Comonomer Units Research Articles

Synthesis and Mass Spectrometry Structural Assessment of Polyesteramides Based on ε-Caprolactone and L-Phenylalanine.

L-Phenylalanine-ε-caprolactone-based polyesteramides (PCPs) were synthesized via melt polycondensation across a diverse range of molar compositions. The copolymer structure was extensively characterized using nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). NMR analysis confirmed the intercalation of the L-Phenylalanine comonomer units within the polyester backbone. MALDI MS characterization further demonstrated the formation of linear PCP chains with carboxyl end groups. A detailed structural analysis through MALDI MS/MS fragmentation indicated that ester bond scission was the predominant fragmentation mechanism, depicting the polyesteramide sequence in the copolymers. The resulting copolymers were primarily amorphous, except for those with molar compositions of 90/10 and 80/20, which exhibited semi-crystalline structures. Additionally, these PCPs showed an increase in glass transition temperatures with higher amino acid contents and demonstrated good thermal stabilities, as evidenced by a 10% mass loss at elevated temperatures.

Impacts of Photooxidation on Commercially Available Homo and Copolymers of Polypropylene on Their Microstructure and Mechanics: A Cross‐Sectional Analysis

ABSTRACTPolyolefin degradation is widely studied to assess the lifetime of packaging materials. In this work, a combination of bulk (DSC, GPC, 13C‐NMR, XRD), surface (FTIR) and cross‐sectional characterization (Raman spectroscopy and nanoindentation) was used to examine changes in the mechanical properties and microstructure of two different commercially‐available polyolefins, with similar crystallinities, produced by injection molding—a polypropylene homopolymer (PPH) and a polypropylene random copolymer (PPRC)—aged under accelerated UV‐A conditions. The aim was to characterize the variations in the crystallinity and microstructure across the cross‐section of these materials. Our results suggest that the presence of ethylene comonomer units in PPRC results, on average, in smaller crystal dimensions, leads to improved packing, and a more homogeneous microstructure and hardness across the cross‐section of the sample. The ethylene monomers stabilize PPRC from oxidation during the first 14 days of accelerated aging, but eventually the rate of degradation matches the PPH at 28 days of aging, probably because of the higher surface area to volume ratio of the smaller crystals. The work emphasizes the importance of incorporating ethylene comonomers into polyolefins to limit variation of the microstructure across the core to the skin layer, for improved future design of packaging that degrades fully.

Low Band Gap Furan‐Flanked Diketopyrrolopyrrole‐Naphthobisthiadiazole Based Conjugated Polymer/Stretchable Blend for Organic Field Effect Transistors

AbstractN‐type organic semiconducting materials that are compatible in stretchable organic field effect transistors (OFETs) still lag in performance behind that of p‐type materials. Herein, a n‐type conjugated polymer (DPPF‐NTz) is reported that comprises a furan flanked diketopyrrolopyrrole (DPPF) as a monomer and napthobisthiadiazole (NTz) as a comonomer units, respectively, in a conjugated polymer backbone. The low band gap of 1.34 eV and suitable frontier energy levels allow its utilization in OFETs as an n‐type semiconducting material. Optimized bottom‐gate top contact OFETs based on chloroform and chloroform: o‐dichlorobenzene processed DPPF‐NTz showed a maximum electron mobility (µe) of 0.00042 cm2 V⁻¹ s⁻¹ and 0.00078 cm2 V⁻¹ s⁻¹, respectively, in devices annealed at 150 °C. Interestingly, upon mixing the DPPF‐NTz with a stretchable polymer, polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS), yielded a stretchable semiconducting polymer composite, which displayed an enhanced µe of 0.0024 cm2 V⁻¹ s⁻¹ in devices annealed at 250 °C over pristine DPPF‐NTz. The improved µe and mechanical stretchability of the DPPF‐NTz: SEBS polymer blend over pristine DPPF‐NTz polymer is examined by nano‐mechanical atomic force microscopy. The research investigation finding provides a critical insight into the structural and nano‐mechanical properties of n‐type stretchable polymer semiconductors, which are essential for the development of next‐generation wearable OFETs.

