Star-shaped lactic acid based systems and their thermosetting resins; synthesis, characterization, potential opportunities and drawbacks

Synthesis of star-shaped poly(lactide)s, poly(valerolactone)s and poly(caprolactone)s via ROP catalyzed by N-donor tin(ii) cations and comparison of their wetting properties with linear analogues

In this study, we report the use of N-coordinated tin(ii) cations [L1→Sn(H2O)][OTf]2·THF (1) and [L1→SnCl][SnCl3] (2) (L1 = 1,2-(C5H4N-2-CH = N)2CH2CH2) as efficient ROP catalysts, which, in combination with benzyl alcohol, afford well-defined linear poly(ε-caprolactone) (PCL) and poly(δ-valerolactones) (PVL) via an activated monomer mechanism (AMM). Thanks to the versatility of complexes 1 and 2 as catalysts, star-shaped PCL, PVL and PLA were also prepared using three-, four-, five- and six-functional alcohols. The number of arms was determined by SEC-MALS-Visco analysis. Spin-coated thin layers of linear and selected six-armed polymers were further studied in terms of their wettability to water. Attention was focused on the influence of the composition and structure of the polymers. Finally, to increase the hydrophobic properties of the studied polymers, stannaboroxines L2(Ph)Sn[(OB-(C6H4-4-CF3))2O] and L2(Ph)Sn[(OB-(C6H4-3,5-CF3)2)2O] (L2 = C6H3-2,6-(Me2NCH2)2) were applied.

Biodegradable thermoset poly(lactic acid) resin containing phosphorus: Flame retardancy, mechanical properties and its soil degradation behavior

With the growing environmental awareness, poly(lactic acid) (PLA) is regarded as one of the most promising varieties of bio-based polyesters owing to its environment-friendly and biodegradable advantages. However, poor thermal stability and flammability disadvantages limit the applications of PLA. Herein, a series of biodegradable intrinsic flame-retardant thermoset PLA resins (DMMP-M4sPLA) were designed. DMMP-M4sPLA resins exhibit excellent flame retardancy, achieving UL 94 V-0 rating and limiting oxygen index (LOI) of 28.1 %-31.7 %. Meanwhile, the cured DMMP-M4sPLA resins show a high glass transition temperature and tensile strength. In addition, the resins demonstrate full degradation with no harmful degradation products. This work provides an advanced design strategy to create bio-based and biodegraded resins with superior flame retardant and mechanical performance, holding great potentials in the fields of aviation interior, automotive, etc.

Linear and star-shaped π-conjugated oligoanilines: a review on molecular design in syntheses and properties

Molecular Design and Synthesis of Linear and Star-shaped π-conjugated Oligoanilines with reversible optoelectrochemical properties.

Shape memory polymer (SMP) scaffolds with improved self-fitting properties

"Self-fitting" shape memory polymer (SMP) scaffolds prepared as semi-interpenetrating networks (semi-IPNs) with crosslinked linear-poly(ε-caprolactone)-diacrylate (PCL-DA, M_n∼10 kg mol^-1) and linear-poly(l-lactic acid) (PLLA, M_n∼15 kg mol^-1) [75/25 wt%] exhibited robust mechanical properties and accelerated degradation rates versus a PCL-DA scaffold control. However, their potential to treat irregular craniomaxillofacial (CMF) bone defects is limited by their relatively high fitting temperature (T_fit∼55 °C; related to the T_m of PCL) required for shape recovery (i.e. expansion) and subsequent shape fixation during press fitting of the scaffold, which can be harmful to surrounding tissue. Additionally, the viscosity of the solvent-based precursor solutions, cast over a fused salt template during fabrication, can limit scaffold size. Thus, in this work, analogous semi-IPN SMP scaffolds were formed with a 4-arm star-PCL-tetracryalate (star-PCL-TA) (M_n∼10 kg mol^-1) and star-PLLA (M_n∼15 kg mol^-1). To assess the impact of a star-polymer architecture, four semi-IPN compositions were prepared: linear-PCL-DA/linear-PLLA (L/L), linear-PCL-DA/star-PLLA (L/S), star-PCL-TA/linear-PLLA (S/L) and star-PCL-TA/star-PLLA (S/S). Two PCL controls were also prepared: LPCL (i.e. 100% linear-PCL-DA) and SPCL (i.e. 100% star-PCL-TA). The S/S semi-IPN scaffold exhibited particularly desirable properties. In addition to achieving a lower, tissue-safe T_fit (∼45 °C), it exhibited the fastest rate of degradation which is anticipated to more favourably permit neotissue infiltration. The radial expansion pressure exerted by the S/S semi-IPN scaffold at T_fit was greater than that of LPCL, which is expected to enhance osseointegration and mechanical stability. The intrinsic viscosity of the S/S semi-IPN macromer solution was also reduced such that larger scaffold specimens could be prepared.

