2 research outputs found
Enzymatic degradation of poly(butylene succinate) copolyesters synthesized with the use of Candida antarctica lipase B
<div><div><div><p>Abstract: Biodegradable polymers are an active area of investigation, particularly ones that can be produced from sustainable, biobased monomers, such as copolymers of poly(butylene succinate) (PBS). In this study, we examine the enzymatic degradation of poly(butylene succinate-dilinoleic succinate) (PBS-DLS) copolymers obtained by âgreenâ enzymatic synthesis using lipase B from Candida antarctica (CALB). The copolymers differed in their hard to soft segments ratio, from 70:30 to 50:50 wt.%. Enzymatic degradation was carried out on electrospun membranes (scaffolds) and compression-moulded films using lipase fromPseudomomas cepacia. Poly(e-caprolactone) (PCL) was used as a reference aliphatic polyester. The degradation process was monitored gravimetrically via water uptake and mass loss. After 24 days, approx. 40% mass loss was observed for fibrous materials prepared from PBS-DLS 70:30 copolymer, as compared to approx. 10% mass loss for PBS-DLS 50:50. Infrared spectroscopy (FTIR) and SEC analysis were used to examine changes in chemical structure. Differential scanning calorimetry (DSC) and scanning light microscopy (LSM) revealed changes in degree of crystallinity, and changes in surface morphology, consistent with a surface erosion mechanism. We conclude that the obtained copolymers are suitable for tissue engineering applications thanks to tuneable degradation and lack of acidification during breakdown.</p></div></div></div
Linear Viscoelastic Properties of Putative Cyclic Polymers Synthesized by Reversible Radical Recombination Polymerization (R3P)
Linear
viscoelastic properties in both melt and solution states
are reported for a series of poly(3,6-dioxa-1,8-octanedithiol) (polyDODT)
made by reversible radical recombination polymerization (R3P) under
conditions designed to produce linear (LDODT), cyclic (RDODT), and
linearâcyclic mixtures (LRDODT). PolyDODT is amorphous (Tg < â50 °C) and highly flexible
(entanglement molecular weight Me,lin â
1850 g/mol for LDODT). PolyDODTâs low Tg and low Me,lin enable characterization
over a wide dynamic range and a wide range of dimensionless weight-average
molecular weight Zw = Mw/Me,lin. Measurements at
temperatures from â57 to 100 °C provide up to 18 decades
of reduced frequency, which is necessary to characterize RDODT melts
with Zw from 23 to 300. The two highest-molecular-weight
polymers in the present RDODT series have such high Mw (406k and 556k g/mol) that mass spectrometry, NMR spectroscopy,
and even chemical assays for chain ends are unable to rule out up
to 2 mol % of linear contaminant. By studying the samples in solution
(using dilution to reduce Zw), we could
compare their dynamics with those of previously established high-purity
polystyrene (PS) rings (limited to Zw â¤
13.6). RDODT solutions with Zw < 15
(concentrations G* that accord with LCCC-purified PS rings in terms of the
frequency dependence (including the absence of a plateau), the progression
of shapes of G* as a function of Zw, and the linear scaling of their zero-shear viscosity
Ρ0 with Mw. The shape
of G* as a function of Zw for solutions of RDODT-406k and -556k also accords with lower Mw RDODT melts (which have â¤1.3 mol %
of linear contaminant). Thus, the measurement of the linear viscoelastic
properties of appropriate concentrations of high Mw (>200k g/mol) putative cyclic polymers, in which
linear
chains evade spectroscopic detection, may provide an alternative means
(though not fully proven) of validation of sample purity. When Zw > 15 (including all seven RDODT melts and
eight of their solutions), G* has a rubbery plateau.
This suggests that the onset of entanglement-like behavior in rings
requires 4â5-fold greater Zw than
is required for linear chains. Further, the plateau moduli of RDODT
samples are indistinguishable from GNo of the corresponding
LDODT (melt or matched-concentration solutions). In entangled linear
polymers, the observation that GNo is independent of Zw follows from limitations on lateral fluctuations due
to neighboring chains becoming independent of position along a given
chain. The present results for RDODT suggest that this holds for sufficiently
long endless chains, too. While the RDODTs have the same GNo as entangled
LDODTs, when Zw > 60, the terminal
relaxation,
if reached at all, of RDODT extends to orders of magnitude lower frequency
than an entangled linear polymer of the same Zw. Consequently, the viscosity of RDODT with Zw > 60 increases with Zw much
more strongly than the 3.4 power observed for entangled linear polymers.
Finally, these novel polymers, with a disulfide-linked backbone and
broad relaxation time distribution, may prove important in relation
to biodegradable elastomers and materials with exceptional low-frequency
dissipation, extending at least 12 decades below the onset of the
rubbery plateau