Long chain branching (LCB) of polylactide (PLA) was successfully prepared by the successive reactions of the end hydroxyl groups of PLA with pyromellitic dianhydride (PMDA) and triglycidyl isocyanurate (TGIC) together.
Due to the formation of ester groups through the reaction between carboxylic acid groups of PLA-g-AA and hydroxyl groups of MWNTs OH, results demonstrated dramatic enhancement in thermal and mechanical properties of PLA, for example, 77 °C increase in initial decomposition temperature with the addition of only 1 wt%.
1H NMR (CDCl3): a (δ = 1.62 ppm, LA repeating unit: -CHCH3), b (δ = 5.21 ppm, LA repeating unit: - CH CH3), c (δ = 3.65 ppm, TPGS repeating unit: -CH2CH2O-), d (δ = 0.50 to 2.40 ppm, CA moiety: -CH2- and -CH-), e (δ = 4.38 ppm, terminal hydroxyl group of CA-PLA: -CH OH). Figure 1B shows the FTIR spectra of the CA-PLA-TPGS copolymer and TPGS.
Two groups of the PLA samples and PLA-based systems featured by starting amorphous structure or semicrystalline structure were considered, respectively.
The 1H NMR analysis showed the presence of new ester linkages that resulted from a reaction between the carboxyl end-groups of the PLA prepolymer and the hydroxyl end-groups of the HTNR, together with the characteristics of the PLA endblock and the HTNR midblock.
Briefly, geometrically various groups of pure PLA scaffolds (interconnected pores of 230 to 390 μm) were fabricated using FDM technique.
Carboxylic acid groups were introduced into the copolymer by reacting the hydroxyl end groups of the PLA macromonomer with succinic anhydride, and the acid groups were neutralized with metal acetates to produce Na-, Cand and Y-PLA ionomers.
Figure 2showed the1H-NMR spectrum of mPEG5-PLA15, wasch was representative for all synthesized mPEG-PLAs: the peaks at 3.65 and 3.36 ppm corresponded to methylene units and CH3O− in the mPEG blocks, signals at 1.58 and 5.18 ppm could be attributed to the hydrogen atoms of CH3- and CH-groups for PLA segments, respectively.
This can be attributed to the formation of hydroxyl or peroxyl groups on the surface of PLA fibers after oxygen plasma treatment.
In "land reform," the working teams of PLA motivated poor people of local ethnic groups to overthrow traditional local authorities, religious or secular.
