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A series of biobased epoxy monomers were prepared from diphenolic acid (DPA) by transforming the free acid into n-alkyl esters and the phenolic hydroxyl groups into diglycidyl ethers. NMR experiments confirmed that the diglycidyl ethers of diphenolates (DGEDP) with methyl and ethyl esters have 6 and 3 mol % of glycidyl ester. Increasing the chain length of DGEDP n-alkyl esters from methyl to n-pentyl resulted in large decreases in epoxy resin viscosity (700-to-11 Pa•s). Storage modulus of DPA epoxy resins, cured with isophorone diamine, also varied with n-alkyl ester chain length (e.g., 3300 and 2100 MPa for the methyl and n-pentyl esters). The alpha transition temperature of the cured materials showed a linear decrease from 158 to 86 °C as the ester length increases. The Young's modulus and tensile strengths were about 1150 and 40 MPa, respectively, for all the cured resins tested (including DGEBA) and varied little as a function of ester length. Degree of cure for the different epoxy resins, determined by FTIR and DSC, closely approached the theoretical maximum. The result of this work demonstrates that diglycidyl ethers of n-alkyl diphenolates represent a new family of biobased liquid epoxy resins that, when cured, have similar properties to those from DGEBA.

Cellulose nanocrystals (CNCs) were modified with natural di-and tricarboxylic acids using two concurrent acid-catalyzed reactions including hydrolysis of amorphous cellulose segments and Fischer esterification, resulting in the introduction of free carboxylic acid functionality onto CNC surfaces. CNC esterification was characterized by Fourier Transform Infrared Spectroscopy, 13 C solid state magic-angle spinning (MAS) and conductometric titration experiments. Average degree of substitution values for malonate, malate, and citrate CNCs are 0.16, 0.22 and 0.18, respectively. Despite differences in organic acid pKa, optimal HCl cocatalyst concentrations were similar for malonic, malic and citric acids. After isolation of modified CNCs, residual cellulose co-products were identified that are similar to microcrystalline cellulose based on SEM and XRD analysis. As proof of concept, recycling experiments were carried to increase the yield of citrate CNCs. The by-product was then recycled by subsequent citric acid/HCl treatments that resulted in 55% total yield of citrate CNCs.The crystallinity, morphology, and substitution of citrate CNCs from recycled cellulose coproduct is similar to modified citrate CNCs formed in the first reaction cycle. Thermal stability of all modified CNCs under air and nitrogen resulted in T 10% and T 50% values above 256 °C and 323 °C, respectively. Thus, they can be used for melt-processing operations performed at moderately high temperatures without thermal decomposition. Nanocomposites of polyvinyl alcohol with modified CNCs (1 wt% malonate-, malate-, citrate and unmodified CNCs) wereprepared. An increase in the thermal decomposition temperature by almost 40 °C was obtained for PVOH-citrate modified CNC nanocomposites.Furthermore, since TGA determined weight loss up to 150°C is attributed to loss of bound water, this provides a tool to determine CNC water affinity. By 150°C, the weight loss of modified and non-modified CNCs is 6% and 2%, respectively. Consequently, modified CNCs with surface carboxylate groups have higher water affinity than non-modified CNCs. Moreover, significant differences in the thermal stability are observed as a function of the di-or triacid used for CNC modification. Based on the peaks of the derivative thermogravimetric curve (DTG, T 50% ), modified CNCs have the following thermal stability: malonate = HCl > malate > citrate CNCs.Corresponding values for T 50% are 366°C, 365°C, 350°C and 345°C, respectively. The amount of residual char at 600°C for HCl, malonate, malate and citrate CNCs is 8, 13, 16 and 20%, respectively. Hence, it follows that increasing the T 50% for di-and tri-acid modified CNCs results in correspondingly lower char formation. Increased char amounts is likely due to CNC functionalizations that lead to relatively larger number of cross-linking events at elevated temperatures.Since the exclusion of air during melt processing is generally not practical, the effect of CNC modification on thermal stability in air was also determined and the correspo...