The Impact of Regiodefects on the Melt-Memory of Isotactic Polypropylene.

The memory of crystalline phase in the melt of isotactic polypropylene (iPP) in regiodefective samples of iPP characterized by different concentrations regiodefects, constituted by secondary 2,1 propene units, is studied. The self-nucleation (SN) experiments have demonstrated that the presence of 2,1 regiodefects produces a strong memory of the crystalline phase in the melt that persists up to temperatures much higher than the melting temperature. The extension of the heterogeneous melt (domain II) containing self-nuclei increases with increasing the concentration of regiodefects. The higher the concentration of regiodefects the higher the temperature at which the self-nuclei are dissolved and the homogeneous melt is achieved. This demonstrates that a strong memory of the crystalline phase of iPP in the melt exists not only in copolymers with noncrystallizable bulky comonomeric units rejected from the crystals but even when small defects are largely included in the crystals.

Polyhydroxyalkanoate Copolymer Production by Recombinant Ralstonia eutropha Strain 1F2 from Fructose or Carbon Dioxide as Sole Carbon Source.

Ralstonia eutropha strain H16 is a chemoautotrophic bacterium that oxidizes hydrogen and accumulates poly[(R)-3-hydroxybutyrate] [P(3HB)], a prominent polyhydroxyalkanoate (PHA), within its cell. R. eutropha utilizes fructose or CO2 as its sole carbon source for this process. A PHA-negative mutant of strain H16, known as R. eutropha strain PHB-4, cannot produce PHA. Strain 1F2, derived from strain PHB-4, is a leucine analog-resistant mutant. Remarkably, the recombinant 1F2 strain exhibits the capacity to synthesize 3HB-based PHA copolymers containing 3-hydroxyvalerate (3HV) and 3-hydroxy-4-methyvalerate (3H4MV) comonomer units from fructose or CO2. This ability is conferred by the expression of a broad substrate-specific PHA synthase and tolerance to feedback inhibition of branched amino acids. However, the total amount of comonomer units incorporated into PHA was up to around 5 mol%. In this study, strain 1F2 underwent genetic engineering to augment the comonomer supply incorporated into PHA. This enhancement involved several modifications, including the additional expression of the broad substrate-specific 3-ketothiolase gene (bktB), the heterologous expression of the 2-ketoacid decarboxylase gene (kivd), and the phenylacetaldehyde dehydrogenase gene (padA). Furthermore, the genome of strain 1F2 was altered through the deletion of the 3-hydroxyacyl-CoA dehydrogenase gene (hbdH). The introduction of bktB-kivd-padA resulted in increased 3HV incorporation, reaching 13.9 mol% from fructose and 6.4 mol% from CO2. Additionally, the hbdH deletion resulted in the production of PHA copolymers containing (S)-3-hydroxy-2-methylpropionate (3H2MP). Interestingly, hbdH deletion increased the weight-average molecular weight of the PHA to over 3.0 × 106 on fructose. Thus, it demonstrates the positive effects of hbdH deletion on the copolymer composition and molecular weight of PHA.

Chemical Structure-Physicochemical Property Relationships of Copolymers Utilizable for Negative-Tone Photoimaging via Chemical Amplification.

