Orthogonal functionalization of alternating polyesters: selective patterning of (AB)_n sequences

Stößer T., Sulley G.S., Gregory G.L., Williams C.K.

Oxygenated block polyols are versatile, potentially bio-based and/or degradable materials widely applied in the manufacture of coatings, resins, polyurethanes and other products. Typical preparations involve multistep syntheses and/or macroinitiator approaches. Here, a straightforward and well-controlled one-pot synthesis of ABA triblocks, namely poly(ether-b-ester-b-ether), and ABCBA pentablocks, of the form poly(ester-b-ether-b-ester’-b-ether-b-ester), using a commercial chromium catalyst system is described. The polymerization catalysis exploits mechanistic switches between anhydride/epoxide ring-opening copolymerization, epoxide ring-opening polymerization and lactone ring-opening polymerization without requiring any external stimuli. Testing a range of anhydrides, epoxides and chain-transfer agents reveals some of the requirements and guidelines for successful catalysis. Following these rules of switch catalysis with multiple monomer additions allows the preparation of multiblock polymers of the form (ABA)n up to 15 blocks. Overall, this switchable catalysis delivers polyols in a straightforward and highly controlled manner. As proof of potential for the materials, methods to post-functionalize and/or couple the polyols to make higher polymers are demonstrated. Multiblock oxygenated polyols often show better properties than the constituent polyols, but their synthesis can be complex and difficult. Here a switchable catalysis concept is described which allows for the efficient preparation of multiblock poly(ether-b-ester) materials starting from mixtures of common monomers.

Nowalk J.A., Swisher J.H., Meyer T.Y.

The extent to which small changes in monomer sequence affect the behaviors of biological macromolecules is studied regularly, yet the dependence of bulk properties on small sequence alterations is underexplored for synthetic copolymers. Investigations of this type are limited by the arduous syntheses required, lack of scalability, and scarcity of examples of polymer systems that are known to exhibit sensitive sequence/property dependencies. Our group has previously explored the hydrolysis behaviors of a library of sequenced poly(lactic-co-glycolic acid)s and found a strong correlation with the L–G sequence. To investigate the degree to which properties are dominated in this system by relatively short-range sequence changes, we have incorporated precisely sequenced and mildly “scrambled” L–G oligomers into cyclic macromonomers and subjected them to entropy-driven ring-opening metathesis polymerization, a method that we have recently shown produces polymers with molecular weight control and sequence preserv...

Nowalk J.A., Fang C., Short A.L., Weiss R.M., Swisher J.H., Liu P., Meyer T.Y.

The bulk properties of a copolymer are directly affected by monomer sequence, yet efficient, scalable, and controllable syntheses of sequenced copolymers remain a defining challenge in polymer science. We have previously demonstrated, using polymers prepared by a step-growth synthesis, that hydrolytic degradation of poly(lactic- co-glycolic acid)s is dramatically affected by sequence. While much was learned, the step-growth mechanism gave no molecular weight control, unpredictable yields, and meager scalability. Herein, we describe the synthesis of closely related sequenced polyesters prepared by entropy-driven ring-opening metathesis polymerization (ED-ROMP) of strainless macromonomers with imbedded monomer sequences of lactic, glycolic, 6-hydroxy hexanoic, and syringic acids. The incorporation of ethylene glycol and metathesis linkers facilitated synthesis and provided the olefin functionality needed for ED-ROMP. Ring-closing to prepare the cyclic macromonomers was demonstrated using both ring-closing metathesis and macrolactonization reactions. Polymerization produced macromolecules with controlled molecular weights on a multigram scale. To further enhance molecular weight control, the macromonomers were prepared with cis-olefins in the metathesis-active segment. Under these selectivity-enhanced (SEED-ROMP) conditions, first-order kinetics and narrow dispersities were observed and the effect of catalyst initiation rate on the polymerization was investigated. Enhanced living character was further demonstrated through the preparation of block copolymers. Computational analysis suggested that the enhanced polymerization kinetics were due to the cis-macrocyclic olefin being less flexible and having a larger population of metathesis-reactive conformers. Although used for polyesters in this investigation, SEED-ROMP represents a general method for incorporation of sequenced segments into molecular weight-controlled polymers.

Andrea K.A., Kerton F.M.

Effective utilization of carbon dioxide as a C1 feedstock is an ongoing challenge for chemists. The catalytic reaction of epoxides and carbon dioxide to produce cyclic or polycarbonates has become ...

Xu Q., Li S., Yu C., Zhou Y.