Synthesis of Lactic Acid-Based Thermosetting Resins and Their Ageing and Biodegradability

The present work is focused on the synthesis of bio-based thermoset polymers and their thermo–oxidative ageing and biodegradability. Toward this aim, bio-based thermoset resins with different chemical architectures were synthesized from lactic acid by direct condensation with ethylene glycol, glycerol and pentaerythritol. The resulting branched molecules with chain lengths (n) of three were then end-functionalized with methacrylic anhydride. The chemical structures of the synthesized lactic acid derivatives were confirmed by proton nuclear magnetic resonance spectroscopy (¹H-NMR) and Fourier transform infrared spectroscopy (FT–IR) before curing. To evaluate the effects of structure on their properties, the samples were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and the tensile testing. The samples went through thermo-oxidative ageing and biodegradation; and their effects were investigated. FT-IR and ¹H-NMR results showed that three different bio-based resins were synthesized using polycondensation and end-functionalization. Lactic acid derivatives showed great potential to be used as matrixes in polymer composites. The glass transition temperature of the cured resins ranged between 44 and 52 °C. Pentaerythritol/lactic acid cured resin had the highest tensile modulus and it was the most thermally stable among all three resins. Degradative processes during ageing of the samples lead to the changes in chemical structures and the variations in Young’s modulus. Microscopic images showed the macro-scale surface degradation on a soil burial test.

Hydrolytic Degradation of Comb-Like Graft Poly (Lactide-co-Trimethylene Carbonate): The Role of Comonomer Compositions and Sequences

The effect of sequence on copolymer properties is rarely studied, especially the degradation behavior of the biomaterials. A series of linear-comb block, gradient, random copolymers were successfully achieved using hydroxylated polybutadiene as the macroinitiator by simple ring-opening polymerization of l-lactide (l-LA) and 1,3-trimethylene carbonate (TMC). The hydrolytic degradation behaviors of the copolymers were systemically evaluated by using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and scanning electron microscopy (SEM) to illustrate the influences of comonomer compositions and sequence structures. The linear-comb block copolymers (lcP(TMC-b-LLA)) with different compositions had different degradation rates, which increased with l-LA content. Thermal property changes were observed with decreased T_m and increased ΔH_m in all block copolymers during the degradation. To combine different sequence structures, unique degradation behaviors were observed for the linear-comb block, gradient and random copolymers even with similar comonomer composition. The degradation rates of linear-comb PLLA-gradient-PTMC (lcP(LLA-grad-TMC)) and linear-comb PLLA-random-PTMC (lcP(LLA-ran-TMC)) were accelerated due to the loss of regularity and crystallinity, resulting in a remarkable decrease on weight retention and molar mass. The hydrolysis degradation rate increased in the order lcP(TMC-b-LLA), lcP(LLA-ran-TMC), lcP(LLA-grad-TMC). Therefore, the hydrolytic degradation behavior of comb-like graft copolymers depends on both the compositions and the sequences dramatically.

Heat-curing polylactide for bone implants: Preparation and investigation on properties relevant to degradation

