Advances in High-Temperature Interaction Chromatography of Polyolefins: A Tutorial on Solvent and Temperature Gradient

The advancement of high-temperature interaction chromatography (HT-IC) is a key milestone in polyolefin characterization. Temperature gradient interaction chromatography (HT-TGIC) and solvent gradient interaction chromatography (HT-SGIC) are the main separation methods. This Tutorial explains these methods, their historical uses, recent improvements, and suitable detectors for each technique.

Network Polymer Properties Engineered Through Polymer Backbone Dispersity and Structure

Dispersity (Ð or Mw/Mn) is an important parameter in material design and as such can significantly impact the properties of polymers. Here, polymer networks with independent control over the molecular weight and dispersity of the linear chains that form the material are developed. Using a RAFT polymerization approach, a library of polymers with dispersity ranging from 1.2-1.9 for backbone chain-length (DP) 100, and 1.4-3.1 for backbone chain-length 200 were developed and transformed to networks through post-polymerization crosslinking to form disulfide linkers. The tensile, swelling, and adhesive properties were explored, finding that both at DP 100 and DP 200 the swelling ratio, tensile strength, and extensibility were superior at intermediate dispersity (1.3-1.5 for DP 100 and 1.6-2.1 for DP 200) compared to materials with either substantially higher or lower dispersity. Furthermore, adhesive properties for materials with chains of intermediate dispersity at DP 200 revealed enhanced performance compared to the very low or high dispersity chains.

Stereochemical Heterogeneity Analysis of Polylactides by Multidimensional Liquid Chromatography

A new and robust high-performance liquid chromatography (HPLC) method that separates poly(lactic acid) (PLA) according to its stereochemical composition is presented. Using this method, poly(l-lactide) incorporating trace amounts of meso-lactide resulting from the racemization is separated from the pristine polymer. To prove this aspect in more detail, a representative poly(l-lactic acid) standard, assumed to be highly homogeneous, was separated using this method. The result showed that this was not the case as a fraction incorporating meso-lactide due to racemization occurring during the synthesis is separated. Employing two-dimensional liquid chromatography (2D-LC), the molar mass differences of the separated species were investigated, and fractions with similar molecular sizes were detected, confirming that the LC separation is solely based on stereochemical heterogeneity. The sample was further fractionated by preparative HPLC, followed by an in-depth analysis of the fractions using homonuclear decoupling in proton nuclear magnetic resonance (1H NMR). Convincing results that unveiled significant differences in the stereochemistry of the isolated PLA fractions were obtained. Subsequent analysis by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) also confirmed oligomer series with different end group structures, indicating that the applied HPLC method is very sensitive to minor variations in stereochemistry and end groups. This integrated approach offers detailed insight into the structural characteristics of PLA polymers, contributing to a better understanding of their composition and potential applications.

Structural analysis of hyperbranched polyhydrocarbon synthesized by electrochemical polymerization

Structure of a hyperbranched polyhydrocarbon obtained by electrochemical polymerization was analyzed by various NMR techniques and modeling. The calculated physical properties from its bulk model system well matched with experimental results.

Linking molecular structure to plant conditions: advanced analysis of a systematic set of mini-plant scale low density polyethylenes

Two sample sets of low density polyethylene (LDPE) were investigated and differentiated via comprehensive analysis of their microstructures with specific emphasis on branching.

Bivariate molecular structure distribution of randomly branched polyethylene by orthogonal preparative fractionation

Orthogonal preparative fractionations provide bivariate molecular structure distributions of randomly branched polyethylene.

Combination of preparative and two-dimensional chromatographic fractionation with thermal analysis for the branching analysis of polyethylene

Multiple preparative fractionation of LDPE provides molar mass and branching fractions that are analyzed regarding their thermal properties.

Comprehensive analysis of novel grafted polyethylenes using multidimensional fractionation methods

Noval graft copolymers HDPE-g-LDPE were prepared using a dual reactor setup and characterized regarding molar mass, branching and grafting efficiency using a multidimensional analytical approach.