Polymer self-assembly has been a hot research topic for several decades. Different types of polymers with various architectures, like block copolymers, brush polymers, hyperbranched polymers and dendrimers, etc., are currently being investigated. Alternating copolymers (ACPs) are regular copolymers with an alternating monomeric unit structure in the polymer backbones. However, despite the great progress in the synthesis of ACPs, their self-assembly is still in an infant stage. Very recently, our group reported a new type of amphiphilic ACPs through click copolymerization and obtained spheres, vesicles, nanotubes, and even hierarchical sea urchin-like aggregates through the self-assembly process. In addition, we have found some intriguing features in the self-assembly of amphiphilic ACPs when compared with other copolymers, including their facile syntheses, readily functionalization, novel self-assembly structures, new folding-chain mechanisms, and uniform but ultrathin feature length. In this Concept article, we present the self-assembly of amphiphilic ACPs together with their unique features by reviewing our latest results and related studies. Moreover, the future perspective on the self-assembly of amphiphilic ACPs is also proposed. Our aim is to capture the attention and interest of chemists in this new area of polymerization.

Stößer T., Mulryan D., Williams C.K.

Switchable polymerisation catalysis enables block polymer sequence selectivity from monomer mixtures, resulting in the formation of multiblock polyesters. The aluminium salphen catalyst switches between two different polymerisation mechanisms and selectively enchains mixtures of commercially available monomers: lactide, phthalic anhydride, and propene oxide. Sequential monomer mixture additions yield multi-block polyesters featuring 3, 7, 11, 15, 19, 23, and 27 blocks. The unparalleled catalytic selectivity can be used to access completely new multi-block polyesters relevant for future applications.

Wang Y., Darensbourg D.J.

Proof of principles studies by Inoue and coworkers in the late 1960s clearly illustrated the poorly controlled coupling of CO2 and epoxides to provide polycarbonates. These early studies utilizing inadequately defined zinc catalysts derived from diethyl zinc and water have led to the development of a variety of catalysts for these processes over the last two decades. Numerous catalyst systems have been shown to be very effective and selective at affording perfectly alternating copolymers, including those with high levels of regio- and stereo-selectivity. The vast majority of the current literature reports upon the synthesis of hydrophobic polycarbonates which lack functionalities. In this review we will summarize the reports which utilize these well-developed metal-catalyzed CO2/epoxides copolymerization processes to prepare high value-added functionalized polymeric materials for a variety of applications.

Chen Y., Wilson J.A., Petersen S.R., Luong D., Sallam S., Mao J., Wesdemiotis C., Becker M.L.

Three functional epoxides were copolymerized with maleic anhydride to yield degradable poly(propylene fumarate) analogues. The polymers were modified post-polymerization and post-printing with either click-type addition reactions or UV deprotection to either attach bioactive species or increase the hydrophilicity. Successful dye attachment, induced wettability, and improved cell spreading show the viability of these analogues in biomaterials applications.

Petersen S.R., Wilson J.A., Becker M.L.

Additive manufacturing has the potential to change medicine, but clinical applications are limited by a lack of resorbable, printable materials. Herein, we report the first synthesis of polylactone and poly(propylene fumarate) (PPF) block copolymers with well-defined molecular masses and molecular mass distributions using sequential, ring-opening polymerization and ring-opening copolymerization methods. These new copolymers represent a diverse platform of resorbable printable materials. Furthermore, these polymers open a previously unexplored range of accessible properties among stereolithographically printable materials, which we demonstrate by printing a polymer with a molecular mass nearly 4 times that of the largest PPF homopolymer previously printed. To further demonstrate the potential of these materials in regenerative medicine, we report the postprinting “click” functionalization of the material using a copper-mediated azide–alkyne cycloaddition.

Chen T.T., Zhu Y., Williams C.K.

Well-defined pentablock copolymers are prepared using a single catalyst, in one pot, from four different monomers: anhydride, epoxide, lactone, and CO2. The dizinc catalyst bridges three distinct polymerization cycles and performs a double switch in polymerization mechanism to produce pentablock copolymers. The new materials are hydroxyl-telechelic and are efficiently postfunctionalized to introduce polar and nonpolar side-chains.

Li G., Sampson N.S.

We report the formation of oligomers with side-chain sequence control using ruthenium-catalyzed alternating ring-opening metathesis polymerization (AROMP). These oligomers are prepared through sequential, stoichiometric addition of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamide (monomer A) at 85 °C and cyclohexene (monomer B) at 45 °C to generate sequences up to 24 monomeric units composed of (A-alt-B) n and (A'-alt-B) n microblocks, where n ranges from 1 to 6. Herein, monomer A has an alkyl side chain, and monomer A' has a glycine methyl ester side chain. Increasing microblock size from one to six results in an increasing water contact angle on spin-coated thin films, despite the constant ratio of hydrophilic and hydrophobic moieties. However, a disproportionately high contact angle was observed when n equals 2. Thus, the unique all-carbon backbone formed in the AROMP of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamides and cyclohexene provides a platform for the nontemplated preparation of materials with specific sequences of side chains.