Several processes have been used to produce polylactide for bone replacement. The challenge remains, however, to produce these devices by a simpler and more economical process. In this study, a method of combining powder and liquid parts was introduced. Star-shaped polylactides with molecular weights ranging from 3 to 16 kg/mol were synthesized and blended with a linear polylactide (Mw = 188 kg/mol) using the technique of emulsion solvent evaporation. The blends in a form of spherical powder were characterized by scanning electron microscopy, gel permeation chromatography, and particle size analysis. The heat-curing polylactide was fabricated by mixing the powder with triethylene glycol dimethacrylate, molded, and then heated in a hot water bath to solidify. The effects of powder composition in terms of amount and molecular weight of the star-shaped polylactide on mechanical properties were investigated. The results showed an increase in flexural strength with increase in the amount of star-shaped polylactide. The powder comprised star-shaped polylactide having the molecular weight of 10,770 g/mol, not less than 80wt%, offered the fabricated heat-curing polylactide with high strength ranging from 95 to 100 MPa. This formulation was further incorporated with hydroxyapatite to improve biocompatibility and subjected to degradation at 37°C. Mechanical test and weight loss determination together with biological test were conducted at certain times during degradation of the materials. Both materials with and without hydroxyapatite showed mechanical stability upon degradation for at least 6 months, but the one with hydroxyapatite revealed significantly better bioactivity at the end of 1-year follow-up study, making it the most promising material for bone implants.

End-Chain Fluorescent Highly Branched Poly(l-lactide)s: Synthesis, Architecture-Dependence, and Fluorescent Visible Paclitaxel-Loaded Microspheres

A facile method in combination of "grafting from" and "end-functionalization" was developed for the synthesis of fluorescent highly branched poly(l-lactide)s (PLLA-COU) via ring opening polymerization (ROP) and esterification end-capping. These resulting PLLA-COU with four kinds of architectures, including linear, star, linear-comb, and star-comb structures, were subjected to characterization and application as fluorescent visible paclitaxel-loaded microspheres. The mutual effects of architecture and end-groups on thermal and fluorescence properties, enzymatic degradation, and drug release behaviors were focused. Contrast to linear and star PLLA-COU, two comb-shaped analogues demonstrated higher fluorescence quantum yield, faster drug release, and lower enzymatic degradation rate. All the fluorescent microspheres could maintain fluorescence traceability. The fluorescent PLLA-COU displayed negligible toxicity and good biocompatibility. This work highlights that the fluorescent highly branched poly(l-lactide)s are properties-tailored and used as fluorescent visible drug delivery systems (DDS) for potential theranostic applications.

Stereocomplexation, Thermal and Mechanical Properties of Conetworks Composed of Star-Shaped l-Lactide, d-Lactide and ε-Caprolactone Oligomers Utilizing Sugar Alcohols as Core Molecules

It is important to develop tailor-made biodegradable/biocompatible polymer networks usable for biomaterials whose thermal and mechanical properties are easily controlled by changing the composition. We synthesized sugar-alcohol-based polymer networks (SPN-mscLAO/3CLO, m = 4, 5 or 6) by the crosslinking reactions of erythritol, xylitol or sorbitol-based m-armed star-shaped l-lactide and d-lactide oligomers (HmSLLAO and HmSDLAO), a glycerol-based 3-armed star-shaped ε-caprolactone oligomer (H3SCLO) and hexamethylene diisocyanate (HDI) at the weight ratios of HmSLLAO/HmSDLAO = 1/1 and (HmSLLAO + HmSDLAO)/H3CLO = 100/0, 75/25, 50/50, 25/75 or 0/100). The influence of the arm number on the crystallization behavior, thermal and mechanical properties of SPN-mscLAO/3CLOs were systematically investigated by comparing with those of sugar-alcohol-based homochiral polymer network (SPN-mLLAO, m = 4, 5 or 6) prepared by the reaction of HmSLLAO and HDI. Stereocomplex (sc) crystallites are dominantly formed for SPN-mscLAO/3CLOs 100/0⁻25/75, whereas SPN-mLLAOs were amorphous. The higher order of melting temperature of sc-crystals for SPN-mscLAO/3CLOs 100/0⁻25/75 was m = 5 > m = 6 > m = 4. The sc-crystallinities of SPN-4scLAO/3CLOs 100/0⁻50/50 were significantly lower than those of SPN-mscLAO/3CLOs 100/0⁻50/50 (m = 5 and 6). The larger order of the sc-spherulite size at crystallization temperature of 110 °C was m = 5 > m = 6 > m = 4 for SPN-mscLAO/3CLO 100/0. The size and number of sc-spherulites decreased with increasing crystallization temperature over the range of 110⁻140 °C and with increasing CLO fraction. Among all the networks, SPN-5scLAO/3CLOs 75/25 and 50/50 exhibited the highest and second highest tensile toughnesses (21.4 and 20.3 MJ·m-3), respectively.