and also with varied substitutional patterns in ester/amido moiety decline the polypropylene activity as well as isotacticity. These donor molecules are ineffective for appropriate coordination on MgCl2 sites on inducing steric hindrance for improved isotacticity; nevertheless also induces poisoning effect for the active Ti centers leading to catalyst fouling in many cases.