Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

Abstract

Experiments are performed to obtain the highest Tm and ΔHm values for poly(l-lactide)s. They also include comparison with literature data and of cyclic and linear species.

About the Influence of (Non‐)Solvents on the Ring Expansion Polymerization of l‐Lactide and the Formation of Extended Ring Crystals

“…who determined that the length of 10 repeat units (lactyl units) in the 10 3 ‐helical conformation of the α ‐modification of PLA amounts to 2.89 nm. [ 45 ] Annealed cPLA typically have crystal thicknesses ( l c ) in the range of 20–28 nm, [ 35,38 ] and the values recorded for the SnBiph catalyzed samples listed in Table 1 fall into this range. For example, a crystal thickness of 25 nm corresponds to chain segment of ≈85 repeat units, including two loops with together 8 units.…”

“…Synthesis and characterization of cPLA have rapidly increased over the past 15 years. [ 7–40 ] The polymerization methods may be subdivided into two categories, first, polymerizations obeying the ROPPOC definition, meaning ring‐opening polymerization with simultaneous polycondensation (including cyclization), [ 41 ] and second, ring‐expansion polymerization (REP) using covalent cyclic catalysts. [ 42 ] The present work is based on REPs catalyzed by two cyclic tin compounds, 2,2‐dibutyl‐2‐stanna‐1,3‐dithiolane (DSTL) and 2‐stanna‐1.3‐dioxa‐4,5,6,7‐dibenzazepine (SnBiph, see Scheme ), because these catalysts have proven in recent REPs conducted in bulk, that they may yield medium and high molecular weight cPLA with average number molecular weights ( M n ) up to 200 000 and average weight molecular weights ( Mw ) up to 400 000) along with extraordinarily high melting temperatures ( T m ) and melting enthalpies (Δ H m ).…”

Microstructure, thermal and rheological properties of poly(L‐lactide‐co‐ε‐caprolactone) tapered block copolymer for potential use in biomedical applications

“…The temperature transitions of the PLC copolymer were investigated by differential scanning calorimetry (DSC). Since these properties, that is, glass transition temperature ( T g ), crystallization temperature ( T c ), melting temperature ( T m ), enthalpy of melting (Δ H m ), and percentage crystallinity, as a results from the varying of the copolymer composition, monomer sequencing, and molecular weight, are responsible for its performance in desired applications 50 …”

“…Since these properties, that is, glass transition temperature (T g ), crystallization temperature (T c ), melting temperature (T m ), enthalpy of melting (ΔH m ), and percentage crystallinity, as a results from the varying of the copolymer composition, monomer sequencing, and molecular weight, are responsible for its performance in desired applications. 50 Differential scanning calorimetry (DSC) thermograms of the PLC copolymer with different heating rate of 5, 10, 20, and 50 C min À1 are as shown in Figure 4. It can be seen that no transition temperature was observed in the first heating scan of the untreated PLC at different rate as shown in Figure 4a.…”

SnOct2‐Catalyzed and Alcohol‐Initiated ROPS of l‐Lactide—Control of the Molecular Weight and the Role of Cyclization

“…In two previous papers it was demonstrated that when the first recrystallization of the PURC L-lactide used for this and previous studies is optimized, the second recrystallization does not enhance the molecular weights. [27,28]…”