Functionalization of polyolefins by reactive processing: influence of starting reagents on content and type of grafted groups

Previous studies carried out in our laboratory on the functionalization of ethylene polymers (homo and copolymers) through free radical processes, using mechanical mixers and/or extruders with diethylmaleate (DEM) and dicumyl peroxide (DCP), have shown that the presence of branched α-olefin blocks favours degradation versus functionalization and crosslinking whereas these last are more effective with linear ethylene blocks. In this contest the present paper reports about attempts to extend the same processes to propylene polymers by benefitting of the indications of previous results. In particular the one step functionalization of EPM with two or more different groups was carried through the use of different monomers. Moreover the procedure was extended to polypropylene thus obtaining a significant functionalization degree flanked by a remarkable decrease of molecular weight.     

Molecular interactions at the interface in blends of ester groups-functionalized polyolefins

Due to the apolarity of the aliphatic backbones, unmodified polyolefins are scarcely miscible with most of other polymers. The functionalization of preformed polyolefins is a way which has been successfully followed to improve the polymer miscibility. The functionalization of linear low density polyethylene (LLDPE) and ethylene-propylene copolymers (EP), with diethyl maleate (DEM) and dicumyl peroxide (DCP) as radical initiator, gives products containing up to 2–5 mol % of well defined functional groups (2-diethyl succinate). Intermolecular interactions of these functional groups are characterized by comparison with suitable low-molecular-weight structural models in the presence of different solvents containing acidic hydrogen atoms. On the basis of these indication evidences of interface molecular interactions in blends with halogenated polymers are described between the functionalized polyolefins and poly(vinyl chloride) (PVC), poly(vinylidene fluoride) (PVDF) or vinylidene fluoride-hexafluoropropene copolymer obtained in semiindustrial Brabender mixers. It is shown that a smooth functionalization of the polyolefins can modify the phase behaviour and structure of these systems. The FT-IR microanalysis supports the occurrence of partial miscibility phenomena which can be accounted for by specific intermolecular interactions involving the inserted functional groups and occurring mainly at the interfaces between domains of polyolefins and of the halogen-containing polymers.     

Influence of processing method and components molecular structure on the phase behaviour of polyethylenes/dye blends

The phase dispersion of terthiophene alkyl derivatives on different polyethylene matrices was investigated. The PE affinity toward dichroic dyes with different structure, the effect of blending process and the influence of a polyolefinic compatibilizer on the homogeneity of host-guest blends were comparatively investigated by calorimetry, DSC and SEM analyses. For these purposes, polyethylenes with different molecular weights and densities and EVAc were used as host matrices. The polymeric compatibilizer was prepared by radical functionalization of a commercial low density polyethylene. The dichroic nature of the guest phase allowed to perform UV-Vis measurements in polarized light on oriented blend film samples. The dyes affinity toward PE is one of the key factor in obtaining oriented polyolefinic films with high optical performances for several applications.     

Molecularly controlled blending of metals and organic metals with polyolefins for the preparation of materials with modulated optical properties

In this paper, after revisiting previous data on terthiophene molecules, several attempts are described to use metal containing species such as nanoclusters and molecular complexes as dispersed chromophores in the same ethylene polymer matrix in order to extend an approach to new classes of molecules and improve some specific optical responses including fluorescence dichroism and behaviour as linear optical polarizers is evaluated. Comparison with typical linear polarizers from the same polymer and terthiophenes of innovative gold clusters is discussed as well as transition metal complexes.