We demonstrate an understanding of different physicochemical properties of copolymers induced by systematic changes in their structural parameters, i.e., the chemical structure of the comonomer unit, composition, molecular weight, and dispersity. The terpolymers were designed to be implemented in a chemically amplified resist (CAR) to form negative-tone patterns. With two basic repeating units of 4-hydroxystyrene and 2-ethyl-2-methacryloxyadamantane as monomers for conventional CARs, the pendant group of the third methacrylate comonomer was varied from aromatic, aliphatic lactone to lactone rings to modulate the interaction capability of the copolymer chains with n-butyl acetate, which is a negative-tone developer. Along with these structures, the monomer composition, molecular weight, and dispersity were also controlled. Physicochemical properties of the synthesized copolymers having controlled structures, i.e., dissolution behaviors and quantified Hansen solubility parameters, surface wetting characteristics, and surface roughness, which can be important properties affecting patterning capability in high-resolution lithography, were explored. Furthermore, the feasibility to use experimentally determined Hansen solubility parameters of the copolymers for the prediction of pattern formation using a coarse-grained model was assessed. Our comprehensive studies on the correlation of the structural parameters of the copolymers with final properties offer fundamental avenues to attain effective designs of the complex CAR system toward the lithographic process to achieve a sub-10 nm dimension, which is close to a single-chain dimension.

Crystal Polymorphism and Phase Transition of Isodimorphic Copolyamides Based on Even–Even and Odd–Even Comonomer Units: Synergistic Effects of Copolymer Composition and Crystallization Temperature

Crystal Polymorphism and Phase Transition of Isodimorphic Copolyamides Based on Even–Even and Odd–Even Comonomer Units: Synergistic Effects of Copolymer Composition and Crystallization Temperature

Peculiar transient behaviors of organic electrochemical transistors governed by ion injection directionality

Despite the growing interest in dynamic behaviors at the frequency domain, there exist very few studies on molecular orientation-dependent transient responses of organic mixed ionic–electronic conductors. In this research, we investigated the effect of ion injection directionality on transient electrochemical transistor behaviors by developing a model mixed conductor system. Two polymers with similar electrical, ionic, and electrochemical characteristics but distinct backbone planarities and molecular orientations were successfully synthesized by varying the co-monomer unit (2,2’-bithiophene or phenylene) in conjunction with a novel 1,4-dithienylphenylene-based monomer. The comprehensive electrochemical analysis suggests that the molecular orientation affects the length of the ion-drift pathway, which is directly correlated with ion mobility, resulting in peculiar OECT transient responses. These results provide the general insight into molecular orientation-dependent ion movement characteristics as well as high-performance device design principles with fine-tuned transient responses.

Crystal Polymorphism of Isodimorphic Polyesters Tuned by cis- and trans-C═C Comonomer Units.

Polymorphism is ubiquitous in polymer crystallization due to the diversified chain conformations and interchain packings in polymer crystals. Controlling chain conformation is effective in tailoring the crystal polymorphism of polymers, which, however, is challenging at the molecular level. Herein, we have synthesized poly(butylene adipate) (PBA)-based copolymers containing C═C units and demonstrated the important role of trans/cis-C═C units in tuning the chain conformation and crystal polymorphism of polymers. Both PBA-based trans- and cis-copolymers show isodimorphic crystallization behavior with the partial inclusion of C═C units in PBA crystals. The presence of trans-C═C units favors the formation of metastable β-crystals of PBA and retards the β-to-α crystal transition upon heating due to the highly conformational matching between trans-C═C units and β-crystals. Conversely, the incorporation of cis-C═C units destroys the regularity of the trans conformation and favors the growth of α-crystals of PBA. This work has elucidated the crucial role of local chain conformation in the crystal polymorphism of polymers.

Fabrication of Plastic Optics from Chalcogenide Hybrid Inorganic/Organic Polymers for Infrared Thermal Imaging

AbstractThe development of infrared (IR) plastic optics for infrared thermal imaging, particularly, in the long‐wave IR (LWIR) spectrum (7–14 µm) is an area of growing technological interest due to the potential advantages associated with plastic optics (e.g., moldability and low cost). The development of a new class of optical polymers, chalcogenide‐based inorganic/organic hybrid polymers (CHIPs) derived from the inverse vulcanization of elemental sulfur, has enabled significant improvements in IR transparency due to reduction of IR absorbing organic comonomer units. The vast majority of effort has focused on new chalcogenide hybrid polymer synthesis and optical property improvements (e.g., refractive index, Abbe number, and LWIR transmission); however, fabrication and IR imaging methodology to prepare optical components has not been demonstrated, which remains critical to develop viable IR plastic optics. A new methodology is reported to fabricate optical components and evaluate LWIR imaging performance of this emerging class of optical polymers. New diffractive flat optics with a Fresnel lens design for these materials have been developed, along with a basic LWIR imaging system to evaluate CHIPs for LWIR imaging. This system‐based approach enables correspondence of copolymer structure‐property correlations with LWIR imaging performance, along with demonstration of room temperature LWIR imaging.