This paper demonstrated the feasibility of conducting an enzymatic ring-opening polymerisation by reactive extrusion (REX) at high shear and temperature conditions. Using immobilized Candida antarctica Lipase B (CALB) as catalyst at temperatures ranging from 90 to 130°C, ω-pentadecalactone (PDL) was converted (>99%) by REX at 60 RPM for 15 min to PPDL with ≥M w 163 000 g mol −1 .The majority of current polymerisation methods use metal catalysts. Residual metal catalysts are often undesirable in materials used for biomedical and electronic applications. 1 Immobilized enzyme-catalysts have been shown to have distinct advantages relative to most metal catalysts including: (1) naturally derived, (2) low toxicity, (3) high chemo-and regioselectivity, (4) activity at relatively low temperatures and (5) no need for strict exclusion of water and oxygen. 2-6 The most commonly employed lipase for enzyme-catalysed ring opening polymerisations (eROP) and polycondensations is the immobilized lipase form of Candida antarctica Lipase B (CALB). Of the many lactonic substrates for which CALB is an active polymerisation catalyst, CALB efficiently catalyses ROP's of larger lactones (e.g. ω-pentadecalactone, PDL). 3 The immobilized CALB catalyst used in ref. 4 and herein is Novozyme 435 (N435). ROP of larger lactones are known to be difficult for many organometallic catalysts because the polymerisations are primarily entropy-driven. 7 Nevertheless, recent progress has resulted in a number of chemical catalysts that successfully convert PDL to high molecular weight polymers. Examples of these catalysts are aluminium salen and terdentate phonoxyimine-amine aluminium. Problems encountered with these catalysts are as follows: (i) synthesis from expensive ligands, (ii) requiring inert reaction conditions (e.g. performed in a glove box) and (iii) the use of solvents. 8,9 The ability of lipases to catalyse ring-opening and condensation polymerisations at relatively low temperatures (e.g. 70-90°C) is advantageous to reduce energy input and to preserve thermally sensitive chemical moieties. However, when high molecular weight polymer synthesis is desired, corresponding diffusional constraints must be overcome by either running reactions at higher temperatures (e.g. 150-220°C), which is generally regarded as not feasible for enzyme-catalysts that denature under such conditions, 10 or by adding solvent. For example, for N435-catalyzed synthesis of high molecular weight (M n > 50 000 g mol −1 ) poly(ω-pentadecalactone), PPDL, and poly(ε-caprolactone, PCL), the viscosity was lowered by the addition of toluene. Subsequently, the final polymer products are obtained by precipitation into a non-solvent such as methanol. 11-13 Solvent-based processes reduce the volumetric productivity of reactions and also require solvent recycling.Reactive extrusion (REX) is an industrially relevant technique because it combines polymerisation and processing into a single step. 14 REX has been used to overcome the aforementioned problems of bulk polymerisations, mai...

Poly­(pentadecalactone)-b-poly­(l-lactide) (PPDL-b-PLLA) diblock copolymers were prepared via the organic catalyzed ring-opening polymerization (ROP) of l-lactide (l-LA) from PPDL macroinitiators using either 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) or 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD). Synthesis of PLLA blocks targeting degrees of polymerization (DP) up to 500 were found to yield diblock copolymers with crystalline PPDL and PLLA segments when TBD was used as the catalyst. The synthesis was further improved in a one-pot, two-step process using the same TBD catalyst for the synthesis of both segments. The application of these diblock copolymers as a compatibilizing agents resulted in homogenization of a biobased PLLA/poly­(ω-hydroxytetradecanoate) (90:10) blend upon a melt-process, yielding enhanced material properties.

A green manufacturing technique, reactive extrusion (REx), was employed to improve the mechanical properties of polylactide (PLA). To achieve this goal, a fully biosourced PLA based polymer blend was conceived by incorporating small quantities of poly(ω-hydroxytetradecanoic acid) (PC14). PLA/PC14 blends were compatibilized by transesterification reactions promoted by 200 ppm titanium tetrabutoxide (Ti(OBu)4) during REx. REx for 15 min at 150 rpm and 200 °C resulted in enhanced blend mechanical properties while minimizing losses in PLA molecular weight. SEM analysis of the resulting compatibilized phase-separated blends showed good adhesion between dispersed PC14 phases within the continuous PLA phase. Direct evidence for in situ synthesis of PLA-b-PC14 copolymers was obtained by HMBC and HSQC NMR experiments. The size of the dispersed phase was tuned by the screw speed to "tailor" the blend morphology. In the presence of 200 ppm Ti(OBu)4, inclusion of only 5% PC14 increased the elongation at break of PLA from 3 to 140% with only a slight decrease in the tensile modulus (3200 to 2900 MPa). Furthermore, PLA's impact strength was increased by 2.4× that of neat PLA for 20% PC14 blends prepared by REx. Blends of PLA and PC14 are expected to expand the potential uses of PLA-based materials.

Despite attractive properties of cellulose nanocrystals (CNCs) such as high natural abundance, inherent biodegradability and high modulus, CNCs tend to degrade and aggregate when exposed to high temperatures during melt processing. In the present work, the surface of CNCs was modified with PMMA to take advantage of the miscibility with various biobased polymers including PLLA when melt-blended. Particular attention was paid to grafting techniques in water medium using two different redox initiators: Fe 2+ /H 2 O 2 (Fenton's reagent) and ceric ammonium nitrate (CAN). The successful synthesis of CNC-g-PMMA was verified by gravimetric analysis, FTIR, CP-MAS 13 C NMR and suspension tests. A high grafting efficiency of 77% was achieved using CAN as the redox initiator. Increasing the PMMA content on CNC surfaces led to higher CNC thermal stability. As a consequence of PMMA grafting in water, modified CNCs were found to be predispersed in a PMMA network. PLLA/CNC nanocomposites were then prepared by melt-blending, i.e., in the absence of solvent, and the quality of the dispersion was confirmed by dynamic rheology, TEM and DMA. The presence of a high amount of PMMA grafts on CNC surfaces reduced CNC aggregation and favors the percolation of CNCs with the development of a weak long-range 3D network. Miscibility between PMMA grafts and PLLA as well as the predispersion of CNCs was found to play a key role in the dispersion of CNCs in PLLA. Thermomechanical analysis revealed that PMMA grafts on CNC surfaces significantly enhanced elastic moduli in the glassy and rubbery state. The high dispersion state (related to high PMMA grafting) also showed a positive effect on O 2 permeability of PLLA and a strong beneficial effect on heat deflection temperature (HDT) reaching outstanding temperatures higher than 130 °C. Thus, free-radical grafting of PMMA in water provides an efficient and green route to dispersible (bio)nanofillers by solvent-free extrusion techniques with PMMA-miscible matrices such as PLLA for high-performance applications.

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