Intramolecular Reaction and Network Properties

Abstract

There has been much activity in recent years relating theoretical and experimental values of the static shear moduli of polymer networks using model systems based on end-linking reactions; essentially non-linear polymerisations^1–11 Almost all the work has assumed that, with stoichiometric reaction mixtures, chemically perfect networks are formed at complete reaction. The number of elastic chains per unit volume is taken to be defined precisely by the molar masses of the monomers and/or prepolymers reacted and the density of the network formed. Attention has then been focussed on whether affine or phantom chain behaviour occurs^2,4,5,7, and whether chain entanglements or interactions contribute additionally to the moduli measured^1–3,7. However, a knowledge of imperfections in the network structure is essential if absolute values of moduli are to be interpreted meaningfully. Thus, it has been shown that in some siloxane systems^l,6 incomplete reaction gives inelastic free chain ends and reduces the modulus whilst entanglements cause it to increase, with the result that apparent perfect, affine behaviour can be observed.