Disappearance of Melt Memory Effect with Comonomer Incorporation in Isodimorphic Random Copolyesters.

Melt memory effects in polymer crystallization have attracted much attention in the past few years. Although progress has been made in understanding how the chemical structure of polymers can affect melt memory, there are still some knowledge gaps. In this work, we study how incorporating a second comonomer unit that is partially included in the crystalline unit cell affects the melt memory effect of the major component in a random isodimorphic copolymer for the first time. This second comonomer unit depresses the melting temperature of the homopolymer, reduces the crystallinity, and distorts the crystalline unit cell. However, its effect on the stability of self-nuclei and the production of melt memory has not been studied so far. To this aim, we have selected poly[(butylene succinate)-ran-(ε-caprolactone)] random copolyesters PBS-ran-PCL that are isodimorphic, i.e., they exhibit a pseudoeutectic point. This point separates the formation of BS-rich crystals from CL-rich crystals as a function of composition. The results reveal that the melt memory effect of these isodimorphic copolymers is strongly reduced with the incorporation of even very small amounts of comonomer unit (i.e., 1 molar %). This indicates that the incorporation of a second comonomer unit in the polymer chain disrupts the intermolecular interactions present between the chain segments in the crystal lattice of the major component and reduces the capacity of the material to produce self-nuclei. This reduction is more drastic for copolymers in which the second comonomer unit is mostly rejected from the crystalline phase. Contrary to olefin-based copolymers, for copolyesters, the second comonomer unit eases the process to reach an isotropic melt state upon melting. This work reveals the impact of introducing comonomer units on the melt memory effect in isodimorphic random copolyesters.

Conjugated Nanohoop Polymers based on Antiaromatic Dibenzopentalenes for Charge Storage in Organic Batteries

AbstractWith their bent π‐systems, cyclic conjugation and inherent cavities, conjugated nanohoops are attractive for organic electronics applications. For ease of processing and morphological stability, an incorporation into polymers is desirable, but to date was hampered with few exceptions by synthetic difficulties. We herein present a unique strategy for the synthesis of conjugated nanohoop polymers using a dibenzo[a,e]pentalene (DBP) as central connector. We demonstrate this versatility by synthesizing three electronically diverse copolymers with dithienyldiketo(pyrrolopyrrol), fluorene and carbazole comonomers, and report the first donor‐acceptor nanohoop polymer. Optoelectronic investigations reveal the prevalence of cyclic or linear conjugation, depending on the comonomer unit, and ambipolar electrochemical properties through the antiaromatic character of the DBP units. As the first report on using conjugated nanohoops for charge storage as positive electrode materials, we show a significant improvement in battery performance in a nanohoop‐containing polymer compared to an equivalent nanohoop‐free reference polymer. We believe this study will pave the way for the synthesis of a diverse range of nanohoop polymers and further stimulate their exploration for charge storage in batteries.

Conjugated Nanohoop Polymers based on Antiaromatic Dibenzopentalenes for Charge Storage in Organic Batteries.

