Initiation and Propagation Steps in the Solid State Polymerization of Vinyl Monomers

Abstract

Several problems raised by initiation and propagation steps in solid-state polymerizations are reviewed on the basis of data taken from the literature as well as from unpublished work. The nature of the initial active centers is briefly considered; their addition to double bonds within the crystal is discussed. Examination of initiation yields in radiation-induced polymerizations shows that the efficiency of chain initiation rises with temperature. In most vinyl monomers, the propagation process, which is severely hindered in the crystal, presumably starts at lattice imperfections and thereafter proceeds on behalf of the additional imperfections introduced by the accumulated polymer. In a few specific cases the orientation of the double bonds in the crystal or their localization in certain regions of the crystal favours chain propagation and may result in a stereocontrolled reaction. The role of crystallite boundaries is emphasized particularly in the case of copolymerizations which take place in eutectic mixtures of two monomers.The polymerization of numerous monomers in the crystalline state has led to a large number of investigations in the past decade and a vast amount of experimental data is now available most of which are summarized and discussed in several review articles [1,2,3] . However, the detailed mechanisms of the individual reaction steps are still scarcely understood. It is the purpose of the present paper to consider some problems raised by the reaction steps in solid-state polymerization with the aim of providing a picture of possible mechanisms. It is clear that a complete analysis of this broad field cannot be covered in this discussion, which will be confined to a few aspects of initiation and propagation in crystalline vinyl monomers.

Towards the planning and execution of an "absolute" asymmetric synthesis of chiral dimers and polymers with quantitative enantiomeric yield

“…Contrary to solid state vinylic polymerization (Refs. [20][21][22][23][24], in this system both the initiation steps (dimerization) and the propagation steps (coupling of dimers and other oligomers), proceed under the control of the crystal lattice of the monomer, and the polymer chain grows in very well defined crystallographic directions.…”