The synthesis of molecularly defined epsilon-caprolactone oligomers and polymers up to the 64-mer, via an exponential growth strategy, is described. By careful selection of orthogonal protecting groups, t-butyldimethylsilyl (TBDMS) ether for the hydroxyl group and benzyl (Bn) ester for the carboxylic acid group, a highly efficient synthetic strategy was developed with yields for both deprotection steps being essentially quantitative and for the coupling reactions using 1,3-dicyclohexylcarbodiimide (DCC), yields of 80-95% were obtained even at high molecular weights. This allows monodisperse dimers, tetramers, octamers, 16-mers, 32-mers and 64-mers to be prepared in gram quantities and fully characterized using mass spectroscopy, size exclusion chromatography (SEC), and IR and NMR spectroscopy. Thermal and physical properties were measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). These results conclusively show a distinct structure/property relationship with a close correlation between the number of repeat units and physical properties. In addition, a number of marked differences were observed on comparison with the parent poly(caprolactone) polymer.

The synthesis of (L)‐lactide oligomers from dimer to 64mer via an exponential growth strategy is described. By careful selection of orthogonal protective groups, the synthesis were conducted using a t‐butyldimethylsilyl (TBDMS) ether as the protective group of the hydroxyl group and benzyl (Bn) ester as the protective group of the carboxylic acid group. The yields of both the deprotection steps and coupling reactions using 1,3‐dicyclohexylcarbodiimide or 1‐[3‐(dimethylamino)propyl]‐3‐ethylcarbodiimide hydrochloride were high (70–100%) and the absence of a requirement for conducting the majority of reactions under an inert atmosphere permitted a robust and efficient synthetic strategy to be developed. This allowed monodisperse dimer, tetramer, octamer, 16mer, 32mer, and 64mer materials to be prepared in gram quantities and fully characterized using mass spectrometry and size exclusion chromatography. Evaluation of the thermal and physical properties using thermogravimetric analysis, differential scanning calorimetry, and small angle X‐ray scattering demonstrated a close correlation between the molecular structure of the well‐defined Poly(lactide) oligomers and their physical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5977–5990, 2008

The field of polymer science has undergone a renaissance in recent years as the ability to design, construct, and functionalize macromolecules to fit targeted applications develops. 1 While these applications are diverse, the majority of the polymer structures are based on polymerization or functionalization of vinyl monomers derived from a limited range of families. 2 Classic examples include the extensively studied and widely used styrenic, acrylate, or R-olefin-based monomer systems. The development of a new vinyl monomer family that combines the attractive features of thermal and chemical stability, yet having functional handles for compositional versatility, would represent a significant advance in the area of functionalized materials.Key considerations in the design of a novel type of vinyl monomer include the synthetic accessibility of the basic monomer unit and its ease of functionalization. Recently, the advantages of using the "click" chemistry concept and, specifically, the Cu(I)-catalyzed cycloaddition of azides and alkynes as a powerful tool in the design and synthesis of materials have been demonstrated. 3 The benign reaction conditions, functional group tolerance, quantitative yields, and broad applicability of this chemistry make it ideal for the development of unique vinylic monomers based on a triazole nucleus. In this report, we describe the first examples of an expanding library of triazole-based monomers, which are certain to have importance as polar and chemically versatile components for materials development.As shown in Figure 1, 4-vinyl-1,2,3-triazole monomers are expected to possess many of the outstanding features of traditional monomers, such as styrenics, vinyl pyridines, and acrylates. These features include an aromatic nucleus, stability to both acid and base treatment, a large dipole moment, and access to structural diversity through substitution at N-1. We now report the synthesis of a family of functionalized 4-vinyl-1,2,3-triazole monomers 4 that combine into a single structure many of the desirable features found in established monomers.Two distinct synthetic methods were examined for the preparation of 4-vinyl-1,2,3-triazoles. An initial one-pot approach was driven by the orthogonality of "click" chemistry which allows multiple chemical transformations to occur in solution without interference. 5 Coupling of a mixture of 1-trimethylsilyl-2-vinyl acetylene, 1, and an alkyl/aryl halide leads in one pot to the desired 4-vinyl-1,2,3-triazole derivatives. This is illustrated in Scheme 1 for iodobenzene, 2, which undergoes an in situ azidation by reaction with sodium azide and L-proline in the presence of Cu(I) to give azidobenzene, 3. Concurrently, 1 undergoes reaction with tetra-nbutylammonium fluoride to give the active terminal acetylene, 4.In situ coupling of 3 and 4, again by Cu(I) catalysis, then leads to 1-phenyl-4-vinyl-1,2,3-triazole, 5, in 73% overall yield (Scheme 1).The modular nature of "click" chemistry can also be exploited in an alternative two-step approach fo...

