STUDIES ON RING-OPENING METATHESIS POLYMERIZATION WITH REFERENCE TO SYNTHESIS OF SOME HIGH PERFORMANCE ELASTOMERS

Abstract

The thesis entitled "Studies on Ring-Opening Metathesis Polymerization with Reference to Synthesis of Some High Performance Elastomers" deals with astudy of the ring-opening metathesis polymerization of norbornene and its derivatives in the presence of simple transition metal salts of ruthenium and indium, their tnphenylphosphine complexes, and salts of tungsten activated by tin alkyl." The subject matter of the thesis has been divided into five chapters. Each chapter contains the pertinent literature survey. Experimental work followed by results and their discussion are described in Chapters 2-4. Chapter 5 contains an exhaustive discussion, particularly, with reference to the structure-property relation followed by acomprehensive bibliography for the entire thesis. Chapter 1surveys the field of ring-opening metathesis Polymenzation(ROMP). Abnef history of the olefin metathesis reaction which was discovered and reported in 1964, its relation with ROMP which was observed in 1950's but could not be properly recognized till the discovery of olefin metathesis, and the subsequent rapid studies made in the field of ROMP are covered. The industrial importance of ROMP, the preparation of monomers suitable for ROMP, and its several applications to date are briefly descnbed. Stress is laid on the mechanism of ROMP besides the nature of the catalysts, their reactivity, and their preparation. Chapter 2deals with the preparation of monomers and catalysts used in the present study. Most of the monomers other than norbornene have been prepared in the laboratory following the literature procedures while often making improvements over the published information. Substituted norboraenes are mainly obtained through the Diels-Alder reaction which was studied in some cases for the effect of solvent and temperature with aview to obtaining largely the preferred isomer. Chapter 3 deals with the study on the ROMP of norbornene and our attemps at copolymerization of norbornene with certain cycloolefins via ROMP. Alarger part of this chapter describes the ROMP of norbornene using tetrakis(triphenylphosphine)dichlororuthenium in a number ofsolvents widely varying in their polarity parameters. The geometry ofthe resulting polymer around the cyclopentenyl divinylene repeat unit has both cis- and trans- forms as shown below:It was observed that while most of the solvents studied gave products with varying ratios of cis- and trans- (predominating in trans) use of tetrahydrofuran resulted in a product with exclusively trans geometry as confirmed by 13C NMR and FT-IR. These results were presented at a seminar held on 'Advances in Polymerization Technology" at the Cochin University of Science and Technology, Cochin in February, 1996. The solvent also affected the yield of the polymer, its molecular weight, and the molecular weight distribution as determined by GPC. The triphenylphosphine complex of ruthenium in non-polar solvents was found to be more active compared to ruthenium chloride trihydrate. IrCl3 was extremely active. In the case of WClg-SnMe4 catalyst system high catalyst-to-monomer ratios were required to experience the activity. With a few catalyst systems copolymerization of norbornene with cyclopentene and cyclooctene was also studied. Evidence for the incorporation of the comonomer was obtained by spectral methods ( IR, 13C NMR, and *H NMR). Chapter 4describes the attempted ROMP of norbornene derivatives by iridium chloride, WCl6-SnMe4 catalyst system, and tnphenylphosphine ruthenium complex. The presence of the polar functionality retards the polymenzation requiring considerably more drastic conditions and higher catalyst/monomer ratios. The products of the ROMP of substituted norbornene dicarboximides have been shown to be high temperature thermoplastics as descnbed in the recent patent literature. The products obtained in our studies were therefore subjected to thermochemical analyses. Special interest centered around the ROMP product from N-cetylnorbornenedicarboximide which has acomb-type structure having long alkyl pendants. Such structures have relevance as liquid crystalline polymers and are known to form micelles in solution. Chapter 5discusses the structure-property relationship. The homopolymers of norbornene obtained via ROMP are known to be plastic elastomers. They have high glass transition temperatures( ~70°C). However, when plasticized suitably the Tg falls to very low values leading to ahigh-performance elastomer. Samples of polynorbornene with different cis- Itrans- geometry have been plasticized with three different hydrocarbon liquids, viz «-alkanes, naphthenes, and aromatic fractions from petroleum distillates. The solvent absorption capacity and elastomeric properties of the plasticized products have been described. Initiation of the ROMP requires generation of a metallocarbene (metal-alkylidene) species. The subsequent fate of the metal-alkylidene depends upon the nature of the monomer molecule and the reactivity ofthe propagating metallocarbene. .......................