With their bent π-systems, cyclic conjugation and inherent cavities, conjugated nanohoops are attractive for organic electronics applications. For ease of processing and morphological stability, an incorporation into polymers is desirable, but to date was hampered with few exceptions by synthetic difficulties. We herein present a unique strategy for the synthesis of conjugated nanohoop polymers using a dibenzo[a,e]pentalene (DBP) as central connector. We demonstrate this versatility by synthesizing three electronically diverse copolymers with dithienyldiketo(pyrrolopyrrol), fluorene and carbazole comonomers, and report the first donor-acceptor nanohoop polymer. Optoelectronic investigations reveal the prevalence of cyclic or linear conjugation, depending on the comonomer unit, and ambipolar electrochemical properties through the antiaromatic character of the DBP units. As the first report on using conjugated nanohoops for charge storage as positive electrode materials, we show a significant improvement in battery performance in a nanohoop-containing polymer compared to an equivalent nanohoop-free reference polymer. We believe this study will pave the way for the synthesis of a diverse range of nanohoop polymers and further stimulate their exploration for charge storage in batteries.

Inclusion/exclusion behavior of comonomer units in isodimorphic crystallization of biobased copolyamides PA6/PA56

A series of semi-crystalline bio-based copolyamides PA6x56y were synthesized via melt polycondensation from caprolactam (6 units) and bio-based Pentamethylene adipamide units (56 units). DSC results show that the melting and crystallization temperature depend on the comonomers composition, and exhibit isodimorphic behavior. Combined with the analysis of WAXD, it is found that the 56 units are more tend to be excluded from rather than incorporated into the PA6 crystals. However, it does not imply a complete exclusion. Unexpectedly, there is a significant relationship between the content of 56 units on the polymorphic crystallization behavior of PA6-type crystals. Moreover, the pseudo-eutectic point appears when 56 units content is 30 mol %, and the spherulite morphology exhibits a strong correlation with the pseudo-eutectic point. In addition, the excess free energy of defects (ε) is calculated by applying the Wending-Suter model, and it is found that the ε-value caused by the insertion of 56 units into the crystal formed by PA6 is higher than that of 6 units into a crystal formed by PA56. Therefore, 6 units are more easily inserted into crystals formed by PA56, i.e., 6 units have better compatibility with PA56 crystals. In summary, this work reveals the involved mechanisms of comonomer units in the crystallization process and provides a potential strategy to guide the development of high-performance copolymers in the future.

Hydrophilic Copolymers with Hydroxamic Acid Groups as a Protective Biocompatible Coating of Maghemite Nanoparticles: Synthesis, Physico-Chemical Characterization and MRI Biodistribution Study.

Superparamagnetic iron oxide nanoparticles (SPION) with a "non-fouling" surface represent a versatile group of biocompatible nanomaterials valuable for medical diagnostics, including oncology. In our study we present a synthesis of novel maghemite (γ-Fe2O3) nanoparticles with positive and negative overall surface charge and their coating by copolymer P(HPMA-co-HAO) prepared by RAFT (reversible addition-fragmentation chain-transfer) copolymerization of N-(2-hydroxypropyl)methacrylamide (HPMA) with N-[2-(hydroxyamino)-2-oxo-ethyl]-2-methyl-prop-2-enamide (HAO). Coating was realized via hydroxamic acid groups of the HAO comonomer units with a strong affinity to maghemite. Dynamic light scattering (DLS) demonstrated high colloidal stability of the coated particles in a wide pH range, high ionic strength, and the presence of phosphate buffer (PBS) and serum albumin (BSE). Transmission electron microscopy (TEM) images show a narrow size distribution and spheroid shape. Alternative coatings were prepared by copolymerization of HPMA with methyl 2-(2-methylprop-2-enoylamino)acetate (MMA) and further post-polymerization modification with hydroxamic acid groups, carboxylic acid and primary-amino functionalities. Nevertheless, their colloidal stability was worse in comparison with P(HPMA-co-HAO). Additionally, P(HPMA-co-HAO)-coated nanoparticles were subjected to a bio-distribution study in mice. They were cleared from the blood stream by the liver relatively slowly, and their half-life in the liver depended on their charge; nevertheless, both cationic and anionic particles revealed a much shorter metabolic clearance rate than that of commercially available ferucarbotran.

