Biocompatible multi‐arm star block copolymers based on poly(L‐lactide) (PLLA) have been prepared by a core‐first approach, using hyperbranched polyglycerol (PG), a polyether polyol, as a polyfunctional initiator. The molecular weight of the hyperbranched initiator‐core was varied from 2 200 to 5 200 g · mol−1, molecular weights of the resulting multi‐arm stars were in the range of 6 700–107 000 g · mol−1 (NMR), depending on the amount of dilactide (LA) added. Various monomer/initiator ratios have been employed in the Sn‐catalyzed LA polymerization in order to vary the length of the lactide arms from $\overline {DP} _{\rm n}$(arm) = 2 to 20 units. Detailed NMR analysis using conventional and 2D‐NMR techniques (e.g., HSQC NMR) revealed that the monomer/initiator‐core ratio indeed permits control of the arm length. SEC measurements showed that the narrow polydispersities of the core molecules ($\overline M _{\rm w} /\overline M _{\rm n}$ = 1.5 and 1.6) became even lower after grafting of PLLA for the multi‐arm star polymers. Size exclusion chromatography (SEC) also demonstrated that the competing homopolymerization of LA could be avoided using suitable reaction conditions. The resulting PG–PLLA star polymers exhibited low polydispersities ($\overline M _{\rm w} /\overline M _{\rm n}$) between 1.15 and 1.7, depending on the length of the PLLA arms. Attachment of the hydrophobic PLLA chains to the hydrophilic polyether structure leads to amphiphilic, core‐shell type structures suitable for guest encapsulation.magnified image
Photoembossing is a convenient and economical process to form complex surface relief structures in polymer thin films. We have improved the aspect ratio of photoembossed microstructures by adding t-butyl hydroquinone (TBHQ) to the polymerization mixture. The mechanism that is proposed is based on the radical transfer principle, where TBHQ converts acrylate radicals into stable phenol radicals that at elevated temperatures act as latent initiators, thereby controlling the kinetics without changing the number of polymerization active sites. As a result, the aspect ratio can be improved with a factor of 5–7 in comparison with previously proposed similar processes.
A series of (hyper)branched poly(l-lactide)(PLLA) copolymers has been prepared by ring-opening multibranching copolymerization of l-lactide with a hydroxyl-functional (ABB′) lactone inimer, 5HDON (5-hydroxymethyl-1,4-dioxane-2-on). Polymerization was conducted in bulk and solution and catalyzed either by stanneous-2-ethyl hexanoate (Sn(Oct)2) or an organic base, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Precise structural characterization of the resulting branched copolyester structures was accomplished by a combination of 2D NMR techniques, relying on the comparison with model compounds. The 5HDON inimer was employed in 1% to 20% fractions and is incorporated either as a dendritic unit or as a focal structure, but hardly in the linear mode. A detailed reaction mechanism was derived from kinetic investigation of the polymerization via NMR spectroscopy, preparative and analytical SEC and MALDI-TOF MS. The evolution and the extent of branching have been monitored and quantified. Both the degree of branching (DB = 2D(HDON)/2D(HDON) + L(lactide); DB = 0.02−0.22) and the molecular weight (M N = 1200−34000 g/mol) could be tailored by variation of the monomer/inimer ratio. For Sn(Oct)2 catalyzed polymerization approximately 50% of the inimer is transformed into dendritic units. In the case of TBD catalysis, the formation of dendritic units was suppressed at room temperature, resulting in linear poly(lactide) functionalized with a lactone end group. The fozcal 5HDON unit of the branched structures is susceptible to further functionalization, for example, by reaction with primary hydroxyl groups, leading to branched polylactide functionalized with precisely one single dye label at the focal moiety. The formation of previously absent linear repeat units from the addition of terminal lactide units to focal 5HDON units was observed when heating the polymers above T g for prolonged times. This reaction was accompanied by a further increase in the molecular weight of the branched copolyesters.
On the basis of a new acetal-protected glycerol monomethacrylate monomer (cis-1,3-benzylidene glycerol methacrylate/BGMA) a series of potentially biocompatible and partially biodegradable homo- and block copolymers were synthesized. ATRP polymerization of BGMA yielded well-defined polyacrylates with pendant benzylidene acetal groups and high glass transition temperatures (115−130 °C). This hydrophobic poly(cis-1,3-benzylidene glycerol methacrylate) could be readily transformed into the hydrophilic and water-soluble poly(1,3-dihydroxypropyl methacrylate), referred to as poly(isoglycerol methacrylate) (PIGMA). It exclusively contains primary hydroxyl groups and therefore differs significantly from the commonly known poly(glycerol methacrylate) (PGMA). Block copolymer systems based on poly(lactide) and BGMA were realized via two orthogonal living polymerization techniques starting from a bifunctional initiator, employing first atom transfer radical polymerization (ATRP) of BGMA and in the second step organo-base catalyzed polymerization of l- or d-lactide. This route provides well-defined block copolymers of low polydispersity (PDI 1.12−1.17) and molecular weights in the range of 7000 to 30 000 g/mol (NMR). Rapid and highly selective acetal hydrolysis of the PBGMA block resulted in the release of the hydrophilic and water-soluble poly(1,3-dihydroxypropyl methacrylate) (poly(isoglycerol methacrylate), PIGMA). Acidic hydrolysis of the acetal protecting groups of poly(BGMA)-b-poly(lactide) copolymers proceeded smoothly to amphiphilic structures, notably without affecting the potentially labile polyester block. The novel PIGMA-b-PLLA copolymers are capable of supramolecular self-assembly to spherical aggregate structures in aqueous environment. The polymers generally exhibited low aggregation constants (CAC: 8−20 mg/L). Because of the unique feature of stereocomplex formation of poly(lactide), the corresponding aggregate morphology could be adjusted by mixing two nearly identical PIGMA-b-PLA copolymers with enantiomeric poly(lactide blocks) in a 1:1 ratio. In this case the uniformly shaped micelles (20 nm) changed to large vesicles with diameters ranging from 600 to 1400 nm. These features render this new type of amphiphilic block copolymers promising for drug delivery applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.