Characterizing Long Chain Branching in Polypropylene

Abstract

In order to improve elongational viscosity of polypropylene, allowing its use in a wide range of applications, different samples of branched polypropylene have been produced by reactive extrusion and evaluated by different techniques. It is known that the long chain branching (LCB) can act as a nucleating agent in the crystallization process. This is confirmed by differential scanning calorimetry (DSC), optical microscopy, and crystallization analysis fractionation (CRYSTAF), where an increase in the crystallization temperature can be observed when comparing linear and branched samples. In the chemical composition distribution profile of the analyzed samples, it is possible to see differences in the amount of crystallized material among the branched PP samples and it is possible to correlate it with the long chain branching content and distribution, measured by Triple Detector Gel Permeation Chromatography (3D-GPC), using the Mark-Houwink plot (MH Plot), conformation plot, and gpcBR methodology. A decrease in dissolution temperature, and an increase in soluble fraction is observed by temperature rising elution fractionation (TREF) at increasing LCB content in the polymer samples. These results indicate that the presence, amount, or distribution of long chain branching affects the crystallization kinetics and the crystal morphology. CRYSTAF and TREF show a good correlation with LCB content measured by GPC.

Branched Propylene Derivatives by Radical-Mediated Grafting of an Acrylate-Functionalized Nitroxyl

“…The data show that relative to linear PP, the gel-free AOTEMPO derivative PP-AO1 nucleates spherulites much more rapidly, resulting in accelerated crystallization and smaller spherulite size. This is consistent with recent reports on PP-LCB crystallization, which attribute this behavior to a nucleating effect of branch points . Although definitive conclusions regarding the nucleation mechanism cannot be drawn from available information, the prodigious nucleation observed in these gel-free branched samples supports the hypothesis that branched structures contribute to the nucleation of polypropylene crystals.…”

Improved melt strength and processability of impact copolymer polypropylene by introducing long‐chain branching via reactive extrusion with “ene” functionalized dendrimer

“…A slight improvement in percentage crystallinity was also observed for the same composition as compared to neat ICP. [ 35–37 ]…”

“…A slight improvement in percentage crystallinity was also observed for the same composition as compared to neat ICP. [35][36][37] Table 3 lists the onset degradation temperature (T onset ) for all the prepared samples. The addition of luperox in ICP caused β-scission in the polymer chains, which led to a sharp decrease in T onset as compared to neat ICP.…”

Nickel‐catalyzed polymerization of a substituted sulfoxonium ylide

“…The polymer appeared to be uniform and linear as a Mark‐Houwink plot revealed a strong correlation between the intrinsic viscosity and molecular weight (R 2 = 0.99) (see Figure 1(C),(D)). 17 The glass transition temperature of the polymer was determined to be −50 °C by differential scanning calorimetry and thermogravimetric analysis revealed that the polymer began to decompose at 412 °C under nitrogen.…”