How 4-(7-Octen-1-yl)-N,N-diphenylaniline co-units induce strong melt memory effects in isotactic polypropylene random copolymers

The random incorporation of comonomer units in isotactic polypropylene usually disrupts the chemical regularity of the macromolecular chain, thereby remarkably affecting the crystallization and melting processes. We study the influence of a novel comonomer 4-(7-Octen-1-yl)-N,N-diphenylaniline (ODPA), in the concentration range of 1.1–6.8 mol%, on the crystallization and self-nucleation behavior of isotactic polypropylene copolymers. Non-isothermal and isothermal differential scanning calorimetry experiments demonstrated that crystallization kinetics are significantly retarded upon comonomer incorporation as the ODPA co-units are excluded to the amorphous regions. Furthermore, ODPA comonomer incorporation leads to a sharp increase in nucleation density; thus, spherulitic superstructures become significantly smaller. Remarkably, the ODPA co-units induce a strong melt memory effect that can persist even above the equilibrium melting temperature for copolymers with 4.4–6.8 mol% ODPA. The width of Domain IIa (exclusive melt-memory domain), an indicator of the self-nucleation strength, starts to increase sharply once the content of ODPA exceeds 1.8 mol%. In contrast, the width of Domain IIb (self-seeding domain) remains constant. We attribute the self-nucleation effect in these ODPA copolymers to the aggregation of co-units in the interlamellar amorphous regions that hinder, upon melting, the motion of the chain sequences that were initially packed within the crystal lattice. In this way, to reach the isotropic melt state, the sample must be heated to much higher temperatures than its apparent or even equilibrium melting point, depending on the comonomer content. Consequently, nucleation upon cooling from the self-nucleated melt becomes easier and faster.

Thermal and Crystallization Properties of a Polyhydroxyalkanoate Binary Copolymer Containing 3-Hydroxybutyrate and 3-Hydroxy-2-Methylvalerate Units

Polyhydroxyalkanoates (PHAs) are aliphatic polyesters synthesized intracellularly by microorganisms as a carbon-storage substance. Among the various PHAs, 3-hydroxybutyrate (3HB)-based copolymers are crystalline polymers widely used as biodegradable plastics. Recently, PHAs containing α-carbon-methylated monomers, such as 3-hydroxy-2-methylbutyrate (3H2MB) and 3-hydroxy-2-methylvalerate (3H2MV), have been synthesized and characterized. However, a binary copolymer of 3HB and 3H2MV, P(3HB-co-3H2MV), had not yet been synthesized, and its material properties had not been investigated. In this study, P(3HB-co-11 mol% 3H2MV) (PHBMV11) was synthesized with recombinant Escherichia coli LSBJ, using trans-2-methyl-2-pentenoic acid as the 3H2MV precursor. The thermal properties of PHBMV11 were characterized using differential scanning calorimetry (DSC), and the results were compared with those of P(3HB-co-12 mol% 3-hydroxyvalerate) (PHBV12) to explore the effect of α-carbon methylation in the comonomer unit. PHBMV11 exhibited a higher enthalpy of fusion during the DSC heating process and higher crystallization temperature during the DSC cooling process than those of PHBV12. The half-crystallization time of PHBMV11 was slightly longer than that of the P(3HB) homopolymer and much shorter than that of PHBV12 previously reported. The α-carbon methylation of the 3H2MV unit also has a positive effect on the crystallization of 3HB-based copolymers, as the 3H2MB unit demonstrated previously.

