Graft copolymer density

Moreover, alcohol functionalities have been introduced into the polynor-bornene (PNB) backbone by copolymerization of norbornene with a few percent of 5-acetate norbornene and subsequent acetate reduction. After transformation of the pendant hydroxyl functions into diethyl aluminum alkoxides, sCL has been ring opening polymerized (Scheme 31). Owing to the controlled/ liv-ing character of both polymerization processes the isolated poly(NB- -CL) graft copolymers were characterized by well-defined composition, controlled molecular weight and branching density, and narrow MWD (PDI=1.2-1.4) [92]. 

The amount of grafted styrene is given by the increase in weight of the film. It may also be calculated quite well from the densities of polyethylene (d ), polystyrene (d2), and the graft copolymer (dj) according to the following Eq.3.31 ... 

In this review we first summarize methods of synthesis of ECM analogs as graft copolymers. The modification of supermolecular structure (crystallinity, crosslink density, porosity) is then discussed. Finally, the relationships between polymer structure and biologic activity are summarized. 

Another graft copolymer having the same composition, but presumably a somewhat greater density of PEO side chains, had the same transparent appearance and low Tg. Modulus as well as dilatometric data exhibited a hysteresis loop between — 20° and 60°C. These results along with x-ray measurements indicate presence of some crystallinity in contrast to the first completely amorphous copolymer. For given composition the relation between the size and distribution of the side chains, and their ability to crystallize is not yet clear. 

Degree of Crafting of the Backbone Polymer. With graft copolymers based on low-density polyethylene, the degree of grafting (defined by grafted PE x 100/total PE) is determined by selective extraction of the homopolymers. With high-density polyethylenes, it is determined by a liquid-solid absorption technique which will be described elsewhere (13). 

Figure 9 shows the mechanical loss curves of a low-density polyethylene, a PVC, a raw VC/PE (50-50) graft copolymer, and a poly (ethylene-g-vinyl chloride) containing 46 weight % of vinyl chloride. 

The curves of the raw graft copolymer and of the poly(ethylene-g-vinyl chloride) are rather close to that of the low-density polyethylene. The outstanding fact is the absence of the PVC transition peak (between 60° and 100°C) in the mechanical loss curves of these two products. This means that they contain no rigid PVC phase in spite of the presence of about 25 weight % of ungrafted polyvinyl chloride in the raw graft copolymer. This PVC seems thus to be strongly compatibilized with the other constituents by the poly(ethylene-g-vinyl chloride). 

In spite of their high contents of grafted and ungrafted PVC, the behavior of the raw graft copolymer and of the poly(ethylene-g-vinyl chloride) is not very different from that of low-density polyethylene. The stiffening action of this PVC is thus rather low. 

Transparency. Alloys of PVC and VC/PE graft copolymer are more transparent than PVC-polyethylene mixtures having the same total polyethylene content. Graft copolymers based on high-density polyethylene give better transparency than do similar graft copolymers based on low-density polyethylene. Perfect transparency, however, cannot be obtained. 

Diblock copolymers, especially those containing a block chemically identical to one of the blend components, are more effective than triblocks or graft copolymers. Thermodynamic calculations indicate that efficient compat-ibilisation can be achieved with multiblock copolymers [47], potentially for heterogeneous mixed blends. Miscibility of particular segments of the copolymer in one of the phases of the bend is required. Compatibilisers for blends consisting of mixtures of polyolefins are of major interest for recyclates. Random poly(ethylene-co-propylene) is an effective compatibiliser for LDPE-PP, HDPE-PP or LLDPE-PP blends. The impact performance of PE-PP was improved by the addition of very low density PE or elastomeric poly(styrene-block-(ethylene-co-butylene-l)-block styrene) triblock copolymers (SEBS) [52]. 

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