No abstract

SAN containing 20 wt % of reactive SAN-X has been melt blended with EPDM containing 50 wt % of EP chains grafted by maleic anhydride (EP-g-MA). Two types of reactive groups (X) have been attached to SAN (2 mol % of X), i.e., a primary amine and a precursor of it at the processing temperature, i.e., a carbamate. The SAN/rubber weight composition was kept constant at 75/25. The development of the phase morphology from pellet-sized rubber particles to dispersed submicrometer droplets has been investigated during reactive mixing for the two types of reactive SAN and has been found to depend on the interpolymer reaction rate and thus on the relative reactivity of the amine and the carbamate groups attached to SAN toward the maleic anhydride function of EP.

The living low temperature polymerization in polar solvents of most methacrylates, even functional ones, can now be performed by direct and experimentally convenient anionic methods, thanks to the use of α‐methylstyrene and of complex‐purified monomers. A diversified family of block copolymers has thus been generated, that are used as compatibilizing agents in the designing of interesting heterophase materials: i.e. blends of polymers and inorganic fillers, and liquid‐solid dispersions. The living polymerization of acrylates (or of methacrylates under more drastic conditions) raises additional requirements: they have been met to a large extent by the use of specific ligands of the growing ion‐pair. Resulting structures such as f.i. block copolymers and end‐functionalized oligomers of a low dispersity, should have a great interest in the molecular engineering of (meth)acrylate‐based products. Finally, these new initiators lend themselves to structural and mechanistic studies which should shed some light on the critical features of these living propagation processes.

SynopsisThe living anionic polymerization of glycidyl methacrylate (GMA) in THF at low temperature initiated with diphenyl hexyl lithium, 9-anthracenyl methyl lithium, and a-methylstyryl lithium leads to well characterized homo-and block copolymers, with predictable and narrow molecular weight distributions and with all the oxirane groups intact. Broadening of the molecular weight distributions above a certain and very critical supported the idea that the living polymerization at low temperature might proceed in micelle-like structures. Diffusional restriction of the monomer access towards the living centers, due to lesser solvation and increasing compactness of the polymer coils is thought to give rise to broadening of the molecular weight distribution of PGMA homoand block copolymers.

We present a detailed experimental and modeling investigation of poly(ethylene-4,4′-biphenyl dicarboxylate) (PEBB) and the related random copolymers poly(ethylene-4,4′-biphenyldicarboxylate-co-2,6-naphthalene dicarboxylate) (PEBB/EN). We find that different polymorphs exist for the PEBB homopolymer and suggest a second crystal unit cell, different from that which is discussed in the literature. PEBB/EN copolymers, which are shown here to be random copolymers, are found to be semicrystalline for all naphthanoate concentrations. By combination of DSC, X-ray, and solid-state NMR experiments, uniform comonomer inclusion is proposed for copolymers containing a high amount of EN; for low EN concentrations, these comonomers are rejected from the crystals. By comparison of the comonomer inclusion Gibbs energy, which was estimated from experiments, to those obtained from thermodynamic integration calculations, it was found that PEBB/EN copolymers are able to cocrystallize by aggregation of like and by segregation of unlike repeat units. Once these comonomer inclusions have reached a considerable size, the average defect Gibbs energy reduces to the thermal energy.