The Study On The Structural Characterization Of The Branching In Polyethlylene

The branch length and amount in polyethylene (PE) have significantimpact on its properties. However, there is no reliable method tocharacterize the branch whenever it exceeds six carbons. A new methodto characterize PE with different branch length by solution¹³C NMRtechnique was introduced in this work. The chemical shift difference (Δδ)between CH(Bn) and CH(B4) was used for the characterization withmethine carbon CH(B4) as internal reference. Similar result was obtainedin naphthalene (10%d8-naphthalene) solvent. The method is reliable aslong as the branch length is less than12carbons. And the method is alsouseful if the difference of branch length is big enough. For example, thePE with16carbons branch can be distinguished from the PE with12carbons or20carbons branch by using this method.The sample EHM6007was characterized by Solution¹³C NMR andMelt¹³C NMR respectively. Convincing evidence was shown in this workthat, for soluble PE materials, the Solution¹³C NMR technique offers stronger signal strength and less noisy than the Melt approach. It isobvious that the Solution technique is superior in Signal-to-Noise Ratio(SNR) at10%g/ml and higher concentrations. A common mistake inSNR assessment of polymer spectra, mixing integral and line height inthe same formulation, was corrected.The content and the distribution of comonomer have significantimpact on properties of PE. The¹³C NMR peak assignment ofethylene-1-butene copolymer was confirmed by the characterization of aseries of copolymers. The calculation of sequence distribution inethylene-1-butene copolymers was improved by the application ofnecessary relationship between sequences.The branches in LDPE were also quantitatively characterized by¹³CNMR in this dissertation. In the comparison of two LDPE samples fromdifferent technology, it was found that the LDPE by autoclave technologyhas more4carbons,5carbons and long chain branches than LDPE fromtubular technology. The fractions of solvent-gradient elution fractionationwere characterized by¹³C NMR. It was found that the fraction withhigher Mwcontained more6+carbons branches and the allylic end groupswere mainly in lower Mwfraction.