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1. Preparation of multiblock copolymers via step-wise addition of l -lactide and trimethylene carbonate

   https://doi.org/10.1039/c7sc04507g  

   Abubekerov, Mark; Wei, Junnian; Swartz, Kevin R.; Xie, Zhixin; Pei, Qibing; Diaconescu, Paula L. (January 2018, Chemical Science)

   Poly( l -lactide) (PLA) is a bioderived and biodegradable polymer that has limited applications due to its hard and brittle nature. Incorporation of 1,3-trimethylene carbonate into PLA, in a block copolymer fashion, improves the mechanical properties, while retaining the biodegradability of the polymer, and broadens its range of applications. However, the preparation of 1,3-trimethylene carbonate (TMC)/ l -lactide (LA) copolymers beyond diblock and triblock structures has not been reported, with explanations focusing mostly on thermodynamic reasons that impede the copolymerization of TMC after lactide. We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and TMC, in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh 2 )(BH[(3,5-Me) 2 pz] 2 )]Zn(μ-OCH 2 Ph)} 2 ([(fc P,B )Zn(μ-OCH 2 Ph)] 2 , fc = 1,1′-ferrocenediyl, pz = pyrazole). The synthesis of up to pentablock copolymers, from various combinations of LA and TMC, was accomplished and the physical, thermal, and mechanical properties of the resulting copolymers evaluated. 

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2. Enhancement of the mechanical property of poly(ε-caprolactone) composites with surface-modified cellulose nanofibers fabricated via electrospinning

   https://doi.org/10.1557/adv.2019.4  

   Ichimura, Hiroki; Kurokawa, Naruki; Hotta, Atsushi (January 2019, MRS Advances)

   Abstract Poly(ε-caprolactone) (PCL) is one of the leading biocompatible and biodegradable polymers. However, the mechanical property of PCL is relatively poor as compared with that of polyolefins, which has limited the active applications of PCL as an industrial material. In this study, to enhance the mechanical property of PCL, cellulose nanofibers (C-NF) with high mechanical property, were employed as reinforcement materials for PCL. The C-NF were fabricated via the electrospinning of cellulose acetate (CA) followed by the subsequent saponification of the CA nanofibers. For the enhancement of the mechanical property of the PCL composite, the compatibility of C-NF and PCL was investigated: the surface modification of the C-NF was introduced by the ring-opening polymerization of the ε-caprolactone on the C-NF surface (C-NF-g-PCL). The polymerization was confirmed by the Fourier transform infrared (FTIR) spectroscopy. Tensile testing was performed to examine the mechanical properties of the C-NF/PCL and the C-NF-g-PCL/PCL. At the fiber concentration of 10 wt%, the Young’s modulus of PCL compounded with neat C-NF increased by 85% as compared with that of pure PCL, while, compounded with C-NF-g-PCL, the increase was 114%. The fracture surface of the composites was analyzed by scanning electron microscopy (SEM). From the SEM images, it was confirmed that the interfacial compatibility between PCL and C-NF was improved by the surface modification. The results demonstrated that the effective surface modification of C-NF contributed to the enhancement of the mechanical property of PCL. 

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3. Bottlebrush Elastomers with Crystallizable Side Chains: Monolayer-like Structure of Backbones Segregated in Intercrystalline Regions

   https://doi.org/10.3390/polym16020296  

   Nikitina, Evgeniia A; Dashtimoghadam, Erfan; Sheiko, Sergei S; Ivanov, Dimitri A (January 2024, Polymers)

   Bottlebrush (BB) elastomers with water-soluble side chains and tissue-mimetic mechanical properties are promising for biomedical applications like tissue implants and drug depots. This work investigates the microstructure and phase transitions of BB elastomers with crystallizable polyethylene oxide (PEO) side chains by real-time synchrotron X-ray scattering. In the melt, the elastomers exhibit the characteristic BB peak corresponding to the backbone-to-backbone correlation. This peak is a distinct feature of BB systems and is observable in small- or medium-angle X-ray scattering curves. In the systems studied, the position of the BB peak ranges from 3.6 to 4.8 nm in BB elastomers. This variation is associated with the degree of polymerization of the polyethylene oxide (PEO) side chains, which ranges from 19 to 40. Upon crystallization of the side chains, the intensity of the peak decays linearly with crystallinity and eventually vanishes due to BB packing disordering within intercrystalline amorphous gaps. This behavior of the bottlebrush peak differs from an earlier study of BBs with poly(ε-caprolactone) side chains, explained by stronger backbone confinement in the case of PEO, a high-crystallinity polymer. Microstructural models based on 1D SAXS correlation function analysis suggest crystalline lamellae of PEO side chains separated by amorphous gaps of monolayer-like BB backbones. 

