The thermal and rheological properties of two types of metallocene-catalysed LLDPEs (mLLDPEs) and two LDPEs, as well as their blends, were studied by DSC and rheometry. The DSC results showed that the mLLDPE-1 based on hexene comonomer was immiscible with both LDPEs in crystalline states, whereas the mLLDPE-2 based on octene comonomer was miscible with the LDPEs. This indicated that increasing the length of short chains in mLLDPEs could promote the miscibility of mLLDPE/LDPE blends. The linear viscoelastic properties confirmed the immiscibility of the mLLDPE-1 with the LDPEs in the molten state and the miscibility of mLLDPE-2 with LDPEs. In addition, the Palierne emulsion model provided good predictions of the linear viscoelastic data for both miscible and immiscible PE blends. As expected, however, the low-frequency data showed a clear influence of the interfacial tension on the elastic modulus of the blends for the immiscible blends. 34 refs.

Several HDPE pipe resins were compared with PE resins prepared in the Phillips loop-slurry process (single reactor) using a catalyst of chromium on modified aluminophosphate. HDPE resins synthesised using this catalyst exhibited primary structural attributes that were unique for chromium-catalysed resins. These multimodal resins had very high molec.wts. and exceptionally broad MWDs. Topologically, these resins were found to have uniform short chain branching distributions across the MWD (as in polymers made from single-site metallocene catalysts) and significantly reduced levels of long chain branching when compared with resins made using chromium catalysts on conventional supports. The results from rheological, fabricated pipe processing and performance studies indicated that these resins should be particularly suitable for high-performance pipe applications. Pipe samples made from these resins were found to meet PE-100 requirements, including low temperature impact properties. 49 refs.

Low density polyethylene was melt blended with two metallocene linear low density polyethylenes (m-LLDPE) and a Ziegler-Natta LLDPE with different degrees of branching (BC) and comonomer distributions (CD). The blends containing m-LLDPE of low BC exhibited separate crystallisation, whilst cocrystallisation was observed in high-BC m-LLDPE blends. Blends containing Ziegler-Natta LLDPE exhibited separate crystallisation and also a co-crystalline phase. The BC also influenced the mechanical properties. Additions of small proportions of LDPE to low-BC m-LLDPE significantly enhanced the toughness. Blends containing high-BC m-LLDPE followed addition rules. Blends of Ziegler-Natta LLDPE with LDPE were more compatible and exhibited superior mechanical properties compared with m-LLDPE blends of the same molecular weight and BC. The mechanical properties followed the rule of mixtures. The CD had a stronger influence on mechanical properties and BC. 37 refs.

The polymerisation of ethylene and propylene using bis(indenyl)zirconium- methylaluminoxane metallocene catalytic systems modified by sterically demanding bridged alicyclic alcohols such as adamantan-1-ol was investigated. The polymers were characterised by GPC, DSC and carbon-13 NMR, and the effects of addition of the alcohols on the molecular weight and molecular structure of the products are discussed. 31 refs.

The transition metal metallocene compound dichlorozirconocene, together with an anionic surfactant, sodium dodecyl sulphate (SDS), as emulsifier, was found to be an effective catalyst for the polymerisation of monomers such as styrene and methyl methacrylate in an aqueous medium. The polymers obtained had very high molecular weights with narrow molecular weight distributions. The added surfactant plays a dual role as a stabiliser for the cation and an emulsifying agent for the monomer. 27 refs.