Manipulating the Co-crystallization Behavior in Isomorphic Copolymers by Introducing a Third Monomeric Unit

Isomorphism is a distinctive kind of co-crystallization behavior of random copolymers and provides opportunities to regulate the crystalline structure and performance without the loss of crystallinity. Though the intrinsic structural differentiation would induce variation of accommodation capacity in the co-crystal lattice for different co-monomeric units, subtle manipulation of isomorphism has not been realized yet. In this study, butylene adipate (BA) as the crystallizable unit is incorporated into an isomorphism system model of poly(butylene succinate-ran-butylene fumarate) (PBSF) to form the terpolymers of PBSFA, and the crystallization features are investigated. It is confirmed that part of BA (i.e., ≤20 mol %) does not hinder the isomorphism formation in the terpolymers of PBSFA but influences the accommodation capacities of the isomorphic counterparts of butylene succinate (BS) and butylene fumarate (BF). When BA with 10 mol % is copolymerized, the adoption of BS unit in isomorphism becomes less favorable in comparison to the biopolymers of PBSF, showing an increase of the defect Gibbs free energy for the co-crystal and a decrease of the accommodation ratio of BS. However, with a further lifting of the BA content to 20 mol %, the accommodation preference of BS and BF in the isomorphism lattice reverses, and BS turns into a favorable unit instead of BF. Such a transition of accommodation capacity might be due to the deterioration of intersegmental interaction caused by the third co-crystallizable unit of BA. This work directly reveals the differentiation of co-monomeric units in the isomorphic lattice and sheds light on the manipulation of isomorphism.

Dynamic covalent exchange in methacrylic anhydride copolymers

Methacrylic anhydride (MAA)-based copolymers were synthesized to probe how the molecular environment around the anhydride moieties impacts the ability of dynamic covalent exchange between anhydrides impacts the ability to recyclable the crosslinked (co)polymers. The comonomers methyl methacrylate (MMA) and n-butyl acrylate (BA) were copolymerized with MAA to yield crosslinked copolymers with varying compositions and their thermal and physical properties were studied as a function of the number of recycling events and copolymer composition. Dynamic covalent exchange was studied via recycling through repetitive grinding and compression molding at elevated temperatures and pressures (130 °C and 152 MPa for 2 h). It is concluded that adjacent anhydride moieties can undergo exchange to produce cyclic anhydrides, as observed through IR spectroscopy after heat treatments. Peak deconvolution was utilized to determine the degree of cyclization. Significant increases in monomer conversion occurred and anhydride cyclization was apparent during the first recycling process. Additional recycling processes continued to change the degree of cyclization, but the extent was dependent on the comonomer type. The degree of cyclization was found to be lower in the copolymers compared to the homopolymer, probably because the interruption of MAA units by the comonomer units along the backbone reduces the ability to cyclize. Thermal properties (glass transition temperature, Tg) of the polymers were also impacted, however the static material properties (modulus and hardness) did not exhibit any dependence on cyclization due to the immobile nature of the highly crosslinked network at room temperature.

Effect of Chemical Composition on Molecular Mobility and Phase Coupling in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with Different Comonomer Contents

Two series of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) with different amounts of hydroxyvalerate (HV) and hydroxyhexanoate (HHx) units are compared. The influence of chemical composition on the molecular mobility in quenched samples is discussed, as well as the consequences on the aptitude to crystallize and the microstructures developed during cold-crystallization. In both quenched PHBHV and PHBHHx, $$T_g$$ decreases as the content of comonomer unit increases. The HHx units (propyl side-groups) are better molecular spacers and produce a stronger $$T_g$$ shift as compared to the HV units (ethyl side-groups). Copolymerization has no striking effect on the width of the glass transition and the cooperativity length in quenched samples, but in cold-crystallized samples the glass transition is dramatically broadened. When the fully amorphous copolymers are heated from the glassy state to room temperature, crystallization occurs but is largely disrupted, suggesting that the molecular environment in the amorphous phase is significantly changed. The HHx units, which are excluded from the host crystals, delay and slow down the crystallization kinetics in a stronger way as compared to the HV units, which can partially co-crystallize. The obtained crystalline phases are prone to reorganization and the residual amorphous phases appear to have strong differences in composition and large density fluctuations. A practical consequence is that microstructures with different coupling between phases, and thus different properties and stability over time, can be obtained by controlling the nature and content of the comonomer units.