Facile synthesis and comparative study of poly(l-lactide) with linear-comb and star-comb architecture

Abstract

In this work, two series of linear-comb and star-comb well defined graft poly(L-lactide) (PLLA) have been synthesized conveniently by one-pot ring-opening polymerization (ROP) of L-lactide using functionalized polybutadiene macroinitiators. The used organocatalyst of 1, 8-diazabicyclo[5,4,0]undec-7-ene (DBU) allows the polymerization of L-lactide proceeds rapidly at room temperature. Kinetic studies of the ROP reaction in this system indicate a first-order kinetic in monomer concentration.1 H NMR and GPC techniques are employed to characterize the synthesized polymers, validating the formation of desired comb structures with controllable chain length. Linear-comb and star-comb graft PLLA were comparatively studied as well as with linear PLLA by DSC and POM. The results reveal that comb structure makes a remarkable improvement of PLLA crystallization ability in both crystallinity and growth rate of spherulites. Furthermore, the more compacted star-comb structure imposes restriction on chain mobility, which weakens the growth effect to some extent. It is found that the glass transition temperature (Tg) and melting temperature (Tm) significantly depend on the side chain length and backbone structure. Rheological studies of both melt and instinct viscosity of the solution show that star-comb PLLA has the lowest hydrodynamic volume compared with linear-comb PLLA and linear PLLA.Polylactide (PLA) derived from renewable resources has drawn significant attention due to its well biodegradable/biocompatible properties and the other concerns associated with the use of petroleum-based products. 1-3 High molecular weight PLA and its copolymers are one of the most widely utilized polymers in the field of biomedical materials 4-8 . Due to the extremely high mechanical strength, it has been used as commodity and industrial materials as well as clinically in medical applications, 9-10 orthopaedic screw, 11-12 scaffolds, 13-15 etc.PLA can be directly prepared from lactic acid by polycondensation under azeotropic distillation conditions referred as poly(lactic acid) [16][17][18] . Ring-opening polymerization (ROP) of lactide is another effective route to synthesize PLA with higher molecular weight and lower polydispersity 19 . Stannous octoate (Sn(Oct)2) is the most common catalyst for ROP of lactide 20 . However, tin based catalysts are less than ideal from both chemical and biological perspective. The organic catalysts now appear as viable substitutes for classical metallic catalysts 21-23 .Non-metallic ROP processes are demanded for sustainable and environmentally friendly products, especially in microelectronic 24 and biomedical 25-26 applications. In 2001, Hedrick et al. first reported N-heterocyclic carbenes as novel metal-free nucleophilic catalysts for the ROP of cyclic ester monomers 27 . Among those catalysts, the commercial available amidine and guanidine (such as 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU)) provide better control of molecular weight and highly efficient at room...

Synthesis and characterisation of fluorescent pyrene‐end‐capped polylactide fibres

“…Figure (A) shows that the decomposition process consists of one stage starting at 208, 179 and 195 °C for AH1, AH2 and AH3, respectively. The char content varied between 7.67 and 9.11 wt% due to the pyrene structure and was in agreement with other studies …”

“…The use of DBU allows a high degree of polymerisation, very narrow controlled molecular weight and low catalyst concentration of 1 mol%. This methodology is preferable to that employing stannous octanoate, one of the most commonly used catalysts currently employed for the promotion of these polymerisation reactions, and is experimentally easy to adopt . Most notably, the DBU‐catalysed process is free from the toxicity associated with the tin‐based systems which limits their potential utility, especially for biomedical use.…”

Synthesis of Star-Comb Double Crystalline Diblock Copolymer of Poly(ε-caprolactone)-block-poly(l-lactide): Effect of Chain Topology on Crystallization Behavior

“…Also, a lHPB was produced in this work in order to be compared. The detailed polymerization processes and characterizations of linear and star shape HPB macroinitiators were described in our previous publication . The molecular weight and distribution of the macroinitiators were showed in Table S1 and Figure S1 (Supporting Information).…”

“…The degree of epoxidation was calculated by 1 H NMR of epoxidized polybutadiene. [12a] By using “grafting from” method, the novel star‐comb PCL‐ b ‐PLLA were obtained by sequential copolymerization of CL and l ‐LA monomers from the sHPB macroinitiator. First, the polymerization of CL is performed in bulk at 130 °C catalyzed by Sn(Oct) 2 .…”

“…All the syntheses and polymerization reactions were carried out under an inert atmosphere, and the glass assembly was dried with three cycles of a flaming/N 2 ‐purging/evacuating before polymerization initiated. The detailed polymerization processes of linear and star hydroxylated polybutadienes (lHPB and sHPB) were described in our previous publication …”