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4. Crystalline aliphatic polyesters from eight‐membered cyclic (di)esters

   https://doi.org/10.1002/pol.20220418  

   Tang, Xiaoyan; Shi, Changxia; Zhang, Zhen; Chen, Eugene Y. ‐X. (October 2022, Journal of Polymer Science)

   Abstract Ring‐opening polymerization (ROP) of lactones or cyclic (di)esters is a powerful method to produce well‐defined, high‐molecular‐weight (bio)degradable aliphatic polyesters. While the ROP of lactones of various ring sizes has been extensively studied, the ROP of the simplest eight‐membered lactone, 7‐heptanolactone (7‐HL), has not been reported using metal‐based catalysts. Accordingly, this contribution reports the ROP of 7‐HL via metal‐catalyzed coordinative‐insertion polymerization to the corresponding high‐molecular‐weight polyester, poly(7‐hydroxyheptanoate) (P7HHp). The resulting P7HHp is a semi‐crystalline material, with aT_mof 68 °C, which is ~10 °C higher than poly(ε‐caprolactone) derived from the seven‐membered lactone. Mechanical testing showed that P7HHp is a hard and tough plastic, with elongation at break >670%. P7HHp‐based polyesters with higherT_mvalues have been achieved through stereoselective copolymerization of 7‐HL with an eight‐membered cyclic diester, racemic dimethyl diolide (rac‐8DL^Me), known to lead to highT_mpoly(3‐hydroxyburtyrate) (P3HB). Notably, catalyst's strong kinetic preference for polymerizingrac‐8DL^Meover 7‐HL in the 1/1 comonomer mixture rendered the formation of di‐block copolymer P3HB‐b‐P7HHp, showing two crystalline domains withT_m1 ~ 65 °C andT_m2 ~ 160 °C. Semi‐crystalline random copolymers withT_mup to 164 °C have also been obtained by adjusting copolymerization conditions. Mechanical testing showed that P3HB‐b‐P7HHp can synergistically combine the high modulus of isotactic P3HB with the high ductility of P7HHp. 

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5. Polymer Brush Growth by Surface‐Initiated Ring‐Opening Polymerization from a Cross‐Linked Polymer Thin Film

   https://doi.org/10.1002/adfm.202420958  

   Betancourt‐Ponce, Miguel; Govindarajan, Bharathan; Pike, Jacob; Gopalan, Padma (December 2024, Advanced Functional Materials)

   Abstract Modification of a surface with polymer brushes has emerged as an effective approach to tune the properties of a substrate. Brushes grown from an inimer‐containing cross‐linkable polymer coating provide significant advantages compared to other “grafting‐from” methods, such as improved stability, increased grafting density, and the potential to control the grafting density. So far, the inimer coating method has only been applied for surface‐initiated controlled radical polymerizations. In this work, an approach is presented for the fabrication of a stable cross‐linked ultra‐thin polymer coating containing hydroxyl groups which serve as initiating sites for surface‐initiated ring‐opening polymerization (SI‐ROP). The polymers used for the fabrication of the coatings consist of 2‐((tetrahydro‐2H‐pyran‐2‐yl)oxy)ethyl methacrylate (THPEMA), a small fraction of a cross‐linkable unit, and a diluent styrene. Three coatings with varying THPEMA and styrene content are fabricated, and poly(dimethyl siloxane) (PDMS) and poly(caprolactone) (PCL) brushes are grown by SI‐ROP of hexamethylcyclotrisiloxane (D₃), and ε‐caprolactone respectively. The brushes are characterized by atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), static contact angle measurements, ellipsometry and size exclusion chromatography (SEC). The results demonstrate a well‐controlled ROP of D₃and ability to control grafting density by tuning the THPEMA content of the coatings. 

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