Living Free Radical Polymerisation Under a Constant Source of Gamma Radiation – An Example of Reversible Addition‐Fragmentation Chain Transfer or Reversible Termination?

The primary mechanism for living polymerisation under a source of gamma radiation at low dose rates is shown to be reversible addition‐fragmentation chain transfer. This was demonstrated by showing that the initial transfer step determines the success of the polymerisation. When an inappropriate leaving group is chosen for the RAFT agent, the polymerisation is non‐living. Under a reversible termination mechanism the ‘living’‐ness should be independent of this initial transfer step.     

Developments in the synthesis of maleated polyolefins by reactive extrusion

The maleation of conventional and metallocene linear low density polyethylenes by reactive extrusion has been explored with a view to defining the conditions necessary for a robust process that provides both high grafting efficiencies (>80%) and minimal degradation or cross-linking. The dependence of grafting efficiency on various operating parameters (maleic anhydride level, maleic anhydride:initiator ratio, throughput rate, direction of screw rotation, temperature) has been established. Literature methods for characterization of the grafted product based on FTIR or ¹H NMR analysis have been critically examined with respect to their ability to distinguish between single unit and oligomeric maleic anhydride grafts and found to yield ambiguous results.     

Phase diagram and thermal and mechanical properties of isotactic polypropylene/hydrogenated oligo(cyclopentadiene) blends

The system formed by isotactic polypropylene (iPP) and hydrogenated oligo(cyclopentadiene) (HOCP) is investigated in order to study the influence of the composition and thermal history on the morphology, phase structure, miscibility and thermal and mechanical properties of the blends. A phase diagram presenting both the lower and the upper cloud point curves is proposed. It is shown that these blends assume different morphologies and consequently present diverse thermal and dynamic-mechanical behaviours depending on quenching processes from one-phase region or two-phase region. From the analyses of the results of optical microscopy, WAXS, DSC and DMTA techniques it is found that: blend films, quenched from the melt of one-phase region to room temperature, contain one amorphous phase and iPP in smectic form; moreover they are transparent and possess a reduced permeability to oxygen and aroma; conversely when the samples are quenched from the melt of two-amorphous phase region there is the formation of two amorphous phases (the iPP-rich phase and the HOCP-rich phase) and at room temperature the iPP crystallizes in the monoclinic α form.     

Tailored polymers by free radical processes

This paper describes a versatile and effective method for the control of free radical polymerization and its use in the preparation of narrow polydispersity polymers of various architectures. Living character is conferred to conventional free radical polymerization by the addition of a thiocarbonylthio compound of general structure S=C(Z)SR, for example, S=C(Ph)SC(CH₃)₂Ph. The mechanism involves Reversible Addition-Fragmentation chain Transfer and, for convenience of referral, we have designated it the RAFT polymerization. The process is compatible with a very wide range of monomers including functional monomers such as acrylic acid, hydroxyethyl methacrylate, and dimethylaminoethyl methacrylate. Examples of narrow polydispersity (≤1.2) homopolymers, copolymers, gradient copolymers, end-functional polymers, star polymers, A-B diblock and A-B-A triblock copolymers are presented.