Stößer T., Williams C.K.

ABA triblock polyesters are synthesized using a commercially available chromium salen catalyst, in one pot, from monomer mixtures comprising epoxide, anhydride and lactone. The catalysis is highly selective and applies a single catalyst in two distinct pathways. It occurs first by epoxide/anhydride ring-opening copolymerization and subsequently by lactone ring-opening polymerization. It is used to produce various new ABA polyester polyols; these polyols can undergo post-functionalization and chain-extension reactions. The ability to use a commercial catalyst and switchable catalysis with monomer mixtures is expected to facilitate future explorations of new classes of block polymers.

Yang G., Zhang Y., Wang Y., Wu G., Xu Z., Darensbourg D.J.

The coupling of epoxides and carbon dioxide to polycarbonates (CO2–PCs) has been the subject of intense research for nearly half a century. Although tremendous progress has been achieved, their aliphatic characteristics and lack of functionalities of CO2–PCs limit the scope of their application in high value-added and functional materials. In this article, the first CO2-based polycarbonate with the ability to autonomously self-heal is constructed via a one-pot synthetic strategy. The key to the success of the synthetic strategy is efficient tandem three different catalytic reactions, i.e., hydrolysis of epoxides, immortal copolymerization of CO2/epoxides, and thiol–ene click reactions in a one-pot process. Based on the standard tensile testing, these CO2-based materials show robust self-healing properties, where the extensibility, maximal strength, and Young’s modulus of the specimens can almost entirely recover to their original value under ambient temperature. Our studies demonstrate that the self-heali...

Scharfenberg M., Hilf J., Frey H.

Sanford M.J., Van Zee N.J., Coates G.

A versatile catalyst system for the synthesis of narrow dispersity polyesters from readily available epoxides and anhydrides is reported.

Li J., Li J., Qiang H., Jiang J., Zhu Y.

Du Y., Hu J., Wang W., Liu X., Liu Y., Duan R., Bian X., Chen X.

Liang X., Lv J., Qiang H., Li J., Wang W., Du J., Zhu Y.

A novel switchable polymerization method enables the one-step/one-pot synthesis of well-defined polyester-b-polypeptoids from a monomer mixture of epoxides, cyclic anhydrides, and N-substituted N-carboxyanhydrides.

Wang K., Li Z., Li Z., Li B.

Bifunctional thiourea–quaternary ammonium salt catalysts exhibited significantly higher activity over a two-component system with a similar structure at a low catalyst loading for the ring-opening copolymerization of epoxides and cyclic anhydrides.

Kerr R.W., Craze A.R., Williams C.K.

The synthesis of poly(ester-alt-ethers) is achieved by controlled ring-opening copolymerizations of commercial anhydrides and epoxides using a Zr(iv) catalyst. The catalysis shows unusual ABB monomer sequence selectivity and polymer properties depend upon both the monomers and the sequence.

Rosetto G., Vidal F., McGuire T.M., Kerr R.W., Williams C.K.

Jung H., Goonesinghe C., Zhang Z., Chang J., Nyamayaro K., Baalbaki H.A., Hatzikiriakos S.G., Mehrkhodavandi P.

Wang M., Ding Z., Shi X., Ma Z., Wang B., Li Y.

Shellard E.J., Diment W.T., Resendiz-Lara D.A., Fiorentini F., Gregory G.L., Williams C.K.

Saumer A., Mecking S.

Merckle D., Weems A.C.

Vat photopolymerization 3D printing has traditionally relied on free radical crosslinking between alkenes to produce non-degradable parts, which may have limited use in the biomedical and clinical spaces. Photopolymer resins...

Vidal F., Smith S., Williams C.K.

de la Cruz-Martínez F., de Sarasa Buchaca M.M., Castro-Osma J.A., Lara-Sánchez A.

Young T.B., Guppy O.G., Draper A.J., Whitington J.M., Kariuki B.M., Paul A., Eaton M., Pope S.J., Ward B.D.

Fluorescent polyesters have been prepared using ring-opening copolymerization by adding a fluorescent monomer to the reaction. The coloured polymers have been depolymerized and white polymer resynthesized from the recovered monomers.

Jeong S.Y., Kim J., Lee E., Son K.