The synthesis of isomeric, functionalized 4-vinyl-1,2,3-triazole and 5-vinyl-1,2,3-triazole monomers is demonstrated using heterogeneous copper (copper-in-charcoal)-catalyzed azide−alkyne cycloaddition (CuAAC) or homogeneous ruthenium (Ru)-catalyzed azide−alkyne cycloadditions (RuAAC) “click” protocols. These reactions are regiospecific, exclusively forming 1,4- and 1,5-disubstituted triazoles as determined by 1H NMR, 13C NMR, and X-ray crystallography analysis. Polymerizations were performed using living free radical procedures to yield materials with divergent properties. In the case of the 1,5-triazole materials, glass transition temperature were significantly higher that for the 1,4-derivatives while solubility was decreased.

Synthetic strategies for the preparation of a new family of vinyl monomers, 4-vinyl-1,2,3-triazoles, have been developed. These monomers are noteworthy as they combine the stability and aromaticity of styrenics with the polarity of vinylpyridines and the structural versatility of acrylate/methacrylate derivatives. To enable the wide adoption of these unique monomers, new methodologies for their synthesis have been elaborated which rely on Cu-catalyzed azide/acetylene cycloaddition reactions-''click chemistry''-as the key step, with the vinyl substituent being formed by either elimination or Wittig-type reactions. In addition, one-pot ''click'' reactions have been developed from alkyl halides, which allow for monomer synthesis without isolation of the intermediate organic azides. The high yield and facile nature of these procedures has allowed a library of new monomers including the parent compound, 1-H-4-vinyl-1,2,3-triazole, to be prepared on large scales.

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Monodisperse ε-caprolactone (CL) oligomers with different end groups (tbutyldimethylsilyl, benzyl, hydroxyl, and carboxylic acid) and different numbers of repeating units (4-64) have been studied by differential scanning calorimetry and small-angle X-ray scattering (SAXS) in order to gather information regarding the melting temperature, long period, and melting enthalpy. Oligomers crystallized at their maximum temperatures (different for the different oligomers) to full crystallinity yielded extended-chain crystals for oligomers with 4, 8, and 16 repeating units with the important exception of the oligomers with four and eight repeating units and hydroxyl and benzyl end groups that showed double-layer crystals. Oligomers with 32 and 64 repeating units exhibited remarkably stable once-folded (32-mer) and thrice-folded (64-mer) crystals. Only the oligomer with 16 repeating units showed two crystallization temperature regimes resulting in once-folded crystals (low temperatures) and extended-chain crystals (high temperatures). The end groups had a profound effect on the structures.Hydrogen-bonding groups promoted the formation of crystal bilayers and led to a very high melting enthalpy (150 J g −1 ) exceeding the melting enthalpy of 100% crystalline poly (ε-caprolactone). The bulky end groups, in particular t-butyldimethylsilyl, reduced the crystallinity and favored chain tilting and probably preventing the unfolding of crystal stems in the oligomers with 32 and 64 repeating units. Melting temperatures of mature crystals obeyed a linear relationship with inverse CL stem length. The intercept (equilibrium melting temperature) was in the range of 350 to 357 K.

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