Chain-Growth Polymerisation without Termination

In contrast to epoxy-amines, water really participates in the cure chemistry of the epoxy-anhydride system and alters the living polymerisation mechanism because of interfering termination reactions [34]. A less dense network structure with altered properties results [35]. 

---

While for step-growth polymerisations (section 2.2.1) and chain-growth polymerisations without termination (section 2.2.2) an overall distribution of reacting species or one type of reacting species (the monomer) is mechanistically characterising the observed reaction rate, the balance between two distinct and mechanistically different species (the monomer and a macro-molecular radical) is determining the observed rate of chain-growth polymerisations with termination. 

Before vitrification, a heat capacity change as a result of chemical reaction, ACp,react, is noticcd. For the anhydride-cured epoxy and the polyester-styrene resin a minor, but reproducible, and almost linear decrease of Cp with conversion is observed. The former system is supposed to be an anionic chain-growth living polymerisation (without termination), the latter is a chain-growth copolymerisation with termination. 

It is difficult to see how the presence of two double bonds in each polymer molecule (reported by Eley and Richards for the polymerisation of 2-ethyl hexyl vinyl ether) can be explained without assuming that the chain is started by an unsaturated entity, and that the second double bond is formed in the termination process. Since the chain growth is almost certainly a carbonium ion process the initiating entity must be a positive ion of some sort. We assume therefore that the ether is split into two ions under the influence of the catalyst. This may obviously occur in two different ways, but energetic considerations can show which of these will in fact take place. 

One of the most distinguishable features of radical polymerisation is its tolerance to water, relative to the ionic counterparts, however the effective polymerization should be performed conventionally under stringent conditions without protonic or basic impurities to insure effective chain propagation and therefore desired polymer growth without unnecessary inhibition and premature termination. Because of their unique features, suspension, dispersion... 

---