Thermal Degradation Studies of Alternating Copolymers and Their Related Homopolymers

Alternating copolymers posses a uniquely regular chain structure in which the two different type of monomer (A and B) units present in strictly alternating ordered sequence in the chain backbone, i.e. -ABABABABA-. These types of material have a novel macromolecular structure. Their thermal degradation behaviour remains largely unexplored and it was the interest in the present research to discover what are the patterns of behaviour and how they compare with those of random copolymers. For the aforesaid reasons, various alternating copolymers and their related homopolymers were synthesised, characterised and their thermal degradation behaviour was studied under programmed and isothermal heating experiments using TVA, TG and DSC techniques. A general description of major types of degradation processes which may occur during thermal decomposition is described in Chapter 1. The brief description of thermal degradation behaviour of the alternating copolymers is also included in this Chapter. Chapter 2 summarises the application and experimental techniques employed in the present study. The first part deals with the thermal analysis techniques and the second part describes the techniques used to identify the degradation products both quantitatively and qualitatively. Monomer preparation, polymerisation and characterisation of monomers is considered in detail in Chapter 3. This also includes a brief description of the calculation determination of monomer feed for the preparation for the copolymers. Vinyl acetate, isopropenyl acetate and methacrylic acid were used in several alternating systems, so it was appropriate to consider the thermal degradation behaviour of these monomers as homopolymer. The thermal degradation behaviour of poly(vinyl acetate) PVA and poly(isopropenyl acetate), PIPAc are described in Chapter 4 and 8. The two homopolymers show degradation features in common. Both show a two stage decomposition under programmed heating, the first involves the elimination of acetic acid in a zipper deacetylation of short zip length. The second stage reaction, occurring at higher temperatures, involves fragmentation of the backbone and the formation of aromatics and cold ring fraction. Chain scission is much more extensive in the case of PIPAc than for PVA, because all the acetate groups are linked to the tertiary C atom, which is considered as a initiation point for the thermal degradation. Hence thermal dissociation is very easy in the case of PIPAc which makes polymer thermally less resistant. In Chapter 5, the studies of the thermal decomposition of poly(methacrylic acid), PMAA are described. PMAA exhibits two decomposition stages. In the first stage, there is intra- and inter molecular anhydride formation between COOH groups with water elimination. In the second stage, between 350 and 50